APU3146(2004) 查看數據表（PDF） - Advanced Power Electronics Corp

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APU3146
(Rev.:2004)

DUAL SYNCHRONOUS PWM CONTROLLER WITH CURRENT SHARING CIRCUITRY AND AUTO-RESTART

Advanced Power Electronics Corp 

APU3146

For a given start up time, the soft-start capacitor can be

calculated by: CSS ≅ 25µA×TSTART/1V

The soft-start is part of Over Current Protection scheme,

during the overload or short circuit condition the external

soft start capacitors will be charged and discharged in

certain slope rate to achieve the hiccup mode function.

25uA

Hiccup

SS1 / SD 20

3uA

The internal current source develops a voltage across

RSET. When the low side switch is turned on, the induc-

tor current flows through the Q2 and results a voltage

which is given by:

VOCSET = IOCSET×RSET-RDS(ON)×iL

---(2)

IOCSET

APU3146

Hiccup

Control

OCSet RSET

Q1

L1

Q2

VOUT

Figure 8 - 3uA current source for discharging soft

start-capacitor during Hiccup mode

Out-of-Phase Operation

The APU3146 drives its two output stages 180 out-of-

phase. In 2-phase configuration, the two inductor ripple

currents cancel each other and result in a reduction of

the output current ripple and yield a smaller output ca-

pacitor for the same ripple voltage requirement.

Figure 9 - Diagram of the over current sensing.

The critical inductor current can be calculated by set-

ting:

VOCSET = IOCSET×RSET - RDS(ON)×IL = 0

= ISET = IL(CRITICAL)

RSET×IOCSET

RDS(ON)

---(3)

In single input voltage applications, the input ripple cur-

rent reduces. This result in much smaller input capacitor's

RMS current and reduces the input capacitor quantity.

Over-Current Protection

The APU3146 can provide two different schemes for Over-

Current Protection (OCP). When the pin Hiccup is pulled

high, the OCP will operate in hiccup mode. In this mode,

during overload or short circuit, the outputs enter hiccup

mode and stay in that mode until the overload or short

circuit is removed. The converter will automatically re-

cover.

When the Hiccup pin is pulled low, the OCP scheme

will be changed to the latch up type, in this mode the

converter will be turned off during Overcurrent or short

circuit. The power needs to be recycled for normal

operation.

Each phase has its own independent OCP circuitry.

The OCP is performed by sensing current through the

RDS(ON) of low side MOSFET. As shown in Figure 9, an

external resistor (RSET) is connected between OCSet pin

and the drain of low side MOSFET (Q2) which sets the

current limit set point.

The value of RSET should be checked in an actual

circuit to ensure that the Over Current Protection

circuit activates as expected. The APU3146 current

limit is designed primarily as disaster preventing, "no

blow up" circuit, and is not useful as a precision

current regulator.

In two independent mode, the output of each channel

is protected independently which means if one output

is under overload or short circuit condition, the other

output will remain functional. The OCP set limit can be

programmed to different levels by using the external

resistors. This is valid for both hiccup mode and latch

up mode.

In 2-phase configuration, the OCP's output depends on

any one channel, which means as soon as one

channel goes to overload or short circuit condition the

output will enter either hiccup or latch-up, dependes on

status of Hiccup pin.

If using one soft start capacitor in dual configuration for a

precise power up the OCP needs to be set to latch mode.

8/28

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