MB39A114 Datasheet, PDF (38/54 Pages) Fuji Electric – DC/DC Converter IC for Charging Li-ion Battery

MB39A114
16.8 V output
Vo
IDip ≥ (Io +
tOFF)
2L
≥ 3.6 A
12.6 V output
Vo
IDip ≥ (Io +
tOFF)
2L
≥ 3.6 A
• Smoothing capacitor
The smoothing capacitor is an indispensable element for reducing ripple voltage in output. In selecting a smooth-
ing capacitor, it is essential to consider equivalent series resistance (ESR) and allowable ripple current. Higher
ESR means higher ripple voltage, so that to reduce ripple voltage it is necessary to select a capacitor with low
ESR. However, the use of a capacitor with low ESR can have substantial effects on loop phase characteristics,
and therefore requires attention to system stability. Care should be also taken to use a capacity with sufficient
margin for allowable ripple current. This application uses the 20SVP22M (OS-CON^TM : SANYO) . The ESR,
capacitance value, and ripple current can be calculated from the following formulas.
Equivalent series resistance :
ESR
∆Vo
ESR ≤
∆IL
1
−
2πfCL
Capacitance value : CL
∆IL
CL ≥
2πf (∆Vo − ∆IL × ESR)
Ripple current : ICLrms
(VIN − Vo) tON
ICLrms ≥
2√3L
Example) Using the 20SVP22M
Rated voltage = 20 V, ESR = 60 mΩ, maximum allowable ripple current = 1450 mArms
Equivalent series resistance
16.8 V output
∆Vo
1
ESR ≤
−
∆IL
2πfCL
0.168
1
≤
−
1.22
2π × 300 × 10³ × 22 × 10^−6
≤ 114 mΩ
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