CS5461 datasheet(17/46 Pages) CIRRUS

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CS5461

DS546PP2

4. FUNCTIONAL DESCRIPTION

4.1 Analog Inputs

The CS5461 has two available full-scale differen-

tial input voltage ranges on the current channel and

one full-scale differential input voltage range on

the voltage channel.

The input ranges are the maximum sinusoidal sig-

nals that can be applied to the current and voltage

channels, yet these values will not result in full

scale registration in the instantaneous current and

voltage registers.

If the current and voltage channels are set to

500 mVP-P, only a 250 mVRMS signal will register

full scale. Yet it would not be practical to inject a

sinusoidal signal with a value of 250 mVRMS.

When such a sine wave enters the higher levels of

its positive crest region (over each cycle), the volt-

age level of this signal exceeds the maximum dif-

ferential input voltage range of the input channels.

The largest sine wave voltage signal that can be

placed across the inputs, with no saturation is:

which is ~70.7% of full-scale. So for sinusoidal in-

puts at the full scale peak-to-peak level the full

scale registration is ~.707.

4.2 Voltage Reference

The CS5461 is specified for operation with a

+2.5 V reference between the VREFIN and VA-

pins. The converter includes an internal 2.5 V ref-

erence (60 ppm/°C drift) that can be used by con-

necting the VREFOUT pin to the VREFIN pin of

the device. If higher accuracy/stability is required,

an external reference can be used.

4.3 Oscillator Characteristics

XIN and XOUT are the input and output of an in-

verting amplifier to provide oscillation and can be

configured as an on-chip oscillator, as shown in

Figure 3. The oscillator circuit is designed to work

with a quartz crystal or a ceramic resonator. To re-

duce circuit cost, two load capacitors C1 and C2 are

integrated in the device. With these load capacitors,

the oscillator circuit is capable of oscillation up to

20 MHz. To drive the device from an external

clock source, XOUT should be left unconnected

while XIN is driven by the external circuitry. There

is an amplifier between XIN and the digital section

which provides CMOS level signals. This amplifier

works with sinusoidal inputs so there are no prob-

lems with slow edge times.

The CS5461 can be driven by an external oscillator

ranging from 2.5 to 20 MHz, but the K divider val-

ue must be set such that the internal DCLK will run

somewhere between 2.5 MHz and 5 MHz. The K

divider value is set with the K[3:0] bits in the Con-

figuration Register. As an example, if XIN =

MCLK = 15 MHz, and K is set to 5, then DCLK is

3 MHz, which is a valid value for DCLK.

4.4 Calibration

4.4.1 Overview of Calibration Process

The CS5461 offers digital calibration for both

channels; AC/DC offset and AC/DC gain. For both

500mV

P-P

= ~176.78mV

RMS

Oscillator

Circuit

DGND

XIN

XOUT

C1 =

22 pF

C2 =

Figure 3. Oscillator Connection

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