Technical Note
10/17
www.rohm.com
2010.06 - Rev.A
© 2010 ROHM Co., Ltd. All rights reserved.
BD7830NUV
●Selection of external components
①Setting gain from desired output
Output Po is determined via the following formula, from which the required gain Av can also be obtained.
Po [W] = Vo
2
[Vrms] / RL [Ω]
Vo = Av ・ Vin
Av ≧
RLPo
・
/ Vin
②Setting input resistance and feedback resistance from gain
Gain Av is determined via the following formula, from which input resistance Rin and feedback resistance Rf can be set.
Av = (Rf / Rin) ・ 2
Rin is set with the input side's drive capacity taken into account.
③Setting input coupling capacitor from low-range cut-off frequency
Low-range cut-off frequency fc is determined via the following formula, from which input coupling capacitor Cin can be set.
fc [Hz] = 1 / (2π ・ Rin ・ Cin)
Cin ≧ 1 / (2π ・ Rin ・ fc)
④Setting bias capacitor and SOFT capacitor to minimize pops
It is recommended that the capacitance of the bias capacitor CB be set to at least 10 times that of the input coupling
capacitor Cin, in order to soften the rise of the bias voltage while improving the Cin following ability.
Also, when a higher gain is used, the capacitance of the SOFT capacitor Cs can be raised to control pop sounds.
Av = 2 (6 dB at BTL) → Cs ・ (80 / fc) ≧ 0.01 µF
Av = 4 (12 dB at BTL) → Cs ・ (80 / fc) ≧ 0.022 µF
Av = 8 (18 dB at BTL) → Cs ・ (80 / fc) ≧ 0.033 µF
Av = 20 (26 dB at BTL) → Cs ・ (80 / fc) ≧ 0.068 µF
●Use when VCC = STBY short
Since this IC is designed on the assumption that it will be used to switch standby mode ON and OFF while the power supply
remains ON, normally STBY should be switched from H to L and the SOFT voltage should be discharged before powering
down. When used while VCC = STBY short, pop sounds may occur if the IC's power supply is reduced prior to discharging
the SOFT voltage.
To prevent pop sounds, you must ① set STBY = H→L before setting VCC = H→L
, and ② forcibly discharge the SOFT
voltage.
A sample circuit in which VCC = STBY short is used is shown below.
・Sample circuit configuration when VCC = STBY short
Rf
STBY
BIAS
SOFT
IN－
OUT2
GND
VCC
OUT1
1μ
Rin
1
2
3
4 5
6
7
8
Cin
Bias
1st Amp
2nd Amp
SOFT
CS
CD
VCC
②
Fast discharge of
SOFT voltage at
power-off
①
STBY = H → L at
power-off
Slow power-off of IC itself
