BD9132MUV_14 Datasheet, PDF (13/26 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD9132MUV
6. Selection of Components Externally Connected
(1) Selection of Inductor (L)
IL
VCC
IL
L
ΔIL
VOUT
Co
Figure 28. Output Ripple Current
The inductance significantly depends on the output ripple current.
As seen in equation (1), the ripple current decreases as the
inductor and/or switching frequency increases.
I _L

V_CC V_OUT
L V_CC
V_OUT
f
A _{・・・(1)}
Appropriate output ripple current should be ±20% of the maximum
output current.
  I _L  0.2 I_OUTMax
A ・・・(2)
L  ^{VCC VOUT VOUT}
I _L V_CC  f
where:
H  ^{・・・(3)}
ΔIL is the Output ripple current, and
f is the Switching frequency.
Note: Current exceeding the current rating of an inductor results in magnetic saturation of the inductor, which decreases
efficiency. The inductor must be selected allowing sufficient margin with which the peak current may not exceed its
current rating.
If VCC=5.0V, VOUT =2.5V, f=1MHz, ΔIL=0.2x3A=0.6A, for example, (BD9132MUV)
L  ^{5  2.5 2.5}  2.08  2.2
0.6  5 1M
H 
Note: Select an inductor with low resistance component (such as DCR and ACR) to minimize dissipation in the inductor for
better efficiency.
(2) Selection of Output Capacitor (CO)
VCC
Output capacitor should be selected with the consideration of the stability region
and the equivalent series resistance required to minimize the ripple voltage.
VOUT
L
ESR
Co
Figure 29. Output Capacitor
Output ripple voltage is determined by the equation (4) ：
V_OUT  I_L  ESR V  ・・・(4)
where:
ΔIL is the Output ripple current.
ESR is the Equivalent series resistance of output capacitor.
Note: Rating of the capacitor should be determined allowing sufficient margin against
output voltage. A 22µF to 100µF ceramic capacitor is recommended.
Less ESR allows reduction in output ripple voltage.
(3) Selection of Input Capacitor (CIN)
VCC
CIN
VOUT
L
Co
Figure 30. Input Capacitor
Input capacitor must be a low ESR capacitor with a capacitance sufficient to
cope with high ripple current to prevent high transient voltage. The ripple
current IRMS is given by the equation (5):
  _{IRMS  IOUT }
V_OUT V_CC  V_OUT
V_CC
A _{・・・(5)}
< Worst case > IRMSMax
When VCC=2xVOUT,
I_RMS
 ^IOUT
2
If VCC=3.3V, VOUT=1.8V, and IOUTMax=3A, (BD9132MUV)
1.83.3 1.8
I_RMS  3
3.3
 1.49
A_RMS 
A low ESR 22µF/10V ceramic capacitor is recommended to reduce ESR dissipation of input capacitor for better
efficiency.
www.rohm.com
© 2012 ROHM Co., Ltd. All rights reserved.
TSZ22111・15・001
13/22
TSZ02201-0J3J0AJ00140-1-2
03.Oct.2014 Rev.002