LT1640ALCS8 datasheet(13/16 Pages) LINER

13 / 16 page

LT1640AL/LT1640AH

VEE

VDD

LT1640AL

SENSE

GND

– 48V

GATE

ACTIVE LOW

ENABLE MODULE

VOUT

–

VIN

1640A F12

VIN

–

PWRGD

DRAIN

VPG

VEE

ON/OFF

–

(SHORT PIN)

* DIODES INC. SMAT70A

–

Figure 12. Active Low Enable Module

When the DRAIN voltage of the LT1640AL is high with

respect to VEE, the internal pull-down transistor Q2 is off

and the PWRGD pin is in a high impedance state (Fig-

ure 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 VPG, 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.

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 VEE. 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.

Drain Pin Protection

A unique feature of the LT1640A is the ruggedness of the

DRAIN pin. The DRAIN is designed to withstand negative

voltages (with respect to VEE) without requiring an exter-

nal diode. A short circuit on the – 48V backplane pulls up

the VEE pin, but due to the storage capacitor C3 (Fig-

ure 12), the DRAIN pin is held more negative than the VEE

pin. The body diode of Q1, plus the I • R drop across R1 (if

R1 is small), holds the DRAIN pin to less than 1.5V below

VEE. A 1.5V reverse voltage gives rise to a 50mA reverse

drain current, which is within the design capability of the

LT1640A. A design with R1 larger than 0.1

Ω may require

a resistor in series with the DRAIN pin to not exceed the

50mA drain current maximum.

APPLICATIO S I FOR ATIO

LT1640ALCS8 Datasheet(PDF) 13 Page - Linear Technology

LT1640ALCS8 Datasheet(HTML) 13 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Datasheet Descarga

Enlace URL