PRELIMINARY TECHNICAL DATA

REV. PrF 09/2003

AD5380

–31–

APPLICATIONS INFORMATION

AD5380 Monitor Function

The AD5380 contains a channel monitor function consisting of a multiplexer addressed via the interface allowing any

channel output to be routed to this pin for monitoring using an external ADC. In channel monitor mode Vout 39 be-

comes the MON_OUT pin, the pin to which all monitored signals are routed. The channel monitor function must be

enabled in the control register before any channels are routed to the MON_OUT pin. Table X contains the decoding

information required to route any channel to the MON_OUT pin. Selecting channel address 63 tristates the

MON_OUT pin. Figure 19 shows a typical monitoring circuit implemented using a 12-bit SAR ADC in a 6-lead sot

package. The controller output port selects the channel to be monitored and the input port reads the converted data from

the ADC.

AD5380

VOUT 39/MON_OUT

SCLK

SDATA

CS

AD7476

.

.

.

.

.

.

VOUT 0

VOUT 38

AVCC

VIN

AVCC

DAC_GND SIGNAL GND

AGND

DIN

SYNC

SCLK

CONTROLLER

INPUT PORT

OUTPUT PORT

GND

Figure 19. Typical Channel Monitoring Circuit

Toggle Mode Function

The toggle mode function allows an output signal to be generated using the

LDAC control signal that switches between

two DAC data registers.

This function is configured using the SFR control register as follows. A write with

REG1=REG0=0, A5-A0=001100 specifies a control register write. The toggle mode function is enabled in groups of 8-

channels using bits CR6 to CR2 in the control register. See AD5380 control register description. Figure 20 shows a

block diagram of the toggle mode implementation. Each of the 40 DAC channels on the AD5380 contain an A and a B

data register. Note, the “B” registers can only be loaded when Toggle mode is enabled.

The sequence of events when

configuring the AD5380 for toggle mode of operation is as follows:

i) Enable Toggle Mode for the required channels via the Control Register

ii) Load Data to A registers

iii) Load Data to B registers.

iv) Apply

LDAC.

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 opti-

cal attenuators. In this case the user writes to the control register and enables the toggle function by setting CR6 to

CR2=1 enabling the five groups of 8 for toggle mode operation. The user must then load data to all 40 “A” registers

and “B” registers. Toggling the

LDAC will set the output values to reflect the data in the A and B registers and the

frequency of the

LDAC will determine the frequency of the squarewave output.

Toggle mode is disabled via the control register, the first LDAC following the disabling of the toggle mode will update

the outputs with the data contained in the “A” registers.