LT1944 WUTYPICAL PERFOR A CE CHARACTERISTICSSwitch Saturation VoltageFeedback Pin Voltage and(VCESAT)Bias CurrentQuiescent Current 0.60 1.25 50 25 VFB = 1.23V 0.55 NOT SWITCHING 0.50 1.24 40 23 BIAS CURRENT (nA) µA) 0.45 VOLTAGE ISWITCH = 500mA 0.40 1.23 30 21 0.35 VIN = 12V 0.30 1.22 CURRENT 20 19 ISWITCH = 300mA SWITCH VOLTAGE (V) 0.25 VIN = 1.2V FEEDBACK VOLTAGE (V) QUIESCENT CURRENT ( 0.20 1.21 10 17 0.15 0.10 1.20 0 15 –50 –25 0 25 50 75 100 –50 –25 0 25 50 75 100 –50 –25 0 25 50 75 100 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) 1944 G01 1944 G02 1944 G03 Switch Off TimeSwitch Current LimitShutdown Pin Current 550 400 25 VIN = 12V 350 500 VIN = 1.2V µA) 20 300 450 250 15 V 400 IN = 1.2V 200 25°C V 10 IN = 12V 150 350 100°C SWITCH OFF TIME (ns) PEAK CURRENT (mA) 100 5 300 SHUTDOWN PIN CURRENT ( 50 250 0 0 –50 –25 0 25 50 75 100 –50 –25 0 25 50 75 100 0 5 10 15 TEMPERATURE (°C) TEMPERATURE (°C) SHUTDOWN PIN VOLTAGE (V) 1944 G04 1944 G05 1944 G03 UUUPI FU CTIO SFB1 (Pin 1): Feedback Pin for Switcher 1. Set the output SW2 (Pin 6): Switch Pin for Switcher 2. This is the voltage by selecting values for R1 and R2. collector of the internal NPN power switch. Minimize the metal trace area connected to the pin to minimize EMI. SHDN1 (Pin 2): Shutdown Pin for Switcher 1. Tie this pin to 0.9V or higher to enable device. Tie below 0.25V to turn PGND (Pins 7, 9): Power Ground. Tie these pins directly it off. to the local ground plane. Both pins must be tied. GND (Pin 3): Ground. Tie this pin directly to the local VIN (Pin 8): Input Supply Pin. Bypass this pin with a ground plane. capacitor as close to the device as possible. SHDN2 (Pin 4): Shutdown Pin for Switcher 2. Tie this pin SW1 (Pin 10): Switch Pin for Switcher 1. This is the to 0.9V or higher to enable device. Tie below 0.25V to turn collector of the internal NPN power switch. Minimize the it off. metal trace area connected to the pin to minimize EMI. FB2 (Pin 5): Feedback Pin for Switcher 2. Set the output voltage by selecting values for R1B and R2B. 3
