AD7731_15 Datasheet, PDF (8/44 Pages) Analog Devices – Low Noise, High Throughput 24-Bit Sigma-Delta ADC

AD7731
PIN FUNCTION DESCRIPTIONS (Continued)
Pin Pin
No. Mnemonic
Function
3 MCLK OUT When the master clock for the device is a crystal/resonator, the crystal/resonator is connected between
MCLK IN and MCLK OUT. If an external clock is applied to the MCLK IN, MCLK OUT provides an
inverted clock signal. This clock can be used to provide a clock source for external circuits and MCLK OUT
is capable of driving one CMOS load.
4 POL
5
SYNC
6
RESET
Clock Polarity. Logic Input. This determines the polarity of the serial clock. If the active edge for the proces-
sor is a high-to-low SCLK transition, this input should be low. In this mode, the AD7731 puts out data on
the DATA OUT line in a read operation on a low-to-high transition of SCLK and clocks in data from the
DATA IN line in a write operation on a high-to-low transition of SCLK. In applications with a noncontinuous
serial clock (such as most microcontroller applications), this means that the serial clock should idle low
between data transfers. If the active edge for the processor is a low-to-high SCLK transition, this input
should be high. In this mode, the AD7731 puts out data on the DATA OUT line in a read operation on a
high-to-low transition of SCLK and clocks in data from the DATA IN line in a write operation on a low-to-
high transition of SCLK. In applications with a noncontinuous serial clock (such as most microcontroller
applications), this means that the serial clock should idle high between data transfers.
Logic Input that allows for synchronization of the digital filters and analog modulators when using a number
of AD7731s. While SYNC is low, the nodes of the digital filter, the filter control logic and the calibration
control logic are reset and the analog modulator is also held in its reset state. SYNC does not affect the
digital interface but does reset RDY to a high state if it is low. While SYNC is asserted, the Mode Bits may
be set up for a subsequent operation that will commence when the SYNC pin is deasserted.
Logic Input. Active low input that resets the control logic, interface logic, digital filter, analog modulator and
all on-chip registers of the part to power-on status. Effectively, everything on the part except for the clock
oscillator is reset when the RESET pin is exercised.
7 NC
No Connect. The user is advised not to connect anything to this pin.
8 AGND
Ground reference point for analog circuitry.
9
AV_DD
10 AIN1
Analog Positive Supply Voltage. The AV_DD to AGND differential is 5 V nominal.
Analog Input Channel 1. Programmable-gain analog input that can be used as a pseudo-differential input
when used with AIN6 or as the positive input of a differential pair when used with AIN2.
11 AIN2
Analog Input Channel 2. Programmable-gain analog input that can be used as a pseudo-differential input
when used with AIN6 or as the negative input of a differential pair when used with AIN1.
12 AIN3/D1
Analog Input Channel 3 or Digital Output 1. This pin can be used as either an analog input or a digital
output bit as determined by the DEN bit of the Mode Register. When selected as a programmable-gain
analog input, it can be used as a pseudo-differential input when used with AIN6 or as the positive input of a
differential pair when used with AIN4. When selected as a digital output, this output can be programmed
over the serial interface using bit D1 of the Mode Register.
13 AIN4/D0
Analog Input Channel 4 or Digital Output 0. This pin can be used as either an analog input or a digital
output bit as determined by the DEN bit of the Mode Register. When selected as a programmable-gain
analog input, it can be used as a pseudo-differential input when used with AIN6 or as the negative input of a
differential pair when used with AIN3. When selected as a digital output, this output can be programmed
over the serial interface using bit D0 of the Mode Register.
14 REF IN(+) Reference Input. Positive terminal of the differential reference input to the AD7731. REF IN(+) can lie
anywhere between AV_DD and AGND. The nominal reference voltage (i.e., the differential voltage between
REF IN(+) and REF IN(–)) should be +2.5 V when the HIREF bit of the Mode Register is 0 and is +5 V
when the HIREF bit of the Mode Register is 1.
15 REF IN(–)
16 AIN5
Reference Input. Negative terminal of the differential reference input to the AD7731. The REF IN(–) can lie
anywhere between AV_DD and AGND.
Analog Input Channel 5. Programmable-gain analog input which can be used is the positive input of a differ-
ential pair when used with AIN6.
17 AIN6
Analog Input Channel 6. Reference point for AIN1 through AIN4 in pseudo-differential mode or as the
negative input of a differential input pair when used with AIN5.
18 STANDBY Logic Input. Taking this pin low shuts down the analog and digital circuitry, reducing current consumption
to the 10 µA range. The on-chip registers retain all their values when the part is in standby mode.
19 CS
Chip Select. Active low Logic Input used to select the AD7731. With this input hardwired low, the
AD7731 can operate in its three-wire interface mode with SCLK, DIN and DOUT used to interface to the
device. CS can be used to select the device in systems with more than one device on the serial bus or as a
frame synchronization signal in communicating with the AD7731.
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