AD5384 Analog Devices, AD5384 Datasheet - Page 33

• Manufacturer Part Number: AD5384
• Description: 40-Channel, 3 V/5 V Single Supply,14-Bit, Serial Voltage-Output DAC
• Manufacturer: Analog Devices

Specifications of AD5384

• Resolution (bits): 14bit
• Dac Update Rate: 125kSPS
• Dac Settling Time: 8µs
• Max Pos Supply (v): +5.5V
• Single-supply: Yes
• Dac Type: Voltage Out
• Dac Input Format: I2C/Ser 2-wire,Ser,SPI

Each of the 40 DAC channels on the AD5384 contains an A and
B data register. Note that the B registers can be loaded only
when toggle mode is enabled. The sequence of events when
configuring the AD5384 for toggle mode is
1.
2.
3.
4.
The LDAC is used to switch between the A and B registers in
determining the analog output. The first LDAC configures the
output to reflect the data in the A registers. This mode offers
significant advantages if the user wants to generate a square
wave at the output of all 40 channels, as might be required to
drive a liquid crystal-based variable optical attenuator. In this
case, the user writes to the control register and enables the
toggle function by setting CR6 to CR2 = 1, thus enabling the
five groups of eight for toggle mode operation. The user must
then load data to all 40 A and B registers. Toggling LDAC sets
the output values to reflect the data in the A and B registers.
The frequency of the LDAC determines the frequency of the
square wave output.
Toggle mode is disabled via the control register. The first LDAC
following the disabling of the toggle mode updates the outputs
with the data contained in the A registers.
Enable toggle mode for the required channels via the
control register.
Load data to A registers.
Load data to B registers.
Apply LDAC .
0.01µF
REFOUT REFINA AVDD
14-BIT DAC
14-BIT DAC
AD5384
5V
VOUT1
VOUT40
Figure 38. AD5384 in a MEMS-Based Optical Switch
OUTPUT RANGE
0V–200V
G = 50
G = 50
Rev. A | Page 33 of 36
ACTUATORS
FOR MEMS
MIRROR
ARRAY
ADSP-21065L
THERMAL MONITOR FUNCTION
The AD5384 contains a temperature shutdown function to
protect the chip if multiple outputs are shorted. The short-
circuit current of each output amplifier is typically 40 mA.
Operating the AD5384 at 5 V leads to a power dissipation of
200 mW per shorted amplifier. With five channels shorted, this
leads to an extra watt of power dissipation. For the 100-lead
CSPBGA, the θ
The thermal monitor is enabled by the user via CR8 in the
control register. The output amplifiers on the AD5384 are
automatically powered down if the die temperature exceeds
approximately 130°C. After a thermal shutdown has occurred,
the user can re-enable the part by executing a soft power-up if
the temperature drops below 130°C, or by turning off the
thermal monitor function via the control register.
AD5384 IN A MEMS-BASED OPTICAL SWITCH
In their feed-forward control paths, MEMS based optical
switches require high resolution DACs that offer high channel
density with 14-bit monotonic behavior. The 40-channel, 14-bit
AD5384 DAC satisfies these requirements. In the circuit in
Figure 38, the 0 V to 5 V outputs of the AD5384 are amplified
to achieve an output range of 0 V to 200 V, which is used to
control actuators that determine the position of MEMS mirrors
in an optical switch. The exact position of each mirror is
measured using sensors. The sensor outputs are multiplexed
into a high resolution ADC in determining the mirror position.
The control loop is closed and driven by an ADSP-21065L, a
32-bit SHARC® DSP with an SPI-compatible SPORT interface.
The ADSP-21065L writes data to the DAC, controls the multi-
plexer, and reads data from the ADC via the serial interface.
MULTIPLEXER
SENSOR
AND
JA
is typically 44°C/W.
SINGLE-CHANNEL
8-CHANNEL ADC
ADC (AD7671)
(AD7856)
OR
AD5384