LT1640L/LT1640H
APPLICATIONS INFORMATION
ACTIVE LOW
ENABLE MODULE
GND
8
R4
3
R5
2
R6
V
EE
SENSE
4
5
C1
R1
– 48V
1640 F11
V
IN+
PWRGD 1
LT1640H
UV
V
DD
R7
5k
Q3
+
Q2
C3
ON/OFF
R5
+
+
–
OV
V
PG
–
V
EE
GATE
6
R2
R3
C2
DRAIN 7
V
IN
–
Q1
Figure 11. Active High Enable Module
pull-up current in the module then flows through R7,
pulling the PWRGD pin high and enabling the module.
When the DRAIN voltage of the LT1640L is high with
respect to V
EE
, the internal pull-down transistor Q2 is off
and the PWRGD pin is in a high impedance state (Figure
12). The PWRGD pin will be pulled high by the module’s
internal pull-up current source, turning the module off.
When the DRAIN voltage drops below V
PG
, Q2 will turn on
and the PWRGD pin will pull low, enabling the module.
The PWRGD signal can also be used to turn on an LED or
optoisolator to indicate that the power is good as shown in
Figure 13.
GND
R4
562k
1%
R5
9.09k
1%
R6
10k
1%
3
UV
LT1640L
PWRGD
2
OV
V
EE
4
SENSE
5
C1
0.033µF
24V
GATE
6
R2
R3
10Ω 10k C2
5% 5% 3.3nF
100V
1640 F13
R1
0.02Ω
5%
– 48V
Figure 13. Using PWRGD to Drive an Optoisolator
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
W
U
U
ACTIVE LOW
ENABLE MODULE
GND
8
R4
3
LT1640L
UV
V
DD
PWRGD
Q2
V
EE
DRAIN
V
EE
SENSE
4
5
C1
R1
– 48V
1640 F12
V
OUT+
V
IN+
1
V
OUT+
+
+
C3
ON/OFF
2
+
–
OV
V
PG
–
7
V
OUT–
R6
GATE
6
R2
R3
C2
V
IN–
V
OUT–
Q1
Figure 12. Active Low Enable Module
Gate Pin Voltage Regulation
When the supply voltage to the chip is more than 15.5V,
the GATE pin voltage is regulated at 13.5V above V
EE
. If the
supply voltage is less than 15.5V, the GATE voltage will be
about 2V below the supply voltage. At the minimum 10V
supply voltage, the gate voltage is guaranteed to be greater
than 6V. The gate voltage will be no greater than 18V for
supply voltages up to 80V.
8
V
DD
1
R7
51k
5%
PWRGD
+
4N25
C3
100µF
100V
DRAIN
7
Q1
IRF530
11
LINER [ LINEAR TECHNOLOGY ]
