MB3889 Fujitsu Microelectronics, Inc., MB3889 Datasheet - Page 25

• Manufacturer Part Number: MB3889
• Description: 2-channel Dc/dc Converter Ic With Overcurrent Protection Symmetrical-phase Type
• Manufacturer: Fujitsu Microelectronics, Inc.

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.
I
applied to the gate capacitors (Ciss
Current per channel
As the current consumption by the IC, excluding I
following equation :
Power consumption : Pc
Pc (W)
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.
B
I
(mean current) is obtained from the following equation, assuming Qg1 and Qg2 as the total gate charges
B
(A)
I
0.015
1
I
2
V
CC
(V)
Vin
VOUT1-1
VOUT2-1
I
I
1
2
2
24
VCC
V
CC
5 V
1
, Ciss
Drive
1-1
Drive
2-1
(V) I
I
I
B
1
I
2
t1
2
B
, Crss
(A)
22
30
29
28
27
26
t
VB
CB1
OUT1-1
VS1
OUT2-1
PGND1
1
B
, Crss
, is about 15 mA, the power consumption is obtained from the
V
t2
B
Crss1
C
(V) I
VB
2
) of external FETs Q1 and Q2.
Q1
Ciss1
B
(A)
Crss2
Ciss2
Bias current
Ibias1 : = 3 mA
Bias current
Ibias1 : = 3 mA
Q2
t
A
L1
V
O1
MB3889
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