AD7750 Datasheet, PDF (1/16 Pages) Analog Devices – Product-to-Frequency Converter

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FEATURES
Two Differential Analog Input Channels
Product of Two Channels
Voltage-to-Frequency Conversion on a Single Channel
Real Power Measurement Capability
< 0.2% Error Over the Range 400% Ibasic to 2% Ibasic
Two or Four Quadrant Operation (Positive and
Negative Power)
Gain Select of 1 or 16 on the Current Channel (Channel 1)
Choice of On-Chip or External Reference
Choice of Output Pulse Frequencies Available
(Pins F1 and F2)
High Frequency Pulse Output for Calibration Purposes
(F_OUT)
HPF on Current Channel for Offset Removal
Single 5 V Supply and Low Power
Product-to-Frequency
Converter
AD7750
FUNCTIONAL BLOCK DIAGRAM
G1
VDD ACDC
ADC1
REVP
V₁₊
2ND ORDER
V_1–
x16
MODULATOR
DELAY
CLKOUT
HPF
CLKIN
ADC2
V₂₊
2ND ORDER
V_2–
x2
MODULATOR
MULT
2.5V
BAND GAP
REFERENCE
LPF
AD7750
DTF
DTF
F1
F2
F_OUT
AGND REFOUT
REFIN
FS S1 S2 DGND
GENERAL DESCRIPTION
The AD7750 is a Product-to-Frequency Converter (PFC)
that can be configured for power measurement or voltage-to-
frequency conversion. The part contains the equivalent of two
channels of A/D conversion, a multiplier, a digital-to-frequency
converter, a reference and other conditioning circuitry. Channel 1
has a differential gain amplifier with selectable gains of 1 or 16.
Channel 2 has a differential gain amplifier with a gain of 2. A high-
pass filter can be switched into the signal path of Channel 1 to
remove any offsets.
The outputs F1 and F2 are fixed width (275 ms) logic low going
pulse streams for output frequencies less than 1.8 Hz. A range
of output frequencies is available and the frequency of F1 and
F2 is proportional to the product of V₁ and V₂. These outputs
are suitable for directly driving an electromechanical pulse
counter or full stepping two phase stepper motors. The outputs
can be configured to represent the result of four-quadrant multi-
plication (i.e., Sign and Magnitude) or to represent the result of
a two quadrant multiplication (i.e., Magnitude Only). In this
configuration the outputs are always positive regardless of the
input polarities. In addition, there is a reverse polarity indicator
output that becomes active when negative power is detected in
the Magnitude Only Mode, see Reverse Polarity Indicator.
The error as a percent (%) of reading is less than 0.3% over a
dynamic range of 1000:1.
The AD7750 is fabricated on 0.6 µ CMOS technology; a pro-
cess that combines low power and low cost.
PRODUCT HIGHLIGHTS
1. The part can be configured for power measurement or
voltage-to-frequency conversion.
2. The output format and maximum frequency is selectable;
from low-frequency outputs, suitable for driving stepper
motors, to higher frequency outputs, suitable for calibration
and test.
3. There is a reverse polarity indicator output that becomes
active when negative power is detected in the Magnitude
Only Mode.
4. Error as a % of reading over a dynamic range of 1000:1 is
< 0.3%.
REV. 0
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© Analog Devices, Inc., 1997