MAX1365 Datasheet, PDF (15/25 Pages) Maxim Integrated Products – Stand-Alone, 4.5-/3.5-Digit Panel Meters with 4-20mA Output

Stand-Alone, 4.5-/3.5-Digit Panel Meters
with 4–20mA Output
Table 5. Current Output Table
ANALOG INPUT
Negative Full Scale
0V
Positive Full Scale
UNIPOLAR MODE
(EN_I = LOW)
0
0
16
CURRENT OUTPUT (mA)
UNIPOLAR MODE
(EN_I = HIGH)
BIPOLAR MODE
(EN_I = LOW)
4
0
4
8
20
16
BIPOLAR MODE
(EN_I = HIGH)
4
12
20
ANALOG SUPPLY
10µF
0.1µF
R_REF
ACTIVE
GAUGE
0.1µF
R
DUMMY
GAUGE
0.1µF
0.1µF
R
FERRITE _0.1µF
10µF
BEAD
0.1µF
AV_DD
REF+
DV_DD
NEGV
REF- MAX1365
MAX1367
4–20mA/0 TO 16mA
AIN+
4-20OUT
CURRENT-LOOP
OUTPUT
AIN-
GND
Figure 6. Strain-Gauge Application with the MAX1365/MAX1367
Bipolar Mode
Set EN_BPM high to engage bipolar operation. In bipo-
lar mode, the current output at 4–20OUT (4–20mA or
0 to 16mA) maps the analog input voltage (±2V or
±200mV). In bipolar mode, a 0V analog input maps to
midscale (12mA). See Table 5 for current output (see
Figures 12 and 13).
5.2V Linear Regulator with Compensation
The MAX1365/MAX1367 feature a 5.2V linear regulator.
The 5.2V regulator consists of an op amp and connec-
tions to an external depletion-mode FET. The 5.2V regu-
lator regulates the loop voltage that powers the
voltage-to-current converter and the rest of the trans-
mitter circuitry. The regulator output voltage is available
at REG_VDD and is given by the equation:
V_{REG_VDD} = 2.54 x V_REF+
The FET breakdown and saturation voltages determine
the usable range of loop voltages (V_EXT). The external
FET parameters such as V_GS (off), I_DSS, and transcon-
ductance must be chosen so that the op amp output on
the REG_FORCE pin can control the FET operating
point while swinging in the range from VREG_AMP to
REG_VDD. See the Selecting Depletion-Mode FET sec-
tion in the Applications Information section.
Connect a 0.1µF capacitor between CMP and
REG_FORCE to ensure stable operation of the regulator.
Applications Information
Power-On Reset
At power-on, the digital filter and modulator circuits
reset. The MAX1365 allows 6s for the reference to sta-
bilize before performing enhanced offset calibration.
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