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DESCRIPTIO
s s s s s s s s s s
Sample-and-Hold 16s Conversion Time 33kHz Sample Rate 0.5LSB Total Unadjusted Error Over Temp Direct 3-Wire Interface to Most MPU Serial Ports and All MPU Parallel I/O Ports
APPLICATI
s s s s s s
Battery-Operated Systems Remote Data Acquisition Battery Monitoring Battery Gas Gauges Temperature Measurement Isolated Data Acquisition
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATI
10W, S8 Package, 8-Bit A/D Samples at 200Hz and Runs Off a 5V Battery
1F 5V
SUPPLY CURRENT, ICC (A)
m o .c U t4 e e h S ta a .D w w w
S
VREF
LTC1096/8 * TA01
The LTC (R)1096/LTC1096L/LTC1098/LTC1098L are micropower, 8-bit A/D converters that draw only 80A of supply current when converting. They automatically power down to 1nA typical supply current whenever they are not performing conversions. They are packaged in 8-pin SO packages and have both 3V (L) and 5V versions. These 8-bit, switched-capacitor, successive approximation ADCs include sample-and-hold. The LTC1096/LTC1096L have a single differential analog input. The LTC1098/LTC1098L offer a software selectable 2-channel MUX. On-chip serial ports allow efficient data transfer to a wide range of microprocessors and microcontrollers over three wires. This, coupled with micropower consumption, makes remote location possible and facilitates transmitting data through isolation barriers. These circuits can be used in ratiometric applications or with an external reference. The high impedance analog inputs and the ability to operate with reduced spans (below 1V full scale) allow direct connection to sensors and transducers in many applications, eliminating the need for gain stages.
Supply Current vs Sample Rate
TA = 25C VCC = VREF = 5V
1000
MPU (e.g., 8051) CS/ VCC SHUTDOWN CLK +IN LTC1096 -IN DOUT GND P1.4 P1.3 P1.2
100
ANALOG INPUT 0V TO 5V RANGE
10
1 0.1
om .c 4U et he aS at .D w w w
1 10 SAMPLE FREQUENCY, fSMPL (kHz) 100
LTC1096/98 * TPC03
U
om .c 4U et he aS FEATUREtS a 80A.Maximum Supply Current D 1nA Typical Supply Current in Shutdown w 8-Pin SO Plastic Package w Operation (LTC1096/LTC1098) w 5V Operation (LTC1096L/LTC1098L)(2.65V Min) 3V
LTC1096/LTC1096L LTC1098/LTC1098L Micropower Sampling 8-Bit Serial I/O A/D Converters
UO
UO
1
LTC1096/LTC1096L LTC1098/LTC1098L ABSOLUTE AXI U RATI GS
Supply Voltage (VCC) to GND ................................... 12V Voltage Analog and Reference ................ -0.3V to VCC + 0.3V Digital Inputs ......................................... -0.3V to 12V Digital Outputs ........................... -0.3V to VCC + 0.3V Power Dissipation .............................................. 500mW Storage Temperature Range ................. - 65C to 150C
PACKAGE/ORDER I FOR ATIO
TOP VIEW CS/ 1 SHUTDOWN +IN 2 -IN 3 GND 4 N8 PACKAGE 8-LEAD PLASTIC DIP 8 7 6 5 VCC CLK DOUT VREF
ORDER PART NUMBER LTC1096ACN8 LTC1096ACS8 LTC1096AIN8 LTC1096AIS8 LTC1096CN8 LTC1096CS8 LTC1096IN8 LTC1096IS8 LTC1096LCS8 LTC1096LIS8
S8 PACKAGE 8-LEAD PLASTIC SOIC
TJMAX = 150C, JA = 130C/W (N8) TJMAX = 150C, JA = 175C/W (S8)
S8 PART MARKING 1096 1096A 1096I 1096IA 1096L 1096LI
Consult factory for Military grade parts.
RECO
SYMBOL VCC
E DED OPERATI G CO DITIO S
CONDITIONS LTC1096 LTC1098 VCC = 5V LTC1096, fCLK = 500kHz LTC1098, fCLK = 500kHz VCC = 5V VCC = 5V, LTC1096 VCC = 5V, LTC1098 VCC = 5V, LTC1096 VCC = 5V, LTC1098 VCC = 5V VCC = 5V MIN 3.0 3.0 25 29 29 150 500 500 10 10 400 0.8 TYP MAX 9 6 500 UNITS V V kHz s s ns ns ns s s ns s
LTC1096/LTC1098
PARAMETER Supply Voltage
VCC = 5V Operation f CLK t CYC t hDI t suCS t WAKEUP Clock Frequency Total Cycle Time Hold Time, DIN After CLK Setup Time CS Before First CLK (See Operating Sequence) Wake-Up Time CS Before First CLK After First CLK (See Figure 1 LTC1096 Operating Sequence) Wake-Up Time CS Before MSBF Bit CLK (See Figure 2 LTC1098 Operating Sequence) t suDI t WHCLK Setup Time, DIN Stable Before CLK CLK High Time
2
U
U
U
U
U
W
WW
U
W
(Notes 1 and 2)
Operating Temperature LTC1096AC/LTC1096C/LTC1096LC/ LTC1098AC/LTC1098C/LTC1098LC ....... 0C to 70C LTC1096AI/LTC1096I/LTC1096LI/ LTC1098AI/LTC1098I/LTC1098LI ..... - 40C to 85C Lead Temperature (Soldering, 10 sec.)................ 300C
(Notes 3)
TOP VIEW CS/ 1 SHUTDOWN CH0 2 CH1 3 GND 4 N8 PACKAGE 8-LEAD PLASTIC DIP 8 7 6 5 VCC(VREF) CLK DOUT DIN
ORDER PART NUMBER LTC1098ACN8 LTC1098ACS8 LTC1098AIN8 LTC1098AIS8 LTC1098CN8 LTC1098CS8 LTC1098IN8 LTC1098IS8 LTC1098LCS8 LTC1098LIS8
S8 PACKAGE 8-LEAD PLASTIC SOIC
TJMAX = 150C, JA = 130C/W (N8) TJMAX = 150C, JA = 175C/W (S8)
S8 PART MARKING 1098 1098A 1098I 1098IA 1098L 1098LI
U WW
LTC1096/LTC1096L LTC1098/LTC1098L
RECO
SYMBOL t WLCLK t WHCS t WLCS
E DED OPERATI G CO DITIO S
CONDITIONS VCC = 5V VCC = 5V LTC1096, fCLK = 500kHz LTC1098, fCLK = 500kHz VCC = 3V LTC1096, fCLK = 250kHz LTC1098, fCLK = 250kHz VCC = 3V VCC = 3V, LTC1096 VCC = 3V, LTC1098 VCC = 3V, LTC1096 VCC = 3V, LTC1098 VCC = 3V VCC = 3V VCC = 3V VCC = 3V LTC1096, fCLK = 250kHz LTC1098, fCLK = 250kHz MIN 0.8 1 28 28 25 58 58 450 1 1 10 10 1 1.6 1.6 2 56 56 250 TYP MAX UNITS s s s s kHz s s ns s s s s s s s s s s
LTC1096/LTC1098
PARAMETER CLK Low Time CS High Time Between Data Transfer Cycles CS Low Time During Data Transfer
VCC = 3V Operation f CLK t CYC t hDI tsuCS t WAKEUP Clock Frequency Total Cycle Time Hold Time, DIN After CLK Setup Time CS Before First CLK (See Operating Sequence) Wake-Up Time CS Before First CLK After First CLK (See Figure 1 LTC1096 Operating Sequence) Wake-Up Time CS Before MSBF Bit CLK (See Figure 2 LTC1098 Operating Sequence) t suDI t WHCLK t WLCLK t WHCS t WLCS Setup Time, DIN Stable Before CLK CLK High Time CLK Low Time CS High Time Between Data Transfer Cycles CS Low Time During Data Transfer
LTC1096L/LTC1098L
SYMBOL VCC f CLK t CYC t hDI t suCS t WAKEUP PARAMETER Supply Voltage Clock Frequency Total Cycle Time Hold Time, DIN After CLK Setup Time CS Before First CLK (See Operating Sequence) Wake-Up Time CS Before First CLK After First CLK (See Figure 1, LTC1096L Operating Sequence) Wake-Up Time CS Before MSBF Bit CLK (See Figure 2, LTC1098L Operating Sequence) t suDI t WHCLK t WLCLK t WHCS t WLCS Setup Time, DIN Stable Before CLK CLK High Time CLK Low Time CS High Time Between Data Transfer Cycles CS Low Time During Data Transfer VCC = 2.65V LTC1096L, fCLK = 250kHz LTC1098L, fCLK = 250kHz VCC = 2.65V VCC = 2.65V, LTC1096L VCC = 2.65V, LTC1098L VCC = 2.65V, LTC1096L VCC = 2.65V, LTC1098L VCC = 2.65V VCC = 2.65V VCC = 2.65V VCC = 2.65V LTC1096L, fCLK = 250kHz LTC1098L, fCLK = 250kHz CONDITIONS MIN 2.65 25 58 58 450 1 1 10 10 1 1.6 1.6 2 56 56 TYP MAX 4.0 250 UNITS V kHz s s ns s s s s s s s s s s
U
U
U
U WW
3
LTC1096/LTC1096L LTC1098/LTC1098L
CO VERTER A D
LTC1096/LTC1098
VCC = 5V, VREF = 5V, fCLK = 500kHz, unless otherwise noted.
PARAMETER Resolution (No Missing Code) Offset Error Linearity Error Full Scale Error Total Unadjusted Error (Note 5) Analog Input Range REF Input Range (Notes 6, 7) Analog Input Leakage Current VREF = 5.000V (Notes 6, 7) 4.5 VCC 6V 6V < VCC 9V, LTC1096 (Note 8)
q
LTC1096/LTC1098
VCC = 3V, VREF = 2.5V, fCLK = 250kHz, unless otherwise noted.
PARAMETER Resolution (No Missing Code) Offset Error Linearity Error Full-Scale Error Total Unadjusted Error (Notes 5, 9) Analog Input Range REF Input Range (Notes 6, 7, 9) Analog Input Leakage Current VREF = 2.500V (Notes 6, 7) 3V VCC 6V (Notes 8, 9)
q
LTC1096L/LTC1098L
VCC = 2.65V, VREF = 2.5V, fCLK = 250kHz, unless otherwise noted.
PARAMETER Resolution (No Missing Code) Offset Error Linearity Error Full-Scale Error Total Unadjusted Error (Notes 5) Analog Input Range REF Input Range (Note 6) Analog Input Leakage Current VREF = 2.5V (Notes 6, 7) 2.65V VCC 4.0V (Note 8)
q
4
WU
U
ULTIPLEXER CHARACTERISTICS
LTC1096A/LTC1098A MIN TYP MAX
q q
CONDITIONS
LTC1096/LTC1098 MIN TYP MAX 8 0.5 0.5 1.0 1.0
UNITS Bits LSB LSB LSB LSB V V V
8 0.5 0.5 0.5 0.5
(Note 4)
q q q
- 0.05V to VCC + 0.05V - 0.05V to VCC + 0.05V - 0.05V to 6V 1.0 1.0
A
CONDITIONS
q q
LTC1096A/LTC1098A MIN TYP MAX 8 0.75 0.5 1.0 1.0
LTC1096/LTC1098 MIN TYP MAX 8 1.0 1.0 1.0 1.5
UNITS Bits LSB LSB LSB LSB V V
(Notes 4, 9)
q q q
- 0.05V to VCC + 0.05V - 0.05V to VCC + 0.05V 1.0 1.0
A
CONDITIONS
q q
MIN 8
LTC1096L/LTC1098L TYP MAX 1.0 1.0 1.0 1.5
UNITS Bits LSB LSB LSB LSB V V
(Note 4)
q q q
- 0.05V to VCC + 0.05V - 0.05V to VCC + 0.05V 1.0
A
LTC1096/LTC1096L LTC1098/LTC1098L
DIGITAL AND DC ELECTRICAL CHARACTERISTICS
LTC1096/LTC1098
VCC = 5V, VREF = 5V, unless otherwise noted.
SYMBOL VIH VIL IIH IIL VOH VOL IOZ ISOURCE ISINK IREF PARAMETER High Level Input Voltage Low Level Input Voltage High Level Input Current Low Level Input Current High Level Output Voltage Low Level Output Voltage Hi-Z Output Leakage Output Source Current Output Sink Current Reference Current CONDITIONS VCC = 5.25V VCC = 4.75V VIN = VCC VIN = 0V VCC = 4.75V, IO = 10A VCC = 4.75V, IO = 360A VCC = 4.75V, IO = 1.6mA CS VIH VOUT = 0V VOUT = VCC CS = VCC tCYC 200s, fCLK 50kHz tCYC = 29s, fCLK = 500kHz CS = VCC LTC1096, tCYC 200s, fCLK 50kHz LTC1096, tCYC = 29s, fCLK = 500kHz LTC1098, tCYC 200s, fCLK 50kHz LTC1098, tCYC = 29s, fCLK = 500kHz
q q q q q q q q q q q q q q q q
ICC
Supply Current
LTC1096/LTC1098
VCC = 3V, VREF = 2.5V, unless otherwise noted.
SYMBOL VIH VIL IIH IIL VOH VOL IOZ ISOURCE ISINK IREF PARAMETER High Level Input Voltage Low Level Input Voltage High Level Input Current (Note 9) Low Level Input Current (Note 9) High Level Output Voltage Low Level Output Voltage Hi-Z Output Leakage (Note 9) Output Source Current (Note 9) Output Sink Current (Note 9) Reference Current (Note 9) CONDITIONS VCC = 3.6V VCC = 3V VIN = VCC VIN = 0V VCC = 3V, IO = 10A VCC = 3V, IO = 360A VCC = 3V, IO = 400A CS VIH VOUT = 0V VOUT = VCC CS = VCC tCYC 200s, fCLK 50kHz tCYC = 58s, fCLK = 250kHz CS = VCC LTC1096, tCYC 200s, fCLK 50kHz LTC1096, tCYC = 58s, fCLK = 250kHz LTC1098, tCYC 200s, fCLK 50kHz LTC1098, tCYC = 58s, fCLK = 250kHz
q q q q q q q q q q q q q q q q
ICC
Supply Current (Note 9)
U
MIN 2.0
TYP
MAX 0.8 2.5 - 2.5
UNITS V V A A V V
4.5 2.4
4.74 4.72 0.4 3.0 - 25 45 0.001 3.500 35.000 0.001 40 120 44 155 2.5 7.5 50.0 3.0 80 180 88 230
V A mA mA A A A A A A A A
MIN 1.9
TYP
MAX 0.45 2.5 - 2.5
UNITS V V A A V V
2.3 2.1
2.69 2.64 0.3 3.0 - 10 15 0.001 3.500 35.000 0.001 40 120 44 155 2.5 7.5 50.0 3.0 80 180 88 230
V A mA mA A A A A A A A A
5
LTC1096/LTC1096L LTC1098/LTC1098L
DIGITAL AND DC ELECTRICAL CHARACTERISTICS
LTC1096L/LTC1098L
VCC = 2.65V, VREF = 2.5V, fCLK = 250kHz, unless otherwise noted.
SYMBOL VIH VIL IIH IIL VOH VOL IOZ ISOURCE ISINK IREF PARAMETER High Level Input Voltage Low Level Input Voltage High Level Input Current Low Level Input Current High Level Output Voltage Low Level Output Voltage Hi-Z Output Leakage Output Source Current Output Sink Current Reference Current CONDITIONS VCC = 3.6V VCC = 2.65V VIN = VCC VIN = 0V VCC = 2.65V, IO = 10A VCC = 2.65V, IO = 360A VCC = 2.65V, IO = 400A CS = High VOUT = 0V VOUT = VCC CS = VCC tCYC 200s, fCLK 50kHz tCYC = 58s, fCLK = 250kHz CS = VCC LTC1096L, LTC1096L, tCYC 200s, fCLK 50kHz tCYC = 58s, fCLK = 250kHz
q q q q q q q q q q q q q q q q
ICC
Supply Current
AC CHARACTERISTICS
LTC1096/LTC1098
VCC = 5V, VREF = 5V, fCLK = 500kHz, unless otherwise noted.
SYMBOL tSMPL fSMPL(MAX) tCONV tdDO tdis ten thDO tf tr CIN PARAMETER Analog Input Sample Time Maximum Sampling Frequency Conversion Time Delay Time, CLK to DOUT Data Valid Delay Time, CS to DOUT Hi-Z Delay Time, CLK to DOUT Enable Time Output Data Remains Valid After CLK DOUT Fall Time DOUT Rise Time Input Capacitance See Operating Sequence See Test Circuits See Test Circuits See Test Circuits CLOAD = 100pF See Test Circuits See Test Circuits Analog Inputs On Channel Analog Inputs Off Channel Digital Input
q q q q q
6
U
MIN 1.9
TYP
MAX 0.45 2.5 - 2.5
UNITS V V A A V V
2.3 2.1
2.64 2.50 0.3 3.0 - 10 15 0.001 3.500 35.000 0.001 40 120 44 155 2.5 7.5 50.0 3.0 80 180 88 230
V A mA mA A A A A A A A A
LTC1098L, tCYC 200s, fCLK 50kHz LTC1098L, tCYC = 58s, fCLK = 250kHz
CONDITIONS See Operating Sequence
q
MIN 33
TYP 1.5 8 200 170 60 180 70 25 25 5 5
MAX
UNITS CLK Cycles kHz CLK Cycles
450 450 250 250 100
ns ns ns ns ns ns pF pF pF
LTC1096/LTC1096L LTC1098/LTC1098L AC CHARACTERISTICS
LTC1096/LTC1098
VCC = 3V, VREF = 2.5V, fCLK = 250kHz, unless otherwise noted.
SYMBOL tSMPL tCONV tdDO tdis ten thDO tf tr CIN PARAMETER Analog Input Sample Time Conversion Time Delay Time, CLK to DOUT Data Valid Delay Time, CS to DOUT Hi-Z Delay Time, CLK to DOUT Enable Time Output Data Remains Valid After CLK DOUT Fall Time DOUT Rise Time Input Capacitance CONDITIONS See Operating Sequence
q
MIN 16.5
TYP 1.5 8
MAX
UNITS CLK Cycles kHz CLK Cycles
fSMPL(MAX) Maximum Sampling Frequency See Operating Sequence See Test Circuits (Note 9) See Test Circuits (Note 9) See Test Circuits (Note 9) CLOAD = 100pF See Test Circuits (Note 9) See Test Circuits (Note 9) Analog Inputs On Channel Analog Inputs Off Channel Digital Input
q q q
500 220 160 400 70 50 25 5 5
1000 800 480 250 150
ns ns ns ns ns ns pF pF pF
q q
LTC1096L/LTC1098L
VCC = 2.65V, VREF = 2.5V, fCLK = 250kHz, unless otherwise noted.
SYMBOL tSMPL tCONV tdDO tdis ten thDO tf tr CIN PARAMETER Analog Input Sample Time Conversion Time Delay Time, CLK to DOUT Data Valid Delay Time, CS to DOUT Hi-Z Delay Time, CLK to DOUT Enable Time Output Data Remains Valid After CLK DOUT Fall Time DOUT Rise Time Input Capacitance CONDITIONS See Operating Sequence
q
MIN 16.5
TYP 1.5 8
MAX
UNITS CLK Cycles kHz CLK Cycles
fSMPL(MAX) Maximum Sampling Frequency See Operating Sequence See Test Circuits See Test Circuits See Test Circuits CLOAD = 100pF See Test Circuits See Test Circuits Analog Inputs On Channel Analog Inputs Off Channel Digital Input The q denotes specifications which apply over the operating temperature range. Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: All voltage values are with respect to GND. Note 3: For the 8-lead PDIP, consult the factory. Note 4: Linearity error is specified between the actual and points of the A/D transfer curve. Note 5: Total unadjusted error includes offset, full scale, linearity, multiplexer and hold step errors. Note 6: Two on-chip diodes are tied to each reference and analog input which will conduct for reference or analog input voltages one diode drop below GND or one diode drop above VCC. This spec allows 50mV forward bias of either diode. This means that as long as the reference or analog
q q q
500 220 160 400 70 50 25 5 5
1000 800 480 250 200
ns ns ns ns ns ns pF pF pF
q q
input does not exceed the supply voltage by more than 50mV, the output code will be correct. To achieve an absolute 0V to 5V input voltage range will therefore require a minimum supply voltage of 4.950V over initial tolerance, temperature variations and loading. For 5.5V < VCC 9V, reference and analog input range cannot exceed 5.55V. If reference and analog input range are greater than 5.55V, the output code will not be guaranteed to be correct. Note 7: The supply voltage range for the LTC1096L/LTC1098L is from 2.65V to 4V. The supply voltage range for the LTC1096 is from 3V to 9V, but the supply voltage range for the LTC1098 is only from 3V to 6V. Note 8: Channel leakage current is measured after the channel selection. Note 9: These specifications are either correlated from 5V specifications or guaranteed by design.
7
LTC1096/LTC1096L LTC1098/LTC1098L
TYPICAL PERFOR A CE CHARACTERISTICS
Supply Current vs Clock Rate for Active and Shutdown Modes
250 200 TA = 25C CS = 0V
SUPPLY CURRENT, ICC (A)
SUPPLY CURRENT, ICC (A)
150 VCC = 5V 100 50 10 CS = VCC 1 10 100 FREQUENCY (kHz) 1000
LTC1096/98 * TPC01
SUPPLY CURRENT, ICC (A)
VCC = 9V
0.002 0
MAGNITUDE OF OFFSET CHANGE (LSB = 1/256 x VREF)
Change in Offset vs Reference Voltage LTC1096
0.50
MAGNITUDE OF OFFSET CHANGE (LSB)
0.25
CHANGE IN LINEARITY (LSB)
TA = 25C VCC = 5V FCLK = 500kHz
0
-0.25
-0.50
0
1
3 4 2 REFERENCE VOLTAGE (V)
Change in Linearity vs Supply Voltage
0.5 0.4
CHANGE IN LINEARTY (LSB)
0.5
0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5 0 1 2
TA = 25C VREF = 2.5V FCLK = 100kHz
CHANGE IN GAIN (LSB)
0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5
CHANGE IN GAIN (LSB)
345678 SUPPLY VOLTAGE, VCC (V)
8
UW
5
LTC1096/98 * TPC04
Supply Current vs Supply Voltage Active and Shutdown Modes
100
1000
Supply Current vs Sample Frequency LTC1096
TA = 25C VCC = VREF = 5V
TA = 25C VREF = 2.5V
80
100
60 "ACTIVE" MODE CS = 0 40
10
20 "SHUTDOWN" MODE CS = VCC
0.001 0 0 1
1
7 3 2 5 6 4 SUPPLY VOLTAGE,VCC (V)
8
9
0.1
1 10 SAMPLE FREQUENCY, fSMPL (kHz)
100
LTC1096/98 * TPC03
LTC1096/98 * TPC02
Change in Offset vs Supply Voltage
0.5 0.4 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5
-O.50 0.50
Change in Linearity vs Reference Voltage LTC1096
TA = 25C VREF = 2.5V FCLK = 100kHz
TA = 25C VCC = 5V FCLK = 500kHz
0.25
0
-0.25
0
1
2
345678 SUPPLY VOLTAGE, VCC (V)
9
10
0
1
3 4 2 REFERENCE VOLTAGE (V)
5
LTC1096/98 * TPC05
LTC1096/98 * TPC06
Change in Gain vs Supply Voltage
0.50
TA = 25C VREF = 2.5V FCLK = 100kHz 0.4 0.3
Change in Gain vs Reference Voltage LTC1096
TA = 25C VCC = 5V FCLK = 500kHz
0.25
0
-0.25
9
10
0
1
2
345678 SUPPLY VOLTAGE, VCC (V)
9
10
-O.50
0
1
3 4 2 VOLTAGE REFERENCE (V)
5
LTC1096/98 * TPC07
LTC1096/98 * TPC08
LTC1096/98 * TPC09
LTC1096/LTC1096L LTC1098/LTC1098L
TYPICAL PERFOR A CE CHARACTERISTICS
Maximum Clock Frequency vs Source Resistance
1
MAXIMUM CLOCK FREQUENCY* (MHz)
VIN + INPUT - INPUT RSOURCE-
MAXIMUM CLOCK FREQUENCY (MHz)
TA = 25C VCC = VREF = 5V 0.75
1.0 0.75 0.5 0.25 0
LOGIC THRESH0LD (V)
0.50
0.25
0 1 10 RSOURCE - (k)
LTC1096/98 * TPC10
Wake-Up Time vs Supply Voltage
4 TA = 25C VREF = 2.5V
10
MINIMUM WAKE-UP TIME (s)
LEAKAGE CURRENT (nA)
3
WAKE-UP TIME (s)
2
1
0
0
2
6 8 4 SUPPLY VOLTAGE, VCC (V)
LTC1096/98 * TPC13
Minimum Clock Frequency for 0.1LSB Error vs Temperature
200 MINIMUM CLOCK FREQUENCY (kHz) 180 160 140 120 100 80 60 40 20 0 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (C)
LTC1096/98 * TPC16
VREF = 5V VCC = 5V
AMPLITUDE (dB)
ENOBs
* Maximum CLK frequency represents the clock frequency at which a 0.1LSB shift in the error at any code transition from its 0.75MHz value is first detected. As the CLK frequency is decreased from 500kHz, minimum CLK frequency (error 0.1LSB) represents the frequency at which a 0.1LSB shift in any code transition from its 500kHz value is first detected.
UW
100
10
Maximum Clock Frequency vs Supply Voltage
1.5 1.25 TA = 25C VREF = 2.5V 4 5
Digital Input Logic Threshold vs Supply Voltage
TA = 25C
3
2
1
0
2
4 6 8 SUPPLY VOLTAGE (V)
10
0
0
2
6 8 4 SUPPLY VOLTAGE, VCC (V)
10
LTC1096/98 * TPC11
LTC1096/98 * TPC12
Minimum Wake-Up Time vs Source Resistance
1000
TA = 25C VREF = 5V 7.5
Input Channel Leakage Current vs Temperature
VREF = 5V VCC = 5V 100
10 ON CHANNEL 1 OFF CHANNEL
5.0
RSOURCE+
2.5
VIN
+ -
0.1
0 1 10 RSOURCE (k)
LTC1096/98 * TPC14
100
0.01 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (C)
LTC1096/98 * TPC15
ENOBs vs Frequency
10 9 8 7 6 5 4 3 2 1 0 1 10 FREQUENCY (kHz) 100
LTC1096/98 * TPC17
FFT Plot
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 0 2 4 10 12 6 8 FREQUENCY (kHz) 14 16 TA = 25C VCC = VREF = 5V fSMPL = 31.25kHz fIN = 5.8kHz
TA = 25C VCC = VREF = 5V fSMPL = 31.25kHz
LTC1096/98 * TPC18
9
LTC1096/LTC1096L LTC1098/LTC1098L
PI FU CTIO S
LTC1096/LTC1096L
CS/SHDN (Pin 1): Chip Select Input. A logic low on this input enables the LTC1096/LTC1096L. A logic high on this input disables the LTC1096/LTC1096L and disconnects the power to the LTC1096/LTC1096L. IN + (Pin 2): Analog Input. This input must be free of noise with respect to GND. IN - (Pin 3): Analog Input. This input must be free of noise with respect to GND. GND (Pin 4): Analog Ground. GND should be tied directly to an analog ground plane. VREF (Pin 5): Reference Input. The reference input defines the span of the A/D converter and must be kept free of noise with respect to GND. DOUT (Pin 6): Digital Data Output. The A/D conversion result is shifted out of this output. CLK (Pin 7): Shift Clock. This clock synchronizes the serial data transfer. VCC (Pin 8): Power Supply Voltage. This pin provides power to the A/D converter. It must be free of noise and ripple by bypassing directly to the analog ground plane.
BLOCK DIAGRA
IN + (CH0)
IN - (CH1)
GND
10
+
-
W
U
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LTC1098/LTC1098L
CS/SHDN (Pin 1): Chip Select Input. A logic low on this input enables the LTC1098/LTC1098L. A logic high on this input disables the LTC1098/LTC1098L and disconnects the power to the LTC1098/LTC1098L. CH0 (Pin 2): Analog Input. This input must be free of noise with respect to GND. CH1 (Pin 3): Analog Input. This input must be free of noise with respect to GND. GND (Pin 4): Analog Ground. GND should be tied directly to an analog ground plane. DIN (Pin 5): Digital Data Input. The multiplexer address is shifted into this pin. DOUT (Pin 6): Digital Data Output. The A/D conversion result is shifted out of this output. CLK (Pin 7): Shift Clock. This clock synchronizes the serial data transfer. VCC (VREF)(Pin 8): Power Supply Voltage. This pin provides power and defines the span of the A/D converter. It must be free of noise and ripple by bypassing directly to the analog ground plane.
LTC1096/LTC1096L
VCC (VCC /VREF) CS (DIN) CLK
BIAS AND SHUTDOWN CIRCUIT
SERIAL PORT
DOUT
CSAMPLE
SAR MICROPOWER COMPARATOR CAPACITIVE DAC
VREF
PIN NAMES IN PARENTHESES REFER TO THE LTC1098/LTC1098L
LTC1096/LTC1096L LTC1098/LTC1098L TEST CIRCUITS
On and Off Channel Leakage Current
5V ION A IOFF A ON CHANNEL
Load Circuit for tdDO, tr and tf
1.4V
3k DOUT 100pF TEST POINT
* * * *
POLARITY
OFF CHANNEL
LTC1096/98 * TC02
LTC1096/98 * TC1
Voltage Waveforms for DOUT Delay Time, tdDO
Voltage Waveforms for DOUT Rise and Fall Times, tr, tf
CLK
VIL tdDO VOH
DOUT
VOH VOL tr tf
DOUT VOL
LTC1096/98 * TC03
LTC1096/98 * TC04
Load Circuit for tdis and ten
Voltage Waveforms for tdis
TEST POINT
CS
3k DOUT 100pF tdis WAVEFORM 1
LTC1096/98 * TC05
2.0V
5V tdis WAVEFORM 2, ten
DOUT WAVEFORM 1 (SEE NOTE 1) tdis DOUT WAVEFORM 2 (SEE NOTE 2)
90%
10%
NOTE 1: WAVEFORM 1 IS FOR AN OUTPUT WITH INTERNAL CONDITIONS SUCH THAT THE OUTPUT IS HIGH UNLESS DISABLED BY THE OUTPUT CONTROL. NOTE 2: WAVEFORM 2 IS FOR AN OUTPUT WITH INTERNAL CONDITIONS SUCH THAT THE OUTPUT IS LOW UNLESS DISABLED BY THE OUTPUT CONTROL.
LTC1096/98 * TC06
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LTC1096/LTC1096L LTC1098/LTC1098L TEST CIRCUITS
Voltage Waveforms for ten
LTC1096/LTC1096L CS t WAKEUP CLK 1
DOUT
LTC1098/LTC1098L CS
B7 VOL ten
LTC1096/98 * TC07
DIN
START
CLK
1
2
3
4
5
DOUT ten
B7 VOL
LTC1096/98 * TC08
APPLICATI
OVERVIEW
S I FOR ATIO
The LTC1096/LTC1096L/LTC1098/LTC1098L are 8-bit micropower, switched-capacitor A/D converters. These sampling ADCs typically draw 120A of supply current when sampling up to 33kHz. Supply current drops linearly as the sample rate is reduced (see Supply Current vs Sample Rate on the first page of this data sheet). The ADCs automatically power down when not performing conversion, drawing only leakage current. They are packaged in 8-pin SO packages. The LTC1096L/LTC1098L operate on a single supply ranging from 2.65V to 4V. The LTC1096 operates on a single supply ranging from 3V to 9V while the LTC1098 operates from 3V to 6V supplies. The LTC1096/LTC1096L/LTC1098/LTC1098L comprise an 8-bit, switched-capacitor ADC, a sample-and-hold and
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a serial port (see Block Diagram). Although they share the same basic design, the LTC1096(L) and LTC1098(L) differ in some respects. The LTC1096(L) has a differential input and has an external reference input pin. It can measure signals floating on a DC common mode voltage and can operate with reduced spans down to 250mV. Reducing the span allows it to achieve 1mV resolution. The LTC1098(L) has a 2-channel input multiplexer and can convert either channel with respect to ground or the difference between the two. SERIAL INTERFACE The LTC1098(L) communicates with microprocessors and other external circuitry via a synchronous, half duplex, 4-wire serial interface while the LTC1096(L) uses a 3-wire interface (see Operating Sequence in Figures 1 and 2).
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LTC1096/LTC1096L LTC1098/LTC1098L
APPLICATI S I FOR ATIO
Power Down and Wake-Up Time The LTC1096(L)/LTC1098(L) draw power when the CS pin is low and shut themselves down when that pin is high. In order to have a correct conversion result, a 10s wake-up time must be provided from CS falling to the first falling clock (CLK) after the first rising CLK for the LTC1096(L) and from CS falling to the MSBF bit CLK falling for the LTC1098(L) (see Operating Sequence). If the LTC1096(L)/ LTC1098(L) are running with clock frequency less than or equal to 100kHz, the wake-up time is inherently provided. Example Two cases are shown at right to illustrate the relationship among wake-up time, setup time and CLK frequency for the LT1096(L). In Case 1 the clock frequency is 100kHz. One clock cycle is 10s which can be the wake-up time, while half of that can be the setup time. In Case 2 the clock frequency is 50kHz, half of the clock cycle plus the setup time (=1s) can be the wake-up time. If the CLK frequency is higher
tCYC
CS
CLK tsuCS tWAKEUP DOUT HI-Z NULL BIT
B7 B6 (MSB)
CS POWER DOWN CLK tsuCS tWAKEUP DOUT Hi-Z NULL BIT
B7
B6
(MSB)
*AFTER COMPLETING THE DATA TRANSFER, IF FURTHER CLOCKS ARE APPLIED WITH CS LOW, THE ADC WILL OUTPUT ZEROS INDEFINITELY.
Figure 1. LTC1096(L) Operating Sequence
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tWAKEUP CS tsu CLK DOUT NULL BIT B7
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Case 1. Timing Diagram
tWAKEUP CS tsu CLK DOUT
LTC1096/98 * AI Ex.
10s
Case 2. Timing Diagram
than 100kHz, Figure 1 shows the relationship between the wake-up time and setup time. The wake-up time is inherently provided for the LTC1098(L) with setup time = 1s (see Figure 2).
POWER DOWN
B5 tCONV
B4
B3
B2
B1
B0
Hi-Z
tCYC
B5 tCONV
B4
B3
B2
B1
B0
B1
B2
B3
B4
B5
B6
B7*
Hi-Z
LTC1096/98 F01
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LTC1096/LTC1096L LTC1098/LTC1098L
APPLICATI S I FOR ATIO
MSB-FIRST DATA (MSBF = 1)
tCYC
CS tWAKEUP CLK tsuCS START DIN SGL/ DIFF DOUT HI-Z tSMPL MSBF NULL BIT B7 B6 (MSB) B5 tCONV B4 B2 B0* ODD/ SIGN DON'T CARE
MSB-FIRST DATA (MSBF = 0)
tCYC
CS tWAKEUP CLK tsuCS START DIN SGL/ DIFF DOUT HI-Z tSMPL MSBF NULL B6 BIT B7 (MSB) B5 tCONV B4 B3 B2 B1 B0 B1 B2 B3 B4 B5 B6 B7* ODD/ SIGN DON'T CARE
*AFTER COMPLETING THE DATA TRANSFER, IF FURTHER CLOCKS ARE APPLIED WITH CS LOW, THE ADC WILL OUTPUT ZEROS INDEFINITELY.
Figure 2. LTC1098(L) Operating Sequence Example: Differential Inputs (CH +, CH -)
Data Transfer The CLK synchronizes the data transfer with each bit being transmitted on the falling CLK edge and captured on the rising CLK edge in both transmitting and receiving systems. The LTC1098(L) first receives input data and then transmits back the A/D conversion result (half duplex). Because of the half duplex operation, DIN and DOUT may be tied together allowing transmission over just three wires: CS, CLK and DATA (DIN/DOUT). Data transfer is initiated by a falling chip select (CS) signal. After CS falls the LTC1098(L) looks for a start bit. After the start bit is received, the 3-bit input word is shifted into the DIN input which configures the LTC1098(L) and starts the conversion. After one null bit, the result of the conversion
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POWER DOWN B3 B1 Hi-Z POWER DOWN Hi-Z
LTC1096/98 F02
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CS DIN 1 DOUT 1 SHIFT MUX ADDRESS IN 1 NULL BIT SHIFT A/D CONVERSION RESULT OUT
LTC1096/98 * AI01
DIN 2 DOUT 2
is output on the DOUT line. At the end of the data exchange CS should be brought high. This resets the LTC1098(L) in preparation for the next data exchange. The LTC1096(L) does not require a configuration input word and has no DIN pin. A falling CS initiates data transfer as shown in the LTC1096(L) operating sequence. After CS falls, the first CLK pulse enables DOUT. After one null bit,
LTC1096/LTC1096L LTC1098/LTC1098L
APPLICATI
S I FOR ATIO
the A/D conversion result is output on the DOUT line. Bringing CS high resets the LTC1096(L) for the next data exchange. Input Data Word The LTC1096(L) requires no DIN word. It is permanently configured to have a single differential input. The conversion result, in which output on the DOUT line is MSB-first sequence, followed by LSB sequence providing easy interface to MSB- or LSB-first serial ports. The LTC1098(L) clocks data into the DIN input on the rising edge of the clock. The input data words are defined as follows:
START SGL/ DIFF ODD/ MSBF SIGN
MUX MSB-FIRST/ ADDRESS LSB-FIRST
LTC1096/8 * AI02
Start Bit The first "logical one" clocked into the DIN input after CS goes low is the start bit. The start bit initiates the data transfer. The LTC1098(L) will ignore all leading zeros which precede this logical one. After the start bit is received, the remaining bits of the input word will be clocked in. Further inputs on the DIN pin are then ignored until the next CS cycle. Multiplexer (MUX) Address The bits of the input word following the START bit assign the MUX configuration for the requested conversion. For a given channel selection, the converter will measure the voltage between the two channels indicated by the "+" and "-" signs in the selected row of the followintg tables. In single-ended mode, all input channels are measured with respect to GND.
LTC1098(L) Channel Selection
MUX ADDRESS SGL/DIFF ODD/SIGN 1 0 1 1 0 0 0 1 CHANNEL # 0 1 + + + - - + GND - -
SINGLE-ENDED MUX MODE DIFFERENTIAL MUX MODE
LTC1096/8 * AI03
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MSB-First/LSB-First (MSBF) The output data of the LTC1098(L) is programmed for MSB-first or LSB-first sequence using the MSBF bit. When the MSBF bit is a logical one, data will appear on the DOUT line in MSB-first format. Logical zeros will be filled in indefinitely following the last data bit. When the MSBF bit is a logical zero, LSB-first data will follow the normal MSB-first data on the DOUT line. (see Operating Sequence) Unipolar Transfer Curve The LTC1096(L)/LTC1098(L) are permanently configured for unipolar only. The input span and code assignment for this conversion type are shown in the following figures for a 5V reference.
Unipolar Transfer Curve
11111111 11111110
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* * *
00000001 00000000
0V 1LSB VREF-1LSB VREF VREF-2LSB
VIN
LTC1096/8 * AI04
Unipolar Output Code
OUTPUT CODE 11111111 11111110 * * * 00000001 00000000 INPUT VOLTAGE VREF - 1LSB VREF - 2LSB * * * 1LSB 0V INPUT VOLTAGE (VREF = 5.000V) 4.9805V 4.9609V * * * 0.0195V 0V
LTC1096/8 * AI05
Operation with DIN and DOUT Tied Together The LTC1098(L) can be operated with DIN and DOUT tied together. This eliminates one of the lines required to communicate to the microprocessor (MPU). Data is transmitted in both directions on a single wire. The processor pin connected to this data line should be configurable as either an input or an output. The LTC1098(L) will take control of the data line and drive it low on the 4th falling
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LTC1096/LTC1096L LTC1098/LTC1098L
APPLICATI
CS
S I FOR ATIO
1 CLK
2
DATA (DIN/DOUT)
START
SGL/DIFF
MPU CONTROLS DATA LINE AND SENDS MUX ADDRESS TO LTC1098(L) PROCESSOR MUST RELEASE DATA LINE AFTER 4TH RISING CLK AND BEFORE THE 4TH FALLING CLK
Figure 3. LTC1098(L) Operation with DIN and DOUT Tied Together
CLK edge after the start bit is received (see Figure 3). Therefore the processor port line must be switched to an input before this happens, to avoid a conflict. In the Typical Applications section, there is an example of interfacing the LTC1098(L) with DIN and DOUT tied together to the Intel 8051 MPU. ACHIEVING MICROPOWER PERFORMANCE
SUPPLY CURRENT, ICC (A)
With typical operating currents of 40A and automatic shutdown between conversions, the LTC1096/LTC1098 achieves extremely low power consumption over a wide range of sample rates (see Figure 4). In systems that convert continuously, the LTC1096/LTC1098 will draw its
1000 TA = 25C VCC = VREF = 5V
SUPPLY CURRENT, ICC (A)
100
10
1 0.1 1 10 SAMPLE FREQUENCY, fSMPL (kHz) 100
LTC1096/98 * TPC03
Figure 4. Automatic Power Shutdown Between Conversions Allows Power Consumption to Drop with Sample Rate
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MSBF BIT LATCHED BY LTC1098(L) 3 4 ODD/SIGN MSBF B7 B6
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***
LTC1098(L) CONTROLS DATA LINE AND SENDS A/D RESULT BACK TO MPU LTC1098(L) TAKES CONTROL OF DATA LINE ON 4TH FALLING CLK
LTC1-96/8 * F03
normal operating power continuously. Figure 5 shows that the typical current varies from 40A at clock rates below 50kHz to 100A at 500kHz. Several things must be taken into account to achieve such a low power consumption.
ACTIVE AND SHUTDOWN MODES 140 120 100 80 60 40 20 SHUTDOWN (CS HIGH) 10k 100k 1k CLOCK FREQUENCY (Hz) 1M ACTIVE (CS LOW) TA = 25C VCC = 5V
0.002 0 100
LTC1096/98 * F05
Figure 5. After a Conversion, When the Microprocessor Drives CS High, the ADC Automatically Shuts Down Until the Next Conversion. The Supply Current, Which Is Very Low During cConversions, Drops to Zero in Shutdown
Shutdown Figures 1 and 2 show the operating sequence of the LTC1096/LTC1098. The converter draws power when the CS pin is low and powers itself down when that pin is high. If the CS pin is not taken to ground when it is low and not taken to supply voltage when it is high, the input buffers of
LTC1096/LTC1096L LTC1098/LTC1098L
APPLICATI S I FOR ATIO
the converter will draw current. This current may be larger than the typical supply current. It is worthwhile to bring the CS pin all the way to ground when it is low and all the way to supply voltage when it is high to obtain the lowest supply current. When the CS pin is high (= supply voltage), the converter is in shutdown mode and draws only leakage current. The status of the DIN and CLK input have no effect on supply current during this time. There is no need to stop DIN and CLK with CS = high, except the MPU may benefit. Minimize CS Low Time In systems that have significant time between conversions, lowest power drain will occur with the minimum CS low time. Bringing CS low, waiting 10s for the wake-up time, transferring data as quickly as possible, and then bringing it back high will result in the lowest current drain. This minimizes the amount of time the device draws power. Even though the device draws more power at high clock rates, the net power is less because the device is on for a shorter time. DOUT Loading Capacitive loading on the digital output can increase power consumption. A 100pF capacitor on the DOUT pin can more than double the 100A supply current drain at a 500kHz clock frequency. An extra 100A or so of current goes into charging and discharging the load capacitor. The same goes for digital lines driven at a high frequency by any logic. The CxVxf currents must be evaluated and the troublesome ones minimized. Lower Supply Voltage For lower supply voltages, LTC offers the LTC1096L/ LTC1098L. These pin compatible devices offer specified performance to 2.65VMIN supply. OPERATING ON OTHER THAN 5V SUPPLIES The LTC1096 operates from 3V to 9V supplies and the LTC1098 operates from 3V to 6V supplies. To operate the LTC1096/LTC1098 on other than 5V supplies, a few things must be kept in mind.
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Wake-Up Time A 10s wake-up time must be provided for the ADCs to convert correctly on a 5V supply. The wake-up time is typically less than 3s over the supply voltage range (see typical curve of Wake-Up Time vs Supply Voltage). With 10s wake-up time provided over the supply range, the ADCs will have adequate time to wake up and acquire input signals. Input Logic Levels The input logic levels of CS, CLK and DIN are made to meet TTL on 5V supply. When the supply voltage varies, the input logic levels also change. For the LTC1096/LTC1098 to sample and convert correctly, the digital inputs have to meet logic low and high levels relative to the operating supply voltage (see typical curve of Digital Input Logic Threshold vs Supply Voltage). If achieving micropower consumption is desirable, the digital inputs must go railto-rail between supply voltage and ground (see ACHIEVING MICROPOWER PERFORMANCE section). Clock Frequency The maximum recommended clock frequency is 500kHz for the LTC1096/LTC1098 running off a 5V supply. With the supply voltage changing, the maximum clock frequency for the devices also changes (see the typical curve of Maximum Clock Rate vs Supply Voltage). If the maximum clock frequency is used, care must be taken to ensure that the device converts correctly. Mixed Supplies It is possible to have a microprocessor running off a 5V supply and communicate with the LTC1096/LTC1098 operating on 3V or 9V supplies. The requirement to achieve this is that the outputs of CS, CLK and DIN from the MPU have to be able to trip the equivalent inputs of the ADCs and the output of DOUT from the ADCs must be able to toggle the equivalent input of the MPU (see typical curve of Digital Input Logic Threshold vs Supply Voltage). With the LTC1096 operating on a 9V supply, the output of DOUT may go between 0V and 9V. The 9V output may damage the MPU running off a 5V supply. The way to get around this possibility is to have a resistor divider on DOUT
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LTC1096/LTC1096L LTC1098/LTC1098L
APPLICATI S I FOR ATIO
(Figure 6) and connect the center point to the MPU input. It should be noted that to get full shutdown, the CS input of the LTC1096/LTC1098 must be driven to the VCC voltage. This would require adding a level shift circuit to the CS signal in Figure 6.
9V
OPTIONAL LEVEL SHIFT
9V 4.7F
MPU (e.g. 8051) CS DIFFERENTIAL INPUTS COMMON MODE RANGE 0V TO 6V +IN -IN GND VCC CLK DOUT VREF 6V 50k 50k P1.4 P1.3 P1.2
LTC1096
LTC1096/98 * F06
Figure 6. Interfacing a 9V Powered LTC1096 to a 5V System
BOARD LAYOUT CONSIDERATIONS Grounding and Bypassing The LTC1096(L)/LTC1098(L) should be used with an analog ground plane and single point grounding techniques. The GND pin should be tied directly to the ground plane.
CS
CLK
DIN
START
DOUT 1ST BIT TEST "-" INPUT MUST SETTLE DURING THIS TIME "+" INPUT
"-" INPUT
Figure 7. LTC1098(L) "+" and "-" Input Settling Windows
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The VCC pin should be bypassed to the ground plane with a 1F tantalum with leads as short as possible. If power supply is clean, the LTC1096(L)/LTC1098(L) can also operate with smaller 0.1F surface mount or ceramic bypass capacitors. All analog inputs should be referenced directly to the single point ground. Digital inputs and outputs should be shielded from and/or routed away from the reference and analog circuitry. SAMPLE-AND-HOLD
5V
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Both the LTC1096(L) and the LTC1098(L) provide a builtin sample-and-hold (S&H) function to acquire signals. The S&H of the LTC1096(L) acquires input signals from "+" input relative to "-" input during the tWAKEUP time (see Figure 1). However, the S&H of the LTC1098(L) can sample input signals in the single-ended mode or in the differential inputs during the tSMPL time (see Figure 7). Single-Ended Inputs The sample-and-hold of the LTC1098(L) allows conversion of rapidly varying signals. The input voltage is sampled during the tSMPL time as shown in Figure 7. The sampling interval begins as the bit preceding the MSBF bit is shifted
SAMPLE "+" INPUT MUST SETTLE DURING THIS TIME tSMPL tCONV HOLD
SGL/DIFF
MSBF
DON'T CARE
B7
LTC1096/8 * F07
LTC1096/LTC1096L LTC1098/LTC1098L
APPLICATI S I FOR ATIO
in and continues until the falling CLK edge after the MSBF bit is received. On this falling edge, the S&H goes into hold mode and the conversion begins. Differential Inputs With differential inputs, the ADC no longer converts just a single voltage but rather the difference between two voltages. In this case, the voltage on the selected "+" input is still sampled and held and therefore may be rapidly time varying just as in single-ended mode. However, the voltage on the selected "-" input must remain constant and be free of noise and ripple throughout the conversion time. Otherwise, the differencing operation may not be performed accurately. The conversion time is 8 CLK cycles. Therefore, a change in the "-" input voltage during this interval can cause conversion errors. For a sinusoidal voltage on the "-" input this error would be: VERROR (MAX) = VPEAK * 2 * * f("-") * 8/fCLK Where f("-") is the frequency of the "-" input voltage, VPEAK is its peak amplitude and fCLK is the frequency of the CLK. In most cases VERROR will not be significant. For a 60Hz signal on the "-" input to generate a 1/4LSB error (5mV) with the converter running at CLK = 500kHz, its peak value would have to be 750mV. ANALOG INPUTS Because of the capacitive redistribution A/D conversion techniques used, the analog inputs of the LTC1096(L)/ LTC1098(L )have capacitive switching input current spikes. These current spikes settle quickly and do not cause a problem. However, if large source resistances are used or if slow settling op amps drive the inputs, care must be taken to ensure that the transients caused by the current spikes settle completely before the conversion begins. "+" Input Settling The input capacitor of the LTC1096(L) is switched onto "+" input during the wake-up time (see Figure 1) and samples the input signal within that time. However, the input capacitor of the LTC1098(L) is switched onto "+" input during the sample phase (tSMPL, see Figure 7). The sample phase is 1.5 CLK cycles before conversion starts. The voltage on the "+" input must settle completely within
VIN + C1 RSOURCE - VIN - C2
LTC1096/8 * F8
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t WAKEUP or tSMPL for the LTC1096(L) or the LTC1098(L) respectively. Minimizing RSOURCE+ and C1 will improve the input settling time. If a large "+" input source resistance must be used, the sample time can be increased by using a slower CLK frequency. "-" Input Settling At the end of the tWAKEUP or tSMPL, the input capacitor switches to the "-" input and conversion starts (see Figures 1 and 7). During the conversion the "+" input voltage is effectively "held" by the sample-and-hold and will not affect the conversion result. However, it is critical that the "-" input voltage settles completely during the first CLK cycle of the conversion time and be free of noise. Minimizing RSOURCE- and C2 will improve settling time. If a large "-" input source resistance must be used, the time allowed for settling can be extended by using a slower CLK frequency. Input Op Amps When driving the analog inputs with an op amp it is important that the op amp settle within the allowed time (see Figure 7). Again, the "+" and "-" input sampling times can be extended as described above to accommodate slower op amps. Most op amps, including the LT1006 and LT1413 single supply op amps, can be made to settle well even with the minimum settling windows of 3s ("+" input) which occur at the maximum clock rate of 500kHz. Source Resistance The analog inputs of the LTC1096/LTC1098 look like a 25pF capacitor (CIN) in series with a 500 resistor (RON) as shown in Figure 8. CIN gets switched between the selected "+" and "-" inputs once during each conversion
RSOURCE + "+" INPUT LTC1096 LTC1098 RON = 500 CIN = 25pF "-" INPUT
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Figure 8. Analog Input Equivalent Circuit
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LTC1096/LTC1096L LTC1098/LTC1098L
APPLICATI S I FOR ATIO
cycle. Large external source resistors and capacitances will slow the settling of the inputs. It is important that the overall RC time constants be short enough to allow the analog inputs to completely settle within the allowed time. RC Input Filtering It is possible to filter the inputs with an RC network as shown in Figure 9. For large values of CF (e.g., 1F), the capacitive input switching currents are averaged into a net DC current. Therefore, a filter should be chosen with a small resistor and large capacitor to prevent DC drops across the resistor. The magnitude of the DC current is approximately IDC = 25pF(VIN /tCYC) and is roughly proportional to VIN. When running at the minimum cycle time of 29s, the input current equals 4.3A at VIN = 5V. In this case, a filter resistor of 390 will cause 0.1LSB of fullscale error. If a larger filter resistor must be used, errors can be eliminated by increasing the cycle time.
RFILTER VIN CFILTER IDC "+" LTC1098 "-"
LTC1096/8 * F9
Figure 9. RC Input Filtering
Input Leakage Current Input leakage currents can also create errors if the source resistance gets too large. For instance, the maximum input leakage specification of 1A (at 125C) flowing through a source resistance of 3.9k will cause a voltage drop of 3.9mV or 0.2LSB. This error will be much reduced at lower temperatures because leakage drops rapidly (see typical curve of Input Channel Leakage Current vs Temperature). REFERENCE INPUTS The voltage on the reference input of the LTC1096 defines the voltage span of the A/D converter. The reference input transient capacitive switching currents due to the switchedcapacitor conversion technique (see Figure 10). During each bit test of the conversion (every CLK cycle), a capaci-
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tive current spike will be generated on the reference pin by the ADC. These current spikes settle quickly and do not cause a problem. Using a slower CLK will allow more time for the reference to settle. Even at the maximum CLK rate of 500kHz most references and op amps can be made to settle within the 2s bit time.
REF+ 5 ROUT VREF GND 4 LTC1096 EVERY CLK CYCLE RON 5pF TO 30pF
LTC1096/8 * F10
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Figure 10. Reference Input Equivalent Circuit
Reduced Reference Operation The minimum reference voltage of the LTC1098 is limited to 3V because the VCC supply and reference are internally tied together. However, the LTC1096 can operate with reference voltages below 1V. The effective resolution of the LTC1096 can be increased by reducing the input span of the converter. The LTC1096 exhibits good linearity and gain over a wide range of reference voltages (see typical curves of Linearity and Full Scale Error vs Reference Voltage). However, care must be taken when operating at low values of VREF because of the reduced LSB step size and the resulting higher accuracy requirement placed on the converter. The following factors must be considered when operating at low VREF values. 1. Offset 2. Noise 3. Conversion speed (CLK frequency) Offset with Reduced VREF The offset of the LTC1096 has a larger effect on the output code when the ADC is operated with reduced reference voltage. The offset (which is typically a fixed voltage) becomes a larger fraction of an LSB as the size of the LSB is reduced. The typical curve of Unadjusted Offset Error vs Reference Voltage shows how offset in LSBs is related to
LTC1096/LTC1096L LTC1098/LTC1098L
APPLICATI S I FOR ATIO
reference voltage for a typical value of VOS. For example, a VOS of 2mV which is 0.1LSB with a 5V reference becomes 0.5LSB with a 1V reference and 2.5LSBs with a 0.2V reference. If this offset is unacceptable, it can be corrected digitally by the receiving system or by offsetting the "-" input of the LTC1096. Noise with Reduced VREF The total input referred noise of the LTC1096 can be reduced to approximately 1mV peak-to-peak using a ground plane, good bypassing, good layout techniques and minimizing noise on the reference inputs. This noise is insignificant with a 5V reference but will become a larger fraction of an LSB as the size of the LSB is reduced. For operation with a 5V reference, the 1mV noise is only 0.05LSB peak-to-peak. In this case, the LTC1096 noise will contribute virtually no uncertainty to the output code. However, for reduced references, the noise may become a significant fraction of an LSB and cause undesirable jitter in the output code. For example, with a 1V reference, this same 1mV noise is 0.25LSB peak-topeak. This will reduce the range of input voltages over which a stable output code can be achieved by 1LSB. If the reference is further reduced to 200mV, the 1mV noise becomes equal to 1.25LSBs and a stable code may be difficult to achieve. In this case averaging readings may be necessary. This noise data was taken in a very clean setup. Any setupinduced noise (noise or ripple on VCC, VREF or VIN) will add to the internal noise. The lower the reference voltage to be used, the more critical it becomes to have a clean, noise free setup. Conversion Speed with Reduced VREF With reduced reference voltages the LSB step size is reduced and the LTC1096 internal comparator overdrive is reduced. Therefore, it may be necessary to reduce the maximum CLK frequency when low values of VREF are used. Input Divider It is OK to use an input divider on the reference input of the LTC1096 as long as the reference input can be made to
AMPLITUDE (dB)
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settle within the bit time at which the clock is running. When using a larger value resistor divider on the reference input the "-" input should be matched with an equivalent resistance. Bypassing Reference Input with Divider Bypassing the reference input with a divider is also possible. However, care must be taken to make sure that the DC voltage on the reference input will not drop too much below the intended reference voltage. AC PERFORMANCE Two commonly used figures of merit for specifying the dynamic performance of the ADCs in digital signal processing applications are the signal-to-noise ratio (SNR) and the effective number of bits (ENOBs). Signal-to-Noise Ratio The signal-to-noise ratio (SNR) is the ratio between the RMS amplitude of the fundamental input frequency to the RMS amplitude of all other frequency components at the A/D output. This includes distortion as well as noise products and for this reason it is sometimes referred to as signal-to-noise + distortion [S/(N + D)]. The output is band limited to frequencies from DC to one half the sampling frequency. Figure 11 shows spectral content from DC to 15.625kHz which is 1/2 the 31.25kHz sampling rate.
0 -10 -20 -30 -40 -50 -60 -70 -80 -90 -100 -110 -120 0 2 4 8 10 12 6 FREQUENCY (kHz) 14 16 fSAMPLE = 31.25kHz fIN = 11.8kHz
LTC1096/8 * F11
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Figure 11. This Clean FFT of an 11.8kHz Input Shows Remarkable Performance for an ADC That Draws Only 100A When Sampling at the 31.25kHz Rate
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LTC1096/LTC1096L LTC1098/LTC1098L
APPLICATI S I FOR ATIO
Effective Number of Bits The effective number of bits (ENOBs) is a measurement of the resolution of an A/D and is directly related to the S/(N + D) by the equation: ENOB = [S/(N + D) -1.76]/6.02 where S/(N + D) is expressed in dB. At the maximum sampling rate of 33kHz the LTC1096 maintains 7.5 ENOBs or better to 40kHz. Above 40kHz the ENOBs gradually decline, as shown in Figure 12, due to increasing second harmonic distortion. The noise floor remains approximately 70dB.
EFFECTIVE NUMBER OF BITS (ENOBs)
TYPICAL APPLICATI
S
Table 1. Microprocessor with Hardware Serial Interfaces Compatible with the LTC1096(L)/LTC1098(L)
PART NUMBER Motorola MC6805S2,S3 MC68HC11 MC68HC05 RCA CDP68HC05 Hitachi HD6305 HD63705 HD6301 HD63701 HD6303 HD64180 National Semiconductor COP400 Family COP800 Family NS8050U HPC16000 Family Texas Instruments TMS7002 TMS7042 TMS70C02 TMS70C42 TMS32011* TMS32020 Serial Port Serial Port Serial Port Serial Port Serial Port Serial Port MICROWIRETM MICROWIRE/PLUSTM MICROWIRE/PLUS MICROWIR/PLUS SCI Synchronous SCI Synchronous SCI Synchronous SCI Synchronous SCI Synchronous CSI/O SPI SPI SPI SPI TYPE OF INTERFACE
MICROPROCESSOR INTERFACES The LTC1096(L)/LTC1098(L) can interface directly (without external hardware to most popular microprocessor (MPU) synchronous serial formats (see Table 1). If an MPU without a dedicated serial port is used, then three or four of the MPU's parallel port lines can be programmed to form the serial link to the LTC1096(L)/LTC1098(L). Included here is one serial interface example and one example showing a parallel port programmed to form the serial interface. Motorola SPI (MC68HC05C4,CM68HC11) The MC68HC05C4 has been chosen as an example of an MPU with a dedicated serial port. This MPU transfer data MSB-first and in 8-bit increments. With two 8-bit transfers, the A/D result is read into the MPU. The first 8-bit transfer sends the DIN word to the LTC1098(L) and clocks into the processor. The second 8-bit transfer clocks the A/D conversion result, B7 through B0, into the MPU. ANDing the first MUP received byte with 00Hex clears the first byte. Notice how the position of the start bit in the first MPU transmit word is used to position the A/D result right-justified in two memory locations.
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8 fSAMPLE = 31.25kHz 7 6 5 4 3 2 1 0 0 20 INPUT FREQUENCY (kHz)
LTC1096/8 * F12
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40
Figure 12. Dynamic Accuracy Is Maintained Up to an Input Frequency of 40kHz
*Requires external hardware
MICROWIRE and MICROWIRE/PLUS are trademarks of National Semiconductor Corp.
LTC1096/LTC1096L LTC1098/LTC1098L
TYPICAL APPLICATI UO
0 ?
0 B3
S
START BIT BYTE 1 SGL/ ODD/ MSBF X DIFF SIGN BYTE 2 (DUMMY) X X X X X X X X
Data Exchange Between LTC1098(L) and MC68HC05C4
MPU TRANSMIT WORD
0
0
1
X = DON'T CARE CS
START DIN SGL/ ODD/ DIFF SIGN MSBF DON'T CARE
CLK
DOUT
B7
B6
B5
B4
B3
B2
B1
B0
MPU RECEIVED WORD
?
?
?
?
?
?
0
B7
B6
B5
B4
B3
B2
B1
B0
LTC1096/8 * TA03
1ST TRANSFER
2ND TRANSFER
Hardware and Software Interface to Motorola MC68HC05C4
CS ANALOG INPUTS CLK LTC1098 DIN DOUT C0 SCK MC68HC05C4 MISO MOSI
LTC1096/8 * TA04
LABEL START
MNEMONIC BCLRn LDA STA TST BPL LDA STA AND STA TST BPL BSETn LDA STA
COMMENTS Bit 0 Port C goes low (CS goes low) Load LTC1098(L) DIN word into Acc. Load LTC1098(L) D IN word into SPI from Acc. Transfer begins. Test status of SPIF Loop to previous instruction if not done with transfer Load contents of SPI data register into Acc. (DOUT MSBs) Start next SPI cycle Clear the first D OUT word Store in memory location A (MSBs) Test status of SPIF Loop to previous instruction if not done with transfer Set B0 of Port C (CS goes high) Load contents of SPI data register into Acc. (D OUT LSBs) Store in memory location A + 1 (LSBs)
DOUT from LTC1098(L) Stored in MC68HC05C4
LOCATION A
0
0
0
0
0
0
0
LSB
BYTE 1
LOCATION A + 1
B7
B6
B5
B4
B2
B1
B0
BYTE 2
LTC1096/8 * TA05
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LTC1096/LTC1096L LTC1098/LTC1098L
TYPICAL APPLICATI
Interfacing to the Parallel Port of the Intel 8051 Family The Intel 8051 has been chosen to demonstrate the interface between the LTC1098(L) and parallel port microprocessors. Normally the CS, CLK and DIN signals would be generated on three port lines and the DOUT signal read on a fourth port line. This works very well. However, we will demonstrate here an interface with the DIN and DOUT of the LTC1098(L) tied together as described in the SERIAL INTERFACE section. This saves one wire. The 8051 first sends the start bit and MUX address to the LTC1098(L) over the data line connected to P1.2. Then P1.2 is reconfigured as an input (by writing to it a one) and the 8051 reads back the 8-bit A/D result over the same data line.
CS LTC1098(L) CLK DOUT DIN P1.4 P1.3 P1.2 MUX ADDRESS A/D RESULT
LTC1096/8 * TA06
ANALOG INPUTS
CS
1 CLK
2
DATA (DIN/DOUT)
START
SGL/ DIFF
ODD/ SIGN
8051 P1.2 OUTPUTS DATA TO LTC1098(L) 8051 P1.2 RECONFIGURED AS AN INPUT AFTER THE 4TH RISING CLK AND BEFORE THE 4TH FALLING CLK
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LABEL MNEMONIC MOV SETB CLR MOV RLC CLR MOV SETB DJNZ MOV CLR MOV MOV RLC SETB CLR DJNZ MOV SETB OPERAND A, #FFH P1.4 P1.4 R4, #04 A P1.3 P1.2, C P1.3 R4, LOOP 1 P1, #04 P1.3 R4, #09 C, P1.2 A P1.3 P1.3 R4, LOOP R2, A P1.4 COMMENTS DIN word for LTC1098(L) Make sure CS is high CS goes low Load counter Rotate DIN bit into Carry CLK goes low Output DIN bit to LTC1098(L) CLK goes high Next bit Bit 2 becomes an input CLK goes low Load counter Read data bit into Carry Rotate data bit into Acc. CLK goes high CLK goes low Next bit Store MSBs in R2 CS goes high
LOOP 1
LOOP
DOUT from LTC1098(L) Stored in 8051 RAM
8051
R2 MSB B7 B6 B5 B4 B3 B2 B1 LSB B0
LTC1096/8 * TA07
MSBF BIT LATCHED BY LTC1098(L)
4
MSBF
B7
B6
B5
B4
B3
B2
B1
B0
LTC1098(L) SENDS A/D RESULT BACK TO 8051 P1.2 LTC1098(L) TAKES CONTROL OF DATA LINE ON 4TH FALLING CLK
LTC1096/8 * TA08
LTC1096/LTC1096L LTC1098/LTC1098L
TYPICAL APPLICATI
A "Quick Look" Circuit for the LTC1096 Users can get a quick look at the function and timing of the LT1096 by using the following simple circuit (Figure 13). VREF is tied to VCC. VIN is applied to the +IN input and the - IN input is tied to the ground. CS is driven at 1/16 the clock rate by the 74C161 and DOUT outputs the data. The output data from the DOUT pin can be viewed on an oscilloscope that is set up to trigger on the falling edge of CS (Figure 14). Note the LSB data is partially clocked out before CS goes high.
4.7F 5V
+
CS VIN CH0 VCC CLR VCC CLK RC A QA B QB 74C161 C QC D QD P T GND LOAD 5V
CLK LTC1096 CH1 DOUT GND VREF
TO OSCILLOSCOPE
Figure 13. "Quick Look" Circuit for the LTC1096
Figure 15 shows a temperature measurement system. The LTC1096 is connected directly to the low cost silicon temperature sensor. The voltage applied to the VREF pin adjusts the full scale of the A/D to the output range of the sensor. The zero point of the converter is matched to the zero output voltage of the sensor by the voltage on the LTC1096's negative input.
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S
CS
CLK
DOUT
NULL BIT
MSB (B7)
LSB (B0)
LSB DATA (B1)
VERTICAL: 5V/DIV HORIZONTAL: 10s/DIV
Figure 14. Scope Trace the LTC1096 "Quick Look" Circuit Showing A/D Output 10101010 (AAHEX)
3V
LM134
0.1F 75k VCC +IN CS TO P
CLOCK IN 150kHz MAX
LTC1096/8 * F13
678
13.5k 182k
-IN LTC1096 CLK VREF LT1004-1.2 GND 0.01F 63.4k DOUT
0.01F
LTC1096/8 * F15
Figure 15. The LTC1096's High Impedance Input Connects Directly to This Temperature Sensor, Eliminating Signal Conditioning Circuitry in This 0C to 70C Thermometer
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LTC1096/LTC1096L LTC1098/LTC1098L
TYPICAL APPLICATI
Remote or Isolated Systems
Figure 16 shows a floating system that sends data to a grounded host system. The floating circuitry is isolated by two optoisolators and powered by a simple capacitor diode charge pump. The system has very low power requirements because the LTC1096 shuts down between
0.001F 2kV 1N5817
5MHz 1N5817 300 CLK 100k
10k DATA 500k
Figure 16. Power for This Floating A/D System Is Provided by a Simple Capacitor Diode Charge Pump. The Two Optoisolators Draw No Current Between Samples, Turning On Only to Send the Clock and Receive Data
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conversions and the optoisolators draw power only when data is being transferred. The system consumes only 50A at a sample rate of 10Hz (1ms on-time and 99ms offtime). This is easily within the current supplied by the charge pump running at 5MHz. If a truly isolated system is required, the system's low power simplifies generating an isolated supply or powering the system from a battery.
FLOATING SYSTEM 1N5817
+
2N3904 47F
0.1F 75k VCC 100k 20k CS LTC1096 +IN -IN ANALOG INPUT VREF LT1004-2.5
0.022F
CLK GND
DOUT
1k
LTC1096/8 * F16
LTC1096/LTC1096L LTC1098/LTC1098L
PACKAGE DESCRIPTIO
*THESE DIMENSIONS DO NOT INCLUDE (6.477 0.381) MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm) 0.300 - 0.325 (7.620 - 8.255)
0.009 - 0.015 (0.229 - 0.381)
(
+0.025 0.325 -0.015 8.255 +0.635 -0.381
)
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 - 0.197* (4.801 - 5.004) 8 7 6 5
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254)
0.016 - 0.050 0.406 - 1.270
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE **DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
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Dimensions in inches (millimeters), unless otherwise noted. N8 Package 8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.400* (10.160) MAX 8 7 6 5
0.255 0.015*
1
2
3
4 0.130 0.005 (3.302 0.127)
0.045 - 0.065 (1.143 - 1.651)
0.065 (1.651) TYP 0.005 (0.127) MIN 0.100 0.010 (2.540 0.254) 0.125 (3.175) MIN 0.018 0.003 (0.457 0.076) 0.015 (0.380) MIN
N8 0695
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
0.053 - 0.069 (1.346 - 1.752) 0- 8 TYP
1
2
3
4 0.004 - 0.010 (0.101 - 0.254)
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) BSC
SO8 0695
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LTC1096/LTC1096L LTC1098/LTC1098L
TYPICAL APPLICATI
A/D Conversion for 3V Systems The LTC1096/LTC1098 are ideal for 3V systems. Figure 17 shows a 3V to 6V battery current monitor that draws only 70A from the battery it monitors. The battery current is sensed with the 0.02 resistor and amplified by the LT1178. The LTC1096 digitizes the amplifier output and sends it to the microprocessor in serial format. The LT1004 provides the full-scale reference for the ADC. The other half of the LTC1178 is used to provide low battery detection. The circuit's 70A supply current is dominated by the op amps and the reference. The circuit can be located near the battery and data transmitted serially to the microprocessor.
0.1F
3V TO 6V 750k
L O A D
24.9k 0.02 FOR 2A FULL SCALE 0.2 FOR 0.2A FULL SCALE
Figure 17. This 0A to 2A Battery Current Monitor Draws Only 70A from a 3V Battery
RELATED PARTS
PART NUMBER LTC1196/LTC1198 LTC1286/LTC1298 LTC1285/LTC1298 LTC1400 LTC1594/LTC1598 LTC1594L/LTC1598L DESCRIPTION 8-Pin SO, 1Msps, 8-Bit ADCs 8-Pin SO, 5V Micropower, 12-Bit ADCs 8-Pin SO, 3V Micropower, 12-Bit ADCs 5V High Speed,Serial 12-Bit ADC 4- and 8-Channel, 5V Micropower, 12-Bit ADCs 4- and 8-Channel, 3V Micropower, 12-Bit ADCs COMMENTS Low Power, Small Size, Low Cost 1- or 2-Channel, Auto Shutdown 1- or 2-Channel, Auto Shutdown 400ksps, Complete with VREF, CLK, Sample-and-Hold Low Power, Small Size, Low Cost Low Power, Small Size, Low Cost
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417q (408) 432-1900 FAX: (408) 434-0507q TELEX: 499-3977 q www.linear-tech.com
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0.1F 73.2k 470k
+
1/2 LT1178
CS
-
VCC CLK LTC1096 D OUT VREF GND
+ -
TO P 20M
+
1/2 LT1178 LT1004-1.2 470k
LO BATTERY
-
LTC1096/8 * F17
10968fb LT/TP 0397 5K REV B * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1994

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