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Final Electrical Specifications
LT1317/LT1317B Micropower, 600kHz PWM DC/DC Converters
January 1998
FEATURES
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DESCRIPTION
The LT (R)1317/LT1317B are micropower, fixed frequency step-up DC/DC converters that operate over a wide input voltage range of 1.5V to 12V. The LT1317 features automatic shifting to power saving Burst ModeTM operation at light loads. High efficiency is maintained over a broad 300A to 100mA load range. Peak switch current during Burst Mode operation is kept below 250mA for most operating conditions which results in low output ripple voltage, even at high input voltages. The LT1317B does not shift into Burst Mode operation at light loads, eliminating low frequency output ripple at the expense of light load efficiency. The LT1317/LT1317B contain an internal low-battery detector with a 200mV reference that stays alive when the device goes into shutdown. No-load quiescent current of the LT1317 is 100A and shuts down to 30A. The internal NPN power switch handles a 650mA current with a voltage drop of just 350mV. The LT1317/LT1317B are available in MS8 and SO-8 packages.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation.
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100A Quiescent Current Operates with VIN as Low as 1.5V 600kHz Fixed Frequency Operation Starts into Full Load Low-Battery Detector Active in Shutdown Automatic Burst Mode Operation at Light Load (LT1317) Continuous Switching at Light Loads (LT1317B) Low VCESAT Switch: 300mV at 500mA Pin for Pin Compatible with the LT1307/LT1307B
APPLICATIONS
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Pagers Cordless Telephones GPS Receivers Battery Backup Portable Electronic Equipment Glucose Meters Diagnostic Medical Instrumentation
TYPICAL APPLICATION
L1 10H
D1
90 2.2VIN 3VIN
+
C1 47F
VIN LBI
SW FB R1 1.02M 1% R2 604k 1%
80
2 CELLS
SHUTDOWN
LT1317 SHDN LBO GND VC RC 33k CC1 3000pF
EFFICIENCY (%)
3.3V 200mA
70
+
C2 47F
60
CC2 100pF
50
D1: MBR0520 L1: SUMIDA CD43-100
1307 F01
40 0.3
Figure 1. 2-Cell to 3.3V Boost Converter
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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Efficiency vs Load Current
1.65VIN
1
10 100 LOAD CURRENT (mA)
1000
1317 TA01
1
LT1317/1317B ABSOLUTE AXI U RATI GS
Current into FB Pin .............................................. 1mA Junction Temperature .......................................... 125C Operating Temperature Range ................... 0C to 70C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................ 300C VIN, LBO Voltage ..................................................... 12V SW Voltage ............................................................. 30V FB Voltage .................................................... VIN + 0.3V VC Voltage ................................................................ 2V LBI Voltage ............................................ 0V VLBI 1V SHDN Voltage ............................................................ 6V
PACKAGE/ORDER I FOR ATIO
TOP VIEW VC FB SHDN GND 1 2 3 4 8 7 6 5 LBO LBI VIN SW
ORDER PART NUMBER LT1317CMS8 LT1317BCMS8 MS8 PART MARKING LTBZ LTDL
VC 1 FB 2 SHDN 3 GND 4
MS8 PACKAGE 8-LEAD PLASTIC MSOP TJMAX = 125C, JA = 160C/W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
VIN = 2V, VSHDN = 2V, TA = 25C, unless otherwise noted.
SYMBOL IQ PARAMETER Quiescent Current CONDITIONS Not Switching, VSHDN = 2V (LT1317) VSHDN = 0V (LT1317/LT1317B) (LT1317B)
q q
VFB IB gm AV
Feedback Voltage
q
FB Pin Bias Current (Note 1) Input Voltage Range Error Amp Transconductance Error Amp Voltage Gain Maximum Duty Cycle Switch Current Limit (Note 2) Burst Mode Operation Switch Current Limit VIN = 2.5V (LT1317) I = 5A
fOSC
Switching Frequency Shutdown Pin Current VSHDN = VIN VSHDN = 0V
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TOP VIEW 8 7 6 5 LBO LBI VIN SW
ORDER PART NUMBER LT1317CS8 LT1317BCS8 S8 PART MARKING 1317 1317B
S8 PACKAGE 8-LEAD PLASTIC SO TJMAX = 125C, JA = 120C/W
MIN
TYP 100 25 3.5
MAX 160 40 6.5 1.26 1.26 40 12 240
UNITS A A mA V V nA V mhos V/V % mA mA
1.22 1.20 1.5 70 80 650 520
1.24 1.24 12 140 700 85 900 200 620 0.015 - 2.3
q q q
q q
q q q
720 0.06 -6
kHz A A
LT1317/LT1317B
ELECTRICAL CHARACTERISTICS
VIN = 2V, VSHDN = 2V, TA = 25C unless otherwise noted.
SYMBOL PARAMETER LBI Threshold Voltage
q
CONDITIONS
MIN 190 180
TYP 200 200 0.15 0.02 5 2000 0.01 300
MAX 210 220 0.25 0.1 40 3 350 400 0.15 6 0.4
UNITS mV mV V A nA V/V A mV mV %/V V V
LBO Output Low LBO Leakage Current LBI Input Bias Current (Note 3) Low-Battery Detector Gain Switch Leakage Current Switch VCE Sat Reference Line Regulation SHDN Input Voltage High SHDN Input Voltage Low The q denotes specifications which apply over the full operating temperature range. Note 1: Bias current flows into FB pin.
ISINK = 10A VLBI = 250mV, VLBO = 5V VLBI = 150mV 1M Load VSW = 5V ISW = 500mA
q q q
q q
1.8V VIN 12V
q q q
0.08 1.4
Note 2: Switch current limit guaranteed by design and/or correlation to static tests. Duty cycle affects current limit due to ramp generator. Note 3: Bias current flows out of LBI pin.
PIN FUNCTIONS
VC (Pin 1): Compensation Pin for Error Amplifier. Connect a series RC network and a capacitor from this pin to ground. Typical values for compensation are a 33k/ 3000pF combination for the RC network and 100pF for the capacitor. Minimize trace area at VC. FB (Pin 2): Feedback Pin. Reference voltage is 1.24V. Connect resistor divider tap here. Minimize trace area at FB. Set VOUT according to: VOUT = 1.24V(1 + R1/R2). SHDN (Pin 3): Shutdown. Pull this pin low for shutdown mode (only the low-battery detector remains active). Tie to a voltage between 1.4V and 6V to enable the device. SHDN pin is logic level and need only meet the logic specification (1.4V for high, 0.4V for low). Unlike the LT1307, SHDN does not need to be tied to VIN for proper operation. Do not float the SHDN pin. GND (Pin 4): Ground. Connect directly to local ground plane. SW (Pin 5): Switch Pin. Connect inductor/diode here. Minimize trace area at this pin to keep EMI down. VIN (Pin 6): Supply Pin. Must be bypassed close to the pin. LBI (Pin 7): Low-Battery Detector Input. 200mV reference. Voltage on LBI must stay between ground and 700mV. Low-battery detector remains active in shutdown mode. LBO (Pin 8): Low-Battery Detector Output. Open collector, can sink 10A. A 1M pull-up is recommended.
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LT1317/1317B
BLOCK DIAGRAM
1.24V REFERENCE FB 2
VOUT BIAS R1 (EXTERNAL) FB RAMP GENERATOR
600kHz OSCILLATOR
APPLICATIONS INFORMATION
OPERATION The LT1317 combines a current mode, fixed frequency PWM architecture with Burst Mode micropower operation to maintain high efficiency at light loads. Operation can best be understood by referring to the Block Diagram. The error amplifier compares voltage at the FB pin with the internal 1.24V bandgap reference and generates an error signal VC. When VC reaches the bias voltage on hysteretic comparator A1, A1's output goes low, turning off all circuitry except the 1.24V reference, error amplifier and low-battery detector. Total current consumption in this state is 100A. As output loading causes the FB voltage to decrease, A1's output goes high, enabling the rest of the IC. Switch current is limited to approximately 250mA initially after A1's output goes high. If the load is light, the output voltage (and FB voltage) will increase until A1's output goes low, turning off the rest of the LT1317. Low frequency ripple voltage appears at the output. The ripple frequency is dependent on load current and output capacitance. This Burst Mode operation keeps the output regulated and reduces average current into the IC, resulting in high efficiency even at load currents of 300A or less. If the output load increases sufficiently, A1's output remains high, resulting in continuous operation. When the LT1317 is running continuously, peak switch current is controlled by VC to regulate the output voltage. The switch is turned on at the beginning of each switch cycle. When the summation of a signal representing switch current and a ramp generator (introduced to avoid subharmonic oscillations at duty factors greater than 50%) exceeds the VC signal, comparator A2 changes state, resetting the flip-flop and turning off the switch. Output voltage increases as switch current is increased. The output, attenuated by a resistor divider, appears at the FB pin, closing the overall loop. Frequency compensation is provided by an external series RC network and a capacitor connected between the VC pin and ground. Low-battery detector A4's open collector
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+
+ +
-
R2 (EXTERNAL)
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LBI
+
gm
VC 1 200mV ENABLE
7
+ -
A4
LBO 8
-
ERROR AMPLIFIER
+ -
SHDN SHUTDOWN 3
A1 COMPARATOR SW 5 FF R A2 COMPARATOR S Q DRIVER Q3
+
A=3 0.15
-
4 GND
1317 BD
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LT1317/LT1317B
APPLICATIONS INFORMATION
output (LBO) pulls low when the LBI pin voltage drops below 200mV. There is no hysteresis in A4, allowing it to be used as an amplifier in some applications. The low-battery detector remains active in shutdown. To enable the converter, SHDN must be tied to a voltage between 1.4V and 6V. The LT1317B differs from the LT1317 in that there is no hysteresis in comparator A1. Also, the bias point on A1 is set lower than on the LT1317 so that switching can occur at inductor current less than 100mA. Because A1 has no hysteresis, there is no Burst Mode operation at light loads and the device continues switching at constant frequency. This results in the absence of low frequency output voltage ripple at the expense of efficiency. The difference between the two devices is clearly illustrated in Figure 2. The top two traces in Figure 2 show an LT1317/LT1317B circuit, using the components indicated in Figure 1, set to a 3.3V output. Input voltage is 2V. Load current is stepped from 2mA to 200mA for both circuits. Low frequency Burst Mode operation voltage ripple is observed on Trace A, while none is observed on Trace B.
LT1317 VOUT 100mV/DIV AC COUPLED LT1317B VOUT 100mV/DIV AC COUPLED 200mA 2mA 1ms/DIV
1317 F02
TRACE A
TRACE B
ILOAD
Figure 2. LT1317 Exhibits Ripple at 2mA Load During Burst Mode Operation, the LT1317B Does Not
LAYOUT HINTS The LT1317 switches current at high speed, mandating careful attention to layout for proper performance. You will not get advertised performance with careless layouts. Figure 3 shows recommended component placement. Follow this closely in your PC layout. Note the direct path
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CC2 CC1
RC
1 2 R1 R2 3 4
LT1317
8 7 6 L 5
KEEP TRACES OR LEADS SHORT!
CIN D COUT
VOUT
GROUND
1317 F03
Figure 3. Recommended Component Placement. Traces Carrying High Current Are Direct. Trace Area at FB Pin and VC Pin is Kept Low. Lead Length to Battery Should be Kept Short.
of the switching loops. Input capacitor CIN must be placed close (< 5mm) to the IC package. As little as 10mm of wire or PC trace from CIN to VIN will cause problems such as inability to regulate or oscillation. COMPONENT SELECTION Inductors Inductors appropriate for use with the LT1317 must possess three attributes. First, they must have low core loss at 600kHz. Most ferrite core units have acceptable losses at this switching frequency. Inexpensive iron powder cores should be viewed suspiciously, as core losses can cause significant efficiency penalties at 600kHz. Second, the inductor must handle current of 800mA without saturating. This places a lower limit on the physical size of the unit. Molded chokes or chip inductors usually do not have enough core to support 800mA current and are unsuitable for the application. Lastly, the inductor should have low DCR (copper wire resistance) to prevent efficiency-killing I2R losses. Linear Technology has identified several inductors suitable for use with the LT1317. This is
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LT1317/1317B
APPLICATIONS INFORMATION
not an exclusive list. There are many magnetics vendors whose components are suitable for use. A few vendor's components are listed in Table 1.
Table 1. Inductors Suitable for Use with the LT1317
PART LQH3C100 DO1608-103 CD43-100 CD54-100 VALUE 10H 10H 10H 10H MAX DCR 0.57 0.16 0.18 0.10 0.50 MFR Murata-Erie Coilcraft Sumida Sumida Coiltronics HEIGHT (mm) 2.0 3.0 3.2 4.5 2.2 Best Efficiency 1210 Footprint
COMMENT Smallest Size
CTX32CT-100 10H
Capacitor Selection Low ESR (Equivalent Series Resistance) capacitors should be used at the output of the LT1317 to minimize output ripple voltage. High quality input bypassing is also required. For surface mount applications AVX TPS series tantalum capacitors are recommended. These have been specifically designed for switch mode power supplies and have low ESR along with high surge current ratings. For through-hole applications Sanyo OS-CON capacitors offer extremely low ESR in a small package size. If peak switch current is reduced using the RSET pin, capacitor requirements can be eased and smaller, higher ESR units can be used. Ordinary generic capacitors can generally be used when peak switch current is less than 100mA, although output voltage ripple may increase. Diodes Most of the application circuits on this data sheet specify the Motorola MBR0520L surface mount Schottky diode. In lower current applications, a 1N4148 can be used, although efficiency will suffer due to the higher forward drop. This effect is particularly noticeable at low output voltages. For higher voltage output applications, such as LCD bias generators, the extra drop is a small percentage of the output voltage so the efficiency penalty is small. The
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low cost of the 1N4148 makes it attractive wherever it can be used. In through hole applications the 1N5818 is the all around best choice. LOW-BATTERY DETECTOR The LT1317's low-battery detector is a simple PNP input gain stage with an open collector NPN output. The negative input of the gain stage is tied internally to a 200mV 5% reference. The positive input is the LBI pin. Arrangement as a low-battery detector is straightforward. Figure 4 details hookup. R1 and R2 need only be low enough in value so that the bias current of the LBI pin doesn't cause large errors. For R2, 100k is adequate. The 200mV reference can also be accessed as shown in Figure 5. The lowbattery detector remains active in shutdown.
3.3V R1 LBI R2 100k VIN LT1317 1M LBO TO PROCESSOR
+ -
200mV INTERNAL REFERENCE GND
1317 F04
R1 =
VLB - 200mV 2A
Figure 4. Setting Low-Battery Detector Trip Point
200k 2N3906 VREF 200mV 10k LBO
VIN LT1317
+
10F
LBI GND
1317 F05
Figure 5. Accessing 200mV Reference
LT1317/LT1317B
PACKAGE DESCRIPTION
0.007 (0.18) 0.021 0.006 (0.53 0.015)
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE ** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
*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
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Dimensions in inches (millimeters) unless otherwise noted. MS8 Package 8-Lead Plastic MSOP
(LTC DWG # 05-08-1660)
0.118 0.004* (3.00 0.102) 8 76 5
0.192 0.004 (4.88 0.10)
0.118 0.004** (3.00 0.102)
1 0.040 0.006 (1.02 0.15) 0 - 6 TYP SEATING PLANE 0.012 (0.30) 0.0256 REF (0.65) TYP
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4 0.034 0.004 (0.86 0.102)
0.006 0.004 (0.15 0.102)
MSOP (MS8) 1197
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
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157** (3.810 - 3.988)
1 0.053 - 0.069 (1.346 - 1.752)
2
3
4
0.004 - 0.010 (0.101 - 0.254)
0.016 - 0.050 0.406 - 1.270
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) TYP
SO8 0996
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LT1317/1317B
TYPICAL APPLICATION
Single Li-Ion Cell to 4V/70mA, - 4V/10mA
D2 C3 15F - 4V 10mA
4.5V TO 2.5V
L1 22H
1F CERAMIC Li-Ion CELL
VIN
SW
C1 10F 1.00M
SHUTDOWN
LT1317 SHDN FB GND VC 47k 680pF
100pF
442k
C1: MURATA GRM235Y5V106Z01 C2: AVX TAJB336M010 C3: AVX TAJA156M010 D1: MBR0520 D2: BAT54S (DUAL DIODE) L1, L2: MURATA LQH3C220K04
RELATED PARTS
PART NUMBER LTC(R)1163 LTC1174 LT1302 LT1304 LT1307 LTC1440/1/2 LTC1516 LT1521 DESCRIPTION Triple High Side Driver for 2-Cell Inputs Micropower Step-Down DC/DC Converter High Output Current Micropower DC/DC Converter 2-Cell Micropower DC/DC Converter Single Cell Micropower 600kHz PWM DC/DC Converter Ultralow Power Single/Dual Comparators with Reference 2-Cell to 5V Regulated Charge Pump Micropower Low Dropout Linear Regulator COMMENTS 1.8V Minimum Input, Drives N-Channel MOSFETs 94% Efficiency, 130A IQ, 9V to 5V at 300mA 5V/600mA from 2V, 2A Internal Switch, 200A IQ Low-Battery Detector Active in Shutdown 3.3V at 75mA from 1 Cell, MSOP Package 2.8A IQ, Adjustable Hysteresis 12A IQ, No Inductors, 5V at 50mA from 3V Input 500mV Dropout, 300mA Current, 12A IQ
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417 q (408) 432-1900 FAX: (408) 434-0507q TELEX: 499-3977 q www.linear-tech.com
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1F CERAMIC
L2 22H
D1 4V 70mA
+
C2 33F
1307 TA02
13177bi LT/TP 0198 4K * PRINTED IN THE USA
(c) LINEAR TECHNOLOGY CORPORATION 1998

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