
3
LT1945
1945f
Quiescent Current
TYPICAL PERFOR AU
Switch Saturation Voltage
(V
CESAT
)
0.60
FB2 Pin Voltage and
Bias Current
TEMPERATURE (
°
C)
–50
–25
0
25
50
75
100
S
1945 G01
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
F
1945 G02
1.25
1.24
1.23
1.22
1.21
1.20
B
50
40
30
20
10
0
CURRENT
VOLTAGE
–25
0
25
50
75
100
TEMPERATURE (
°
C)
F
1945 G03
–1.25
–1.24
–1.23
–1.22
–1.21
–1.20
–50
–25
0
0
1
2
3
4
5
25
50
75
100
VOLTAGE
CURRENT
B
μ
A
PIU
NFB1 (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)
S
1945 G04
550
500
450
400
350
300
250–50
–25
0
25
50
75
100
V
IN
= 1.2V
V
IN
= 12V
TEMPERATURE (
°
C)
P
1945 G05
400
350
300
250
200
150
100
50
0–50
–25
0
25
50
75
100
V
IN
= 12V
V
IN
= 1.2V
Switch Off Time
Switch Current Limit
NFB1 Pin Voltage and
Bias Current
TEMPERATURE (
°
C)
Q
μ
A
1945 G06
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