IP1206PBF datasheet(11/30 Pages) IRF

11 / 30 page

2/26/2008

www.irf.com

iP1206PbF

Internal Regulator

iP1206 features an on-board regulator capable of

sourcing current up to 100mA. This integrated

regulator can be used to generate the necessary

bias voltage for drivers. An example of how this

can be used is shown in Fig. 25. The output of

the regulator is protected for short circuit and

thermal shutdown.

Out-of-Phase Operation

The iP1206 drives its two output stages 180o out-

of-phase. In current share mode (single output),

the two inductor ripple currents cancel each other

and result in a reduction of the output current

ripple and yield a smaller output capacitor for the

same ripple voltage requirement. Fig. 7 shows

two channels inductor current and the resulting

voltage ripple at output.

IL1

IL2

HDRV1

HDRV2

0DT

Mode Selection

The iP1206 can operate as a dual output

independently regulated buck converter, or as a

2 phase single output buck converter (in current

share mode). The SS2 pin is used for mode

selection. In current share mode this pin should

be floating and in dual output mode a soft start

capacitor must be connected from this pin to

ground to program the start time for the second

output.

Independent Mode

In this mode the iP1206 provides control to two

independent output power supplies with either

common or different input voltages. The output

voltage of each individual channel is set and

controlled by the output of the error amplifier,

which is the amplified error signal from the

sensed output voltage and the reference voltage.

The error amplifier output voltage is compared to

the ramp signal thus generating fixed frequency

pulses of variable duty-cycle, (PWM) which are

applied to the internal MOSEFT drivers. Fig. 25b

shows

typical

schematic

for

such

application.

Fig. 7: Current ripple cancellation for output

In addition, the 180o out of phase operation

contributes to input current cancellation. This

results in a much smaller input capacitor - RMS

current thereby reducing the input capacitor

quantity. Fig. 8 shows the equivalent RMS

current.

Single Phase

2 Phase

Duty Cycle (Vo/Vin)

Fig. 8: Input RMS value vs. Duty Cycle

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