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ADP1754ACPZ-1.0-R7 Arkusz danych(PDF) 11 Page - Analog Devices |
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ADP1754ACPZ-1.0-R7 Arkusz danych(HTML) 11 Page - Analog Devices |
11 / 20 page Data Sheet ADP1754/ADP1755 Rev. F | Page 11 of 20 THEORY OF OPERATION The ADP1754/ADP1755 are low dropout linear regulators that use an advanced, proprietary architecture to provide high power supply rejection ratio (PSRR) and excellent line and load transient response with only a small 4.7 µF ceramic output capacitor. Both devices operate from a 1.6 V to 3.6 V input rail and provide up to 1.2 A of output current. Supply current in shutdown mode is typically 2 µA. UVLO VOUT VIN SENSE SS SHORT-CIRCUIT AND THERMAL PROTECTION R1 0.5V REF R2 SHUTDOWN EN PG GND ADP1754 REVERSE POLARITY PROTECTION PG DETECT 0.9µA Figure 24. ADP1754 Internal Block Diagram UVLO VOUT VIN ADJ SS SHORT-CIRCUIT AND THERMAL PROTECTION 0.5V REF SHUTDOWN EN PG GND ADP1755 REVERSE POLARITY PROTECTION PG DETECT 0.9µA Figure 25. ADP1755 Internal Block Diagram Internally, the ADP1754/ADP1755 consist of a reference, an error amplifier, a feedback voltage divider, and a PMOS pass transistor. Output current is delivered via the PMOS pass transistor, 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 ADP1754 is available in seven fixed output voltage options between 0.75 V and 2.5 V. The ADP1754 allows for connection of an external soft start capacitor that controls the output voltage ramp during startup. The ADP1755 is the adjustable version with an output voltage that can be set to a value between 0.75 V and 3.3 V by an external voltage divider. Both devices are controlled by an enable pin (EN). SOFT START FUNCTION (ADP1754/ADP1755) For applications that require a controlled startup, the ADP1754/ ADP1755 provide a programmable soft start function. The programmable soft start is useful for reducing inrush current upon startup and for providing voltage sequencing. To implement soft start, connect a small ceramic capacitor from SS to GND. Upon startup, a 0.9 µA current source charges this capacitor. The ADP1754/ADP1755 start-up output voltage is limited by the voltage at SS, providing a smooth ramp-up to the nominal output voltage. The soft start time is calculated as follows: tSS = VREF× (CSS/ISS) (1) where: tSS is the soft start period. VREF is the 0.5 V reference voltage. CSS is the soft start capacitance from SS to GND. ISS is the current sourced from SS (0.9 µA). When the ADP1754/ADP1755 is disabled (using the EN pin), the soft start capacitor is discharged to GND through an internal 100 Ω resistor. 2.50 0 0.25 0.50 0.75 1.00 1.25 1.50 1.75 2.00 2.25 0 2 4 6 8 10 TIME (ms) EN 1nF 4.7nF 10nF Figure 26. VOUT Ramp-Up with External Soft Start Capacitor |
Podobny numer części - ADP1754ACPZ-1.0-R7 |
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Podobny opis - ADP1754ACPZ-1.0-R7 |
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