9-3155; Rev 0; 5/04 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP The MAX8543/MAX8544 current-mode, constant-frequency PWM buck controllers operate from a 3V to 13.2V input supply and generate adjustable 0.8V to 0.9 x VIN output voltages at loads up to 25A. They feature adjustable switching frequency and synchronization for noise-sensitive applications. The MAX8543/MAX8544 can start with (or without) a preexisting bias on the output, without discharging the output.
MAX8543/MAX8544 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP ABSOLUTE MAXIMUM RATINGS IN, EN, CS+, CS- to GND .......................................-0.3V to +14V BST, DH to LX ..........................................................-0.3V to +6V BST to GND ............................................................-0.3V to +20V DL, COMP, ILIM2, SS, SYNCO, FSYNC to GND .......................................-0.3V to (VVL + 0.
Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP (VIN = 13.2V, VBST - VLX = 5V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS VCS+ - VCS-, VILIM1 = 0V MIN TYP MAX UNITS 38.5 50 56.5 VCS+ - VCS-, VILIM1 = (1/3)VVL 85 100 115 VCS+ - VCS-, VILIM1 = (2/3)VVL 127.5 150 172.5 170 200 230 VLX - VPGND, RILIM2 = 50kΩ (MAX8544 only) -42.5 -50 -57.
MAX8543/MAX8544 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP ELECTRICAL CHARACTERISTICS (continued) (VIN = 13.2V, VBST - VLX = 5V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS 88 91 94 % POK Power-OK Threshold VFB rising, percent of VOUT, typical hysteresis is 3% POK Output Voltage, Low VFB = 0.6V, IPOK = 2mA POK Leakage Current, High VPOK = 5.5V 25 200 mV 0.
Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP MAX8543/MAX8544 ELECTRICAL CHARACTERISTICS (continued) (VIN = 13.2V, VBST - VLX = 5V, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MIN MAX UNITS VILIM1 = 0V 8.8 13.2 VILIM1 = (1/3)VVL 4.8 7.2 VILIM1 = (2/3)VVL 3.2 4.8 VILIM1 = VVL 2.4 3.6 4.2 5.
MAX8543/MAX8544 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP ELECTRICAL CHARACTERISTICS (continued) (VIN = 13.2V, VBST - VLX = 5V, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER CONDITIONS MIN MAX UNITS 88 94 % 200 mV 1 µA +120 % 0.4 V POK Power-OK Threshold VFB rising, percent of VOUT, typical hysteresis is 3% POK Output Voltage, Low VFB = 0.6V, IPOK = 2mA POK Leakage Current, High VPOK = 5.
Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP EFFICIENCY vs. LOAD CURRENT WITH 3.3V INPUT VOUT = 2.5V 60 50 40 VOUT = 1.8V 50 20 10 10 1 2.51 2.50 2.49 2.48 2.46 fS = 500kHz 0.1 1 2.45 0 100 10 3 6 9 12 LOAD CURRENT (A) LOAD CURRENT (A) LINE REGULATION WITH 12V INPUT AND 2.5V OUTPUT LINE REGULATION 3.0V TO 3.6V INPUT OSCILLATOR FREQUENCY vs. INPUT VOLTAGE NO LOAD 2.502 2.500 15A LOAD 2.496 2.494 NO LOAD 2.50 15A LOAD fS = 350kHz 2.
MAX8543/MAX8544 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) MAX8544 STEP-LOAD RESPONSE 7.5A TO 15A TO 7.5A (5A/μs) MAX8544 STEP-LOAD RESPONSE 1.5A TO 15A TO 1.
Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP MAX8544 ENABLE WAVEFORMS FSYNC AND SYNCO WAVEFORMS MAX8543 toc14 MAX8543 toc15 VOUT 1V/div VEN 5V/div VLX 10V/div VOUT 2V/div VPOK VFSYNC 5V/div VSYNCO 5V/div 5V/div 10A/div IL 0 2μs/div 2ms/div OVERVOLTAGE PROTECTION WITH 15A LOAD SHORT CIRCUIT AND RECOVERY MAX8543 toc17 MAX8543 toc16 VIN 10V/div 12V VOUT 1V/div 5V 1V/div VOUT 0V VDH 10V/div 0V 5V 10A/div IL 0 10A/div IIN VDL 5V/div 0 4
MAX8543/MAX8544 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP Typical Operating Characteristics (continued) (TA = +25°C, unless otherwise noted.) BODE PLOT, 600kHz, 15A LOAD BODE PLOT, 600kHz, NO LOAD MAX8543 toc19 MAX8543 toc20 SWEEP TIME 10.000s 0dB SWEEP TIME 10.
Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP PIN NAME FUNCTION MAX8543 MAX8544 13 16 LX Inductor Connection 14 17 DH High-Side MOSFET Gate-Driver Output. Connect DH to the gate of the high-side external MOSFETs. DH is pulled low in shutdown. 15 18 BST Boost Capacitor Connection. Connect a 0.1µF or larger ceramic capacitor from BST to LX. BST provides power for the high-side MOSFET gate drive. 16 19 FSYNC Frequency Set and Synchronization.
MAX8543/MAX8544 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP VIN = (10.8V TO 13.2V) VL C12 9 SYNC IN C1 ILIM1 IN D2 R6 19 ON OFF 6 D1 FSYNC BST EN DH 2 18 17 N1 C4A N2 MAX8544EEP SS C7 LX VL DL R3 4 14 5 10 R8 1 VL VOUT = 2.5V UP TO 15A L1 16 VL 13 N3 C6A R4 N4 C6B C9 COMP PGND R2 C4C C3 C2 C8 C4B GND C5 3 15 12 R5 FB CS+ MODE ILIM2 CSSYNCO C10 8 7 20 C11 SYNC OUT R1 R9 11 POK POK R7 Figure 1.
Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP MAX8543/MAX8544 Table 1. Suggested Components for Figure 1 DESIGNATION QTY DESCRIPTION C1 1 1µF ±20%, 16V X5R ceramic capacitor (0603) Panasonic ECJ1VB1C105M or equivalent C2 1 10µF ±20%, 6.3V X5R ceramic capacitor (0805) Panasonic ECJ2FB0J106M or Taiyo Yuden JMK212BJ106MG C3 1 0.
MAX8543/MAX8544 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP VIN = (3V TO 3.6V) C12 8 SYNC IN C1 ILIM IN D2 R6 16 ON OFF 5 1 12 D1 FSYNC BST EN MAX8543 DH 15 14 N1 C4A N2 SS LX 11 VL DL 3 IN 4 FB CS+ 6 10 N3 C6A R4 N4 C6B C9 COMP PGND R2 VOUT = 2.5V UP TO 15A L1 C2 R3 C4D C3 13 C7 C8 C4C GND C5 2 C4B 9 7 CSC11 C10 R1 R5 Figure 2. Typical Applications Circuit with 3.3V (±10%) Input, 2.
Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP MAX8543/MAX8544 Table 2. Suggested Components for Figure 2 DESIGNATION QTY DESCRIPTION C1 1 1µF ±10%, 16V X5R ceramic capacitor (0603) Panasonic ECJ1VB1C105K or equivalent C2 1 10µF ±20%, 6.3V X5R ceramic capacitor (0805) Panasonic ECJ2FB0J106M or Taiyo Yuden JMK212BJ106MG C3 1 0.
MAX8543/MAX8544 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP Detailed Description DC-DC Converter Control Architecture The MAX8543/MAX8544 step-down controllers use a PWM, current-mode control scheme. An internal transconductance amplifier establishes an integrated error voltage.
Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP High-Side Gate-Drive Supply (BST) A flying capacitor boost circuit (Figure 3) generates the gate-drive voltage for the high-side n-channel MOSFET. The capacitor between BST and LX is charged from VL up to VVL minus the diode forward-voltage drop while the low-side MOSFET is on.
IPEAK ILOAD INDUCTOR CURRENT MAX8543/MAX8544 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP MAX8543/ MAX8544 LX R1 IVALLEY FB R2 TIME Figure 4. Inductor-Current Waveform Switching Frequency and Synchronization The MAX8543/MAX8544 have an adjustable internal oscillator that can be set to any frequency from 200kHz to 1MHz. To set the switching frequency, connect a resistor from FSYNC to GND.
Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP L= Ensure that ILIM is equal to or greater than the maximum load current at peak current limit (see the Peak Current Limit section): VOUT × (VIN − VOUT ) VIN × fS × ILOAD(MAX) × LIR where fS is the switching frequency. Choose a standardvalue inductor close to the calculated value. The exact inductor value is not critical and can be adjusted to make trade-offs among size, cost, and efficiency.
MAX8543/MAX8544 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP 2) If the resulting value of R ILIM is negative, either increase PFB or choose a low-side MOSFET with a lower RDS(ON). The latter is preferred as it increases the efficiency and results in a lower short-circuit current. To set the constant current limit for the latch-up mode, only RILIM is used. The equation for RILIM below sets the current-limit threshold at 1.
Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP For proper thermal-management design, the power dissipation must be calculated at the desired maximum operating junction temperature, maximum output current, and worst-case input voltage (for the low-side MOSFET, worst case is at VIN(MAX); for the high-side MOSFET, it could be either at VIN(MAX) or VIN(MIN)). The high-side and low-side MOSFETs have different loss components due to the circuit operation.
MAX8543/MAX8544 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP MOSFET Snubber Circuit Fast switching transitions cause ringing because of resonating circuit parasitic inductance and capacitance at the switching nodes. This high-frequency ringing occurs at LX’s rising and falling transitions and can interfere with circuit performance and generate EMI. To dampen this ringing, a series RC snubber circuit is added across each switch.
Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP Compensation Design The MAX8543/MAX8544 use an internal transconductance error amplifier whose output compensates the control loop. The external inductor, output capacitor, compensation resistor, and compensation capacitors determine the loop stability. The inductor and output capacitor are chosen based on performance, size, and cost.
MAX8543/MAX8544 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP fzEA = fpEA = For the case where fzMOD is less than fC: The power-modulator gain at fC is: 1 2π × CC × RC GMOD( fc) = GMOD(dc) × 1 2π × CF × RC fzMOD The error-amplifier gain at fC is: The crossover frequency, fC, should be much higher than the power-modulator pole fPMOD. Also, fC should be less than or equal to 1/5th the switching frequency.
Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP fpMOD = = PC Board Layout Guidelines ⎛R ⎞ ×f ×L 2π × COUT × ⎜ LOAD S + ESR⎟ ⎝ RLOAD + fS × L ⎠ 1 = 3.43kHz ⎛ 0.167 × (600 × 103 ) × ⎛ 0.8 × 10 −6 ⎞ ⎞ ⎝ ⎠ ⎜ ⎟ −6 2π × (360 × 10 ) × ⎜ + 0.005⎟ ⎜ 0.167 + (600 × 103 ) × ⎛⎝ 0.8 × 10 −6 ⎞⎠ ⎟ ⎝ ⎠ f fpMOD << fC ≤ S 5 3.43kHz << fC < 120kHz; select fC = 120kHz. fzMOD = = 1 2π × COUT × ESR 1 2π × (360 × 10 −6 ) × 0.005 = 88.4kHz Since fzMOD < fC: GMOD( fc) = GMOD(dc) × = 4.
MAX8543/MAX8544 Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP Table 4. Suggested Component Manufacturers MANUFACTURER COMPONENT WEBSITE Central Semiconductor PHONE Diodes www.centralsemi.com 631-435-1110 Coilcraft Inductors www.coilcraft.com 800-322-2645 International Rectifier MOSFETs www.irf.com 310-322-3331 Kamaya Resistors www.kamaya.com 260-489-1533 Panasonic Capacitors www.panasonic.com 714-373-7366 Sanyo Capacitors www.sanyo.
Step-Down Controllers with Prebias Startup, Lossless Sensing, Synchronization, and OVP QSOP.EPS Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
