Datasheet

22Maxim Integrated
MAX5318
18-Bit, High-Accuracy Voltage Output DAC with
Digital Gain, Offset Control, and SPI Interface
Detailed Description
The MAX5318 is a high-accuracy, 18-bit, serial SPI input,
buffered voltage output digital-to-analog converter (DAC) in
a 4.4mm x 7.8mm, 24-lead TSSOP package. The device fea-
tures Q2 LSB INL (max) accuracy and a Q1 LSB DNL (max)
accuracy over the full temperature range of -40NC to +105NC.
The DAC voltage output is buffered resulting in a fast settling
time of 3Fs and a low offset and gain drift of Q0.5ppm/NC of
FSR (typ). The force-sense output (OUT) maintains accuracy
while driving loads with long lead lengths. Additionally, a
separate AVSS supply allows the output amplifier to go to 0V
(GND) while maintaining full linearity performance.
The MAX5318 includes user-programmable digital gain and
offset correction capability to enable easy system calibration.
At power-up, the device resets its outputs to zero or mid-
scale, providing additional safety for applications, which
drive valves or other transducers that need to be off on
power-up. This is selected by the state of the M/Z input on
power-up.
The wide 2.7V to 5.5V supply voltage range and integrated
low-drift, low-noise reference buffer amplifier makes for ease
of use. Since the reference buffer input has a high input
resistance, an external buffer is not required. The device
accepts an external reference between 2.4V and V
AVDD
-
0.1V for maximum flexibility and rail-to-rail operation.
The MAX5318 features a 50MHz, 3-wire SPI, QSPI,
MICROWIRE, and DSP-compatible serial interface. The sep-
arate digital interface supply voltage input (V
DDIO
) is com-
patible with a wide range of digital logic levels from 1.8V to
5.5V, eliminating the need for separate voltage translators.
DAC Reference Buffer
The external reference input has a high input (REF) imped-
ance of 10MI||10pF and accepts an input voltage from
+2.4V to V
AVDD
- 0.1V. Connect an external reference
supply between REF and AGND. Bypass the reference
buffer output REFO to AGND with a 100pF capacitor.
Connect the anode of an external Schottky diode to REF
and the cathode to AVDD1 to prevent internal ESD diode
conduction in the event that the reference voltage comes
up before AVDD at power up. Follow the recommenda-
tions described in the Power-Supply Sequencing section.
Visit www.maximintegrated.com/products/references
for a list of available external voltage-reference devices.
Output Amplifier (OUT)
The MAX5318 includes an internal buffer for the DAC
output. The internal buffer provides improved load
regulation for the DAC output. The output buffer slews at
5V/Fs and drives up to 2kI in parallel with 200pF. The
buffer has a rail-to-rail output capable of swinging to
within 100mV of AVDD_ and AVSS.
The positive analog supply voltage (AVDD_) determines
the maximum output voltage of the device as AVDD_
powers the output buffer.
The output is diode clamped to ground, preventing nega-
tive voltage excursions beyond approximately -0.6V.
Negative Supply Voltage (AVSS)
The negative supply voltage (AVSS) determines the mini-
mum output voltage. If AVSS is connected to ground, the
output voltage can be set to as low as 100mV without
degrading linearity. For operation down to 0V, connect
AVSS to a negative supply voltage between -0.1V and
-1.5V. The MAX1735 is recommended for generating
-1.25V from a -5V supply.
Force/Sense
The MAX5318 uses force/sense techniques to ensure
that the load is regulated to the desired output volt-
age despite line drops due to long lead lengths. Since
AGND_F and AGND_S have code dependent ground
currents, a ground impedance less than 13mω ensures
that the INL will not degrade by more than 0.1 LSB. Form
a star ground connection (Figure 2a) near the device
with AGND_F, AGND_S, and AGND tied together. Always
refer remote DAC loads to this system ground for best
performance. Figure 2b shows how to configure the
device and an external op amp for proper force/sense
operation. The amplifier provides as much drive as
needed to force the sensed voltage (measured between
RFB and AGND_S) to equal the desired voltage.