CS4299 datasheet(39/52 Pages) CIRRUS

39 / 52 page

CS4299

6.3

Miscellaneous Analog Signals

The AFLT1 and AFLT2 pins must have a 1000 pF

NPO capacitor to analog ground. These capacitors

provide a single-pole low-pass filter at the inputs to

the ADCs. This makes low-pass filters at each ana-

log input pin unnecessary.

The REFFLT pin must have a 1

µF and a 0.1 µF ca-

pacitor connected to analog ground with a short,

wide trace to this pin (see Figure 21 in Section 8,

Grounding and Layout, for an example). The 1

µF

capacitor must not be replaced with any value high-

er than 1

µF. No other connection should be made,

as any coupling onto this pin will degrade the ana-

log performance of the CS4299. Likewise, digital

signals should be kept away from REFFLT for sim-

ilar reasons.

The Vrefout pin is typically 2.3 V and provides a

common mode signal for single-supply external

circuits. Vrefout only supports light DC loads and

should be buffered if AC loading is needed. For

typical use the Vrefout pin should have a 1

µF and

a 0.1

µF capacitor connected to analog ground.

6.4

Power Supplies

The power supplies providing analog power should

be as clean as possible to minimize coupling into

the analog section which could degrade analog per-

formance. The analog power pins, AVdd1 and

AVdd2, supply power to all the analog circuitry on

the CS4299. The +5 V analog supply should be

generated from a linear voltage regulator (7805

type) connected to a +12 V supply. This helps iso-

late the analog circuitry from noise typically found

on +5 V digital supplies. A typical voltage regula-

tor

circuit

for

analog

power

using

MC78M05CDT +5 V regulator is shown in

Figure 19. The digital power pins, DVdd1 and

DVdd2, should be connected to the same digital

supply as the controller AC-link interface. The dig-

ital interface on the CS4299 may operate at either

+3.3 V or +5 V and proper connection of these pins

will depend on the digital power supply of the con-

troller.

6.5

Reference Design

See Section 11 for a CS4299 reference design.

Figure 19. Voltage Regulator

+12VD

AGND

DGND

+5VA

0.1µF

Y5V

10µF

ELEC

10µF

ELEC

MC78M05CDT

OUT

GND

0.1µF

Y5V

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