FEATURES
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LTC1923
High Efficiency Thermoelectric
Cooler Controller
DESCRIPTIO
The LTC
®
1923 is a pulse width modulator intended for
thermoelectric cooler (TEC) or heater applications requir-
ing either unidirectional or bidirectional drive circuits. All
of the necessary control circuitry and two sets of comple-
mentary output drivers are integrated into the LTC1923 to
drive a full bridge, providing an efficient means of bidirec-
tional current flow to the TEC. An accurate temperature
control loop to stabilize the temperature of a laser diode
system is easily achieved with the addition of just a few
external components. Typical temperature setpoint accu-
racy of 0.1°C is achievable with the LTC1923. Adding an
instrumentation amplifier front end allows setpoint stabil-
ity of 0.01°C.
The part features independent adjustable heating and
cooling pulse-by-pulse current limit, current soft-start for
controlled start-up, output slew rate control to reduce
system noise, differential current sense and voltage am-
plifiers and a host of auxiliary circuits to protect the laser
and provide redundant system monitoring.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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High Efficiency, Low Noise Topology
Adjustable Output Slew Rate Reduces EMI
Full-Bridge Controller for Bidirectional
Current Control
Adjustable Pulse-by-Pulse Bidirectional TEC
Current Limit
Open/Shorted Thermistor Indication
Solution Footprint in Less Than 0.6"
×
0.8"
(Double-Sided PCB)
Available in 5mm x 5mm QFN and
28-Pin SSOP Packages
TEC Voltage Clamping
TEC Current, Voltage and Heat/Cool Status Outputs
Adjustable/Synchronizable Oscillator Frequency
Reduces Filter Component Size and System Noise
2.5V Reference Voltage Output
2.7V Minimum Operating Voltage
APPLICATIO S
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Laser-Based Fiber Optic Links
Medical Instruments
CPU Temperature Regulators
TYPICAL APPLICATIO
10k
0.1%
Laser Temperature Control Loop Achieving Setpoint Stability of 0.01°C
10k
PLLLPF
82k
REF
10k
NTC
TMP
CMD
LTC1658
V
OUT
R
T
C
T
V
REF
PDRVB
NDRVB
V
DD
LTC1923
1µF
AGND
SS
I
LIM
V
SET
FAULT
V
THRM
C1, C2: TAIYO YUDEN JMK325BJ226MM-T (X7R)
L1, L2: SUMIDA CDRH6D2B-220NC
*MNA, MPA: SILICONIX Si9801
**MNB, MPB: SILICONIX Si9801
H/C
V
TEC
PGND
NDRVA
PDRVA
CS
+
CS
–
I
TEC
TEC
+
TEC
–
4
3
1
R
S
2
1µF
MPA*
L1
10µH
C1
MNB** 22µF
COOLER
TEC
L2
10µH
C2
22µF
MNA*
V
REF
330pF
1µF
+
–
R
SLEW
V
DD
SDSYNC
CNTRL
EAOUT
FB
REF
LTC2053
A = 10
4.7µF
10M
100k
U
U
U
V
DD
10µF
MPB**
1923 TA01
1923f
1
LTC1923
ABSOLUTE
AXI U
RATI GS
V
DD
to GND................................................. – 0.3V to 6V
SDSYNC, R
SLEW
......................................... – 0.3V to 6V
FB, CNTRL, V
THRM
, I
LIM
, V
SET
..................... – 0.3V to 6V
CS
+
, CS
–
, TEC
+
, TEC
–
.................................– 0.3V to 6V
PACKAGE/ORDER I FOR ATIO
SDSYNC
PLLLPF
R
SLEW
V
REF
NC
NC
R
T
C
T
ORDER PART
NUMBER
LTC1923EUH
24 PDRVB
23 NDRVB
22 V
DD
21 V
DD
20 PGND
19 NDRVA
18 PDRVA
17 CS
+
32 31 30 29 28 27 26 25
CNTRL 1
EAOUT 2
FB 3
AGND 4
NC 5
SS 6
I
LIM
7
V
SET
8
9 10 11 12 13 14 15 16
FAULT
H/C
V
TEC
V
THRM
TEC
–
TEC
+
I
TEC
–
PIN 1
TOP VIEW
CS
UH PACKAGE
32-LEAD PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W
EXPOSED PAD IS PGND
(MUST BE SOLDERED TO PCB)
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
DD
= 5V, R
SLEW
= V
DD
, SDSYNC = V
DD
, R
T
= 10k, C
T
= 330pF unless otherwise noted.
SYMBOL PARAMETER
Input Supply
VDD
UVLO
UVHYST
I
DD
I
DDSHDN
SHDNTH
Operating Supply Voltage
Undervoltage Lockout
Hysteresis
Operating Supply Current
Shutdown I
DD
Shutdown Threshold
Low to High Threshold
High to Low
No Output Load, Outputs Not Switching
SDSYNC = 0V
Measured at PDRVA, PDRVB
0.3
q
q
q
CONDITIONS
2
U
U
W
W W
U
W
(Note 1)
FAULT, H/C ................................................. – 0.3V to 6V
Operating Temperature Range (Note 2) .. – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 125°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
PLLLPF
R
SLEW
SDSYNC
CNTRL
EAOUT
FB
AGND
SS
I
LIM
1
2
3
4
5
6
7
8
9
28 R
T
27 C
T
26 V
REF
25 PDRVB
24 NDRVB
23 V
DD
22 PGND
21 NDRVA
20 PDRVA
19 CS
+
18 CS
–
17 I
TEC
16 TEC
+
15 TEC
–
ORDER PART
NUMBER
LTC1923EGN
V
SET
10
FAULT 11
V
THRM
12
H/C 13
V
TEC
14
GN PACKAGE
28-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 120°C/W
MIN
2.7
TYP
MAX
5.5
UNITS
V
V
mV
mA
µA
V
2.6
50
130
2
10
0.8
2.7
4
25
1.4
1923f
LTC1923
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
DD
= 5V, R
SLEW
= V
DD
, SDSYNC = V
DD
, R
T
= 10k, C
T
= 330pF unless otherwise noted.
SYMBOL PARAMETER
Reference
V
REF
V
REFGD
LDREG
V
REFISC
f
OSCI
f
OSC
OSCPK
OSCVLY
C
TICH
C
TIDIS
I
PLLLPF
Reference Output Voltage
V
REF
Good Threshold
Load Regulation
Short-Circuit Current
Initial Oscillator Frequency
Frequency Variation
C
T
Ramp Peak
C
T
Ramp Valley
C
T
Charge Current
C
T
Discharge Current
Phase Detector Output Current
Sinking
Sourcing
Master Threshold On PLLLPF Pin
Shutdown Delay to Output
Input Offset Voltage
Open-Loop Gain
Common Mode Input Range
FB and CNTRL Input Bias Currents
Output High
Output Low
Sourcing Current
Sinking Current
Gain-Bandwidth Product
Amplifier Gain
Amplifier Offset
Output Sourcing Load Regulation
Output Sinking Load Regulation
–3dB Frequency
Current Limit Threshold
Current Limit Delay to Output
Soft-Start Charge Current
Soft-Start Current Limit Threshold
I
LIM
Current Limit Threshold
SS = 0.75V
SS = 0.5V, Measured at CS
+
, CS
–
I
LIM
= 0.5V, Measured at CS
+
, CS
–
– 2.5
50
50
Measured at I
TEC
CS
+
- CS
–
= 100mV, I
LOAD
= 0 to – 50µA
CS
+
- CS
–
= 100mV, I
LOAD
= 0 to 50µA
(Note 3)
Measured at CS
+
, CS
–
q
CONDITIONS
No Load
q
MIN
2.462
2.450
TYP
2.5
2.25
10
5
MAX
2.538
2.550
2.45
25
20
UNITS
V
V
V
mV
mV
mA
V
REF
Rising Threshold
I
LOAD
= –1mA to –10mA
V
DD
= 2.7V to 5.5V
V
REF
= 0V
R
T
= 10k, C
T
= 330pF
V
DD
= 2.7V to 5V, C
T
= 330pF, R
T
= 10k
q
LINEREG Line Regulation
Oscillator and Phase-Locked Loop
10
190
q
20
225
225
1.5
0.5
–150
150
260
270
1.6
0.6
kHz
kHz
V
V
µA
µA
165
1.4
0.4
C
T
= 0.3V, R
T
= 10k
C
T
= 1.8V, R
T
= 10k
– 1.1
f
SYNC
< f
OSC
f
SYNC
> f
OSC
Measured at SDSYNC Pin
20
EAOUT = 1V, V
CM
= 2.5V
EAOUT = 0.45V to 1.55V, CNTRL = 2.5V
EAOUT = 1V
FB = CNTRL = 1.25
I
LOAD
= – 100µA
I
LOAD
= 100µA
EAOUT = 1V, FB = 2.4V, CNTRL = 2.5V
EAOUT = 1V, FB = 5V, CNTRL = 2.5V
f = 100kHz (Note 3)
1
0.2
– 100
–18
PLLGAIN Gain from PLLLPF to R
T
– 0.9
12
–12
– 0.7
V/V
µA
µA
V
µs
MSTTH
SDDLY
V
OS
AOL
V
CM
I
IB
V
OH
V
OL
I
SOURCE
I
SINK
GBW
ACS
CSOFF
I
TECH
I
TECL
f3dB
I
LIMTH
I
LIMDLY
SSI
CHG
SSI
LIM
I
LIM
V
DD
– 0.7 V
DD
– 0.4
45
18
80
V
DD
+ 0.2
100
1.65
0.3
–1.5
2
2
10
– 15
–2
0.1
0.1
500
125
145
300
– 1.5
70
70
165
450
– 0.5
90
90
10
0.2
0.2
0.45
– 0.5
Error Amplifier
mV
dB
V
nA
V
V
mA
mA
MHz
V/V
mV
V
V
kHz
mV
ns
µA
mV
mV
Current Sense Amplifier
1923f
3
LTC1923
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C.
V
DD
= 5V, R
SLEW
= V
DD
, SDSYNC = V
DD
, R
T
= 10k, C
T
= 330pF unless otherwise noted.
SYMBOL PARAMETER
TEC Voltage Amplifier
ATEC
TECOFF
TECCMR
V
TECH
V
TECL
f3dB
OUTH
OUTL
t
RISE
t
FALL
t
rSLEW
t
fSLEW
t
rSLEW
t
fSLEW
SLEWVT
DLY
Fault
OPENTH
SHRTTH
FLTV
DIRH
DIRL
HCV
Open Thermistor Threshold
Shorted Thermistor Threshold
Fault Output Low Voltage
Low-to-High Threshold
High-to-Low Threshold
H/C Output Low Voltage
V
SET
= 5V, Measured with Respect to V
SET
V
SET
= 5V, Measured with Respect to GND
1mA Into FAULT, During Fault
TEC
–
= 2.5V, Measured with Respect to TEC
–
Sensed When H/C Toggles Low
TEC
–
= 2.5V, Measured with Respect to TEC
–
Sensed When H/C Toggles High
1mA Into Pin
– 410
0.975
150
50
– 50
150
Note 3:
Guaranteed by design, not tested in production.
300
300
mV
V
mV
mV
mV
mV
Amplifier Gain
Amplifier Offset
Common Mode Rejection
Output High Voltage
Output Low Voltage
–3dB Frequency
Output High Voltage
Output Low Voltage
Output Rise Time
Output Fall Time
Output Rise Time
Output Fall Time
Output Rise Time
Output Slew Fall Time
R
SLEW
Disable Threshold
Output Dead Time
R
T
= 10k
Measured at V
TEC
, V
CM
= 2.5V
0.1V < V
CM
< 4.9V
I
LOAD
= –50µA
I
LOAD
= 50µA
(Note 3)
I
OUT
= – 100mA
I
OUT
= 100mA
C
LOAD
= 1nF
C
LOAD
= 1nF
C
LOAD
= 1nF, R
SLEW
= 10k
C
LOAD
= 1nF, R
SLEW
= 10k
C
LOAD
= 1nF, R
SLEW
= 100k
C
LOAD
= 1nF, R
SLEW
= 100k
4
4.7
0.98
1
–7
60
4.9
0.1
1
4.5
0.7
20
20
20
20
90
90
2.75
90
1.2
0.3
1.02
V/V
mV
dB
V
V
MHz
V
V
ns
ns
ns
ns
ns
ns
V
ns
CONDITIONS
MIN
TYP
MAX
UNITS
Output Drivers
Direction Comparator
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LTC1923E is guaranteed to meet specifications from 0°C to
70°C. Specifications over the –40°C to 85°C operating temperature range
are assured by design, characterization and correlation with statistical
process controls.
1923f
4
LTC1923
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
vs Temperature
265
OSCILLATOR FREQUENCY (kHz)
OSCILLATOR FREQUENCY (kHz)
1800
C
T
= 330pF
R
T
= 10k
245
1000
800
600
400
200
C
T
= 150pF
205
V
REF
(V)
225
185
165
–50
–20
10
40
70
TEMPERATURE (°C)
V
REF
vs I
REF
for Different
Temperatures
2.515
2.510
2.505
125
T
A
= 125°C
150
DEAD TIME (ns)
V
REF
(V)
2.495
2.490
2.485
2.480
2.475
2.470
0
5
I
REF
(mA)
1923 G04
100
V
DD
= 5V
75
RISE TIME (ns)
2.500
T
A
= 25°C
T
A
= –50°C
10
Error Amplifier Offset Voltage
vs Temperature
1.5
OPEN THERMISTOR THRESHOLD (V)
4.60
SHORTED THERMISTOR THRESHOLD (V)
ERROR AMPLIFIER V
IO
(mV)
1.0
0.5
0
–0.5
–1.0
–50
–20
10
40
70
TEMPERATURE (°C)
U W
100
100
Oscillator Frequency vs R
T
1600
1400
1200
C
T
= 68pF
2.500
V
DD
= 2.7V, 5V
T
A
= 25°C
2.510
V
REF
vs Temperature
2.505
2.495
2.490
C
T
= 330pF
130
0
5
10
R
T
(kΩ)
15
20
1923 G02
2.485
–50
–20
10
40
70
TEMPERATURE (°C)
100
130
1923 G01
1923 G03
Output Dead Time vs R
T
T
A
= 25°C
250
Output Rise/Fall Time vs R
SLEW
T
A
= 25°C
200
V
DD
= 2.7V
150
100
50
50
15
25
5
7.5
10
R
T
(kΩ)
12.5
15
1923 G05
0
0
100
200
R
SLEW
(kΩ)
300
1923 G06
Open Thermistor Threshold
vs Temperature
1.00
V
SET
= 5V
4.59
Shorted Thermistor Threshold
vs Temperature
V
SET
= 5V
0.99
4.58
0.98
4.57
0.97
4.56
0.96
130
4.55
–50
–20
10
40
70
TEMPERATURE (°C)
100
130
0.95
–50
–20
10
40
70
TEMPERATURE (°C)
100
130
1923 G07
1923 G08
1923 G09
1923f
5
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