Datasheet

3
LT1931/LT1931A
1931fa
TYPICAL PERFOR A CE CHARACTERISTICS
UW
Quiescent Current
TEMPERATURE (°C)
–50
QUIESCENT CURRENT (mA)
4.5
5.0
5.5
25
75
1931 G01
4.0
3.5
3.0
–25 0 50
6.0
6.5
7.0
100
NOT SWITCHING
LT1931A
LT1931
TEMPERATURE (°C)
–50
–1.28
–1.27
–1.26
–1.25
–1.24
–1.22
–25
02550
1931 G02
75 100
–1.23
FEEDBACK VOLTAGE (V)
SHDN PIN VOLTAGE (V)
0
–10
SHDN PIN CURRENT (µA)
10
30
50
1
2
34
1931 G03
5
70
90
0
20
40
60
80
6
LT1931A
T
A
= 25°C
LT1931
Feedback Pin Voltage Shutdown Pin Current
Current Limit Switch Saturation Voltage Oscillator Frequency
DUTY CYCLE (%)
10
CURRENT LIMIT (A)
0.8
1.2
90
1931 G04
0.4
0
30
50
70
20
40
60
80
1.6
0.6
1.0
0.2
1.4
T
A
= 25°C
SWITCH CURRENT (A)
0
0
V
CESAT
(V)
0.05
0.15
0.20
0.25
0.8
0.45
1931 G05
0.10
0.4
0.2
1.0
0.6 1.2
0.30
0.35
0.40
T
A
= 25°C
TEMPERATURE (°C)
–50
0.5
FREQUENCY (MHz)
0.9
1.3
1.7
–25
0
25 50
1931 G06
75
2.1
2.5
0.7
1.1
1.5
1.9
2.3
100
LT1931A
LT1931
UU
U
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 LT R
V
R
OUT
1931 1
1 255
1 255
2
410
6
:
||–.
.
•
–
=
+
()
For LT A R
V
R
OUT
1931 1
1 255
1 255
2
810
6
:
||–.
.
•
–
=
+
()
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.