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Final Electrical Specifications
LT1614 Inverting 600kHz Switching Regulator
July 1998
FEATURES
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DESCRIPTION
The LT (R)1614 is a fixed frequency, inverting mode switching reglator that operates from an input voltage as low as 1V. Utilizing a low noise topology, the LT1614 can generate a negative output down to - 24V from a 1V to 5V input. Fixed frequency switching ensures a clean output free from low frequency noise. The device contains a lowbattery detector with a 200mV reference and shuts down to less than 10A. No load quiescent current of the LT1614 is 1mA and the internal NPN power switch handles a 500mA current with a voltage drop of just 295mV. High frequency switching enables the use of small inductors and capacitors. Ceramic capacitors can be used in many applications, eliminating the need for bulky tantalum types. The LT1614 is available in 8-lead MSOP or SO packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Better Regulation Than a Charge Pump 0.1 Effective Output Impedance - 5V at 200mA from a 5V Input 600kHz Fixed Frequency Operation Operates with VIN as Low as 1V 1mA Quiescent Current Low Shutdown Current: 10A Low-Battery Detector Low VCESAT Switch: 295mV at 500mA
APPLICATIONS
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MR Head Bias LCD Bias GaAs FET Bias Positive-to-Negative Conversion
TYPICAL APPLICATION
5V to - 5V Converter
L1 22H C3 1F L2 22H
5V to - 5V Converter Efficiency
90
VIN 5V
80
SHDN LT1614 VC NFB GND
EFFICIENCY (%)
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VIN C1 33F 100k 1nF C1, C2: AVX TAJB336M010 C3: AVX 1206CY106 D1: MBR0520 L1, L2: MURATA LQH3C220
SW 69.8k D1 24.9k
VOUT - 5V 200mA C2 33F
70
60
50
1614 TA01
40 3 100 10 30 LOAD CURRENT (mA) 300
1614 TA02
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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LT1614 ABSOLUTE AXI U RATI GS
Operating Temperature Range LT1614C ................................................. 0C to 70C LT1614I ............................................. - 40C to 85C Extended Commercial Temperature Range (Note 1) .................. - 40C to 85C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C VIN, SHDN, LBO Voltage ......................................... 12V SW Voltage ............................................... - 0.4V to 30V NFB Voltage ............................................................ - 3V VC Voltage ................................................................ 2V LBI Voltage ............................................ 0V VLBI 1V Current into FB Pin .............................................. 1mA Junction Temperature ........................................... 125C
PACKAGE/ORDER I FOR ATIO
ORDER PART NUMBER
TOP VIEW NFB VC SHDN GND 1 2 3 4 8 7 6 5 LBO LBI VIN SW
TOP VIEW
LT1614CMS8
MS8 PACKAGE 8-LEAD PLASTIC MSOP
TJMAX = 125C, JA = 160C/W
MS8 PART MARKING LTEJ
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
Commercial Grade 0C to 70C. VIN = 1.5V, VSHDN = VIN, TA = 25C unless otherwise noted.
PARAMETER Quiescent Current VSHDN = 0V Feedback Voltage NFB Pin Bias Current (Note 2) Reference Line Regulation Minimum Input Voltage Maximum Input Voltage Error Amp Transconductance Error Amp Voltage Gain Switching Frequency Maximum Duty Cycle
q q q q
CONDITIONS
VNFB = -1.24V 1V VIN 2V 2V VIN 6V
I = 5A 500 73 70 0.75
Switch Current Limit (Note 3)
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WW
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ORDER PART NUMBER
NFB 1 VC 2 SHDN 3 GND 4 8 7 6 5 LBO LBI VIN SW
LT1614CS8 LT1614IS8
S8 PACKAGE 8-LEAD PLASTIC SO
S8 PART MARKING 1614 1614I
TJMAX = 125C, JA = 120C/W
MIN
TYP 1 5
MAX 2 10 - 1.27 -7 1.1 0.8 1 6
UNITS mA A V A %/V %/V V V mhos V/V
- 1.21 - 2.5
- 1.24 - 4.5 0.6 0.3 0.92 16 100 600 80 80 1.2
q
750
kHz % % A
LT1614
ELECTRICAL CHARACTERISTICS
Commercial Grade 0C to 70C. VIN = 1.5V, VSHDN = VIN, TA = 25C unless otherwise noted.
PARAMETER Switch VCESAT Shutdown Pin Current LBI Threshold Voltage
q
CONDITIONS ISW = 500mA (25C, 0C) ISW = 500mA (70C) VSHDN = VIN VSHDN = 0V
MIN
TYP 295 10 -5
MAX 350 400 20 - 10 210 215 0.25 0.1 50 3
UNITS mV mV A A mV mV V A nA V/V A
190 185
200 0.1 0.01 10 1000 0.01
LBO Output Low LBO Leakage Current LBI Input Bias Current (Note 4) Low-Battery Detector Gain Switch Leakage Current
ISINK = 10A VLBI = 250mV, VLBO = 5V VLBI = 150mV 1M Load VSW = 5V
Industrial Grade - 40C to 85C. VIN = 1.5V, VSHDN = VIN unless otherwise noted.
PARAMETER Quiescent Current VSHDN = 0V Feedback Voltage NFB Pin Bias Current (Note 2) Reference Line Regulation Minimum Input Voltage Maximum Input Voltage Error Amp Transconductance Error Amp Voltage Gain Switching Frequency Maximum Duty Cycle Switch Current Limit (Note 3) Switch VCESAT Shutdown Pin Current LBI Threshold Voltage LBO Output Low LBO Leakage Current LBI Input Bias Current (Note 4) Low-Battery Detector Gain Switch Leakage Current ISINK = 10A VLBI = 250mV, VLBO = 5V VLBI = 150mV 1M Load VSW = 5V ISW = 500mA (- 40C) ISW = 500mA (85C) VSHDN = VIN VSHDN = 0V
q q q q
CONDITIONS
MIN
TYP 1 5
MAX 2 10 - 1.27 - 7.5 1.1 0.8 1.25 1.0 6
UNITS mA A V A %/V %/V V V V mhos V/V
- 1.21 -2
- 1.24 - 4.5 0.6 0.3 1.1 0.8
VNFB = - 1.24V 1V VIN 2V 2V VIN 6V - 40C 85C
q
q
I = 5A 500 70 0.75
16 100 600 80 1.2 250 330 10 -5 180 200 0.1 0.1 5 1000 0.01 3 350 400 20 - 10 220 0.25 0.3 30 750
kHz % A mV mV A A mV V A nA V/V A
The q denotes specifications which apply over the full operating temperature range. Note 1: The LT1614C is guaranteed to meet specified performance from 0C to 70C and is designed, characterized and expected to meet these extended temperature limits, but is not tested at - 40C and 85C. The LT1614I is guaranteed to meet the extended temperature limits.
Note 2: Bias current flows out of NFB pin. Note 3: Switch current limit guaranteed by design and/or correlation to static tests. Duty cycle affects current limit due to ramp generator. Note 4: Bias current flows out of LBI pin.
3
LT1614
PIN FUNCTIONS
NFB (Pin 1): Negative Feedback Pin. Reference voltage is - 1.24V. Connect resistive divider tap here. The suggested value for R2 is 24.9k. Set R1 and R2 according to:
R1 = | VOUT | - 1.24 1.24 + 4.5 * 10 - 6 R2
VC (Pin 2): Compensation Pin for Error Amplifier. Connect a series RC from this pin to ground. Typical values are 100k and 1nF. Minimize trace area at VC. SHDN (Pin 3): Shutdown. Ground this pin to turn off switcher. Must be tied to VIN (or higher voltage) to enable switcher. Do not float the SHDN pin.
BLOCK DIAGRAM
VIN 6 R5 40k
Q1
VOUT R1 (EXTERNAL) NFB R2 (EXTERNAL)
NFB
RAMP GENERATOR
600kHz OSCILLATOR
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GND (Pin 4): Ground. Connect directly to local ground plane. SW (Pin 5): Switch Pin. Minimize trace area at this pin to keep EMI down. VIN (Pin 6): Supply Pin. Must have 1F ceramic bypass capacitor right at the pin, connected directly to ground. LBI (Pin 7): Low-Battery Detector Input. 200mV reference. Voltage on LBI must stay between ground and 700mV. Float this pin if not used. LBO (Pin 8): Low-Battery Detector Output. Open collector, can sink 10A. A 1M pull-up is recommended. Float this pin if not used.
VIN R6 40k
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gm
VC 2 LBI
SHDN SHUTDOWN 3
-
Q2 x10 R3 30k R4 140k 1 ERROR AMPLIFIER
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ENABLE BIAS
7
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A4
LBO 8
-
A1
200mV
COMPARATOR FF R A2 S Q DRIVER
SW 5 Q3
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A=3 0.15
-
4 GND
1614 BD
LT1614
APPLICATIONS INFORMATION
Shutdown Pin The LT1614 has a Shutdown pin (SHDN) that must be grounded to shut the device down or tied to a voltage equal or greater than VIN to operate. The shutdown circuit is shown in Figure 1. Note that allowing SHDN to float turns on both the startup current (Q2) and the shutdown current (Q3) for VIN > 2VBE. The LT1614 doesn't know what to do in this situation and behaves erratically. SHDN voltage above VIN is allowed. This merely reverse-biases Q3's base emitter junction, a benign condition.
VIN Q3 R2 400k SHDN 200k START-UP CURRENT Q2 Q1
1614 F01
SHUTDOWN CURRENT
Figure 1. Shutdown Circuit
Low-Battery Detector The LT1614'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 reference. The positive input is the LBI pin. Arrangement as a low-battery detector is straightforward. Figure 2 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 3.
100k 1nF
24.9k
C1, C2: AVX TAJB336M010 C3: AVX 1206CY106 D1: MBR0520 L1: COILTRONICS CTX10-1
Figure 4. 5V to - 5V Converter with Coupled Inductor
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3.3V R1 LBI R2 100k VIN LT1614 1M LBO TO PROCESSOR
+ -
200mV INTERNAL REFERENCE GND
1614 F02
R1 =
VLB - 200mV 2A
Figure 2. Setting Low-Battery Detector Trip Point
200k 2N3906 VREF 200mV 10k LBO
VIN LT1614
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10F
LBI GND
1614 F03
Figure 3. Accessing 200mV Reference
Coupled Inductors The applications shown in this data sheet use two uncoupled inductors because the Murata units specified are small and inexpensive. This topology can also be used with a coupled inductor as shown in Figure 4. Be sure to get the phasing right.
L1A 10H C3 1F L1B 10H
VIN 5V
*
SW 69.8k
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VIN C1 33F
SHDN LT1614 VC NFB GND
VOUT - 5V 200mA D1 C2 33F
1614 F04
5
LT1614
TYPICAL APPLICATION
5V to - 15V/80mA DC/DC Converter
L1 22H C1 1F L2 22H
VIN 5V
100k 1nF
GND
24.9k
C1: 25V, Y5V D1: MBR0520 L1, L2: MURATA LQH3C220
5V to - 15V Converter Efficiency
80 75
EFFICIENCY (%)
70 65 60 55 50 1 10 LOAD CURRENT (mA) 100
1614 TA06
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22F
VIN
SW 255k D1
SHDN LT1614 NFB VC
VOUT -15V 80mA 10F 25V
1614 TA05
LT1614
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
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
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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
23
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)
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) TYP
SO8 0996
7
LT1614
TYPICAL APPLICATION
3.3V to - 3.1V/200mA DC/DC Converter
L1 22H C1 1F L2 22H
VIN 3.3V VIN
100k 1nF
GND
12.7k
C1: AVX1206CY106 D1: MBR0520 L1, L2: MURATA LQH3C220
3.3V to - 3.1V Converter Efficiency
80 70
EFFICIENCY (%)
60 50 40 30 20 3 10 30 100 LOAD CURRENT (mA) 300
1614 TA04
RELATED PARTS
PART NUMBER LTC(R)1174 LT1307 LT1308 LT1316 LT1317 LTC1474 LT1610 DESCRIPTION High Efficiency Step-Down and Inverting DC/DC Converter Single Cell Micropower 600kHz PWM DC/DC Converter Single Cell High Current Micropower 600kHz Boost Converter Micropower Boost DC/DC Converter Micropower 600kHz PWM DC/DC Converter Low Quiescent Current High Efficiency DC/DC Converter 1.7MHz Single Cell Micropower DC/DC Converter COMMENTS Selectable IPEAK = 300mA or 600mA 3.3V at 75mA from 1 Cell, MSOP Package 5V at 1A from a Single Li-Ion Cell, SO-8 Package Programmable Peak Current Limit, MSOP Package 2 Cells to 3.3V at 200mA, MSOP Package IQ = 10A, Programmable Peak Current Limit, MSOP 5V at 200mA from 3.3V, MSOP Package
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
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SW 18.7k FB D1
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22F
SHDN LT1614 VC
VOUT - 3.1V 200mA 22F
1614 TA03
1614i LT/GP 0798 4K * PRINTED IN THE USA
(c) LINEAR TECHNOLOGY CORPORATION 1998

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