Electromagnetic Compatibility (Emc) Circuitry - Cirrus Logic CS42L42 Manual

2.1 Electromagnetic Compatibility (EMC) Circuitry

The circuit in Fig. 2-3 may be applied to signals not local to the CS42L42 (i.e., that traverse significant distances) for EMC.
To/from DUT
2.1.1 Low-Profile Charge-Pump Capacitors
In the typical connection for analog mics
2.2 µF, rated as X7R/X5R or better. The following low-profile versions of these capacitors are suitable for the application:
• Description: 2.2 µF ±20%, 6.3 V, X5R, 0201
• Manufacturer, Part Number: Murata, GRM033R60J225ME47, nominal height = 0.3 mm
• Manufacturer, Part Number: AVX, 02016D225MAT2A, nominal height = 0.33 mm
Note: Although the 0201 capacitors described are suitable, larger capacitors such as 0402 or larger may provide
acceptable performance.
2.1.2 Ceramic Capacitor Derating
Note 4 in Fig. 2-1 highlights that ceramic capacitor derating factors can significantly affect in-circuit capacitance values
and, in turn, CS42L42 performance. Under typical conditions, numerous types and brands of large-value ceramic
capacitors in small packages exhibit effective capacitances well below their ±20% tolerance, with some being derated by
as much as –50%. These same capacitors, when tested by a multimeter, read much closer to their rated value. A similar
derating effect has not been observed with tantalum capacitors.
The derating observed varied with manufacturer and physical size: Larger capacitors performed better, as did ones from
Kemet Electronics Corp. and TDK Corp. of any size. This derating effect is described in data sheets and in applications
notes from capacitor manufacturers. For instance, as DC and AC voltages are varied from the standard test points (applied
DC and AC voltages for standard test points versus PSRR test are 0 and 1 V
@ 20 Hz–20 kHz), it is documented that the capacitances vary significantly.
DS1083F2
L1 L2
D1
Figure 2-3. Optional EMC Circuit
(Fig. 2-1), the recommended capacitor values for the charge-pump circuitry are
2.1 Electromagnetic Compatibility (EMC) Circuitry
To/from
other Notes:
circuits
L1 and L2: Ferrite:
f = 30–100 MHz
27 pF Transition
DCR = 0.09–0.30 
X7R
D1: Transorb:
V
Breakdown
voltage of signal
@ 1 kHz versus 0.9 V and ~1 mV
RMS
CS42L42
> Normal operating peak
RMS
11