LT1945
TYPICAL PERFOR A CE CHARACTERISTICS
Switch Saturation Voltage
(V
CESAT
)
0.60
0.55
0.50
1.24
40
FEEDBACK VOLTAGE (V)
FEEDBACK VOLTAGE (V)
SWITCH VOLTAGE (V)
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1945 G01
I
SWITCH
= 500mA
I
SWITCH
= 300mA
Switch Off Time
550
500
400
350
SWITCH OFF TIME (ns)
450
400
350
300
250
–50
V
IN
= 1.2V
V
IN
= 12V
PEAK CURRENT (mA)
300
250
200
150
100
50
QUIESCENT CURRENT (µA)
–25
0
25
50
TEMPERATURE (°C)
PI FU CTIO S
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.
1945f
U W
75
1945 G04
FB2 Pin Voltage and
Bias Current
1.25
50
–1.25
NFB1 Pin Voltage and
Bias Current
5
–1.24
VOLTAGE
–1.23
4
BIAS CURRENT (µA)
VOLTAGE
1.23
30
BIAS CURRENT (nA)
3
1.22
CURRENT
20
–1.22
CURRENT
–1.21
2
1.21
10
1
1.20
–50
–25
0
25
50
TEMPERATURE (°C)
75
0
100
1945 G02
–1.20
–50
–25
0
25
50
TEMPERATURE (°C)
75
0
100
1945 G03
Switch Current Limit
V
IN
= 12V
V
IN
= 1.2V
25
Quiescent Current
V
FB
= 1.23V
NOT SWITCHING
23
21
V
IN
= 12V
19
V
IN
= 1.2V
17
100
0
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1945 G05
15
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
1945 G06
U
U
U
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.
3
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