CS5530 datasheet(28/36 Pages) CIRRUS

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CS5530

DS742F2

2.9 Clock Generator

The CS5530 includes an on-chip inverting amplifi-

er which can be connected with an external crystal

to provide the master clock for the chip. Figure 17

illustrates the on-chip oscillator. It includes loading

capacitors and a feedback resistor to form a Pierce

oscillator configuration. The chips are designed to

operate using a 4.9152 MHz crystal; however, oth-

er crystals with frequencies between 1 MHz to 5

MHz can be used. One lead of the crystal should be

connected to OSC1 and the other to OSC2. Lead

lengths should be minimized to reduce stray capac-

itance. Note that while using the on-chip oscillator,

neither OSC1 or OSC2 is capable of directly driv-

ing any off chip logic. When the on-chip oscillator

is used, the voltage on OSC2 is typically 1/2 V

peak-to-peak. This signal is not compatible with

external logic unless additional external circuitry is

added. The OSC2 output should be used if the on-

chip oscillator output is used to drive other circuit-

ry.

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 microampere output

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

chip circuitry. In this scheme, OSC1 should be left

unconnected.

2.10 Power Supply Arrangements

The CS5530 is designed to operate from single or

dual analog supplies and a single digital supply.

The following power supply connections are possi-

ble:

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

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

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

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 18 illustrates the CS5530 connected with a

single +5.0 V supply to measure differential inputs

relative to a common mode of 2.5 V. Figure 19 il-

lustrates the CS5530 connected with ±2.5 V bipolar

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

to measure ground referenced bipolar signals. Fig-

ures 20 illustrates the CS5532 connected with ±3 V

analog supplies and a +3 V digital supply to mea-

sure ground referenced bipolar signals.

OSC1

MCLK

NOTE: 20 pF capacitors are on chip and

should not be added externally.

1 M

OSC2

20 pF

VTH

~60 μA

Figure 17. On-chip Oscillator Model

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