Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - power management - special purpose 21 mA TQFN 20 EP (5x5)

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 TQFN pack-

age and its switching frequency is adjustable up to

1MHz through an external resistor. The MAX8521 is

also available in a 5mm x 5mm TQFN 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.

Applications

SFF/SFP Modules

Fiber Optic Laser Modules

Fiber Optic Network Equipment

ATE

Biotech Lab Equipment

Features

o Circuit Footprint 0.31in

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)

MAX8520/MAX8521

Smallest TEC Power Drivers for Optical

Modules

________________________________________________________________

Maxim Integrated Products

Ordering Information

19-2586; Rev 2; 2/11

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.

EVALUATION KIT

AVAILABLE

PART

TEMP RANGE

PIN-PACKAGE

MAX8520ETP+

-40°C to +85°C

20 TQFN - E P * 5m m x 5m m

MAX8521EBX

-40°C to +85°C

6 x 6 U C S P 3m m x 3m m

MAX8521ETP+

-40°C to +85°C

20 TQFN - E P * 5m m x 5m m

MAX8521EWX+

-40°C to +85°C

36 WLP ** 3m m x 3m m

UCSP is a trademark of Maxim Integrated Products, Inc.

INPUT

3V TO 5.5V

PVDD_

COMP

GND

SHDN

ITEC

OFF

TEC CURRENT

MONITOR

CTLI

LX1

PGND1

OS1

OS2

LX2

PGND2

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

Denotes a lead(Pb)-free/RoHS-compliant package.

EP = Exposed pad.

Four center bumps depopulated.

Summary of content (18 pages)

PAGE 1
9-2586; Rev 2; 2/11 KIT ATION EVALU E L B A AVAIL Smallest TEC Power Drivers for Optical Modules Features 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. o Circuit Footprint 0.
PAGE 2
MAX8520/MAX8521 Smallest TEC Power Drivers for Optical Modules ABSOLUTE MAXIMUM RATINGS VDD 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 (VDD + 0.3V) PVDD1, PVDD2 to GND .............................-0.3V to (VDD + 0.3V) PVDD1, PVDD2 to VDD ...............................
PAGE 3
Smallest TEC Power Drivers for Optical Modules (VDD = VPVDD1 = VPVDD2 = V SHDN = 5V, 1MHz mode (Note 4). PGND1 = PGND2 = GND, CTLI = MAXV = MAXIP = MAXIN = REF, TA = 0°C to +85°C, unless otherwise noted. Typical values at TA = +25°C.) PARAMETER No-Load Supply Current Shutdown Supply Current Thermal Shutdown SYMBOL CONDITIONS MIN 500kHz mode 11 14 1MHz mode 16 21 LOAD) VCOMP = VREF = 1.500V, VDD = 3.
PAGE 4
MAX8520/MAX8521 Smallest TEC Power Drivers for Optical Modules ELECTRICAL CHARACTERISTICS (VDD = VPVDD1 = VPVDD2 = VSHDN = 5V, 1MHz mode (Note 4). PGND1 = PGND2 = GND, CTLI = MAXV = MAXIP = MAXIN = REF, TA = -40°C to +85°C, unless otherwise noted.) (Note 8) PARAMETER Input Supply Range SYMBOL CONDITIONS VDD Reference Load Regulation VREF ∆VREF VDD = 3V to 5.
PAGE 5
Smallest TEC Power Drivers for Optical Modules (VDD = VPVDD1 = VPVDD2 = VSHDN = 5V, 1MHz mode (Note 4). PGND1 = PGND2 = GND, CTLI = MAXV = MAXIP = MAXIN = REF, TA = -40°C to +85°C, unless otherwise noted.) (Note 8) PARAMETER SYMBOL MAXV Threshold Accuracy IMAXVBIAS, MAXV, MAXI_ Input Bias Current MIN MAX UNITS VMAXV = VREF x 0.67, VOS1 to VOS2 = ±4V, VDD = 5V CONDITIONS -2 +2 % VMAXV = VREF x 0.33, VOS1 to VOS2 = ±2V, VDD = 3V -3 +3 % VMAXV = VMAXI_ = 0.1V or 1.5V -0.1 +0.1 µA 10.
PAGE 6
Typical Operating Characteristics (continued) (VDD = 5V, circuit of Figure 1, TA = +25°C unless otherwise noted.) DIFFERENTIAL OUTPUT VOLTAGE RIPPLE TEC CURRENT RIPPLE VDD RIPPLE MAX8520/21 toc06 MAX8520/21 toc05 MAX8520/21 toc04 C2 = C7 = 1µF 1.5A VOS2 - VOS1 1mV/div AC-COUPLED VDD 20mV/div AC-COUPLED ITEC = 1A ITEC = 1A 10mA/div AC-COUPLED 0A 400ns/div 400ns/div 400ns/div ZERO-CROSSING TEC CURRENT MAX8520/21 toc07 VITEC vs. TEC CURRENT MAX8520/21 toc08 VCTLI 1V/div 3.0 2.
PAGE 7
Smallest TEC Power Drivers for Optical Modules 600 FREQ = 500kHz 400 800 VDD = 5V 700 0 400 4.0 4.5 5.0 MAX8520/21 toc14 REF SOURCING 150µA 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -1.0 -1.2 -1.4 60 5.5 80 100 120 140 3.0 160 3.5 4.0 4.5 5.0 5.5 VDD (V) REXT (kΩ) VDD (V) REFERENCE VOLTAGE CHANGE vs. TEMPERATURE REFERENCE VOLTAGE CHANGE vs.
PAGE 8
MAX8520/MAX8521 Smallest TEC Power Drivers for Optical Modules Typical Operating Characteristics (continued) (VDD = 5V, circuit of Figure 1, TA = +25°C unless otherwise noted.) THERMAL STABILITY, COOLING MODE THERMAL STABILITY, ROOM TEMPERATURE MAX8520/21 toc20 THERMAL STABILITY, HEATING MODE MAX8520/21 toc21 TEMPERATURE 0.001°C/div TTEC = +25°C TA = +45°C MAX8520/21 toc22 TEMPERATURE 0.001°C/div TTEC = +25°C TA = +25°C 4s/div TEMPERATURE 0.
PAGE 9
Smallest TEC Power Drivers for Optical Modules PIN TQFN NAME UCSP/WLP FUNCTION TEC Current-Control Input. Sets TEC current. Center point is 1.50V (no TEC current). The current is given by: ITEC = (VOS1 - VCS) / RSENSE = (VCTLI - 1.50) / (10 x RSENSE). When (VCTLI - VREF) > 0V then VOS2 > VOS1 > VCS. 10 A5 CTLI 11 A6 GND Analog Ground. Star connect to PGND at underside exposed pad for TQFN package. 12 B6 VDD Analog Supply Voltage Input. Bypass VDD to GND with a 1µF ceramic capacitor.
PAGE 10
MAX8520/MAX8521 Smallest TEC Power Drivers for Optical Modules Detailed Description The MAX8520/MAX8521 TEC drivers consist of two switching buck regulators that operate together to directly control the TEC current. This configuration creates a differential voltage across the TEC, allowing bidirectional TEC current for controlled cooling and heating. Controlled cooling and heating allow accurate TEC temperature control to within 0.01°C. The voltage at CTLI directly sets the TEC current.
PAGE 11
Smallest TEC Power Drivers for Optical Modules MAX8520/MAX8521 VDD L1 4.7µH LX1 VDD C1 1µF REF C2 1µF CS RSENSE 0.09Ω PVDD1 R2 OS1 C3 1µF RTHER PGND1 C5 10µF U1 PVDD2 MAX8521 C4 1µF OS2 PGND2 L2 4.7µH REF LX2 C6 0.1µF COMP C8 0.1µF C7 1µF VDD MAXIP FREQ MAXIN 49.9kΩ ITEC ON MAXV 100kΩ SHDN CTLI OFF GND 0.022µF 10kΩ 243kΩ 1µF 10µF U3A U2 MAX4475 MAX4477 510kΩ TO REF VDD DAC INPUTS 10kΩ 100kΩ U4 MAX5144 U3B MAX4477 Figure 1.
PAGE 12
MAX8520/MAX8521 Smallest TEC Power Drivers for Optical Modules VDD L1 4.7µH LX1 VDD C1 1µF REF C2 1µF CS RSENSE 0.09Ω PVDD1 R2 OS1 C3 1µF RTHER PGND1 C5 10µF U1 PVDD2 C4 1µF MAX8520 OS2 PGND2 L2 4.7µH REF LX2 C6 0.1µF COMP C7 1µF C8 0.1µF MAXIP FREQ MAXIN 49.9kΩ REXT 60kΩ ITEC MAXV 100kΩ ON SHDN CTLI OFF GND 0.022µF 1kΩ 243kΩ 10µF 10µF U2 50kΩ MAX4238 0.01µF DAC INPUTS VDD REF U4 MAX5144 Figure 2.
PAGE 13
Smallest TEC Power Drivers for Optical Modules MAX8520/MAX8521 3/4 VDD 1/4 VDD LX2 -1.2 REF COMP PWM 4X 1.2X gm CTLI RSENSE CCOMP 1 LX1 R R +1.2 0.5X CS 10X OS1 Figure 3. Functional Diagram of the Current-Control Loop Inductor Selection The MAX8520/MAX8521 dual buck converters operate in-phase and in complementary mode to drive the TEC differentially in a current-mode control scheme.
PAGE 14
MAX8520/MAX8521 Smallest TEC Power Drivers for Optical Modules The output common-mode ripple voltage can be calculated as follows: VRIPPLEpk-pk = LIR x ITEC(MAX) (ESR + 1/8 x C x fs) A 1µF ceramic capacitor with ESR of 10 mΩ with LIR = 12% and ITEC(MAX) = 1.5A will result in VRIPPLE(P-P) of 24.3mV. For size-constraint application, the capacitor can be made smaller at the expense of higher ripple voltage.
PAGE 15
Smallest TEC Power Drivers for Optical Modules Setting Max TEC Voltage Apply a voltage to the MAXV pin to control the maximum differential TEC voltage. VMAXV can vary from 0V to V REF . The voltage across the TEC is four times VMAXV and can be positive or negative: |VOS1 - VOS2| = 4 x VMAXV or VDD, whichever is lower Set VMAXV with a resistor-divider between REF and GND using resistors from 10kΩ to 100kΩ. VMAXV can vary from 0V to VREF.
PAGE 16
6) To ensure high DC-loop gain and minimum loop error, keep the board layout adjacent to the negative input pin of the integrator (U2 in Figure1) clean and free of moisture. Any contamination or leakage current into this node can act to lower the DC gain of the integrator which can degrade the accuracy of the thermal loop. If space is available, it can also be helpful to surround the negative input node of the integrator with a grounded guard ring.
PAGE 17
Smallest TEC Power Drivers for Optical Modules ON OFF SHDN REF FREQ (MAX8521) REF 3V TO 5.5V VDD PVDD1 MAXV MAX VTEC = VMAXV × 4 OR VDD LX1 MAXIP MAXIN MAX ITEC = (VMAXIP/VREF) × (0.15V/RSENSE) PWM CONTROL AND GATE CONTROL MAX ITEC = (VMAXIN/VREF) × (0.
PAGE 18
MAX8520/MAX8521 Smallest TEC Power Drivers for Optical Modules Revision History REVISION NUMBER REVISION DATE 0 10/02 Initial release 1 12/08 Added WLP package to Ordering Information, updated Electrical Characteristics, Absolute Maximum Ratings, Pin Description, and Package Information.