19-2586; Rev 1; 12/08
KIT
ATION
EVALU
BLE
AVAILA
Smallest TEC Power Drivers for Optical
Modules
General Description
The MAX8520/MAX8521 are designed to drive thermo-
electric coolers (TECs) in space-constrained optical
modules. Both devices deliver ±1.5A output current
and control the TEC current to eliminate harmful current
surges. On-chip FETs minimize external components
and high switching frequency reduces the size of exter-
nal components.
The MAX8520/MAX8521 operate from a single supply and
bias the TEC between the outputs of two synchronous
buck regulators. This operation allows for temperature
control without “dead zones” or other nonlinearities at
low current. This arrangement ensures that the control
system does not hunt when the set-point is very close
to the natural operating point, requiring a small amount
of heating or cooling. An analog control signal precisely
sets the TEC current.
Both devices feature accurate, individually-adjustable
heating current limit and cooling current limit along with
maximum TEC voltage limit to improve the reliability of
optical modules. An analog output signal monitors the
TEC current. A unique ripple cancellation scheme helps
reduce noise.
The MAX8520 is available in a 5mm x 5mm thin QFN
package and its switching frequency is adjustable up
to 1MHz through an external resistor. The MAX8521 is
also available in a 5mm x 5mm thin QFN as well as
space-saving 3mm x 3mm UCSP™ and 36-bump WLP
(3mm x 3mm) packages, with a pin-selectable switch-
ing frequency of 500kHz or 1MHz.
o
Circuit Footprint 0.31in
2
o
Low Profile Design
o
On-Chip Power MOSFETs
o
High-Efficiency Switch-Mode Design
o
Ripple Cancellation for Low Noise
o
Direct Current Control Prevents TEC Current
Surges
o
5% Accurate Adjustable Heating/Cooling Current
Limits
o
2% Accurate TEC Voltage Limit
o
No Dead Zone or Hunting at Low Output Current
o
ITEC Monitors TEC Current
o
1% Accurate Voltage Reference
o
Switching Frequency up to 1MHz
o
Synchronization (MAX8521)
Features
MAX8520/MAX8521
Ordering Information
PART
MAX8520ETP
MAX8521EBX
MAX8521ETP
MAX8521EWX+
TEMP RANGE
PIN-PACKAGE
-40°C to +85°C 20 Thin QFN-EP* 5mm x 5mm
-40°C to +85°C 6 x 6 UCSP 3mm x 3mm
-40°C to +85°C 20 Thin QFN-EP* 5mm x 5mm
-40°C to +85°C 36 WLP** 3mm x 3mm
Applications
SFF/SFP Modules
Fiber Optic Laser Modules
Fiber Optic Network Equipment
ATE
Biotech Lab Equipment
+Denotes
a lead(Pb)-free/RoHS-compliant package.
*EP
= Exposed pad.
**Four
center bumps depopulated.
Typical Operating Circuit
INPUT
3V TO 5.5V
V
DD
PV
DD
FREQ
ON
OFF
TEC CURRENT
MONITOR
CURRENT-
CONTROL
SIGNAL
SHDN
ITEC
MAX8521
CTLI
COMP
REF
GND
PGND2
OS1
OS2
LX2
TEC
OUTPUT
I
TEC
=
±
1.5A
CS
LX1
PGND1
Pin Configurations appear at end of data sheet
ANALOG /DIGITAL
TEMPERATURE CONTROL
UCSP is a trademark of Maxim Integrated Products, Inc.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Smallest TEC Power Drivers for Optical
Modules
MAX8520/MAX8521
ABSOLUTE MAXIMUM RATINGS
V
DD
to GND ..............................................................-0.3V to +6V
SHDN,
MAXV, MAXIP, MAXIN,
CTLI to GND .........................................................-0.3V to +6V
COMP, FREQ, OS1, OS2, CS, REF,
ITEC to GND...........................................-0.3V to (V
DD
+ 0.3V)
PV
DD
1, PV
DD
2 to GND...............................-0.3V to (V
DD
+ 0.3V)
PV
DD
1, PV
DD
2 to V
DD
...........................................-0.3V to +0.3V
PGND1, PGND2 to GND .......................................-0.3V to +0.3V
COMP, REF, ITEC short to GND....................................Indefinite
LX Current (Note 1) ........................................±2.25A LX Current
Continuous Power Dissipation (T
A
= +70°C)
6 x 6 UCSP (derate 22mW/°C above +70°C) ...............1.75W
20-Pin 5mm x 5mm x 0.9mm TQFN (derate 20.8mW/°C
above +70°C) (Note 2)...................................................1.67W
36-Bump WLP (derate 22mW/°C above +70°C)............1.75W
Operating Temperature Range ...........................-40°C to +85°C
Maximum Junction Temperature .....................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Note 1:
LX has internal clamp diodes to PGND and PVDD. Applications that forward bias these diodes should take care not to
exceed the IC’s package power dissipation limits.
Note 2:
Solders underside metal slug to PCB ground plane.
ELECTRICAL CHARACTERISTICS
(V
DD
= V
PVDD1
= V
PVDD2
= V
SHDN
= 5V, 1MHz mode (Note 3). PGND1 = PGND2 = GND, CTLI = MAXV = MAXIP = MAXIN = REF,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values at T
A
= +25°C.)
PARAMETER
Input Supply Range
Maximum TEC Current
Reference Voltage
Reference Load Regulation
MAXIP/MAXIN Threshold
Accuracy
V
REF
∆V
REF
V
DD
= 3V to 5.5V, I
REF
= 150µA
V
DD
= 3V to 5V, I
REF
= 10µA to 1mA
V
DD
= 5V
V
DD
= 3V
NFET On-Resistance
PFET On-Resistance
NFET Leakage
PFET Leakage
R
DS(ON-N)
R
DS(ON-P)
I
LEAK(N)
I
LEAK(P)
V
DD
= 5V, I = 0.2A
V
DD
= 3V, I = 0.2A
V
DD
= 5V, I = 0.2A
V
DD
= 3V, I = 0.2A
V
LX
= V
DD
= 5V, T
A
= +25°C
V
LX
= V
DD
= 5V T
A
= +85°C
V
LX
= 0, T
A
= +25°C
V
LX
= 0, T
A
= +85°C
V
COMP
= V
REF
=
1.500V, V
DD
= 5V
V
COMP
= V
REF
=
1.500V, V
DD
= 3.3V
500kHz mode
1MHz mode
500kHz mode
1MHz mode
V
MAXI_
= V
REF
V
MAXI_
= V
REF
/3
V
MAXI_
= V
REF
V
MAXI_
= V
REF
/3
140
40
143
45
SYMBOL
V
DD
CONDITIONS
MIN
3.0
±1.5
1.485
1.500
1.2
150
50
150
50
0.09
0.11
0.14
0.17
0.03
0.3
0.03
0.3
11
16
8
11
2
+165
2.50
2.40
2.65
2.55
2.80
2.70
14
21
11
14
3
mA
°C
V
mA
4.00
1.515
5.0
160
60
155
55
0.14
0.16
0.23
0.30
4.00
Ω
Ω
µA
µA
mV
TYP
MAX
5.5
UNITS
V
A
V
mV
No-Load Supply Current
I
DD(NO
LOAD)
Shutdown Supply Current
Thermal Shutdown
UVLO Threshold
I
DD-SD
SHDN = GND, V
DD
= 5V, (Note 4)
V
DD
rising
V
DD
falling
T
SHUTDOWN
Hysteresis = 15°C
V
UVLO
2
_______________________________________________________________________________________
Smallest TEC Power Drivers for Optical
Modules
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= V
PVDD1
= V
PVDD2
= V
SHDN
= 5V, 1MHz mode (Note 3). PGND1 = PGND2 = GND, CTLI = MAXV = MAXIP = MAXIN = REF,
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values at T
A
= +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MAX8521, FREQ = V
DD
, V
DD
= 3V to 5V
MAX8521, FREQ = 0, V
DD
= 3V to 5V
Internal Oscillator Switching
Frequency
f
SW-INT
MAX8520, R
EXT
= 60kΩ, V
DD
= 5V
MAX8520, R
EXT
= 60kΩ, V
DD
= 3V
MAX8520, R
EXT
= 150kΩ, V
DD
= 5V
MAX8520, R
EXT
= 150kΩ, V
DD
= 3V
External Sync Frequency Range
LX_ Duty Cycle
OS1, OS2, CS Input Current
SHDN,
FREQ Input Current
SHDN,
FREQ Input Low Voltage
SHDN,
FREQ Input High Voltage
I
OS1
, I
OS2
,
I
CS
I
SHDN
,
I
FREQ
V
IL
V
IH
25% < duty cycle <75% (MAX8521 only)
(Note 5)
0 or V
DD
0 or V
DD
, FREQ applicable for the
MAX8521 only
V
DD
= 3V to 5.5V, FREQ applicable for the
MAX8521 only
V
DD
= 3V to 5.5V, FREQ applicable for the
MAX8521 only
V
MAXV
= V
REF
x 0.67, V
OS1
to V
OS2
=
±4V,
V
DD
= 5V
V
MAXV
= V
REF
x 0.33, V
OS1
to V
OS2
=
±2V,
V
DD
= 3V
I
MAXV-BIAS
,
I
MAXI_-BIAS
A
CTLI
R
CTLI
g
m
V
OS1
to V
CS
=
±100mV
V
OS1
= V
DD
/2
V
MAXV
= V
MAXI_
= 0.1V or 1.5V
V
CTLI
= 0.5V to 2.5V (Note 6)
1MΩ terminated at REF
V
DD
x
0.75
-2
-3
+2
+3
MIN
0.8
0.4
0.8
0.76
0.4
0.36
0.7
0
-100
-5
TYP
1.0
0.5
1.0
0.93
0.5
0.46
MAX
1.2
0.6
1.2
1.10
0.6
0.56
1.2
100
+100
+5
V
DD
x
0.25
MHz
%
µA
µA
V
V
%
%
MHz
UNITS
MAX8520/MAX8521
MAXV Threshold Accuracy
MAXV, MAXI_ Input Bias Current
CTLI Gain
CTLI Input Resistance
Error-Amp Transconductance
V
ITEC
Accuracy
-0.1
9.5
0.5
50
-10
10.0
1.0
100
+0.1
10.5
2.0
160
+10
µA
V/V
MΩ
µS
%
_______________________________________________________________________________________
3
Smallest TEC Power Drivers for Optical
Modules
MAX8520/MAX8521
ELECTRICAL CHARACTERISTICS
(V
DD
= V
PVDD1
= V
PVDD2
= V
SHDN
= 5V, 1MHz mode (Note2). PGND1 = PGND2 = GND, CTLI = MAXV = MAXIP = MAXIN = REF,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 7)
PARAMETER
Input Supply Range
Maximum TEC Current
Reference Voltage
Reference Load Regulation
V
REF
∆V
REF
V
DD
= 3V to 5.5V, I
REF
= 150µA
V
DD
= 3V to 5V, I
REF
= 10µA to 1mA
V
DD
= 5V
V
DD
= 3V
NFET On-Resistance
PFET On-Resistance
R
DS(ON-N)
R
DS(ON-P)
V
DD
= 5V, I = 0.2A
V
DD
= 3V, I = 0.2A
V
DD
= 5V, I = 0.2A
V
DD
= 3V, I = 0.2A
V
COMP
= V
REF
=
1.500V, V
DD
= 5V
V
COMP
= V
REF
=
1.500V, V
DD
= 3.3V
V
DD
Rising
V
DD
Falling
MAX8521, FREQ = V
DD
, V
DD
= 3V to 5V
MAX8521, FREQ = 0, V
DD
= 3V to 5V
Internal Oscillator Switching
Frequency
f
SW-INT
MAX8520, R
EXT
= 60kΩ, V
DD
= 5V
MAX8520, R
EXT
= 60kΩ, V
DD
= 3V
MAX8520, R
EXT
= 150kΩ, V
DD
= 5V
MAX8520, R
EXT
= 150kΩ, V
DD
= 3V
External Sync Frequency Range
LX_ Duty Cycle
OS1, OS2, CS Input Current
SHDN,
FREQ Input Current
SHDN,
FREQ Input Low Voltage
SHDN,
FREQ Input High Voltage
25% < duty cycle <75% (MAX8521 only)
Note 5
I
OS1
, I
OS2
,
0 or V
DD
I
CS
I
SHDN
,
I
FREQ
V
IL
V
IH
0 or V
DD
, FREQ applicable for the MAX8521
only
V
DD
= 3V to 5.5V, FREQ applicable for the
MAX8521 only
V
DD
= 3V to 5.5V, FREQ applicable for the
MAX8521 only
V
DD
x
0.75
500kHz mode
1MHz mode
V
MAXI_
= V
REF
V
MAXI_
= V
REF
/3
V
MAXI_
= V
REF
V
MAXI_
= V
REF
/3
140
40
143
45
SYMBOL
V
DD
CONDITIONS
MIN
3.0
±1.5
1.480
1.515
5
160
60
155
55
0.14
0.16
0.23
0.30
14
21
11
14
3
2.50
2.40
0.8
0.4
0.8
0.76
0.4
0.36
0.7
0
-100
-5
2.80
2.70
1.2
0.6
1.2
1.10
0.6
0.56
1.2
100
+100
+5
V
DD
x
0.25
MHz
%
µA
µA
V
V
MHz
Ω
Ω
mV
MAX
5.5
UNITS
V
A
V
mV
MAXIP/MAXIN Threshold
Accuracy
No Load Supply Current
I
DD(NO
LOAD)
Shutdown Supply Current
UVLO Threshold
I
DD-SD
V
UVLO
500kHz mode
1MHz mode
SHDN = GND, V
DD
= 5V, (Note 4)
mA
mA
V
4
_______________________________________________________________________________________
Smallest TEC Power Drivers for Optical
Modules
ELECTRICAL CHARACTERISTICS (continued)
(V
DD
= V
PVDD1
= V
PVDD2
= V
SHDN
= 5V, 1MHz mode (Note2). PGND1 = PGND2 = GND, CTLI = MAXV = MAXIP = MAXIN = REF,
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 7)
PARAMETER
SYMBOL
CONDITIONS
V
MAXV
= V
REF
x 0.67, V
OS1
to V
OS2
=
±4V,
V
DD
= 5V
V
MAXV
= V
REF
x 0.33, V
OS1
to V
OS2
=
±2V,
V
DD
= 3V
I
MAXV-
BIAS
,
I
MAXI_-BIAS
CTLI Gain
CTLI Input Resistance
Error-Amp Transconductance
V
ITEC
Accuracy
A
CTLI
R
CTLI
g
m
V
OS1
to V
CS
=
±100mV
V
OS1
= V
DD
/2
V
CTLI
= 0.5V to 2.5V (Note 6)
1MΩ terminated at REF
9.5
0.5
50
-10
10.5
2.0
160
+10
V/V
MΩ
µS
%
V
MAXV
= V
MAXI_
= 0.1V or 1.5V
MIN
-2
-3
MAX
+2
+3
UNITS
%
%
MAX8520/MAX8521
MAXV Threshold Accuracy
MAXV, MAXI_ Input Bias Current
-0.1
+0.1
µA
Note 3:
Enter 1MHz mode by connecting a 60kΩ resistor from FREQ to ground for the MAX8520, and connecting FREQ to V
DD
for
the MAX8521.
Note 4:
Includes power FET leakage.
Note 5:
Duty-cycle specification is guaranteed by design and not production tested.
Note 6:
CTLI Gain is defined as:
A
CTLI
=
∆
V
CTLI
∆
(
V
OS1
−
V
CS
)
Note 7:
Specifications to -40°C are guaranteed by design and not production tested.
Typical Operating Characteristics
(V
DD
= 5V, circuit of Figure 1, T
A
= +25°C unless otherwise noted)
EFFICIENCY vs. TEC CURRENT
V
DD
= 5V, R
TEC
= 2Ω
MAX8520/21 toc01
EFFICIENCY vs. TEC CURRENT
V
DD
= 3.3V, R
TEC
= 1.3Ω
80
70
EFFICIENCY (%)
60
50
40
30
20
10
0
FREQ = 500kHz
FREQ = 1MHz
MAX8520/21 toc02
COMMON-MODE
OUTPUT VOLTAGE RIPPLE
MAX8520/21 toc03
90
80
70
FREQ = 1MHz
EFFICIENCY (%)
60
50
40
30
20
10
0
0
0.2
0.4
0.6
0.8
1
1.2
1.4
FREQ = 500kHz
90
C
2
= C
7
= 1µF
V
OS2
20mV/div
AC-COUPLED
V
OS1
20mV/div
AC-COUPLED
I
TEC
= 1A
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
400ns/div
1.6
TEC CURENT (A)
TEC CURRENT (A)
_______________________________________________________________________________________
5
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