Datasheet

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General Description

The MAX15035 pulse-width modulation (PWM) controller

provides high efficiency, excellent transient response,

and high DC-output accuracy. Combined with the inter-

nal low on-resistance MOSFETs, the MAX15035 pro-

vides a highly efficient and compact solution for small

form factor applications that need a high-power density.

Maxim’s proprietary Quick-PWM™ quick-response,

constant on-time PWM control scheme handles wide

input/output voltage ratios (low-duty-cycle applications)

with ease and provides 100ns instant-on response to

load transients while maintaining a relatively constant

switching frequency. The output voltage can be dynam-

ically controlled using the dynamic REFIN, which sup-

ports input voltages between 0V to 2V. The REFIN

adjustability combined with a resistive voltage-divider

on the feedback input allows the MAX15035 to be con-

figured for any output voltage between 0V to 0.9V

The controller senses the current across the synchro-

nous rectifier to achieve a low-cost and highly efficient

valley current-limit protection. External current-limit con-

trol is provided to allow higher current-limit settings for

applications with heatsinks and air flow, or for lower

current applications that need lower current-limit set-

tings to avoid overdesigning the application circuit. The

adjustable current limit provides a high degree of flexi-

bility, allowing thermally compensated protection or

foldback current-limit protection using a voltage-divider

partially derived from the output.

The MAX15035 includes a voltage-controlled soft-start

and soft-shutdown to limit the input surge current, pro-

vide a monotonic power-up into a precharged output,

and provide a predictable soft-start time. The controller

also includes output fault protection—undervoltage and

overvoltage protection—as well as thermal-fault protec-

tion.

The MAX15035 is available in a small 40-pin, 6mm x 6mm,

TQFN package.

Applications

Server Computers

GPU Core Supplies

DDR Memory—VDDQ or VTT

Point-of-Load Applications

Step-Down Power Supplies

Storage Power Supplies

Features

o 4.5V to 26V Input Voltage Range

o Fast Transient Response

o Monotonic Power-Up with Precharged Output

o Supports Any Output Capacitor

No Compensation Required with Polymers/

Tantalum

Stable with Ceramic Output Capacitors Using

External Compensation

o Dynamically Adjustable Output Voltage

0.5% V

OUT

Accuracy Over Line and Load

o Adjustable Valley Current-Limit Protection

Thermal Compensation with NTC

Supports Foldback Current Limit

o Programmable Switching Frequency

o Overvoltage Protection

o Undervoltage Protection

o Voltage Soft-Start and Soft-Shutdown

o Power-Good Window Comparator

MAX15035

15A Step-Down Regulator with Internal Switches

________________________________________________________________

Maxim Integrated Products

MAX15035

THIN QFN

(6mm x 6mm)

TOP VIEW

PGND

N.C.

AGND

TON

BST

REFIN

4567

27282930 26 24 23 22

REF

SKIP

N.C.

PGND

AGND

PGND

PGOOD

N.C.

PGND

ILIM

PGND

8910

N.C.

EP1 EP3

AGND

EP2

Pin Configuration

19-4123; Rev 2; 10/08

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

Quick-PWM is a trademark of Maxim Integrated Products, Inc.

Ordering Information

Denotes a lead-free/RoHS-compliant package.

EP = Exposed pad.

PART TEMP RANGE

PIN-PACKAGE

MAX15035ETL+ - 40°C to + 85°C 40 TQFN - E P *

Summary of content (27 pages)

PAGE 1
9-4123; Rev 2; 10/08 KIT ATION EVALU E L B A AVAIL 15A Step-Down Regulator with Internal Switches o Fast Transient Response o Monotonic Power-Up with Precharged Output o Supports Any Output Capacitor No Compensation Required with Polymers/ Tantalum Stable with Ceramic Output Capacitors Using External Compensation o Dynamically Adjustable Output Voltage 0.
PAGE 2
MAX15035 15A Step-Down Regulator with Internal Switches ABSOLUTE MAXIMUM RATINGS IN to PGND.............................................................-0.3V to +28V TON to GND ...........................................................-0.3V to +28V VDD to GND ..............................................................-0.3V to +6V VCC to GND ................................................-0.3V to (VDD + 0.3V) EN, SKIP, PGOOD to GND.......................................-0.3V to +6V REF, REFIN to GND...
PAGE 3
15A Step-Down Regulator with Internal Switches (Circuit of Figure 1, VIN = 12V, VDD = VCC = VEN = 5V, REFIN = ILIM = REF, SKIP = GND. TA = 0°C to +85°C, unless otherwise specified. Typical values are at TA = +25°C.) (Note 1) PARAMETER Soft-Start/Soft-Stop Slew Rate Dynamic REFIN Slew Rate SYMBOL SSSR DYNSR CONDITIONS MIN TYP MAX UNITS 0.4 1.2 2.2 mV/μs 3 9.45 18 mV/μs No load 1.990 2.00 2.010 IREF = -10μA to +50μA 1.
PAGE 4
MAX15035 15A Step-Down Regulator with Internal Switches ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 1, VIN = 12V, VDD = VCC = VEN = 5V, REFIN = ILIM = REF, SKIP = GND. TA = 0°C to +85°C, unless otherwise specified. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL MIN SKIP = open (3.
PAGE 5
15A Step-Down Regulator with Internal Switches (Circuit of Figure 1, VIN = 12V, VDD = VCC = VEN = 5V, REFIN = ILIM = REF, SKIP = GND. TA = -40°C to +85°C, unless otherwise specified.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN MAX UNITS 1.985 2.015 V REFERENCE Reference Voltage VREF VDD = 4.5V to 5.
PAGE 6
Typical Operating Characteristics (MAX15035 Circuit of Figure 1, VIN = 12V, VDD = 5V, SKIP = GND, RTON = 200kΩ, TA = +25°C, unless otherwise noted.) 20V 60 50 40 60 50 ULTRASONIC MODE 40 SKIP MODE PWM MODE 30 SKIP MODE PWM MODE 1.495 1.485 20 0.1 0.01 1 10 100 LOAD CURRENT (A) LOAD CURRENT (A) 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 LOAD CURRENT (A) 1.05V OUTPUT EFFICIENCY vs. LOAD CURRENT 1.05V OUTPUT EFFICIENCY vs. LOAD CURRENT 1.05V OUTPUT VOLTAGE vs.
PAGE 7
15A Step-Down Regulator with Internal Switches PWM MODE SWITCHING FREQUENCY vs. INPUT VOLTAGE 250 200 150 100 ULTRASONIC MODE SKIP MODE 0 0.01 0.1 1 NO LOAD MAX15035 toc12 370 360 ILOAD = 5A 6 8 12 10 14 16 18 20 22 -40 24 -20 0 20 40 60 80 LOAD CURRENT (A) INPUT VOLTAGE (V) TEMPERATURE (°C) MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE MAXIMUM OUTPUT CURRENT vs. AMBIENT TEMPERATURE NO-LOAD SUPPLY CURRENT (IBIAS) vs. INPUT VOLTAGE MAXIMUM OUTPUT CURRENT (A) 15.60 15 15.
PAGE 8
MAX15035 15A Step-Down Regulator with Internal Switches Typical Operating Characteristics (continued) (MAX15035 Circuit of Figure 1, VIN = 12V, VDD = 5V, SKIP = GND, RTON = 200kΩ, TA = +25°C, unless otherwise noted.) SOFT-START WAVEFORM (LIGHT LOAD) SOFT-START WAVEFORM (HEAVY LOAD) MAX15035 toc19 MAX15035 toc18 5V A 5V A 0 5V B 0 5V 0 B 1.5V C 0 1.5V C 0 0 D 8A D 1A 0 0 A. EN, 5V/div B. PGOOD, 5V/div IOUT = 8A 200µs/div C. VOUT, 1V/div B. INDUCTOR CURRENT, 10A/div A. EN, 5V/div B.
PAGE 9
15A Step-Down Regulator with Internal Switches LOAD-TRANSIENT RESPONSE (SKIP MODE) OUTPUT OVERVOLTAGE WAVEFORM OUTPUT OVERCURRENT WAVEFORM MAX15035 toc22 MAX15035 toc24 MAX15035 toc23 20A 8A 1A A A 1.5V A 0 B 1.5V MAX15035 Typical Operating Characteristics (continued) (MAX15035 Circuit of Figure 1, VIN = 12V, VDD = 5V, SKIP = GND, RTON = 200kΩ, TA = +25°C, unless otherwise noted.) 0 1.5V B 0 5V 8A C 0A 5V C 0 20µs/div B. VOUT, 20mV/div C.
PAGE 10
MAX15035 15A Step-Down Regulator with Internal Switches Typical Operating Characteristics (continued) (MAX15035 Circuit of Figure 1, VIN = 12V, VDD = 5V, SKIP = GND, RTON = 200kΩ, TA = +25°C, unless otherwise noted.) DYNAMIC OUTPUT-VOLTAGE TRANSITION (PWM MODE) DYNAMIC OUTPUT-VOLTAGE TRANSITION (SKIP MODE) MAX15035 toc28 1.5V MAX15035 toc29 1.5V A A 1.05V 1.05V 1.5V 1.5V B B 1.05V 1.05V 0 -6A 10A C C 0 12V 12V D 0 D 0 A. REFIN, 500mV/div B. VOUT, 200mV/div IOUT = 2A 40µs/div C.
PAGE 11
15A Step-Down Regulator with Internal Switches PIN NAME FUNCTION 32 FB Feedback Voltage Sense Connection. Connect directly to the positive terminal of the output capacitors for output voltages less than 2V as shown in Figure 1. For fixed-output voltages greater than 2V, connect REFIN to REF and use a resistive divider to set the output voltage (Figure 6). FB senses the output voltage to determine the on-time for the high-side switching MOSFET. 33 ILIM Current-Limit Threshold Adjustment.
PAGE 12
MAX15035 15A Step-Down Regulator with Internal Switches 4 5V BIAS SUPPLY C1 1μF C2 1μF BST 36 GND/OPEN/REF/VDD C3 1000pF 35 AGND LO PGND PGOOD EN MAX15035 FB SKIP COUT 6–15 PWR 32 RT 60.4kΩ REF REFIN ILIM AGND 33 R4 40.2kΩ NTC 10kΩ B = 3435 R5 49.4kΩ 3, 28, EP1 PWR AGND OUTPUT 1.05V/1.50V 15A (MAX) PWR R2 54.9kΩ HI PWR L1 5, 16, EP2 R1 49.9kΩ 34 R3 97.6kΩ CIN CBST 0.
PAGE 13
15A Step-Down Regulator with Internal Switches The MAX15035 standard application circuit (Figure 1) generates a 1.5V or 1.05V output rail for general-purpose use. See Table 1 for component selections. Table 2 lists the component suppliers. Detailed Description The MAX15035 step-down controller is ideal for lowduty-cycle (high-input voltage to low-output voltage) applications.
PAGE 14
MAX15035 15A Step-Down Regulator with Internal Switches TON ON-TIME COMPUTE IN tOFF(MIN) FB ONE-SHOT S tON TRIG BST TRIG Q Q IN Q R LX ONE-SHOT INTEGRATOR (CCV) ERROR AMPLIFIER VDD S Q R PGND FB QUADLEVEL DECODE SKIP FAULT BLANK EA + 0.3V ZERO CROSSING PGOOD AND FAULT PROTECTION VALLEY CURRENT LIMIT ILIM REF EA - 0.2V EN SOFT-START/ SOFT-STOP PGOOD 2V REF REFIN EA BLANK MAX15035 DYNAMIC OUTPUT TRANSITION DETECTION Figure 2.
PAGE 15
A Step-Down Regulator with Internal Switches The soft-start circuitry does not use a variable current limit, so full output current is available immediately. PGOOD becomes high impedance approximately 200μs after the target REFIN voltage has been reached. The MAX15035 automatically uses pulse-skipping mode during soft-start and uses forced-PWM mode during soft-shutdown, regardless of the SKIP configuration. For automatic startup, the input voltage should be present before VCC.
PAGE 16
MAX15035 15A Step-Down Regulator with Internal Switches When the on-time expires, the controller re-enables the low-side MOSFET until the controller detects that the inductor current drops below the zero-crossing threshold. Starting with a negative inductor current pulse greatly reduces the peak output voltage when compared to starting with a positive inductor current pulse.
PAGE 17
15A Step-Down Regulator with Internal Switches MAX15035 DYNAMIC REFIN WINDOW REFIN OUTPUT VOLTAGE INTERNAL PWM CONTROL INTERNAL EA TARGET = ACTUAL VOUT PWM PWM SKIP SKIP LX PGOOD BLANK HIGH-Z OVP SET TO REF + 300mV BLANK HIGH-Z EA TARGET + 300mV EA TARGET + 300mV DYNAMIC TRANSITION WHEN SKIP = REF Figure 5.
PAGE 18
MAX15035 15A Step-Down Regulator with Internal Switches 4 5V BIAS SUPPLY C1 1μF C2 1μF PWR BST LX 2 OFF 36 GND/OPEN/REF/VDD C3 1000pF 18–26, EP3 INPUT 7V TO 24V CIN 30 CBST 0.1μF VCC R10 100kΩ 38 ON TON IN 37 AGND VDD RTON 332kΩ 29 PGND 5, 16, EP2 PWR FB SKIP L1 OUTPUT 3.3V 6–15 PGOOD EN PWR R7 20kΩ REF AGND AGND 34 PWR 32 MAX15035 35 COUT R6 13.0kΩ REFIN ILIM 33 AGND 3, 28, EP1 R4 49.9kΩ REF R5 49.4kΩ 7V TO 15V INPUT 1kΩ AGND PWR AGND 5VBIAS 5.
PAGE 19
15A Step-Down Regulator with Internal Switches MAX15035 TARGET + 300mV TARGET - 200mV POWER-GOOD AND FAULT PROTECTION FB EN OVP SOFT-START COMPLETE UVP OVP ENABLED ONESHOT 200μs FAULT LATCH FAULT POWER-GOOD IN OUT CLK Figure 7. Power-Good and Fault Protection output voltage, connect an external pullup resistor between PGOOD and VDD. A 100kΩ pullup resistor works well in most applications. Figure 7 shows the power-good and fault-protection circuitry. high impedance on LX.
PAGE 20
MAX15035 15A Step-Down Regulator with Internal Switches • • Switching frequency: This choice determines the basic trade-off between size and efficiency. The optimal frequency is largely a function of maximum input voltage due to MOSFET switching losses that are proportional to frequency and VIN2. The optimum frequency is also a moving target, due to rapid improvements in MOSFET technology that are making higher frequencies more practical.
PAGE 21
15A Step-Down Regulator with Internal Switches C1 1μF C2 1μF BST PWR R10 100kΩ 2 OFF 36 GND/OPEN/REF/VDD C3 1000pF AGND 35 AGND PGND 18–26, EP3 R2 54.9kΩ CIN CBST 0.1μF 5, 16, EP2 PWR L1 6–15 PGOOD EN MAX15035 FB SKIP OUTPUT 1.50V 10A 1.05V 7A COUT PWR PWR 32 REF R8 100kΩ REFIN ILIM R4 49.9kΩ 33 REF AGND R5 49.4kΩ 3, 28, EP1 LO INPUT 7V TO 24V 30 R1 49.9kΩ 34 R3 97.
PAGE 22
MAX15035 15A Step-Down Regulator with Internal Switches With most chemistries (polymer, tantalum, aluminum electrolytic), the actual capacitance value required relates to the physical size needed to achieve low ESR and the chemistry limits of the selected capacitor technology. Ceramic capacitors provide low ESR, but the capacitance and voltage rating (after derating) are determined by the capacity needed to prevent VSAG and VSOAR from causing problems during load transients.
PAGE 23
15A Step-Down Regulator with Internal Switches The DC-coupling requires fewer external compensation capacitors, but this also creates an output load line that depends on the inductor’s DCR (parasitic resistance). Alternatively, the current-sense information may be ACcoupled, allowing stability to be dependent only on the inductance value and compensation components and eliminating the DC load line.
PAGE 24
MAX15035 15A Step-Down Regulator with Internal Switches When only using ceramic output capacitors, output overshoot (VSOAR) typically determines the minimum output capacitance requirement. Their relatively low capacitance value may allow significant output overshoot when stepping from full-load to no-load conditions, unless designed with a small inductance value and high switching frequency to minimize the energy transferred from the inductor to the capacitor during load-step recovery.
PAGE 25
15A Step-Down Regulator with Internal Switches Calculating again with h = 1 gives the absolute limit of dropout: 3.3V − 0V + 150mV ⎡ ⎤ VIN(MIN) = ⎢ ⎥ = 3.52V ⎣1 − (1.0 × 350ns × 300kHz) ⎦ Therefore, VIN must be greater than 3.52V, even with very large output capacitance, and a practical input voltage with reasonable output capacitance would be 3.74V. Applications Information PCB Layout Guidelines Careful PCB layout is critical to achieve low switching losses and clean, stable operation.
PAGE 26
MAX15035 15A Step-Down Regulator with Internal Switches Package Information Chip Information TRANSISTOR COUNT: 7169 PROCESS: BiCMOS 26 For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
PAGE 27
15A Step-Down Regulator with Internal Switches PAGES CHANGED REVISION NUMBER REVISION DATE 0 5/08 Initial release — 1 7/08 Modified Figure 1, Tables 1 and 2. 12 2 10/08 Updated Pin Description, Figure 1, and Detailed Description. DESCRIPTION 11, 12, 13, 16, 18–21, 24 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.