APW7057 datasheet(4/15 Pages) ANPEC

4 / 15 page

Rev. A.5 - Jun., 2008

APW7057

www.anpec.com.tw

APW7057

Symbol

Parameter

Test Conditions

Min.

Typ.

Max.

Unit

SOFT-START AND SHUTDOWN

TSS

Soft-Start Interval

Shutdown Threshold

VOCSET Falling

1.25

OCSET Shutdown Hysteresis

An over current condition will cycle the soft-start function.

After three consecutive cycles and if the fault condition

persists, the controller will be shut down. To restart the

controller, either recycle the V

CC supply or momentarily

pull the OSCSET pin below 1.25V.

VCC (Pin 5)

Electrical Characteristics (Cont.)

Unless otherwise specified, these specifications apply over V

CC=5V, VBOOT=12V and TA= 0~70

oC. Typical values are

at T

=25oC.

Function Pin Description

GND (Pin 3)

BOOT (Pin 1)

This pin provides the supply voltage to the high side

MOSFET driver. A voltage no greater than 13V can be con-

nected to this pin as a supply to the driver. For driving

logic level N-channel MOSEFT, a bootstrap circuit can be

use to create a suitable driver’s supply.

UGATE (Pin 2)

This pin provides gate drive for the high-side MOSFET.

Signal and power ground for the IC. All voltage levels are

measured with respect to this pin. Tie this pin to the ground

plane through the lowest impedance connection available.

LGATE (Pin 4)

This pin provides the gate drive signal for the low side

MOSFET.

This is the main bias supply for the controller and its low

side MOSFET driver. Must be closely decoupled to GND

(Pin 3). DO NOT apply a voltage greater than 5.5V to this

pin.

FB (Pin 6)

This pin is the inverting input of the error amplifier and it

receives the feedback voltage from an external resistive

divider across the output (V

OUT). The output voltage is de-

termined by:

VOUT = 0.8V(1+

)

ROUT

RGND

where ROUT is the resistor connected between VOUT

and FB while RGND is the resistor connected from FB to

GND.

OCSET (Pin 7)

This pin serves two functions: as a shutdown control and

for setting the over current limit threshold. Pulling this pin

below 1.25V shuts the controller down, forcing the UGATE

and LGATE signals to be at 0V. A soft-start cycle will be

initiated upon the release of this pin.

A resistor (R

ocset) connected between this pin and the drain

of the high side MOSFET will determine the over current

limit. An internally generated 40

µA current source will flow

through this resistor, creating a voltage drop. This volt-

age will be compared with the voltage across the high

side MOSFET. The threshold of the over current limit is

therefore given by:

IOI =

40uA x ROCSET

RDS(ON)

PHASE (Pin 8)

This pin is connected to the source of the high-side

MOSFET and is used to monitor the voltage drop across

the high-side MOSFET for over-current protection.

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