AD5734R datasheet(30/32 Pages) AD

30 / 32 page

AD5724R/AD5734R/AD5754R

Preliminary Technical Data

Rev. PrC | Page 30 of 32

FEATURES

ANALOG OUTPUT CONTROL

In many industrial process control applications, it is vital that

the output voltage be controlled during power-up. When the

supply voltages change during power-up, the VOUT pins are

clamped to 0 V via a low impedance path (approxiamately

4kΩ). To prevent the output amplifiers from being shorted to

0 V during this time, Transmission Gate G1 is also opened (see

Figure 46). These conditions are maintained until the power

supplies have stabilized and a valid word is written to a DAC

VOUTA

VOLTAGE

MONITOR

AND

CONTROL

Figure 46. Analog Output Control Circuitry

POWER-DOWN MODE

Each DAC channel of the AD5724R/AD5734R/AD5754R can

be individually powered-down. By default all channels are in

power-down mode. The power status is controlled by the

POWER CONTROL register, see Table 28 and Table 29 for

details. When a channel is in power-down mode its output pin

is clamped to ground through a resistance of approx. 4kΩ and

the output of the amplifier is disconnected from the output pin.

OVERCURRENT PROTECTION

Each DAC channel of the AD5724R/AD5734R/AD5754R

incorporates individual overcurrent protection. The user has

two options for the configuration of the overcurrent protection,

constant current clamp, or automatic channel power-down. The

configuration of the overcurrent protection is selected via the

CLAMP ENABLE bit in the control register.

Constant Current Clamp (CLAMP ENABLE = 1)

If a short circuit occurs, in this configuration the current is

clamped at 20 mA. This event is signaled to the user by the

setting of the appropriate overcurrent (OCX) bit in the power

control register. Upon removal of the short-circuit fault, the

OCX bit is cleared.

Automatic Channel Power-Down (CLAMP ENABLE = 0)

If a short circuit occurs, in this configuration the shorted

channel powers down and its output is clamped to ground via a

resistance of approx. 4kΩ, also at this time the output of the

amplifier is disconnected from the output pin. The short-circuit

event is signaled to the user via the overcurrent (OCX) bits,

while the power-up (PUX ) bits indicate which channels have

powered down. After the fault is rectified, the channels can be

powered up again by setting the PUX bits.

THERMAL SHUTDOWN

The AD5724R/AD5734R/AD5754R incorporate a thermal

shutdown feature that automatically shuts down the device if

the core temperature exceeds approximately 150°C. The thermal

shutdown feature is disabled by default and can be enabled via

the TSD ENABLE bit of the control register. In the event of a

thermal shutdown, the TSD bit of the power control register is set.

INTERNAL REFERENCE

The on-chip voltage reference is powered down by default. If an

external voltage reference source is to be used, the internal

reference must remain powered down at all times. If the internal

reference is to be used as the reference source, it must be

powered up via the PUREF bit of the power control register. The

internal reference voltage is accessible at the REFIN/REFOUT pin

for use as a reference source for other devices within the system.

If the internal reference is to be used external to the

AD5724R/AD5734R/AD5754R, it must first be buffered.

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