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G914 Datasheet(PDF) 4 Page - Global Mixed-mode Technology Inc |
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G914 Datasheet(HTML) 4 Page - Global Mixed-mode Technology Inc |
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4 / 6 page  Ver 0.1 Preliminary Nov 05, 2001 TEL: 886-3-5788833 http://www.gmt.com.tw 4 G914 Global Mixed-mode Technology Inc. Figure 2. Adjustable Output Using External Feedback Resistors Over Current Protection The G914 use a current mirror to monitor the output current. A small portion of the PMOS output transis- tor’s current is mirrored onto a resistor such that the voltage across this resistor is proportional to the out- put current. This voltage is compared against the ref- erence voltage. Once the output current exceeds the limit, the PMOS output transistor enters constant cur- rent mode. The current is set to 370mA typically. Over Temperature Protection To prevent abnormal temperature from occurring, the G914 has a built-in temperature monitoring circuit. When it detects the temperature is above 150 oC, the output transistor is turned off. When the IC is cooled down to below 135 oC, the output is turned on again. In this way, the G914 will be protected against abnormal junction temperature during operation. Shutdown Mode When the SHDN pin is connected a logic low voltage, the G914 enters shutdown mode. All the analog cir- cuits are turned off completely, which reduces the current consumption to only the leakage current. The output is disconnected from the input. When the out- put has no load at all, the output voltage will be dis- charged to ground through the internal resistor voltage divider. Operating Region and Power Dissipation Since the G914 is a linear regulator, its power dissipa- tion is always given by P = IOUT (VIN – VOUT). The maximum power dissipation is given by: PD(MAX) = (TJ–TA)/θJA,=150 oC-25oC/220oC/W= 568mW Where (TJ–TA) is the temperature difference the G914 die and the ambient air,θJA, is the thermal resistance of the chosen package to the ambient air. In the case of a SOT23-5 package, the thermal resistance is typi- cally 220 oC/Watt. The die attachment area of the G914’s lead frame is connected to pin 2, which is the GND pin. Therefore, the GND pin of G914 can carry away the heat of the G914 die very effectively. To improve the power dis- sipation, 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 1µF capacitor on the output of the G914. Larger input ca- pacitor values and lower ESR provide better sup- ply-noise rejection and transient response. A higher- value input capacitor (10µF) may be necessary if large, fast transients are anticipated and the device is lo- cated several inches from the power source. Power-Supply Rejection and Operation from Sources Other than Batteries The G914 is designed to deliver low dropout voltages and low quiescent currents in battery powered sys- tems. Power-supply rejection is 42dB at low frequen- cies. 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 G914 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 0mA to 100mA is 12mV. Increasing the output capacitor's value and decreasing its ESR attenuates transient spikes. Input-Output (Dropout) Voltage A regulator's minimum input-output voltage differential (or dropout voltage) determines the lowest usable supply voltage. In battery-powered systems, this will determine the useful end-of-life battery voltage. Be- cause the G914 use a P-channel MOSFET pass tran- sistor, their dropout voltage is a function of RDS(ON) multiplied by the load current. IN OUT SHDN ADJ GND G914 ＋ － BATTERYCIN 1µF R1 R2 C OUT 1µF OUTPUT VOLTAGE 470pF R L IN OUT SHDN ADJ GND G914 ＋ － BATTERYCIN 1µF R1 R2 C OUT 1µF OUTPUT VOLTAGE 470pF R L |
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Similar Description - G914 |
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