MC33470 Datasheet, PDF(11/16 Page) ON Semiconductor – SYNCHRONOUS RECTIFICATION DC/DC CONVERTER PROGRAMMABLE INTEGRATED CONTROLLER

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MC33470

PIN FUNCTION DESCRIPTION

Name

Description

This is a high current dual totem pole output Gate Drive for the Lower, or rectifier, Nâchannel

MOSFET. Its output swings from ground to PVCC . During initial power application, both G2

and G1 are held low until both VCC and PVCC have reached proper levels.

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PVCC

This is a separate power source connection for driving Nâchannel MOSFETs from the G1 and

G2 outputs. It may be connected to 12 V.

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PGnd

This is a separate power ground return that is connected back to the power source. It is used to

reduce the effects of switching transient noise on the control circuitry.

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AGnd

This pin is the ground for the control circuitry.

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VCC

This pin is the positive supply of the control IC.

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Sense

This pin is used for feedback from the output of the power supply. It has a 20 ÂµA current source

ÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃÃ to ground which can be used to provide offset in the converter output voltage.

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Imax

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IFB

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This pin sets the current limit threshold. 190 ÂµA must be sourced into the pin. The external

resistor is determined from the following equation: R = ([RDS(on)] [ILIM]/[190 ÂµA])

This pin has two functions. First, it provides cycleâbyâcycle current limiting. Second, if the

current is excessive, this pin will reinitiate a softâstart cycle. If the voltage at the IFB pin drops

below the voltage at the Imax pin when G1 is on, the controller will go into current limit. The

current limit circuit can be disabled by floating the Imax pin and shorting the IFB pin to VCC.

This is the softâstart pin. A capacitor at this pin, in conjunction with a 10 ÂµA internal current

source, sets the softâstart time. During moderate overload (current limit with VO > 50% of the

set value), the softâstart capacitor will be discharged by an internal 90 ÂµA current source in

order to reduce the duty cycle of G1. During hard current limit (current limit with VO < 50% of

set value), the softâstart capacitor will be discharged by a 64 mA current source.

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Comp

This pin is provided for compensating the error amp for poles and zeros encountered in the

power supply system, mostly the output LC filter.

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This is the over temperature fault pin. OT is an open drain output that will be pulled low if the

OUTEN pin is less than 2.0 V.

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Fault

This pin indicates a fault condition. Fault is an open drain output that switches low if VO

exceeds 115% of its set value. Once triggered, the controller will remain in this state until the

power supply is recycled or the OUTEN pin is toggled.

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Pwrgd

This pin is an open drain output which indicates that VO is properly regulated. A high level on

" Pwrgd indicates that VO is within 4% of its set value for more than 400 Âµs. Pwrgd will switch

" low if VO is outside 4% for more than 100 Âµs.

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VID4

Voltage ID pin. This CMOSâcompatible input programs the output voltage as shown in Table 2.