Datasheet

ManualsBrandsMAXIM INTEGRATED ManualsPMICsPMIC - voltage regulators - DC DC switch controllers QSOP 24

General Description

The MAX8650 synchronous PWM buck controller oper-

ates from a 4.5V to 28V input and generates an

adjustable 0.7V to 5.5V output voltage at loads up to 25A.

The MAX8650 uses a peak current-mode control archi-

tecture with an adjustable (200kHz to 1.2MHz) constant

switching frequency and is externally synchronizable. The

IC’s current limit uses the inductor’s DC resistance to

improve efficiency or an external sense resistor for high

accuracy. The current-limit threshold is adjusted with an

external resistor. Foldback-type current limit can be

implemented to reduce the power dissipation in overload

or short-circuit conditions. Short-circuit protection is

provided based on sensing the current in the low-side

MOSFET. A reference input is provided for use with a

high-accuracy external reference or for double-data-rate

(DDR)-tracking applications.

Monotonic prebiased startup is available for a safe-start

in applications where the output capacitor may have an

initial charge. This feature prevents the output from

pulling low during startup, which is a common charac-

teristic of conventional buck regulators.

A 180° out-of–phase synchronization output is available

for synchronizing with another converter.

Features

o Operates from 4.5V to 28V Supply

o 1% FB Voltage Accuracy Over Temperature

o Adjustable Output Voltage Down to 0.7V or REFIN

o Adjustable Switching Frequency or External

Synchronization from 200kHz to 1.2MHz

o 180° Phase-Shifted Clock Output

o Adjustable Overcurrent Limit

o Adjustable Foldback Current Limit

o Adjustable Slope Compensation

o Selectable Current-Limit Mode: Latch-Off or

Automatic Recovery

o Monotonic Output-Voltage Rise at Startup

o Output Sources and Sinks Current

o Enable Input

o Power-OK (POK) Output

o Adjustable Soft-Start

o Independently Adjustable Overvoltage Protection

MAX8650

________________________________________________________________

Maxim Integrated Products

SYNC

FSYNC

POK

SYNCO

SCOMP

ILIM2

REFIN

ILIM1

COMP

OVP

MODE

BST

PGND

AVL

CS+

CS-

GND

OUT

0.7V TO 5.5V

7V TO 28V

C10

C11

OFF

POK

SYNCO

MAX8650EEG

Typical Operating Circuit

19-3973; Rev 1; 8/08

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.

Pin Configuration appears at end of data sheet.

EVALUATION KIT

AVAILABLE

4.5V to 28V Input Current-Mode Step-

Down Controller with Adjustable Frequency

Applications

Base Stations DDR

Network and Telecom Power Modules

Storage IBA Applications

Servers

Ordering Information

PART TEMP RANGE PIN-PACKAGE

MAX8650EEG+ -40°C to +85°C

24 QSOP

Denotes a lead-free/RoHS-compliant package.

Summary of content (25 pages)

PAGE 1
9-3973; Rev 1; 8/08 KIT ATION EVALU E L B A AVAIL 4.5V to 28V Input Current-Mode StepDown Controller with Adjustable Frequency Features The MAX8650 synchronous PWM buck controller operates from a 4.5V to 28V input and generates an adjustable 0.7V to 5.5V output voltage at loads up to 25A. The MAX8650 uses a peak current-mode control architecture with an adjustable (200kHz to 1.2MHz) constant switching frequency and is externally synchronizable.
PAGE 2
MAX8650 4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency ABSOLUTE MAXIMUM RATINGS IN, EN to GND ........................................................-0.3V to +30V BST to LX...............................................................-0.3V to +7.5V DH to LX ....................................................-0.3V to (VBST + 0.3V) LX to GND .................... -1V (-2.5V for < 50ns transient) to +30V DL to PGND.................................................-0.
PAGE 3
4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency (VIN = 12V, VBST - VLX = 6.5V, TA = -40°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER CONDITIONS MIN TYP MAX 0.693 0.7 0.707 UNITS ERROR AMPLIFIER REFIN = AVL FB Regulation Voltage VREFIN = 0.7V to 1.5V Transconductance VREFIN VREFIN 0.00375 70 VREFIN + 0.
PAGE 4
MAX8650 4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency ELECTRICAL CHARACTERISTICS (continued) (VIN = 12V, VBST - VLX = 6.5V, TA = -40°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.
PAGE 5
4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency (VIN = 12V, VBST - VLX = 6.5V, TA = -40°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER CONDITIONS MIN TYP MAX UNITS REFIN = AVL, VFB rising, typical hysteresis is 3% 629.0 650.0 671.0 VREFIN = 0.7V to 1.5V, VFB rising, typical hysteresis is 3% 88.7 91.7 94.7 mV % of 25 200 mV 1 µA POK Power-OK Threshold POK Output Voltage, Low VFB = 0.
PAGE 6
Typical Operating Characteristics (Circuit of Figure 3, 500kHz switching, VIN = 17V, VOUT = 3.3V, TA = +25°C, unless otherwise noted.) EFFICIENCY vs. LOAD CURRENT (CIRCUIT OF FIGURE 4) 50 40 60 50 12V INPUT, 0.9V OUTPUT 40 30 30 20 20 10 10 0 100 RILIM1 vs. PEAK CURRENT LIMIT OSCILLATOR FREQUENCY vs. INPUT VOLTAGE 50 RILIM1 (kΩ) 3.295 3.290 3.285 5 10 LOAD CURRENT (A) 55 NO LOAD 3.300 LOAD CURRENT (A) 15A LOAD 45 40 35 30 3.280 25 3.275 20 0.03 3.
PAGE 7
4.
PAGE 8
4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency MAX8650 Pin Description PIN NAME 1 FSYNC Frequency Set and Synchronization. Connect a resistor from FSYNC to GND to set the switching frequency, or drive with an external clock signal between 160kHz and 1.2MHz. See the Switching Frequency and Synchronization section. 2 MODE Current-Limit Operating-Mode Selection. Connect MODE to AVL for latch-off current limit or connect MODE to GND for automatic-recovery current limit.
PAGE 9
4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency PIN NAME FUNCTION 17 OVP Output Voltage Sensing for Overvoltage Protection. Connect OVP to the center of a resistor-divider from OUT to GND to set the FB independent output overvoltage trip point. Connect OVP to FB if this independence is not desired. The OVP threshold is 115% of the nominal FB regulation voltage. 18 FB Feedback Input.
PAGE 10
MAX8650 4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency IN MAX8650 BST 6.5V LDO REGULATOR EN UVLO VL LEVEL SHIFT DH THERMAL SHDN LX VL 5V AVL LDO AVL PWM CONTROL LOGIC VOLTAGE REFERENCE DL PGND REF SELECT LOGIC REF REFIN SYNCO SOFT-START CIRCUITRY OVP SS 1.
PAGE 11
4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency DC-DC Converter Control Architecture The MAX8650 step-down controller uses a PWM, current-mode control scheme. An internal transconductance amplifier establishes an integrated error voltage.
PAGE 12
MAX8650 4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency VL BST DH N MAX8650 LX DL N Figure 2. DH Boost Circuit to 20 squares (50 mils to 100 mils wide if the MOSFET is 1in from the device) for the gate drive. The dead time at the other edge (DH turning off) also has an adaptive dead-time circuit operating in a similar manner. For both edges, there is an additional 20ns fixed dead time after the adaptive dead time expires.
PAGE 13
4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency The MAX8650 can also be synchronized to an external clock by connecting the clock signal to FSYNC. In addition, SYNCO is provided to synchronize a second MAX8650 controller 180° out-of-phase with the first by connecting SYNCO of the first controller to FSYNC of the second. When the first controller is synchronized to an external clock, the external clock is inverted to generate SYNCO.
PAGE 14
MAX8650 4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency Table 1. Component List for Figure 3 COMPONENT VENDOR/PART QUANTITY C1, C2, C3 10µF, 25V X5R ceramic capacitors TDK C3225X5R1E106M (1210) 3 C5, C6 0.1µF, 10V X7R ceramic capacitors Kemet C0603C104M9RAC (0603) 2 C7 220pF, 50V X7R ceramic capacitor TDK C1608X7R1H271K 1 C8 Not installed — 0 C9A, C9B 150µF ±20%, 4V, 7mΩ ESR polymer aluminum electrolytic capacitors Panasonic EEFSDOG151R 2 C10, C14 0.
PAGE 15
4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency MAX8650 VIN 10.8V TO 13.2V R2 R1 D1 SYNC ON EN OFF POK 1 OPTIONAL 11 24 SYNCO 3 23 R5 22 FSYNC EN BST POK DH VREFIN 0.9VDC 21 C4 20 SYNCO SCOMP MAX8650 C6 R8 PGND VL SS ILIM1 COMP CS- R10 18 17 VOUT 0.
PAGE 16
MAX8650 4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency Table 2. Component List for Figure 4 COMPONENT DESCRIPTION VENDOR / PART QUANTITY C1, C2 10µF, 16V X5R ceramic capacitors (1210) Taiyo Yuden EMK325BJ106MN 2 C3 0.01µF, 10V X7R ceramic capacitor (0603) Kemet C0603C103M9RAC 1 C4, C5 0.
PAGE 17
4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency MAX8650 IPEAK INDUCTOR CURRENT AVL ILOAD MAX8650 R4 IVALLEY SCOMP R3 TIME Figure 5. Inductor-Current Waveform Design Procedure Setting the Output Voltage To set the output voltage for the MAX8650, connect FB to the center of an external resistor-divider from the output to GND (R9 and R10 of Figure 3).
PAGE 18
MAX8650 4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency 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 between size, cost, and efficiency. Lower inductor values minimize size and cost, but they also increase the output ripple and reduce the efficiency due to higher peak currents.
PAGE 19
4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency L1 VOUT MAX8650 LX MAX8650 MAX8650 R3 L1 VOUT LX R4 R4 C9 C9 R5 CS+ C13 R5 CS+ C13 CS- CS- Figure 8. Current Sense Using the Inductor’s DC Resistance Figure 9. Using a Current-Sense Resistor for Improved CurrentSense Accuracy The DC resistance of the inductor’s copper wire has a +0.22%/°C temperature coefficient.
PAGE 20
MAX8650 4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency ⎛ ⎞ V PLSCC = ⎜1 − OUT ⎟ × I2LOAD × RDS(ON) VIN ⎠ ⎝ Use RDS(ON) at TJ(MAX): PLSDC = 2 × ILOAD × VF × tDT × fS where VF is the body-diode forward-voltage drop, tDT is the dead time between high-side and low-side switching transitions (30ns typ), and fS is the switching frequency.
PAGE 21
4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency IP−P 8 × COUT × fS where IP-P is the peak-to-peak inductor current: V − VOUT VOUT IP−P = IN × fS × L VIN These equations are suitable for initial capacitor selection, but final values should be chosen based on a prototype or evaluation circuit. As a general rule, a smaller current ripple results in less output-voltage ripple.
PAGE 22
MAX8650 4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency CLOSE LOOP CLOSE LOOP GAIN (dB) GAIN (dB) POWER MODULATOR POWER MODULATOR ERROR AMP ERROR AMP fC 0dB FREQUENCY fpMOD FB DIVIDER 0dB FB DIVIDER fzMOD FREQUENCY fpMOD fC fzMOD Figure 10. Simplified Gain Plot for the fzMOD > fC Case Figure 11.
PAGE 23
4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency GMOD( fc) = GMOD(dc) × fpMOD = fpMOD = fzMOD The error-amplifier gain at fC is: f GEA ( fc) = gmEA × RC × zMOD fC 1 ⎛R ⎞ ×f ×L 2π × COUT × ⎜ LOAD S + ESR⎟ ⎝ RLOAD + fS × L ⎠ 1 ⎛ ⎞ ⎛ 3 −6 ⎞ ⎜ 0.22 × (500 × 10 ) × ⎜⎝1.2 × 10 ⎟⎠ ⎟ −6 2π × (300 × 10 ) × ⎜ + 0.0035⎟ ⎜ 0.22 + (500 × 103 ) × ⎛1.2 × 10 −6 ⎞ ⎟ ⎜ ⎟ ⎜ ⎟ ⎝ ⎠ ⎝ ⎠ = 3.23kHz f fpMOD << fC ≤ S 5 RC is calculated as: 3.
PAGE 24
MAX8650 4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency Applications Information PCB Layout Guidelines Careful PCB layout is critical to achieve low switching losses and clean, stable operation. The switching power stage requires particular attention. Follow these guidelines for good PCB layout: 1) Place IC decoupling capacitors as close to IC pins as possible. Keep the power ground plane and signal ground plane separate.
PAGE 25
4.5V to 28V Input Current-Mode Step-Down Controller with Adjustable Frequency REVISION NUMBER REVISION DATE 0 1/06 Initial release 1 8/08 Updated Table 1 and added Package Information table. DESCRIPTION PAGES CHANGED — 14, 19, 25 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.