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G923-370T1U Datasheet(PDF) 7 Page - Global Mixed-mode Technology Inc |
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G923-370T1U Datasheet(HTML) 7 Page - Global Mixed-mode Technology Inc |
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7 / 9 page  Ver: 1.5 Jan 16, 2007 TEL: 886-3-5788833 http://www.gmt.com.tw 7 G923 Global Mixed-mode Technology Inc. Figure 2. Adjustable Output Using External Feedback Resistors Over Current Protection The G923 uses a current sense-resistor to monitor the output current. A portion of the PMOS output transis- tor’s current is mirrored to a resistor such that the voltage across this resistor is proportional to the output current. Once the output current exceeds limit thresh- old, G923 would be protected with a limited output current. Further more, when the output is short to ground, the output current would be folded-back to a less limit. Over Temperature Protection To prevent abnormal temperature from occurring, the G923 has a built-in temperature monitoring circuit. When it detects the temperature is above 145°C, the output transistor is turned off. When the IC is cooled down to below 120°C, the output is turned on again. In this way, the G923 will be protected against abnormal junction temperature during operation. Shutdown Mode When the SHDN pin is connected a logic low voltage, the G923 enters shutdown mode. All the analog cir- cuits are turned off completely, which reduces the current consumption to only the leakage current. The G923 output pass transistor would get into high im- pedance level. There is an internal discharge path to help to shorten discharge delay time. Operating Region and Power Dissipation Since the G923 is a linear regulator, its power dissipa- tion is always given by P = IOUT (VIN - VOUT). The maxi- mum power dissipation is given by: PD(MAX) = (TJ - TA) /θJA,=(150°C-25°C)/240°C/W = 520mW Where (TJ -TA) is the temperature difference the G923 die and the ambient air,θJA, is the thermal resistance of the chosen package to the ambient air. For surface mount device, heat sinking is accomplished by using the heat spreading capabilities of the PC board and its copper traces. In the case of a SOT-23-5 package, the thermal resistance is typically 240°C/Watt. (See Recommended Minimum Footprint) [Figure 3] Refer to Figure 4 is the G923 valid operating region (Safe Op- erating Area) & refer to Figure 5 is maximum power dissipation of SOT-23-5. The die attachment area of the G923’s lead frame is connected to pin 2, which is the GND pin. Therefore, the GND pin of G923 can carry away the heat of the G923 die very effectively. To improve the maximum power providing capability, connect the GND pin to ground using a large ground plane near the GND pin. Applications Information Capacitor Selection and Regulator Stability Normally, use a 1µF capacitor on the input and a 4.7µF capacitor on the output of the G923. Larger in- put capacitor values and lower ESR provide better supply-noise rejection and transient response. A higher- value input capacitor (10µF) may be necessary if large, fast transients are anticipated and the device is located several inches from the power source. Power-Supply Rejection and Operation from Sources Other than Batteries The G923 is designed to deliver low dropout voltages and low quiescent currents in battery powered sys- tems. Power-supply rejection is 65dB at low frequen- cies. As the frequency increases above 20kHz, the output capacitor is the major contributor to the rejec- tion of power-supply noise. When operating from sources other than batteries, improve supply-noise rejection and transient response by increasing the values of the input and output ca- pacitors, and using passive filtering techniques. Load Transient Considerations The G923 load-transient response graphs show two components of the output response: a DC shift of the output voltage due to the different load currents, and the transient response. Typical overshoot for step changes in the load current from 10mA to 300mA is 8mV. Increasing the output capacitor's value and de- creasing its ESR attenuates transient spikes. Input-Output (Dropout) Voltage A regulator's minimum input-output voltage differential (or dropout voltage) determines the lowest usable sup- ply voltage. In battery-powered systems, this will de- termine the useful end-of-life battery voltage. Because the G923 use a P-channel MOSFET pass transistor, their dropout voltage is a function of RDS(ON) multiplied by the load current. IN OUT SHDN SET GND G923 ＋ － BATTERY CIN 1µF R1 R2 C OUT 4.7µF R L OUTPUT VOLTAGE IN OUT SHDN SET GND G923 ＋ － BATTERY CIN 1µF R1 R2 C OUT 4.7µF R L OUTPUT VOLTAGE |
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