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MAX8521
Technical data
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MAXIM MAX8520, MAX8521 Technical data

General Description
The MAX8520/MAX8521 are designed to drive thermo­electric 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 external components.
The MAX8520 and 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 a space­saving 3mm x 3mm UCSP™, with a pin-selectable switching frequency of 500kHz or 1MHz.
Applications
SFF/SFP Modules
Fiber-Optic Laser Modules
Fiber-Optic Network Equipment
ATE
Biotech Lab Equipment
Features
♦ Circuit Footprint of 0.31in
2
♦ Low-Profile Design
♦ On-Chip Power MOSFETs
♦ High-Efficiency Switch-Mode Design
♦ Ripple Cancellation for Low Noise
♦ Direct Current Control Prevents TEC Current
Surges
♦ 5% Accurate Adjustable Heating/Cooling Current
Limits
♦ 2% Accurate TEC Voltage Limit
♦ No Dead Zone or Hunting at Low Output Current
♦ ITEC Monitors TEC Current
♦ 1% Accurate Voltage Reference
♦ Switching Frequency Up to 1MHz
♦ Synchronization (MAX8521)
MAX8520/MAX8521
Smallest TEC Power Drivers for
Optical Modules
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
19-2586; Rev 0; 10/02
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE PIN-PACKAGE
MAX8520ETP
20 Thin QFN 5mm x 5mm
MAX8521EBX
36 UCSP 3mm x 3mm
MAX8521ETP
20 Thin QFN 5mm x 5mm
UCSP is a trademark of Maxim Integrated Products, Inc.
INPUT
3V TO 5.5V
V
DD
PV
DD
COMP
GND
SHDN
ITEC
ON
OFF
TEC CURRENT
MONITOR
CTLI
LX1
PGND1
CS
OS1
OS2 LX2
PGND2
TEC
I
TEC
= ± 1.5A
REF
CURRENT-
CONTROL
SIGNAL
FREQ
ANALOG /DIGITAL
TEMPERATURE CONTROL
OUTPUT
MAX8521
Typical Operating Circuit
Pin Configurations appear at end of data sheet.
3mm x 3mm
CSP
5mm x 5mm
QFN
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
MAX8520/MAX8521
Smallest TEC Power Drivers for Optical Modules
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.
VDDto 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, PVDD2 to GND...............................-0.3V to (VDD+ 0.3V)
PV
DD
1, PVDD2 to VDD...........................................-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) 20-Pin 5mm x 5mm x 0.9mm QFN (derate 20.8mW/°C
above +70°C) (Note 2)...................................................1.67W
3mm x 3mm UCSP (derate 22mW/°C
above +70°C).................................................................1.75W
Maximum Junction Temperature .....................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Temperature (soldering 10s) ..................................+300°C
ELECTRICAL CHARACTERISTICS
(VDD= PVDD1 = PVDD2 = 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 TA= +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Input Supply Range V
DD
3.0 5.5 V
Maximum TEC Current
A
Reference Voltage V
REF
V
DD
= 3V to 5.5V, I
REF
= 150µA
1.5
V
Reference Load Regulation ∆V
REF
V
DD
= 3V to 5V, I
REF
= 10µA to 1mA 1.2 5.0 mV
V
MAXI_
= V
REF
160
V
DD
= 5V
V
MAXI_
= V
REF
/3 40 50 60
V
MAXI_
= V
REF
155
MAXIP/MAXIN Threshold Accuracy
V
DD
= 3V
V
MAXI_
= V
REF
/3 45 50 55
mV
V
DD
= 5V, I = 0.2A
NFET On-Resistance
)
V
DD
= 3V, I = 0.2A
Ω
V
DD
= 5V, I = 0.2A
PFET On-Resistance
)
V
DD
= 3V, I = 0.2A
Ω
VLX = V
DD
= 5V, TA = +25°C
4
NFET Leakage I
LEAK(N)
VLX = V
DD
= 5V, TA = +85°C 0.3
µA
VLX = 0, TA = +25°C
4
PFET Leakage I
LEAK(P)
VLX = 0, TA = +85°C 0.3
µA
500kHz mode 11 14
V
COMP
= V
REF
=
1.500V, V
DD
= 5V
1MHz mode 16 21
500kHz mode 8 11
No-Load Supply Current
I
DD(NO
LOAD)
V
COMP
= V
REF
=
1MHz mode 11 14
mA
Shutdown Supply Current I
DD-SD
SHDN = GND, V
DD
= 5V (Note 4) 2 3 mA
Thermal Shutdown
Hysteresis = 15°C
°C
VDD rising
UVLO Threshold V
UVLO
VDD falling
V
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: Solder underside metal slug to PC board ground plane.
R
DS(ON-N
R
DS(ON-P
T
SHUTDOWN
1.500V, V
DD
= 3.3V
±1.5
1.485
1.515
140 150
143 150
0.09 0.14
0.11 0.16
0.14 0.23
0.17 0.30
0.03
0.03
+165
2.50 2.65 2.80
2.40 2.55 2.70
MAX8520/MAX8521
Smallest TEC Power Drivers for
Optical Modules
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VDD= PVDD1 = PVDD2 = 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 TA= +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX8521, FREQ= VDD, V
DD
= 3V to 5V 0.8 1 1.2
MAX8521, FREQ= 0, V
DD
= 3V to 5V 0.4 0.5 0.6
MAX8520, R
EXT
= 60kΩ, V
DD
= 5V 0.8 1 1.2
MAX8520, R
EXT
= 60kΩ, V
DD
= 3V
MAX8520, R
EXT
= 150kΩ, V
DD
= 5V 0.4 0.5 0.6
Internal Oscillator Switching Frequency
f
SW-INT
MAX8520, R
EXT
= 150kΩ, V
DD
= 3V
MHz
External Sync Frequency Range
25% < duty cycle <75% (MAX8521 only) 0.7 1.2
MHz
LX_ Duty Cycle (Note 5) 0 100 %
OS1, OS2, CS Input Current
I
OS1
, I
OS2
,
I
CS
0 or V
DD
µA
SHDN, FREQ Input Current
I
SHDN
,
I
FREQ
0 or VDD, FREQ applicable for the MAX8521 only
-5 +5 µA
SHDN, FREQ Input Low Voltage V
IL
V
DD
= 3V to 5.5V, FREQ applicable for the
MAX8521 only
V
SHDN, FREQ Input High Voltage
V
IH
V
DD
= 3V to 5.5V, FREQ applicable for the
MAX8521 only
VDD x
V
V
MAXV
= V
REF
x 0.67, V
OS1
to V
OS2
= ±4V,
V
DD
= 5V
-2 +2 %
MAXV Threshold Accuracy
V
MAXV
= V
REF
x 0.33, V
OS1
to V
OS2
= ±2V,
V
DD
= 3V
-3 +3 %
MAXV, MAXI_ Input Bias Current
I
MAXV-BIAS
,
V
MAXV
= V
MAXI_
= 0.1V or 1.5V
µA
CTLI Gain A
CTLI
V
CTLI
= 0.5V to 2.5V (Note 6) 9.5 10
V/V
CTLI Input Resistance R
CTLI
1MΩ terminated at REF 0.5 1 2.0 MΩ
Error-Amp Transconductance g
m
50
160 µS
V
ITEC
Accuracy V
OS1
to VCS = ±100mV, V
OS1
= VDD/2 -10
%
0.76 0.93 1.10
0.36 0.46 0.56
-100 +100
0.75
I
MAXI_-BIAS
-0.1 +0.1
100
VDD x
0.25
10.5
+10
MAX8520/MAX8521
Smallest TEC Power Drivers for Optical Modules
4 _______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS
(VDD= PVDD1 = PVDD2 = SHDN = 5V, 1MHz mode (Note 2). PGND1 = PGND2 = GND, CTLI = MAXV = MAXIP = MAXIN = REF, TA=
-40°C to +85°C, unless otherwise noted.) (Note 7)
PARAMETER
SYMBOL
CONDITIONS
MIN
MAX
UNITS
Input Supply Range V
DD
3.0 5.5 V
Maximum TEC Current
A
Reference Voltage V
REF
V
DD
= 3V to 5.5V, I
REF
= 150µA
V
Reference Load Regulation ∆V
REF
V
DD
= 3V to 5V, I
REF
= 10µA to 1mA 5 mV
V
MAXI_
= V
REF
140 160
V
DD
= 5V
V
MAXI_
= V
REF
/3 40 60
V
MAXI_
= V
REF
143 155
MAXIP/MAXIN Threshold Accuracy
V
DD
= 3V
V
MAXI_
= V
REF
/3 45 55
mV
V
DD
= 5V, I = 0.2A
NFET On-Resistance
)
V
DD
= 3V, I = 0.2A
Ω
V
DD
= 5V, I = 0.2A
PFET On-Resistance
)
V
DD
= 3V, I = 0.2A
Ω
500kHz mode 14
V
COMP
= V
REF
=
1.500V, V
DD
= 5V
1MHz mode 21
500kHz mode 11
No-Load Supply Current
I
DD(NO
LOAD)
V
COMP
= V
REF
=
1MHz mode 14
mA
Shutdown Supply Current I
DD-SD
SHDN = GND, V
DD
= 5V (Note 4) 3 mA
VDD rising
UVLO Threshold V
UVLO
VDD falling
V
MAX8521, FREQ = VDD, V
DD
= 3V to 5V 0.8 1.2
MAX8521, FREQ = 0, V
DD
= 3V to 5V 0.4 0.6
MAX8520, R
EXT
= 60kΩ, V
DD
= 5V 0.8 1.2
MAX8520, R
EXT
= 60kΩ, V
DD
= 3V
MAX8520, R
EXT
= 150kΩ, V
DD
= 5V 0.4 0.6
Internal Oscillator Switching Frequency
f
SW-INT
MAX8520, R
EXT
= 150kΩ, V
DD
= 3V
MHz
25% < duty cycle <75% (MAX8521 only) 0.7 1.2
MHz
LX_ Duty Cycle (Note 5) 0 100 %
OS1, OS2, CS Input Current
I
OS1
, I
OS2
,
I
CS
0 or V
DD
µA
SHDN, FREQ Input Current
I
SHDN
,
I
FREQ
0 or VDD, FREQ applicable for the MAX8521 only
-5 +5 µA
SHDN, FREQ Input Low Voltage V
IL
V
DD
= 3V to 5.5V, FREQ applicable for the
MAX8521 only
VDD x
V
V
IH
V
DD
= 3V to 5.5V, FREQ applicable for the
MAX8521 only
VDD x
V
±1.5
1.480 1.515
R
DS(ON-N
External Sync Frequency Range
SHDN, FREQ Input High Voltage
R
DS(ON-P
1.500V, V
DD
= 3.3V
2.50 2.80
2.40 2.70
0.76 1.10
0.36 0.56
-100 +100
0.75
0.14
0.16
0.23
0.30
0.25
MAX8520/MAX8521
Smallest TEC Power Drivers for
Optical Modules
_______________________________________________________________________________________ 5
ELECTRICAL CHARACTERISTICS (continued)
(VDD= PVDD1 = PVDD2 = SHDN = 5V, 1MHz mode (Note 2). PGND1 = PGND2 = GND, CTLI = MAXV = MAXIP = MAXIN = REF, TA=
-40°C to +85°C, unless otherwise noted.) (Note 7)
PARAMETER
CONDITIONS
UNITS
V
MAXV
= V
REF
x 0.67, V
OS1
to V
OS2
= ±4V,
V
DD
= 5V
-2 +2 %
MAXV Threshold Accuracy
V
MAXV
= V
REF
x 0.33, V
OS1
to V
OS2
= ±2V,
V
DD
= 3V
-3 +3 %
I
MAXV-
BIAS
,
V
MAXV
= V
MAXI_
= 0.1V or 1.5V
µA
CTLI Gain A
CTLI
V
CTLI
= 0.5V to 2.5V (Note 6) 9.5
V/V
CTLI Input Resistance R
CTLI
1MΩ terminated at REF 0.5 2.0 MΩ
Error-Amp Transconductance g
m
50 160 µS
V
ITEC
Accuracy V
OS1
to VCS = ±100mV, V
OS1
= VDD/2 -10
%
Note 3: Enter 1MHz mode by tying a 60kΩ resistor from FREQ to ground for the MAX8520, and tying FREQ to VDDfor the MAX8521. Note 4: Includes PFET leakage. Note 5: Duty-cycle specification is guaranteed by design and not production tested. Note 6: CTLI Gain is defined as:
Note 7: Specifications to -40°C are guaranteed by design and not production tested.
A
V
VV
CTLI
CTLI
OS CS
=
−
()
∆
∆
1
Typical Operating Characteristics
(VDD= 5V, circuit of Figure 1, TA= +25°C, unless otherwise noted)
EFFICIENCY vs. TEC CURRENT
(V
DD
= 5V, R
TEC
= 2Ω)
MAX8520/21 toc01
TEC CURENT (A)
EFFICIENCY (%)
1.41.20.8 1.00.4 0.60.2
10
20
30
40
50
60
70
80
90
0
0 1.6
FREQ = 500kHz
FREQ = 1MHz
EFFICIENCY vs. TEC CURRENT
(V
DD
= 3.3V, R
TEC
= 1.3Ω)
MAX8520/21 toc02
TEC CURRENT (A)
EFFICIENCY (%)
1.41.20.8 1.00.4 0.60.2
10
20
30
40
50
60
70
80
90
0
0 1.6
FREQ = 500kHz
FREQ = 1MHz
COMMON-MODE
OUTPUT VOLTAGE RIPPLE
MAX8520/21 toc03
400ns/div
V
OS2
20mV/div AC-COUPLED
V
OS1
20mV/div AC-COUPLED
I
TEC
= 1A
C
2
= C7 = 1µF
MAXV, MAXI_ Input Bias Current
SYMBOL
I
MAXI_-BIAS
MIN MAX
-0.1 +0.1
10.5
+10
MAX8520/MAX8521
Smallest TEC Power Drivers for Optical Modules
6 _______________________________________________________________________________________
DIFFERENTIAL
OUTPUT VOLTAGE RIPPLE
MAX8520/21 toc04
400ns/div
V
OS2
- V
OS1
1mV/div AC-COUPLED
C
2
= C7 = 1µF
I
TEC
= 1A
VDD RIPPLE
MAX8520/21 toc05
400ns/div
V
DD
20mV/div AC-COUPLED
I
TEC
= 1A
TEC CURRENT RIPPLE
MAX8520/21 toc06
400ns/div
10mA/div AC-COUPLED
0A
1.5A
TEC CURRENT vs. CTLI VOLTAGE
MAX8520/21 toc07
20ms/div
V
CTLI
1V/div
I
TEC
1A/div
0A
0V
ZERO-CROSSING TEC CURRENT
MAX8520/21 toc08
1ms/div
V
CTLI
I00mV/div
I
TEC
100mA/div
0A
1.5V
V
ITEC
vs. TEC CURRENT
MAX8520/21 toc09
TEC CURRENT (A)
V
ITEC
(V)
1.51.00.50-0.5-1.0-1.5
0.5
1.0
1.5
2.0
2.5
3.0
0
-2.0 2.0
Typical Operating Characteristics (continued)
(VDD= 5V, circuit of Figure 1, TA= +25°C, unless otherwise noted)
I
TEC
vs. AMBIENT TEMPERATURE
MAX8520/21 toc10
AMBIENT TEMPERATURE (°C)
TEC CURRENT (A)
6040200-20
0.460
0.470
0.480
0.490
0.500
0.510
0.520
0.450
-40 80
FREQ = 1MHz V
CTLI
= 2V
R
TEC
= 1Ω
SWITCHING FREQUENCY
vs. TEMPERATURE
MAX8520/21 toc11
TEMPERATURE (°C)
SWITCHING FREQUENCY (kHz)
806040200-20
500
600
700
800
900
1000
1100
400
-40
FREQ = 1MHz
V
CTLI
= 1.5V
R
TEC
= 1Ω
FREQ = 500kHz
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