Datasheet

11
LT1640L/LT1640H
1640lhfb
APPLICATIONS INFORMATION
WUU
U
Undervoltage and Overvoltage Detection
The UV (Pin 3) and OV (Pin 2) pins can be used to detect
undervoltage and overvoltage conditions at the power
supply input. The UV and OV pins are internally connected
to analog comparators with 20mV of hysteresis. When the
UV pin falls below its threshold or the OV pin rises above
its threshold, the GATE pin is immediately pulled low. The
GATE pin will be held low until UV is high and OV is low.
The undervoltage and overvoltage trip voltages can be
programmed using a three resistor divider as shown in
Figure 10a. With R4 = 562k, R5 = 9.09k and R6 = 10K, the
undervoltage threshold is set to 37V and the overvoltage
threshold is set to 71V. The resistor divider will also gain
up the 20mV hysteresis at the UV pin and OV pin to 0.6V
and 1.2V at the input respectively.
More hysteresis can be added to the UV threshold by
connecting resistor R3 between the UV pin and the GATE
pin as shown in Figure 10b.
Figure 10a. Undervoltage and Overvoltage Sensing
V
EE
V
DD
LT1640L
LT1640H
R4
R5
R6
4
1640 F10a
OV
GND
GND
3
2
48V
UV
8
V
UV
= 1.223
R4 + R5+ R6
R5 + R6
()
V
OV
= 1.223
R4 + R5+ R6
R6
()
(SHORT PIN)
V
EE
V
DD
LT1640L/LT1640H
SENSE
C1
150nF
25V
Q1
IRF530
R6
10
5%
R1
562k
1%
R3
1.62M
1%
R2
16.9k
1%
R4
506k
1%
R5
8.87k
1%
R1
0.02
5%
4
2
3
UV = 37.6V
UV = 43V
GND
GND
48V
UV
OV
56
8
GATE
1640 F10b
OV = 71V
(SHORT PIN)
*
* DIODES INC. SMAT70A
43
21
Figure 10b. Programmable Hysteresis for Undervoltage Detection