AD5379ABC datasheet(35/40 Pages) AD

35 / 40 page

AD5382

Rev. 0 | Page 35 of 40

14-BIT DAC

DAC

INPUT

DATA

INPUT

DATA

A/B

VOUT

LDAC

CONTROL INPUT

Figure 42. Toggle Mode Function

ACTUATORS

FOR MEMS

MIRROR

ARRAY

SENSOR

AND

MULTIPLEXER

8-CHANNEL ADC

(AD7856)

SINGLE CHANNEL

ADC (AD7671)

AD5382

14-BIT DAC

REFOUT REFIN AVDD

VO1

VO31

G = 50

OUTPUT RANGE

0–200V

ADSP-21065L

0.01

µF

+5V

Figure 43. AD5382 in a MEMS Based Optical Switch

THERMAL MONITOR FUNCTION

The AD5382 contains a temperature shutdown function to

protect the chip in case multiple outputs are shorted. The short

circuit current of each output amplifier is typically 40 mA.

Operating the AD5382 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

LQFP, the θJA is typically 44°C/W.

The thermal monitor is enabled by the user via CR8 in the

control register. The output amplifiers on the AD5382 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 has dropped below 130°C or by turning off the

thermal monitor function via the control register.

AD5382 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 32-channel, 14-bit

AD5382 DAC satisfies these requirements. In the circuit in

Figure 43, the 0 V to 5 V outputs of the AD5382 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 multiplexer, and

reads data from the ADC via the serial interface.

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