Datasheet

MPY634
5
SBFS017A
www.ti.com
TYPICAL PERFORMANCE CURVES (CONT)
T
A
= +25°C, V
S
= ±15VDC, unless otherwise noted.
THEORY OF OPERATION
The transfer function for the MPY634 is:
V
OUT
= A – (Z
1
– Z
2
)
where:
A = open-loop gain of the output amplifier (typically
85dB at DC).
SF = Scale Factor. Laser-trimmed to 10V but adjustable
over a 3V to 10V range using external resistors.
X, Y, Z are input voltages. Full-scale input voltage
is equal to the selected SF. (Max input voltage =
±1.25 SF).
An intuitive understanding of transfer function can be gained
by analogy to the op amp. By assuming that the open-loop
gain, A, of the output operational amplifier is infinite,
(X
1
– X
2
) (Y
1
– Y
2
)
SF
inspection of the transfer function reveals that any V
OUT
can
be created with an infinitesimally small quantity within the
brackets. Then, an application circuit can be analyzed by
assigning circuit voltages for all X, Y and Z inputs and
setting the bracketed quantity equal to zero. For example,
the basic multiplier connection in Figure 1, Z
1
= V
OUT
and
Z
2
= 0. The quantity within the brackets then reduces to:
– (V
OUT
– 0) = 0
This approach leads to a simple relationship which can be
solved for V
OUT
to provide the closed-loop transfer function.
The scale factor is accurately factory adjusted to 10V and is
typically accurate to within 0.1% or less. The scale factor
may be adjusted by connecting a resistor or potentiometer
between pin SF and the –V
S
power supply. The value of the
external resistor can be approximated by:
(X
1
– X
2
) (Y
1
– Y
2
)
SF
14
12
10
8
6
4
81012 161820
Positive or Negative Supply (V)
INPUT/OUTPUT SIGNAL RANGE
vs SUPPLY VOLTAGES
Peak Positive or Negative Signal (V)
14
Output, R
L
≥ 2kΩ
All inputs, SF = 10V
–10
INPUT DIFFERENTIAL-MODE/
COMMON-MODE VOLTAGE
–12 12
10
–5
5
–5510–10
Specified
Accuracy
V
S
= ±15V
Functional
Derated Accuracy
V
CM
V
DIFF
800
700
600
500
400
300
200
100
0
–20 0 60 100 140
Temperature (°C)
BIAS CURRENTS vs TEMPERATURE
(X,Y or Z Inputs)
Bias Current (nA)
20–40 40 80 120
Scaling Voltage = 10V
Scaling Voltage = 3V
–60