Data Sheet AD536A
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, C
AV
, 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.
00504-006
14
13
12
11
10
9
8
1
2
3
4
5
6
7
25kΩ
AD536A
C
AV
V
IN
–V
S
V
OUT
+V
S
ABSOLUTE
VALUE
SQUARER/
DIVIDER
CURRENT
MIRROR
V
IN
NC
–V
S
C
AV
+V
S
NC
NC
NC
dB
COM
BUF OUT
R
L
BUF IN
I
OUT
BUF
Figure 13. 14-Lead Standard RMS Connection
AD536A
25kΩ
V
OUT
I
OUT
+V
S
C
AV
V
IN
–V
S
ABSOLUTE
VALUE
SQUARER/
DIVIDER
CURRENT
MIRROR
00504-020
C
AV
+V
S
dB
COM
BUF IN
BUF OUT
R
L
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
+V
S
C
AV
V
IN
–V
S
V
OUT
25kΩ
ABSOLUTE
VALUE
SQUARER/
DIVIDER
CURRENT
MIRROR
00504-021
NC
–V
S
C
AV
NC
NC
NC
COM
BUF OUT
R
L
BUF IN
I
OUT
NC
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 (I
OUT
, 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, V
IN
, 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 V
IN
.
2. Connect the desired full-scale input level to V
IN
, 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.
Rev. F | Page 11 of 15
