19-5132; Rev 1; 3/10 TION KIT EVALUA BLE A IL A V A 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications Features The MAX15059 constant-frequency pulse-width modulating (PWM) step-up DC-DC converter features an internal switch and a high-side current monitor with highspeed adjustable current limiting. This device is capable of generating output voltages up to 76V (300mW for the MAX15059A and 200mW for the MAX15059B) and provides current monitoring up to 4mA. The MAX15059 operates from 2.8V to 5.5V. S Input Voltage Range: +2.8V to +5.5V The constant-frequency (400kHz) current-mode PWM architecture provides low-noise-output voltage that is easy to filter. A high-voltage internal power MOSFET allows this device to boost output voltages up to 76V. Internal soft-start circuitry limits the input current when the boost converter starts. The MAX15059 features a shutdown mode to save power. (1µs Response Time) S Open-Drain Current-Limit Indicator Flag S 400kHz Fixed-Switching Frequency S Constant PWM Frequency Provides Easy Filtering in Low-Noise Applications S Internal Soft-Start S 2µA (max) Shutdown Current S -40NC to +85NC Temperature Range S Small, Thermally Enhanced, 3mm x 3mm, LeadFree, 16-Pin TQFN-EP Package The MAX15059 includes a current monitor with more than three decades of dynamic range and monitors current ranging from 500nA to 4mA with high accuracy. Resistor-adjustable current limiting protects the APD from optical power transients. A clamp diode protects the monitor’s output from overvoltage conditions. Other protection features include cycle-by-cycle current limiting of the boost converter switch, undervoltage lockout (UVLO), and thermal shutdown if the die temperature reaches +150NC. The MAX15059 is available in a thermally enhanced, lead-free, 16-pin TQFN-EP package and operates over the -40NC to +85NC temperature range. Applications S Wide Output-Voltage Range from (VIN + 5V) to 76V S Internal 1I (typ) 80V MOSFET S Boost Converter Output Power: 300mW S 200mW Version Available for Smaller Inductor S Accurate Q5% (1:1 and 5:1) High-Side Current Monitor S Resistor-Adjustable Ultra-Fast APD Current Limit Ordering Information MAXIMUM POWER (mW) IAPD: IMOUT PINPACKAGE MAX15059AETE+ 300 1:1 16 TQFN-EP* MAX15059BETE+ 200 5:1 16 TQFN-EP* PART Note: All devices operate over the -40°C to +85°C temperature range. +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. Avalanche Photodiode Biasing and Monitoring Typical Operating Circuit PIN Diode Bias Supply Low-Noise Varactor Diode Bias Supply FBON Modules L1 4.7µH VIN = 2.8V TO 5.5V D1 CIN 1µF GPON Modules IN COUT 0.1µF LX CNTRL VOUT R2 348kI RADJ PGND R1 6.34kI BIAS MAX15059 FB SHDN GPIO ILIM RLIM GPIO VDD CLAMP RLIM 2.87kI SGND (76V MAX) APD VDD DAC µC ADC MOUT APD TIA RMOUT 1kI CMOUT OPTIONAL (10nF) ________________________________________________________________ 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. MAX15059 General Description MAX15059 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications ABSOLUTE MAXIMUM RATINGS Junction-to-Case Thermal Resistance (BJC) (Note 1) 16-Pin TQFN-EP.......................................................... +7NC/W Junction-to-Ambient Thermal Resistance (BJA) (Note 1) 16-Pin TQFN-EP........................................................ +48NC/W Operating Temperature Range........................... -40NC to +85NC Maximum Junction Temperature......................................+150NC Storage Temperature Range............................. -65NC to +150NC Lead Temperature (soldering, 10s).................................+300NC Soldering Temperature (reflow).......................................+260NC IN, SHDN, FB, ILIM, RLIM, CNTRL to SGND...........-0.3V to +6V LX to PGND............................................................-0.3V to +80V BIAS to SGND .......................................................-0.3V to +79V APD, CLAMP to SGND............................ -0.3V to (VBIAS + 0.3V) PGND to SGND.....................................................-0.3V to +0.3V MOUT to SGND................................... -0.3V to (VCLAMP + 0.3V) Continuous Power Dissipation (TA = +70NC) 16-Pin TQFN-EP (derate 20.8mW/NC above +70NC)..........................................................1666.7mW Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial. 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. ELECTRICAL CHARACTERISTICS (VIN = VSHDN = VCNTRL = 3.3V, CIN = 1FF, VPGND = VSGND = 0V, VBIAS = 40V, LX = APD = CLAMP = ILIM = unconnected, VMOUT = VRLIM = 0V, TA = -40NC to +85NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS INPUT SUPPLY Supply Voltage Range 2.8 VIN Supply Current ISUPPLY VFB = 1.4V, no switching Undervoltage-Lockout Threshold VUVLO VIN rising 2.475 Shutdown BIAS Current V 1.2 mA 2.6 2.775 V 200 Undervoltage-Lockout Hysteresis VUVLO_HYS Shutdown Current 5.5 1 mV VSHDN = 0V 2 FA IBIAS_SHDN VBIAS = 3.3V, VSHDN = 0V 20 FA 76 V ISHDN BOOST CONVERTER Output-Voltage Adjustment Range VIN + 5 Switching Frequency fSW Maximum Duty Cycle DCLK FB Set-Point Voltage VFB_SET FB Input-Bias Current IFB Internal Switch On-Resistance Peak Switch Current Limit RON ILIM_LX VIN = 5V 380 400 420 kHz VIN = 2.8V 88 90 92 % 1.2054 1.23 1.2546 V 500 nA I VFB = VFB_SET, TA = +25NC ILX = 100mA, VIN = 2.8V 1 2 MAX15059A 1.1 1.2 1.3 MAX15059B 0.825 0.9 0.975 Peak Current-Limit Response 100 LX Leakage Current VLX = 76V, TA = +25NC Line Regulation 2.8V P VIN P 5.5V, ILOAD = 4.5mA Load Regulation 0 P ILOAD P 4.5mA A ns 1 FA 0.2 % 1 % Soft-Start Duration 8 ms Soft-Start Steps 32 Steps 1.2 V CONTROL INPUT (CNTRL) Maximum Control Input Voltage Range FB set point is controlled to VCNTRL 2 _______________________________________________________________________________________ 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications (VIN = VSHDN = VCNTRL = 3.3V, CIN = 1FF, VPGND = VSGND = 0V, VBIAS = 40V, LX = APD = CLAMP = ILIM = unconnected, VMOUT = 0V, TA = -40NC to +85NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN CNTRL-to-REF Transition Threshold VFB = VREF above this voltage CNTRL Input-Bias Current VCNTRL = VFB_SET, TA = +25NC TYP MAX 1.3 UNITS V 500 nA 76 V CURRENT MONITOR Bias Voltage Range 10 VBIAS IAPD = 500nA Bias Quiescent Current IBIAS IAPD = 2mA Voltage Drop Dynamic Output Resistance at MOUT MAX15059A 150 250 MAX15059B 150 250 MAX15059A 4 6 MAX15059B 3 4 2.7 3.5 VDROP IAPD = 2mA, VDROP = VBIAS - VAPD RMOUT RMOUT = DVMOUT/DIMOUT, IAPD = 2.5mA APD Current-Step Response MAX15059A Step load on IAPD = 20FA to 1mA MOUT Output Leakage Output Clamp Voltage VMOUT VCLAMP Output Clamp Leakage Current MOUT Voltage Range Forward diode current = 500FA VBIAS = VCLAMP = 76V VMOUT IMOUT/IAPD IAPD = 2mA Power-Supply Rejection Ratio APD Input Current Limit PSRR Power-Up Settling Time tS V GI 25 ns 1 nA 0.7 0.95 V nA VBIAS 2.7 V MAX15059A 0. 95 1 1.1 MAX15059B 0.19 0.2 0.22 MAX15059A 0.965 1 1.035 MAX15059B mA/mA 0.193 0.2 0.207 (DIMOUT/IMOUT)/DVBIAS, MAX15059A VBIAS = 10V to 76V and IAPD MAX15059B = 5FA to 1mA (Note 3) 35 300 610 35 300 700 4 4.6 5.2 mA 9.75kI R RLIM R 0 0.9 5.2 mA ILIM_APD Current-Limit Adjustment Range mA 5 1 10V P VBIAS P 76V, 0 P IAPD P 1mA, CLAMP is unconnected IAPD = 500nA Current Gain 0.45 FA IMOUT settles to within 0.1%, IAPD = 500nA 10nF connected from APD to IAPD = 2.5mA ground ppm/V 7.5 ms 90 Fs LOGIC I/O 0.8 V SHDN Input Voltage Low VIL SHDN Input Voltage High VIH ILIM Output Voltage Low VOL ILIM = 2mA 0.1 V ILIM Output Leakage Current THERMAL PROTECTION IOH TA = +25NC 1 FA Thermal-Shutdown Temperature Thermal-Shutdown Hysteresis 2.1 Temperature rising V +150 NC 15 NC Note 2: All MIN/MAX parameters are tested at TA = +25NC. Limits overtemperature are guaranteed by design. Note 3: Guaranteed by design and not production tested. _______________________________________________________________________________________ 3 MAX15059 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VIN = 3.3V, VOUT = 70V, TA = +25°C, unless otherwise noted.) 80 80 EFFICIENCY (%) VOUT = 30V 70 60 50 40 VOUT = 50V 30 60 50 0 0 1.0 1.5 VOUT = 70V 20 10 0.5 VOUT = 50V 40 10 0 VOUT = 30V 70 30 VOUT = 70V 20 VIN = 5V 90 2.0 2.5 3.0 3.5 4.0 2.61 2.60 2.59 2.58 2.57 1.0 1.5 2.0 2.5 3.0 3.5 0 4.0 0.5 1.0 2.0 2.5 MAX15059 toc05 50 MAX15059 toc04 45 40 SUPPLY CURRENT (mA) VFB = 1.4V 1.4 1.2 TA = +25°C 1.5 LOAD CURRENT (mA) NO-LOAD SUPPLY CURRENT vs. SUPPLY VOLTAGE 1.6 SUPPLY CURRENT (mA) 2.62 LOAD CURRENT (mA) 2.0 0.8 2.63 2.55 0.5 0 SUPPLY CURRENT vs. SUPPLY VOLTAGE 1.0 2.64 2.56 LOAD CURRENT (mA) 1.8 2.65 MAX15059 toc03 VIN = 3.3V MINIMUM STARTUP VOLTAGE (V) 100 MAX15059 toc01 100 90 MINIMUM STARTUP VOLTAGE vs. LOAD CURRENT EFFICIENCY vs. LOAD CURRENT MAX15059 toc02 EFFICIENCY vs. LOAD CURRENT EFFICIENCY (%) MAX15059 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications TA = +85°C 0.6 0.4 35 TA = +25°C 30 TA = +85°C 25 20 15 10 TA = -40°C 0.2 TA = -40°C 5 0 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 2.5 SUPPLY VOLTAGE (V) 3.0 3.5 4.0 4.5 5.0 5.5 SUPPLY VOLTAGE (V) EXITING SHUTDOWN ENTERING SHUTDOWN MAX15059 toc06 MAX15059 toc07 SHDN 2V/div SHDN 2V/div INDUCTOR CURRENT 500mA/div INDUCTOR CURRENT 500mA/div VOUT 50V/div VOUT 50V/div 1ms/div 4ms/div 4 _______________________________________________________________________________________ 3.0 3.5 4.0 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications LIGHT-LOAD SWITCHING WAVEFORMS WITH RC FILTER HEAVY-LOAD SWITCHING WAVEFORMS WITH RC FILTER MAX15059 toc08 MAX15059 toc09 VBIAS (AC-COUPLED) 20mV/div VBIAS (AC-COUPLED) 50mV/div VLX 50V/div VLX 50V/div IL 500mA/div IL 1A/div 1µs/div 1µs/div LOAD-TRANSIENT RESPONSE LINE-TRANSIENT RESPONSE MAX15059 toc10 MAX15059 toc11 VIN 2V/div IAPD 2mA/div 0mA 3.3V VBIAS (AC-COUPLED) 500mV/div VBIAS (AC-COUPLED) 50mV/div 100µs/div 100µs/div 0.3 6 5 4 80 70 0.2 0.1 0 -0.1 40 30 2 -0.3 20 1 -0.4 10 0 -0.5 0 10 35 TEMPERATURE (°C) 60 85 0 0.5 1.0 1.5 2.0 2.5 LOAD CURRENT (mA) 3.0 3.5 4.0 B C 50 -0.2 -15 A 60 3 -40 A: VOUT = 30V, B: VOUT = 35V, C: VOUT = 45V, D: VOUT = 55V, E: VOUT = 60V, F: VOUT = 70V 90 IOUT(MAX) (mA) 7 0.4 REGULATION (%) LX LEAKAGE CURRENT (nA) 8 100 MAX15059 toc13 CURRENT INTO LX PINS VLX = 70V 9 0.5 MAX15059 toc12 10 MAXIMUM LOAD CURRENT vs. SUPPLY VOLTAGE LOAD REGULATION MAX15059 toc14 LX LEAKAGE CURRENT vs. TEMPERATURE D 2.5 3.0 3.5 E 4.0 4.5 F 5.0 5.5 SUPPLY VOLTAGE (V) _______________________________________________________________________________________ 5 MAX15059 Typical Operating Characteristics (continued) (VIN = 3.3V, VOUT = 70V, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VIN = 3.3V, VOUT = 70V, TA = +25°C, unless otherwise noted.) BIAS CURRENT vs. APD CURRENT BIAS CURRENT (mA) 0.1 10 MAX15059 toc16 MAX15059 toc15 BIAS CURRENT (mA) BIAS CURRENT (mA) IAPD = 2mA 1 BIAS CURRENT vs. TEMPERATURE 10 1 0.1 MAX15059 toc17 BIAS CURRENT vs. BIAS VOLTAGE 10 IAPD = 2mA 1 IAPD = 500nA IAPD = 500nA VBIAS = 70V 0.01 0.0001 20 30 40 50 60 70 80 0.1 0.001 BIAS VOLTAGE (V) GAIN ERROR vs. APD CURRENT 5 MAX15059 toc18 1 0 -1 3 -2 -3 VBIAS = 70V -5 100 1000 10,000 1 0 -1 -1.6 -2.0 1000 10,000 IAPD = 2mA -40 -15 35 GAIN ERROR vs. BIAS VOLTAGE IAPD = 0.5µA 0.4 0 IAPD = 500µA IAPD = 50µA 10 2.0 MAX15059 toc19b IAPD = 2mA 1.6 IAPD = 50µA 1.2 IAPD = 5µA 0.8 0.4 0 -0.4 IAPD = 500µA IAPD = 0.5µA IAPD = 2mA -0.8 IAPD = 5µA -1.2 -1.2 -1.6 -1.6 -2.0 -2.0 -40 -15 10 35 TEMPERATURE (°C) 60 85 IAPD = 50µA TEMPERATURE (°C) GAIN ERROR (%) GAIN ERROR (%) 1.2 85 IAPD = 500µA IAPD (µA) GAIN ERROR vs. TEMPERATURE -0.8 0 -0.4 -5 1.6 60 0.4 -1.2 100 IAPD = 5µA 0.8 -4 10 IAPD = 0.5µA 1.2 -3 2.0 -0.4 1.6 -0.8 1 35 2.0 -2 0.1 10 GAIN ERROR vs. TEMPERATURE 2 IAPD (µA) 0.8 -15 -40 TEMPERATURE (°C) VBIAS = 70V 4 GAIN ERROR (%) 2 10 10 GAIN ERROR (%) 3 1 1 GAIN ERROR vs. APD CURRENT 4 0.1 0.1 APD CURRENT (mA) 5 -4 0.01 MAX15059 toc19 10 MAX15059 toc18b 0 MAX15059 toc20 0.01 GAIN ERROR (%) MAX15059 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications 10 20 30 40 50 60 70 BIAS VOLTAGE (V) 6 _______________________________________________________________________________________ 80 60 85 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications GAIN ERROR vs. BIAS VOLTAGE APD TRANSIENT RESPONSE MAX15059 toc21 MAX15059 toc20b 2.0 1.6 GAIN ERROR (%) 1.2 0.8 IAPD = 500µA 0.4 IAPD = 5µA IAPD 2mA/div 0mA IAPD = 2mA IMOUT 2mA/div 0mA VAPD (AC-COUPLED) 2V/div 0 -0.4 IAPD = 50µA -0.8 IAPD = 0.5µA -1.2 -1.6 -2.0 10 20 30 40 50 60 70 80 20µs/div BIAS VOLTAGE (V) STARTUP DELAY STARTUP DELAY MAX15059 toc22 MAX15059 toc23 SHDN 5V/div SHDN 5V/div VBIAS 50V/div VBIAS 50V/div IMOUT 1mA/div IMOUT 500nA/div VBIAS = 70V IAPD = 2mA VBIAS = 70V, IAPD = 500nA 2ms/div 1ms/div STARTUP DELAY STARTUP DELAY MAX15059 toc25 MAX15059 toc24 SHDN 5V/div SHDN 5V/div VBIAS 5V/div VBIAS 5V/div IMOUT 1mA/div IMOUT 500nA/div VBIAS = 10V, IAPD = 500nA 200µs/div 400µs/div _______________________________________________________________________________________ 7 MAX15059 Typical Operating Characteristics (continued) (VIN = 3.3V, VOUT = 70V, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VIN = 3.3V, VOUT = 70V, TA = +25°C, unless otherwise noted.) SWITCHING FREQUENCY vs. TEMPERATURE VOLTAGE DROP vs. APD CURRENT MAX15059 toc26 2.5 IILIM 5V/div TA = -40°C 2.0 1.5 TA = +25°C 1.0 409 408 FREQUENCY (kHz) TA = +85°C 0.5 407 406 405 404 403 402 401 0 1 0.1 2µs/div 10 100 1000 400 10,000 -40 -15 IAPD (µA) SWITCHING FREQUENCY vs. INPUT VOLTAGE 406 404 402 400 398 MAX15059 toc30 410 50 DUTY CYCLE 406 40 404 35 402 30 400 25 SWITCHING FREQUENCY 398 20 396 15 394 10 392 392 5 390 390 396 394 2.5 3.0 3.5 4.0 4.5 5.0 5.5 0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 INPUT VOLTAGE (V) LOAD CURRENT (mA) FB SET POINT vs. TEMPERATURE APD OUTPUT RIPPLE VOLTAGE (0.1µF FROM APD TO GROUND, VBIAS = 70V, LAPD = 1mA) MAX15059 toc32 MAX15059 toc31 1.240 1.238 1.236 60 45 408 SWITCHING FREQUENCY (kHz) SWITCHING FREQUENCY (kHz) 408 35 SWITCHING FREQUENCY AND DUTY CYCLE vs. LOAD CURRENT MAX15059 toc29 410 10 TEMPERATURE (°C) DUTY CYCLE (%) IMOUT 2mA/div VBIAS - VAPD (V) VAPD 50V/div 410 MAX15059 toc27 3.0 RLIM = 3.16kI MAX15059 toc28 SHORT-CIRCUIT RESPONSE FB SET POINT (V) MAX15059 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications 1.234 1.232 VAPD AC-COUPLED, 70V 1mV/div 1.230 1.228 1.226 1.224 VIN = 3.3V 1.222 1.220 -40 -15 10 35 60 85 1µs/div TEMPERATURE (°C) 8 _______________________________________________________________________________________ 85 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications APD CLAMP MOUT RLIM TOP VIEW 12 11 10 9 BIAS 13 LX 14 MAX15059 LX 15 + 1 2 3 4 IN SHDN SGND EP PGND PGND 16 8 SGND 7 ILIM 6 CNTRL 5 FB TQFN Pin Description PIN NAME FUNCTION 1, 16 PGND 2 IN 3 SHDN Active-Low Shutdown Control Input. Apply a logic-low voltage to SHDN to shut down the device. Connect SHDN to IN for normal operation. Ensure that VSHDN is not greater than the input voltage, VIN. SHDN is internally pulled low. The converter is disabled when SHDN is left unconnected. 4, 8 SGND Signal Ground. Connect directly to the local ground plane. Connect SGND to PGND at a single point, typically near the return terminal of the output capacitor. 5 FB Feedback Regulation Input. Connect FB to the center tap of a resistive voltage-divider from the boost output to SGND to set the output voltage. The FB voltage regulates to 1.23V (typ) when VCNTRL is above 1.3V (typ) and to VCNTRL when VCNTRL is below 1.2V (typ). 6 CNTRL 7 ILIM Open-Drain Current-Limit Indicator. ILIM asserts low when the APD current limit has been exceeded. 9 RLIM Current-Limit Resistor Connection. Connect a resistor from RLIM to SGND to program the APD currentlimit threshold. When RLIM is connected to SGND, the current limit is set to 4.6mA. 10 MOUT Current-Monitor Output. For the MAX15059A, MOUT sources a current equal to IAPD. For the MAX15059B, MOUT sources a current equal to 1/5 of IAPD. 11 CLAMP Clamp Voltage Input. CLAMP is the external potential used for voltage clamping of MOUT. Power Ground. Connect the negative terminals of the input and output capacitors to PGND. Connect PGND externally to SGND at a single point, typically at the return terminal of the output capacitor. Input-Supply Voltage. Bypass IN to PGND with a ceramic capacitor of 1FF minimum value. Control Input for Boost Converter Output-Voltage Programmability. CNTRL allows the feedback set-point voltage to be set externally by CNTRL when CNTRL is less than 1.2V. Pull CNTRL above 1.3V (typ) to use the internal 1.23V (typ) feedback set-point voltage. _______________________________________________________________________________________ 9 MAX15059 Pin Configuration MAX15059 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications Pin Description (continued) PIN NAME 12 APD Reference Current Output. APD provides the source current to the cathode of the photodiode. FUNCTION 13 BIAS Bias-Voltage Input. Connect BIAS to the boost converter output (VOUT) either directly or through a lowpass filter for ripple attenuation. BIAS provides the voltage bias for the current monitor and is the current source for APD. 14, 15 LX Drain of Internal 80V n-Channel DMOS. Connect inductor to LX. Minimize the trace area at LX to reduce switching-noise emission. — EP Exposed Paddle. Connect to a large copper plane at the SGND and PGND potential to improve thermal dissipation. Do not use as the only ground connection. Functional Diagram FB CNTRL VREF OUTPUT ERROR AND CURRENT COMPARATOR -A +A MUX SGND -C SOFTSTART +C VREF PEAK CURRENT-LIMIT COMPARATOR LX 80V DMOS SWITCH CONTROL LOGIC PGND REFERENCE COMPARATOR SWITCH CURRENT SENSE VREF BIAS AND REF IN CLAMP THERMAL SHUTDOWN UVLO MOUT 1X CURRENTLIMIT ADJUSTMENT CONTROL MONITOR CLK 1X (A) 5X (B) OSCILLATOR 400kHz CURRENT LIMIT RLIM APD ILIM MAX15059 SHDN BIAS 10 ������������������������������������������������������������������������������������� 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications The MAX15059 constant-frequency, current-mode, PWM boost converters are intended for low-voltage systems that require a locally generated high voltage. These devices are capable of generating a low-noise, high output voltage required for PIN and varactor diode biasing. The MAX15059 operates from +2.8V to +5.5V. The MAX15059 operates in discontinuous mode in order to reduce the switching noise caused by reverse recovery charge of the rectifier diode and eliminates the need for external compensation components. Other continuous-mode boost converters generate large voltage spikes at the output when the LX switch turns on because there is a conduction path between the output, diode, and switch to ground during the time needed for the diode to turn off and reverse its bias voltage. To reduce the output noise even further, the LX switch turns off by taking 10ns typically to transition from on to off. As a consequence, the positive slew rate of the LX node is reduced and the current from the inductor does not “force” the output voltage as hard as would be the case if the LX switch were to turn off faster. The constant-frequency (400kHz) PWM architecture generates an output voltage ripple that is easy to filter. An 80V lateral DMOS device used as the internal power switch is ideal for boost converters with output voltages up to 76V. The MAX15059 can also be used in other topologies where the PWM switch is grounded, like SEPIC and flyback converters. The MAX15059 includes a versatile current monitor intended for monitoring the APD, PIN, or varactor diode DC current in fiber and other applications. The MAX15059 features more than three decades of dynamic current ranging from 500nA to 4mA and provides an output current accurately proportional to the APD current at MOUT. MOUT output accuracy is Q10% from 500nA to 1mA and Q5% from 1mA to 2mA. The MAX15059 also features a shutdown logic input to disable the device and reduce its standby current to 2FA (max). Fixed-Frequency PWM Controller The heart of the MAX15059 current-mode PWM controller is a BiCMOS multi-input comparator that simultaneously processes the output-error signal and switch current signal. The main PWM comparator uses direct summing, lacking a traditional error amplifier and its associated phase shift. The direct summing configura- tion approaches ideal cycle-by-cycle control over the output voltage since there is no conventional error amplifier in the feedback path. The devices operate in PWM mode using a fixedfrequency, current-mode operation. The current-mode frequency loop regulates the peak inductor current as a function of the output-voltage error signal. The current-mode PWM controller is intended for DCM operation. No internal slope compensation is added to the current signal. Current Limit The current limit of the current monitor is programmable from 1mA to 4.6mA (typ). Connect RLIM to SGND to get a default current-limit threshold of 4.6mA or connect a resistor from RLIM to SGND to program the current-limit threshold below the default setting of 4.6mA. Calculate the value of the external resistor, RLIM, for a given current limit, ILIM, using the following equation: 1.23V R LIM(kΩ) = x 10 − 2.67(kΩ) I (mA) LIM Clamping the Monitor Output Voltage (MOUT) CLAMP provides a means for diode clamping the voltage at MOUT; thus, VMOUT is limited to (VCLAMP + 0.6V). CLAMP can be connected to either an external supply or BIAS. Leave CLAMP unconnected if voltage clamping is not required. Shutdown The MAX15059 features an active-low shutdown input (SHDN). Pull SHDN low or leave it unconnected to enter shutdown. During shutdown, the supply current drops to 2FA (max). The output remains connected to the input through the inductor and output rectifier, holding the output voltage to one diode drop below IN when the MAX15059 is in shutdown. Connect SHDN to IN for always-on operation. Adjusting the Feedback Set-Point/Reference Voltage Apply a voltage to the CNTRL input to set the feedback set-point reference voltage, VREF (see the Functional Diagram). For VCNTRL > 1.3V, the internal 1.23V (typ) reference voltage is used as the feedback set point and for VCNTRL < 1.2V, the CNTRL voltage is used as the reference voltage (VFB set equal to VCNTRL). ______________________________________________________________________________________ 11 MAX15059 Detailed Description MAX15059 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications Design Procedure Setting the Output Voltage Set the MAX15059 output voltage by connecting a resistive divider from the output to FB to SGND (Figure 1). Select R1 (FB to SGND resistor) between 5kI and 10kI. Calculate R2 (VOUT to FB resistor) using the following equation: V R 2 = R1 OUT − 1 V REF where VOUT can range from (VIN + 5V) to 76V. Apply a voltage to the CNTRL input to set the feedback set-point reference voltage, VREF (see the Functional Diagram). For VCNTRL > 1.3V, the internal 1.23 (typ) reference voltage is used as the feedback set point and for VCNTRL < 1.2V, VREF = VCNTRL. See the Adjusting the Feedback Set-Point/Reference Voltage section for more information on adjusting the feedback reference voltage, VREF. Determining Peak Inductor Current If the boost converter remains in the discontinuous mode of operation, then the approximate peak inductor current, ILPEAK (in A), is represented by the formula below: ILPEAK = 2 × t S × (VOUT − VIN _MIN ) × I OUT_MAX η×L where tS is the switching period in Fs, VOUT is the output voltage in volts, VIN_MIN is the minimum input voltage in volts, IOUT_MAX is the maximum output current in amps, L is the inductor value in FH, and E is the efficiency of the boost converter (see the Typical Operating Characteristics). R2 FB VCNTRL > 1.3V, VFB = 1.23V VCNTRL < 1.2V, VFB = VCNTRL R1 Use the following formula to calculate the lower bound of the inductor value at different output voltages and output currents. This is the minimum inductance value for discontinuous mode operation for supplying full 300mW of output power: L MIN[µH] = 2 × t S × I OUT × (VOUT − VIN_MIN ) 2 η × ILIM_LX where VIN_MIN, VOUT (both in volts), and IOUT (in amps) are typical values (so that efficiency is optimum for typical conditions), tS (in Fs) is the period, E is the efficiency, and ILIM_LX is the peak switch current in amps (see the Electrical Characteristics table). Calculate the optimum value of L (LOPTIMUM) to ensure the full output power without reaching the boundary between continuous-conduction mode (CCM) and discontinuous-conduction mode (DCM) using the following formula: L [µH] L OPTIMUM [µH] = MAX 2.25 where: V2 (VOUT − VIN_MIN ) × t S × η L MAX [µH] = IN_MIN 2 2 × I OUT × VOUT For a design in which VIN = 3.3V, VOUT = 70V, IOUT = 3mA, E = 45%, ILIM_LX = 1.2A, and tS = 2.5Fs: LMAX = 27FH and LMIN = 1.5FH. VOUT MAX15059 Determining the Inductor Value Three key inductor parameters must be specified for operation with the MAX15059: inductance value (L), inductor saturation current (ISAT), and DC resistance (DCR). In general, the inductor should have a saturation current rating greater than the maximum peak switch current-limit value (ILIM_LX = 1.3A). DC series resistance (DCR) should be be low for reasonable efficiency. For a worse-case scenario in which VIN = 2.8V, VOUT = 70V, IOUT = 4mA, η = 43%, ILIM_LX = 1.2A, and tS = 2.5Fs: LMAX = 15FH and LMIN = 2.2FH. The choice of 4.7FH is reasonable given the worst-case scenario above. In general, the higher the inductance, the lower the switching noise. Load regulation is also better with higher inductance. Figure 1. Adjustable Output Voltage 12 ������������������������������������������������������������������������������������� 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications VIN = 2.8V TO 5.5V CIN IN CNTRL C OUT[µF] = I OUT ILPEAK x L OPTIMUM t S − 0.5 x ∆VOUT (VOUT − VIN_MIN ) ESR[mΩ] = 0.5 x ∆VOUT I OUT For very-low-output-ripple applications, the output of the boost converter can be followed by an RC filter to further reduce the ripple. Figure 2 shows a 100I, 0.1FF (RF CF) filter used to reduce the switching output ripple to 1mVPP with a 0.1mA load or 1mVP-P with a 4mA load. The output voltage regulation resistive divider must remain connected to the diode/output capacitor node. Use X7R ceramic capacitors for more stability over the full temperature range. LX D1 RF VOUT SHDN Output Filter Capacitor Selection For most applications, use a small output capacitor of 0.1FF or greater. To achieve low output ripple, a capacitor with low ESR, low ESL, and high capacitance value should be selected. If tantalum or electrolytic capacitors are used to achieve high capacitance values, always add a smaller ceramic capacitor in parallel to bypass the high-frequency components of the diode current. The higher ESR and ESL of electrolytic capacitors increase the output ripple and peak-to-peak transient voltage. Assuming the contribution from the ESR and capacitor discharge equals 50% (proportions may vary), calculate the output capacitance and ESR required for a specified ripple using the following equations: L1 R2 MAX15059 CIN FB COUT CF R1 PGND BIAS SGND Figure 2. Typical Operating Circuit with RC Filter Input-Capacitor Selection Bypass IN to PGND with a 1FF (min) ceramic capacitor. Depending on the supply source impedance, higher values may be needed. Make sure that the input capacitors are close enough to the IC to provide adequate decoupling at IN as well. If the layout cannot achieve this, add another 0.1FF ceramic capacitor between IN and PGND in the immediate vicinity of the IC. Bulk aluminum electrolytic capacitors may be needed to avoid chattering at low-input voltage. In case of aluminum electrolytic capacitors, calculate the capacitor value and ESR of the input capacitor using the following equations: CIN[µF] = VOUT x I OUT ILPEAK x L OPTIMUM x VOUT t S − η x VIN_MIN x 0.5 x ∆VIN VIN_MIN (VOUT − VIN_MIN ) ESR[mΩ] = 0.5 x ∆VIN x η x VIN_MIN VOUT x IOUT ______________________________________________________________________________________ 13 MAX15059 Diode Selection The MAX15059’s high switching frequency demands a high-speed rectifier. Schottky diodes are recommended for most applications because of their fast recovery time and low forward-voltage drop. Ensure that the diode’s peak current rating is greater than the peak inductor current. Also, the diode breakdown voltage must be greater than VOUT. MAX15059 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications Applications Information Using APD or PIN Photodiodes in Fiber Applications When using the MAX15059 to monitor APD or PIN photodiode currents in fiber applications, several issues must be addressed. In applications where the photodiode must be fully depleted, keep track of voltages budgeted for each component with respect to the available supply voltage(s). The current monitors require as much as 3.5V between BIAS and APD, which must be considered part of the overall voltage budget. Additional voltage margin can be created if a negative supply is used in place of a ground connection, as long as the overall voltage drop experienced by the MAX15059 is less than or equal to 76V. For this type of application, the MAX15059 is suggested so the output can be referenced to “true” ground and not the negative supply. The MAX15059’s output current can be referenced as desired with either a resistor to ground or a transimpedance amplifier. Take care to ensure that output voltage excursions do not interfere with the required margin between BIAS and MOUT. In many fiber applications, MOUT is connected directly to an ADC that operates from a supply voltage that is less than the voltage at BIAS. Connecting the MAX15059’s clamping diode output, CLAMP, to the ADC power supply helps avoid damage to the ADC. Without this protection, voltages can develop at MOUT that might destroy the ADC. This protection is less critical when MOUT is connected directly to subsequent transimpedance amplifiers (linear or logarithmic) that have low-impedance, near-groundreferenced inputs. If a transimpedance amp is used on the low side of the photodiode, its voltage drop must also be considered. Leakage from the clamping diode is most often insignificant over nominal operating conditions, but grows with temperature. To maintain low levels of wideband noise, lowpass filtering the output signal is suggested in applications where only DC measurements are required. Connect the filter capacitor at MOUT. Determining the required filtering components is straightforward, as the MAX15059 exhibits a very high output impedance of 5GI. In some applications where pilot tones are used to identify specific fiber channels, higher bandwidths are desired at MOUT to detect these tones. Consider the minimum and maximum currents to be detected, then consult the frequency response and noise typical operating curves. If the minimum current is too small, insufficient bandwidth could result, while too high a current could result in excessive noise across the desired bandwidth. Layout Considerations Careful PCB layout is critical to achieve low switching losses and clean and stable operation. Protect sensitive analog grounds by using a star ground configuration. Connect SGND and PGND together close to the device at the return terminal of the output bypass capacitor. Do not connect them together anywhere else. Keep all PCB traces as short as possible to reduce stray capacitance, trace resistance, and radiated noise. Ensure that the feedback connection to FB is short and direct. Route high-speed switching nodes away from the sensitive analog areas. Use an internal PCB layer for SGND as an EMI shield to keep radiated noise away from the device, feedback dividers, and analog bypass capacitors. Refer to the MAX15059 Evaluation Kit data sheet for a layout example. Chip Information PROCESS: BiCMOS Package Information For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE Document No. 16 TQFN-EP T1633-4 21-0136 14 ������������������������������������������������������������������������������������� 76V, 300mW Boost Converter and Current Monitor for APD Bias Applications REVISION NUMBER REVISION DATE DESCRIPTION 0 1/10 Initial release 1 3/10 Replaced five TOCs, added three TOCs, updated text PAGES CHANGED — 1, 2, 3, 5–8, 11 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2010 Maxim Integrated Products 15 Maxim is a registered trademark of Maxim Integrated Products, Inc. MAX15059 Revision History