lt1931a Linear Technology Corporation, lt1931a Datasheet

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lt1931a

Manufacturer Part Number
lt1931a
Description
Lt1931a - 1.2mhz/2.2mhz Inverting Dc/dc Converters In Thinsot
Manufacturer
Linear Technology Corporation
Datasheet

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FEATURES
TYPICAL APPLICATIO
APPLICATIO S
Fixed Frequency 1.2MHz/2.2MHz Operation
Very Low Noise: 1mV
– 5V at 350mA from 5V Input
–12V at 150mA from 5V Input
Uses Small Surface Mount Components
Wide Input Range: 2.6V to 16V
Low Shutdown Current: <1µA
Low V
Pin-for-Pin Compatible with the LT1611
Low Profile (1mm) ThinSOT
Disk Drive MR Head Bias
Digital Camera CCD Bias
LCD Bias
GaAs FET Bias
Local Low Noise/Low Impedance Negative Supply
V
5V
IN
CESAT
C1: TAIYO YUDEN X5R JMK212BJ475MG
C2: TAIYO YUDEN X5R LMK212BJ105MG
C3: TAIYO YUDEN X5R JMK325BJ226MM
D1: ON SEMICONDUCTOR MBR0520
L1: SUMIDA CLS62-100
Figure 1. 5V to –5V, 350mA Inverting DC/DC Converter
C1
4.7µF
Switch: 400mV at 1A
V
SHDN
IN
U
LT1931
10µH
GND
L1A
P-P
NFB
SW
Output Ripple
TM
Package
U
R1
29.4k
R2
10k
1µF
C2
C4
220pF
D1
10µH
L1B
DC/DC Converters in ThinSOT
1931 F01
C3
22µF
V
–5V
350mA
OUT
DESCRIPTIO
The LT
inverting SOT-23 current mode DC/DC converters. Both
parts include a 1A integrated switch allowing high current
outputs to be generated in a small footprint. The LT1931
switches at 1.2MHz while the LT1931A switches at 2.2MHz.
These high speeds enable the use of tiny, low cost
capacitors and inductors 2mm or less in height. The
LT1931 is capable of generating – 5V at 350mA or –12V
at 150mA from a 5V supply, while the LT1931A can
generate –5V at 300mA using significantly smaller induc-
tors. Both parts are easy pin-for-pin upgrades for higher
power LT1611 applications.
The LT1931/LT1931A operate in a dual inductor inverting
topology that filters both the input side and output side
current. Very low output voltage ripple approaching 1mV
can be achieved when ceramic output capacitors are used.
Fixed frequency switching ensures a clean output free
from low frequency noise typically present with charge
pump solutions. The low impedance output remains within
1% of nominal during large load steps. The 36V switch
allows V
The LT1931/LT1931A are available in the 5-lead ThinSOT
package.
trademark of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
, LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a
1.2MHz/2.2MHz Inverting
®
1931/LT1931A are the industry’s highest power
IN
to V
OUT
100
95
90
85
80
75
70
65
60
55
50
0
differential of up to 34V.
U
50
100
LOAD CURRENT (mA)
LT1931/LT1931A
Efficiency
150
200
250
300
1931 TA01
350
1931fa
1
P-P

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lt1931a Summary of contents

Page 1

... These high speeds enable the use of tiny, low cost capacitors and inductors 2mm or less in height. The LT1931 is capable of generating – 350mA or –12V at 150mA from a 5V supply, while the LT1931A can generate –5V at 300mA using significantly smaller induc- tors. Both parts are easy pin-for-pin upgrades for higher power LT1611 applications ...

Page 2

... SHDN Pin Bias Current V V Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LT1931E/LT1931AE are guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the – 40°C to 85° PACKAGE/ORDER I FOR ATIO ...

Page 3

... Input Supply Pin. Must be locally bypassed – 6 LT1931/LT1931A Shutdown Pin Current 25° LT1931A –10 100 SHDN PIN VOLTAGE (V) 1931 G02 Oscillator Frequency 2.5 2.3 LT1931A 2.1 1.9 1.7 1.5 1.3 1.1 0.9 0.7 0.5 –50 – 1.2 TEMPERATURE (°C) 1931 G05 | V | – 255 OUT = 255 . + – ...

Page 4

... SR latch is reset regardless of the state of comparator A2. This current limit protects the power switch as well as various external components connected to the LT1931. ) and m The Block Diagram for the LT1931A is identical except that the oscillator is 2.2MHz and resistors are one-half the LT1931 values. 1 COMPARATOR – ...

Page 5

... INDUCTOR SELECTION Several inductors that work well with the LT1931 are listed in Table 1 and those for the LT1931A are listed in Table 2. Besides these, there are many other inductors that can be used. Consult each manufacturer for detailed information and for their entire selection of related parts ...

Page 6

... LT1931/LT1931A U U APPLICATIO S I FOR ATIO The inductors shown in Table 2 for use with the LT1931A were chosen for their small size. For better efficiency, use similar valued inductors with a larger volume. For in- stance, the Sumida CR43 series, in values ranging from 3.3µH to 10µH, will give a LT1931A application a few percentage points increase in efficiency ...

Page 7

... Figure 5. Transient Response of Inverting Converter with 22µF Tantalum Output Capacitor and No Phase Lead Capacitor START-UP/SOFT-START For most LT1931/LT1931A applications, the start-up in- rush current can be high. This is an inherent feature of switching regulators in general since the feedback loop is saturated due to V being far from its final value ...

Page 8

... U DIODE SELECTION A Schottky diode is recommended for use with the LT1931/ LT1931A. The Motorola MBR0520 is a very good choice. Where the input to output voltage differential exceeds 20V, use the MBR0530 (a 30V diode). These diodes are rated to handle an average forward current of 0 applications ...

Page 9

... SHDN R1 220pF LT1931 29.4k C1 4.7µF NFB GND R2 10k L2 4.7µ OUT –5V 300mA C4 180pF C3 4.7µF 1931 TA05a LT1931/LT1931A Efficiency 100 100 125 150 50 LOAD CURRENT (mA) 1931 TA03 L2 10µ OUT –5V 300mA C3 22µ ...

Page 10

... Converter Uses Tiny Chip Inductors L1 3.3µ SHDN R1 LT1931A 28.7k C1 2.2µF NFB GND C1: TAIYO YUDEN X5R JMK212BJ225MG C2: TAIYO YUDEN X5R LMK212BJ105MG C3: TAIYO YUDEN X5R JMK212BJ475MG D1: ON SEMICONDUCTOR MBR0520 L1, L2: PANASONIC ELJPC3R3MF SLIC Power Supply with – 33V and – 68V Outputs, Uses Soft-Start ...

Page 11

... C4 1µF 35V U S5 Package 5-Lead Plastic TSOT-23 (Reference LTC DWG # 05-08-1635) 0.95 REF 1.22 REF 1.50 – 1.75 2.80 BSC 1.4 MIN (NOTE 4) PIN ONE 0.95 BSC 0.80 – 0.90 1.00 MAX 0.09 – 0.20 (NOTE 3) LT1931/LT1931A COM C5 4.7µF 1 25V V OUT1 –21.6V 48mA 4.7µF 25V 4.7µ ...

Page 12

... McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 ● ● C2 L1A 0.1µF 4.7µ SHDN R1 LT1931A 28.7k C1 2.2µF NFB GND R2 10k C1: TAIYO YUDEN Y5V EMK212F225ZG C2: 0.1µF 25V X5R C3: TAIYO YUDEN X5R JMK212BJ475MG D1: ON SEMICONDUCTOR MBR0520 L1: SUMIDA CLQ4D10-4R7 DRAWING #5382-T039 Efficiency ...

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