Philips TDA1562Q Application Note page 21

Philips Semiconductors
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Application note
CMRR(dB)
-20
-30
-40
-50
C
-60
-70
B
-80
-90
A
-100
0.01
A: Ideal input capacitors ("infinite" capacitance")
B: 470nF input capacitors, randomly selected
C: 100nF capacitors, matched values (difference < 0.1%)
D: 100nF capacitors, randomly selected (difference 5%)
Fig 9. The influence of input capacitors on the Common Mode Ripple Rejection
Fig. 9 clearly shows the influence of the input capacitors on the CMRR. At low
frequencies the impedance of the input capacitors will increase and any difference in
the impedance between the two input capacitors will immediately be translated to a
worse CMRR.
When a very high CMRR is required it is therefore best to use input capacitors with a
high capacitance, preferably matched or 1% accuracy types.
The reference decoupling capacitor Cref:
This capacitor at pin 14 serves to stabilize the internal voltage reference, and during
switching on of the amplifier it is used as a timing device.
A recommended value for this capacitor is 10µF. Using a smaller capacitor than this
may result in worse supply voltage ripple rejection and possibly malfunction of the
load detection circuit during start-up.
The supply decoupling capacitors Csup1 and Csup2:
Csup1 is the supply decoupling electrolytic capacitor. This capacitor acts as a buffer
in order to reduce supply voltage ripple when high currents are drawn from the power
supply. The bigger the capacitance of this capacitor, the better the supply ripple
reduction. The standard value for this capacitor is 2200µF/16V
Csup2 is the HF decoupling capacitor for the power supply. The main purpose of this
capacitor is to suppress high frequency oscillations at the supply lines. This capacitor
should be placed as close as possible to the Vp and Gnd pins of the device. The
standard value for this component is 100nF. Usually a film capacitor or a good quality
surface mount ceramic capacitor is used. Choosing a smaller value than 100nF could
lead to oscillations in the supply lines.
Rev. 01.02 — 05 May 2006
CMRR vs Freq
V c m = 0 . 7 V r m s
D
0.1 1
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TDA1562Q application note
F (kHz)
10 100
© Koninklijke Philips Electronics N.V. 2004. All rights reserved.
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