LTC1923EGN Linear Technology, LTC1923EGN Datasheet - Page 14

• Manufacturer Part Number: LTC1923EGN
• Description: IC CONTROLLER TEC HI EFF 28SSOP
• Manufacturer: Linear Technology

Specifications of LTC1923EGN

• Applications: Thermoelectric Cooler/Heater
• Current - Supply: 2mA
• Voltage - Supply: 2.7 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

OPERATIO
LTC1923
pulled to V
bridge to operate as described earlier. When a fault occurs
and FAULT is asserted low, M1 is shut off, forcing the gate
of M2 high, shutting that device off. The power path is thus
opened, ensuring no current is delivered to the TEC. M2
wants to have low R
minimize the power losses associated with it). R
R
The lower comparator threshold level is 20% (twenty
percent) of V
is 350mV below V
the V
thermistor divider so that any variations will track out.
The V
down voltage can be supplied to this pin to modify the
acceptable thermistor impedance range. This is shown in
Figure 6. The voltage applied to the V
minimum of 2V. The lower thermistor impedance thresh-
old is:
The upper impedance threshold is:
where
Changing R1 also changes the valid thermistor impedance
range.
14
P2
R
R
can be selected on the order of 100k.
TH LOWER
TH UPPER
SET
Figure 6. Modifying the Acceptable Thermistor Range
SET
(
(
pin. V
= 0.35/V
pin has a high input impedance so that a divided-
DD
SET
forcing the gate of M2 low, which allows the
)
)
SET
and the upper comparator threshold level
R R
V
SET
U
R
SET
is typically tied to the bias source for the
REF
0 2
1 3
2 0 8
R
. •
R1
, where V
.
DS(ON)
2
R
10k
NTC
TH
R2
R R
– (
. •
1
•
(
R
(less than the value of R
R
R
2
3
SET
3
2
R3
R
is the voltage applied on
R
3
3
)
V
V
1923 F06
SET
THRM
)
SET
pin must be a
P1
S
and
to
Example: V
The acceptable thermistor impedance range before caus-
ing a fault is 2.5k to 61k . This corresponds to a valid
temperature range of between about –10 C and 60 C.
To ensure the part does not power up with a latched fault
at start-up, a fault will not be latched until soft-start has
completed. This corresponds to the voltage on SS reach-
ing 1.5V. For a 1 F soft-start capacitor, this delay is
approximately 1 second. This provides enough time for all
supplies (V
their final values.
TEC Voltage Clamping
An internal clamp circuit is included to protect the TEC
from an overvoltage condition. When the differential volt-
age across the TEC exceeds 2.5V, the error amplifier
output voltage at the input of the PWM comparator is
limited. This clamps the duty cycle of the output drivers,
and therefore, the voltage across the TEC. The voltage
where clamping occurs can be increased by placing a
resistor divider in parallel with the TEC and by making the
appropriate connections to TEC
Figure 7. The divider increases the voltage across the TEC,
V
TECOOLER
R1 = 10k, R2 = 0 , R3 = open
R
cient of – 4.4%/C at 25 C.
V
TECOOLER
TH
= 10k NTC thermistor with a temperature coeffi-
Figure 7. Increasing Voltage Clamp Threshold
, where the clamp activates, to:
REF
DD
, setpoint reference and V
= V
TEC
TEC
1
SET
+
–
R
R
= 2.5V
TE
TE
R
2
1
+
V
TE2
TECOOLER
TEC
100
R
1923 F07
R
TE
–
TE1
1
+
1
k
and TEC
200
R
• . –
TE
V
2 5
CM
1
k
REF
–
V
) to settle at
as shown in
CM
200
R
TE
1
k
1923f