19-3485; Rev 0; 11/04 KIT ATION EVALU E L B AVAILA High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs The MAX8595X/MAX8596X drive up to nine white LEDs with constant current and high efficiency to provide LCD backlighting in cell phones, PDAs, and other handheld devices. The series connection allows the LED currents to be identical for uniform brightness and minimizes the number of traces to the LEDs. The MAX8595X regulates constant LED current over the entire temperature range. The MAX8596X features an ambient-temperature derating function to avoid overdriving the white LEDs during high ambient temperatures, enabling higher drive current below +42°C. A single Dual Mode™ input provides a simple means of brightness adjustment and on/off control. Fast 1MHz current-mode PWM operation allows for small input and output capacitors and a small inductor while minimizing ripple on the input supply/battery. Soft-start eliminates inrush current during startup. The MAX8595X/MAX8596X are available in a spacesaving, 8-pin, 3mm x 3mm TDFN package. Applications Features ♦ Up to Nine LEDs at 25mA ♦ Temperature Derating Function to Allow Fewer LEDs for Same Light (MAX8596X) ♦ 86% Efficiency (PLEDs / PIN) ♦ 1.7% Current-Regulation Accuracy ♦ Output Overvoltage Protection ♦ Flexible Dimming Control Analog Direct-PWM Internal Filter ♦ 1MHz PWM Switching Frequency ♦ 0.1µF Output Capacitor ♦ 12mVP-P Low Input Ripple ♦ Soft-Start Eliminates Inrush Current ♦ 2.6V to 5.5V Input Range ♦ 0.3µA Shutdown Current Cell Phones and Smart Phones ♦ Pin Compatible with the MAX1561 and MAX1599 PDAs, Palmtops, and Wireless Handhelds ♦ TDFN 3mm x 3mm x 0.8mm Package with Exposed Paddle e-Books and Subnotebooks White LED Display Backlighting Ordering Information PART TEMP RANGE PIN-PACKAGE PKG CODE MAX8595XETA -40°C to +85°C 8 TDFN 3mm x 3mm T833-1 MAX8596XETA* -40°C to +85°C 8 TDFN 3mm x 3mm T833-1 Dual Mode is a trademark of Maxim Integrated Products, Inc. *Future product—contact factory for availability. Pin Configuration Typical Operating Circuit IN ANALOG OR PWM DIMMING PGND GND COMP 2.2µF TOP VIEW LX OUTPUT UP TO 38V INPUT 2.6V TO 5.5V 8 7 6 5 LX OUT MAX8595X CTRL MAX8596X PGND MAX8595X MAX8596X 0.1µF 2 TO 9 LEDs 1 2 3 4 CS CS CTRL GND IN COMP OUT 200Hz TO 200kHz TDFN 3mm x 3mm x 0.8mm ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX8595X/MAX8596X General Description MAX8595X/MAX8596X High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs ABSOLUTE MAXIMUM RATINGS IN to GND .................................................................-0.3V to +6V PGND to GND .......................................................-0.3V to +0.3V LX, OUT to GND .....................................................-0.3V to +40V CTRL to GND...................-0.3V to the lower of +6V or (VIN + 2V) COMP, CS to GND ......................................-0.3V to (VIN + 0.3V) ILX ...................................................................................1.0ARMS Continuous Power Dissipation (TA = +70°C) 8-Pin TDFN 3mm x 3mm (derate 24.4mW/°C above +70°C) ............................ 1950mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VIN = 3.0V, L = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 13Ω, VCTRL = 1.5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER CONDITIONS Supply Voltage UVLO Threshold MIN TYP 2.6 VIN rising or falling 2.10 UVLO Hysteresis 2.38 MAX UNITS 5.5 V 2.55 30 V mV Quiescent Current No switching 0.5 0.7 TA = +25°C 0.3 2 TA = +85°C 1 Shutdown Supply Current CTRL = GND, VOUT = VIN OVLO Threshold VOUT rising 36 38 VOUT = 32V, VCTRL > 0.24V 9 20 35 0.01 1 µA 36 V OVLO Hysteresis OUT Input Bias Current Output Voltage Range 40 2 OUT = IN, CTRL = GND TA = +25°C TA = +85°C µA V V 0.1 VIN VD (Note 2) mA ERROR AMPLIFIER CTRL to CS Regulation CS Input Bias Current VCTRL = 1.50V, VIN = 2.6V to 5.5V VCS = VCTRL / 5 TA = +25°C 0.295 0.300 0.305 TA = 0°C to +85°C 0.292 0.300 0.308 TA = -40°C to +85°C 0.290 0.300 0.310 TA = +25°C 0.01 1 TA = +85°C 0.03 MAX8595X, VCTRL = 3.0V CS Maximum Brightness Clamp Voltage CTRL Voltage for CS Maximum Brightness Clamp CS Derating Function Start Temperature 2 MAX8596X, VCTRL = 3.0V TA = -40°C to +25°C 310 330 347 330 345 360 TA = +42°C 343 TA = +85°C 106.5 MAX8595Z 1.65 MAX8596Z 1.72 MAX8596Z, VCTRL = 3.0V +42 _______________________________________________________________________________________ V µA mV V °C High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs (VIN = 3.0V, L = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 13Ω, VCTRL = 1.5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER CONDITIONS CS Derating Function Slope MAX8596X, VCTRL = 3.0V, TA = +42°C to +85°C CTRL Input Resistance VCTRL < 1.5V CTRL Dual-Mode Threshold MIN TYP MAX -5.5 mV/°C 250 500 780 100 170 240 CTRL Dual-Mode Hysteresis UNITS 5 kΩ mV mV CTRL Shutdown Enable Delay (Note 3) 6.0 8.2 10.5 ms CS to COMP Transconductance VCOMP = 1.5V 32 50 82 µS COMP Input Resistance to Ground In shutdown, UVLO or OVLO 20 kΩ OSCILLATOR Operating Frequency Minimum Duty Cycle Maximum Duty Cycle 0.75 1.0 PWM mode 12 Pulse skipping 0 CTRL = IN, CS = GND 94 1.25 MHz % 95 % n-CHANNEL SWITCH LX On-Resistance ILX = 190mA LX Leakage Current VLX = 36V, CTRL = GND LX Current Limit Duty cycle = 90% 0.8 1.35 TA = +25°C 0.01 5 TA = +85°C 1 500 700 900 Ω µA mA Note 1: Parameters are 100% production tested at TA = +25°C. Limits over the operating temperature range are regulated by design and characterization. Note 2: VD is the forward-voltage drop of the Schottky diode in Figure 1. Note 3: Time from CTRL going below the Dual-Mode threshold to IC shutdown. _______________________________________________________________________________________ 3 MAX8595X/MAX8596X ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (Circuit of Figure 1, VIN = 3.6V, ILED = 25mA, L = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 13Ω, 4 LEDs, TA = +25°C, unless otherwise noted.) EFFICIENCY vs. LED CURRENT EFFICIENCY vs. INPUT VOLTAGE 3 LEDs 80 75 4 LEDs 70 6 LEDs 85 EFFICIENCY (%) EFFICIENCY (%) 85 6 LEDs 65 8 LEDs 60 MAX8595X toc02 95 90 90 MAX8595X toc01 100 80 8 LEDs 3 LEDs 75 70 65 55 50 60 2 3 4 6 5 0 5 10 15 20 25 INPUT VOLTAGE (V) LED CURRENT (mA) LED CURRENT vs. DIRECT-PWM DIMMING LED CURRENT vs. AMBIENT TEMPERATURE 22 20 15 10 MAX8595X toc04 24 LED CURRENT (mA) 25 30 26 MAX8595X toc03 30 LED CURRENT (mA) MAX8595X/MAX8596X High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs MAX8596, ILED = 25mA AT TA = +25°C 20 18 MAX8595, ILED = 15mA 16 14 12 5 10 0 8 0 20 40 60 80 100 -40 DUTY CYCLE (%) -20 0 20 40 SWITCHING WAVEFORMS VCTRL 2V/div 0 10V/div IIN 100mA/div 0 200mV/div AC-COUPLED VOUT ILED 40mA/div 0 100mA/div IL 100 MAX8595X toc06 20mV/div AC-COUPLED VLX 80 SOFT-START AND SHUTDOWN RESPONSE MAX8595X toc05 VIN 60 TEMPERATURE (°C) VOUT 10V/div 0 500ns/div 4 20ms/div _______________________________________________________________________________________ High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs DIRECT-PWM DIMMING RESPONSE CTRL STEP RESPONSE MAX8595X toc08 MAX8595X toc07 VCTRL 1V/div 2V/div 32kHz 50% DUTY CYCLE 0 VCTRL 0 IIN 100mA/div 20mV/div AC-COUPLED VIN 0 0 ILED 40mA/div 0 VOUT 10V/div 500mV/div AC-COUPLED VOUT 0 ILED 10mA/div 0 0 10µs/div 20ms/div Pin Description PIN NAME 1 OUT 2 IN FUNCTION Overvoltage Sense. When VOUT is greater than 38V (typ), the internal n-channel MOSFET turns off until VOUT drops below 36V (typ), then the IC reenters soft-start. Connect a 0.1µF ceramic capacitor from OUT to ground. In shutdown, VOUT is one diode drop below VIN. Input Voltage Supply. The input voltage range is 2.6V to 5.5V. Connect a 2.2µF ceramic capacitor from IN to GND. 3 CTRL Brightness Control Input. The voltage applied to CTRL controls LED brightness. Varying the voltage from 0.24V to 1.65V (1.72V for the MAX8596X) adjusts the brightness from dim to 100% brightness, respectively. Any voltage above 1.65V (1.72V) does not increase brightness. Hold CTRL below 100mV to shut down the IC after an 8.2ms delay. 4 CS Current-Sense Feedback Input. Connect a resistor from CS to GND to set the LED bias current. The voltage at CS regulates to VCTRL / 5 or 0.330V (0.343V for the MAX8596X), whichever is lower. 5 COMP Compensation Input. Connect a 0.1µF ceramic capacitor (CCOMP) from COMP to GND. CCOMP stabilizes the converter, controls soft-start, and lowpass filters direct PWM dimming at CTRL. CCOMP discharges to 0V through an internal 20kΩ resistor in shutdown. 6 GND 7 PGND Ground. Connect to PGND and the exposed pad directly under the IC. Power Ground. Connect to GND and the exposed pad directly under the IC. 8 LX Inductor Connection. Connect LX to the node between the inductor and the Schottky diode. LX is high impedance in shutdown. — EP Exposed Pad. Connect to a large ground plane for maximum package heat dissipation. Connect directly to GND and PGND under the IC. _______________________________________________________________________________________ 5 MAX8595X/MAX8596X Typical Operating Characteristics (continued) (Circuit of Figure 1, VIN = 3.6V, ILED = 25mA, L = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 13Ω, 4 LEDs, TA = +25°C, unless otherwise noted.) MAX8595X/MAX8596X High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs Detailed Description The high efficiency and small size of the MAX8595X/ MAX8596X make them ideally suited to drive up to nine series-connected LEDs. These devices operate as a boost DC-DC converter that regulates output current rather than voltage. The MAX8595X/MAX8596X provide even illumination by sourcing the same output current through each LED, eliminating the need for expensive factory calibration. The fast 1MHz internal oscillator allows for a small inductor and small input and output capacitors while minimizing input and output ripple. The single analog control input (CTRL) allows easy adjustment of LED brightness and on/off control. This allows simple logic-level on/off control, analog voltage control, or PWM duty-cycle control of both brightness and shutdown. In shutdown, supply current is reduced to a low 0.3µA (typ). A soft-start gradually illuminates the LEDs, eliminating the inrush current during startup. The MAX8596X has the additional feature of derating LED current as ambient temperature rises. Above +42°C, the CS regulation voltage is reduced at a rate of 5.5mV/°C, thus reducing the LED current. 2.6V TO 5.5V 2.2µF 22µH IN LX PWM CONTROL PGND fOSC 1MHz OUT OVERVOLTAGE PROTECT 0.1µF 0.1µF COMP 1.25V CLAMP OR TEMP DERATE CLAMP gm CTRL ANALOG OR DIRECT PWM DIMMING 121kΩ 279kΩ 100kΩ CS RSENSE 13Ω Soft-Start The MAX8595X/MAX8596X attain soft-start by charging CCOMP gradually with a current source. When VCOMP rises above 1.25V, the internal MOSFET begins switching at a reduced duty cycle. When VCOMP rises above 2.25V, the duty cycle is at its maximum. See the Typical Operating Characteristics for an example of soft-start operation. Shutdown The MAX8595X/MAX8596X enter shutdown when VCTRL is less than 100mV for more than 8.2ms. In shutdown, supply current is reduced to 0.3µA (typ) by powering down the entire IC except for the CTRL voltage-detection circuitry. CCOMP is discharged during shutdown, allowing the device to reinitiate soft-start when it is enabled. Although the internal n-channel MOSFET does not switch in shutdown, there is still a DC current path between the input and the LEDs through the inductor and Schottky diode. The minimum forward voltage of the LED array must exceed the maximum input voltage to ensure that the LEDs remain off in shutdown. However, with two or more LEDs, the forward voltage is large enough to keep leakage current low, less than 1µA (typ). Typical shutdown timing characteristics are shown in the Typical Operating Characteristics. Overvoltage Protection Overvoltage lockout (OVLO) occurs when V OUT is above 38V (typ). The protection circuitry stops the inter6 8.2ms 170mV SHUTDOWN GND Figure 1. Functional Diagram and Typical Application Circuit nal MOSFET from switching and causes V COMP to decay towards 0V. The device comes out of OVLO and into soft-start when VOUT falls below 36V (typ). Ambient Temperature Derating Function (MAX8596X) The MAX8596X limits the maximum LED current depending on the die temperature. VCS is limited to 343mV up to +42°C. Once the temperature reaches +42°C, the maximum VCS declines by 5.5mV/°C until the minimum 106.5mV threshold is reached at +85°C. Due to the package’s exposed paddle, the die temperature is always very close to the PC board temperature. The temperature derating function allows the LED current to be safely set higher at normal operating temperatures, thereby allowing either a brighter display or fewer LEDs to be used for normal display brightness. See the Typical Operating Characteristics for LED Current vs. Ambient Temperature. _______________________________________________________________________________________ High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs Adjusting LED Current Adjusting the output current of the MAX8595X/ MAX8596X changes the brightness of the LEDs. An analog input (CTRL) and the sense-resistor value set the output current. Output current is given by: ILED = VCTRL / (5 x RSENSE) The VCTRL voltage range for adjusting output current is 0.24V to 1.65V (or 1.72V for the MAX8596X). To set the maximum current, calculate RSENSE when VCTRL is at its maximum as follows: For the MAX8595X, RSENSE = 1.65 / (5 x ILED(MAX)) For the MAX8596X, RSENSE = 1.72 / (5 x ILED(MAX)) Power dissipation in RSENSE is typically less than 10mW, allowing the use of a small surface-mount resistor. PWM Dimming Control CTRL is also used as a digital input allowing LED brightness control with a logic-level PWM signal applied directly to CTRL. The frequency range is from 200Hz to 200kHz, while 0% duty cycle corresponds to zero current and 100% duty cycle corresponds to full current. The error amplifier and compensation capacitor form a lowpass filter so PWM dimming results in DC current to the LEDs without the need for any additional RC filters; see the Typical Operating Characteristics. Capacitor Selection Ceramic capacitors with X5R, X7R, or better dielectric are recommended for stable operation over the entire operating temperature range. The exact values of input and output capacitors are not critical. The typical value for the input capacitor is 2.2µF, and the typical value for the output capacitor is 0.1µF. Higher value capacitors can be used to reduce input and output ripple, but at the expense of size and higher cost. CCOMP stabilizes the converter and controls soft-start. Connect a 0.1µF capacitor from COMP to GND. For stable operation, COUT must not exceed 10 times CCOMP. Inductor Selection Inductor values range from 10µH to 47µH. A 22µH inductor optimizes the efficiency for most applications while maintaining low 12mVP-P input ripple. With input voltages near 5V, a larger value of inductance can be more efficient. To prevent core saturation, ensure that the inductor-saturation current rating exceeds the peak inductor current for the application. Calculate the peak inductor current with the following formula: IPEAK = VOUT(MAX) × ILED(MAX) 0.9 × VIN(MIN) + VIN(MIN) × 0.9µs 2 ×L Schottky Diode Selection The high switching frequency of the MAX8595X/ MAX8596X demands a high-speed rectification diode (D1) for optimum efficiency. A Schottky diode is recommended due to its fast recovery time and low forwardvoltage drop. Ensure that the diode’s average and peak current rating exceed the average output current and peak inductor current. In addition, the diode’s reverse breakdown voltage must exceed VOUT. The RMS diode current can be approximated from: IDIODE(RMS) = IOUT × IPEAK Applications Information PC Board Layout Due to fast switching waveforms and high-current paths, careful PC board layout is required. An evaluation kit (MAX8596XEVKIT) is available to speed design. When laying out a board, minimize trace lengths between the IC and RSENSE, the inductor, the diode, the input capacitor, and the output capacitor. Keep traces short, direct, and wide. Keep noisy traces, such as the LX node trace, away from CS. The IN bypass capacitor (CIN) should be placed as close to the IC as possible. PGND and GND should be connected directly to the exposed paddle underneath the IC. The ground connections of CIN and COUT should be as close together as possible. The traces from IN to the inductor and from the Schottky diode to the LEDs can be longer. Chip Information TRANSISTOR COUNT: 2143 PROCESS: BiCMOS _______________________________________________________________________________________ 7 MAX8595X/MAX8596X Design Procedure 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.) 6, 8, &10L, DFN THIN.EPS MAX8595X/MAX8596X High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs D N PIN 1 INDEX AREA E E2 DETAIL A CL CL L A L e e PACKAGE OUTLINE, 6, 8, 10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm 21-0137 NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY F 1 2 COMMON DIMENSIONS SYMBOL A MIN. 0.70 0.80 D 2.90 3.10 2.90 3.10 0.00 0.05 E A1 L k MAX. 0.40 0.20 0.25 MIN. A2 0.20 REF. PACKAGE VARIATIONS PKG. CODE N D2 E2 e JEDEC SPEC b T633-1 6 1.50±0.10 2.30±0.10 0.95 BSC MO229 / WEEA 0.40±0.05 1.90 REF T833-1 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF 2.00 REF [(N/2)-1] x e T1033-1 10 1.50±0.10 2.30±0.10 0.50 BSC MO229 / WEED-3 0.25±0.05 T1433-1 14 1.70±0.10 2.30±0.10 0.40 BSC ---- 0.20±0.03 2.40 REF T1433-2 14 1.70±0.10 2.30±0.10 0.40 BSC ---- 0.20±0.03 2.40 REF PACKAGE OUTLINE, 6, 8, 10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm 21-0137 F 2 2 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. 8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.