Datasheet
3
LT1944-1
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Switch Saturation Voltage
(V
CESAT
) Quiescent Current
Feedback Pin Voltage and
Bias Current
TEMPERATURE (°C)
–50
FEEDBACK VOLTAGE (V)
1944-1 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)
1944-1 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.
SHUTDOWN PIN VOLTAGE (V)
SHUTDOWN PIN CURRENT (µA)
1944-1 G03
25
20
15
10
5
0
0 5 10 15
25°C
100°C
Switch Off Time Shutdown Pin CurrentSwitch Current Limit
TEMPERATURE (°C)
–50
SWITCH VOLTAGE (V)
0.15
0.13
0.10
0.08
0.05
0.03
0
–25
02550
1944-1 G01
75 100
I
SWITCH
= 100mA
I
SWITCH
= 70mA
TEMPERATURE (°C)
–50
SWITCH OFF TIME (ns)
–25
0
25 50 75
2000
1800
1600
1400
1200
1000
800
600
400
200
0
100
SWITCHER 2
SWITCHER 1
1944-1 G04
TEMPERATURE (°C)
–50
PEAK CURRENT (mA)
200
175
150
125
100
75
50
–25
02550
1944-1 G05
75 100
V
IN
= 12V
V
IN
= 1.2V
V
IN
= 12V
V
IN
= 1.2V
SWITCHER 1
SWITCHER 2