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19-3485; Rev 0; 11/04
KIT ATION EVALU BLE AVAILA
High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs
General Description 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 0.1F Output Capacitor 12mVP-P Low Input Ripple Soft-Start Eliminates Inrush Current 2.6V to 5.5V Input Range 0.3A Shutdown Current Pin Compatible with the MAX1561 and MAX1599 TDFN 3mm x 3mm x 0.8mm Package with Exposed Paddle
MAX8595X/MAX8596X
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 +42C. A single Dual ModeTM 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
Cell Phones and Smart Phones PDAs, Palmtops, and Wireless Handhelds e-Books and Subnotebooks White LED Display Backlighting
Ordering Information
PART TEMP RANGE PIN-PACKAGE PKG CODE
MAX8595XETA -40C to +85C 8 TDFN 3mm x 3mm T833-1 MAX8596XETA* -40C to +85C 8 TDFN 3mm x 3mm T833-1
Dual Mode is a trademark of Maxim Integrated Products, Inc.
*Future product--contact factory for availability.
Typical Operating Circuit
PGND
INPUT 2.6V TO 5.5V 2.2F IN ANALOG OR PWM DIMMING LX OUT OUTPUT UP TO 38V
Pin Configuration
LX GND COMP
TOP VIEW
8
7
6
5
MAX8595X CTRL MAX8596X PGND
COMP GND CS
0.1F
MAX8595X MAX8596X
1 OUT 2 IN 3 CTRL 4 CS
200Hz TO 200kHz
2 TO 9 LEDs
TDFN 3mm x 3mm x 0.8mm
________________________________________________________________ Maxim Integrated Products
1
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.
High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs MAX8595X/MAX8596X
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 = +70C) 8-Pin TDFN 3mm x 3mm (derate 24.4mW/C above +70C) ............................ 1950mW Operating Temperature Range ...........................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10s) .................................+300C
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 = 22H, CIN = 2.2F, COUT = 0.1F, CCOMP = 0.1F, RSENSE = 13, VCTRL = 1.5V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER Supply Voltage UVLO Threshold UVLO Hysteresis Quiescent Current Shutdown Supply Current OVLO Threshold OVLO Hysteresis VOUT = 32V, VCTRL > 0.24V OUT Input Bias Current OUT = IN, CTRL = GND (Note 2) TA = +25C TA = +85C VIN VD TA = +25C TA = 0C to +85C TA = -40C to +85C TA = +25C TA = +85C 310 TA = -40C to +25C TA = +42C TA = +85C 330 0.295 0.292 0.290 0.300 0.300 0.300 0.01 0.03 330 345 343 106.5 1.65 1.72 +42 V C 347 360 mV 9 No switching CTRL = GND, VOUT = VIN VOUT rising TA = +25C TA = +85C 36 VIN rising or falling CONDITIONS MIN 2.6 2.10 2.38 30 0.5 0.3 1 38 2 20 0.01 0.1 36 V 35 1 A 40 0.7 2 TYP MAX 5.5 2.55 UNITS V V mV mA A V V
Output Voltage Range ERROR AMPLIFIER
0.305 0.308 0.310 1 A V
CTRL to CS Regulation
VCTRL = 1.50V, VIN = 2.6V to 5.5V VCS = VCTRL / 5 MAX8595X, VCTRL = 3.0V
CS Input Bias Current
CS Maximum Brightness Clamp Voltage
MAX8596X, VCTRL = 3.0V MAX8595Z MAX8596Z MAX8596Z, VCTRL = 3.0V
CTRL Voltage for CS Maximum Brightness Clamp CS Derating Function Start Temperature
2
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High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 3.0V, L = 22H, CIN = 2.2F, COUT = 0.1F, CCOMP = 0.1F, RSENSE = 13, VCTRL = 1.5V, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) (Note 1)
PARAMETER CS Derating Function Slope CTRL Input Resistance CTRL Dual-Mode Threshold CTRL Dual-Mode Hysteresis CTRL Shutdown Enable Delay CS to COMP Transconductance COMP Input Resistance to Ground OSCILLATOR Operating Frequency Minimum Duty Cycle Maximum Duty Cycle n-CHANNEL SWITCH LX On-Resistance LX Leakage Current LX Current Limit ILX = 190mA VLX = 36V, CTRL = GND Duty cycle = 90% TA = +25C TA = +85C 500 0.8 0.01 1 700 900 1.35 5 A mA PWM mode Pulse skipping CTRL = IN, CS = GND 94 0.75 1.0 12 0 95 1.25 MHz % % (Note 3) VCOMP = 1.5V In shutdown, UVLO or OVLO 6.0 32 VCTRL < 1.5V CONDITIONS MAX8596X, VCTRL = 3.0V, TA = +42C to +85C 250 100 MIN TYP -5.5 500 170 5 8.2 50 20 10.5 82 780 240 MAX UNITS mV/C k mV mV ms S k
MAX8595X/MAX8596X
Note 1: Parameters are 100% production tested at TA = +25C. 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.
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High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs MAX8595X/MAX8596X
Typical Operating Characteristics
(Circuit of Figure 1, VIN = 3.6V, ILED = 25mA, L = 22H, CIN = 2.2F, COUT = 0.1F, CCOMP = 0.1F, RSENSE = 13, 4 LEDs, TA = +25C, unless otherwise noted.)
EFFICIENCY vs. INPUT VOLTAGE
MAX8595X toc01
EFFICIENCY vs. LED CURRENT
6 LEDs 85 EFFICIENCY (%) 80 75 70 65 60 3 LEDs
MAX8595X toc02
100 95 90 EFFICIENCY (%) 85 80 75 70 65 60 55 50 2 3 4 INPUT VOLTAGE (V) 5 6 8 LEDs 4 LEDs 6 LEDs 3 LEDs
90
8 LEDs
0
5
10
15
20
25
30
LED CURRENT (mA)
LED CURRENT vs. DIRECT-PWM DIMMING
MAX8595X toc03
LED CURRENT vs. AMBIENT TEMPERATURE
24 22 LED CURRENT (mA) 20 18 16 14 12 MAX8595, ILED = 15mA MAX8596, ILED = 25mA AT TA = +25C
MAX8595X toc04
30 25 LED CURRENT (mA) 20 15 10 5
26
10 0 0 20 40 60 80 100 DUTY CYCLE (%) 8 -40 -20 0 20 40 60 80 100 TEMPERATURE (C)
SWITCHING WAVEFORMS
MAX8595X toc05
SOFT-START AND SHUTDOWN RESPONSE
MAX8595X toc06
VIN
20mV/div AC-COUPLED 10V/div
VCTRL
2V/div 0
VLX
IIN VOUT 200mV/div AC-COUPLED ILED IL 100mA/div VOUT
100mA/div 0 40mA/div 0 10V/div 0
500ns/div
20ms/div
4
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High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 3.6V, ILED = 25mA, L = 22H, CIN = 2.2F, COUT = 0.1F, CCOMP = 0.1F, RSENSE = 13, 4 LEDs, TA = +25C, unless otherwise noted.)
MAX8595X/MAX8596X
CTRL STEP RESPONSE
MAX8595X toc07
DIRECT-PWM DIMMING RESPONSE
MAX8595X toc08
VCTRL
1V/div 0
VCTRL
2V/div 32kHz 50% DUTY CYCLE 0 20mV/div AC-COUPLED 0 500mV/div AC-COUPLED 0
IIN
100mA/div 0
VIN
ILED
40mA/div 0 10V/div 0 20ms/div
VOUT
VOUT
ILED 0 10s/div
10mA/div
Pin Description
PIN 1 NAME OUT 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 0.1F 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 2.2F ceramic capacitor from IN to GND. 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. 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. Compensation Input. Connect a 0.1F 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 20k resistor in shutdown. 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. Inductor Connection. Connect LX to the node between the inductor and the Schottky diode. LX is high impedance in shutdown. Exposed Pad. Connect to a large ground plane for maximum package heat dissipation. Connect directly to GND and PGND under the IC.
2
IN
3
CTRL
4
CS
5 6 7 8 --
COMP GND PGND LX EP
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High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs MAX8595X/MAX8596X
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 0.3A (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 +42C, the CS regulation voltage is reduced at a rate of 5.5mV/C, thus reducing the LED current.
2.6V TO 5.5V 2.2F 22H IN PWM CONTROL PGND fOSC 1MHz OVERVOLTAGE PROTECT 0.1F COMP 1.25V CLAMP OR TEMP DERATE CLAMP CTRL ANALOG OR DIRECT PWM DIMMING 121k 279k 100k CS RSENSE 13 170mV 8.2ms SHUTDOWN OUT 0.1F LX
gm
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.
GND
Figure 1. Functional Diagram and Typical Application Circuit
Shutdown
The MAX8595X/MAX8596X enter shutdown when VCTRL is less than 100mV for more than 8.2ms. In shutdown, supply current is reduced to 0.3A (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 1A (typ). Typical shutdown timing characteristics are shown in the Typical Operating Characteristics.
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 +42C. Once the temperature reaches +42C, the maximum VCS declines by 5.5mV/C until the minimum 106.5mV threshold is reached at +85C. 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.
Overvoltage Protection
Overvoltage lockout (OVLO) occurs when V OUT is above 38V (typ). The protection circuitry stops the inter6
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High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs
Design Procedure
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. 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) x ILED(MAX) 0.9 x VIN(MIN) + VIN(MIN) x 0.9s 2 xL
MAX8595X/MAX8596X
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 x IPEAK
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.
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.
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 2.2F, and the typical value for the output capacitor is 0.1F. 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 0.1F capacitor from COMP to GND. For stable operation, COUT must not exceed 10 times CCOMP.
Chip Information
TRANSISTOR COUNT: 2143 PROCESS: BiCMOS
Inductor Selection
Inductor values range from 10H to 47H. A 22H 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
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High-Efficiency, 36V Step-Up Converters with TA Derating Option for 2 to 9 White LEDs MAX8595X/MAX8596X
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
C L
D
N
PIN 1 INDEX AREA
E
DETAIL A
E2
C L
L A e e
L
PACKAGE OUTLINE, 6, 8, 10 & 14L, TDFN, EXPOSED PAD, 3x3x0.80 mm
NUMBER OF LEADS SHOWN ARE FOR REFERENCE ONLY
21-0137
F
1
2
COMMON DIMENSIONS SYMBOL A D E A1 L k A2 MIN. 0.70 2.90 2.90 0.00 MAX. 0.80 3.10 3.10 0.05
0.40 0.20 0.25 MIN. 0.20 REF.
PACKAGE VARIATIONS PKG. CODE T633-1 T833-1 T1033-1 T1433-1 T1433-2 N 6 8 10 14 14 D2 1.500.10 1.500.10 1.500.10 1.700.10 1.700.10 E2 2.300.10 2.300.10 2.300.10 2.300.10 2.300.10 e 0.95 BSC 0.65 BSC 0.50 BSC 0.40 BSC 0.40 BSC JEDEC SPEC MO229 / WEEA MO229 / WEEC MO229 / WEED-3 ------b 0.400.05 0.300.05 0.250.05 0.200.03 0.200.03 [(N/2)-1] x e 1.90 REF 1.95 REF 2.00 REF 2.40 REF 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 (c) 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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