LTC1923 LINER [Linear Technology], LTC1923 Datasheet - Page 21

• Manufacturer Part Number: LTC1923
• Description: High Efficiency Thermoelectric Cooler Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
with C
response. Adjust the values based on observing whether
the transient response was improved or not with the goal
of reducing C
thermal poles can vary between “identical” laser modules
(i.e., same manufacturer and model), care must be taken
to ensure that the values selected provide the desired
response even with these thermal term variations. Com-
pensation should also be tailored for each unique laser
module as thermal terms can vary significantly between
different brands. C
mizing noise in the outputs. It is typically about 25 times
smaller than C
Temperature Stability
It is important to differentiate between temperature accu-
racy and stability. Since each laser’s output maximizes at
some temperature, temperature setpoint is typically
incremented until this peak is achieved. After this, only
temperature stability is required. The predominant param-
eters which affect temperature stability are the thermistor,
the thermistor biasing resistor and any offset drift of the
front-end electrical circuitry. Sufficient loop gain ensures
that any downstream variations do not contribute signifi-
A
on the order of C
B
B
. C
to improve settling time. As the system
A
C
, C
U
rolls off high frequency gain , mini-
B
and C
U
B
and note its affect on system
C
NTC
should be film capacitors.
10k
W
Figure 13. Simplifed Temperature Control Loop Omitting
the LTC2053 Instrumentation Amplifier Front End
10k
CMD
TMP
U
LTC1658
REF
V
OUT
100k
10M
cantly to temperature stability. The relatively mild operat-
ing conditions inside the laser module promote good long-
term thermistor stability. A high quality, low temperature
coefficient resistor should be selected to bias the ther-
mistor. If the 10k resistor has a 100ppm/ C temperature
coefficient, this translates into a 0.18 C setpoint tempera-
ture differential over a 0 C to 70 C ambient for a desired
25 C laser setpoint. Depending upon the temperature
stability requirements of the system, this is very signifi-
cant. A lower temperature coefficient resistor may there-
fore be desired. The LTC2053 has maximum offset drift to
50nV/ C which translates into less than 0.001 C change
for a 0 C to 70 C ambient.
The offset drift of the LTC1923 error amplifier divided by
the gain of the LTC2053 also affects temperature stability.
The offset drift of the LTC1923 (see characteristic curves)
is typically 1mV over a 0 C to 70 C ambient. After attenu-
ation by the LTC2053 gain, this translates into a tempera-
ture setpoint variation of 0.004 C. Neither of these offsets
drifts significantly with aging. Depending upon the setpoint
temperature stability requirements of the system, the
LTC2053 instrumentation amplifier may not be necessary.
Figure 13 shows a simplified schematic with the LTC2053
omitted.
CNTRL
EAOUT
4.7 F
FB
4
6
5
+
–
LTC1923
AMPLIFIER
ERROR
1923 F13
LTC1923
21
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