AD5765CSUZ datasheet(24/31 Pages) AD

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AD5765

Rev. PrA | Page 24 of 31

AD5765 FEATURES

ANALOG OUTPUT CONTROL

In many industrial process control applications, it is vital that

the output voltage be controlled during power-up and during

brownout conditions. When the supply voltages are changing,

the output pins are clamped to 0 V via a low impedance path.

To prevent the output amp being shorted to 0 V during this

time, transmission gate G1 is also opened (see Figure 34). These

conditions are maintained until the power supplies stabilize and

a valid word is written to the DAC register. At this time, G2

opens and G1 closes. Both transmission gates are also externally

controllable via the reset logic (RSTIN) control input. For

instance, if RSTIN is driven from a battery supervisor chip, the

RSTIN input is driven low to open G1 and close G2 on power-

down or during a brownout. Conversely, the on-chip voltage

detector output (RSTOUT) is also available to the user to

control other parts of the system. The basic transmission gate

functionality is shown in Figure 34.

RSTOUT

RSTIN

VOUTA

AGNDA

VOLTAGE

MONITOR

AND

CONTROL

Figure 34. Analog Output Control Circuitry

DIGITAL OFFSET AND GAIN CONTROL

The AD5765 incorporates a digital offset adjust function with a

±16 LSB adjust range and 0.125 LSB resolution. The gain

range. The full-scale output can be programmed to achieve full-

scale ranges of ±4.096 V, ±4.201 V, and ±4.311 V. A fine gain

trim is also provided.

PROGRAMMABLE SHORT-CIRCUIT PROTECTION

The short-circuit current of the output amplifiers can be pro-

grammed by inserting an external resistor between the ISCC

pin and PGND. The programmable range for the current is

500 µA to 10 mA, corresponding to a resistor range of 120 kΩ

to 6 kΩ. The resistor value is calculated as follows:

≈

If the ISCC pin is left unconnected, the short-circuit current

limit defaults to 5 mA. It should be noted that limiting the short

circuit current to a small value can affect the slew rate of the

output when driving into a capacitive load, therefore, the value

of short-circuit current programmed should take into account

the size of the capacitive load being driven.

DIGITAL I/O PORT

The AD5765 contains a 2-bit digital I/O port (D1 and D0).

These bits can be configured as inputs or outputs independently,

and can be driven or have their values read back via the serial

interface. The I/O port signals are referenced to DVCC and

DGND. When configured as outputs, they can be used as

control signals to multiplexers or can be used to control

calibration circuitry elsewhere in the system. When configured

as inputs, the logic signals from limit switches, for example, can

be applied to D0 and D1 and can be read back via the digital

interface.

DIE TEMPERATURE SENSOR

The on-chip die temperature sensor provides a voltage output

that is linearly proportional to the centigrade temperature scale.

Its nominal output voltage is 1.4 V at +25°C die temperature,

varying at 5 mV/°C, giving a typical output range of 1.175 V to

1.9 V over the full temperature range. Its low output impedance,

and linear output simplify interfacing to temperature control

circuitry and A/D converters. The temperature sensor is

provided as more of a convenience rather than a precise feature;

it is intended for indicating a die temperature change for

recalibration purposes.

LOCAL GROUND OFFSET ADJUST

The AD5765 incorporates a local-ground-offset adjust feature

which, when enabled in the function register, adjusts the DAC

outputs for voltage differences between the individual DAC

ground pins and the REFGND pin ensuring that the DAC

output voltages are always with respect to the local DAC ground

pin. For instance, if pin AGNDA is at +5 mV with respect to the

REFGND pin and VOUTA is measured with respect to

AGNDA, then a −5 mV error results, enabling the local-

ground-offset adjust feature adjusts VOUTA by +5 mV,

eliminating the error.

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