MB3889 Datasheet, PDF (25/35 Pages) Fujitsu Component Limited. – 2-Channel DC/DC Converter IC with Overcurrent Protection Symmetrical-Phase Type

MB3889
s NOTE ON IC’S INTERNAL POWER CONSUMPTION
The oscillation frequency of an IC and the total gate charge of FETs largely affects the internal dissipation of
the IC.
Pay attention to the following point with respect to the internal power consumption of the IC when applications
are used.
IB (mean current) is obtained from the following equation, assuming Qg1 and Qg2 as the total gate charges
applied to the gate capacitors (Ciss1, Ciss2, Crss1, Crss2) of external FETs Q1 and Q2.
Current per channel
IB (A) = I1 + I2
As the current consumption by the IC, excluding IB, is about 15 mA, the power consumption is obtained from the
following equation :
Power consumption : Pc
Pc (W) = 0.015 × VCC (V) + 2 × VCC (V) •IB (A) − VB (V) •IB (A)
Vin
VCC
24
IB
5V
I1
Drive
1-1
I2
Drive
2-1
VB
22
CVB
30 ^CB1
Q1
A
L1 VO1
Crss1
Crss2
OUT1-1
29
Ciss1 ^Q2
28 ^VS1
27 ^OUT2-1
26 ^PGND1
Ciss2
t
VOUT1-1
VOUT2-1
Bias current
I1
Ibias1 =: 3 mA
t1
Bias current
I2
Ibias1 =: 3 mA
t2
t
See “Power Consumption vs. Input Voltage” on the next page as a reference and use the above method of
obtaining the power consumption to design your application of the IC taking account of the “Power Dissipation
vs. Ambient Temperature” characteristic in the “TYPICAL CHARACTERISTICS” section.
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