LT1931/LT1931A
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current
Feedback Pin Voltage
Shutdown Pin Current
–1.28
–1.27
–1.26
–1.25
–1.24
–1.23
–1.22
7.0
6.5
6.0
5.5
90
80
70
60
50
40
30
20
10
0
NOT SWITCHING
T
= 25°C
A
LT1931A
LT1931A
LT1931
50
5.0
4.5
LT1931
4.0
3.5
3.0
–10
–50
0
25
50
75
100
–25
–25
0
–50
75
100
25
0
1
3
4
5
6
2
TEMPERATURE (°C)
SHDN PIN VOLTAGE (V)
TEMPERATURE (°C)
1931 G02
1931 G01
1931 G03
Current Limit
Switch Saturation Voltage
Oscillator Frequency
0.45
0.40
0.35
0.30
0.25
0.20
0.15
0.10
0.05
2.5
2.3
2.1
1.9
1.7
1.5
1.3
1.1
0.9
0.7
0.5
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
T
= 25°C
T
= 25°C
A
A
LT1931A
LT1931
0
–50
–25
25
50
75
100
0
50 60
0
0.2
0.4
0.6
1.2
10 20 30 40
70 80 90
0.8
1.0
TEMPERATURE (°C)
SWITCH CURRENT (A)
DUTY CYCLE (%)
1931 G06
1931 G04
1931 G05
U
U
U
PI FU CTIO S
SW (Pin 1): Switch Pin. Connect inductor/diode here.
| VOUT | –1.255
For LT1931A: R1=
Minimize trace area at this pin to keep EMI down.
1.255
+ 8 •10–6
(
)
R2
GND (Pin 2): Ground. Tie directly to local ground plane.
SHDN(Pin4):ShutdownPin.Tieto2.4Vormoretoenable
NFB (Pin 3): Feedback Pin. Reference voltage is –1.255V.
Connect resistive divider tap here. Minimize trace area.
The NFB bias current flows out of the pin. Set R1 and R2
according to:
device. Ground to shut down.
VIN (Pin 5): Input Supply Pin. Must be locally bypassed.
| VOUT | –1.255
For LT1931: R1=
1.255
+ 4 •10–6
(
)
R2
1931fa
3
Linear [ Linear ]
