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LT1109 Micropower Low Cost DC/DC Converter Adjustable and Fixed 5V, 12V
FEATURES
s s s s s s s s s s
DESCRIPTIO
Uses Off-the-Shelf Inductors Only 33H Inductor Required Low Cost 3-Lead TO-92, SO8, or 8-Pin DIP Adjustable or Fixed 5V or 12V Output 120kHz Oscillator Only Three External Components Required 320A IQ 1.6V Minimum Start-Up Voltage Logic Controlled Shutdown
The LT1109 is a simple step-up DC/DC converter. Available in 8-pin SO, 3-lead TO-92 (fixed output only) or miniDIP packages, the devices require only three external components to construct a complete DC/DC converter. Current drain is just 320A at no load, making the device ideal for cost-sensitive applications where standby current must be kept to a minimum. The LT1109-5 can deliver 5V at 100mA from a 3V input and the LT1109-12 can deliver 12V at 60mA from a 5V input. The 8-pin versions also feature a logic controlled SHUTDOWN pin that turns off the oscillator when taken low. The gated-oscillator design requires no frequency compensation components. The high frequency 120kHz oscillator permits the use of small surface mount inductors and capacitors. For a 5V to 12V at 120mA converter, see the LT1109A. Foa a 5V to 12V at 200mA converter with 20A shutdown current, see the LT1301.
APPLICATI
s s s s s s s
S
Flash Memory VPP Generators 3V to 5V Converters 5V to 12V Converters Disk Drives PC Plug-In Cards Peripherals Battery-Powered Equipment
TYPICAL APPLICATI
L1| 33H 3 VIN 5V 1 SW VIN SENSE 8 MBRS120T3
All Surface Mount Flash Memory VPP Generator
15
Output Voltage
VIN = 5V 12 OUTPUT VOLTAGE (V)
VOUT 12V 80mA
9 SHUTDOWN 5V/DIV 6 1ms/DIV
LT1109 * TA02
LT1109CS8-12 7 SHUTDOWN* GND 4 SHUTDOWN PROGRAM
LT1109 * TA01
+
C1** 22F 16V
3
* 8-PIN PACKAGE ONLY | L1 = SUMIDA CD54-330LC (I OUT = 80mA) COILTRONICS CTX33-1 (80mA) MURATA-ERIE LQH4N330K (I OUT = 50mA) ISI LCS2414-330K (IOUT = 50mA) **C1 = MATSUO 267M1602226 OR EQUIVALENT
0 0 10 20 30 40 50 60 70 80 90 100 OUTPUT CURRENT (mA)
LT1109 * TPC01
U
Flash Memory Program Output
VOUT 5V/DIV OV
UO
UO
1
LT1109 ABSOLUTE AXI U RATI GS
Operating Temperature Range ..................... 0C to 70C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec.)................. 300C Switch Current ........................................................ 1.2A (Voltages Referred to GND Pin) Supply Voltage (VOUT) .............................. - 0.4V to 20V SW Pin Voltage .......................................... - 0.4V to 50V SHUTDOWN Pin Voltage......................................... 6.0V Maximum Power Dissipation ............................. 300mW
PACKAGE/ORDER I FOR ATIO
TOP VIEW VIN 1 NC 2 SW 3 GND 4 8 7 6 5 SENSE SHUTDOWN NC NC VIN 1 NC 2 SW 3 GND 4
N8 PACKAGE 8-LEAD PLASTIC DIP
LT1109 * PO102
S8 PACKAGE 8-LEAD PLASTIC SOIC
TJMAX = 100C, JA = 130C/W
TJMAX = 100C, JA = 150C/W
ORDER PART NUMBER LT1109CN8 LT1109CN8-5 LT1109CN8-12
ORDER PART NUMBER LT1109CS8 LT1109CS8-5 LT1109CS8-12
ELECTRICAL CHARACTERISTICS TA = 25C, VIN = 3V (LT1109CN8, LT1109CS8), unless otherwise specified.
SYMBOL IQ PARAMETER Quiescent Current Minimum Start-Up Voltage at VOUT Pin (Z Package) VIN VOUT Input Voltage (N8, S8 Package) Comparative Trip Point Voltage Output Voltage Comparator Hysteresis Output Voltage Ripple fOSC tON DC VCESAT Oscillator Frequency
q q
CONDITIONS Switch Off
q
LT1109 LT1109-5; 3V VIN 5V LT1109-12; 3V VIN 12V LT1109 LT1109-5 LT1109-12
Switch ON Time
q
Duty Cycle Switch Saturation Voltage
Full Load ISW = 500mA LT1109-5: VIN = 3V; LT1109-12: VIN = 5V
2
U
U
W
WW
U
W
TOP VIEW 8 7 6 5 SENSE SHUTDOWN NC NC
BOTTOM VIEW 3 VOUT 2 SW 1 GND
LT1109 * PO103
Z PACKAGE 3-LEAD TO-92 PLASTIC
LT1109 * POI01
TJMAX = 100C, JA = 160C/W
S8 PART MARKING 1109 10905 10912
ORDER PART NUMBER LT1109CZ-5 LT1109CZ-12
MIN 1.6 3 1.20 4.75 11.52
TYP 320
MAX 550
UNITS A V V
q q q q q q
1.25 5.00 12.00 8 25 60
1.30 5.25 12.55 12.5 50 120 140 150 5.3 5.5 60 0.7 0.8
V V V mV mV mV kHz kHz s s % V V
100 90 3.3 3.0 45
120 4.2 50 0.4 0.5
q q
LT1109
ELECTRICAL CHARACTERISTICS TA = 25C, VIN = 3V (LT1109CN8, LT1109CS8), unless otherwise specified.
SYMBOL VIH VIL IIH IIL PARAMETER Switch Leakage Current SHUTDOWN Pin High SHUTDOWN Pin Low SHUTDOWN Pin Input Current SHUTDOWN Pin Input Current CONDITIONS VSW = 12V N8, S8 Package N8, S8 Package N8, S8 Package, VSHUTDOWN = 4V N8, S8 Package, VSHUTDOWN = 0V
q q q q
MIN 2.0
TYP 1
MAX 10 0.8 10 20
UNITS A V V A A
The q denotes the specifications which apply over the full operating temperature range.
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
160
140
OSCILLATOR FREQUENCY (kHz)
FREQUENCY (kHz)
124 122 120 118 116 114 112
120
SWITCH ON TIME (s)
0 2 4 6 8 10 12 14 16 18 20
LT1109 * TPC03
100
80
60 -50
-25
0
25
50
TEMPERATURE (C)
LT1109 * TPC02
Duty Cycle
70 65 60 700 600 500
DUTY CYCLE (%)
VCESAT (mV)
400 300 200 100 0 -50
50 45 40 35 30 -50 -25 0 25 50 75 100
VCESAT (V)
55
TEMPERATURE (C)
LT1109 * TPC05
UW
75
Oscillator Frequency
130 128 126
6 7
Switch ON Time
5
4
100
110 INPUT VOLTAGE (V)
3 -50
-25
0
25
50
75
100
TEMPERATURE (C)
LT1109 * TPC04
Switch Saturation Voltage
1.2 ISW = 500mA 1.0 0.8 0.6 0.4 0.2 0 -25 0 25 50 75 100
Switch Saturation Voltage
VIN = 5V TA = 25C
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 SWITCH CURRENT (A)
LT1109 * TPC07
TEMPERATURE (C)
LT1109 * TPC06
3
LT1109
TYPICAL PERFOR A CE CHARACTERISTICS
Minimum/Maximum Oscillator Frequency vs tON
160 150
OSCILLATOR FREQUENCY (kHz)
0C TA 70C
QUIESCENT CURRENT (A)
140 130 120 110 100 90 80 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 TON (s)
LT1109 * TPC08
QUIESCENT CURRENT (A)
0 2 4 6 8 10 12 14 16 18 20
LT1109 * TPC09
TA = 25C
BLOCK DIAGRA S
LT1109-5, -12 Z Package
VOUT
VIN
R2 250k 1.25V REFERENCE + A1 - COMPARATOR R1 120kHz OSCILLATOR DRIVER
GND
LT1109-5: R1 = 83k LT1109-12: R1 = 29k
LT1109 * TA03
LT1109Z OPERATIO
The LT1109Z-5 and LT1109Z-12 are fixed output voltage step-up DC/DC converters in a 3-pin TO-92 package. Power for internal regulator circuitry is taken from the VOUT pin, a technique known as "bootstrapping." Circuit operation can be best understood by referring to the block diagram. VOUT, attenuated by R1 and R2, is applied to the negative input of comparator A1. When this voltage falls below the 1.25V reference voltage, the oscillator is turned on and the power switch Q1 cycles at the oscillator
4
UW
U
Quiescent Current
450 TA = 25C 400 400 380 360 340 320 300 280 260 240 220 200 INPUT VOLTAGE (V)
Quiescent Current
350
300
250
200 -50
-25
0
25
50
75
100
TEMPERATURE (C)
LT1109 * TPC10
W
LT1109-5, -12 N8, S8 Package
FB SENSE R2 250k SW
SW
1.25V REFERENCE
COMPARATOR + A1 120kHz OSCILLATOR DRIVER R1 Q1
Q1
-
GND
SHUTDOWN
LT1109 * TA04
ON FIXED VERSION PIN 8 IS SENSE ON ADJUSTABLE VERSION PIN 8 IS FB AND R1 AND R2 ARE DISCONNECTED
frequency of 120kHz. Switch cycling alternately builds current in the inductor, then dumps it into the output capacitor, increasing the output voltage. When A1's negative input rises above 1.25V, it turns off the oscillator. A small amount of hysteresis in A1 obviates the need for frequency compensation circuitry. When Q1 is off, current into the VOUT pin drops to just 320A. Quiescent current from the battery will be higher because the device operates off the stepped-up voltage.
LT1109
LT1109 S8 A D 8 OPERATIO
The 8-pin versions of the LT1109 have separate pins for VIN and SENSE or FB and also have a SHUTDOWN pin. Separating the device VIN pin from the SENSE pin allows the device to be powered from the (lower) input voltage rather than the (higher) output voltage. Although quiescent current remains constant, quiescent power will be
APPLICATI
S I FOR ATIO
Inductor Selection A DC/DC converter operates by storing energy as magnetic flux in an inductor core, and then switching this energy into the load. To operate as an efficient energy transfer element, the inductor must fulfill three requirements. First, the inductance must be low enough for the inductor to store adequate energy under the worst case condition of minimum input voltage and switch-ON time. The inductance must also be high enough so that maximum current ratings of the LT1109 and inductor are not exceeded at the other worst case condition of maximum input voltage and ON time. Additionally, the inductor core must be able to store the required flux; i.e., it must not saturate. At power levels generally encountered with LT1109 designs, small ferrite surface-mount inductors will function well. Lastly, the inductor must have sufficiently low DC resistance so that excessive power is not lost as heat in the windings. Look for DCR values in the inductors' specification tables; values under 0.5 will give best efficiency. An additional consideration is ElectroMagnetic Interference (EMI). Toroid and pot core type inductors are recommended in applications where EMI must be kept to a minimum; for example, where there are sensitive analog circuitry or transducers nearby. Rod core types are a less expensive choice where EMI is not a problem. Specifying a proper inductor for an application requires first establishing minimum and maximum input voltage, output voltage, and output current. In a step-up converter, the inductive events add to the input voltage to produce the output voltage. Power required from the inductor is determined by PL = (VOUT + VD - VIN) (IOUT) (01)
U
reduced by using the 8-pin version since the quiescent current flows from a lower voltage source. The SHUTDOWN pin disables the oscillator when taken to a logic "0." If left floating or tied high, the converter operates normally. With SHUTDOWN low, quiescent current remains at 320A. where VD is the diode drop (0.5V for a 1N5818 Schottky). Energy required by the inductor per cycle must be equal or greater than
PL FOSC
U
W
U
UU
UO
(02)
in order for the converter to regulate the output. When the switch is closed, current in the inductor builds according to
-R't V IL t = IN 1 - e L R'
()
(03)
where R' is the sum of the switch equivalent resistance (0.8 typical at 25C) and the inductor DC resistance. When the drop across the switch is small compared to VIN, the simple lossless equation
V IL t = IN t L
()
(04)
can be used. These equations assume that at t = 0, inductor current is zero. This situation is called "discontinuous mode operation" in switching regulator parlance. Setting "t" to the switch-ON time from the LT1109 specification table (typically 4.2s) will yield IPEAK for a specific "L" and VIN. Once IPEAK is known, energy in the inductor at the end of the switch-ON time can be calculated as
EL =
12 LI 2 PEAK
(05)
EL must be greater than PL/FOSC for the converter to deliver the required power. For best efficiency IPEAK should be
5
LT1109
APPLICATI
S I FOR ATIO
kept to 600mA or less. Higher switch currents will cause excessive drop across the switch resulting in reduced efficiency. In general, switch current should be held to as low a value as possible in order to keep switch, diode and inductor losses at a minimum. As an example, suppose 12V at 60mA is to be generated from a 4.5V input. Recalling Equation 01, PL = (12V + 0.5V - 4.5V) (60mA) = 480mW. Energy required from the inductor is PL FOSC = 480mW = 4.0J. 120kHz (06)
Picking an inductor value of 33H with 0.2 DCR results in a peak switch current of
I PEAK =
-1.0 * 4.2 s 4.5 V 1 - e 33H = 538m A. 1.0
Substituting IPEAK into Equation 03 results in
EL =
2 1 33H 0.538 A = 4.77J. 2
(
)(
)
Since 4.77J > 4J the 33H inductor will work. This trialand-error approach can be used to select the optimum inductor. Keep in mind the switch current maximum rating of 1.2A. If the calculated peak current exceeds this, the input voltage must be increased or the load decreased. Capacitor Selection The output capacitor should be chosen on the basis of its equivalent series resistance (ESR). Surface-mount tantalum electrolytics can be used provided the ESR value is sufficiently low. An ESR of 0.1 will result in a 50mV step at the output of the converter when the peak inductor current is 500mA. Physically larger capacitors have lower ESR. Diode Selection Speed, forward drop, and leakage current are the three main considerations in selecting a catch diode for LT1109 converters. General purpose rectifiers such as the 1N4001
6
U
W
U
UO
(07)
are unsuitable for use in any switching regulator application. Although they are rated at 1A, the switching time of a 1N4001 is in the 10s-50s range. At best, efficiency will be severely compromised when these diodes are used; at worst, the circuit may not work at all. Most LT1109 circuits will be well served by a 1N5818 Schottky diode. The combination of 500mV forward drop at 1A current, fast turn-ON and turn-OFF time, and 4A to 10A leakage current fit nicely with LT1109 requirements. At peak switch currents of 100mA or less, a 1N4148 signal diode may be used. This diode has leakage current in the 1nA to 5nA range at 25C and lower cost than a 1N5818.
Table 1. Inductor Manufacturers
MANUFACTURER Caddell-Burns 258 East Second Street Mineola, NY 11501 516-746-2310 Coiltronics Incorporated 6000 Park of Commerce Blvd. Boca Raton, FL 33487 407-241-7876 Coilcraft 1102 Silver Lake Road Cary, IL 60013 708-639-6400 Sumida Electric Co., Ltd. 637 E. Golf Road, Suite 209 Arlington Heights, IL 60005 708-956-0666 PART NUMBERS 7120 Series
(08)
Surface Mount CTX33-1
DT3316 Series
(09)
CD54 CD105 Surface Mount
Table 2. Capacitor Manufacturers
MANUFACTURER Sanyo Video Components 2001 Sanyo Avenue San Diego, CA 92173 619-661-6835 Matsuo Electronics 2134 Main Street, Suite 200 Huntington Beach, CA 92648 714-969-2491 Kemet Electronics Corporation Box 5928 Greenville, SC 29606 803-963-6621 Philips Components 2001 W. Blue Heron Blvd. P.O. Box 10330 Riviera Beach, FL 33404 407-881-3200 PART NUMBERS OS-CON Series
267 Series
T491 Series
49MC Series
LT1109
TYPICAL APPLICATI UO
+
GND
S
3V to 5V Converter
22H CADDELL-BURNS 7120-17
3-Pin Package Flash Memory VPP Generator
33H CADDELL-BURNS 7120-19
1N4933 12V 30mA 10k 2N4403
1N5818
VIN 5V
5V 100mA AT 3V INPUT 20mA AT 2V INPUT
SW VOUT 2 CELLS
SW VOUT LT1109CZ-12 10k GND
+
LT1109CZ-5
10F 20V
+
GND
22F 16V
LT1109 * TA06
SHUTDOWN
PROGRAM
VN2222
QUIESCENT CURRENT = 0 IN SHUTDOWN
LT1109 * TA05
3V to 12V Converter
22H CADDELL-BURNS 7120-17
3V to 5V Converter with Shutdown
L1* 22H
12V 40mA AT 3V INPUT 15mA AT 2V INPUT
1N5818
SW VOUT 2 CELLS LT1109CZ-12 10F 20V
VIN SW 2 CELLS LT1109CS8-5 SDN GND SENSE 5V OUTPUT MBRS120T3
+
22F 16V
LT1109 * TA07
SHUTDOWN
*L1 = SUMIDA CD54-220LC
LT1109 * TA08
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.
7
LT1109
PACKAGE DESCRIPTIO U
Dimensions in inches (millimeters) unless otherwise noted. N8 Package 8-Lead Plastic DIP
0.300 - 0.320 (7.620 - 8.128) 0.045 - 0.065 (1.143 - 1.651) 0.130 0.005 (3.302 0.127) 0.400 (10.160) MAX 8 7 6 5
0.009 - 0.015 (0.229 - 0.381)
0.065 (1.651) TYP 0.125 (3.175) MIN 0.020 (0.508) MIN
0.250 0.010 (6.350 0.254)
(
+0.025 0.325 -0.015 +0.635 8.255 -0.381
)
0.045 0.015 (1.143 0.381) 0.100 0.010 (2.540 0.254)
1
2
3
4
0.018 0.003 (0.457 0.076)
N8 0392
S8 Package 8-Lead Plastic SOIC
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 0.053 - 0.069 (1.346 - 1.752) 0.004 - 0.010 (0.101 - 0.254) 0.228 - 0.244 (5.791 - 6.197) 8
0.189 - 0.197 (4.801 - 5.004) 7 6 5
0- 8 TYP
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) BSC
0.150 - 0.157 (3.810 - 3.988)
1
2
3
4
SO8 0392
Z Package 3-Lead TO-92 Plastic
0.060 0.005 (1.524 0.127) DIA 0.180 0.005 (4.572 0.127) 0.060 0.010 (1.524 0.254) 0.90 (2.286) NOM
0.180 0.005 (4.572 0.127)
0.140 0.010 (3.556 0.127)
0.500 (12.79) MIN
0.050 (1.270) MAX UNCONTROLLED LEAD DIA 0.020 0.003 (0.508 0.076) 0.016 0.03 (0.406 0.076)
5 NOM
10 NOM
0.015 0.02 (0.381 0.051)
Z3 1191
0.050 0.005 (1.270 0.127)
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
LT/GP 1093 5K REV B * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1993

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