Data Sheet

AD7609

Rev. A | Page 25 of 36

CONVERSION CONTROL

Simultaneous Sampling on All Analog Input Channels

The AD7609 allows simultaneous sampling of all analog input

channels. All channels are sampled simultaneously when both

CONVST x pins (CONVST A, CONVST B) are tied together. A

single CONVST x signal is used to control both CONVST x inputs.

The rising edge of this common CONVST x signal initiates

simultaneous sampling on all analog input channels.

The AD7609 contains an on-chip oscillator that is used to

perform the conversions. The conversion time for all ADC

conversions are in progress, so that when the rising edge of

CONVST x is applied, BUSY goes logic high and transitions low

at the end of the entire conversion process. The falling edge of

the BUSY signal is used to place all eight track-and-hold

amplifiers back into track mode. The falling edge of BUSY also

indicates that the new data can now be read from the parallel

Simultaneously Sampling Two Sets of Channels

The AD7609 also allows the analog input channels to be

sampled simultaneously in two sets. This can be used in power

line protection and measurement systems to compensate for

phase differences between PT and CT transformers. In a 50 Hz

system, this allows for up to 9° of phase compensation, and in a

60 Hz system, it allows for up to 10° of phase compensation.

This is accomplished by pulsing the two CONVST x pins inde-

pendently and is only possible if oversampling is not in use.

CONVST A is used to initiate simultaneous sampling of the first

set of channels (V1 to V4). CONVST B is used to initiate

simultaneous sampling on the second set of analog input

channels (V5 to V8), as illustrated in Figure 42. On the rising

edge of CONVST A, the track-and-hold amplifiers for the first

set of channels are placed into hold mode. On the rising edge

of CONVST B, the track-and-hold amplifiers for the second set

of channels are placed into hold mode. The conversion process

begins after both rising edges of CONVST x have occurred;

therefore, BUSY goes high on the rising edge of the later

CONVST x signal. The falling edge of BUSY also indicates that

the new data can now be read from the parallel bus or the serial

read process when using two separate CONVST x signals.

Connect all unused analog input channel to AGND. The results

for any unused channels are still included in the data read

because all channels are always converted.

CONVST A

CONVST B

BUSY

CS, RD

DATA: DB[15:0]

FRSTDATA

V1 TO V4 TRACK-AND-HOLD

ENTER HOLD

V5 TO V8 TRACK-AND-HOLD

ENTER HOLD

AD7609 CONVERTS

ON ALL 8 CHANNELS

V1

V8

V2

Figure 42. Simultaneous Sampling on Channel Sets Using Independent CONVST A/CONVST B Signals—Parallel Mode