EVALUATION KIT AVAILABLE MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters General Description The MAX16993 power-management integrated circuit (PMIC) is a 2.1MHz, multichannel, DC-DC converter designed for automotive applications. The device integrates three supplies in a small footprint. The device includes one high-voltage step-down controller (OUT1) designed to run directly from a car battery and two lowvoltage step-down converters (OUT2/OUT3) cascaded from OUT1. Under no-load conditions, the MAX16993 consumes only 30µA of quiescent current, making it ideal for automotive applications. The high-voltage synchronous step-down DC-DC controller (OUT1) operates from a voltage up to 36V continuous and is protected from load-dump transients up to 42V. There is a pin-selectable frequency option of either 2.1MHz or a factoryset frequency for 1.05MHz, 525kHz, 420kHz, or 350kHz. The low-voltage, synchronous step-down DC-DC converters run directly from OUT1 and can supply output currents up to 3A. The device provides a spread-spectrum enable input (SSEN) to provide quick improvement in electromagnetic interference when needed. There is also a SYNC I/O for providing either an input to synchronize to an external clock source or an output of the internally generated clock (see the Selector Guide). The device includes overtemperature shutdown and overcurrent limiting. The device also includes individual RESET_ outputs and individual enable inputs. The individual RESET_ outputs provide voltage monitoring for all output channels. The MAX16993 is available in a 32-pin side-wettable TQFNEP package and is specified for operation over the -40°C to +125°C automotive temperature range. Applications ● Automotive ● Industrial 19-6684; Rev 0; 5/13 Features ● High-Voltage DC-DC Controller • 3.5V to 36V Operating Supply Voltage • 42V Load-Dump Protection • Output Voltage: Pin Selectable, Fixed or Resistor-Divider Adjustable • 350kHz to 2.1MHz Operation • 30μA Quiescent Current with DC-DC Controller Enabled ● Dual High-Efficiency 2.1MHz DC-DC Converters • • • • • Run Directly from OUT1 3A Integrated FETs 0.8V to 3.95V Output Voltage Fixed or Resistor-Divider-Adjustable Output Voltage 180° Out-of-Phase Operation ● Individual Enable Inputs ● Individual RESET_ Outputs ● Thermal-Warning Indication Output ● Forced-PWM and Skip Modes ● Overtemperature and Short-Circuit Protection ● 32-Pin (5mm x 5mm x 0.8mm) Side-Wettable TQFN-EP ● -40°C to +125°C Operating Temperature Range Ordering Information and Selector Guide appear at end of data sheet. MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Absolute Maximum Ratings VSUP, EN1 to GND................................................-0.3V to +45V PV_ to GND..........................................................-0.3V to +6.0V PV_ to GND..........................................................-0.3V to +6.0V PV2 to GND, PV2 to PGND2................................-0.3V to +6.0V PV3 to GND, PV3 to PGND3................................-0.3V to +6.0V PGND2–PGND3 to GND......................................-0.3V to +0.3V LX1 to GND................................................-6.0V to VSUP + 6.0V BST1 to LX1..........................................................-0.3V to +6.0V DH1 to LX1 ................................................-0.3V to BST1 + 0.3V BIAS to GND.........................................................-0.3V to +6.0V DL1 to GND..................................................-0.3V to PV1 + 0.3V LX2 to PGND2.............................................-0.3V to PV2 + 0.3V LX3 to PGND3.............................................-0.3V to PV3 + 0.3V OUT1, CS1, OUT2, OUT3 to GND.......................-0.3V to +6.0V FB1, EN2, EN3 to GND........................................-0.3V to +6.0V RESET_, ERR to GND..........................................-0.3V to +6.0V CS1 to OUT1.........................................................-0.3V to +0.3V CSEL1, SYNC, SSEN to GND..............................-0.3V to +6.0V COMP1 to GND..............................................-0.3V to PV + 0.3V LX2, LX3 Output Short-Circuit Duration.....................Continuous Continuous Power Dissipation (TA = +70ºC) Side-Wettable TQFN (derate 27mW/ºC above +70ºC)................................2160mW Operating Temperature Range...........................-40ºC to +125°C Junction Temperature.......................................................+150°C Storage Temperature Range..............................-65ºC to +150°C Lead Temperature (soldering, 10s).................................. +300°C Soldering Temperature (reflow)........................................+260°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Package Thermal Characteristics (Note 1) Side-Wettable TQFN Junction-to-Ambient Thermal Resistance (θJA).......... 37°C/W Junction-to-Case Thermal Resistance (θJC)................. 2.8°C/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 = 14V, VPV1 = VBIAS, VPV2 = VPV3 = VOUT1; TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C under normal conditions, unless otherwise noted.) (Note 2) PARAMETER SYMBOL Supply Voltage Startup Threshold VSUP,STARTUP Supply Voltage Range VSUP Supply Current ISUP Oscillator Frequency fSW CONDITIONS MIN TYP MAX UNITS VSUP rising 4.25 4.5 4.75 V Normal operation, after Buck 1 startup 3.5 36 V VEN1 = VEN2 = VEN3 = 0V 4 15 VEN1 = 5V, VEN2 = VEN3 = 0V (no load) 20 40 2.1 2.2 MHz 2.4 MHz 2.0 SYNC Input Frequency Range 1.7 Spread-Spectrum Range BIAS Regulator Voltage PV_ POR www.maximintegrated.com VBIAS VSSEN = VGND 0 VSSEN = VBIAS +6 % 6V ≤ VSUP ≤ 42V, no switchover 4.6 5.0 5.4 VBIAS falling 2.5 2.7 2.9 Hysteresis 0.45 µA V V Maxim Integrated │ 2 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Electrical Characteristics (continued) (VSUP = 14V, VPV1 = VBIAS, VPV2 = VPV3 = VOUT1; TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C under normal conditions, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS OUT1: HIGH-VOLTAGE SYNCHRONOUS STEP-DOWN DC-DC CONTROLLER OUT1 Switching Frequency Voltage fSW1 VOUT1 FB1 Regulation Voltage Internally generated (see the Selector Guide) Fixed option (see the Selector Guide) VCSEL1 = VGND 2100 VCSEL1 = VBIAS (factory option) 1050 VCSEL1 = VBIAS (factory option) 525 VCSEL1 = VBIAS (factory option) 420 VCSEL1 = VBIAS (factory option) 350 VFB1 = VGND 3.3 VFB1 = VBIAS (factory option) 5.0 VFB1 = VBIAS (factory option) 3.15 Adjustable option (see the Selector Guide) Error Amplifier Transconductance gMEA Voltage Accuracy VOUT1 5.5V ≤ VSUP ≤ 18V, 0 < VLIM1 < 75mV, PWM mode kHz V 0.985 1.0 1.019 V 300 700 1200 µS +2.5 % -2.0 DC Load Regulation PWM mode 0.02 %/A DC Line Regulation PWM mode 0.03 %/V OUT1 Discharge Resistance VEN1 = VGND or VSUP 100 200 High-Side Output Drive Resistance VDH1 rising, IDH1 = 100mA 2 4 VDH1 falling, IDH1 = 100mA 1 4 Low-Side Output Drive Resistance VDL1 rising, IDL1 = 100mA 2.5 5 VDL1 falling, IDL1 = 100mA 1.5 3 Ω Ω Ω Output Current-Limit Threshold VLIM1 CSI – OUT1 100 120 150 mV Skip Current Threshold ISKIP CS1 – OUT1, no load 10 35 60 mV Soft-Start Ramp Time LX_ Leakage Current VLX1 = VSUP Duty-Cycle Range PWM mode Minimum On-Time OUT1 OV Threshold www.maximintegrated.com 107 4 ms 0.01 µA 97.2 % 60 75 ns 110 113 % Maxim Integrated │ 3 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Electrical Characteristics (continued) (VSUP = 14V, VPV1 = VBIAS, VPV2 = VPV3 = VOUT1; TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C under normal conditions, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 5.5 V 5 µA OUT2 AND OUT3: LOW-VOLTAGE SYNCHRONOUS STEP-DOWN DC-DC CONVERTERS Supply Voltage Range VSUP 2.7 Supply Current IPV_ VEN_ = 5V, no load VOUT 0A ≤ ILOAD ≤ IMAX, PWM mode -3.0 Feedback-Voltage Accuracy Adjustable mode, IOUT2 = 0mA 0.806 0.815 Load Regulation 0A ≤ ILOAD ≤ IMAX (PWM mode) -1.5 -1.0 LX_ On-Resistance High ILX_ = -800mA 70 110 mΩ LX_ On-Resistance Low ILX_ = 800mA 50 90 mΩ 0.1 Skip Mode Peak Current Voltage Accuracy Current-Limit Threshold LX_ Rise/Fall Time 0.2 x ILMAX ILMAX IMAX = 3.0A option (see the Selector Guide) 5.0 5.6 IMAX = 1.5A option (see the Selector Guide) 2.5 3.0 0.824 %/A A 4 ns Soft-Start Ramp Time 2.5 ms LX_ Leakage Current 0.01 µA Duty-Cycle Range PV2 = PV3 = 3.3V, IOUT_ = 2A mA +3.0 PWM mode 15 LX_ Discharge Resistance RESET_ Reset Threshold OUT1 Active Timeout Period OUT2, OUT3 Active Timeout Period Output Low Level Propagation Time www.maximintegrated.com 100 % 22 48 Ω % Rising (relative to nominal output voltage) 92 95 98 Falling (relative to nominal output voltage) 90 92 95 See the Selector Guide (16,384 clocks) 7.8 See the Selector Guide (8192 clocks) 3.9 See the Selector Guide (4096 clocks) 1.9 See the Selector Guide (256 clocks) 0.1 See the Selector Guide (16,384 clocks) 7.8 See the Selector Guide (8192 clocks) 3.9 See the Selector Guide (4096 clocks) 1.9 See the Selector Guide (256 clocks) 0.1 ISINK = 3mA 0.1 0.2 V ms ms OUT1, 5% below threshold 5 10 20 µs OUT2/OUT3, 5% below threshold 2 4 8 µs Maxim Integrated │ 4 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Electrical Characteristics (continued) (VSUP = 14V, VPV1 = VBIAS, VPV2 = VPV3 = VOUT1; TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C under normal conditions, unless otherwise noted.) (Note 2) ERR PARAMETER Output Low Level SYMBOL CONDITIONS MIN ISINK = 3mA TYP MAX UNITS 0.1 0.2 V THERMAL OVERLOAD Thermal-Warning Temperature +150 °C Thermal-Shutdown Temperature +170 °C Thermal-Shutdown Hysteresis 15 °C ENABLE INPUTS (EN_) Input High VEN_ rising 1.6 Hysteresis EN Input Current 1.8 2.0 0.2 VEN_ = 5V 0.5 Input High SYNC input option (see the Selector Guide) 1.8 Input Low SYNC input option (see the Selector Guide) Input Current SYNC input option (see the Selector Guide); VSYNC = 5V Output High Level SYNC output option (see the Selector Guide); VPV = 5V, ISINK = 1mA Output Low Level SYNC output option (see the Selector Guide); ISINK = 1mA 1.0 V V 2.0 µA SYNCHRONIZATION I/O (SYNC) V 50 4.9 V 80 µA 4.98 0.02 Pulldown Resistance 0.8 V 0.1 100 V kΩ LOGIC INPUTS (CSEL1, SSEN) Input High 1.4 Input Low Input Current TA = +25°C V 0.5 V 2 µA Note 2: All units are 100% production tested at TA = +25°C. All temperature limits are guaranteed by design. Note 3: Guaranteed by design. Not production tested. www.maximintegrated.com Maxim Integrated │ 5 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Typical Operating Characteristics (VSUP = 14V, TA = +25°C, unless otherwise noted) 40 30 PWM MODE 5.015 TA = +25ºC 5.010 5.005 4.990 0 1.00E-06 1.00E-04 1.00E-02 1.00E+00 0 1 2 3 TA = +25ºC 100.1 100.0 99.9 99.8 TA = -40ºC 99.7 15 20 25 30 35 100.0 99.8 99.6 99.0 40 IOUT1 = 3.75A 5.010 5.005 5.000 4.995 4.990 0 5 10 15 20 25 100.3 100.1 50 100 TEMPERATURE (ºC) www.maximintegrated.com 30 35 99.9 99.5 40 BUCK 2 EFFICIENCY 90 80 70 150 60 50 PWM MODE 40 30 0 1.00E-06 3.19 0 5 10 15 20 fSW = 2.1MHz, VSUP = 14V, VPV2 = 5.0V, VOUT2 = 3.15V 1.00E-04 25 30 35 40 1.00E-02 IOUT3 (A) 1.00E+00 BUCK 2 LOAD REGULATION (PWM MODE) VPV2 = 5.0V, IMAX = 1.5A, VOUT2 = 3.15V 3.18 3.17 3.16 SKIP MODE 10 0 6 VSUP (V) 20 4.985 5 99.7 100 EFFICIENCY (%) VOUT1 (V) 5.015 4 100.5 VSUP (V) VOUT1 vs. TEMPERATURE -50 3 100.7 VOUT2 (V) 10 2 VOUT1 = 3.3V 100.9 99.4 5.020 4.980 MAX16993 toc05 100.2 MAX16993 toc07 5.025 VOUT1 = 5.0V MAX16993 toc08 5 1 BUCK 1 LINE REGULATION (SKIP MODE) 99.2 0 0 IOUT1 (A) 100.4 VSUP (V) 5.030 4.90 6 5 100.6 99.6 99.5 4 VOUT1 (% NOMINAL) TA = +125ºC TA = -40ºC 4.94 BUCK 1 LINE REGULATION (SKIP MODE) 100.8 VOUT1 (% NOMINAL) VOUT1 (% NOMINAL) 100.3 100.2 101.0 MAX16993 toc04 VOUT1 = 5.0V 4.98 IOUT1 (A) BUCK 1 LINE REGULATION (PWM MODE) 100.4 5.00 4.92 IOUT1 (A) 100.5 TA = +25ºC 5.02 4.96 TA = -40ºC 4.995 10 TA = +125ºC 5.04 5.000 20 5.06 MAX16993 toc06 SKIP MODE 5.08 VOUT1 (V) 50 MAX16993 toc03 5.020 70 60 TA = +125ºC 5.025 VOUT1 (V) EFFICIENCY (%) 80 BUCK 1 LOAD REGULATION (SKIP) 5.10 MAX16993 toc09 MAX16993 toc01 90 BUCK 1 LOAD REGULATION (PWM) 5.030 MAX16993 toc02 BUCK 1 EFFICIENCY 100 TA = +125ºC 3.15 3.14 3.13 TA = +25ºC 3.12 3.11 TA = -40ºC 3.10 3.09 3.08 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 IOUT2 (A) Maxim Integrated │ 6 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Typical Operating Characteristics (continued) (VSUP = 14V, TA = +25°C, unless otherwise noted) 3.325 3.320 3.135 3.130 TA = +25ºC 99.6 99.4 3.315 1.5 2.0 2.5 3.0 3.5 IOUT2 (A) BUCK 3 EFFICIENCY 90 80 60 SKIP MODE PWM MODE 40 30 10 1.00E-02 VPV3 = 5.0V, IMAX = 1.5A, VOUT3 = 1.8V 1.82 TA = +25ºC 1.80 1.77 0.2 0.4 0.8 1.0 TA = +25ºC 99.8 1.224 1.222 1.220 1.2 1.4 1.6 0 0.5 1.0 1.810 TA = -40ºC 4.3 VPV3 (V) 4.8 2.0 2.5 3.0 3.5 IOUT3 (A) VOUT3 vs. TEMPERATURE IOUT3 = 1.125A 1.805 1.795 1.790 99.7 99.6 1.5 1.800 100.0 99.9 VPV3 = 5.0V IMAX = 3A VOUT3 = 1.2V IOUT3 (A) TA = +125ºC 100.1 150 1.216 MAX16993 toc16 100.2 100 1.218 VOUT3 (V) VOUT3 (% NOMINAL) 0.6 50 BUCK 3 LOAD REGULATION (PWM MODE) 1.226 1.214 0 100.3 www.maximintegrated.com 0 -50 1.228 TA = -40ºC 1.78 1.00E+00 3.8 1.230 TA = +125ºC VOUT3 = 1.8V 3.3 3.100 5.7 TEMPERATURE (ºC) BUCK 3 LINE REGULATION (PWM MODE) 100.4 99.5 5.2 BUCK 3 LOAD REGULATION (PWM MODE) IOUT3 (A) 100.5 4.7 1.79 fSW = 2.1MHz, VSUP = 14V, VPV3 = 5.0V, VOUT3 = 1.8V 20 1.00E-04 4.2 1.81 50 0 1.00E-06 1.83 VOUT3 (V) 70 3.7 VPV2 (V) MAX16993 toc13 100 3.2 2.7 MAX16993 toc17 1.0 3.105 VOUT3 (V) 0.5 3.120 3.110 MAX16993 toc14 0 3.125 3.115 TA = -40ºC 99.2 99.0 MAX16993 toc12 3.140 100.2 99.8 IOUT2 = 1.125A 3.145 100.4 100.0 VOUT2 vs. TEMPERATURE 3.150 MAX16993 toc15 VOUT2 (% NOMINAL) VOUT2 (V) TA = +125ºC 100.6 3.330 EFFICIENCY (%) VOUT2 = 3.15V 100.8 3.335 3.310 BUCK 2 LINE REGULATION (PWM MODE) VOUT2 (V) VPV2 = 5.0V IMAX = 3A VOUT2 = 3.3V 3.340 101.0 MAX16993 toc11 BUCK 2 LOAD REGULATION (PWM MODE) MAX16993 toc10 3.345 5.3 1.785 1.780 -50 0 50 100 150 TEMPERATURE (ºC) Maxim Integrated │ 7 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Typical Operating Characteristics (continued) (VSUP = 14V, TA = +25°C, unless otherwise noted) MAX16993 toc18 120 SUPPLY CURRENT (µA) 5V/div 5V/div VOUT1 VRESET1 5V/div 5V/div VOUT2 VRESET2 80 40 TA = +25ºC 20 5V/div VRESET3 TA = +125ºC 60 5V/div VOUT3 VFB = VGND SKIP MODE ALL THREE BUCKS ENABLED MEASURED AT VSUP 100 5V/div VEN1 SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX16993 toc19 STARTUP SEQUENCE (VEN2 = VEN3 = VOUT1) TA = -40ºC 0 2ms/div 0 5 10 15 20 25 30 35 40 VSUP (V) VOUT1 = 5.0V, SKIP MODE ONLY BUCK CONTROLLER ENABLED 60 SUPPLY CURRENT (µA) LOAD TRANSIENT RESPONSE (PWM MODE) SUPPLY CURRENT vs. SUPPLY VOLTAGE 50 MAX16993 toc21 MAX16993 toc20 70 TA = +125ºC VOUT1 100mV/div 40 TA = +25ºC 30 20 10 0 IOUT1 TA = -40ºC 0 5 10 15 20 25 30 1A/div 200µs/div 40 35 VSUP (V) 101 100 99 98 97 8 7 TA = +125ºC 6 5 4 3 TA = -40ºC 2 -50 0 50 100 TEMPERATURE (ºC) www.maximintegrated.com 150 0 0 5 10 15 40 SS DISABLED SS ENABLED 30 20 10 0 TA = +25ºC 1 50 SPECTRAL ENERGY DENSITY MAX16993 toc24 VEN1 = VEN2 = VEN3 = VGND MEASURED AT VSUP 9 60 OUTPUT SPECTRUM (dBµV) 102 MAX16993 toc23 fSW = 2.1MHz SHUTDOWN CURRENT vs. SUPPLY VOLTAGE 10 SHUTDOWN CURRENT (µA) MAX16993 toc22 SWITCHING FREQUENCY (% NOMINAL) 103 fSW vs. TEMPERATURE 20 VSUP (V) 25 30 35 40 -10 1.90 1.95 2.00 2.05 2.10 2.15 2.20 2.25 2.30 FREQUENCY (MHz) Maxim Integrated │ 8 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters PV2 LX2 PGND2 PGND3 LX3 PV3 RESET3 TOP VIEW RESET2 Pin Configuration 24 23 22 21 20 19 18 17 OUT2 25 16 OUT3 CSEL1 26 15 EN3 SSEN 27 14 EN2 13 OUT1 12 CS1 11 FB1 RESET1 28 MAX16993 GND 29 COMP1 30 ERR 31 EP = GND 4 5 6 7 8 LX1 BST1 VSUP EN1 3 DH1 2 GND PV1 1 DL1 + SYNC 32 10 PV 9 BIAS SIDE-WETTABLE TQFN Pin Description PIN NAME FUNCTION 1 PV1 Supply Input for Buck 1 Low-Side Gate Drive. Connect a ceramic bypass capacitor of at least 0.1µF from PV1 to GND. 2 DL1 Low-Side Gate-Drive Output for Buck 1. DL1 output voltage swings from VGND to VPV1. 3 GND Power Ground for Buck 1 4 LX1 Inductor Connection for Buck 1. Connect LX1 to the switched side of the inductor. LX1 serves as the lower supply rail for the DH1 high-side gate drive. 5 DH1 High-Side Gate-Drive Output for Buck 1. DH1 output voltage swings from VLX1 to VBST1. 6 BST1 Bootstrap Capacitor Connection for High-Side Gate Drive of Buck 1. Connect a high-voltage diode between BIAS and BST1. Connect a ceramic capacitor between BST1 and LX1. See the High-Side Gate-Drive Supply (BST1) section. 7 VSUP Supply Input. Bypass VSUP with a minimum 0.1µF capacitor as close as possible to the device. 8 EN1 High-Voltage Tolerant, Active-High Digital Enable Input for Buck 1. Driving EN1 high enables Buck 1. 9 BIAS 5V Internal Linear Regulator Output. Bypass BIAS to GND with a low-ESR ceramic capacitor of 2.2µF minimum value. BIAS provides the power to the internal circuitry. See the Linear Regulator (BIAS) section. 10 PV Analog Supply. Connect PV to BIAS through a 10Ω resistor and connect a 0.1µF ceramic capacitor from PV to ground. FB1 Feedback Input for Buck 1. For the fixed output-voltage option, connect FB1 to BIAS for the factory-trimmed (3.0V to 3.75V or 4.6V to 5.35V) fixed output. Connect FB1 to GND for the 3.3V fixed output. For the resistordivider adjustable output-voltage option, connect FB1 to a resistive divider between OUT1 and GND to adjust the output voltage between 3.0V and 5.5V. In adjustable mode, FB1 regulates to 1.0V (typ). See the OUT1 Adjustable Output-Voltage Option section. 11 www.maximintegrated.com Maxim Integrated │ 9 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Pin Description (continued) PIN NAME FUNCTION 12 CS1 13 OUT1 14 EN2 Active-High Digital Enable Input for Buck 2. Driving EN2 high enables Buck 2. 15 EN3 Active-High Digital Enable Input for Buck 3. Driving EN3 high enables Buck 3. 16 OUT3 17 RESET3 18 PV3 Buck 3 Voltage Input. Connect a 2.2µF or larger ceramic capacitor from PV3 to PGND3. Connect PV3 to OUT1. 19 LX3 Buck 3 Switching Node. LX3 is high impedance when the device is off. 20 PGND3 Power Ground for Buck 3 21 PGND2 Power Ground for Buck 2 Positive Current-Sense Input for Buck 1. Connect CS1 to the positive terminal of the current-sense resistor. See the Current-Limit/Short-Circuit Protection and Current-Sense Measurement sections. Output Sense and Negative Current-Sense Input for Buck 1. The buck uses OUT1 to sense the output voltage. Connect OUT1 to the negative terminal of the current-sense resistor. See the Current-Limit/Short-Circuit Protection and Current-Sense Measurement sections. Buck Converter 3 Voltage-Sense Input. Connect OUT3 to the output of Buck 3. Connect OUT3 to an external feedback divider when setting DC-DC3 voltage externally. See the OUT2/OUT3 Adjustable Output-Voltage Option section. Open-Drain Buck 3 Reset Output. RESET3 remains low for a fixed time after the output of Buck 3 has reached its regulation level (see the Selector Guide). To obtain a logic signal, pull up RESET3 with an external resistor connected to a positive voltage lower than 5V. 22 LX2 Buck 2 Switching Node. LX2 is high impedance when the device is off. 23 PV2 Buck 2 Voltage Input. Connect a 2.2µF or larger ceramic capacitor from PV2 to PGND2. Connect PV2 to OUT1. 24 RESET2 25 OUT2 Buck Converter 2 Voltage-Sense Input. Connect OUT2 to the output of Buck 2. Connect OUT2 to an external feedback divider when setting DC-DC2 voltage externally. See the OUT2/OUT3 Adjustable Output-Voltage Option section. 26 CSEL1 Buck 1 Clock Select. Connect CSEL1 to GND for 2.1MHz operation. Connect CSEL1 to BIAS for an OTPprogrammable divide-down operation. See the Selector Guide for the fSW1 divide ratio. 27 SSEN Spread-Spectrum Enable. Connect SSEN to GND for standard oscillator operation. Connect SSEN to BIAS to enable the spread-spectrum oscillator. 28 RESET1 29 GND 30 COMP1 31 ERR 32 SYNC — EP Open-Drain Buck 2 Reset Output. This output remains low for a fixed time after the output of Buck 2 has reached its regulation level (see the Selector Guide). To obtain a logic signal, pull up RESET2 with an external resistor connected to a positive voltage lower than 5V. Open-Drain Buck 1 Reset Output. RESET1 remains low for a fixed time after the output of Buck 1 has reached its regulation level (see the Selector Guide). To obtain a logic signal, pull up RESET1 with an external resistor connected to a positive voltage lower than 5V. Analog Ground Compensation for Buck 1. See the Compensation Network section. Open-Drain Error-Status Output. ERR signals a thermal-warning/shutdown condition. To obtain a logic signal, pull up ERR with an external resistor connected to a positive voltage lower than 5V. Synchronization Input. SYNC allows the device to synchronize to other supplies. Connect SYNC to GND or leave unconnected to enable skip-mode operation under light loads. Connect SYNC to BIAS or an external clock to enable fixed-frequency forced-PWM-mode operation. Exposed Pad. Connect the exposed pad to ground. Connecting the exposed pad to ground does not remove the requirement for proper ground connections to PGND2–PGND3 and GND. The exposed pad is attached with epoxy to the substrate of the die, making it an excellent path to remove heat from the IC. www.maximintegrated.com Maxim Integrated │ 10 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Typical Operating Circuit BIAS GND LINEAR REGULATOR MAX16993 BIAS PV1 BST1 PV VSUP VBATP PV3 N VOUT1 DH1 P LX1 N STEP-DOWN PWM OUT3 DL1 GND CS1 STEP-DOWN CONTROLLER OUT1 OUT1 FB1 COMP1 PWM EN LX3 PGND3 OUT3 0.8V TO 3.95V 1.5A TO 3.0A PWM EN RESET1 VOUT1 P LX2 RESET2 STEP-DOWN PWM OUT2 RESET3 EN1 EN3 VOUT3 N PV2 EN2 VOUT1 POR GENERATION AND CONTROL 0.8V TO 3.95V 1.5A TO 3.0A VOUT2 N PGND2 OUT2 ERR SSEN PWM EN CSEL1 SYNC EP www.maximintegrated.com Maxim Integrated │ 11 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Detailed Description Enable Inputs (EN_) The 2.1MHz, high-voltage buck controller operates with a 3.5V to 36V input voltage range and is protected from load-dump transients up to 42V. The high-frequency operation eliminates AM band interference and reduces the solution footprint. It can provide an output voltage between 3.0V and 5.5V set at the factory or with external resistors. Each device has two frequency options that are pin selectable: 2.1MHz or a lower frequency based on factory setting. Available factory-set frequencies are 1.05MHz, 525kHz, 420kHz, or 350kHz. Under no-load conditions, the device consumes only 30µA of quiescent current with OUT1 enabled. Reset Outputs (RESET_) The MAX16993 power-management integrated circuit (PMIC) is a 2.1MHz, multichannel, DC-DC converter designed for automotive applications. The device includes one high-voltage step-down controller (OUT1) designed to run directly from a car battery and two low-voltage stepdown converters (OUT2/OUT3) cascaded from OUT1. The dual buck converters can deliver 1.5A or 3.0A of load current per output. They operate directly from OUT1 and provide 0.8V to 3.95V output voltage range. Factory trimmed output voltages achieve ±3% output error over load, line, and temperature without using expensive ±0.1% resistors. In addition, adjustable output-voltage versions can be set to any desired values between 0.8V and 3.6V using an external resistive divider. On-board low RDS(ON) switches help minimize efficiency losses at heavy loads and reduce critical/parasitic inductance, making the layout a much simpler task with respect to discrete solutions. Following a simple layout and footprint ensures first-pass success in new designs (see the PCB Layout Guidelines section). The device features either a SYNC input or SYNC output (see the Synchronization (SYNC) section and the Selector Guide). An optional spread-spectrum frequency modulation minimizes radiated electromagnetic emissions due to the switching frequency, and a factory-programmable synchronization I/O (SYNC) allows better noise immunity. Additional features include a 4ms fixed soft-start for OUT1 and 2.5ms for OUT2/OUT3, individual RESET_ outputs, overcurrent, and overtemperature protections. See the Selector Guide for the available options. www.maximintegrated.com All three regulators have their own enable input. When EN1 exceeds the EN1 high threshold, the internal linear regulator is switched on. When VSUP exceeds the VSUP,STARTUP threshold, Buck 1 is enabled and OUT1 starts to ramp up with a 3ms soft-start. Once the Buck 1 soft-start is complete, Buck 2 and Buck 3 can be enabled. When either Buck 2 or Buck 3 is enabled, the corresponding output ramps up with a 2.5ms soft-start. When an enable input is pulled low, the converter is switched off and the corresponding OUT_ and RESET_ are driven low. If EN1 is low, all regulators are disabled. The device features individual open-drain RESET_ outputs for each buck output that asserts when the buck output voltage drops 6% below the regulated voltage. RESET_ remains asserted for a fixed timeout period after the buck output rises up to its regulated voltage. The fixed timeout period is programmable between 0.1ms and 7.4ms (see the Selector Guide). To obtain a logic signal, pull up RESET_ with an external resistor connected to a positive voltage lower than 5V. Linear Regulator (BIAS) The device features a 5V internal linear regulator (BIAS). Connect BIAS to PV, which acts as a supply for internal circuitry. Also connect BIAS to PV1, which acts as a supply for the low-side gate driver of Buck 1. Bypass BIAS with a 2.2µF or larger ceramic capacitor as close as possible to the device. BIAS can provide up to 100mA (max), but is not designed to supply external loads. Internal Oscillator Buck 1 Clock Select (CSEL1) The device offers a Buck 1 clock-select input. Connect CSEL1 to GND for 2.1MHz operation. Connect CSEL1 to BIAS to divide down the Buck 1 clock frequency by 2, 4, 5, or 6 (see the Selector Guide). Buck 2 and Buck 3 switch at 2.1MHz (typ) and are not controlled by CSEL1. Maxim Integrated │ 12 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters fSW + 6% INTERNAL OSCILLATOR FREQUENCY fSW t t + 250µs t + 500µs t + 750µs TIME Figure 1. Effect of Spread Spectrum on Internal Oscillator Spread-Spectrum Enable (SSEN) The device features a spread-spectrum enable (SSEN) input that can quickly enable spread-spectrum operation to reduce radiated emissions. Connect SSEN to BIAS to enable the spread-spectrum oscillator. Connect SSEN to GND for standard oscillator operation. When spread spectrum is enabled, the internal oscillator frequency is varied between fSW and (fSW + 6%). The change in frequency has a sawtooth shape and a frequency of 4kHz (see Figure 1). This function does not apply to externally applied oscillation frequency. See the Selector Guide for available options. Synchronization (SYNC) SYNC is factory-programmable I/O. See the Selector Guide for available options. When SYNC is configured as an input, a logic-high on SYNC enables fixed-frequency, forced-PWM mode. Apply an external clock on the SYNC input to synchronize the internal oscillator to an external clock. The SYNC input accepts signal frequencies in the range of 1.7MHz < fSYNC < 2.4MHz. The external clock should have a duty cycle of 50%. A logic-low at the SYNC input enables the device to enter a low-power skip mode www.maximintegrated.com under light-load conditions. When SYNC is configured as an output, SYNC outputs the internally generated 2.1MHz clock that switches from VPV to VGND. All converters operate in forced-PWM mode when SYNC is configured as an output. Common Protection Features Undervoltage Lockout The device offers an undervoltage-lockout feature. Undervoltage detection is performed on the PV input. If VSUP decreases to the point where Buck 1 is in dropout, PV begins to decrease. If PV falls below the UVLO threshold (2.7V, typ), all three converters switch off and the RESET_ outputs assert low. Once the device has been switched off, VSUP must exceed the VSUP,STARTUP threshold before Buck 1 turns back on. Output Overvoltage Protection The device features overvoltage protection on the buck converter outputs. If the FB1 input exceeds the output overvoltage threshold, a discharge current is switched on at OUT1 and RESET1 asserts low. Maxim Integrated │ 13 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Soft-Start The device includes a 4ms fixed soft-start time on OUT1 and 2.5ms fixed soft-start time on OUT2/OUT3. Soft-start time limits startup inrush current by forcing the output voltage to ramp up towards its regulation point. If OUT1 is prebiased above 1.25V, all three buck converters do not start up until the prebias has been removed. Once the prebias has been removed, OUT1 self-discharges to GND and then goes into soft-start. Thermal Warning and Overtemperature Protection The device features an open-drain, thermal-warning indicator (ERR). ERR asserts low when the junction temperature exceeds +145°C (typ). For a logic signal, connect a pullup resistor from ERR to a supply less than or equal to 5V. When the junction temperature exceeds +170°C (typ), an internal thermal sensor shuts down the buck converters, allowing the device to cool. The thermal sensor turns the device on again after the junction temperature cools by 30°C (typ). Buck 1 (OUT1) Buck controller 1 uses a PWM current-mode control scheme. An internal transconductance amplifier establishes an integrated error voltage. The heart of the PWM controller is an open-loop comparator that compares the integrated voltage-feedback signal against the amplified current-sense signal plus the slope-compensation ramp, which are summed into the main PWM comparator to preserve inner-loop stability and eliminate inductor staircasing. At each rising edge of the internal clock, the highside MOSFET turns on until the PWM comparator trips or the maximum duty cycle is reached, or the peak current limit is reached. During this on-time, current ramps up through the inductor, storing energy in a magnetic field and sourcing current to the output. The current-mode feedback system regulates the peak inductor current as a function of the output-voltage error signal. The circuit acts as a switch-mode transconductance amplifier and pushes the output LC filter pole normally found in a voltage-mode PWM to a higher frequency. During the second half of the cycle, the high-side MOSFET turns off and the low-side MOSFET turns on. The inductor releases the stored energy as the current ramps down, providing current to the output. The output capacitor stores charge when the inductor current exceeds the required load current and discharges when the inductor current is lower, smoothing the voltage across the load. Under soft-overload conditions, when the www.maximintegrated.com peak inductor current exceeds the selected current limit (see the Current-Limit/Short-Circuit Protection section), the high-side MOSFET is turned off immediately and the low-side MOSFET is turned on and remains on to let the inductor current ramp down until the next clock cycle. PWM/Skip Modes The device features a synchronization input that puts all the buck regulators either in skip mode or forced-PWM mode of operation (see the Synchronization (SYNC) section). In the PWM mode of operation, the regulator switches at a constant frequency with variable on-time. In the skip mode of operation, the regulator’s switching frequency is load dependent until the output load reaches a certain threshold. At higher load current, the switching frequency does not change and the operating mode is similar to the PWM mode. Skip mode helps improve efficiency in light-load applications by allowing the regulator to turn on the high-side switch only when the output voltage falls below a set threshold. As such, the regulator does not switch MOSFETs on and off as often as is the case in the PWM mode. Consequently, the gate charge and switching losses are much lower in skip mode. Minimum On-Time and Duty Cycle The high-side gate driver for Buck 1 has a minimum ontime of 75ns (max). This helps ensure no skipped pulses when operating the device in PWM mode at 2.1MHz with supply voltage up to 18V and output voltage down to 3.3V. Pulse skipping can occur if the on-time falls below the minimum allowed (see the Electrical Characteristics). Current-Limit /Short-Circuit Protection OUT1 offers a current-limit feature that protects Buck 1 against short-circuit and overload conditions on the buck controller. Buck 1 offers a current-limit sense input (CS1). Place a sense resistor in the path of the channel 1 current flow. Connect CS1 to the high side of the sense resistor and OUT1 to the low side of the sense resistor. Currentlimit protection activates once the voltage across the sense resistor increases above the 120mV (typ) currentlimit threshold. In the event of a short-circuit or overload condition, the high-side MOSFET remains on until the inductor current reaches the current-limit threshold. The converter then turns on the low-side MOSFET and the inductor current ramps down. The converter allows the high-side MOSFET to turn on only when the voltage across the current-sense resistor ramps down to below 120mV (typ). This cycle repeats until the short or overload condition is removed. Maxim Integrated │ 14 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Current-Sense Measurement For the best current-sense accuracy and overcurrent protection, use a 1% tolerance current-sense resistor between the inductor and output, as shown in Figure 2A. This configuration constantly monitors the inductor current, allowing accurate current-limit protection. Use low-inductance current-sense resistors for accurate measurement. Lossless Inductor DCR Sensing High-power applications that do not require highly accurate current-limit protection can reduce the overall power dissipation by connecting a series RC circuit across the inductor (see Figure 2B) with an equivalent time constant: R2 R CSEQ = R1 + R 2 And: R DCR 1 1 R DCR = + C EQ R 1 R 2 L where RCSEQ is the required current-sense resistor and RDCR is the inductor’s series DC resistance. Use the inductance and RDCR values provided by the inductor manufacturer. Carefully observe the PCB layout guidelines to ensure the noise and DC errors do not corrupt the differential currentsense signals seen by CS1 and OUT1. Place the sense resistor close to the device with short, direct traces, making a Kelvin-sense connection to the current-sense resistor. High-Side Gate-Drive Supply (BST1) The high-side MOSFET is turned on by closing an inter nal switch between BST1 and DH1 and transferring the bootstrap capacitor’s (at BST1) charge to the gate of the high-side MOSFET. This charge refreshes when the highside MOSFET turns off and the LX1 voltage drops down to ground potential, taking the negative terminal of the capacitor to the same potential. At this time, the bootstrap diode recharges the positive terminal of the bootstrap capacitor. The selected n-channel high-side MOSFET determines the appropriate boost capacitance values (CBST1 in the Typical Operating Circuit) according to the following equation: QG C BST 1 = ∆VBST 1 where QG is the total gate charge of the high-side MOSFET and ΔVBST1 is the voltage variation allowed on the high-side MOSFET driver after turn-on. Choose www.maximintegrated.com MAX16993 DH1 CIN N LX1 DL1 L1 VSUP RCS COUT N GND CS1 OUT1 A) OUTPUT SERIES RESISITOR SENSING CIN MAX16993 DH1 DL1 INDUCTOR N LX1 N VSUP L1 RDCR R1 R2 COUT CEQ GND CS1 OUT1 RCSEQ = B) LOSSLESS INDUCTOR DCR SENSING RDCR = R1 RDCR R1 + R2 L CEQ 1 + 1 R1 R2 Figure 2. Current-Sense Configurations ΔVBST1 such that the available gate-drive voltage is not significantly degraded (e.g., ΔVBST1 = 100mV to 300mV) when determining CBST1. Use a Schottky diode when efficiency is most important, as this maximizes the gatedrive voltage. If the quiescent current at high temperature is important, it may be necessary to use a low-leakage switching diode. The boost capacitor should be a low-ESR ceramic capacitor. A minimum value of 100nF works in most cases. A minimum value of 470nF is recommended when using a Schottky diode. Maxim Integrated │ 15 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Dropout When OUT1 input voltage is lower than the desired output voltage, the converter is in dropout mode. Buck 1 continuously draws current from the bootstrap capacitor when the high-side switch is on. Therefore, the bootstrap capacitor needs to be refreshed periodically. When in dropout, the Buck 1 high-side gate drive shuts off every 8µs, at which point the low-side gate drive turns on for 120ns. Buck 2 and Buck 3 (OUT2 and OUT3) Buck converters 2 and 3 are high-efficiency, low-voltage converters with integrated FETs. They use a PWM current-mode control scheme that is operated at 2.1MHz to optimize component size and efficiency, while eliminating AM band intererence. The buck converters can be configured to deliver 1.5A or 3.0A per channel. They operate directly from OUT1 and have either fixed or resistor-programmable (see the Selector Guide) output voltages that range from 0.8V to 3.95V. Buck 2 and Buck 3 feature low on-resistance internal FETs that contribute to high efficiency and smaller system cost and board space. Integration of the p-channel high-side FET enables both channels to operate with 100% duty cycle when the input voltage falls to near the output voltage. They feature a programmable active timeout period (see the Selector Guide) that adds a fixed delay before the corresponding RESET_ can go high. FPWM/Skip Modes The MAX16993 features an input (SYNC) that puts the converter either in skip mode or forced PWM (FPWM) mode of operation. See the Internal Oscillator section. In FPWM mode, the converter switches at a constant frequency with variable on-time. In skip mode, the converter’s switching frequency is load-dependent until the output load reaches a certain threshold. 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 highside switch only when the output voltage falls below a set threshold. As such, the converter does 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. Current-Limit/Short-Circuit Protection Buck converters 2 and 3 feature current limit that protects the device against short-circuit and overload conditions at their outputs. The current limit value is dependent on the version selected, 1.5A or 3.0A maximum DC current. See www.maximintegrated.com the Selector Guide for the current limit value of the chosen option and the Electrical Characteristics table for the corresponding current limit. In the event of a short-circuit or overload condition at an output, the high-side MOSFET remains on until the inductor current reaches the highside MOSFET’s current-limit threshold. The converter then turns on the low-side MOSFET and the inductor current ramps down. The converter allows the high-side MOSFET to turn off only when the inductor current ramps down to the lowside MOSFET’s current threshold. This cycle repeats until the short or overload condition is removed. Applications Information OUT1 Adjustable Output-Voltage Option The device’s adjustable output-voltage version (see the Selector Guide for details) allows the customer to set OUT1 voltage between 3.0V and 5.5V. Connect a resistive divider from OUT1 to FB1 to GND to set the output voltage (Figure 3). Select R2 (FB1 to GND resistor) less than or equal to 100kΩ. Calculate R1 (VOUT1 to FB1 resistor) with the following equation: VOUT 1 = R 1 R 2 − 1 VFB 1 where VFB1 = 1.0V (see the Electrical Characteristics). The external feedback resistive divider must be frequency compensated for proper operation. Place a capacitor across R1 in the resistive divider network. Use the following equation to determine the value of the capacitor: if R2/R1 > 1, C1 = C(R2/R1) else, C1 = C, where C = 10pF. For fixed output options, connect FB1 to BIAS for the factory-programmed, fixed output voltage. Connect FB1 to GND for a fixed 3.3V output voltage. VOUT1 OUT1 MAX16993 R1 C1 FB1 R2 Figure 3. Adjustable OUT1 Voltage Configuration Maxim Integrated │ 16 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters OUT1 Current-Sense Resistor Selection saturation current (ISAT), and DC resistance (RDCR). Use the following formulas to determine the minimum inductor value: The formula for calculating the current-sense resistor is: VOUT 1 ( VSUPMAX − VOUT 1 ) × VSUPMAX L MIN 1 [ H =] 1.3 × 1 × f SW 1 × I OUTMAX × K INDMAX Choose the current-sense resistor based on the maximum inductor current ripple (KINDMAX) and minimum current-limit threshold across current-sense resistor (VLIM1MIN = 0.1V). VLIM1MIN Rcs MAX = I OUTMAX × ( 1 + K INDMAX 2 ) where IOUTMAX is the maximum load current for Buck 1 and KINDMAX is the maximum inductor current ripple. The maximum inductor current ripple is a function of the inductor chosen, as well as the operating conditions, and is typically chosen between 0.3 and 0.4: K INDMAX = where fSW1 is the operating frequency and 1.3 is a coefficient that accounts for inductance initial precision. or L MIN 2 [ µH ] = 1.3 × ( VSUP − VOUT ) × D I OUTMAX × f SW 1 [MHz] × L [µH] × A V_CS × where D is the duty cycle. Below is a numerical example to calculate the current-sense resistor in Figure 2A. The maximum inductor current ripple is chosen at the maximum supply voltage (36V) to be 0.4: Rcs MAX = 0.1 VOUT1 0.8 × R CS 2.1 × 10 6 f SW1 where AV_CS is current-sense amplifier gain (8V/V, typ). For proper operation, the chosen inductor value must be greater than or equal to LMIN1 and LMIN2. The maximum inductor value recommended is twice the chosen value from the above formulas. Table 1 lists some of the inductor values for 5A output current and several switching frequencies and output voltages. K INDMAX I OUTMAX × 1 + 2 0.1 = = 0.0166 Ω 0.4 5 × 1 + 2 Buck 1 Input Capacitor OUT1 Inductor Selection Three key inductor parameters must be specified for operation with the device: inductance value (L), inductor The device is designed to operate with a single 0.1µF capacitor on the VSUP input and a single 0.1µF capacitor on the PV1 input. Place these capacitors as close as possible to their corresponding inputs to ensure the best EMI and jitter performance. Table 1. Inductor Values vs. (VSUPMAX, VOUT1) VSUPMAX to VOUT1 (V) VSUPMAX = 36V, VOUT1 = 5V VSUPMAX = 36V, VOUT1 = 3.3V fSW1 (MHz) 2.1 1.05 0.525 0.420 0.350 2.1 1.05 0.525 0.420 0.350 INDUCTOR (µH), ILOAD = 5A 1.5 3.3 5.6 6.8 8.2 1.0 2.2 4.7 4.7 6.8 www.maximintegrated.com Maxim Integrated │ 17 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters OUT1 Output Capacitor The primary purpose of the OUT1 output capacitor is to reduce the change in VOUT1 during load transient conditions. The minimum capacitor depends on the output voltage, maximum current, and load regulation accuracy. Use the following formula to determine the minimum output capacitor for Buck 1: I OUT1(MAX) C OUT ≥ ∆VOUT1 2π × f CO × × VOUT1 VOUT1 where fCO is the crossover frequency set by RC and CC, and ΔVOUT1 is the allowable change in voltage during a load transient condition. For proper functionality, ceramic capacitors must be used. Make sure that the self-resonance of the ceramic capacitors is above 1MHz to avoid instability. Buck 1 MOSFET Selection Buck 1 drives two external logic-level n-channel MOSFETs as the circuit switch elements. The key selection parameters to choose these MOSFETs are: ● On-resistance (RDS(ON)) ● Maximum drain-to-source voltage (VDS(MAX)) ● Minimum threshold voltage (VTH(MIN)) ● Total gate charge (QG) ● Reverse transfer capacitance (CRSS) ● Power dissipation Both n-channel MOSFETs must be logic-level types with guaranteed on-resistance specifications at VGS = 4.5V when VOUT1 is set to 5V or VGS = 3V when VOUT1 is set to 3.3V. The conduction losses at minimum input voltage should not exceed MOSFET package thermal limits or violate the overall thermal budget. Also, ensure that the conduction losses plus switching losses at the maximum input voltage do not exceed package ratings or violate the overall thermal budget. In particular, check that the dV/dt caused by DH1 turning on does not pull up the DL1 gate through its drain-to-gate capacitance. This is the most frequent cause of cross-conduction problems. Gate-charge losses are dissipated by the driver and do not heat the MOSFET. Therefore, the power dissipation in the device due to drive losses must be checked. Both MOSFETs must be selected so that their total gate charge is low enough; therefore, PV1/ VOUT1 can power both drivers without overheating the device: PDRIVE = VOUT1 x (QGTOTH + QGTOTL) x fSW1 www.maximintegrated.com where QGTOTL is the low-side MOSFET total gate charge and QGTOTH is the high-side MOSFET total gate charge. Select MOSFETs with a QG_ total of less than 10nC. The n-channel MOSFETs must deliver the average current to the load and the peak current during switching. Dual MOSFETs in a single package can be an economical solution. To reduce switching noise for smaller MOSFETs, use a series resistor in the DH1 path and additional gate capacitance. Contact the factory for guidance using gate resistors. Compensation Network The device uses a current-mode-control scheme that regulates the output voltage by forcing the required current through the external inductor, so the controller uses the voltage drop across the DC resistance of the inductor or the alternate series current-sense resistor to measure the 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 and requiring less elaborate error-amplifier compensation than voltage-mode control. A single series resistor (RC) and capacitor (CC) is all that is required to have a stable, high-bandwidth loop in applications where ceramic capacitors are used for output filtering (see 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 COMP1 to GND to cancel this ESR zero. gmc = 1/(AVCS x RDC) CS_ OUT_ RESR COUT CURRENT-MODE POWER MODULATION gMEA = 660µS R1 FB_ R2 VREF ERROR AMP COMP_ 30MΩ RC CF CC Figure 4. Compensation Network Maxim Integrated │ 18 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters The basic regulator loop is modeled as a power modulator, output feedback divider, and an error amplifier (see Figure 4). The power modulator has a DC gain set by gmc x RLOAD, with a pole and zero pair set by RLOAD, the output capacitor (COUT), and its ESR. The loop response is set by the following equation: Thus: f dpEA = f zEA = GAINMOD(dc) = gmc x RLOAD where RLOAD = VOUT /ILOUT(MAX) in Ω and gmc = 1/ (AV_CS x RDC) in S. AV_CS is the voltage gain of the current-sense amplifier and is typically 8V/V. RDC is the DC resistance of the inductor or the current-sense resistor in Ω. In a current-mode step-down converter, the output capacitor and the load resistance introduce a pole at the following frequency: 1 f pMOD = 2 π × C OUT × R LOAD The unity-gain frequency of the power stage is set by COUT and gmc: f UGAINpMOD = g mc 2 π × C OUT 1 2 π × ESR × C OUT When COUT is composed of “n” identical capacitors in parallel, the resulting COUT = n x COUT(EACH), and ESR = ESR(EACH) /n. Note that the capacitor zero for a parallel combination of like-value 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 x ROUT,EA, where gm,EA is the error amplifier transconductance, which is 660µS (typ), and ROUT,EA is the output resistance of the error amplifier, which is 30MΩ (typ). 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 crossover frequency (fC, where the loop gain equals 1 (0dB)). www.maximintegrated.com 1 2 π × CC × RC 1 f pEA = 2 π × CF × R C The loop-gain crossover frequency (fC) should be set below 1/5 of the switching frequency and much higher than the power-modulator pole (fpMOD). Select a value for fC in the range: f SW f pMOD << f C ≤ 5 At the crossover frequency, the total loop gain must be equal to 1. Thus: GAINMOD ( f ) × C VFB VOUT × GAINEA ( R ) = 1 C GAINEA= (f C ) g m,EA × f C The output capacitor and its ESR also introduce a zero at: f zMOD = 1 2 π × C C × ( R OUT,EA + R C ) GAIN = MOD ( f C ) GAINMOD ( dc ) × Therefore: GAINMOD (f ) × C VFB VOUT f pMOD fC × g m,EA × R C = 1 Solving for RC: RC = VOUT g m,EA × VFB × GAINMOD (f ) C Set the error-amplifier compensation zero formed by RC and CC at the fpMOD. Calculate the value of CC as follows: 1 CC = 2 π × f pMOD × R C If fzMOD is less than 5 x fC, add a second capacitor CF from COMP1 to GND. The value of CF is: 1 CF = 2 π × f zMOD × R C Maxim Integrated │ 19 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters As the load current decreases, the modulator pole also decreases; however, the modulator gain increases accordingly and the crossover frequency remains the same. Below is a numerical example to calculate the compensation network component values of Figure 4: AV_CS = 8V/V RDCR = 22mΩ gmc = 1/(AV_CS x RDC) = 1/(8 x 0.022) = 5.68 VOUT = 5V IOUT(MAX) = 5A RLOAD = VOUT/IOUT(MAX) = 5V/6A = 0.833Ω COUT = 4 x 47µF = 188µF ESR = 9mΩ/4 = 2.25mΩ fSW = 0.420MHz GAINMOD(dc) = 5.68 x 0.833 = 4.73 1 = ≈ 1kHz f pMOD 2 π × 188 µF × 0.833 f SW f pMOD << f C ≤ 5 1kHz << f C ≤ 80.6 kHz , Select f C = 20 kHz = f zMOD 1 ≈ 376 kHz 2 π × 2.25 mΩ × 188 µF Since fzMOD > fC: RC ≈ 33kΩ CC ≈ 4.7nF CF ≈ 12pF OUT2/OUT3 Adjustable Output-Voltage Option The device’s adjustable output-voltage version (see the Selector Guide for details) allows the customer to set the outputs to any voltage between 0.8V and 3.95V. Connect a resistive divider from the buck converter output (VOUT_(BUCK)) to OUT_ to GND to set the output voltage (Figure 5). Select R4 (OUT_ to GND resistor) less than or equal to 100kΩ. Calculate R3 (VOUT_(BUCK)) to OUT_ resistor) with the following equation: VOUT_( BUCK ) = R 3 R 4 VOUT_ where VOUT_ = 812mV (see the Electrical Characteristics). The external feedback resistive divider must be frequency compensated for proper operation. Place a capacitor across R1 in the resistive divider network. Use the following equation to determine the value of the capacitor: if R4/R3 > 1, C2 = C(R4/R3) else, C2 = C, where C = 10pF. For fixed output-voltage options, connect OUT_ to VOUT_ for the factory-programmed, fixed-output voltage between 0.8V and 3.95V. OUT2/OUT3 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). Use the following formulas to determine the minimum inductor value: ( R3 C2 OUT_ R4 VOUT_ VIN × 3 f OP ⋅ VREF ⋅ G CS VREF Reference voltage, VREF = 1.25V. GCS Internal current sense conductance. See the Selector Guide for the value for each specific part number. GCS = 0.8S; for 1.5A output channels GCS = 1.6S; for 3.0A output channels fOP Operating frequency. This value is 2.1MHz, unless externally synchronized to a different frequency. VOUT_(BUCK) MAX16993 ) L MIN1 = VIN − VOUT_ × LX_ − 1 Figure 5. Adjustable OUT2/OUT3 Voltage Configuration www.maximintegrated.com Maxim Integrated │ 20 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Table 2. Inductor Values vs. (VPV_, VOUT) VPV2/3 = 5.5V, VOUT2/3 = 3.3V VPV2/3 = 5.5V, VOUT2/3 = 2.5V VPV2/3 = 5.5V, VOUT2/3 = 1.5V VPV2/3 = 3.0V, VOUT2/3 = 0.8V INDUCTOR (µH), ILOAD = 1.5A 2.2 1.5 1.0 0.56 INDUCTOR (µH), ILOAD = 3.0A 1.0 0.68 0.56 0.33 VPV_ TO VOUT (V) Table 3. Output Capacitor Values vs. VOUT VOUT (V) 3.3 2.5 1.5 0.8 COUT (µF), IMAX = 1.5A ≥ 12 ≥ 15 ≥ 25 ≥ 48 input capacitance by cancelling input ripple currents. Place the bypass capacitors as close as possible to their corresponding PV_ input to ensure the best EMI and jitter performance. OUT2 /OUT3 Output Capacitor The next equation ensures that the inductor current down slope is less than the internal slope compensation. For this to be the case, the following equation needs to be satisfied: m2 −m ≥ 2 -m Slope compensation, [0.8 x VREF/(µs x GCS)] m2 Inductor current downslope, [VOUT/L] Solving for L: L= MIN2 VOUT × µs 1.6 ⋅ VREF ⋅ G CS The equation that provides the bigger inductor value must be chosed for proper operation. LMIN = max(LMIN1, LMIN2) The maximum inductor value recommended is twice the chosen value from the above formula. LMAX = 2 x LMIN OUT2/OUT3 Input Capacitor Place a single 4.7µF ceramic bypass capacitor on the PV2 and PV3 inputs. Phase interleaving of the two lowvoltage buck converters contributes to a lower required www.maximintegrated.com The minimum capacitor required depends on output voltage, maximum device current capability, and the error amplifier voltage gain. Use the following formula to determine the required output capacitor value: C OUT(MIN) = VREF ⋅ G CS ⋅ G EAMP 2π ⋅ f CO ⋅ VOUT VREF Reference voltage, VREF = 1.25V. GCS Internal current sense conductance. See the Selector Guide for the value for each specific part number. GCS = 0.8S; for 1.5A output channels GCS = 1.6S; for 3.0A output channels fCO Target crossover frequency, 250kHz. GEAMP Error amplifier voltage gain is 50V/V GEAMP = 50V/V where VREF is the crossover frequency. Table 3 lists some of the capacitor values for 1.5A output current and several output voltages. For proper functionality, ceramic capacitors must be used. Make sure that the self-resonance of the ceramic capacitors at the converters’ output converter is above 1MHz to avoid instability. Maxim Integrated │ 21 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Thermal Considerations How much power the package can dissipate strongly depends on the mounting method of the IC to the PCB and the copper area for cooling. Using the JEDEC test standard, the maximum power dissipation allowed is 2160mW in the side-wettable TQFN package. More power dissipation can be handled by the package if great attention is given during PCB layout. For example, using the top and bottom copper as a heatsink and connecting the thermal vias to one of the middle layers (GND) transfers the heat from the package into the board more efficiently, resulting in lower junction temperature at high power dissipation in some MAX16993 applications. Furthermore, the solder mask around the IC area on both top and bottom layers can be removed to radiate the heat directly into the air. The maximum allowable power dissipation in the IC is as follows: PMAX = (TJ ( MAX ) − T A ) θ JC + θ CA where TJ(MAX) is the maximum junction temperature (+150°C), TA is the ambient air temperature, θJC (2.8°C/W for the side-wettable TQFN) is the thermal resistance from the junction to the case, and θCA is the thermal resistance from the case to the surrounding air through the PCB, copper traces, and the package materials. θCA is directly related to system-level variables and can be modified to increase the maximum power dissipation. The TQFN package has an exposed thermal pad on its underside. This pad provides a low thermal-resistance path for heat transfer into the PCB. This low thermally resistive path carries a majority of the heat away from the IC. The PCB is effectively a heatsink for the IC. The exposed pad should be connected to a large ground plane for proper thermal and electrical performance. The minimum size of the ground plane is dependent upon many system www.maximintegrated.com variables. To create an efficient path, the exposed pad should be soldered to a thermal landing, which is connected to the ground plane by thermal vias. The thermal landing should be at least as large as the exposed pad and can be made larger depending on the amount of free space from the exposed pad to the other pin landings. A sample layout is available on the MAX16993 Evaluation Kit to speed designs. 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 device package. Ensure that all heat-dissipating components have adequate cooling. 2) Isolate the power components and high-current path from the sensitive analog circuitry. This 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 comprising of 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. This ensures integrity of sensitive signals feeding back into the device. 6)Use a single ground plane to reduce the chance of ground-potential differences. With a single ground plane, enough isolation between analog return signals and high-power signals must be maintained. Maxim Integrated │ 22 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Typical Application Circuit BIAS BIAS BIAS D2 VBATP 0.1µF D1 0.1µF VOUT1 (5V, 5A) 47µF 47µF 0.1µF BST1 FB1 PV VSUP 0.1µF 22mΩ 47µF PV1 2.2µF 220µF 2.2µH 0.1µF 10Ω 1µF 1µF VOUT1 DH1 N1 LX1 PV3 47µF 10µF DL1 N2 GND BIAS LX3 47µF PGND3 47µF MAX16993 20pF 10kΩ FB1 VSUP 40kΩ 4.7nF CS1 OUT1 VOUT3 (1.2V, 3A) 0.6µH OUT3 47pF 20kΩ VOUT1 VOUT1 5.1kΩ RESET1 RESET1 RESET2 RESET2 RESET3 RESET3 PV2 10µF VBATP 100kΩ VOUT1 5.1kΩ ERR LX2 EN1 47µF PGND2 BIAS EN2 EN3 75kΩ 47µF 3.3pF OUT2 ERR BIAS 24kΩ SYNC SYNC 100kΩ www.maximintegrated.com VOUT2 (3.3V, 3A) 1µH CSEL1 SSEN EP GND Maxim Integrated │ 23 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Selector Guide BUCK 1 BUCK 2 fSW1 FIXED ACTIVE DIVIDE OPTION OUTPUT TIMEOUT RATIO VOLTAGE PERIOD FROM fSW (V) (ms) BUCK 3 MAX FIXED OUTPUT OUTPUT CURRENT VOLTAGE (A) ACTIVE TIMEOUT PERIOD (ms) ACTIVE TIMEOUT PERIOD (SAME AS BUCK 2) (ms) MAX FIXED OUTPUT OUTPUT CURRENT VOLTAGE (A) SYNC A 3.3/5.0 ÷5 3.9 ADJ 3.0 3.9 ADJ 3.0 3.9 Input B 3.3/5.0 ÷5 3.9 3.15V 1.5 3.9 1.8V 1.5 3.9 Input C 3.3/5.0 ÷5 1.9 ADJ 1.5 1.9 ADJ 1.5 1.9 Input D* 3.3/3.15 ÷2 3.9 1.35V 3.0 3.9 1.2V 1.5 3.9 Input E 3.3/5.0 ÷5 3.9 3.30V 1.5 3.9 1.5V 1.5 3.9 Input Ordering Information Package Information PART TEMP RANGE PIN-PACKAGE MAX16993AGJ_/VY+ -40°C to +125°C 32 TQFN-EP** Note: Insert the desired suffix letter (from the Selector Guide) into the blank to indicate buck switching frequency, active timeout period, fixed or adjustable output voltages, maximum output current, and SYNC functionality. / V denotes an automotive qualified part. +Denotes a lead(Pb)-free/RoHS-compliant package. *Future product—contact factory for availability. **EP = Exposed pad/side-wettable flanked package. www.maximintegrated.com 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. 32 TQFN-EP G3255Y+1 21-0563 90-0361 Maxim Integrated │ 24 MAX16993 Step-Down Controller with Dual 2.1MHz Step-Down DC-DC Converters Revision History REVISION NUMBER REVISION DATE 0 5/13 DESCRIPTION Initial release PAGES CHANGED — 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. 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 and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2013 Maxim Integrated Products, Inc. │ 25