AD5751 datasheet(19/22 Pages) AD

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Preliminary Technical Data

AD5751

Rev. PrA | Page 19 of 22

FEATURES

OUTPUT FAULT ALERT – SOFTWARE MODE

In Software mode, the AD5751 is equipped with one FAULT

pin, this is an open-drain output allowing several AD5751

devices to be connected together to one pull-up resistor for

global fault detection. In software control mode, the FAULT pin

is forced active high by any one of the following fault scenarios;

The Voltage at IOUT attempts to rise above the

compliance range, due to an open-loop circuit or

insufficient power supply voltage. The internal

circuitry that develops the fault output avoids using a

comparator with “window limits” since this would

require an actual output error before the FAULT

output becomes active. Instead, the signal is generated

when the internal amplifier in the output stage has less

than approximately one volt of remaining drive

capability. Thus the FAULT output activates slightly

before the compliance limit is reached. Since the

comparison is made within the feedback loop of the

output amplifier, the output accuracy is maintained by

its open-loop gain and an output error does not occur

before the FAULT output becomes active.

A short is detected on the voltage output pin. Short

circuit current limited to 25ma.

An interface error is detected due to the PEC error

checking failure. See PEC error checking section.

A range change is detected without the user writing to

the Interface.

If the core temperature of the AD5751 exceeds approx.

150°C.

OUTPUT FAULT ALERT – HARDWARE MODE

In Hardware mode, the AD5751 is equipped with 3 FAULT

pins, VFAULT, IFAULT, TEMP. These are an open-drain

outputs allowing several AD5751 devices to be connected

together to one pull-up resistor for global fault detection. In

hardware control mode, these fault pins are forced active by any

one of the following fault scenarios;

Open Circuit Detect. The Voltage at IOUT attempts to

rise above the compliance range, due to an open-loop

circuit or insufficient power supply voltage. The

internal circuitry that develops the fault output avoids

using a comparator with “window limits” since this

would require an actual output error before the

FAULT output becomes active. Instead, the signal is

generated when the internal amplifier in the output

stage has less than approximately one volt of

remaining drive capability. Thus the FAULT output

activates slightly before the compliance limit is

reached. Since the comparison is made within the

feedback loop of the output amplifier, the output

accuracy is maintained by its open-loop gain and an

output error does not occur before the FAULT output

becomes active.

If this fault is detected the IFAULT pin is forced low.

A short is detected on the voltage output pin. Short

circuit current limited to 25ma. If this fault is detected

the VFAULT pin is forced low.

If the core temperature of the AD5751 exceeds approx.

150°C. If this fault is detected the TEMP pin is forced

low.

VOLTAGE OUTPUT SHORT CIRCUIT PROTECTION

Under normal operation the voltage output will sink/source

5mA and maintain specified operation. The maximum current

that the voltage output will deliver is 25mA, this is the short

circuit current.

ASYNCHRONOUS CLEAR (CLEAR)

CLEAR is an active high clear that allows the voltage output to

be cleared to either zero-scale code or mid-scale code, user-

selectable via the CLRSEL pin or the CLRSEL bit of the INPUT

logical OR function of the CLR SELECT pin and the CLRSEL

bit). The Current loop output will clear to the bottom of its

programmed range. It is necessary to maintain CLEAR high for a

minimum amount of time (see Figure 2) to complete the

operation. When the CLEAR signal is returned low, the output

returns to its programmed value or a new value if programmed.

A clear operation can also be performed via the CLEAR

command in the control register.

Table 11. CLEAR SELECT Options

CLR

SELECT

Output CLR Value

Unipolar Output Voltage

Range

0 V

Mid-Scale

Unipolar Current Output

Range

Zero-Scale e.g.

4ma on 4-20ma

0ma on 0-20ma etc...

Mid-Scale e.g.

12ma on 4-20ma

10ma on 0-20ma

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