MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current General Description The MAX16936 is a 2.5A current-mode step-down converter with integrated high-side and low-side MOSFETs designed to operate with an external Schottky diode for better efficiency. The low-side MOSFET enables fixed-frequency forced-PWM (FPWM) operation under light-load applications. The device operates with input voltages from 3.5V to 36V, while using only 28FA quiescent current at no load. The switching frequency is resistor programmable from 220kHz to 2.2MHz and can be synchronized to an external clock. The MAX16936’s output voltage is available as 5V/3.3V fixed or adjustable from 1V to 10V. The wide input voltage range along with its ability to operate at 98% duty cycle during undervoltage transients make the MAX16936 ideal for automotive and industrial applications. Under light-load applications, the FSYNC logic input allows the MAX16936 to either operate in skip mode for reduced current consumption or fixed-frequency FPWM mode to eliminate frequency variation to minimize EMI. Fixed-frequency FPWM mode is extremely useful for power supplies designed for RF transceivers where tight emission control is necessary. Protection features include cycle-by-cycle current limit and thermal shutdown with automatic recovery. Additional features include a powergood monitor to ease power-supply sequencing and a 180N out-of-phase clock output relative to the internal oscillator at SYNCOUT to create cascaded power supplies with multiple MAX16936s. The MAX16936 operates over the -40NC to +125NC automotive temperature range and is available in 16-pin TSSOP-EP and 5mm x 5mm, 16-pin TQFN-EP packages. Features SWide 3.5V to 36V Input Voltage Range S42V Load Dump Protection SEnhanced Current-Mode Control Architecture SFixed Output Voltage with ±2% Accuracy (5V/3.3V) or Externally Resistor Adjustable (1V to 10V) S220kHz to 2.2MHz Switching Frequency with Three Operation Modes 28µA Ultra-Low Quiescent Current Skip Mode Forced Fixed-Frequency Operation External Frequency Synchronization SSpread-Spectrum Frequency Modulation SAutomatic LX Slew Rate Adjustment for Optimum Efficiency Across Operating Frequency Range S180° Out-of-Phase Clock Output at SYNCOUT SLow-BOM-Count Current-Mode Control Architecture SPower-Good Output SEnable Input Compatible from 3.3V Logic Level to 42V SThermal Shutdown Protection S-40°C to +125°C Automotive Temperature Range SAEC-Q100 Qualified Applications Point of Load Applications Distributed DC Power Systems Navigation and Radio Head Units Ordering Information/Selector Guide appears at end of data sheet. Typical Application Circuit appears at end of data sheet. For related parts and recommended products to use with this part, refer to: www.maximintegrated.com/MAX16936.related For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com. 19-6626; Rev 1; 4/13 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current ABSOLUTE MAXIMUM RATINGS SUP, SUPSW, LX, EN to PGND.............................-0.3V to +42V SUP to SUPSW......................................................-0.3V to +0.3V BIAS to AGND..........................................................-0.3V to +6V SYNCOUT, FOSC, COMP, FSYNC, PGOOD, FB to AGND......................... -0.3V to (VBIAS + 0.3V) OUT to PGND.........................................................-0.3V to +12V BST to LX..................................................................-0.3V to +6V AGND to PGND....................................................-0.3V to + 0.3V LX Continuous RMS Current....................................................3A Output Short-Circuit Duration.....................................Continuous Continuous Power Dissipation (TA = +70NC)* TSSOP (derate 26.1mw/NC above +70NC)..............2088.8mW TQFN (derate 28.6mw/NC above +70NC)................2285.7mW Operating Temperature Range......................... -40NC to +125NC Junction Temperature......................................................+150NC Storage Temperature Range............................. -65NC to +150NC Lead Temperature (soldering, 10s).................................+300NC Soldering Temperature (reflow).......................................+260NC *As per JEDEC51 standard (multilayer board). 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. PACKAGE THERMAL CHARACTERISTICS (Note 1) TSSOP TQFN Junction-to-Ambient Thermal Resistance (BJA)........38.3NC/W Junction-to-Case Thermal Resistance (BJC)..................3NC/W Junction-to-Ambient Thermal Resistance (BJA)........... 35NC/W Junction-to-Case Thermal Resistance (BJC)...............2.7NC/W Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial. ELECTRICAL CHARACTERISTICS (VSUP = VSUPSW = 14V, VEN = 14V, L1 = 2.2FH, CIN = 4.7FF, COUT = 22FF, CBIAS = 1FF, CBST = 0.1FF, RFOSC = 12kI, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.) PARAMETER Supply Voltage Load Dump Event Supply Voltage Supply Current SYMBOL CONDITIONS VSUP, VSUPSW VSUP_LD ISUP_STANDBY MIN TYP 3.5 tLD < 1s MAX UNITS 36 V 42 V Standby mode, no load, VOUT = 5V, VFSYNC = 0V 28 40 FA 5 8 FA Shutdown Supply Current ISHDN VEN = 0V BIAS Regulator Voltage VBIAS VSUP = VSUPSW = 6V to 42V, IBIAS = 0 to 10mA 4.7 5 5.4 V VBIAS rising 2.95 3.15 3.40 V 450 650 mV BIAS Undervoltage Lockout VUVBIAS BIAS Undervoltage Lockout Hysteresis Thermal Shutdown Threshold +175 NC Thermal Shutdown Threshold Hysteresis 15 NC OUTPUT VOLTAGE (OUT) FPWM Mode Output Voltage Maxim Integrated VOUT VFB = VBIAS, 6V < VSUPSW < 36V, fixed-frequency mode (Note 2) 4.9 5 5.1 V 2 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current ELECTRICAL CHARACTERISTICS (continued) (VSUP = VSUPSW = 14V, VEN = 14V, L1 = 2.2FH, CIN = 4.7FF, COUT = 22FF, CBIAS = 1FF, CBST = 0.1FF, RFOSC = 12kI, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.) PARAMETER Skip Mode Output Voltage SYMBOL CONDITIONS MIN VOUT_SKIP No load, VFB = VBIAS, skip mode (Note 3) 4.9 TYP MAX 5 5.15 UNITS V Load Regulation VFB = VBIAS, 300mA < ILOAD < 2.5A 0.5 % Line Regulation VFB = VBIAS, 6V < VSUPSW < 36V 0.02 %/V BST Input Current IBST_ON High-side MOSFET on, VBST - VLX = 5V IBST_OFF High-side MOSFET off, VBST - VLX = 5V, TA = +25°C LX Current Limit ILX LX Rise Time Skip Mode Current Threshold ISKIP_TH TA = +25°C RON_H 150 Low-Side Switch Leakage Current 3.75 2 mA 5 FA 4.5 A 300 ns 400 mA 100 220 mI 1 3 FA 1.5 3 I 1 FA 20 100 nA 1.0 1.015 V fOSC Q6% ILX = 1A, VBIAS = 5V High-side MOSFET off, VSUP = 36V, VLX = 0V, TA = +25NC RON_L 1.5 4 Spread spectrum enabled High-Side Switch Leakage Current Low-Side Switch On-Resistance 3 RFOSC = 12kW Spread Spectrum High-Side Switch On-Resistance Peak inductor current 1 ILX = 0.2A, VBIAS = 5V VLX = 36V, TA = +25NC TRANSCONDUCTANCE AMPLIFIER (COMP) FB Input Current IFB FB Regulation Voltage VFB FB Line Regulation DVLINE Transconductance (from FB to COMP) gm Minimum On-Time tON_MIN Maximum Duty Cycle DCMAX FB connected to an external resistor divider, 6V < VSUPSW < 36V (Note 4) 0.99 6V < VSUPSW < 36V 0.02 %/V VFB = 1V, VBIAS = 5V 700 FS (Note 3) 80 ns 98 % OSCILLATOR FREQUENCY Oscillator Frequency RFOSC = 73.2kI 340 400 460 kHz RFOSC = 12kI 2.0 2.2 2.4 MHz EXTERNAL CLOCK INPUT (FSYNC) External Input Clock Acquisition time tFSYNC External Input Clock Frequency External Input Clock High Threshold Maxim Integrated VFSYNC_HI 1 RFOSC = 12kI (Note 5) 1.8 VFSYNC rising 1.4 Cycles 2.6 Hz V 3 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current ELECTRICAL CHARACTERISTICS (continued) (VSUP = VSUPSW = 14V, VEN = 14V, L1 = 2.2FH, CIN = 4.7FF, COUT = 22FF, CBIAS = 1FF, CBST = 0.1FF, RFOSC = 12kI, TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.) PARAMETER External Input Clock Low Threshold Soft-Start Time SYMBOL VFSYNC_LO CONDITIONS MIN TYP VFSYNC falling tSS 5.6 Enable Input High Threshold VEN_HI 2.4 Enable Input Low Threshold VEN_LO Enable Threshold Voltage Hysteresis VEN_HYS 8 MAX UNITS 0.4 V 12 ms ENABLE INPUT (EN) Enable Input Current IEN V 0.6 0.2 TA = +25NC V 0.1 1 FA POWER GOOD (PGOOD) PGOOD Switching Level VTH_RISING VFB rising, VPGOOD = high 93 95 97 VTH_FALLING VFB falling, VPGOOD =low 90 92 94 10 25 PGOOD Debounce Time %VFB 50 Fs 0.4 V 1 FA ISINK = 5mA 0.4 V SYNCOUT Leakage Current TA = +25NC 1 FA FSYNC Leakage Current TA = +25NC 1 FA PGOOD Output Low Voltage ISINK = 5mA PGOOD Leakage Current VOUT in regulation, TA = +25NC SYNCOUT Low Voltage OVERVOLTAGE PROTECTION Overvoltage Protection Threshold Note Note Note Note VOUT rising (monitored at FB pin) 107 VOUT falling (monitored at FB pin) 105 % 2: Device not in dropout condition. 3: Guaranteed by design; not production tested. 4: FB regulation voltage is 1%, 1.01V (max), for -40°C < TA < +105°C. 5: Contact the factory for SYNC frequency outside the specified range. Maxim Integrated 4 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current Typical Operating Characteristics (VSUP = VSUPSW = 14V, VEN = 14V, VOUT = 5V, VFYSNC = 0V, RFOSC = 12kI, TA = +25NC, unless otherwise noted.) 50 5V 40 PWM MODE 5V 60 40 4.98 4.96 4.94 10 10 4.92 0 0 0.1 10 0.001 2.26 4.98 433 2.22 2.20 2.18 430 429 427 426 4.90 2.10 2.0 2.5 425 0 0.5 ILOAD (A) 2.5 2.16 2.12 2.08 VOUT = 3.3V -40 -25 -10 5 20 35 50 65 80 95 110 125 Maxim Integrated 0.5 1.0 2.00 1.50 1.25 1.00 0.75 0.50 45 40 35 30 25 20 5V/2.2MHz SKIP MODE 15 0.25 72 RFOSC (kΩ) 2.5 SUPPLY CURRENT vs. SUPPLY VOLTAGE 1.75 42 2.0 50 MAX16936 toc08 2.25 12 1.5 ILOAD (A) 0 2.00 TEMPERATURE (°C) 0 SUPPLY CURRENT (µA) VOUT = 5V 2.20 2.04 2.0 2.50 SWITCHING FREQUENCY (MHz) 2.24 1.5 SWITCHING FREQUENCY vs. RFOSC MAX16936 toc07 VIN = 14V, PWM MODE 1.0 ILOAD (A) FSW vs. TEMPERATURE 2.28 VOUT = 3.3V 428 VOUT = 3.3V 2.12 1.5 2.5 431 2.14 1.0 2.0 VOUT = 5V 432 4.92 0.5 1.5 VIN = 14V, PWM MODE 434 VOUT = 5V 2.16 2.2MHz 0 1.0 FSW vs. LOAD CURRENT 435 FSW (MHz) FSW (MHz) 5.00 4.94 VIN = 14V, PWM MODE 2.28 2.24 400kHz 4.96 0.5 ILOAD (A) MAX16936 toc05 5.06 5.02 0 10 FSW vs. LOAD CURRENT 2.30 MAX16936 toc04 VOUT = 5V, VIN = 14V PWM MODE 5.04 0.1 LOAD CURRENT (A) VOUT LOAD REGULATION 5.08 2.2MHz 4.90 0 LOAD CURRENT (A) 5.10 MAX16936 toc03 5.00 20 0.001 400kHz 5.02 30 0 VOUT (V) PWM MODE 20 30 FSW (MHz) 5.04 3.3V 3.3V 50 5.06 MAX16936 toc09 3.3V 5V 70 VOUT = 5V, VIN = 14V SKIP MODE 5.08 MAX16936 toc06 3.3V 60 SKIP MODE 80 EFFICIENCY (%) 70 fSW = 400kHz, VIN = 14V 90 5.10 VOUT (V) SKIP MODE 5V 80 EFFICIENCY (%) MAX16936 toc01 fSW = 2.2MHz, VIN = 14V 90 VOUT LOAD REGULATION EFFICIENCY vs. LOAD CURRENT 100 MAX16936 toc02 EFFICIENCY vs. LOAD CURRENT 100 102 132 10 6 16 26 36 SUPPLY VOLTAGE (V) 5 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current Typical Operating Characteristics (continued) (VSUP = VSUPSW = 14V, VEN = 14V, VOUT = 5V, VFYSNC = 0V, RFOSC = 12kI, TA = +25NC, unless otherwise noted.) 4.99 7 5 4 3 5.02 5V/2.2MHz SKIP MODE 0 6 5.05 12 18 24 30 36 5.00 4.98 4.96 4.94 VIN = 14V, PWM MODE 4.92 4.90 6 12 18 24 30 36 42 VIN (V) SUPPLY VOLTAGE (V) TEMPERATURE (°C) VOUT vs. VIN FULL-LOAD STARTUP BEHAVIOR SLOW VIN RAMP BEHAVIOR MAX16936 toc14 5V/400kHz PWM MODE ILOAD = 0A 5.03 4.96 4.95 4.94 -40 -25 -10 5 20 35 50 65 80 95 110 125 MAX16936 toc13 1 4.97 4.93 4.92 4.91 4.90 MAX16936 toc12 5.04 VOUT (V) VBIAS (V) 6 5V/2.2MHz PWM MODE ILOAD = 0A 5.06 4.98 2 VOUT (V) ILOAD = 0A 5.01 5.00 5.08 MAX16936 toc11 8 SUPPLY CURRENT (µA) 5.02 MAX16936 toc10 9 VOUT vs. VIN VBIAS vs. TEMPERATURE SHDN CURRENT vs. SUPPLY VOLTAGE 10 MAX16936 toc15 10V/div 0V 5V/div 0V VIN VOUT 5.01 VIN 0V VOUT 0V 5V/div 1A/div 4.99 10V/div 5V/div 0A VPGOOD 5V/div ILOAD 4.97 VPGOOD 0V 2A/div 0V ILOAD 4.95 6 12 18 24 30 2ms 36 0A 4s VIN (V) SLOW VIN RAMP BEHAVIOR SYNC FUNCTION MAX16936 toc16 DIPS AND DROPS TEST MAX16936 toc17 MAX16936 toc18 10V/div 10V/div VIN 0V VIN 5V/div VLX 5V/div 0V VPGOOD VFSYNC 2V/div 0V 10V/div VLX 0V 2A/div ILOAD Maxim Integrated 5V/div VPGOOD 0A 4s 0V 5V/div VOUT 0V VOUT 5V/2.2MHz 5V/div 200ns 0V 10ms 6 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current Typical Operating Characteristics (continued) (VSUP = VSUPSW = 14V, VEN = 14V, VOUT = 5V, VFYSNC = 0V, RFOSC = 12kI, TA = +25NC, unless otherwise noted.) COLD CRANK LOAD DUMP MAX16936 toc19 MAX16936 toc20 VIN 2V/div VOUT 2V/div VPGOOD 10V/div VIN 0V VOUT 5V/div 2V/div 0V 0V 400ms 100ms SHORT CIRCUIT IN PWM MODE LOAD TRANSIENT (PWM MODE) MAX16936 toc22 MAX16936 toc21 FSW = 2.2MHz VOUT = 5V VOUT (AC-COUPLED) 2V/div 200mV/div VOUT 0V INDUCTOR CURRENT 0A 2A/div 2A/div LOAD CURRENT 0A 5V/div PGOOD 100µs Maxim Integrated 0V 10ms 7 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current LX SUPSW SUP EN 16 15 14 13 12 11 10 BST EN SUPSW SUP LX LX PGND TOP VIEW PGOOD Pin Configurations 12 11 10 9 9 LX 13 PGND 14 MAX16936 MAXX16936 PGOOD 15 SYNCOUT 16 7 8 1 2 3 FSYNC FOSC OUT FOSC 6 BIAS FSYNC 5 AGND SYNCOUT 4 COMP 3 FB 2 OUT 1 EP + BST 7 AGND 6 BIAS 5 COMP 4 FB EP + 8 TQFN TSSOP Pin Descriptions PIN NAME FUNCTION TSSOP TQFN 1 16 SYNCOUT 2 1 FSYNC Synchronization Input. The device synchronizes to an external signal applied to FSYNC. Connect FSYNC to AGND to enable skip mode operation. Connect to BIAS or to an external clock to enable fixed-frequency forced PWM mode operation. 3 2 FOSC Resistor-Programmable Switching Frequency Setting Control Input. Connect a resistor from FOSC to AGND to set the switching frequency. 4 3 OUT Switching Regulator Output. OUT also provides power to the internal circuitry when the output voltage of the converter is set between 3V to 5V during standby mode. 5 4 FB Feedback Input. Connect an external resistive divider from OUT to FB and AGND to set the output voltage. Connect to BIAS to set the output voltage to 5V. 6 5 COMP 7 6 BIAS 8 7 AGND 9 8 BST Maxim Integrated Open-Drain Clock Output. SYNCOUT outputs 180N out-of-phase signal relative to the internal oscillator. Connect to OUT with a resistor between 100I and 1kW for 2MHz operation. For low frequency operation, use a resistor between 1kW and 10kW. Error Amplifier Output. Connect an RC network from COMP to AGND for stable operation. See the Compensation Network section for more information. Linear Regulator Output. BIAS powers up the internal circuitry. Bypass with a 1FF capacitor to ground. Analog Ground High-Side Driver Supply. Connect a 0.22FF capacitor between LX and BST for proper operation. 8 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current Pin Descriptions (continued) PIN NAME FUNCTION 9 EN SUP Voltage Compatible Enable Input. Drive EN low to disable the device. Drive EN high to enable the device. 11 10 SUP Voltage Supply Input. SUP powers up the internal linear regulator. Bypass SUP to PGND with a 4.7FF ceramic capacitor. 12 11 SUPSW 13, 14 12, 13 LX 15 14 PGND 16 15 PGOOD — — EP TSSOP TQFN 10 Internal High-Side Switch Supply Input. SUPSW provides power to the internal switch. Bypass SUPSW to PGND with 0.1FF and 4.7FF ceramic capacitors. Inductor Switching Node. Connect a Schottky diode between LX and AGND. Power Ground Open-Drain, Active-Low Reset Output. PGOOD asserts when VOUT is above 95% regulation point. PGOOD goes low when VOUT is below 92% regulation point. Exposed Pad. Connect EP to a large-area contiguous copper ground plane for effective power dissipation. Do not use as the only IC ground connection. EP must be connected to PGND. Detailed Description The MAX16936 is a 2.5A current-mode step-down converter with integrated high-side and low-side MOSFETs designed to operate with an external Schottky diode for better efficiency. The low-side MOSFET enables fixedfrequency forced-PWM (FPWM) operation under light-load applications. The device operates with input voltages from 3.5V to 36V, while using only 28FA quiescent current at no load. The switching frequency is resistor programmable from 220kHz to 2.2MHz and can be synchronized to an external clock. The output voltage is available as 5V/3.3V fixed or adjustable from 1V to 10V. The wide input voltage range along with its ability to operate at 98% duty cycle during undervoltage transients make the device ideal for automotive and industrial applications. Under light-load applications, the FSYNC logic input allows the device to either operate in skip mode for reduced current consumption or fixed-frequency FPWM mode to eliminate frequency variation to minimize EMI. Fixed frequency FPWM mode is extremely useful for power supplies designed for RF transceivers where tight emission control is necessary. Protection features include cycle-by-cycle current limit, overvoltage protection, and thermal shutdown with automatic recovery. Additional fea- Maxim Integrated tures include a power-good monitor to ease power-supply sequencing and a 180N out-of-phase clock output relative to the internal oscillator at SYNCOUT to create cascaded power supplies with multiple devices. Wide Input Voltage Range The device includes two separate supply inputs (SUP and SUPSW) specified for a wide 3.5V to 36V input voltage range. VSUP provides power to the device and VSUPSW provides power to the internal switch. When the device is operating with a 3.5V input supply, conditions such as cold crank can cause the voltage at SUP and SUPSW to drop below the programmed output voltage. Under such conditions, the device operates in a high duty-cycle mode to facilitate minimum dropout from input to output. Linear Regulator Output (BIAS) The device includes a 5V linear regulator (BIAS) that provides power to the internal circuit blocks. Connect a 1FF ceramic capacitor from BIAS to AGND. Power-Good Output (PGOOD) The device features an open-drain power-good output, PGOOD. PGOOD asserts when VOUT rises above 95% of its regulation voltage. PGOOD deasserts when VOUT drops below 92% of its regulation voltage. Connect PGOOD to BIAS with a 10kI resistor. 9 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current OUT COMP FB FBSW PGOOD FBOK EN SUP AON HVLDO BIAS SWITCH OVER BST SUPSW EAMP LOGIC PWM HSD REF LX CS SOFT START BIAS LSD MAX16936 PGND SLOPE COMP SYNCOUT OSC FSYNC FOSC AGND Figure 1. Internal Block Diagram Synchronization Input (FSYNC) System Enable (EN) FSYNC is a logic-level input useful for operating mode selection and frequency control. Connecting FSYNC to BIAS or to an external clock enables fixed-frequency FPWM operation. Connecting FSYNC to AGND enables skip mode operation. An enable control input (EN) activates the device from its low-power shutdown mode. EN is compatible with inputs from automotive battery level down to 3.5V. The high voltage compatibility allows EN to be connected to SUP, KEY/KL30, or the inhibit pin (INH) of a CAN transceiver. The external clock frequency at FSYNC can be higher or lower than the internal clock by 20%. Ensure the duty cycle of the external clock used has a minimum pulse width of 100ns. The device synchronizes to the external clock within one cycle. When the external clock signal at FSYNC is absent for more than two clock cycles, the device reverts back to the internal clock. EN turns on the internal regulator. Once VBIAS is above the internal lockout threshold, VUVL = 3.15V (typ), the controller activates and the output voltage ramps up within 8ms. Maxim Integrated A logic-low at EN shuts down the device. During shutdown, the internal linear regulator and gate drivers turn off. Shutdown is the lowest power state and reduces the quiescent current to 5FA (typ). Drive EN high to bring the device out of shutdown. 10 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current Spread-Spectrum Option The MAX16936 has an internal spread-spectrum option to optimize EMI performance. This is factory set and the S-version of the IC should be ordered. For spreadspectrum-enabled ICs, the operating frequency is varied ±6% centered on FOSC. The modulation signal is a triangular wave with a period of 110µs at 2.2MHz. Therefore, FOSC will ramp down 6% and back to 2.2MHz in 110µs and also ramp up 6% and back to 2.2MHz in 110µs. The cycle repeats. For operations at FOSC values other than 2.2MHz, the modulation signal scales proportionally, e.g., at 400kHz, the 110µs modulation period increases to 110µs x 2.2MHz/400MHz = 550µs. The internal spread spectrum is disabled if the IC is synced to an external clock. However, the IC does not filter the input clock and passes any modulation (including spread-spectrum) present on the driving external clock to the SYNCOUT pin. Automatic Slew-Rate Control on LX The MAX16936 has automatic slew-rate adjustment that optimizes the rise times on the internal HSFET gate drive to minimize EMI. The IC detects the internal clock frequency and adjusts the slew rate accordingly. When the user selects the external frequency setting resistor RFOSC such that the frequency is > 1.1MHz, the HSFET is turned on in 4ns (typ). When the frequency is < 1.1MHz the HSFET is turned on in 8ns (typ). This slew-rate control optimizes the rise time on LX node externally to minimize EMI while maintaining good efficiency. Internal Oscillator (FOSC) The switching frequency, fSW, is set by a resistor (RFOSC) connected from FOSC to AGND. See Figure 3 to select the correct RFOSC value for the desired switching frequency. For example, a 400kHz switching frequency is set with RFOSC = 732kI. Higher frequencies allow designs with lower inductor values and less output capacitance. Consequently, peak currents and I2R losses are lower at higher switching frequencies, but core losses, gate charge currents, and switching losses increase. Synchronizing Output (SYNCOUT) SYNCOUT is an open-drain output that outputs a 180N out-of-phase signal relative to the internal oscillator. down the internal bias regulator and the step-down controller, allowing the device to cool. The thermal sensor turns on the device again after the junction temperature cools by 15NC. Applications Information Setting the Output Voltage Connect FB to BIAS for a fixed +5V/+3.3 output voltage. To set the output to other voltages between 1V and 10V, connect a resistive divider from output (OUT) to FB to AGND (Figure 2). Use the following formula to determine the RFB2 of the resistive divider network: RFB2 = RTOTAL x VFB/VOUT where VFB = 1V, RTOTAL = selected total resistance of RFB1, RFB2 in ω, and VOUT is the desired output in volts. Calculate RFB1 (OUT to FB resistor) with the following equation: V = R FB1 R FB2 OUT − 1 VFB where VFB = 1V (see the Electrical Characteristics table). FPWM/Skip Modes The MAX16936 offers a pin selectable skip mode or fixed-frequency PWM mode option. The IC has an internal LS MOSFET that turns on when the FSYNC pin is connected to VBIAS or if there is a clock present on the FSYNC pin. This enables the fixed-frequency-forced PWM mode operation over the entire load range. This option allows the user to maintain fixed frequency over the entire load range in applications that require tight control on EMI. Even though the MAX16936 has an internal LS MOSFET for fixed-frequency operation, an external Schottky diode is still required to support the entire load range. If the FSYNC pin is connected to GND, the skip mode is enabled on the MAX16936. VOUT RFB1 MAX16936 FB RFB2 Overtemperature Protection Thermal-overload protection limits the total power dissipation in the device. When the junction temperature exceeds 175NC (typ), an internal thermal sensor shuts Maxim Integrated Figure 2. Adjustable Output Voltage Setting 11 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current In skip mode of operation, the converter’s switching frequency is load dependent. At higher load current, the switching frequency does not change and the operating mode is similar to the FPWM mode. Skip mode helps improve efficiency in light-load applications by allowing the converters to turn on the high-side switch only when the output voltage falls below a set threshold. As such, the converters do not switch MOSFETs on and off as often as is the case in the FPWM mode. Consequently, the gate charge and switching losses are much lower in skip mode. Inductor Selection Three key inductor parameters must be specified for operation with the device: inductance value (L), inductor saturation current (ISAT), and DC resistance (RDCR). To select inductance value, the ratio of inductor peak-topeak AC current to DC average current (LIR) must be selected first. A good compromise between size and loss is a 30% peak-to-peak ripple current to average current ratio (LIR = 0.3). The switching frequency, input voltage, output voltage, and selected LIR then determine the inductor value as follows: V (V − VOUT ) L = OUT SUP VSUP fSW IOUT LIR where VSUP, VOUT, and IOUT are typical values (so that efficiency is optimum for typical conditions). The switching frequency is set by RFOSC (see Figure 3). Input Capacitor The input filter capacitor reduces peak currents drawn from the power source and reduces noise and voltage ripple on the input caused by the circuit’s switching. The input capacitor RMS current requirement (IRMS) is defined by the following equation: IRMS = ILOAD(MAX) IRMS has a maximum value when the input voltage equals twice the output voltage (VSUP = 2VOUT), so IRMS(MAX) = ILOAD(MAX) /2. Choose an input capacitor that exhibits less than +10NC self-heating temperature rise at the RMS input current for optimal long-term reliability. The input voltage ripple is composed of DVQ (caused by the capacitor discharge) and DVESR (caused by the ESR of the capacitor). Use low-ESR ceramic capacitors with high ripple current capability at the input. Assume the contribution from the ESR and capacitor discharge equal to 50%. Calculate the input capacitance and ESR required for a specified input voltage ripple using the following equations: ESRIN = MAX16936 toc08 SWITCHING FREQUENCY (MHz) 2.25 2.00 1.50 2 − VOUT ) × VOUT (V ∆IL = SUP VSUP × fSW × L and: IOUT × D(1 − D) VOUT = and D ∆VQ × fSW VSUPSW where IOUT is the maximum output current and D is the duty cycle. 1.25 1.00 0.75 0.50 0.25 0 12 42 72 RFOSC (kΩ) Figure 3. Switching Frequency vs. RFOSC Maxim Integrated ∆IL where: = CIN 1.75 ∆VESR IOUT + SWITCHING FREQUENCY vs. RFOSC 2.50 VOUT (VSUP − VOUT ) VSUP 102 132 Output Capacitor The output filter capacitor must have low enough ESR to meet output ripple and load transient requirements. The output capacitance must be high enough to absorb the inductor energy while transitioning from full-load to no-load conditions without tripping the overvoltage fault protection. When using high-capacitance, low-ESR capacitors, the filter capacitor’s ESR dominates the output 12 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current voltage ripple. So the size of the output capacitor depends on the maximum ESR required to meet the output voltage ripple (VRIPPLE(P-P)) specifications: VOUT R1 VRIPPLE (P −P ) = ESR × ILOAD (MAX ) × LIR The actual capacitance value required relates to the physical size needed to achieve low ESR, as well as to the chemistry of the capacitor technology. Thus, the capacitor is usually selected by ESR and voltage rating rather than by capacitance value. When using low-capacity filter capacitors, such as ceramic capacitors, size is usually determined by the capacity needed to prevent voltage droop and voltage rise from causing problems during load transients. Generally, once enough capacitance is added to meet the overshoot requirement, undershoot at the rising load edge is no longer a problem. However, low capacity filter capacitors typically have high ESR zeros that can affect the overall stability. Rectifier Selection The device requires an external Schottky diode rectifier as a freewheeling diode when the device is configured for skip mode operation. Connect this rectifier close to the device using short leads and short PCB traces. In FPWM mode, the Schottky diode helps minimize efficiency losses by diverting the inductor current that would otherwise flow through the low-side MOSFET. Choose a rectifier with a voltage rating greater than the maximum expected input voltage, VSUPSW. Use a low forward-voltage-drop Schottky rectifier to limit the negative voltage at LX. Avoid higher than necessary reverse-voltage Schottky rectifiers that have higher forward-voltage drops. Compensation Network The device uses an internal transconductance error amplifier with its inverting input and its output available to the user for external frequency compensation. The output capacitor and compensation network determine the loop stability. The inductor and the output capacitor are chosen based on performance, size, and cost. Additionally, the compensation network optimizes the control-loop stability. The controller uses a current-mode control scheme that regulates the output voltage by forcing the required current through the external inductor. The device uses the voltage drop across the high-side MOSFET to sense inductor current. Current-mode control eliminates the double pole in the feedback loop caused by the inductor and output capacitor, resulting in a smaller phase shift Maxim Integrated COMP gm R2 VREF RC CF CC Figure 4. Compensation Network and requiring less elaborate error-amplifier compensation than voltage-mode control. Only a simple single-series resistor (RC) and capacitor (CC) are required to have a stable, high-bandwidth loop in applications where ceramic capacitors are used for output filtering (Figure 4). For other types of capacitors, due to the higher capacitance and ESR, the frequency of the zero created by the capacitance and ESR is lower than the desired closed-loop crossover frequency. To stabilize a nonceramic output capacitor loop, add another compensation capacitor (CF) from COMP to GND to cancel this ESR zero. The basic regulator loop is modeled as a power modulator, output feedback divider, and an error amplifier. The power modulator has a DC gain set by gm O RLOAD, with a pole and zero pair set by RLOAD, the output capacitor (COUT), and its ESR. The following equations allow to approximate the value for the gain of the power modulator (GAINMOD(dc)), neglecting the effect of the ramp stabilization. Ramp stabilization is necessary when the duty cycle is above 50% and is internally done for the device. GAINMOD ( dc = ) g m × R LOAD where RLOAD = VOUT /ILOUT(MAX) in I and gm = 35FS. In a current-mode step-down converter, the output capacitor, its ESR, and the load resistance introduce a pole at the following frequency: fpMOD = 1 π × C OUT × R LOAD 2 The output capacitor and its ESR also introduce a zero at: fzMOD = 1 2 π × ESR × C OUT 13 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current When COUT is composed of “n” identical capacitors in parallel, the resulting COUT = n O COUT(EACH), and ESR = ESR(EACH)/n. Note that the capacitor zero for a parallel combination of alike capacitors is the same as for an individual capacitor. The feedback voltage-divider has a gain of GAINFB = VFB / VOUT, where VFB is 1V (typ). The transconductance error amplifier has a DC gain of GAINEA(dc) = gm,EA O ROUT,EA, where gm,EA is the error amplifier transconductance, which is 700FS (typ), and ROUT,EA is the output resistance of the error amplifier 50MI. A dominant pole (fdpEA) is set by the compensation capacitor (CC) and the amplifier output resistance (ROUT,EA). A zero (fzEA) is set by the compensation resistor (RC) and the compensation capacitor (CC). There is an optional pole (fpEA) set by CF and RC to cancel the output capacitor ESR zero if it occurs near the cross over frequency (fC, where the loop gain equals 1 (0dB)). Thus: fdpEA = 1 2 π × C C × (R OUT,EA + R C ) fzEA = 1 2π × C C × R C fpEA = 1 2π × CF × R C The loop-gain crossover frequency (fC) should be set below 1/5th of the switching frequency and much higher than the power-modulator pole (fpMOD): f fpMOD << fC ≤ SW 5 The total loop gain as the product of the modulator gain, the feedback voltage-divider gain, and the error amplifier gain at fC should be equal to 1. So: GAINMOD(fC) × VFB × GAINEA(fC) = 1 VOUT = g m, EA × R C GAINEA(fC) fpMOD = GAIN MOD(fC) GAINMOD(dc) × fC Therefore: GAINMOD(fC) × Maxim Integrated VFB × g m,EA × R C = 1 VOUT Solving for RC: RC = VOUT g m,EA × VFB × GAINMOD(fC) Set the error-amplifier compensation zero formed by RC and CC (fzEA) at the fpMOD. Calculate the value of CC a follows: CC = 1 2 π × fpMOD × R C If fzMOD is less than 5 x fC, add a second capacitor, CF, from COMP to GND and set the compensation pole formed by RC and CF (fpEA) at the fzMOD. Calculate the value of CF as follows: CF = 1 2 π × fzMOD × R C As the load current decreases, the modulator pole also decreases; however, the modulator gain increases accordingly and the crossover frequency remains the same. PCB Layout Guidelines Careful PCB layout is critical to achieve low switching losses and clean, stable operation. Use a multilayer board whenever possible for better noise immunity and power dissipation. Follow these guidelines for good PCB layout: 1)Use a large contiguous copper plane under the IC package. Ensure that all heat-dissipating components have adequate cooling. The bottom pad of the IC must be soldered down to this copper plane for effective heat dissipation and for getting the full power out of the IC. Use multiple vias or a single large via in this plane for heat dissipation. 2)Isolate the power components and high current path from the sensitive analog circuitry. Doing so is essential to prevent any noise coupling into the analog signals. 3)Keep the high-current paths short, especially at the ground terminals. This practice is essential for stable, jitter-free operation. The high-current path composed of the input capacitor, high-side FET, inductor, and the output capacitor should be as short as possible. 4) Keep the power traces and load connections short. This practice is essential for high efficiency. Use thick copper PCBs (2oz vs. 1oz) to enhance full-load efficiency. 5) The analog signal lines should be routed away from the high-frequency planes. Doing so ensures integrity of sensitive signals feeding back into the IC. 14 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current 6) The ground connection for the analog and power section should be close to the IC. This keeps the ground current loops to a minimum. In cases where only one ground is used, enough isolation between analog return signals and high power signals must be maintained. Typical Application Circuit VBAT CIN1 CIN2 SUP LX FSYNC MAX16936 CCOMP1 1000pF RCOMP 20kI VOUT FOSC VBIAS RSYNCOUT 100I BIAS PGOOD SYNCOUT PGND Maxim Integrated COUT 22µF D1 VBIAS VOUT 5V AT 2.5A FB RFOSC 12kI CBIAS 1µF VOUT OUT COMP CCOMP2 12pF L1 2.2µH BST EN OSC SYNC PULSE CBST 0.22µF SUPSW RPGOOD 10kI POWER-GOOD OUTPUT 180° OUT-OF-PHASE OUTPUT AGND 15 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current Ordering Information/Selector Guide VOUT ADJUSTABLE (FB CONNECTED TO RESISTIVE DIVIDER) (V) FIXED (FB CONNECTED TO BIAS) (V) SPREAD SPECTRUM TEMP RANGE MAX16936RAUEA+* 1 to 10 5 Off -40°C to +125°C 16 TSSOP-EP** MAX16936RAUEA/V+* 1 to 10 5 Off -40°C to +125°C 16 TSSOP-EP** MAX16936RAUEB+* 1 to 10 3.3 Off -40°C to +125°C 16 TSSOP-EP** MAX16936RAUEB/V+* 1 to 10 3.3 Off -40°C to +125°C 16 TSSOP-EP** MAX16936SAUEA+* 1 to 10 5 On -40°C to +125°C 16 TSSOP-EP** MAX16936SAUEA/V+* 1 to 10 5 On -40°C to +125°C 16 TSSOP-EP** MAX16936SAUEB+* 1 to 10 3.3 On -40°C to +125°C 16 TSSOP-EP** MAX16936SAUEB/V+* 1 to 10 3.3 On -40°C to +125°C 16 TSSOP-EP** MAX16936RATEA+ 1 to 10 5 Off -40°C to +125°C 16 TQFN-EP** MAX16936RATEA/V+ 1 to 10 5 Off -40°C to +125°C 16 TQFN-EP** MAX16936RATEB+* 1 to 10 3.3 Off -40°C to +125°C 16 TQFN-EP** MAX16936RATEB/V+* 1 to 10 3.3 Off -40°C to +125°C 16 TQFN-EP** MAX16936SATEA+* 1 to 10 5 On -40°C to +125°C 16 TQFN-EP** MAX16936SATEA/V+* 1 to 10 5 On -40°C to +125°C 16 TQFN-EP** MAX16936SATEB+* 1 to 10 3.3 On -40°C to +125°C 16 TQFN-EP** MAX16936SATEB/V+* 1 to 10 3.3 On -40°C to +125°C 16 TQFN-EP** PART PIN-PACKAGE /V denotes an automotive qualified part. +Denotes a lead(Pb)-free/RoHS-compliant package. *Future product—contact factory for availability. **EP = Exposed pad. Chip Information PROCESS: BiCMOS Maxim Integrated Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.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 OUTLINE NO. LAND PATTERN NO. 16 TSSOP-EP U16E+3 21-0108 90-0120 16 TQFN-EP T1655-4 21-0140 90-0121 16 MAX16936 36V, 220kHz to 2.2MHz Step-Down Converter with 28µA Quiescent Current Revision History REVISION NUMBER REVISION DATE 0 3/13 Initial release — 1 4/13 Added non-automotive OPNs to Ordering Information 16 DESCRIPTION PAGES CHANGED Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000 © 2013 Maxim Integrated Products, Inc. 17 Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.