LT1640AL datasheet(15/34 Pages) LINER

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LTC4253/LTC4253A

425353afe

APPLICATIONS INFORMATION

An OV hysteretic comparator detects overvoltage condi-

tions at the OV pin, with the following thresholds:

OV low-to-high (VOVHI) = 6.150V

OV high-to-low (VOVLO) = 5.850V

The UV and OV trip point ratio is designed to match the

standard telecom operating range of 43V to 82V when

connected together as in the Typical Application. A resistive

divider is used to scale the supply voltage. Using 402k and

32.4k gives a typical operating range of 43.2V to 82.5V.

The undervoltage shutdown and overvoltage recovery

thresholds are then 39.2V and 78.4V. 1% divider resistors

are recommended to preserve threshold accuracy.

The resistive divider values shown set a standing current

of slightly more than 100μA and define an impedance at

UV/OV of 30kΩ. In most applications, 30kΩ impedance

coupled with 300mV UV hysteresis make the LTC4253

insensitive to noise. If more noise immunity is desired,

add a 1nF to 10nF filter capacitor from UV/OV to VEE.

pulse. To protect VIN against damage from higher am-

plitude spikes, clamp VIN to VEE with a 13V Zener diode.

Star connect VEE and all VEE-referred components to the

sense resistor Kelvin terminal as illustrated in Figure 3,

keeping trace lengths between VIN, CIN, DIN and VEE as

short as possible.

INTERNAL UNDERVOLTAGE LOCKOUT (UVLO)

A hysteretic comparator, UVLO, monitors VINforundervolt-

age. The thresholds are defined by VLKO and its hysteresis

VLKH. When VIN rises above VLKO, the chip is enabled;

below (VLKO – VLKH), it is disabled and GATE is pulled low.

The UVLO function at VIN should not be confused with the

UV and OV pins. These are completely separate functions.

UV/OV COMPARATORS (LTC4253)

A UV hysteretic comparator detects undervoltage condi-

tions at the UV pin, with the following thresholds:

UV low-to-high (VUVHI) = 3.225V

UV high-to-low (VUVLO) = 2.925V

Figure 3. –48V/2.5A Application for the LTC4253A

(Refer to Block Diagram)

2.2k

PWRGD1

VIN

VEE

LTC4253A

POWER

MODULE 1

PWRGD2

PWRGD3

EN3

EN2

RESET

DRAIN

GATE

SQTIMER

SENSE

TIMER

POWER

MODULE 2

POWER

MODULE 3

RIN

10k

20k(1/4W)/2

PUSH

RESET

EN3

4253 F03

EN2

10Ω

RD 1M

0.02Ω

IRF530S

FZT857

VIN1

10nF

0.68μF

10nF

CSQ

0.1μF

CSS 33nF

POWER

MODULE 1

OUTPUT

POWER

MODULE 2

OUTPUT

VIN1

100μF

CIN

1μF

30.1k

392k

47k

R3 22k

VIN1

††

†

– 48V RTN

(SHORT PIN)

– 48V RTN

(LONG PIN)

– 48V

(LONG PIN)

DIN

††

DDZ13B*

*DIODES, INC.

†MOC207

††RECOMMENDED FOR HARSH ENVIRONMENTS.

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