View EL763006_1038072.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

(R)
EL7630
Data Sheet February 22, 2006 FN7371.1
White LED Boost Regulator
The EL7630 represents a high efficiency, constant frequency PWM regulator for use in white LED driving applications. With efficiencies up to 86%, the EL7630 operates at 1.35MHz switching frequency while operating from an input voltage of between 2.7V and 5.5V. The maximum output voltage of 27V enables the EL7630 to drive up to 6 LEDs in series. It is also possible to use the EL7630 to drive LEDs in series/parallel combination for applications requiring up to 15 LEDs. Available in the 6 Ld SC-70 and the 5 Ld TSOT packages, the EL7630 features the same pinout as competitive products but offers higher efficiency, constant frequency operation. It is specified for operation over the -40C to +85C ambient temperature range.
Features
* Up to 6 LEDs in series * 27V maximum output * 2.7V to 5.5V input * Up to 86% efficient * 1.35MHz constant frequency * Enable/PWM dimming control * Pb-free plus anneal available (RoHS compliant)
Applications
* LED backlighting * Cell phones * PDAs
Pinouts
EL7630 (6 LD SC-70) TOP VIEW
LX 1 GND 2 FB 3 6 VIN 5 PGND 4 ENAB
* Handheld devices
Ordering Information
PART NUMBER PART (See Note) MARKING EL7630ICZ-T7 EL7630ICZ-T7A BCA BCA BAAC TAPE & REEL 7" (3K pcs) 7" (250 pcs) 7" (3K pcs) 7" (250 pcs) PACKAGE (Pb-free) 6 Ld SC-70 6 Ld SC-70 5 Ld TSOT 5 Ld TSOT PKG. DWG. # P6.049 P6.049 MDP0049 MDP0049
EL7630 (5 LD TSOT) TOP VIEW
LX 1 GND 2 FB 3 4 ENAB 5 VIN
EL7630IWTZ-T7
EL7630IWTZ-T7A BAAC
NOTE: Intersil Pb-free plus anneal products employ special Pb-free material sets; molding compounds/die attach materials and 100% matte tin plate termination finish, which are RoHS compliant and compatible with both SnPb and Pb-free soldering operations. Intersil Pb-free products are MSL classified at Pb-free peak reflow temperatures that meet or exceed the Pb-free requirements of IPC/JEDEC J STD-020.
1
CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2006. All Rights Reserved All other trademarks mentioned are the property of their respective owners.
EL7630
Absolute Maximum Ratings (TA = 25C)
Input Voltage (VIN) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6V LX Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +27V FB Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6V ENAB Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +6V PGND to GND (SC-70 package) . . . . . . . . . . . . . . . . -0.3V to +0.3V Operating Temperature . . . . . . . . . . . . . . . . . . . . . . .-40C to +85C Maximum Junction Temperature . . . . . . . . . . . . . . . . . . . . . . +125C Storage Temperature . . . . . . . . . . . . . . . . . . . . . . . .-65C to +150C Lead Temperature (soldering, 10s) . . . . . . . . . . . . . . . . . . . . +300C
CAUTION: Stresses above those listed in "Absolute Maximum Ratings" may cause permanent damage to the device. This is a stress only rating and operation of the device at these or any other conditions above those indicated in the operational sections of this specification is not implied. IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typ values are for information purposes only. Unless otherwise noted, all tests are at the specified temperature and are pulsed tests, therefore: TJ = TC = TA
Electrical Specifications
PARAMETER VIN-MIN VIN-MAX VFB
VIN = 3V, VENAB = 3V, over temperature from -40C to 85C unless otherwise specified. CONDITION VOUT = 16V, ILED = 20mA VOUT = 25V, ILED = 20mA TA = 25C 86 80 95 95 MIN 2.7 5.5 104 115 100 ENAB = 3V, output not switching ENAB = 0V 0.6 1.0 1 0.8 0.8 1.35 1.35 90 90 350 350 750 0.01 2.5 0.6 1 VIN = 2.7V to 5V 0.2 1 1.8 1.9 TYP MAX UNIT V V mV mV nA mA A MHz MHz % % mA mA m A V V A %/V
DESCRIPTION Minimum Operating Voltage Maximum Operating Voltage Feedback Voltage
IFB IIN
FB Pin Bias Current Supply Current
FOSC
Switching Frequency
TA = 25C
DMAX
Maximum Duty Cycle
TA = 25C
85 82
ILIM
Switch Current Limit
TA = 25C
280 250
rDS(ON) ILEAK VENAB-HI VENAB-LO IENAB ILED/VIN
Switch On Resistance Switch Leakage Current ENAB Voltage High ENAB Voltage Low ENAB Pin Bias Current Line Regulation
ILX = 100mA VLX = 27V
2
FN7371.1 February 22, 2006
EL7630 Typical Application
L1 22H VDD LEDs LX C2 0.22F RSET 4.75 EFFICIENCY (%) VIN 2.7V~5.5V C1 1F OFF/ON D1 90 85 80 75 70 65 0 5 10 15 20 25 30 LED CURRENT (mA)
EL7630 ENAB FB GND
FIGURE 1. TYPICAL APPLICATION CIRCUIT AND EFFICIENCY vs LED CURRENT
Typical Performance Curves
0.7 QUIESCENT CURRENT (mA) 0.6 0.5 0.4 0.3 0.2 0.1 0 0 1 2 3 VIN (V) 4 5 6 LED CURRENT (mA) 24.6 24.595 24.59 24.585 24.58 24.575 24.57 24.565 24.56 0 5 10 VOUT (V) 15 20
FIGURE 2. QUIESCENT CURRENT (ENABLE)
FIGURE 3. LOAD REGULATION (VIN=4V)
SWITCHING FREQUENCY (MHz)
24.7 24.68 LED CURRENT (mA) 24.66 24.64 24.62 24.6 24.58 24.56 2.5 3 3.5 4 VIN (V) 4.5 5 5.5
1.34 1.32 1.3 1.28 1.26 1.24 1.22 1.2 -40
10 TEMPERATURE (C)
60
FIGURE 4. LINE REGULATION
FIGURE 5. SWITCHING FREQUENCY vs TEMPERATURE
3
FN7371.1 February 22, 2006
EL7630 Typical Performance Curves
22 20 16 IOUT (mA) 12 8 4 0 0 20 40 60 80 100 DUTY-CYCLE (D)
FIGURE 6. PWM DIMMING CURVE (400Hz)
Block Diagram
Vin 1.2MHz Oscillator and Ramp Generator Enable
EL7630
LX
PWM Comparator
PWM Logic Controller
FET Driver
Current Sense
PGND GM Amplifier FB 95mV Bandgap Reference Generator
GM Amp Compensation
(shared with PGND in TSOT5 package) GND
FIGURE 7. EL7630 BLOCK DIAGRAM
Pin Functions
LX (Pin 1) - Switching Pin. Connect to inductor and diode. GND (Pin 2) - Ground Pin. Connect to local ground. FB (Pin 3) - Feedback Pin. Connect to the cathode of lowest LED and the sense resistor. ENAB (Pin 4) - Enable Pin. Connect to enable signal to turn-on or off the device.
PGND (Pin 5, SC-70 Package) - Ground Pin. Connect to Pin 2 and to local ground. VIN (Pin5/Pin6 SC-70 Package) - Input Supply Pin. Connect to the input supply voltage.
4
FN7371.1 February 22, 2006
EL7630 Detailed Description
EL7630 uses a constant frequency, current mode control scheme to provide excellent line and load regulation. It can drive up to 6 LEDs in series or 15 LEDs in parallel/series configuration, with efficiencies of up 86%. EL7630 operates from an input voltage of 2.7V to 5.5V and can boost up to 27V.
25 20
IOUT (mA)
15
1kHz
Steady-State Operation
EL7630 operates with constant frequency PWM. The switching frequency is around 1.2MHz. Depending on the input voltage, inductance, number of LEDs and the LED current, the converter operates in either continuous conduction mode or discontinuous conduction mode. Both are normal. The forward current of the LED is set using the RSET resistor. In steady state mode, this current is given by the equation:
V FB I LED = -------------R SET (EQ. 1)
10
400Hz
5
0 0 10 20 30 40 50 60 70 80 90 10 DUTY-CYCLE (%)
FIGURE 8. PWM DIMMING LINEAR RANGE (FOR 400Hz AND 1kHz PWM FREQUENCIES CONDITION, COUT = 0.22F)
Shut-Down
The ENAB pin, when taken low places EL7630 into power down mode. When in power down, the supply current reduced to less than 1A.
Dimming Control
The ENAB pin also doubles as a brightness control. There are two different types of dimming control methods. The first dimming control is controlled through the duty-cycle of the ENAB input PWM waveform, which can operate at frequencies of 400Hz to 1kHz. The LEDs operate at either zero or full current. This is called PWM dimming control method. The relationship between the average LED current and the duty-cycle (D) of the ENAB pin's waveform is as follows:
V FB average I LED = -------------- D R SET (EQ. 2)
The second dimming control is to apply a variable DC voltage to adjust the LED current. This is called analog dimming control. The dimming control using a DC voltage is shown in Figure 9. As the DC dimming signal voltage increases, the voltages drop on R1 and R2 increases and the voltage drop on RSET decreases. Thus, the LED current decreases. The DC dimming signal voltage can be a variable DC voltage or a DC voltage generated from a PWM control signal. For some application areas, the PWM control signal is a high frequency signal. To make dimming controllable with these high frequency PWM signals, the high frequency components of the PWM control signal should be filtered to get the equivalent DC voltage. The equivalent DC voltage is then used as the variable DC voltage for dimming LED current.
V FB R 1 + R 2 V Dim R 1 I LED = -------------- -------------------- - -------------------------R SET R2 R SET R 2 (EQ. 3)
The magnitude of the PWM signal should be higher than the minimum ENAB voltage high. The bench PWM dimming test results are shown in Figure 8. In the test, two PWM frequencies 400Hz and 1kHz are chosen to compare the linear dimming range. It is clear that for lower PWM frequency, the linear dimming range is wider than one for higher PWM frequency. In the PWM dimming test, the output capacitor is 0.22F.
R2 R1 V Dim = ------ V FB 1 + ------ - F R1 R2
(EQ. 4)
where F is the brightness with respect to the undimmed value.
5
FN7371.1 February 22, 2006
EL7630
L1 22H VIN 2.7V~5.5V C1 1F OFF/ON
Components Selection
D1
VDD
LX
LEDs
EL7630 ENAB FB GND R1 RSET 4.75
C2 0.22F
The input capacitance is normally 0.22F~4.7F and the output capacitor is 0.22F~1F. X5R or X7R type of ceramic capacitor with the correct voltage rating is recommended. The output capacitor value will affect PWM dimming performance. For lower output capacitor values, the range of PWM dimming is wider than for higher values of output capacitor. When choosing an inductor, make sure the inductor can handle the average and peak currents given by the following formulas (80% efficiency assumed):
I LED V OUT I LAVG = -------------------------------0.8 V IN 1 I LPK = I LAVG + -- I L 2 V IN ( V OUT - V IN ) I L = -------------------------------------------------L V OUT f OSC
R2
DIMMING SIGNAL
FIGURE 9. ANALOG DIMMING CONTROL APPLICATION CIRCUIT
(EQ. 6)
For a required LED current ILED and chosen values of R1 and R2, the dimming DC voltage VDim can be expressed as:
R2 V Dim = V FB + ( V FB - I LED R SET ) -----R1 (EQ. 5)
(EQ. 7)
It is clear that as the required LED current ILED is closed to the rate current VFB/RSET, VDim is closed to VFB. As the required LED current is lower than the rate current, the dimming DC voltage VDim is increased in R2/R1 factor.
(EQ. 8)
Where: * IL is the peak-to-peak inductor current ripple in Ampere * L inductance in H. * fOSC switching frequency, typically 1.2MHz The boost inductor can be chosen in a wide range of inductance (10H~82H). For 10H inductor value, the boost inductor current will be in discontinuous mode. As the inductor value decreases further, the ripple of the boost inductor current is increased and can even trigger overcurrent protection. For high boost inductor value, the boost inductor current will be in continuous mode. For general boost converter, as the converter operates in continuous mode, there is right half plane zero (RHPZ). If RHPZ frequency is less than or close to the control loop crossover frequency, there is a stability issue. In EL7630, the compensation network is well designed and there is no RHPZ stability issue even if the inductor value is over 82H. For the same series of inductors, a lower inductance has lower DC resistance (DCR), which causes less conducting loss, but higher peak to peak current variation, which generates more RMS current loss. Figure 11 shows the efficiency of the demo board with different LED load for a specific series of inductor. The diode used should be a schottky type with minimum reverse voltage of 28V. The diode's peak current is the same as the inductor's peak current. The schottky RMS current is:
I RMS =
2 2 1 D 2 I LAVG + -- I L 6
Open-Voltage Protection
In some applications, it is possible that the output is opened, e.g. when the LEDs are disconnected from the circuit or the LEDs fail. In this case the feedback voltage will be zero. The EL7630 will then switch to a high duty cycle resulting in a high output voltage, which may cause the LX pin voltage to exceed its maximum 27V rating. To implement overvoltage protection, a zener diode Dz and a resistor R1 can be used at the output and FB pin to limit the voltage on the LX pin as shown in Figure 10. It is clear that as the zener is turned on, due to the overvoltage, the zener diode's current will set up a voltage on R1 and RSET and this voltage is applied on FB pin as the feedback node. This feedback will prevent the output from reaching the overvoltage condition. In the overvoltage protection circuit design, the zener voltage should be larger than the maximum forward voltage of the LED string.
L1 22H VIN 2.7V~5.5V C1 1F OFF/ON ENAB FB GND VDD LX Dz R1 RSET 4.75 LEDs D1
EL7630
C2 0.22F
(EQ. 9)
FIGURE 10. LED DRIVER WITH OVERVOLTAGE PROTECTION CIRCUIT
6
FN7371.1 February 22, 2006
EL7630
The efficiency bench test results are shown in Figure 11. In the test, the input voltage is 4V and 2, 3, 4, 5 and 6 LEDs are used as the load (boost inductor L = 22H Sumida CDRH5D28R-220NC).
90 85 EFFICIENCY (%) 80 75 70 6LED 65 3LED 60 55 0 10 20 30 LED CURRENT (mA) 4LED 2LED 5LED
PCB Layout Considerations
The PCB layout is very important for the converter to function properly. For the SC-70 6 pin package, Power Ground and Signal Ground should be separated to ensure the high pulse current in the power ground does not interfere with the sensitive signals connected to Signal Ground. Both grounds should only be connected at one point right at the chip. The heavy current loops (VIN-L1-LX-PGND, and VIN L1-D1-C2-PGND) should be as short as possible. For the TSOT 5 pin package, there is no separated GND. All return GNDs should be connected in GND pin but with no sharing branch. Based on the signal level on each branch, the lower power level of the branch, the closer the branch to GND pin in order to minimize the branch interactive. The FB pin is most important. The current sense resistor RS ET should be very close to this pin. If a long trace is required to the LEDs, a small decoupling capacitor should be placed at this pin. The heat of the IC is mainly dissipated through the PGND pin. Maximizing the copper area connected to this pin is preferable. In addition, a solid ground plane is always helpful for the EMI performance. The demo board is a good example of layout based on the principle. Please refer to the EL7630 Application Brief for the layout.
22H,VIN=4V
FIGURE 11. EFFICIENCY CURVE WITH 2, 3, 4, 5 AND 6 LEDs LOAD
White LED Connections
One leg of LEDs connected in series will ensure brightness uniformity. The 27V maximum output voltage specification enables up to 6 LEDs to be placed in series. In order to output more power to drive more LEDs, LEDs should be in series/parallel connection. Due to the LED's negative temperature coefficient, in each parallel branch, the driving source should be high impedance, to balance the LED current in each branch. One of the ways to ensure the brightness uniformity is to add mirror current balance circuit, built up with three transistors for the 15 LEDs series/parallel connection application shown in Figure 12.
D1 L1
VIN 2.7V~5.5V C1 OFF/ON
VDD
LX
C2
EL7630 ENAB FB ENAB FB GND LEDs RSET
FIGURE 12. LEDs IN SERIES/PARALLEL WITH MIRROR CURRENT BALANCE
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems. Intersil Corporation's quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com 7
FN7371.1 February 22, 2006

▲Up To Search▲

Price & Availability of EL763006

	To Download EL763006 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .