IR3476 datasheet(13/21 Pages) IRF

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August 8, 2012 | ADVANCED DATASHEET | V2.1 | PD97603

IR3476

12A Highly Integrated SupIRBuck

UNDER/OVER VOLTAGE MONITOR

The IR3476 monitors the voltage at the FB node through a

350ns filter. If the FB voltage is below the under voltage

threshold, UV# is set to LOW holding PGOOD to be LOW. If

the FB voltage is above the over voltage threshold, OV# is

set to LOW, the shutdown signal (SD) is set to HIGH,

MOSFET gates are turned off, and PGOOD signal is pulled

low. Toggling VCC or EN will allow the next start up. Figure

24 and 25 show PGOOD status change when UV/OV is

detected. The over voltage and under voltage thresholds

can be found in the Electrical Specification section.

* typical filter delay

Figure 24: Under/Over Voltage Monitor

* typical filter delay

Figure 25: Over Voltage Protection

OVER CURRENT MONITOR

The over-current circuitry monitors the output current

during each switching cycle. The voltage across the lower

MOSFET, VPHASE, is monitored for over current and zero

crossing. The OCP circuit evaluates VPHASE for an over

current condition typically 270ns after the lower MOSFET

is gated on. This delay functions to filter out switching

noise. The minimum lower gate interval allows time to

sample VPHASE.

The over current trip point is programmed with a resistor

from the ISET pin to PHASE pin, as shown in equation 4.

When over current is detected, the MOSFET gates are tri-

state and SS voltage is pulled to 0V. This initiates a new

soft start cycle. If there is a total of four OC events, the

IR3476 will disable switching. Toggling VCC or EN will allow

the next start up.

Figure 26: Over Current Protection

UNDER VOLTAGE LOCK-OUT

The IR3476 has VCC and EN under voltage lock-out (UVLO)

protection. When either VCC or EN is below their UVLO

threshold, IR3476 is disabled. IR3476 will restart when

both VCC and EN are above their UVLO thresholds.

OVER TEMPERATURE PROTECTION

When the IR3476 exceeds its over temperature threshold,

the MOSFET gates are tri-state and PGOOD is pulled low.

Switching resumes once temperature drops below the over

temperature hysteresis level.

(4)

DSON

SET

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