Document
LT1931/LT1931A 1.2MHz/2.2MHz Inverting DC/DC Converters in ThinSOT
FEATURES
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DESCRIPTIO
Fixed Frequency 1.2MHz/2.2MHz Operation Very Low Noise: 1mVP-P Output Ripple – 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 VCESAT Switch: 400mV at 1A Low Profile (1mm) ThinSOTTM Package Pin-for-Pin Compatible with the LT1611
U APPLICATIO S
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The LT®1931/LT1931A are the industry’s highest power 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 inductors. 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 1mVP-P 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 VIN to VOUT differential of up to 34V. The LT1931/LT1931A are available in the 5-lead ThinSOT package.
, LTC and LT are registered trademarks of Linear Technology Corporation. ThinSOT is a trademark of Linear Technology Corporation.
Disk Drive MR Head Bias Digital Camera CCD Bias LCD Bias GaAs FET Bias Local Low Noise/Low Impedance Negative Supply
TYPICAL APPLICATIO
VIN 5V VIN SHDN C1 4.7µF LT1931 NFB GND L1A 10µH
C2 1µF
L1B 10µH
100 95
D1 SW R1 29.4k R2 10k C4 220pF
EFFICIENCY (%)
VOUT –5V 350mA C3 22µF
90 85 80 75 70 65 60
C1: TAIYO YUDEN X5R JMK212BJ475MG C2: TAIYO YUDEN X5R LMK212BJ105MG C3: TAIYO YUDEN X5R JMK325BJ226MM D1: ON SEMICONDUCTOR MBR0520 L1: SUMIDA CLS62-100
1931 F01
55 50 0 50 100 150 200 250 LOAD CURRENT (mA) 300 350
Figure 1. 5V to –5V, 350mA Inverting DC/DC Converter
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Efficiency
1931 TA01
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1
LT1931/LT1931A
ABSOLUTE
(Note 1)
AXI U
RATI GS
U U W PACKAGE/ORDER I FOR ATIO
TOP VIEW SW 1 GND 2 NFB 3 4 SHDN 5 VIN
VIN Voltage .............................................................. 16V SW Voltage ................................................– 0.4V to 36V NFB Voltage ............................................................. – 2V Current Into NFB Pin ............................................ ±1mA SHDN Voltage .......................................................... 16V Maximum Junction Temperature .......................... 125°C Operating Temperature Range (Note 2) .. – 40°C to 85°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C
ELECTRICAL CHARACTERISTICS
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. VIN = 3V, VSHDN = VIN, unless otherwise noted. (Note 2)
PARAMETER Minimum Operating Voltage Maximum Operating Voltage Feedback Voltage
q
CONDITIONS
NFB Pin Bias Current Quiescent Current Quiescent Current in Shutdown Reference Line Regulation Switching Frequency
VNFB = –1.255V VSHDN = 2.4V, Not Switching VSHDN = 0V, VIN = 3V 2.6V ≤ VIN ≤ 16V
Maximum Duty Cycle Switch Current Limit Switch VCESAT Switch Leakage Current SHDN Input Voltage, High SHDN Input Voltage, Low SHDN Pin Bias Current VSHDN = 3V VSHDN = 0V (Note 3) ISW = 1A VSW = 5V
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°C
2
U
W W
W
ORDER PART NUMBER LT1931ES5 LT1931AES5 S5 PART MARKING LTRA LTSP
S5 PACKAGE 5-LEAD PLASTIC SOT-23
TJMAX = 125°C, θJA = 256°C/ W
Consult factory for parts specified with wider operating temperature ranges.
MIN
LT1931 TYP 2.45
MAX 2.6 16
MIN
LT1931A TYP MAX 2.45 2.6 16
UNITS V V V V µA mA µA %/V MHz MHz % A mV µA V V µA µA
– 1.275 – 1.255 – 1.235 – 1.280 – 1.230 4 4.2 0.01 0.01 1 0.85 84 1 1.2 90 1.2 400 0.01 2.4 0.5 16 0 32 0.1 2 600 1 8 6 1 0.05 1.4 1.6
–1.275 –1.255 –1.235 –1.280 –1.230 8 5.8 0.01 0.01 1.8 1.6 75 1 2.2 82 1.2 400 0.01 2.4 0.5 35 0 70 0.1 2.5 600 1 16 8 1 0.05 2.6 2.9
q
q q
operating temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: Current limit guaranteed by design and/or correlation to static test.
LT1931/LT1931A TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current
7.0 6.5
QUIESCENT CURRENT (mA)
NOT SWITCH.