1B21AN Analog Devices Inc, 1B21AN Datasheet - Page 5

• Manufacturer Part Number: 1B21AN
• Description: IC CONV V TO I HYBRID 38-DIP
• Manufacturer: Analog Devices Inc
• Type: Voltage and Current Controllerr

Specifications of 1B21AN

• Rohs Status: RoHS non-compliant
• Full Scale: ±50ppm/°C
• Linearity: ±0.02%
• Mounting Type: Through Hole
• Package / Case: 38-DIP (0.500", 12.70mm), 8 Leads
• Ic Function: Voltage To Current Converter IC
• Supply Voltage Range: 14.25V To 15.75V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: DIP
• No. Of Pins: 38
• Lead Free Status / Rohs Status: Not Compliant

INSIDE THE 1B21
Referring to the functional block diagram (see Figure 3), the
±15 V power inputs provide power to both the input side
circuitry and the power oscillator. The 25 kHz power oscillator
provides both the timing information for the signal modulator
and drives transformer T2 for the output side power supplies.
The secondary winding of T2 is full wave rectified and filtered
to create the output side power.
INPUT
The input stage is configured as an inverting amplifier with
three user-supplied resistors for gain, offset, and feedback.
The conditioned signal is modulated to generate a square wave
with a peak-to-peak amplitude proportional to V
drives the signal transformer T1. An internal reference with a
nominal output voltage of +6.225 V and tempco of ±15 ppm/°C
is provided to develop a 4 mA offset for 4 mA to 20 mA current
loop applications.
After passing through signal transformer T1, the amplitude
modulated signal is demodulated and filtered by a single pole
filter. Timing information for the output side is derived from
the power transformer T2. The filtered output provides the
control signal for the voltage-to-current converter stage. An
external power supply is required in series with the load to
complete the current loop.
USING THE 1B21
Input Configurations
The 1B21 has been designed with a flexible input stage for a
variety of input and output ranges. The basic interconnection
for setting gain and offset is shown in Figure 4. The output of
the internal amplifier is constrained to 0 to −5 V, which maps
into 0 to 20 mA across the isolation barrier. Thus to create a
4 mA offset at the output, the input amplifier has to be offset
by 1 V.
For example, for 0 to 20 mA operation, the transfer function for
the input stage is
and no offset resistor is needed. For 4 mA to 20 mA operation
one gets
+15V
–15V
COM
OUT
REF
FB
5/V
4/V
18
17
19
20
22
21
IN
IN
= R
= R
REF
F
F
/R
/R
Figure 3. 1B21 Functional Block Diagram
I
I
TIMING
MODULATOR
OSCILLATOR
ISOLATION
ISOLATION
SIGNAL
POWER
T1
T2
DEMODULATOR
RECTIFIER
TIMING
IN
1B21
. The signal
38
1
OUT
HIGH
OUT
LOW
Rev. C | Page 5 of 8
This maps the input voltage into a 4 V span. To create a 1 V
offset at the output of the internal amplifier (4 mA at the output
of the 1B21) a current derived from the reference can be fed
into the summing node. The offset resistor (for a 1 V output
offset) is given by the equation: R
applications, it is recommended that R
range. Resistor values for typical input and output ranges are
shown in Table 2.
Table 2. Resistor Values for Typical Ranges
Input Volts
0 to 5
0 to 10
0 to 5
0 to 10
1 to 5
Adjustments
Figure 5 is an example of using potentiometers for trimming
gain and offset for a 0 V to 5 V input and 0 V to 20 mA output.
The network for offset adjustment keeps the resistors relatively
small to minimize noise effects while giving a sensitivity of ±1%
of span. For more adjustment range, resistors smaller than 274 k
can be used. Resistor values from Table 2 can be substituted for
other input and output ranges.
In general, any bipolar voltage can be input to the 1B21 as
long as it is offset to meet the 0 V to −5 V constraint of the
modulator and the input signal range is 1 V minimum.
+15V
COM
–15V
V
V
IN
IN
50kΩ
+15V
–15V
4.7µF/20V
1kΩ
R
I
274kΩ
19.6kΩ
+
+
R
R
F
O
18
17
19
20
21
22
Figure 5. Offset and Span Adjustment
20kΩ
1kΩ
Output mA
0-20
0-20
4-20
4-20
4-20
FB
+15V
COM
–15V
INPUT
20kΩ
Figure 4. Basic Interconnections
REF
18
17
19
20
21
22
OSCILLATOR
FB
INPUT
REF
OSCILLATOR
O
= 6.225 R
R
25
50
25
50
25
I
1B21
kΩ
F
be in the 25 kΩ ±20%
RECTIFIER
1B21
F
. For most
R
25
25
20
20
25
F
RECTIFIER
kΩ
38
1
R
V
LOAD
LOOP
1B21
R
Open
Open
124.3
124.3
Open
38
1
O
kΩ