GM1937 GAMMA | Alldatasheet
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Technical content
Features
High Efficiency: 84% Typical 36V internal Switch Fast 1.2MHz Switching Frequency Drives Up to three LEDs from a 2.8V Supply Drives Up to six LEDs from a 5V Supply External Matched LED Current Uses Tiny 1mm height inductor Requires Only 0.22 F Output Capacitor Low profile TSOT package Application Cellular Phones PDA, Handheld Computers Digital Cameras MPS3 Players GPS Receivers GM1937 VIN SW FB GND CE 0.22µF 1µF 22µH 6.34Ω VIN 3V to 5V OFF ON Figure 1 Li-Ion Powered Driver for Three White LEDs
2 GM1937V2.00 GM1937 WHITE LED STEP-UP CONVERTER Marking Information and Pin Configurations (Top View) SOT25 WL: Device Code, Green Product Y: Year W: Week code A: Assembly/testing site Pin Descriptions Pin Number Pin Name Pin Function 1 SW Switch Pin, (Minimize trace area at this pin to reduce EMI.)
2 GND Ground
Feedback Pin. Reference voltage is 95 mV. (Calculate resistor value according to the formula RFB=95 mV / ILED .) 4 CE Shutdown Pin (Connect to 1.5 V or higher to enable device; 0.4 V or less to disable device) 5 V CC Input Supply Pin. (Must be locally bypassed) Order Information Ordering Number Package Shipping GM1937ST25RG SOT-25 3,000 Units/Tape and Reel WLYWA VCC FB CE GND SW
WHITE LED STEP-UP CONVERTER GM1937V2.00 Absolute Maximum Ratings PARAMETER SYMBOL RATINGS UNITS Input Voltage V IN 10 V SW Voltage 36 V FB Voltage 10 V CE Voltage 10 V Continuous Total Power Dissipation SOT-25 P D 300 mW Operating Ambient Temperature T A - 40 to 85 ℃ Storage Temperature T stg - 65 to 150 ℃ Lead Temperature (Soldering, 10 sec) + 300 ℃ Block Diagram VREF 1.25V VIN FB SW GND CE
4 SHUTDWON
S DRIVER 0.2Ω RAMP GENERATOR 1.2MHz OSCILATOR Figure 2
4 GM1937V2.00 GM1937 WHITE LED STEP-UP CONVERTER Electrical Characteristics (TA = 25℃, Vcc = 3V, VCE = 3V, unless otherwise noted) Parameter Symbol Condition Min Typ Max Unit Feeback Voltage V FB ISW = 100mA, Duty Cycle = 66% 86 95 104 mV FB Pin Bias Current IFB 10 45 100 nA ICC(ON) 1.9 2.5 mA Supply Current ICC(OFF) VCE = 0V 0.1 1.0 µA Switching Frequency f SW 0.8 1.2 1.6 MHz Maximum Duty Cycle D MAX 85 90 % Switch Current Limit I SW 320 mA Switch VCESAT V SAT ISW = 250mA 350 mV Switch Leakage current I LEAK VSW = 5V 0.00 1 5 µA CE Voltage High 1.5 V CE Voltage Low 0.4 V CE Pin Bias Current I CE 65 µA
WHITE LED STEP-UP CONVERTER GM1937V2.00
Application Information
GM1937 is designed with a constant frequency, current mode control scheme to provide excellent line and load regulation. Operation can be best understood by referring to the block diagram in Figure 2. At the start of each oscillator cycle, the SR latch is set, which turns on the power switch Q1. A voltage proportional to the switch current is added to a stabilizing ramp and the resulting sum is fed into the positive terminal of the PWM comparator A2. When this voltage exceeds the level at the negative input of A2, the SR latch is reset turning off the power switch. The level at the negative input of A2 is set by the error amplifier A1, and is simply an amplified version of the difference between the feedback voltage and the reference voltage of 95mV. In this manner, the error amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier’s output increases, more current is delivered to the output; if it decreases, less current is delivered. Minimum Output Current GM 1937 can regulate three series LEDs connected a low output current. down to approximately 4mA from a 4.2V supply, without pulse skipping, using the same external components as specified for 15mA operation. As current is further reduced, the device will begin skipping pulses.This will result in some low frequency ripple, although the LED current remains regulated on an average basis down to zero. Inductor Selection A 22mH inductor is recommended for most GM1937 applications. Although small size and high efficiency are major concerns, the inductor should 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. Table 1. Recommended Inductors
Table 2. Recommended Schottky Diodes The LED current is controlled by the feedback resistor (R1 in Figure 1). The feedback reference is 95mV. Table 3. R1 Resistor Value Selection Figure 3. LED Driver with Open-Circuit Protection
8 GM1937V2.00 GM1937 WHITE LED STEP-UP CONVERTER Pad Layout 0.028 1.0 (Inches ) 0.039 0.094 2.4 0.037 0.95 0.037 0.95 0.074 1.9 0.7 mm 0.13 0~0.1 0.8 ± 0.05 2.9 ± 0.1 2.8 ± 0.35 ± 0.03 1.9 ± 0.05 0.95 ± 0.038 1.5 ± 0.05 0.1 0.65 ± 0.05 1.10 ± 0.1 Unit:mm Package Outline Dimensions – SOT 25
WHITE LED STEP-UP CONVERTER GM1937V2.00 Ordering Number GM 1937 ST25 R G APM Gamma Micro Circuit Type Package Type Shipping Type ST25: SOT 25 R: Tape & Reel Blank: Pb-free G:Green Note: Pb-free products: ♦ RoHS compliant and compatible with the cu rrent require-ments of IPC/JEDEC J-STD-020. ♦ Suitable for use in SnPb or Pb-free soldering processes with 100% matte tin (Sn) plating. Green products: ♦ Lead-free (RoHS compliant) ♦ Halogen free(Br or Cl does not exceed 900ppm by weight in homogeneous material and total of Br and Cl does not exceed 1500ppm by weight)