AD7293 datasheet(23/79 Pages) AD

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Data Sheet

AD7293

Rev. D | Page 23 of 79

ANALOG INPUTS

The AD7293 has four analog inputs, VIN3 to VIN0. Depending

on the configuration register setup, they can be configured as

four single-ended inputs or two fully differential channels.

Single-Ended Mode

The AD7293 can have four single-ended analog input channels.

In applications where the signal source is high impedance, it is

recommended to buffer the analog input before applying it to the

ADC. The analog input range is programmed to the following

modes: 0 V to REFADC, 0 V to 2 × REFADC, or 4 × REFADC mode.

The voltage, with respect to AGND on the ADC analog input

pins, cannot exceed AVDD.

Differential Mode

The AD7293 can have two differential input pairs (VIN3 and VIN2,

VIN1 and VIN0). The amplitude of the differential signal is the

difference between the signals at VIN+ and VIN− (VIN0 and VIN1,

or VIN3 and VIN2). Simultaneously drive VIN+ and VIN− by two

signals, each of amplitude REFADC, 2 × REFADC, or 4 × REFADC,

depending on the range chosen, which are 180° out of phase.

VIN+

AD72931

VIN–

ADCREF p-p

COMMON-MODE

VOLTAGE

1ADDITIONAL PINS OMITTED FOR CLARITY.

Figure 37. Differential Input (VIN+/VIN− Refer to VIN0 to VIN3)

Assuming that the 0 V to REFADC range is selected, the amplitude

of the differential signal is, therefore, −REFADC to +REFADC peak

to peak, regardless of the common-mode voltage (VCM).

The common-mode voltage is the average of the two signals.

(VIN+ + VIN−)/2

The common-mode voltage is the voltage on which the two

inputs are centered. The result is that the span of each input is

VCM ± REFADC/2. This common-mode voltage must be set up

externally.

When a conversion takes place, the common-mode voltage is

rejected, resulting in a virtually noise free signal of amplitude

−REFADC to +REFADC, corresponding to the digital output codes

of −2048 to +2047 in twos complement format.

When using the 2 × REFADC range, the input signal amplitude

extends from −2 × REFADC (VIN+ = 0 V and VIN− = REFADC) to

+2 × REFADC (VIN− = 0 V and VIN+ = REFADC).

Similarly, when using the 4 × REFADC range, the input signal

amplitude extends from −4 × REFADC (VIN+ = 0 V and VIN− =

REFADC) to +4 × REFADC (VIN− = 0 V and VIN+ = REFADC).

Pseudo Differential Mode

The four uncommitted analog input channels can be configured

as two pseudo differential pairs. Two uncommitted inputs, VIN0

and VIN1, are a pseudo differential pair, as are VIN2 and VIN3. In

this mode, VIN+ is connected to the signal source, which can have

a maximum amplitude of REFADC, 2 × REFADC, or 4 × REFADC,

depending on the range that is chosen, to make use of the full

dynamic range of the device. A dc input is applied to VIN−. The

voltage applied to this input provides an offset from ground or a

pseudo ground for the VIN+ input. The ADC channel allocation

determines the channel specified as VIN+. The differential mode

must be selected to operate in the pseudo differential mode. The

resulting converted pseudo differential data is stored in twos

complement format in the result register.

For VIN0, the governing equation for the pseudo differential

mode is

VOUT = 2(VIN+ − VIN−) − REFADC

where:

VIN+ is the single-ended signal.

VIN− is a dc voltage.

REFADC = 1.25 V.

The benefit of pseudo differential inputs is that they separate

the analog input signal ground from the ADC ground, allowing

dc common-mode voltages to be cancelled.

1ADDITIONAL PINS OMITTED FOR CLARITY.

AD72931

VIN+

VIN–

DC INPUT

VOLTAGE

VREF p-p

Figure 38. Pseudo Differential Input (VIN+/VIN− Refer to VIN0 to VIN3)

CURRENT SENSOR

Four bidirectional high-side current sense amplifiers are

provided that can accurately amplify differential current shunt

voltages in the presence of high common-mode voltages from

AVDD up to AVSS + 60 V. The current sensors can be read

directly, or optionally, they can be set to operate as part of the four

independent closed-loop, drain current controllers. See the

Closed-Loop Mode section for more information.

In open-loop operation, the current sense amplifiers measure

the current through a shunt resistor. Each amplifier can accept

differential inputs up to ±200 mV. A selectable gain amplifies

the measured voltage drop across the current sensor.

AD7293 Datasheet(PDF) 23 Page - Analog Devices

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