HM5167 datasheet(13/18 Pages) HMSEMI

13 / 18 page

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2.9.

Output Capacitor Selection (VOUT pin)

To be simplified, we recommend low-ESR capacitors of 1uF//10uF//10uF//470uF (“//” represents paralleled)

be placed as close as possible to VOUT pin for small output voltage ripple.

Capacitors can lose most of their capacitance at rated voltage. Therefore, leave margin on the voltage

rating to ensure adequate effective capacitance.

In detail, for the require output voltage ripple, use the following equations to calculate the minimum required

effective capacitance COUT

��_�� =

(�� − ��

�� ) × ��

�� × �� × ��

��_�� = �� × ��_��

Where

•

Vripple_dis is output voltage ripple caused by charging and discharging of the output capacitor.

•

Vripple_ESR is output voltage ripple caused by ESR of the output capacitor.

•

VIN_MIN is the minimum input voltage of boost converter..

•

VOUT is the output voltage..

•

IOUT is the output current.

•

ILpeak is the peak current of the inductor.

• ƒSW

is the converter switching frequency.

•

RC_ESR is the ESR of the output capacitors.

2.10.

Loop Stability (COMP pin)

The HM5167 requires external compensation, which allows the loop response to be optimized for each

application. The COMP pin is the output of the internal error amplifier. An external compensation network

comprised of resister RC, ceramic capacitors CC and CP is connected to the COMP pin.

To be simplified, RC is 56kΩ, CC is 3.3nF, and CP can be floating. But notice that this setting can only be

adopted in most cases. In detail, the compensation network parameters can be calculated as follows.

(1)

Set the cross over frequency, ƒc

The first step is to set the loop crossover frequency, ƒC. The higher crossover frequency, the faster the loop

response is. It is generally accepted that the loop gain cross over no higher than the lower of either 1/10 of

the switching frequency, ƒSW, or 1/5 of the RHPZ frequency, ƒRHPZ. It’s proper to use a fixed parameter of

10kHz for ƒC.

�� =

�� × (1 − ��)2

2�� × ��

(2)

Set the compensation resistor, RC.

�� =

2�� × �� × �� × �� × ��

(1 − ��) × �� × ��

(3)

Set the compensation zero capacitor, CC

�� =

�� × ��

2 × ��

(4)

Set the compensation pole capacitor, CP

�� =

�� × ��

��

HM516

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