AD5381BSTZ-5 datasheet(34/40 Pages) AD

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AD5381

Data Sheet

Rev. D | Page 34 of 40

MONITOR FUNCTION

The AD5381 channel monitor function consists of a multiplexer

addressedvia the interface, allowing any channel output to be

routed to this pin for monitoring using an external ADC. In

channel monitor mode, VOUT39 becomes the MON_OUTpin,

to which all monitoredsignals are routed. The channel monitor

function must be enabled in the control register beforeany

channels are routed to MON_OUT. Table17 contains the

decoding information required to route anychannel to

MON_OUT.Selecting Channel Address 63 three-states

MON_OUT.Figure 41 shows a typical monitoring circuit

implemented using a 12-bit SAR ADC in a 6-lead SOT-23

package. The controller output port selects the channel to be

monitored, and the input port readsthe converteddata from

the ADC.

AD7476

GND

SDATA

SCLK

VDD

VIN

VOUT39/MON_OUT

AGND

DIN

SYNC

SCLK

DAC_GND SIGNAL_GND

VOUT0

VOUT38

AVDD

AD5381

OUTPUT PORT

INPUT PORT

CONTROLLER

Figure 41. Typical Channel Monitoring Circuit

TOGGLE MODE FUNCTION

The toggle mode function allows an output signal to be gener-

ated using the LDACcontrolsignalthat switches between two

DAC data registers. This function is configured using the SFR

control register as follows. A write with REG1 = REG0 = 0 and

A5 to A0 = 001100 specifies a control register write. The toggle

mode function is enabled in groups of eight channels using Bit

CR4 to Bit CR0 in the control register. See the AD5381 control

mode implementation. Each of the 40 DAC channels on the

AD5381 contain an A and B data register.

Note that B registers can only be loadedwhen toggle mode is

enabled. The sequence of events whenconfiguring the AD5381

for toggle mode is

1. Enable toggle mode for the required channels via the

control register.

2. Load data to the A registers.

3. Load data to the B registers.

4. Apply LDAC.

LDACis used to switch between the A and B registers in

determining the analog output. Thefirst LDACconfiguresthe

output to reflect data in the A registers. This modeofferssignif-

icant advantages if the user wants to generatea square waveat

the output of all 40 channels, as might be required to drivea

liquid crystal-based variableoptical attenuator.

In this case, the user writes to the control register and enables

the toggle function by setting CR4 to CR2 = 0, thus enabling the

five groups of eight for toggle modeoperation. The user must

then load data to all 40 A and B registers. Toggling LDACsets

the output values to reflect the data in the A and B registers.

The frequency of the LDACdetermines the frequency of the

square waveoutput.

Toggle mode is disabled via the control register. The first LDAC

following the disabling of the toggle mode will update the out-

puts with the data contained in the A registers.

THERMAL MONITOR FUNCTION

The AD5381 contains a temperature shutdown function to

protect the chip if multiple outputs areshorted. The short-

circuit current of each output amplifier is typically 40 mA.

Operating the AD5381 at 5 V leads to a power dissipation of

200 mW per shorted amplifier. Withfive channels shorted, this

leads to an extra watt of powerdissipation. Forthe 100-lead

LQFP, the θ

JA is typically 44°C/W.

The thermal monitoris enabledby the user via CR6 in the

control register. The outputamplifiers on the AD5381 are

automatically powered down if the die temperatureexceeds

approximately 130°C. After a thermal shutdown hasoccurred,

the user can re-enable the part by executing a soft power-upif

the temperature has droppedbelow130°C or by turning off the

thermal monitorfunction via the control register.

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