MB3885 Datasheet, PDF (21/29 Pages) Fujitsu Component Limited. – 1-channel DC/DC Converter IC with Synchronous Rectifier

MB3885
s PRECAUTIONS RELATED TO SUPPLY VOLTAGE RANGE
Although the supply voltage range listed under recommended operating requirements is 5.5V-18V, generation
of heat limits the maximum operating supply voltage since the IC’s internal loss varies with the frequency of
oscillation and FET’s total gate charge. When using the MB 3885 in an application, caution must be taken in
relation to supply voltage range.
As shown below, IB (average current) can be determined from the total gate charge Qg1, Qg2, charged from the
gate capacitance (Ciss1, Ciss2, Crss1, Crss2) of the external FET Q1, Q2, by the following formula.
IB (A) = I1 + I2
= Ibias1 ×
T1 Qg1
T2 Qg2
T ⁺ T ^{+ Ibias2 ×} T ⁺ T
(Ibias1 = Ibias2 =: 2 mA)
Because IC current consumption other than IB is 6.5 mA, power consumption can be determined from the
following formula.
Power consumption : Pc
Pc (W) =: 0.0065 × VCC + VCC × IB − 1 / 2 × VB × IB
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