LT1945 LINER [Linear Technology], LT1945 Datasheet - Page 3

• Manufacturer Part Number: LT1945
• Description: Dual Micropower DC/DC Converter with Positive and Negative Outputs
• Manufacturer: LINER [Linear Technology]

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.
TYPICAL PERFOR A CE CHARACTERISTICS
550
500
450
400
350
300
250
U
0.60
0.55
0.50
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
–50
–50
Switch Off Time
Switch Saturation Voltage
(V
CESAT
–25
–25
U
)
TEMPERATURE ( C)
TEMPERATURE ( C)
0
0
V
IN
= 1.2V
I
I
25
SWITCH
SWITCH
V
25
U
IN
= 12V
= 500mA
= 300mA
50
50
W
75
75
1945 G04
1945 G01
U
100
100
1.25
1.24
1.23
1.22
1.21
1.20
–50
400
350
300
250
200
150
100
FB2 Pin Voltage and
Bias Current
50
0
–50
Switch Current Limit
–25
V
IN
–25
= 12V
TEMPERATURE ( C)
0
VOLTAGE
TEMPERATURE ( C)
CURRENT
0
25
25
V
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
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.
IN
IN
50
= 1.2V
(Pin 8): Input Supply Pin. Bypass this pin with a
50
75
1945 G02
75
1945 G05
100
50
40
30
20
10
0
100
–1.25
–1.24
–1.23
–1.22
–1.21
–1.20
25
23
21
19
17
15
–50
–50
NFB1 Pin Voltage and
Bias Current
Quiescent Current
V
NOT SWITCHING
FB
–25
–25
= 1.23V
TEMPERATURE ( C)
TEMPERATURE ( C)
0
0
VOLTAGE
V
IN
25
= 12V
CURRENT
25
V
IN
= 1.2V
LT1945
50
50
75
75
1945 G03
1945 G06
100
3
1945f
5
4
3
2
1
0
100