LT1931/LT1931A
TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current
7.0
6.5
QUIESCENT CURRENT (mA)
NOT SWITCHING
–1.27
6.0
5.5
5.0
4.5
4.0
3.5
3.0
–50
–25
LT1931A
SHDN PIN CURRENT (µA)
FEEDBACK VOLTAGE (V)
LT1931
50
25
TEMPERATURE (°C)
0
Current Limit
1.6
1.4
CURRENT LIMIT (A)
1.2
V
CESAT
(V)
0.30
1.0
0.8
0.6
0.4
0.2
0
10
20
30
40 50 60 70
DUTY CYCLE (%)
80
90
FREQUENCY (MHz)
PI FU CTIO S
SW (Pin 1):
Switch Pin. Connect inductor/diode here.
Minimize trace area at this pin to keep EMI down.
GND (Pin 2):
Ground. Tie directly to local ground plane.
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:
For LT1931: R1
=
| V
OUT
| – 1.255
1.255
+
4 • 10
– 6
R2
For LT1931A: R1
=
| V
OUT
| – 1.255
1.255
+
8 • 10
– 6
R2
U W
75
1931 G01
Feedback Pin Voltage
–1.28
90
80
70
60
50
40
30
20
10
0
Shutdown Pin Current
T
A
= 25°C
LT1931A
–1.26
–1.25
–1.24
–1.23
–1.22
–50
LT1931
100
–25
0
25
50
TEMPERATURE (°C)
75
100
1931 G02
–10
0
1
3
4
2
SHDN PIN VOLTAGE (V)
5
6
1931 G03
Switch Saturation Voltage
0.45
Oscillator Frequency
2.5
2.3
2.1
1.9
1.7
1.5
1.3
1.1
0.9
0.7
LT1931
LT1931A
T
A
= 25°C
T
A
= 25°C
0.40
0.35
0.25
0.20
0.15
0.10
0.05
0
0
0.2
0.4
0.6
0.8
SWITCH CURRENT (A)
1.0
1.2
0.5
–50
–25
25
50
0
TEMPERATURE (°C)
75
100
1931 G06
1931 G04
1931 G05
U
U
U
(
)
SHDN (Pin 4):
Shutdown Pin. Tie to 2.4V or more to enable
device. Ground to shut down.
V
IN
(Pin 5):
Input Supply Pin. Must be locally bypassed.
(
)
1931fa
3
LINER [ LINEAR TECHNOLOGY ]
