CS5504 データシートの表示（PDF） - Cirrus Logic

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CS5504

Low-power, 20-bit A/D Converter

Cirrus Logic 

CS5504

CS5504

output code. The only difference is that in bipo-

lar mode the on-chip microcontroller offsets the

computed output word by a code value of

8000H. This means that the bipolar measure-

ment range is not calibrated from full scale

positive to full scale negative. Instead it is cali-

brated from the bipolar zero scale point to full

scale positive. The slope factor is then extended

below bipolar zero to accommodate the negative

input signals. The converter can be used to con-

vert both unipolar and bipolar signals by

changing the BP/UP pin. Recalibration is not re-

quired when switching between unipolar and

bipolar modes.

At the end of the calibration cycle, the on-chip

micro controller checks the logic state of the

CONV signal. If the CONV input is low the de-

vice will enter the standby mode where it waits

for further instruction. If the CONV signal is

high at the end of the calibration cycle, the con-

verter will enter the conversion state and

perform a conversion on the input channel. The

CAL signal can be returned low any time after

calibration is initiated. CONV can also be re-

turned low, but it should never be taken low and

then taken back high until the calibration period

has ended and the converter is in the standby

state. If CONV is taken low and then high

again with CAL high while the converter is cali-

brating, the device will interrupt the current

calibration cycle and start a new one. If CAL is

taken low and CONV is taken low and then high

during calibration, the calibration cycle will

continue as the conversion command is disre-

garded. The state of BP/UP is not important

during calibrations.

If an "end of calibration" signal is desired, pulse

the CAL signal high while leaving the CONV

signal high continuously. Once the calibration is

completed, a conversion will be performed. At

the end of the conversion, DRDY will fall to in-

dicate the first valid conversion after the

calibration has been completed.

DS126F12

Conversion

The conversion state can be entered at the end of

the calibration cycle, or whenever the converter

is idle in the standby mode. If CONV is taken

high to initiate a calibration cycle ( CAL also

high), and remains high until the calibration cy-

cle is completed (CAL is taken low after CONV

transitions high), the converter will begin a con-

version upon completion of the calibration

period. The device will perform a conversion on

the input channel selected by A0 when CONV

transitions high. Table 1 indicates the multi-

plexer channel selection truth table.

A0

Channel Addressed

0

AIN1

1

AIN2

Table 1. Multiplexer Truth Table

The A0 input is latched internal to the CS5504

when CONV rises. A0 has internal pull-down

circuits which default the multiplexer to channel

AIN1.

The BP/UP pin is not a latched input. The

BP/UP pin controls how the output word from

the digital filter is processed. In bipolar mode

the output word computed by the digital filter is

offset by 80000H (see Understanding Converter

Calibration). BP/UP can be changed after a con-

version is started as long as it is stable for 82

clock cycles of the conversion period prior to

DRDY falling. If one wishes to intermix meas-

urement of bipolar and unipolar signals on

various input channels, it is best to switch the

BP/UP pin immediately after DRDY falls and

leave BP/UP stable until DRDY falls again.

The digital filter in the CS5504 has a Finite Im-

pulse Response and is designed to settle to full

accuracy in one conversion time.

If CONV is left high, the CS5504 will perform

continuous conversions. The conversion time

will be 1622 clock cycles. If conversion is initi-

11

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