11

LT1640AL/LT1640AH

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

amplify 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

LT1640AL

LT1640AH

R4

R5

R6

4

1640A F10a

OV

GND

GND

3

2

– 48V

UV

8

R4 + R5+ R6

R5 + R6

()

R4 + R5+ R6

R6

()

(SHORT PIN)

LT1640AL /LT1640AH

SENSE

C1

150nF

25V

Q1

IRF530

R6

10

Ω

5%

R1

562k

1%

R3

1.62M

1%

R2

16.9k

1%

R4

506k

1%

R5

8.87k

1%

R1

0.02

Ω

5%

4

2

3

UV

= 37.6V

UV

= 43V

GND

GND

– 48V

UV

OV

56

8

GATE

1640A F10b

OV

= 71V

(SHORT PIN)

*

* DIODES INC. SMAT70A

4

3

2

1

Figure 10b. Programmable Hysteresis for Undervoltage Detection

APPLICATIO S I FOR ATIO