CS5571

DS768PP1

31

3/25/08

10:56

BP/UP – Bipolar/Unipolar Select, Pin 11

The BP/UP pin determines the span and the output coding of the converter. When set high to

select BP (bipolar), the input span of the converter is -2.048 volts to +2.048 volts (assuming the

voltage reference is 4.096 volts) and output data is coded in two's complement format. When

set low to select UP (unipolar), the input span is 0 to +2.048 and the output data is coded in

binary format.

DITHER – Dither Select, Pin 12

When DITHER is high (DITHER = VL), output conversion words will be dithered. When DITHER

is low (DITHER = VLR), output words will be dominated by quantization.

RST – Reset, Pin 13

Reset is necessary after power is initially applied to the converter. When the RST input is taken

low, the logic in the converter will be reset. When RST is released to go high, certain portions of

the analog circuitry are started. RDY falls when reset is complete.

CONV – Convert, Pin 15

The CONV pin initiates a conversion cycle if taken low, a previous conversion is in progress.

When the conversion cycle is completed, the conversion word is output to the serial port register

and the RDY signal goes low. If CONV is held low and remains low when RDY falls, another

conversion cycle will be started.

DCR – Digital Core Regulator, Pin 16

DCR is the output of the on-chip regulator for the digital logic core. DCR should be bypassed

with a capacitor to V2-. The DCR pin is not designed to power any external load.

V2+ – Positive Power 2, Pin 17

The V1+ and V2+ pins provide a positive supply voltage to the circuitry of the chip. These two

pins should be decoupled as shown in the application block diagrams. V1+ and V2+ should be

supplied from the same source voltage. For single-supply operation, these two voltages are

nominally +5 V. For dual-supply operation, they are nominally +2.5 V.

V2- – Negative Power 2, Pin 18

The V1- and V2- pins provide a negative supply voltage to the circuitry of the chip. These two

pins should be decoupled as shown in the application block diagrams. V1- and V2- should be

supplied from the same source voltage. For single-supply operation, these two voltages are

nominally 0 V (Ground). For dual-supply operation, they are nominally -2.5 V.

MCLK – Master Clock, Pin 19

The master clock pin (MCLK) is a multi-function pin. If tied low (MCLK = VLR), the on-chip oscil-

lator will be enabled. If tied high (MCLK = VL), all clocks to the internal circuitry of the converter

will stop. When MCLK is held high the internal oscillator will also be stopped. MCLK can also

function as the input for an external CMOS-compatible clock that conforms to supply voltages

on the VL and VLR pins.

VLR2, VLR, VL – Logic Interface Power/Return, Pins 14, 20, 21

VL and VLR are the supply voltages for the digital logic interface. VL and VLR can be config-

ured with a wide range of common mode voltage. The following interface pins function from the

VL/VLR supply: SMODE, CS, SCLK, TST, SDO, RDY, DITHER, CONV, RST, BP/UP, and

MCLK.

SDO – Serial Data Output, Pin 22

SDO is the output pin for the serial output port. Data from this pin will be output at a rate deter-

mined by SCLK and in a format determined by the BP/UP pin. Data is output MSB first and

advances to the next data bit on the rising edges of SCLK. SDO will be in a high impedance

state when CS is high.