MIC2174 datasheet(17/24 Pages) MICREL

Part #	MIC2174

Description	300kHz, Synchronous Buck Controller 300kHz, Synchronous Buck Controller

PDF	24 Pages

Scroll/Zoom	100%

Manufacturer	MICREL [Micrel Semiconductor]

Direct Link	http://www.micrel.com

Logo

17 / 24 page

Micrel, Inc.

MIC2174

September 2009

M9999-090409-B

If the voltage divider resistors R1 and R2 are in the kΩ

range, a Cff of 1nF to 100nF can easily satisfy the large

time constant consumption. Also, a 100nF injection

capacitor Cinj is used in order to be considered as short

for a wide range of the frequencies.

The process of sizing the ripple injection resistor and

capacitors is:

Step 1.

Select Cff to feed all output ripples into the

feedback pin and make sure the large time constant

assumption is satisfied. Typical choice of Cff is 1nF to

100nF if R1 and R2 are in kΩ range.

Step 2.

Select Rinj according to the expected feedback

voltage ripple. According to the equation (33),

ΔV

HSD

FB(pp)

div

−

(34)

Then the value of Rinj is obtained as:

(

(R1//R2)

div

inj

−

(35)

Step 3.

Select Cinj as 100nF, which could be considered

as short for a wide range of the frequencies.

MIC2174 Datasheet(PDF) 17 Page - Micrel Semiconductor