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LT1944
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Switch Saturation Voltage
(V
CESAT
) Quiescent Current
Feedback Pin Voltage and
Bias Current
TEMPERATURE (°C)
–50
–25 0 25 50 75 100
SWITCH VOLTAGE (V)
1944 G01
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
I
SWITCH
= 500mA
I
SWITCH
= 300mA
TEMPERATURE (°C)
–50
FEEDBACK VOLTAGE (V)
1944 G02
1.25
1.24
1.23
1.22
1.21
1.20
BIAS CURRENT (nA)
50
40
30
20
10
0
CURRENT
VOLTAGE
–25 0 25 50 75 100
TEMPERATURE (°C)
QUIESCENT CURRENT (µA)
1944 G03
25
23
21
19
17
15
–50 –25 0 25 50 75 100
V
IN
= 12V
V
IN
= 1.2V
V
FB
= 1.23V
NOT SWITCHING
PI FU CTIO S
UUU
FB1 (Pin 1): Feedback Pin for Switcher 1. Set the output
voltage by selecting values for R1 and R2.
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
it off.
GND (Pin 3): Ground. Tie this pin directly to the local
ground plane.
SHDN2 (Pin 4): Shutdown Pin for Switcher 2. Tie this pin
to 0.9V or higher to enable device. Tie below 0.25V to turn
it off.
FB2 (Pin 5): Feedback Pin for Switcher 2. Set the output
voltage by selecting values for R1B and R2B.
SW2 (Pin 6): Switch Pin for Switcher 2. This is the
collector of the internal NPN power switch. Minimize the
metal trace area connected to the pin to minimize EMI.
PGND (Pins 7, 9): Power Ground. Tie these pins directly
to the local ground plane. Both pins must be tied.
V
IN
(Pin 8): Input Supply Pin. Bypass this pin with a
capacitor as close to the device as possible.
SW1 (Pin 10): Switch Pin for Switcher 1. This is the
collector of the internal NPN power switch. Minimize the
metal trace area connected to the pin to minimize EMI.
TEMPERATURE (°C)
SWITCH OFF TIME (ns)
1944 G04
550
500
450
400
350
300
250
–50 –25 0 25 50 75 100
V
IN
= 1.2V
V
IN
= 12V
TEMPERATURE (°C)
PEAK CURRENT (mA)
1944 G05
400
350
300
250
200
150
100
50
0
–50 –25 0 25 50 75 100
V
IN
= 12V
V
IN
= 1.2V
SHUTDOWN PIN VOLTAGE (V)
SHUTDOWN PIN CURRENT (µA)
1944 G03
25
20
15
10
5
0
0 5 10 15
25°C
100°C
Switch Off Time Shutdown Pin CurrentSwitch Current Limit