BD5468GUL Datasheet, PDF (10/20 Pages) Rohm – Analog Input Monaural Class-D Speaker Amplifier

BD5468GUL
Technical Note
2) Differential Input
+Battery
Cs
Shutdown Signal
H：IC Active
L：^{IC Shutdown}
SDNB
C2
Input Impedance
VDD ^{B1 B2} PVDD
Shutdown
Control
150k
(Typ.)
ALC
BIAS
OSC
Front IC
Ro
Ro
LPF
RLPF
Ci
RLPF
CLPF
Ci
CLPF
IN+ _Ri
A1
IN-
C1
Ri
Rf
PWM
H-
Bridge
Rf
GND _{A2 B3} PGND
OUT+
C3
A3
OUT-
Speaker
■Caution during External LPF Setting
External LPF Resistor R_LPF which is composed of IC input resistor Ri, forms input impedance.
The bigger the resistor value of LPF resistor R_LPF, the more it will decrease the gain.
When the input capacitor Ci has enough large capacity value, the relation among external LPF resistor R_LPF and IC input
resistor Ri and Gain will become:
Gain = 20×log | Rf / (Ri + R_LPF ) | [dB]
Input resistor Ri of BD5468GUL and resistor value of feedback resistor Rf will become the following below,
during ALC operation, changes at ±1dB step, and becomes 16 stages switch specs.
#1. Ri=55kΩ(Typ.), Rf=245kΩ(Typ.) @Gain=13dB
#2. Ri=60kΩ(Typ.), Rf=240kΩ(Typ.) @Gain=12dB
#3. Ri=66kΩ(Typ.), Rf=234kΩ(Typ.) @Gain=11dB
↓
#15. Ri=159kΩ(Typ.), Rf=141kΩ(Typ.) @Gain=-1dB
#16. Ri=167kΩ(Typ.), Rf=132kΩ(Typ.) @Gain=-2dB
Also with the driver ability of previous IC step, after checking, constant setting of external LPF and Resistor R_LPF.
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10/19
2010.09 - Rev.A