IP1837 datasheet(20/40 Pages) IRF

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iP1837

Highly Integrated 35A Single‐input Voltage,

Synchronous Buck Regulator

March 5, 2012 | V1.26

97600

DESIGN PROCEDURE

APPLICATION INFORMATION

Design Example

The following example is a typical application for iP1837.

The application circuit is shown on page 1.

Vin = 12V (13.2V max)

Vo = 1.8V

Io = 35A

ΔVo (transient) ≤ ±90mV for ΔIo = 10.5A @ 2.5A/µs

ΔVo (ripple) ≤ ±13.5mV (±0.75%)

Fs = 600kHz

ENABLING THE IP1837

As explained earlier, the precise threshold of the Enable

lends itself well to implementation of a UVLO for the

Bus Voltage.

iP1837

Vin

Enable

For a typical Enable threshold of VEN = 1.2 V

(6)

1.2

(min)





(7)

min

)

in(





For a Vin (min) = 10.2V, R1 = 49.9K and R2 = 7.5K is a good

choice.

PROGRAMMING THE FREQUENCY

For Fs = 600 kHz, select Rt = 36.5 kΩ, using Table 1.

OUTPUT VOLTAGE PROGRAMMING

Output voltage is programmed by the reference voltage

and external voltage divider. If the remote sense feature is

used, the divider is connected to the Vosp and Vosm pins.

If only local sensing is used for feedback, with the remote

sense amplifier used only in the over‐voltage protection,

circuit, the resistive divider should be connected to the

Fb pin.

For this design, with high output current requirements, we

choose to use the true differential remote sense feature.

The Fb pin is the inverting input of the error amplifier,

which is internally referenced to 0.6V. This references the

output of the remote sense amplifier to 0.6V also. In order

to satisfy this condition, the voltage between the Vosp and

Vosm pins of the error amplifier should be 0.6V when the

output is at its desired value. The output voltage is defined

by using the following equation:

(8)



















bot

top

ref

when an external resistor divider is connected to the

output as shown in Figure 16.

Equation (8) can be rewritten as:

(9)



















ref

bot

top

iP1837

Vout

Vosp

Rtop

Rbot

Figure 16: Typical application of the iP1837

for programming the output voltage

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