Datasheet LT1931, LT1931A (Analog Devices) - 3

LT1931/LT1931A
W U TYPICAL PERFOR A CE CHARACTERISTICS Quiescent Current Feedback Pin Voltage Shutdown Pin Current
7.0 –1.28 90 NOT SWITCHING TA = 25°C 6.5 80 –1.27 LT1931A 70 6.0 LT1931A µA) –1.26 60 5.5 50 5.0 –1.25 40 4.5 30 LT1931 –1.24 LT1931 20 4.0 FEEDBACK VOLTAGE (V) QUIESCENT CURRENT (mA) SHDN PIN CURRENT ( –1.23 10 3.5 0 3.0 –1.22 –10 –50 –25 0 25 50 75 100 –50 –25 0 25 50 75 100 0 1 2 3 4 5 6 TEMPERATURE (°C) TEMPERATURE (°C) SHDN PIN VOLTAGE (V) 1931 G01 1931 G02 1931 G03
Current Limit Switch Saturation Voltage Oscillator Frequency
1.6 0.45 2.5 T T A = 25°C A = 25°C 2.3 1.4 0.40 LT1931A 0.35 2.1 1.2 1.9 0.30 1.0 1.7 (V) 0.25 0.8 1.5 CESAT 0.20 V 1.3 0.6 LT1931 CURRENT LIMIT (A) 0.15 FREQUENCY (MHz) 1.1 0.4 0.10 0.9 0.2 0.05 0.7 0 0 0.5 10 20 30 40 50 60 70 80 90 0 0.2 0.4 0.6 0.8 1.0 1.2 –50 –25 0 25 50 75 100 DUTY CYCLE (%) SWITCH CURRENT (A) TEMPERATURE (°C) 1931 G04 1931 G05 1931 G06
U U U PI FU CTIO S SW (Pin 1):
Switch Pin. Connect inductor/diode here. | V | – 1 255 . For LT A: R OUT 1931 1= Minimize trace area at this pin to keep EMI down. 1 255 . + 8 • 10–6 ( )
GND (Pin 2):
Ground. Tie directly to local ground plane. R2
NFB (Pin 3):
Feedback Pin. Reference voltage is –1.255V.
SHDN (Pin 4):
Shutdown Pin. Tie to 2.4V or more to enable Connect resistive divider tap here. Minimize trace area. device. Ground to shut down. The NFB bias current flows out of the pin. Set R1 and R2
V
according to:
IN (Pin 5):
Input Supply Pin. Must be locally bypassed. | V | – 1 255 . For LT : R OUT 1931 1= 1.255 + 4•10–6 ( ) R2 1931fa 3