APW7066 datasheet(21/34 Pages) ANPEC

21 / 34 page

Rev. A.4 - Jun., 2005

APW7066

www.anpec.com.tw

Function Descriptions (Cont.)

Soft-Start/Enable

The three SS/EN pins control the soft-start and enable

or disable the controller. In Independent mode, the

three regulators all have independent soft-start and

enable functions. Connect a soft-start capacitor from

each SS/EN pin to the GND to set the soft-start

interval, and an open drain logic signal for each SS/EN

pin will enable or disable the respective output.

Figure 4. Shows the soft-start interval. When both VCC

and VCC12 reach their Power-On-Reset threshold

4.23V and 7.8V, a 30uA current source starts to

charge the capacitor. When the SS reaches the

enabled threshold about 1V, the internal 0.6V

reference starts to rise and follows the SS; the error

amplifier output (COMP) suddenly raises to 1.1V, which

is the valley of the oscillator’s triangle wave, leads the

VOUT to start up. Until the SS reaches about 3.0V,

the internal reference completes the soft-start interval

and reaches to 0.6V; then VOUT1 is in regulation. The

SS1 still rises to 3.5V and then stops.

Figure 4. Soft-Start Interval

TIME

VOLTAGE

VSS

VOUT

Start

Soft

⋅

−

PGOOD

The PGOOD output is an open-drain device, when the

VCC is present; the gate of open-drain device will be

high, forcing the PGOOD pin to go low. The three

SS/EN pins and the SCP signals control the PGOOD

signal (see block diagram), after the three SS/EN

signals are over threshold high 3.3V and three outputs

have no short-circuit, the PGOOD goes high to

indicate all regulators are ready. If any of the SS/EN

pins goes below threshold low 3.2V, the PGOOD will

go low. Also, if any of the outputs has a short, the

PGOOD pull low and if short-circuit condition

continues for 1-2 clock pulses, all regulators will shut

down. If the short-circuit is not long enough to shut

down, it may still cause PGOOD to go low momentarily.

Because the PGOOD is an open-drain device, the

typical range of the value to connect a pull high

resistor to VCC will be 1k

Ω to 10kΩ; if PGOOD is not

used, leave it open.

Shunt Regulator

The APW7066 must have two power supplies VCC

(5V) and VCC12 (12V) to drive the IC; VCC (5V) is for

the control circuit and VCC12 (12V) is for the drivers

of outputs. But it can also operate only VCC12,

because the shunt regulator 5.8V was designed for

VCC (5V); the range of the shunt regulator was de-

signed over the usual range 4.5V to 5.5V of typical 5V

power supplies.

Connect a resistor from VCC12 to VCC for shunt

regulator and for the supply current. The input supply

current of VCC is 7mA; minimum shunt regulator

current is about 7mA, and therefore the 20mA shunt

regulator current is enough; thus, the typical value,

300Ω of the resistor is recommended. The relation

among minimun shunt regulator current, required shunt

regulator current and supply current is:

Where:

CSS = external Soft-Start capacitor

ISS = Soft-Start current = 30

µA

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