
PRELIMINARY TECHNICAL DATA
AD7755
7
PRELIM B2 10/98
PIN CONFIGURATION
DIP & SSOP PACKAGES
Pin No.
MNEMONIC
DESCRIPTION
15,16
G1, G0
These logic inputs are used to select one of four possible gains for the analog inputs V1A and
V1B. The possible gains are 1, 2, 8 and 16. See Analog Input section.
17
CLKIN
An external clock can be provided at this logic input. Alternatively a crystal can be connected
across CLKIN and CLKOUT to provide a clock source for the AD7755. The clock frequency
for specified operation is 3.58MHz. Crystal load capacitors of 33pF ceramic should be used the
with gate oscillator circuit.
18
CLKOUT
A crystal can be connected across this pin and CLKIN as described above to provide a clock
source for the AD7755. The CLKOUT pin can drive one CMOS load when an external clock
is supplied at CLKIN.
20
REVP
This logic output will go logic high when negative power is detected, i.e. when the voltage and
current signals at 180° out of phase. This output is not latched and will be reset when positive
power is once again detected. The output will go high or low at the same time as a pulse output
on F1 and F2.
21
DGND
This provides the ground reference for the digital circuitry in the AD7755, i.e. multiplier, filters
and digital to frequency converter. This pin should be tied to the digital ground plane of the
PCB. The digital ground plane is the ground reference for all digital circuitry, e.g. counters
(mechanical and digital), MCUs and indicator LEDs. For good noise suppression the analog
ground plane should only connected to the digital ground plane at the DGND pin.
22
CF
Calibration Frequency logic output. The CF logic output gives instantaneous real power
information. This output is intended to be used for calibration purposes. Also see SCF pin
description.
23, 24
F2, F1
Low frequency logic outputs. F1 and F2 supply average real power information. The logic
outputs can be used to directly drive electromechanical counters and two phase stepper motors.
See AD7755 Transfer Function.
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
F1
F2
CF
DGND
REVP
CLKOUT
CLKIN
SCF
S0
S1
RESET
AD7755
TOP VIEW
(Not to Scale)
AGND
G0
DVDD
AVDD
AC/DC
V1P
V1N
V2N
V2P
G1
REF
IN/OUT
11
12
24
23
22
21
NC*
NC*
*NC = No Connection