LTC1599BIN View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC1599BIN' PDF : 20 Pages View PDF
LTC1599
APPLICATIONS INFORMATION
or 10V full-scale systems. However, as the circuit band-
widths increase, filtering the output of the reference may
be required to minimize output noise.
Table 5. Partial List of LTC Precision References Recommended
for Use with the LTC1599, with Relevant Specifications
INITIAL
TEMPERATURE
REFERENCE TOLERANCE
DRIFT
0.1Hz to 10Hz
NOISE
LT1019A-5,
LT1019A-10
±0.05%
5ppm
12µVP-P
LT1236A-5,
LT1236A-10
LT1460A-5,
LT1460A-10
±0.05%
±0.075%
5ppm
10ppm
3µVP-P
20µVP-P
Grounding
As with any high resolution converter, clean grounding is
important. A low impedance analog ground plane and star
grounding should be used. IOUT2F and IOUT2S must be tied
to the star ground with as low a resistance as possible.
When it is not possible to locate star ground close to
IOUT2F and IOUT2S, separate traces should be used to route
these pins to star ground. This minimizes the voltage drop
from these pins to ground caused by the code dependent
current flowing to ground. When the resistance of these
circuit board traces becomes greater than 1Ω, the circuit
in Figure 4 eliminates voltage drop errors caused by high
resistance traces. This preserves the excellent accuracy
(1LSB INL and DNL) of the LTC1599.
A 16-Bit, 4mA to 20mA Current Loop Controller
for Industrial Applications
Modern process control systems must often deal with
legacy 4mA to 20mA analog current loops as a means of
interfacing with actuators and valves located at a distance.
The circuit in Figure 5 provides an output to a current loop
controlled by an LTC1599, a 16-bit current output DAC. A
dual rail-to-rail op amp (U1, LT1366) controls a P-channel
power FET (Q2) to produce a current mirror with a precise
8:1 ratio as defined by a resistor array. The input current
to this mirror circuit is produced by a grounded base
cascode stage using a high gain transistor (Q1). The use
of a bipolar transistor in this location results in an error
term associated with U1B and Q1’s base current (– 0.2%
for the device shown). For control applications however,
absolute accuracy of the output to an actuator is usually
not required. If a higher degree of absolute accuracy is
required, Q1 can be replaced with an N-channel JFET;
however, this requires a single amplifier at U1B with the
ability to drive the gate below ground. An enhancement
mode N-channel FET can be used in place of Q1 but
MOSFET leakage current must be considered and gate
overdrive must be avoided.
2
15V
6 10V
4 LT1236A-10
5V
0.1µF
4
3
21
R1
RCOM R2 REF
8
DATA
INPUTS
14 TO 18,
21 TO 23
R1
R2
LTC1599
13
MLBYTE
MLBYTE
WR LD CLR CLVL
WR
LD
CLR
CLVL
12 11 24 10
20 5
6
VCC ROFS
RFB
33pF
ROFS RFB
IOUT1 7
2–
16-BIT DAC
6
LT1001
IOUT2F 8 3 +
DGND
19
IOUT2S
9
3
6
LT1001
2
VOUT
0V TO –10V
1599 F04
Figure 4. Driving IOUT2F and IOUT2S with a Force/Sense Amplifier
sn1599 1599fs
13
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