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ADP1752 Datasheet(PDF) 11 Page - Analog Devices |
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ADP1752 Datasheet(HTML) 11 Page - Analog Devices |
11 / 20 page Data Sheet ADP1752/ADP1753 Rev. E | Page 11 of 20 THEORY OF OPERATION The ADP1752/ADP1753 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 0.8 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 ADP1752 REVERSE POLARITY PROTECTION PG DETECT 0.9µA Figure 24. ADP1752 Internal Block Diagram UVLO VOUT VIN ADJ SS SHORT-CIRCUIT AND THERMAL PROTECTION 0.5V REF SHUTDOWN EN PG GND ADP1753 REVERSE POLARITY PROTECTION PG DETECT 0.9µA Figure 25. ADP1753 Internal Block Diagram Internally, the ADP1752/ADP1753 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 ADP1752 is available in seven fixed output voltage options between 0.75 V and 2.5 V. The ADP1752 allows for connection of an external soft start capacitor that controls the output voltage ramp during startup. The ADP1753 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 con- trolled by an enable pin (EN). SOFT START FUNCTION (ADP1752/ADP1753) For applications that require a controlled startup, the ADP1752/ ADP1753 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 ADP1752/ADP1753 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 ADP1752/ADP1753 are disabled (using EN), 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 |
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