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G5115T1U Datasheet(PDF) 6 Page - Global Mixed-mode Technology Inc |
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G5115T1U Datasheet(HTML) 6 Page - Global Mixed-mode Technology Inc |
6 / 9 page Ver: 1.1 Sep 20, 2004 TEL: 886-3-5788833 http://www.gmt.com.tw 6 G5115/G5117/G5119 Global Mixed-mode Technology Inc. Pin Description PIN G5115 G5117 G5119 SOT-23-5 SOT-23-5 MSOP-8 NAME FUNCTION 1 1 8 SW Switch Pin. The drain of the internal NMOS power switch. Connect this pin to inductor. 2 PGND Power Ground Pin. 2 2 7 AGND Analog Ground Pin. 3 3 6 FB Feedback Pin. 4 5 SHDN Active Low Shutdown Pin. Tie this pin to logical high to enable the device or tied it to logical low to turn this device off. Internal 1.5M Ω pulled high. 4 4 OVP Over Voltage Protection Sense Pin. 5 5 1 VCC Input Supply Pin. Bypass this pin with a capacitor as close to the device as possible. Function Description Operation The G5115/G5117/G5119 are boost converters with NMOS switch embedded. They operate in a PFM scheme with constant peak current control. The opera- tion frequency is up to 1MHz and is determined by the current limit, inductor value, input voltage and minimum off time. The boost cycle is started when FB pin voltage drop below 0.25V as the NMOS switch turns on. During the switch on period, the inductor current ramps up until 250mA current limit is reached. Then turns the switch off, while the inductor current flows through external schottky diode, and ramps down to zero. During the switch off period, the inductor current provides for load current and also charges output capacitor. It makes the LED current higher and results in larger voltage drop on sense resistor Rs. The cycle stop when FB pin voltage is above 0.25V. The current limit function acts as an inherent soft start by controlling the inrush current. PWM Dimming To control the brightness of the LEDs, use a low fre- quency PWM waveform to turn G5117/G5119 on for duty 0%~100%. How bright the LEDs at 100% duty are determined by sense resistor Rs. Overvoltage Protection (OVP) OVP is designed to prevent the damage of internal NMOS switch in case the increased impedance of the LED load (include the LED opened). Once the device detects over voltage at the output, the internal NMOS switch is kept off until the output voltage drops below 14V. Applications Information Inductor Selection The PFM peak current control scheme of the G5115/G5117/G5119 is inherently stable. The inductor value does not affect the stability of the regulator. The selected inductor must have a saturation current that meets the maximum peak current of the converter. An- other important inductor parameter is the DC resistance. The lower DC resistance has the higher the efficiency of the converter. Table 1. Recommended Inductors PART VALUE(µH) MAX DCR ( Ω) VENDOR LQH32CN100K1 1 10 0.39 MURATA 972AS-100M 10 0.48 TOKO 960AW-100M 10 0.18 TOKO Output Capacitor Selection For better output voltage filtering, a low ESR output capacitor is recommended. Ceramic capacitors have a low ESR value, but depending on the application, tan- talum capacitors can be used. The selection of the output capacitor value directly influences the output voltage ripple of the converter which also influences line regulation. The larger output voltage ripple, the larger line regulation, which means that the LED cur- rent changes if the input voltage changes. If a certain change in LED current gives a noticeable change in LED brightness, depends on the LED manufacturer and on the application. Applications requiring good line regulation ±1%/V (TYP) must use output capacitor val- ues ±1µF. |
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