MB39A123 Datasheet, PDF (30/44 Pages) Fujitsu Component Limited. – 6 ch DC/DC Converter IC with Synchronous Rectification

MB39A123
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)
DUTY (ON) Max =: ^{Vdt − 0.4 V} × 100 (%) =: 80% ± 0.2% ⋅ ⋅ ⋅ ⋅ (2)
0.5 V
Based on (1) and (2) above, selecting external resistances to 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.
■ PROCESSING WHEN NOT USING ch.4 INV AMP
Short-circuit the - INA terminal (pin 19) and OUTA terminal (pin 18) in the shortest distance when not using ch.4
INV Amp.
• When not using ch.4 INV Amp
19 −INA
18 OUTA
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