CS5342

18

DS608PP2

4.4

Power-up Sequence

Reliable power-up can be accomplished by keeping the device in reset until the power supplies, clocks and config-

uration pins are stable. It is also recommended that reset be enabled if the analog or digital supplies drop below the

minimum specified operating voltages to prevent power glitch related issues.

4.5

Analog Connections

The analog modulator samples the input at 6.144 MHz. The digital filter will reject signals within the stopband of the

filter. However, there is no rejection for input signals which are multiples of the input sampling frequency

(n

energy at 6.144 MHz, in addition to providing the optimum source impedance for the modulators. The use of capac-

itors which have a large voltage coefficient (such as general purpose ceramics) must be avoided since these can

degrade signal linearity.

4.6

Grounding and Power Supply Decoupling

As with any high resolution converter, the CS5342 requires careful attention to power supply and grounding arrange-

ments if its potential performance is to be realized. Figure 17 shows the recommended power arrangements, with

VA and VL connected to clean supplies. VD, which powers the digital filter, may be run from the system logic supply

or may be powered from the analog supply via a resistor. In this case, no additional devices should be powered from

VD. Decoupling capacitors should be as near to the ADC as possible, with the low value ceramic capacitor being

the nearest. All signals, especially clocks, should be kept away from the FILT+ and VQ pins in order to avoid un-

wanted coupling into the modulators. The FILT+ and VQ decoupling capacitors, particularly the 0.1 µF, must be po-

sitioned to minimize the electrical path from FILT+ and REF_GND. The CDB5342 evaluation board demonstrates

the optimum layout and power supply arrangements. To minimize digital noise, connect the ADC digital outputs only

to CMOS inputs.

4.7 uF

100 k

Ω

100 k

Ω

VA

634

Ω

91

Ω

470 pF

COG

2200 pF

CS5342 AINL

AINL

4.7 uF

100 k

Ω

100 k

Ω

VA

634

Ω

91

Ω

470 pF

COG

CS5342 AINL

AINL

2200 pF

Figure 21. CS5342 Recommended Analog Input Buffer