ADR395 AD [Analog Devices], ADR395 Datasheet - Page 28

• Manufacturer Part Number: ADR395
• Description: Complete Dual, 16-Bit, High Accuracy, Serial Input, Bipolar Voltage Output DACs
• Manufacturer: AD [Analog Devices]

AD5762R
AD5762R 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 VOUT 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 41). 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 In ( 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-
off 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 41.
DIGITAL OFFSET AND GAIN CONTROL
The AD5762R incorporates a digital offset adjust function with
a ±16 LSB adjust range and 0.125 LSB resolution. The gain
register allows the user to adjust the AD5762R’s full-scale
output range. The full-scale output can be programmed to
achieve full-scale ranges of ±10 V, ±10.25 V, and ±10.5 V. A fine
gain trim is also available.
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:
R
=
Isc
60
VOLTAGE
CONTROL
MONITOR
AND
Figure 41. Analog Output Control Circuitry
RSTOUT
G1
G2
RSTIN
VOUTA
AGNDA
Rev. PrA | Page 28 of 33
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 AD5762R contain 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 DV
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 AD5762R 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 −5mV error results, enabling the local-ground-
offset adjust feature adjusts VOUTA by +5 mV, eliminating the
error.
Preliminary Technical Data
CC
and