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19-4719; Rev 3; 6/14

General Description

The MAX15046 synchronous step-down controller oper-

ates from a 4.5V to 40V input voltage range and gener-

ates an adjustable output voltage from 85% of the input

voltage down to 0.6V, supporting loads up to 25A. The

device allows monotonic startup into a prebiased bus

without discharging the output and features adaptive

internal digital soft-start.

The MAX15046 offers the ability to adjust the switching fre-

quency from 100kHz to 1MHz with an external resistor. The

MAX15046’s adaptive synchronous rectification eliminates

the need for an external freewheeling Schottky diode.

The device also utilizes the external low-side MOSFET’s

on-resistance as a current-sense element, eliminating the

need for a current-sense resistor. This protects the DC-DC

components from damage during output overloaded con-

ditions or output short-circuit faults without requiring a

current-sense resistor. Hiccup-mode current limit reduc-

es power dissipation during short-circuit conditions. The

MAX15046 includes a power-good output and an enable

input with precise turn-on/turn-off threshold, which can be

used for input supply monitoring and power sequencing.

Additional protection features include sink-mode current

limit and thermal shutdown. Sink-mode current limit pre-

vents reverse inductor current from reaching dangerous

levels when the device is sinking current from the output.

The MAX15046A/MAX15046B feature soft-stop opera-

tion. Soft-stop operation is disabled in the MAX15046C.

The MAX15046 is available in a 16-pin QSOP or 16-pin

QSOP-EP package and operates over the -40°C to

+125°C temperature range.

Features

● Input Voltage Ranges from 4.5V to 40V or 5V ±10%

● Adjustable Outputs from 0.85 x V

Down to 0.6V

● Adjustable Switching Frequency (100kHz to 1MHz)

with ±10% (1MHz) Accuracy

● Adaptive Internal Digital Soft-Start

● Up to 25A Output Capability

● Cycle-by-Cycle Valley-Mode Current Limit with

Adjustable, Temperature-Compensated Threshold

(30mV to 300mV)

● Monotonic Startup into Prebiased Output

● ±1% Accurate Voltage Reference

● 90% Maximum Duty Cycle (MAX15046C)

● 3A Peak Gate Drivers

● Hiccup-Mode Short-Circuit Protection

● Overtemperature Shutdown

● Power-Good (PGOOD) Output and Enable Input

(EN) with ±5% Accurate Threshold

● Thermally Enhanced 16-Pin QSOP Package

Applications

● Industrial Power Supplies (PLC, Industrial Computers,

Fieldbus Components, Fieldbus Couplers)

● Telecom Power Supplies

● Base Stations

Ordering Information and Pin Configurations appear at end

of data sheet.

MAX15046

CSP

BST

DRV

PGND

GND

PGOOD

LIM

COMP

0.6V TO 0.85V x V

OUT

4.5V TO 40V

OFF

MAX15046 40V, High-Performance, Synchronous

Buck Controller

Typical Operating Circuit

EVALUATION KIT AVAILABLE

Summary of content (23 pages)

PAGE 1
EVALUATION KIT AVAILABLE MAX15046 40V, High-Performance, Synchronous Buck Controller General Description Features The MAX15046 synchronous step-down controller operates from a 4.5V to 40V input voltage range and generates an adjustable output voltage from 85% of the input voltage down to 0.6V, supporting loads up to 25A. The device allows monotonic startup into a prebiased bus without discharging the output and features adaptive internal digital soft-start.
PAGE 2
MAX15046 40V, High-Performance, Synchronous Buck Controller Absolute Maximum Ratings IN to GND...............................................................-0.3V to +45V VCC to GND..................... -0.3V to lower of (VIN + 0.6V) and 6V EN, DRV to GND......................................................-0.3V to +6V PGOOD to GND.....................................................-0.3V to +45V PGND to GND.......................................................-0.3V to +0.3V DL to PGND..................
PAGE 3
MAX15046 40V, High-Performance, Synchronous Buck Controller Electrical Characteristics (continued) (VIN = 24V, VEN = 5V, VGND = VPGND = 0V, CIN = 1µF, CVCC = 4.7µF, RRT = 49.9kΩ, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN VCOMP-RAMP Minimum Voltage COMP Source/Sink Current TYP MAX 200 ICOMP VCOMP = 1.4V EN Input High VEN_H VEN rising EN Input Low VEN_L VEN falling IEN VEN = 5.
PAGE 4
MAX15046 40V, High-Performance, Synchronous Buck Controller Electrical Characteristics (continued) (VIN = 24V, VEN = 5V, VGND = VPGND = 0V, CIN = 1µF, CVCC = 4.7µF, RRT = 49.9kΩ, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2) PARAMETER SYMBOL DL Peak Current CONDITIONS CLOAD = 10nF DH, DL Break-Before-Make Time (Dead Time) MIN TYP Sinking, VDRV = VCC = 5.25V 3 Sourcing, VDRV = VCC = 5.
PAGE 5
MAX15046 40V, High-Performance, Synchronous Buck Controller Typical Operating Characteristics (VIN = 24V, TA = +25°C, unless otherwise noted.) 30 40 30 20 20 10 10 3 0 9 12 0 15 12 VCC LINE REGULATION 5.248 10 15 20 25 30 35 40 4.6 4.0 45 SWITCHING FREQUENCY vs. RRT 1200 MAX15046 toc07 900 800 600 500 400 300 200 100 40 80 RRT (kΩ) www.maximintegrated.com 120 160 800 MAX15046 toc03 6 8 10 12 VCC vs. TEMPERATURE ILOAD = 5mA 5.263 0 5 10 15 20 5.
PAGE 6
MAX15046 40V, High-Performance, Synchronous Buck Controller Typical Operating Characteristics (continued) (VIN = 24V, TA = +25°C, unless otherwise noted.) CURRENT (FA) 70 65 60 55 50 45 40 SINK AND SOURCE CURRENT LIMIT THRESHOLDS vs. RESISTANCE (RILIM) LOAD TRANSIENT ON OUT (1A TO 10A) MAX15046 toc12a MAX15046 toc11 75 0.20 CURRENT-LIMIT THRESHOLD (V) MAX15046 toc10 80 LIM REFERENCE CURRENT vs. TEMPERATURE 0.15 0.10 0.05 VOUT 200mV/div SINK CURRENT LIMIT 0 -0.05 -0.
PAGE 7
MAX15046 40V, High-Performance, Synchronous Buck Controller Typical Operating Characteristics (continued) (VIN = 24V, TA = +25°C, unless otherwise noted.) STARTUP WITH PREBIASED OUTPUT (2V) MAX15046 toc15c VOUT = 3.3V SINK CURRENT-LIMIT WAVEFORMS (5V PREBIASED) STARTUP WITH PREBIASED OUTPUT (0.5V) MAX15046 toc16 MAX15046 toc15d 24V 24V IN 10V/div VIN 10V/div 2V 0.5V VOUT 2V/div VOUT 2V/div PGOOD 5V/div PGOOD 5V/div VOUT 500mV/div VLX 50V/div ILX 5A/div VOUT = 3.
PAGE 8
MAX15046 40V, High-Performance, Synchronous Buck Controller Pin Description PIN NAME 1 IN Regulator Input. Connect to the input rail of the buck converter. Bypass IN to PGND with a 100nF minimum ceramic capacitor. When operating in the 5V ±10% range, connect IN to VCC. 2 VCC 5.25V Linear Regulator Output. Bypass VCC to PGND with a ceramic capacitor of at least 4.7µF when VCC supplies MOSFET gate-driver current at DRV or 2.2µF when VCC is not used to power DRV.
PAGE 9
MAX15046 40V, High-Performance, Synchronous Buck Controller Functional Diagram VREF OSCILLATOR RT FB HICCUP CK SOFT-START/STOP AND HICCUP LOGIC VREF EN CK OSC ENABLE ENABLE COMPARATOR GM COMP DAC_VREF HICCUP TIMEOUT ENABLE DH_DL_ENABLE EN_INT PWM COMPARATOR VREF BGAP_OK V_BGAP VIN_OK V_BGAP VCC BGAP_OK BGAP_OK V_DRV VIN_OK LIM IN BANDGAP OK GENERATOR VREF RAMP BST INTERNAL VOLTAGE REGULATOR VCC UVLO PWM RAMP GENERATOR CK BGAP_OK CK DC-DC OSCILLATOR AND ENABLE LOGIC DH_D
PAGE 10
MAX15046 Detailed Description The MAX15046 synchronous step-down controller operates from a 4.5V to 40V input-voltage range and generates an adjustable output voltage from 85% of the inputvoltage down to 0.6V while supporting loads up to 25A. As long as the device supply voltage is within 5.0V to 5.5V, the input power bus (VIN) can be as low as 3.3V. The MAX15046 offers adjustable switching frequency from 100kHz to 1MHz with an external resistor.
PAGE 11
MAX15046 40V, High-Performance, Synchronous Buck Controller discharge path can cause the sense circuitry to interpret the MOSFET gate as “off” while the VGS of the MOSFET is still high. To minimize stray impedance, use very short, wide traces. Synchronous rectification reduces conduction losses in the rectifier by replacing the normal low-side Schottky catch diode with a low-resistance MOSFET switch. The MAX15046 features a robust internal pulldown transistor with a typical 1Ω RDS(ON) to drive DL low.
PAGE 12
MAX15046 When the valley current limit is reached during soft-start, the MAX15046 regulates to the output impedance times the limited inductor current and turns off after 4096 clock cycles. When starting up into a large capacitive load (for example), the inrush current will not exceed the currentlimit value. If the soft-start is not completed before 4096 clock cycles, the device turns off. The device remains off for 8192 clock cycles before trying to soft-start again.
PAGE 13
MAX15046 40V, High-Performance, Synchronous Buck Controller cycles (hiccup timeout delay) before attempting a new soft-start sequence. The hiccup-mode protection remains active during the soft-start time. Undervoltage Lockout The maximum voltage conversion ratio is limited by the maximum duty cycle (Dmax): VOUT D × VDROP2 + (1-D max ) × VDROP1 < D max - max VIN VIN The MAX15046 provides an internal undervoltage lockout (UVLO) circuit to monitor the voltage on VCC.
PAGE 14
MAX15046 40V, High-Performance, Synchronous Buck Controller Setting the Switching Frequency An external resistor connecting RT to GND sets the switching frequency (fSW). The relationship between fSW and RRT is: 15.14 × 10 9 RRT = f SW + (1 x 10 -7 ) (f SW 2 ) where fSW is in Hz and RRT is in Ω. For example, a 300kHz switching frequency is set with RRT = 49.9kΩ. Higher frequencies allow designs with lower inductor values and less output capacitance.
PAGE 15
MAX15046 40V, High-Performance, Synchronous Buck Controller An RLIM resistance range of 6kΩ to 60kΩ corresponds to a current-limit threshold of 30mV to 300mV. Use 1% tolerance resistors when adjusting the current limit to minimize error in the current-limit threshold. Input Capacitor The input filter capacitor reduces peak current drawn from the power source and reduces noise and voltage ripple on the input caused by the switching circuitry.
PAGE 16
MAX15046 40V, High-Performance, Synchronous Buck Controller To choose the appropriate compensation network type, the power-supply poles and zeros, the zero-crossover frequency, and the type of the output capacitor must be determined first.
PAGE 17
MAX15046 40V, High-Performance, Synchronous Buck Controller VOUT 1 C × C CF 2π × R F × F C F + C CF f P3 = R1 COMP gM R2 VREF RF CF CCF Figure 3. Type II Compensation Network Solving for CF: CF = 1 2π × R F × f PO × 0.75 fP3 attenuates the high-frequency output ripple. Place the zeros and poles such that the phase margin peaks around fO. Ensure that RF >> 2/gM and the parallel resistance of R1, R2, and RI is greater than 1/gM.
PAGE 18
MAX15046 40V, High-Performance, Synchronous Buck Controller and maintains -20dB/decade slope up to 1/2 of the switching frequency. This is likely to occur if the output capacitor is low-ESR tantalum. Set fP2 = fZO. When using a ceramic capacitor, the capacitor ESR zero (fZO) is likely to be located even above one half of the switching frequency, fPO < fO < fSW/2 < fZO.
PAGE 19
MAX15046 40V, High-Performance, Synchronous Buck Controller ΔVBST such that the available gate-drive voltage is not significantly degraded (e.g. ΔVBST = 100mV to 300mV) when determining CBST. Use a low-ESR ceramic capacitor as the boost capacitor with a minimum value of 100nF. A small-signal diode can be used for the bootstrap circuit and must have a minimum voltage rating of VIN + 3V to withstand the maximum BST voltage.
PAGE 20
MAX15046 40V, High-Performance, Synchronous Buck Controller Typical Application Circuits TYPICAL APPLICATION CIRCUIT 1 VIN +24V C1 100µF C2 10µF C3 10µF C4 0.1µF C16 1µF CSP IN R7 51kΩ VCC MAX15046 PGOOD ON Q1 LX OFF EN BST LIM DL C5 0.47µF Q2 COMP C13 68pF R8 22.6kΩ C14 1500pF C15 15pF FB PGND RT GND R5 43.2kΩ R6 23.2kΩ DRV C12 220pF R3 3.65kΩ R1 10Ω C8 100µF C9 100µF C10 47µF C7 1000pF D1 R9 32.4kΩ VOUT +3.3V L1 1.5µH DH C6 2.2µF R2 2.2Ω C11 4.
PAGE 21
MAX15046 40V, High-Performance, Synchronous Buck Controller Typical Application Circuits (continued) TYPICAL APPLICATION CIRCUIT 2 VIN +4.5V TO +5.5V C1 C2 CSP IN VCC MAX15046 Q1 DH PGOOD PGOOD ENABLE EN BST LIM DL L1 LX C3 VOUT C4 Q2 C5 D1 R4 COMP C7 R3 DRV C6 C8 C9 R1 FB PGND RT GND R3 R2 TYPICAL APPLICATION CIRCUIT 3 VIN +24V VAUX +4.5V TO +5.
PAGE 22
MAX15046 40V, High-Performance, Synchronous Buck Controller Pin Configurations TOP VIEW IN 1 + IN 1 16 CSP + 16 CSP VCC 2 15 DH VCC 2 15 DH PGOOD 3 14 LX PGOOD 3 14 LX EN 4 MAX15046A EN 4 13 BST LIM 5 12 DL LIM 5 COMP 6 11 DRV FB 7 RT 8 MAX15046B MAX15046C FB 7 9 RT 8 GND 12 DL 11 DRV COMP 6 10 PGND 13 BST EXPOSED PAD 10 PGND 9 GND QSOP-EP QSOP Ordering Information Package Information PART TEMP RANGE PIN-PACKAGE MAX15046AAEE+ -40°C to +125°C 16 QSOP MAX15046BAEE
PAGE 23
MAX15046 40V, High-Performance, Synchronous Buck Controller Revision History REVISION NUMBER REVISION DATE PAGES CHANGED 0 7/09 Initial release 1 2/10 Corrected Minimum Low-Side On-Time conditions in Electrical Characteristics; corrected TOCs 2, 18, and 19; corrected MOSFET Gate Drivers (DH, DL), Setting the Switching Frequency, Setting the Valley Current Limit, MOSFET Selection, and Power Dissipation sections; corrected Typical Application Circuit 1 2 1/13 Added MAX15046C 3 6/14 Modify the