IP1203 Datasheet, PDF(12/23 Page) International Rectifier – Single Output Full Function Synchronous Buck Power Block

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IP1203 Datasheet, PDF (12/23 Pages) International Rectifier – Single Output Full Function Synchronous Buck Power Block

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iP1203

iP1203 Design Procedure

Only a few external components are required to com-

plete a dual output synchronous buck power supply

using iP1203. The following procedure will guide the

designer through the design and selection process

of these external components.

A typical application for the iP1203 is:

VIN = 12V, VOUT = 1.5V, IOUT = 15A, fsw = 300kHz, Vp-p =

= 50mV

Setting the Output Voltage

The output voltage of the iP1203 is set by the 0.8V

reference VREF and external voltage dividers.

Vout

iP1203

R26

FBS

C14

R27

(Optional)

Fig. 14: Typical Scheme for Output Voltage Setting

For Type II compensation,

VOUT is set according to equation (1):

VOUT = VREF x (1 + R2 /R5 ) (see Fig. 14)

(1)

Setting R2 to 1K, VOUT to 1.5V and VREF to 0.8V, will

result in R5= 1.14 Kohms. Final values can be se-

lected according to the desired accuracy of the out-

put.

To set the output voltage for Type III compensation,

refer to equation (24) in Type III compensation sec-

tion.

Setting the Overvoltage Trip

The output of the iP1203 will shut down if it experi-

ences a voltage in the range of 115% of VOUT. The

overvoltage sense pin FBs is connected to the out-

put through voltage dividers, R26 and R27 (Fig. 14),

and the trip setpoint is programmed according to

equation (1). A separate overvoltage sense pin FBs

is provided to protect the power supply output if for

some reason the main feedback loop is lost (for in-

stance, loss of feedback resistors). An optional 100pF

capacitor (C14) is used for delay and filtering.

If this redundancy is not required and if a Type II con-

trol loop compensation scheme is utilized, FBs pin

can be connected to FB.

Selecting the Soft-Start Capacitor

The soft start capacitor Css is selected according to

equation (2):

tss = 40 x Css

(2)

where,

tss is the output voltage ramp time in milliseconds,

and Css is the soft start capacitor in ÂµF.

A 0.1ÂµF capacitor will provide an output voltage ramp-

up time of about 4ms.

Input Capacitor Selection

The switching currents impose RMS current require-

ments on the input capacitors. Equation (3) allows

the selection of the input capacitors.

I RMS = Iout D(1 â D)

(3)

where, Iout is the output current, and D is the duty

cycle and is expressed as:

D = VOUT / VIN.

For the above example D= 0.13 and, using equation

(3) the capacitor rms current yields 5.0A.

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