LT1640 Linear Technology, LT1640 Datasheet - Page 11

• Manufacturer Part Number: LT1640
• Description: Negative Voltage Hot Swap Controller
• Manufacturer: Linear Technology

APPLICATIONS
– 48V
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
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
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
R5
R6
3
2
UV
OV
LT1640H
+
–
Figure 11. Active High Enable Module
EE
V
4
EE
V
R1
, the internal pull-down transistor Q2 is off
PG
SENSE
+
–
5
U
– 48V
GND
V
DD
C1
9.09k
INFORMATION
8
562k
R7
10k
1%
1%
1%
5k
U
GATE
R4
R5
R6
Q1
V
EE
Q3
6
R2
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.
PWRGD
Q2
R3
DRAIN
3
2
UV
OV
V
EE
W
C2
4
0.02
Figure 13. Using PWRGD to Drive an Optoisolator
1
7
5%
R1
+
PG
SENSE
1640 F11
, Q2 will turn on
5
C3
ENABLE MODULE
V
V
ON/OFF
ACTIVE LOW
IN
IN
C1
0.033 F
24V
U
+
–
LT1640L
V
V
V
DD
IRF530
OUT
OUT
GATE
8
Q1
6
+
–
R2
10
5%
10k
5%
R3
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
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.
– 48V
3.3nF
100V
GND
C2
PWRGD
DRAIN
R4
R5
R6
7
3
2
1
LT1640L
UV
OV
+
–
V
Figure 12. Active Low Enable Module
4
EE
4N25
V
R7
51k
5%
R1
PG
SENSE
+
–
5
V
C1
+
DD
GATE
8
Q1
LT1640L/LT1640H
6
R2
C3
100 F
100V
1640 F13
PWRGD
DRAIN
R3
V
EE
Q2
PWRGD
C2
1
7
+
1640 F12
C3
ENABLE MODULE
V
ON/OFF
V
ACTIVE LOW
IN
IN
+
–
V
V
EE
OUT
OUT
11
. If the
+
–