BD8313HFN

Technical Note

11/17

www.rohm.com

2010.06- Rev.C

© 2010 ROHM Co., Ltd. All rights reserved.



Output ripple voltage

BD8313HFN is controlled by PWM(Pulse Width

Modulation)mode.

PWM output made by comparison SLOPE with FB(error amp

output) controls switching of IC under the PWM mode.

When FB level is completely lower than SLOPE level, DC/DC

converter switches as non- synchronous step-down switching

mode not to make output voltage level drop quickly caused by

full ON state of Low side Nch FET.

Ripple voltage of output voltage in non-synchronous mode is

larger than that in synchronous mode.

When voltage difference between input and output voltage is large and output current is small, DCDC converter switches as

this non-synchronous mode then ripple voltage of output voltage could be large.

In the reference data above ( output ripple 1 to 4 ), ripple voltage at 12V input 1.2V output , output current is smaller than

100mA is larger than other region.

0.75

0.25

FB

SLOPE

PWMoutput

出力リプル=1 0.4mVp- p

出力リプル=38.4mVp-p

出力リプル= 9.2mVp-p

出力リプル=14 .8mVp- p

Fig.44 Output ripple 1

(VCC=12V, Io=40mA)

Vout(20m/Div)

出力リプル=2 4.4mVp- p

2 0usec/Div

24.4mVpp

Fig.45 Output ripple 2

(VCC=12V, Io=100mA)

Fig.46 Output ripple 3

(VCC=12V, Io=140mA)

Fig.47 Output ripple 4

(VCC=12V, Io=170mA)

Fig.48 Output ripple 5

(VCC=12V, Io=900mA)

38.4mVpp

9.2mVpp

10.4mVpp

14.8mVpp

Vout(20m/Div)

20usec/ Div

Vout(20m/Div)

20usec/ Div

Vout(20m/Div)

20usec/ Div

Vout(20m/Div)

20usec/ Div