Data Sheet

AD536A

Rev. G | Page 11 of 15

APPLICATIONS INFORMATION

TYPICAL CONNECTIONS

The AD536A is simple to connect to for the majority of high

accuracy rms measurements, requiring only an external capaci-

tor to set the averaging time constant. The standard connection

is shown in Figure 13 through Figure 15. In this configuration,

the AD536A measures the rms of the ac and dc levels present at

the input, but shows an error for low frequency input as a function

of the filter capacitor, CAV, as shown in Figure 19. Thus, if a 4 μF

capacitor is used, the additional average error at 10 Hz is 0.1%;

at 3 Hz, the additional average error is 1%.

The accuracy at higher frequencies is according to specification.

To reject the dc input, add a capacitor in series with the input,

as shown in Figure 17. Note that the capacitor must be nonpolar.

If the AD536A supply rails contain a considerable amount of

high frequency ripple, it is advisable to bypass both supply pins

to ground with 0.1 μF ceramic capacitors, located as close to the

device as possible.

14

13

12

11

10

9

8

1

2

3

4

5

6

7

25kΩ

AD536A

CAV

VIN

–VS

VOUT

+VS

ABSOLUTE

VALUE

SQUARER/

DIVIDER

CURRENT

MIRROR

VIN

NC

–VS

CAV

+VS

NC

NC

NC

dB

COM

BUF OUT

RL

BUF IN

IOUT

BUF

Figure 13. 14-Lead Standard RMS Connection

AD536A

25kΩ

VOUT

IOUT

+VS

CAV

VIN

–VS

ABSOLUTE

VALUE

SQUARER/

DIVIDER

CURRENT

MIRROR

CAV

+VS

dB

COM

BUF IN

BUF OUT

RL

BUF

Figure 14. 10-Pin Standard RMS Connection

4

5

6

7

8

3

2

1

20

19

18

17

16

15

14

9

10

11

12

13

AD536A

dB

+VS

CAV

VIN

–VS

VOUT

25kΩ

ABSOLUTE

VALUE

SQUARER/

DIVIDER

CURRENT

MIRROR

NC

–VS

CAV

NC

NC

NC

COM

NC

NC

NC

NC

NC

BUF

Figure 15. 20-Terminal Standard RMS Connection

The input and output signal ranges are a function of the supply

voltages; these ranges are shown in Figure 11 and Figure 12.

The AD536A can also be used in an unbuffered voltage output

mode by disconnecting the input to the buffer. The output then

appears unbuffered across the 25 kΩ resistor. The buffer ampli-

fier can then be used for other purposes. Further, the AD536A

can be used in a current output mode by disconnecting the

25 kΩ resistor from ground. The output current is available at

Pin 8 (IOUT, Pin 10 on the H-10 package) with a nominal scale of

40 μA per V rms input positive output.

OPTIONAL EXTERNAL TRIMS FOR HIGH

ACCURACY

The accuracy and offset voltage of the AD536A is adjustable

with external trims, as shown in Figure 16. R4 trims the offset.

Note that the offset trim circuit adds 365 Ω in series with the

internal 25 kΩ resistor. This causes a 1.5% increase in scale factor,

which is compensated for by R1. The scale factor adjustment

range is ±1.5%.

The trimming procedure is as follows:

1.

Ground the input signal, VIN, and adjust R4 to provide 0 V

output from Pin 6. Alternatively, adjust R4 to provide the

correct output with the lowest expected value of VIN.

2.

Connect the desired full-scale input level to VIN, either dc

or a calibrated ac signal (1 kHz is the optimum frequency).

3.

Trim R1 to provide the correct output at Pin 6. For example,

1.000 V dc input provides 1.000 V dc output. A ±1.000 V

peak-to-peak sine wave should provide a 0.707 V dc output.

Any residual errors are caused by device nonlinearity.

The major advantage of external trimming is to optimize device

performance for a reduced signal range; the AD536A is

internally trimmed for a 7 V rms full-scale range.