LTC1923 LINER [Linear Technology], LTC1923 Datasheet - Page 19

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

APPLICATIO S I FOR ATIO
This voltage error translates back into a temperature
setpoint error.
Example:
For this thermistor with a 25 C temperature setpoint, the
change in thermistor voltage with temperature is given by
– 25mV/ C. In order to maintain a 0.01 C temperature
accuracy, this translates into a 250 V error signal, V
minimum loop gain can now be calculated from the above
equation:
A 25 C setpoint temperature requires V
V
There are two handles to adjust the loop gain, K
while the other handles are fixed and depend upon the TEC
and thermistor characteristics (K
R1 (K
power gain product is given by:
REF
R
NTC with 4.4%/ C at 25 C
R1 = 10k
V
T = 25 C
V
REF
E
THRM
= 2.5V. The required loop gain is 5000 or 74dB.
THRM
= V
= 2.5V
IN
= 10k
) and V
/(1 + T)
K
V
THRM
REF
R1
10k
DD
10k
NTC
U
(K
V
MOD
IN
V
+
–
U
E
and K
+
–
LTC2053
TEC
PWR
K
IA
W
and K
R
). The modulator and
A
Figure 11. Simplified Loop Block Diagram
THRM
IN
LTC1923
–
+
ERROR
= 1.25V for
AMP
IA
), V
U
K
EA
and K
SET
R
C
E
F
F
. The
and
C
EA
T
,
–
+
where V
The TEC gain depends upon the TEC selected and corre-
sponds to the relationship between the voltage across the
device and what temperature differential is created. This
gain term changes with operating temperature, and whether
the TEC is heating or cooling. TECs are inherently more
efficient at heating (and therefore have a higher gain) as
compared to cooling. A worst-case rough estimation of
the gain can be obtained by taking the maximum TEC
voltage required to force a given change in temperature
from the TEC specifications:
The thermistor gain should be linearized around tempera-
ture setpoint.
Example:
K
MOD
K
K
Setpoint T = 25 C
V
R
R1 = 10k
V
dT/V
MOD
TEC
DD
REF
THRM
= 5V
TEC(MAX)
CT
= dT/V
= 2.5V
• K
= 10k NTC with 4.4%/ C at 25 C
= the C
POWER
PWR
STAGE
K
PWR
TEC(MAX)
= 45 C/1.5V = 30 C/V
= 2 • V
T
voltage which has a fixed 1V amplitude.
DD
V
/V
TECOOLER
CT
+
= 2 • V
K
TEC
TEC
DD
LTC1923
1923 F11
19
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