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EUP2595
32V Step-Up Converters for Two to Nine White LEDs
DESCRIPTION
The EUP2595 is a constant current step-up converter specially designed for driving white LEDs. The step-up converter topology allows series connection of the white LEDs so the LED currents are identical for uniform brightness. The EUP2595 can drive 9 LEDs in series. The brightness of the LEDs can be adjusted through a voltage level on the CTRL pin or by applying a PWM signal to CRTL pin. 1MHz current-mode, pulse-width modulated (PWM) operation allows for small input and output capacitors and a small inductor while minimizing ripple on the input supply/battery. Programmable soft-start eliminates inrush current during startup. The EUP2595 is available in a space-saving, 8-pin 3mm x 3mm TDFN package.
FEATURES
2.6V to 5.5V Input Range 32V (max) Output with Overvoltage Protection Up to 90% Efficiency Flexible Analog or PWM Dimming Control Internal High Power MOSFET Switch < 1A shutdown Current Fast 1MHz PWM Operation Small, Low-Profile Inductors and Capacitors 3mm x 3mm TDFN-8 Package RoHS Compliant and 100% Lead (Pb)-Free
APPLICATIONS
Cell Phones and Smart Phones PDAs, Palmtops, and Wireless Handhelds e-Books and Subnotebooks White LED Display Backlighting
Typical Application Circuit
Figure 1. Typical Application Circuit
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Pin Configurations
Package Type Pin Configurations
TDFN-8
Pin Description
PIN OUT IN CTRL CS COMP GND PGND LX Pin 1 2 3 4 5 6 7 8 DESCRIPTION WLED output overvoltage sense pin. Add a 1k resistor to improve overvoltage sense accuracy. Input Supply Voltage. Brightness Control Input. LED brightness is controlled by the voltage applied to CTRL. Varying the voltage from 0.24V to 1.65V adjusts the brightness from dim to bright, respectively. Any voltage above 1.65V does not increase brightness. 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, whichever is lower. Compensation Input. Connect a 0.1F capacitor (CCOMP) from COMP to GND. CCOMP stabilizes the converter and controls soft-start. CCOMP discharges to GND when in shutdown. Common 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. This pin is high impedance during shutdown.
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Ordering Information
Order Number EUP2595JIR1 Package Type TDFN-8 Marking Operating Temperature Range -40 C to 85C
xxxxx 2595A
EUP2595
1/4
1/4
1/4
1/4
Lead Free Code 1: Lead Free 0: Lead Packing R: Tape & Reel Operating temperature range I: Industry Standard Package Type J: TDFN-8
Block Diagram
Figure 2.
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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 35V CTRL to GND -------------------------------------- -0.3V to the lower of 6V or (VIN +0.5V) COMP,CS to GND ---------------------------------------------------------- -0.3V to (VIN +0.3V) ILX ------------------------------------------------------------------------------------- 1A Thermal Resistance TDFN-8 -------------------------------------------------------------------------------- 50C /W Junction Temperature ---------------------------------------------------------------- 150C Storage Temperature Range ------------------------------------------------------ -65C to 150C Lead Temperature (Soldering, 10sec.) --------------------------------------------- 260C
Recommended Operating Conditions
Supply Voltage, VIN ---------------------------------------------------------------- 2.6V to 5.5V Operating Temperature Rang ----------------------------------------------------- -40C to 85C
Electrical Characteristics
(VIN = 3V, Lin = 22H, CIN = 2.2, COUT = 0.1, CCOMP = 0.1F, RSENSE = 13, VCTRL = 1.5V, TA =-40C to +85C, unless otherwise noted. Typical values are at TA =25C.)
Parameter
Supply Voltage UVLO Threshold UVLO Hysteresis Quiescent Current Shutdown Supply Current OVLO Threshold OVLO Hysteresis OUT Input Bias Current Output Voltage Range ERROR AMPLIFIER CTRL to CS Regulation CS Input Bias Current CTRL Input Resistance CTRL Dual-Mode Threshold CS Maximum Brightness Clamp Voltage COMP Input Resistance to Ground VIN Rising
Conditions
Min
2.6 2.23 2.20
EUP2595 Typ Max.
5.5 2.40 2.35 30 350 2.60 2.55 700 1.50 35 32.8 25 1 32 300 530 190 330 23.3 310 1 850 245 347 35
Unit
V V mV A A V V A V mV A k[ mV mV k[
VIN Falling No Switching, VCTRL=VCS=1V VOUT1=V+, EN1=EN2=GND Rising Falling VOUT=32V,VCTRL> 0.24V VOUT=VIN, CTRL=GND
32 30
0.15 33.5 31.3 2.20 15
VIN-VD VCTRL = 1.5V, VIN= 2.6V to 5.5V VCS = VCTRL/5 0DS2595
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Electrical Characteristics (Continued)
(VIN = 3V, Lin = 22H, CIN = 2.2, COUT = 0.1, CCOMP = 0.1F, RSENSE = 13, VCTRL = 1.5V, TA =-40C to +85C, unless otherwise noted. Typical values are at TA =25C.)
Parameter
Conditions
EUP2595 Min Typ Max.
20 0.78 52 1 12 0 93.5 0.35 95 0.86 1150 97.2 1.40 1 550 1720 85 1.25
Unit
S MHz % % [ A mA
CS-to-COMP Transconductance Vcomp=1V OSCILLATOR Operating Frequency Minimal Duty Cycle Maximum Duty Cycle N-CHANNEL SWITCH LX On-Resistance LX Leakage Current LX Current Limit Vlx=32V, CTRL=GND Maximum Duty Cycle PWM Mode Pulse Skipping CTRL=IN , CS=GND
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Typical Operating Characteristics
EFFICIENCY VS INPUT VOLTAGE
93 91 89 87 85 83 81 79 77 75 2 3 4 5 INPUT VOLTAGE (V) 6 3 LEDs 4 LEDs 6 LEDs 8 LEDs
EFFICIENCY (%)
EFFICIENCY VS LED CURRENT 92 90 88 86 84
3 LEDs
EFFICIENCY(%)
82 80 78
0 10 20
6 LEDs 8 LEDs
30
LED CURRENT (m A)
LED CURRENT vs DIRECT-PWM DIMMING 30
LED CURRENT (mA)
25 20 15 10 5 0 0 20 40 60 80 100 DUTY CYCLE (%)
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Application Information
Soft-Start The EUP2595 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 EUP2595 enter shutdown when VCTRL is less than 100mV for more than 8.2ms. In shutdown, supply current is reduced to 0.3A 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. Overvoltage Protection Overvoltage lockout (OVLO) occurs when VOUT is above 32V.The protection circuitry stops the internal MOSFET from switching and causes VCOMP to decay to 0V. The device comes out of OVLO and into softstart when VOUT falls below 2.2V. Adjusting LED Current Adjusting the EUP2595 output current changes the brightness of the LEDs. An analog input (CTRL) and the sense-resistor value set the output current. Output current is given by:
VCTRL I LED = 5 x R SENSE
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 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. Larger 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 controlls soft-start. Connect a 0.1F capacitor from COMP to GND. For stable operation, COUT must not exceed 10 times CCOMP. Inductor Selection Inductor values range from 10H to 47H. A 22H inductor optimizes the efficiency for most applications while maintaining low 15mVP-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:
I PEAK = + VOUT ( MAX) x I LED( MAX) 0.9 x VIN( MIN)
VIN( MIN) x 0.9s 2xL
Schottky Diode Selection The EUP2595 high switching frequency demands a high-speed rectification diode (D1) for optimum efficiency. A Schottky diode is recommended due to its fast recovery time and low forward-voltage 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 calculated from:
I DIODE(RMS) I OUT x I PEAK
The VCTRL voltage range for adjusting output current is 0.24V to 1.65V. To set the maximum current, calculate RSENSE when VCTRL is at its maximum as follows:
1.65V 5 x I LED( MAX)
R SENSE =
Power dissipation in RSENSE is typically less than 10mW, making a standard chip resistor sufficient.
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PC Board Layout Due to fast switching waveforms and high-current paths, careful PC board layout is required. An evaluation kit 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 may be longer.
Figure 3. Typical Operating Circuit 21 WLEDs
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Packaging Information
TDFN-8
DETAIL A
SYMBOLS A A1 b D D1 E E1 e L
MILLIMETERS MIN. MAX. 0.70 0.80 0.00 0.05 0.20 0.40 2.90 3.10 2.30 2.90 3.10 1.50 0.65 0.25 0.45
INCHES MIN. 0.028 0.000 0.008 0.114 0.090 0.114 0.059 0.026 0.010 0.018 0.122 MAX. 0.031 0.002 0.016 0.122
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