SM8237 SAMHOP | Alldatasheet

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Technical content

The information in this document is subject to change without notice. SAMHOP Microelectronics Corp. All Rights Reserved. 台北縣新店市民權路100號7樓 7F,No.100,Min-Chyuan Road, Hsintien, Taipei Hsien, Taiwan, R.O.C. TEL: 886-2-2218-3978/2820 FAX: 886-2-2218-3320 Email : info@samhop.com.tw c SAMHOP Microelectronics Corp. 三合微科股份有限公司 1.2MHz STEP-UP CONVERTER

The SM8237 is a step-up DC/DC converter specifically designed to drive white LEDs with a constant current. The device can drive two, three or four LEDs in series from a Li-ion cell. Series connection of the LEDs provides identical LED currents resulting in uniform brightness and eliminating the need for ballast resistors. The SM8237 switches at 1.2 MHz, allowing the use of tiny external components. The output capacitor can be as small as 0.22 μF, saving space and cost versus alternative solutions. A low 95mV feedback voltage minimizes power lo ss in the current setting resistor for better efficiency.

FEATURES

  • Inherently matched LED current * High efficiency : 84% typical * Drives up to four LEDs from a 2.8V supply * Drives up to six LEDs from a 5V supply * 36V rugged bipolar switch * Fast 1.2MHz switching frequency * Uses tiny 1 mm tall inductors * Requires only 0.22μF output capacitor * Low profile TSOT package SAMHOP Microelectronics Corp. 1.2MHz STEP-UP CONVERTER TYPICAL APPLICATION C1 , C2 : X7R Dielectric D1 : Frontier electronics SS14 L1 : Frontier electronics CSS0218P-22ON-LFR 4.80 4.85 4.90 4.95 5.00 5.05 5.10 5.15 5.20 0 1 02 03 04 05 06 07 08 09 0 1 0 0 1 0 5 OUTPUT CURRENT (mA) OUTPUT VOLTAGE (V) Page 1 V.1.3 Aug 28,2007 EFFICIENCY (%) 100 0 1 02 03 04 05 06 07 08 09 0 1 0 0 1 0 5 OUTPUT CURRINT (mA) EFFICIENCY (%) OUTPUT VOLTAGE vs. LOAD CURRENT EFFICIENCY vs. LOAD CURRENT Output Voltage (V) Output Current (mA) Vin = 3.3V Vin = 3.3V Vout = 5V Efficiency (%) Output Current (mA) SM8237 Vin SW SD FB GND 22 uH D1 51 K 1 uf Vout 5V / 100 mA 1 K 4.7 uf Vin 3.3 V OFF ON

SAMHOP Microelectronics Corp. 1.2MHz STEP-UP CONVERTER MAXIMUM RATINGS Input voltage (VIN) 10 V Characteristic UnitRating SW voltage 36 V FB voltage 10 V SHDN voltage 10 V Operating temperature range -4 0 ~ 8 5 Maximum junction temperature 125 V Storage temperature range - 65 ~ 150 V Lead temperature (soldering, 10 sec) 300 V oC Page 2 PIN DESCRIPTIONS NO. Function Pin name 1 SW Switch Pin. Connect inductor / diode here. Minimize trace area at this pin to reduce EMI. 2 GND Ground Pin. Connect directly to local ground plane 3 FB Feedback Pin. Reference voltage is 95mV. Connect cathode of lowest LED and resistor here. Calculate resistor value according to the formula: R FB =95mV/ILED 4 SHDN Shutdown Pin. Connect to 1.5V or higher to enable device; 0.4V or less to disable device. 5 GND (SOT-26) Ground Pin. Connect to Pin 2 and local ground plane. 6 VIN (SOT-26) Input supply Pin. Must be locally bypassed.

APPLICATIONS

  • Cellular phone * PDAs, handheld computer * Digital camera * MP3 player * GPS receiver * DC to DC Converter PIN ASSIGNMENTS (TOP VIEW) SOT-25 FB GND VIN SHDN SW SOT-26 SW FB GND VIN SHDN GND TSOT-25 (TSOT-23-5) FB GND VIN SHDN SW V.1.3 Aug 28,2007

SAMHOP Microelectronics Corp. 1.2MHz STEP-UP CONVERTER

ELECTRICAL CHARACTERISTICS

(TA =25oC, VIN =3V, VSHDN = 3V, unless otherwise noted) Characteristic UnitMin. Typ. Max.Condition Minimum operating voltage V2.5 - - Maximum operating voltage V- - 10 Feedback voltage mV86 95 104ISW =100mA, Duty cycle=66% FB pin bias current nA10 45 100 Supply current mA- 1.9 2.5 SHDN=0V μA- 0.1 1.0 Switching frequency MHz0.8 1.2 1.6 Maximum duty cycle %85 90 - Switch current limit mA- 320 - Switch VCESAT mV- 350 -ISW =250mA Switch leakage current μA- 0.01 5 SHDN voltage high V1.5 - - VSW =5V SHDN voltage low V- - 0.4 SHDN pin bias current - 65 - μA Note : 1. Absolute maximum ratings are those values beyond which the life of the device may be impaired. 2. The SM8237 is guatanteed to meet specification from 0 oC to 70 oC. Specification over the -40oC to 85oC operating temperature range are assured by design, characterization and correlation with statistical process controls. Page 3 V.1.3 Aug 28,2007

SAMHOP Microelectronics Corp. Figure 1. SM8237 function block diagram

SAMHOP Microelectronics Corp. 1.2MHz STEP-UP CONVERTER TYPICAL APPLICATION SM8237 SM8237 Page 5 V.1.3 Aug 28,2007

SAMHOP Microelectronics Corp. 1.2MHz STEP-UP CONVERTER TYPICAL APPLICATION Page 6 SM8237 SM8237 V.1.3 Aug 28,2007

SAMHOP Microelectronics Corp. 1.2MHz STEP-UP CONVERTER TYPICAL APPLICATION Page 7 SM8237 SM8237 V.1.3 Aug 28,2007

SAMHOP Microelectronics Corp. amplifier's output increases, more current is delivered to the output; if it decreases, less current is delivered. frequency ripple, although the LED current remains regulated on an average basis down to zero. major concerns, the inductor shoul d have low core losses at 1.2MHz and low DCR (copper wire resistance). Some inductors in this category with small size are listed in Table 1. sufficient for most SM8237 applications. Table 1. Recommended inductors Table 2. Recommended Schottky diodes

SAMHOP Microelectronics Corp. formula and table for R1 selection are shown below. Table 1. R1 resistor value selection Figure 2. LED driver with open-circuit protection of the LED string. The current rating zener should be larger than 0.1mA.

  1. Using a PWM signal to SHDN pin

magnitude of the PWM signal should be higher than the minimum SHDN voltage high. Please see the typical application on page 1.

SAMHOP Microelectronics Corp. 1.2MHz STEP-UP CONVERTER D b C B e H12 3 L PACKAGE SM8237 Surface Mount SOT-25 Unit : mm A SYMBOL MIN. MOM. A 0.889 1.295 A1 0.000 0.152 B 1.397 1.803 b 0.356 0.559 C D 2.591 2.997 2.692 3.099 e 0.838 1.041 L 0.300 0.610 H 0.080 0.254 Page 11 V.1.3 Aug 28,2007

SAMHOP Microelectronics Corp. 1.2MHz STEP-UP CONVERTER D b C B e H12 3 65 4 L PACKAGE SM8237 Surface Mount SOT-26 Unit : mm A SYMBOL MIN. MOM. A 0.889 1.295 A1 0.000 0.152 B 1.397 1.803 b 0.250 0.560 C D 2.591 2.997 2.692 3.099 e 0.838 1.041 L 0.300 0.610 H 0.080 0.254 Page 12 V.1.3 Aug 28,2007

SAMHOP Microelectronics Corp. 1.2MHz STEP-UP CONVERTER D b E e c12 3 L PACKAGE SM8237 Surface Mount TSOT-25 (TSOT-23-5) Unit : mm SYMBOL MIN. A 0.75 A1 0.00 A2 0.70 b 0.35 c D 0.10 2.80 Page 13 Gauge plane R A y 4xθ1 θ MOM. 0.75 2.90 MOM. 0.90 0.10 0.80 0.51 0.25 3.00 e1 1.90 BSC e 0.95 BSC L 0.37 L2 0.25 BSC L1 0.60 REF y - θ 0° R 0.10 0.10 θ1 7° Nom θ2 5° Nom 2.80E 2.60 3.00 1.60E1 1.50 1.70 V.1.3 Aug 28,2007