IP1206PBF datasheet(17/30 Pages) IRF

17 / 30 page

2/26/2008

www.irf.com

iP1206PbF

Fig. 18: Switching Frequency vs. External Resistor (Rt)

Shutdown using Soft Start pins

The outputs

can be shutdown by pulling the

soft-start pin below 0.25V. This can be easily

done

using

external

small

signal

transistor.

During

shutdown

both

MOSFET

drivers will be turned off. Normal operation will

resume by cycling soft start pin.

Operating Frequency Selection

The switching frequency is determined by

connecting an external resistor (Rt) to ground.

Fig. 18 provides a graph of oscillator frequency

versus

Rt.

The

maximum

recommended

channel frequency is 600kHz.

100

200

300

400

500

600

700

1020

3040

5060

Rt (kOhm)

Frequency Synchronization

The iP1206 is capable of accepting an external

digital synchronization signal. Synchronization

will be enabled by the rising edge at an external

clock. Per–channel switching frequency is set by

external

resistor

(Rt).

The

free

running

frequency oscillator frequency is twice the per-

channel frequency. During synchronization, Rt is

selected such that the free running frequency is

20%

below

the

synchronization

frequency.

Synchronization capability is provided for both

single output current share mode and dual

output

configuration. When unused, the sync

pin will remain floating and is noise immune.

Thermal Shutdown

Temperature sensing is provided inside iP1206.

The trip threshold is typically set to 135oC.

When

trip

threshold

exceeded,

thermal

shutdown turns off both MOSFETs. Thermal

shutdown is not latched and automatic restart is

initiated when the sensed temperature drops to

normal range. There is a 20oC hysteresis in the

shutdown threshold.

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