ES51999
4 3/4 and 5 3/4 A/D AUTO
DC/AC voltage measurement
A re-configurable voltage divider provides a suitable full-scale range voltage
measurement mode. The following table summarizes the full-scale ranges in each
configuration.
Configuration
VR1
Full Scale Range
440.00mV
4.4000V
Divider Ratio
1
Resister Connection
-
VR2
1/10
R2 / (R1+R2)
R3 / (R1+R3)
R4 / (R1+R4)
R5 / (R1+R5)
VR3
44.000V
1/100
1/1000
1/10000
VR3
440.00V
4400.0V
VR5
In configuration VR1, the full range is 440mV, and the voltage inputs from V400m pin to
prevent the influence of noise when floating. In other configurations, the voltage inputs
from VR1 pin.
Pin 19 to 23 are used for AC measurement. Figure 4.1 is the AC-to-DC circuit. AC-
to-DC circuit extracts the AC part of the voltage (ADO - TEST5). ADC then converts the
voltage of (ACVH – ACVL) to acquire the AC value of input voltage. Variable resistor
5KΩ is used to adjust the DC offset. Light shielding for diode D1 and D2 is required to
prevent leakage current. This circuit works properly only when the input voltage is
sinusoidal. If the input is not sinusoidal (e.g., square waves), a true RMS-to-DC
converter chip will be needed to obtain the correct true RMS value of input signal.
If ADO and ADI short directly, ADI is the divided voltage of the input signal.
Therefore, it can be used for oscillator display.
AGND
OVSG
VR4
VR3
VR2
ADO
ADI
ACVH
ACVL
TEST5
V
R
5K
Voltage input
Figure 4.1 AC-to-DC circuit
12
07/07/06
CYRUSTEK [ Cyrustek corporation ]
