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ADP125ARHZ 데이터시트(PDF) 11 Page - Analog Devices |
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ADP125ARHZ 데이터시트(HTML) 11 Page - Analog Devices |
11 / 20 page Data Sheet ADP124/ADP125 Rev. C | Page 11 of 20 THEORY OF OPERATION The ADP124/ADP125 are low quiescent current, low dropout linear regulators that operate from 2.3 V to 5.5 V and can provide up to 500 mA of output current. Drawing a low 210 µA of quies- cent current (typical) at full load makes the ADP124/ADP125 ideal for battery-operated portable equipment. Shutdown current consumption is typically 100 nA. Optimized for use with small 1 µF ceramic capacitors, the ADP124/ADP125 provide excellent transient performance. Internally, the ADP124/ADP125 consist of a reference, an error amplifier, a feedback voltage divider, and a PMOS pass transistor. Output current is delivered via the PMOS pass device, which is controlled by the error amplifier. The error amplifier compares the reference voltage with the feedback voltage from the output and amplifies the difference. If the feedback voltage is lower than the reference voltage, the gate of the PMOS device is pulled lower, allowing more current to pass and increasing the output voltage. If the feedback voltage is higher than the reference voltage, the gate of the PMOS device is pulled higher, allowing less current to pass and decreasing the output voltage. The adjustable ADP125 has an output voltage range of 0.8 V to 5.0 V. The output voltage is set by the ratio of two external resistors, as shown in Figure 2. The device servos the output to maintain the voltage at the ADJ pin at 0.5 V referenced to ground. The current in R1 is then equal to 0.5 V/R2 and the current in R1 is the current in R2 plus the ADJ pin bias current. The ADJ pin bias current, 15 nA at 25°C, flows through R1 into the ADJ pin. The output voltage can be calculated using the equation: VOUT = 0.5 V(1 + R1/R2) + (ADJI-BIAS)(R1) The value of R1 should be less than 200 kΩ to minimize errors in the output voltage caused by the ADJ pin bias current. For example, when R1 and R2 each equal 200 kΩ, the output voltage is 1.0 V. The output voltage error introduced by the ADJ pin bias current is 3 mV or 0.3%, assuming a typical ADJ pin bias current of 15 nA at 25°C. Note that in shutdown, the output is turned off and the divider current is 0. The ADP124/ADP125 use the EN pin to enable and disable the VOUT pin under normal operating conditions. When EN is high, VOUT turns on; when EN is low, VOUT turns off. For automatic startup, EN can be tied to VIN. SHORT CIRCUIT, UVLO, AND THERMAL PROTECT 0.5V REFERENCE ADP124 SHUTDOWN VIN VOUT R1 R2 GND NOTES 1. R1 AND R2 ARE INTERNAL RESISTORS, AVAILABLE ON THE ADP124 ONLY. EN VOUT SENSE Figure 28. ADP124 Internal Block Diagram (Fixed Output) SHORT CIRCUIT, UVLO, AND THERMAL PROTECT 0.5V REFERENCE SHUTDOWN VIN VOUT GND EN ADP125 ADJ Figure 29. ADP125 Internal Block Diagram (Adjustable Output) |
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