AD5764 데이터 시트보기 (PDF) - Analog Devices
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AD5764 Datasheet PDF : 27 Pages
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AD5744/64 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 pin is 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. 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 10.
RSTOUT
RSTIN
VOLTAGE
MONITOR
AND
CONTROL
G1
G2
VOUTA
AGNDA
Figure 10. Analog Output Control Circuitry
DIGITAL OFFSET AND GAIN CONTROL
The AD5744/64 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 AD5744/64’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, allowing a trim range of ±16 LSB in 1
LSB steps.
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 AGND. The programmable range for the current is
500 µA to 10 mA, corresponding to a resistor range of 120 kΩ
to 6 kΩ.
Preliminary Technical Data
The resistor value is calculated as follows;
R = 60
Isc
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 AD5744/64 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 con-
trol 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.
TEMPERATURE SENSOR
The on-chip temperature sensor provides a voltage output that
is linearly proportional to the Centigrade temperature scale.
The typical accuracy of the temperature sensor is ±1°C at +25°C
and ±5°C over the −40°C to +105°C range. Its nominal output
voltage is 1.5V at +25°C, varying at 5 mV/°C, giving a typical
output range of 1.175V to 1.9 V over the full temperature range.
Its low output impedance, low self heating, and linear output
simplify interfacing to temperature control circuitry and A/D
converters.
LOCAL GROUND OFFSET ADJUST
The AD5744/64 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 +5mV with respect to the
REFGND pin and VOUTA is measured with respect to
AGNDA then a +5mV error will result, enabling the Local
Ground Offset Adjust feature will offset VOUTA by +5mV
eliminating the error.
Rev. PrA 15-Nov-04| Page 22 of 27
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