MB39A115 Datasheet, PDF (26/42 Pages) Fujitsu Component Limited. – 5 ch DC/DC Converter IC with Synchronous Rectification

MB39A115
• When dead time is set :
(Setting by external resistors)
VREF
11
Ra
R1 : 131.9 kΩ
DTCX
To PWM
Comp.X
Vdt
Rb
GND
14
R2 : 97.5 kΩ
X : Each channel number
Setting example (for an aim maximum ON duty of 80% (Vdt = 0.8 V) with Ra = 13.7 kΩ and Rb = 9.1 kΩ)
• Calculation using external resistors Ra and Rb only
Rb
Vdt =
× VREF =: 0.80 V
Ra + Rb
DUTY (ON) Max=: ^{Vdt − 0.4 V} × 100 (%) =: 80% ⋅ ⋅ ⋅ ⋅ (1)
0.5 V
• Calculation taking account of the built-in resistor (tolerance ± 20%) also
(Rb, R2 Combined resistance)
Vdt =
× VREF =: 0.80 V ± 0.13%
(Ra, R1 Combined resistance) + (Rb, R2 Combined resistance)
Vdt − 0.4 V
DUTY (ON) Max=:
× 100 (%) =: 80% ± 0.2% • • • • (2)
0.5 V
Based on (1) and (2) above, selecting external resistances of 1/10th or less of the built-in resistance enables
the built-in resistance to be ignored.
As for the duty dispersion, please expect ± 5% at (fosc = 1 MHz) due to the dispersion of a triangular wave
amplitude.
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