Datasheet

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General Description

The MAX1536 constant-off-time, pulse-width-modulated

(PWM) step-down DC-to-DC converter is ideal for use in

+5.0V and +3.3V to low voltages for notebook and sub-

notebook computers. The MAX1536 features an internal

PMOS power switch and internal synchronous rectifica-

tion for high efficiency and reduced component count. No

external Schottky diode is required across the internal

synchronous rectifier switch. The internal 54mΩ PMOS

power switch and 47mΩ NMOS synchronous-rectifier

switch easily deliver continuous load currents up to 3.6A.

The MAX1536 produces dynamically adjustable output

voltages for chipsets and graphics processor cores using

a logic-level control signal. The MAX1536 achieves effi-

ciencies as high as 96%.

The MAX1536 uses a unique current-mode, constant-off-

time, PWM control scheme. It has selectable Idle

Mode

to maintain high efficiency during light-load

operation, or fixed-PWM mode for low output ripple. The

programmable constant-off-time architecture allows a

wide range of switching frequencies up to 1.4MHz, opti-

mizing performance trade-offs between efficiency, output

switching noise, component size, and cost. The

MAX1536 features a digital soft-start to limit surge cur-

rents during startup, a 100% duty-cycle mode for low-

dropout operation, and a low-power shutdown mode that

disconnects the input from the output and reduces supply

current below 1µA. The MAX1536 is available in a 28-pin

thin QFN package with an exposed backside pad.

________________________Applications

Features

♦ Dynamically Selectable Output Voltage from

+0.7V to V

♦ Internal PMOS/NMOS Switches

54mΩ/47mΩ On-Resistance at V

= +4.5V

63mΩ/53mΩ On-Resistance at V

= +3.0V

♦ +3.0V to +5.5V Input Voltage Range

♦ 1.4MHz Maximum Switching Frequency

♦ 2V ±0.75% Reference Output

♦ Constant-Off-Time PWM Operation

♦ Selectable Idle Mode/PWM Operation at Light

Loads

♦ 100% Duty Factor in Dropout

♦ Digital Soft-Start Inrush Current Limiting

♦ <1µA Typical Shutdown Supply Current

♦ <750µA Quiescent Supply Current

♦ Thermal Shutdown

♦ 1% V

OUT

Accuracy Over Line and Load

♦ External Reference Input

♦ Power-Good Window Comparator

♦ Selectable Power-Good Blanking Time During

Output-Voltage Transition

19-2729; Rev 1; 8/05

MAX1536

3.6A, 1.4MHz, Low-Voltage, Internal-Switch Step-

Down Regulator with Dynamic Output Voltage Control

________________________________________________________________ Maxim Integrated Products 1

Minimal Operating Circuit

Ordering Information

Idle Mode is a trademark of Maxim Integrated Products, Inc.

PART

TEMP RANGE

PIN-PACKAGE

MAX1536ETI

-40

C to +85

28 Thin QFN 5mm x 5mm

MAX1536ETI+

-40

C to +85

28 Thin QFN 5mm x 5mm

MAX1536

SKIP

TOFF

PGOOD

SHDN

COMP

PGND

AGND

REF

REFIN

+3.0V TO +5.5V

OUT

+0.7V TO V

Pin Configuration

SHDN

SKIP

COMP

PGOOD

FBLANK

AGND

PGND

N.C.

PGND

REF

REFIN

GATE

TOFF

N.C.

TOP VIEW

THIN QFN

PGND

15161718192021

7654321

MAX1536

EXPOSED PADDLE

A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES.

Chipset/Graphics Cores

with Dual-Supply Voltages

Active Termination Buses

Notebook Computers

DDR Memory Termination

EVALUATION KIT

AVAILABLE

+Denotes lead-free package.

Summary of content (19 pages)

PAGE 1
KIT ATION EVALU E L B A IL AVA 19-2729; Rev 1; 8/05 3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control The MAX1536 constant-off-time, pulse-width-modulated (PWM) step-down DC-to-DC converter is ideal for use in +5.0V and +3.3V to low voltages for notebook and subnotebook computers. The MAX1536 features an internal PMOS power switch and internal synchronous rectification for high efficiency and reduced component count.
PAGE 2
MAX1536 3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control ABSOLUTE MAXIMUM RATINGS VCC, IN, SHDN, SKIP to AGND ................................-0.3V to +6V OD, OD, GATE, PGOOD to AGND...........................-0.3V to +6V COMP, FB, REF to AGND.........................................-0.3V to +6V TOFF, REFIN, FBLANK to AGND .............................-0.3V to +6V IN to VCC ...............................................................-0.3V to +0.
PAGE 3
.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control (Circuit of Figure 1, VIN = VCC = V SHDN = +3.3V, VREFIN = +1.5V, SKIP = AGND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL TYP MAX SHDN = AGND; current into VCC and IN; LX = 0 or +3.3V 0.2 20 IIN SHDN = AGND; current into IN; LX = 0 0.2 20 ILX SHDN = AGND; current into LX; LX = +3.3V 0.1 20 2.000 2.
PAGE 4
MAX1536 3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control ELECTRICAL CHARACTERISTICS (Circuit of Figure 1, VIN = VCC = V SHDN = +3.3V, VREFIN = +1.5V, SKIP = AGND, TA = -40°C to +85°C, unless otherwise noted.) (Note 5) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 3.0 5.5 V VCC = VIN = +3.0V to +5.
PAGE 5
3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control (Circuit of Figure 1, VIN = VCC = V SHDN = +3.3V, VREFIN = +1.5V, SKIP = AGND, TA = -40°C to +85°C, unless otherwise noted.) (Note 5) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS INPUTS AND OUTPUTS V SHDN, V SKIP, V GATE Logic Input Threshold SHDN, SKIP, GATE, VIN = VCC = +3.3V, rising edge, hysteresis = 100mV 0.9 1.6 SHDN, SKIP, GATE, VIN = VCC = +5.0V, rising edge, hysteresis = 100mV 1.15 1.
PAGE 6
Typical Operating Characteristics (continued) (MAX1536 Circuit of Figure 1, TA = +25°C, unless otherwise noted.) OUTPUT VOLTAGE vs. OUTPUT CURRENT (VIN = 3.3V, L = 1.2µH) 100 1.804 90 80 EFFICIENCY (%) 1.802 1.800 IDLE MODE 70 VIN = 3.3V L = 2.2µH RTOFF = 147kΩ 60 50 40 VIN = 5V L = 3.3µH RTOFF = 221kΩ 30 20 1.796 PWM MODE IDLE MODE 10 1.794 0 0.001 0.01 0.1 1 10 0.001 0.01 OUTPUT CURRENT (A) EFFICIENCY vs. OUTPUT CURRENT (VIN = 3.3V, VOUT = 1.8V) 40 700 600 500 400 30 20 10 0 L = 0.
PAGE 7
3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control STARTUP AND SHUTDOWN (LIGHT LOAD) STARTUP AND SHUTDOWN (HEAVY LOAD) MAX1536 toc11 MAX1536 toc10 VSHDN 5V/div VPGOOD 5V/div VSHDN 5V/div VPGOOD 5V/div ILX 2A/div ILX 1A/div VOUT 1V/div VOUT 1V/div 400µs/div 400µs/div VIN = 3.3V, VOUT = 1.8V, RLOAD = 3Ω VIN = 3.3V, VOUT = 1.8V, RLOAD = 0.
PAGE 8
MAX1536 3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control Pin Description PIN NAME FUNCTION 1, 21, 24, 26 LX Inductor Connection. Connection for the drains of the PMOS power switch and NMOS synchronous-rectifier switch. Connect all LX pins together. 2, 3, 19, 20 IN Power Input. Power input for the internal PMOS switch. Connect all IN pins together. 4 SHDN 5 SKIP 6 FB Pulse-Skipping Control Input.
PAGE 9
3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control The MAX1536 standard application circuit (Figure 1) generates a dynamically adjustable output voltage typical of graphic processor core requirements. See Table 1 for component selections. Table 2 lists the component manufacturers. Detailed Description The MAX1536 synchronous, current-mode, constantoff-time, PWM DC-to-DC converter steps down an input voltage (VIN) from +3.0V to +5.
PAGE 10
MAX1536 3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control L1 1.2µH, SUMIDA CDR7D28MN-1R2 VIN +3.0V TO +5.5V CIN 2 X 10µF +6.3V X5R 10Ω 2.2µF 100kΩ CCOMP 470pF RA VCC COUT 100µF, +6.3V POSCAP FB RB PGND COMP AGND PGOOD POWER GOOD VOUT +0.7V TO VIN LX IN REF MAX1536 PWM MODE SKIP CREF 0.
PAGE 11
3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control MAX1536 Table 2. Component Manufacturers SUPPLIER COMPONENT PHONE WEBSITE Coilcraft Inductors 800-322-2645 (USA) www.coilcraft.com Coiltronics Inductors 561-752-5000 (USA) www.coiltronics.com Kemet Capacitors 408-986-0424 (USA) www.kemet.com Sanyo Capacitors 818-998-7322 (USA) www.sanyo.com Inductors 408-982-9660 (USA) www.sumida.
PAGE 12
MAX1536 3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control Shutdown (SHDN) Drive SHDN low to disable the MAX1536 and reduce the supply current to less than 1µA. In shutdown, all circuitry and internal MOSFETs turn off, and the LX node becomes high impedance. Drive SHDN high or connect to VCC for normal operation.
PAGE 13
3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control Thermal Resistance Junction-to-ambient thermal resistance, θJA, is highly dependent on the amount of copper area connected to the exposed backside pad. Airflow over the board significantly reduces θJA. For heat-sinking purposes, evenly distribute the copper area connected at the IC among the high-current pins. Refer to the Maxim website (www.maxim-ic.com) for QFN thermal considerations.
PAGE 14
MAX1536 3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control  VOUT  RA = RB  - 1  VFB  where VFB = VREFIN. Setting Dynamic Output Voltages with REFIN The MAX1536 regulates VFB to be equal to VREFIN. Changing VREFIN allows for a dynamic output voltage that changes between two set points (see the Multioutput Voltage Settings section for information on three or more output-voltage set points).
PAGE 15
3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control 110kΩ 1.00µs VTOFF is typically 1.1V and the recommended values for RTOFF range from 30.1kΩ to 499kΩ for off-times of 0.3µs to 4.5µs.
PAGE 16
MAX1536 3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control Applications Information Multioutput Voltage Settings The MAX1536 is optimized to work in applications that require two dynamic output voltages; however, discrete logic or a DAC connected to REFIN allows three or more dynamic output voltages. Figure 6 shows an application circuit providing four voltage levels using discrete logic.
PAGE 17
3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control 3) Place the LX node components as close together and as near to the device as possible. This reduces noise, resistive losses, and switching losses. 4) A ground plane is essential for optimal performance. In most applications, the circuit is located on a multilayer board, and full use of the four or more layers is recommended.
PAGE 18
MAX1536 3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) D D/2 MARKING XXXXX E/2 (NE-1) X e E DETAIL A PIN # 1 I.D.
PAGE 19
3.6A, 1.4MHz, Low-Voltage, Internal-Switch StepDown Regulator with Dynamic Output Voltage Control (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) D D/2 MARKING XXXXX E/2 (NE-1) X e E DETAIL A PIN # 1 I.D. e L1 L Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied.