SP7601

SP7601 29V High Voltage LED Driver FEATURES Wide Input Voltage Range 4.5V – 29V 1.2MHz Constant Frequency Operation Low 0.2V Reference Voltage Adjustable Overcurrent Protection PWM Dimming and Power sequencing Control RoHS Compliant, Lead Free Packaging: Small 6-Pin TSOT Package DESCRIPTION The SP7601 is a high current DC to DC Switching Buck LED Driver that features low component count and high efficiency due to a very low 0.2V reference voltage. High 1.2MHz switching frequency allows use of very small external components. The SP7601 is compatible with PWM dimming up to a frequency of 1kHz at 10% Duty Cycle. TYPICAL APPLICATION CIRCUIT M1 L1 VIN Cin 1 Vin Vo / LED + up to 29V 2 Gate 6 LX D1 Rs LED1 GND C1 0.1uF 3 SP7601 LEDn VDR GND D2 5 Dimming and Power sequencing FB 4 Rf b Rset Sept25-07 Rev D SP7601 29V High Voltage LED Driver Page 1 © 2007 Exar Corporation ABSOLUTE MAXIMUM RATINGS These are stress ratings only, and functional operation of the device at these ratings or any other above those indicated in the operation sections of the specifications below is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability. Input Voltage….................................................-0.3V to 30V Lx………………………………………………….…-2V to 30V FB……………..................................................-0.3V to 5.5V Storage Temperature..…………….…..……-65 °C to 150 °C Junction Temperature...................................-40°C to 125°C Lead Temperature (Soldering, 10 sec)….….………..300 °C ESD Rating………...……1kV LX, 2kV all other nodes, HBM ELECTRICAL SPECIFICATIONS Specifications are for TAMB=TJ=25°C, and those denoted by ♦ apply over the full operating range, -40°C< Tj 1.2V). The regulator is now in standby and once VIN has reached steady-state, then FB is transitioned from a high to a low state. The controller then starts operating at nominal frequency. Another benefit of using power sequencing for power up is that it ensures all internal circuitry is alive and fully operational before the device is required to regulate the current through the LEDs. Depending on the operating conditions, there may be short duration ( 1.2 Cin (uF) 2.2 4.7 2 x 4.7 350mV ⎛ ⎞ Rds(ON ) ≤ ⎜ ⎟ ……….. (5) ⎝ 1.5 × 1.5 × 1.05 × Io ⎠ Within this constraint, selecting MOSFETs with lower RDS(ON) will reduce conduction losses at the expense of increased switching losses. If a choice of several MOSFETs is available, select the highest RDS(ON) MOSFET that meets the above criteria. Schottky Rectifier selection Select the Schottky D1 for Voltage rating VR and current rating If. Voltage rating should be selected using the same guidelines outlined for MOSFET voltage selection. Current rating can be calculated from: ⎛ Vo ⎞ If ≥ ⎜1 − ⎟ × Io ……………………… (6) ⎝ Vin ⎠ Table1- CIN selection Sept25-07 Rev D SP7601 29V High Voltage LED Driver Page 6 © 2007 Exar Corporation GENERAL OVERVIEW Note that in applications where duty cycle is low, Schottky losses comprise a larger percentage of converter losses. In order to improve the efficiency in these applications choose a Schottky that meets the calculated current rating and has a lower VF. Feedback resistor RFB RFB is part of the SP7601 loop compensation network. Use a 30kΩ RFB for VIN of 20V and larger. Use RFB of 60KΩ for VIN less than 20V. Capacitor C1 This is the decoupling capacitor for the power supply to the internal driver. Use a 0.1μF capacitor and place it as closely to the VDR and VIN pins as possible. 4. RDS(ON) is calculated from equation (5): 350mV ⎛ ⎞ RDS (ON ) ≤ ⎜ ⎟ = 0.42Ohm ⎝ 1.5 × 1.5 × 1.05 × 0.35 A ⎠ BVDSS should be at least 30V and QGD should be less than 10nC. An ANPEC APM4427K with RDS(ON)=0.14 Ohm, BVDSS=30V and QGD=1.1nC can be used. 5. Schottky current rating IF can be calculated from (6): If ≥ 3 . 3V ⎞ ⎛ ⎜1 − ⎟ × 0 . 35 A = 0 . 3 A 12 V ⎠ ⎝ Voltage rating should be 30V. An SL03 rated at 30V/1.1A or equivalent can be used. 6. Calculate Rs from equation (2): Design example- Design a drive circuit for a 0.35A LED with a 12V input voltage. Nominal LED voltage is 3.3V. 1. Calculate RSET from equation (1): Rs = 0.35V − (1.5 × 1.05 × 0.525 A × 0.14Ohm ) = 7098Ohm 33uA Use the maximum recommended Rs of 3kΩ since the calculated value is larger. M1, ANPEC APM4427K 30V, 0.14 Ohm Rset = 0.2V = 0.57Ohm 0.35 A VIN L1, COILTRONICS LD1-560 56uH, 0.5Arms 2. Calculate inductor value L1 from (3): 12V 2.2uF 1 Vin 2 Gate 6 LX 3k D1, Vishay SL03 30V, 1.1A 3.3V × (12V − 3.3V ) L1 = = 57uH 12V × 1.2MHz × 0.035 A A COILTRONICS LD-560 inductor rated at 56μH, 0.5ARMS and 0.57ASAT can be used. 3. Select input capacitor: A 2.2μF CIN is needed as shown in table 1. From equation (4), the ripple current rating of CIN is a fraction of 0.35A. A 2.2uF, 16V ceramic capacitor easily meets this requirement and offers low ESR and ESL. GND C1 0.1uF 3 LED1 SP7601 4 VDR GND 5 FB 60k 1N4148 Dimming and Power sequencing 0.57 Ohm Figure 4. Circuit schematic for design example Sept25-07 Rev D SP7601 29V High Voltage LED Driver Page 7 © 2007 Exar Corporation PACKAGE: 6PIN TSOT Sept25-07 Rev D EXAR SP7601 29V High Voltage LED Driver Page 8 © 2007 Exar Corporation ORDERING INFORMATION RoHS/ Theta JA Min Max MSL Level Lead ºC/W Temp ºC Temp ºC Free SP7601EK1-L -40 125 Yes 134 L1 @ 260ºC SP7601EK1-L/TR -40 125 Yes 134 L1 @ 260ºC Part Number SP7601_EB -40 125 Pack Type Canister Tape & Reel Quantity Any 2500 Package 6 Pin TSOT 6 Pin TSOT Board Not Applicable to Evaluation Board For further assistance: Email: WWW Support page: Application Notes: Sipexsupport@sipex.com http://www.sipex.com/content.aspx?p=support http://www.sipex.com/applicationNotes.aspx EXAR Corporation reserves the right to make changes to the products contained in this publication in order to improve design, performance or reliability. EXAR Corporation assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and makes no representation that the circuits are free of patent infringement. Charts and schedules contained here in are only for illustration purposes and may vary depending upon a user’s specific application. While the information in this publication has been carefully checked; no responsibility, however, is assumed for inaccuracies. EXAR Corporation does not recommend the use of any of its products in life support applications where the failure or malfunction of the product can reasonably be expected to cause failure of the life support system or to significantly affect its safety or effectiveness. Products are not authorized for use in such applications unless EXAR Corporation receives, in writing, assurances to its satisfaction that: (a) the risk of injury or damage has been minimized; (b) the user assumes all such risks; (c) potential liability of EXAR Corporation is adequately protected under the circumstances. Sept25-07 Rev D SP7601 29V High Voltage LED Driver Page 9 © 2007 Exar Corporation