ES636_09 View Datasheet(PDF) - Cyrustek corporation

Part Name

Description

Manufacturer

ES636_09

True RMS-to-DC Converters

Cyrustek corporation 

ES636

True RMS-to-DC Converters

The dB output is obtained by the voltage at the emitter of Q3, which is proportional to

the -log VIN. The emitter follower Q5 buffers and level shifts this voltage so that the dB

output is zero when the externally set emitter current for Q5 approximates I3.

V+

BUFIN

7

+

A4

-

BUFOUT

6

Absolute value/voltage-current converter

i upper

I1

R4

Vin

20K

R4

+

i lower

Vin

1

+

A1

8K

-

-

A2

+

R3

8K

10K

R1

I3

6K

8 I OUT

RL

4 CAV

9

R2

10K

A3

I4

Q1

Q3

5 dB

OUT

Q2

Q4

One-Quadrant

square/divider

Q5

V-

Figure 1. ES636 Simplified Schematic

Standard Connection (Figure 2)

The standard RMS connection requires only one external component, CAV. In this

configuration the ES636 measures the RMS of the AC and DC levels present at the

input, but shows an error for low-frequency inputs as a function of the CAV filter

capacitor. Figure 3 gives practical values of CAV for various values of averaging error

over frequency for the standard RMS connections (no post filtering). If a 3uF capacitor

is chosen, the additional error at 30Hz will be 1%. If the DC error can be rejected, a

capacitor should be connected in series with the input, as would typically be the case in

single-supply operation.

The input and output signal ranges are a function of the supply voltages. Refer to the

electrical characteristics for guaranteed performance. The buffer amplifier can be used

either for lowering the output impedance of the circuit, or for other applications such as

buffering high-impedance input signals. The ES636 can be used in current output mode

by disconnecting the internal load resistor, RL, from ground. The current output is

available at pin 8 with a nominal scale of 100μA/ VRMS input for the ES636. The

7

09/02/16

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