CS5531-AS datasheet(39/50 Pages) CIRRUS

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CS5531/32/33/34-AS

DS289F5

2.10. Clock Generator

The CS5531/32/33/34 include an on-chip inverting

amplifier which can be connected with an external

crystal to provide the master clock for the chip. Fig-

ure 20 illustrates the on-chip oscillator. It includes

loading capacitors and a feedback resistor to form

a Pierce oscillator configuration. The chips are de-

signed to operate using a 4.9152 MHz crystal;

however, other crystals with frequencies between

1 MHz to 5 MHz can be used. One lead of the crys-

tal should be connected to OSC1 and the other to

OSC2. Lead lengths should be minimized to reduce

stray capacitance. Note that while using the on-chip

oscillator, neither OSC1 or OSC2 is capable of di-

rectly driving any off-chip logic. When the on-chip

oscillator is used, the voltage on OSC2 is typically

0.5 V peak-to-peak. This signal is not compatible

with external logic unless additional external cir-

cuitry is added. The OSC2 output should be used if

the on-chip oscillator output is used to drive other

circuitry.

The designer can use an external CMOS-compati-

ble oscillator to drive OSC2 with a 1 MHz to

5 MHz clock for the ADC. The external clock into

OSC2 must overdrive the 60

µA output of the on-

chip amplifier. This will not harm the on-chip cir-

cuitry. In this scheme, OSC1 should be left uncon-

nected.

2.11. Power Supply Arrangements

The CS5531/32/33/34 are designed to operate from

single or dual analog supplies and a single digital

supply. The following power supply connections

are possible:

VA+ = +5V; VA- = 0V; VD+ = +3V to +5V

VA+ = +2.5V; VA- = -2.5V; VD+ = +3V to +5V

VA+ = +3V; VA- = -3V; VD+ = +3V

A VA+ supply of +2.5 V, +3.0 V, or +5.0 V should

be maintained at ±5% tolerance. A VA- supply of

-2.5 V or -3.0 V should be maintained at ±5% tol-

erance. VD+ can extend from +2.7 V to +5.5 V

with the additional restriction that:

[(VD+) - (VA-)] < 7.5 V.

Figure 21 illustrates the CS5532 connected with a

single +5.0 V supply to measure differential inputs

relative to a common mode of 2.5 V. Figure 22 il-

lustrates the CS5532 connected with ±2.5 V bipo-

lar analog supplies and a +3 V to +5 V digital

supply to measure ground referenced bipolar sig-

nals. Figures 23 and 24 illustrate the CS5532 con-

nected with ±3 V analog supplies and a +3 V

digital supply to measure ground-referenced bipo-

lar signals.

Figure 25 illustrates alternate bridge configurations

which can be measured with the converter. Voltage

V1 can be measured with the PGIA gain set to 1x

as the input amplifier on this gain setting can go

rail-to-rail. Voltage V2 should be measured with

the PGIA gain set at 2x or higher as the instrumen-

1 M

Ω

OSC1

OSC2

20 pF

MCLK

~ 60 µA

NOTE: 20 pF capacitors are on

chip and should not be added

externally.

Figure 20. On-chip Oscillator Model

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