Datasheet

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General Description

The MAX17112 is a high-performance, step-up, DC-DC

converter that provides a regulated supply voltage for

active-matrix thin-film transistor (TFT) liquid-crystal dis-

plays (LCDs). The MAX17112 incorporates current-

mode, fixed-frequency (1MHz), pulse-width modulation

(PWM) circuitry with a built-in, n-channel power MOSFET

to achieve high efficiency and fast-transient response.

The input overvoltage protection (OVP) function pre-

vents damage to the MAX17112 from an input surge

voltage (up to 24V).

The high switching frequency (1MHz) allows the use of

ultra-small inductors and low-ESR ceramic capacitors.

The current-mode architecture provides fast-transient

response to pulsed loads. A compensation pin (COMP)

gives users flexibility in adjusting loop dynamics. The

internal MOSFET can generate output voltages up to

20V from an input voltage between 2.6V and 5.5V.

Soft-start slowly ramps the input current and is pro-

grammable with an external capacitor. The MAX17112

is available in a 10-pin TDFN package.

Applications

Notebook Computer Displays

LCD Monitor Panels

Features

o Input Overvoltage Protection

o Adjustable Output from V

to 20V

o 2.6V to 5.5V Input Supply Range

o Input Supply Undervoltage Lockout

o 1MHz Fixed Switching Frequency

o Programmable Soft-Start

o Small 10-Pin, TDFN Package

o Thermal-Overload Protection

MAX17112

High-Performance, Step-Up, DC-DC Converter

________________________________________________________________

Maxim Integrated Products

COMP

GND

MAX17112

SHDNFB

*EP

*EXPOSED PAD

GND

TDFN

3mm × 3mm

TOP VIEW

Pin Configuration

Ordering Information

LX LX

GND

COMP

OUT

2.6V TO 5.5V

SHDN

MAX17112

Simplified Operating Circuit

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

PART TEMP RANGE PIN-PACKAGE

MAX17112ETB+ -40°C to +85°C 10 TDFN-EP*

Denotes a lead(Pb)-free/RoHS-compliant package.

EP = Exposed pad.

19-4393; Rev 0; 12/08

Summary of content (12 pages)

PAGE 1
9-4393; Rev 0; 12/08 KIT ATION EVALU LE B A IL A AV High-Performance, Step-Up, DC-DC Converter The MAX17112 is a high-performance, step-up, DC-DC converter that provides a regulated supply voltage for active-matrix thin-film transistor (TFT) liquid-crystal displays (LCDs). The MAX17112 incorporates currentmode, fixed-frequency (1MHz), pulse-width modulation (PWM) circuitry with a built-in, n-channel power MOSFET to achieve high efficiency and fast-transient response.
PAGE 2
MAX17112 High-Performance, Step-Up, DC-DC Converter ABSOLUTE MAXIMUM RATINGS LX to GND ..............................................................-0.3V to +24V IN to GND ...............................................................-0.3V to +24V SHDN, VL to GND..................................................-0.3V to +7.5V COMP, SS, FB to GND ..................................-0.3V to (VL + 0.3V) LX Switch Maximum Continuous RMS Current .....................3.
PAGE 3
High-Performance, Step-Up, DC-DC Converter (VVL = 3V, TA = 0°C to +85°C, unless otherwise noted.) PARAMETER CONDITIONS MIN TYP MAX UNITS 25 VSS = 1.2V 1.5 3.5 5.5 μA SHDN rising 1.1 1.16 1.22 SOFT-START Reset Switch Resistance Charge Current CONTROL INPUTS SHDN Threshold SHDN Input Hysteresis SHDN Discharge Resistance 60 VL < UVLO 20 SHDN Charge Current 4.25 Charge Current Delay Time 5 V mV 5.
PAGE 4
ELECTRICAL CHARACTERISTICS (continued) (VVL = 3V, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER CONDITIONS MIN MAX UNITS VFB = 1V, 75% duty cycle, VL = 5V 3.9 5.3 A n-CHANNEL MOSFET Current Limit On-Resistance Current-Sense Transresistance VL = 5V 170 VL = 3V 210 m VL = 5V 0.09 0.25 V/A 25 VSS = 1.2V 1.5 5.5 μA SHDN rising 1.19 1.29 V 4.25 5.
PAGE 5
High-Performance, Step-Up, DC-DC Converter MAX17112 toc05 3.5 SUPPLY CURRENT (mA) 1000 MAX17112 toc06 4.0 MAX17112 toc04 1100 SWITCHING FREQUENCY (kHz) SOFT-START (RLOAD = 30Ω) SUPPLY CURRENT vs. SUPPLY VOLTAGE SWITCHING FREQUENCY vs. INPUT VOLTAGE VOUT 5V/div 3.0 2.5 SWITCHING 0 2.0 1.5 INDUCTOR CURRENT 1A/div 1.0 900 0 NONSWITCHING 0.5 0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 2.5 3.5 3.0 4.0 4.5 5.0 2ms/div 5.
PAGE 6
High-Performance, Step-Up, DC-DC Converter MAX17112 Pin Description PIN NAME FUNCTION 1 COMP 2 FB Feedback. The FB regulation voltage is 1.24V nominal. Connect an external resistor-divider center tap here and minimize the trace area. Set V OUT according to the Output Voltage Selection section. 3 VL IC Supply. There is an internal switch between IN and VL and the switch disconnects when an overvoltage condition on IN is detected. Bypass VL to GND with a 1μF capacitor. 4, 5 GND 6, 7 LX Switch.
PAGE 7
High-Performance, Step-Up, DC-DC Converter VMAIN IN OVP IC SUPPLY VOLTAGE VL LX LOGIC AND DRIVER CLOCK GND SLOPE COMPENSATION 1.2MHz OSCILLATOR PWM COMPARATOR CURRENT SENSE 4μA ERROR AMPLIFIER FB SOFT-START SHUTDOWN 1.24V COMP SHDN SS Figure 2. Functional Diagram Detailed Description The MAX17112 is a highly efficient, power-management IC that employs a current-mode, fixed-frequency, PWM architecture for fast-transient response and low-noise operation.
PAGE 8
MAX17112 High-Performance, Step-Up, DC-DC Converter Output Current Capability The output current capability of the MAX17112 is a function of current limit, input voltage, operating frequency, and inductor value. Because of the slope compensation used to stabilize the feedback loop, the inductor current limit depends on the duty cycle. The current limit is determined by the following equation: ILIM = (1.26 - 0.
PAGE 9
High-Performance, Step-Up, DC-DC Converter C1 4.7μF 10V L1 2.7μH VOUT +15V/600mA D1 C7 10μF 25V C2 4.7μF 10V 8 LX U1 IN C3 1μF LOGIC INPUT 10kΩ MAX17112 9 SHDN PROTECTION RESISTOR C9 1μF LX 3 10 C4 3.3nF SHDN GND GND VL FB SS GND MAX17112 VIN 4.5V TO 5.5V C8 10μF 25V 6 7 5 4 R4 221kΩ 2 EP COMP R3 20kΩ 1 R2 47kΩ C5 560pF C6 OPEN Figure 3. Application Circuit Using Logic Input at SHDN Table 1. Component List DESIGNATION C1, C2 C7, C8 L1 DESCRIPTION 4.
PAGE 10
MAX17112 High-Performance, Step-Up, DC-DC Converter The maximum output current, input voltage, output voltage, and switching frequency determine the inductor value. Very high inductance values minimize the current ripple, and therefore, reduce the peak current, which decreases core losses in the inductor and I2R losses in the entire power path. However, large inductor values also require more energy storage and more turns of wire, which increase physical size and can increase I2R losses in the inductor.
PAGE 11
High-Performance, Step-Up, DC-DC Converter VRIPPLE(ESR) ≈ IPEAKRESR(COUT) where I PEAK is the peak inductor current (see the Inductor Selection section). For ceramic capacitors, the output voltage ripple is typically dominated by VRIPPLE(C). The voltage rating and temperature characteristics of the output capacitor must also be considered. Input Capacitor Selection The input capacitor (CIN) reduces the current peaks drawn from the input supply and reduces noise injection into the IC. Two 4.
PAGE 12
MAX17112 High-Performance, Step-Up, DC-DC Converter 2) Create a power ground island (PGND) consisting of the input and output capacitor grounds and GND pins. Connect all of these together with short, wide traces or a small ground plane. Maximizing the width of the power ground traces improves efficiency and reduces output voltage ripple and noise spikes.