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ADP175ARMZ-0.9-R7 Arkusz danych(PDF) 10 Page - Analog Devices |
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ADP175ARMZ-0.9-R7 Arkusz danych(HTML) 10 Page - Analog Devices |
10 / 20 page ADP1715/ADP1716 Rev. 0 | Page 10 of 20 THEORY OF OPERATION The ADP1715/ADP1716 are low dropout, CMOS linear regulators that use an advanced, proprietary architecture to provide high power supply rejection ratio (PSRR) and excellent line and load transient response with just a small 2.2 μF ceramic output capacitor. Both devices operate from a 2.5 V to 5.5 V input rail and provide up to 500 mA of output current. Supply current in shutdown mode is typically 100 nA. SOFT START REFERENCE CURRENT LIMIT THERMAL PROTECT SHUTDOWN GND OUT SS/ ADJ/ TRK IN EN Figure 26. Internal Block Diagram Internally, the ADP1715/ADP1716 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 ADP1715 is available in two versions, one with fixed output voltage options and one with an adjustable output voltage. The fixed output voltage options are set internally to one of sixteen values between 0.75 V and 3.3 V, using an internal feedback network. The adjustable output voltage can be set to between 0.8 V and 5.0 V by an external voltage divider connected from OUT to ADJ. The fixed output version of ADP1715 allows for connection of an external soft-start capacitor, which controls the output voltage ramp during startup. The ADP1716 features a track pin and is available with fixed output voltage options. All devices are controlled by an enable pin (EN). SOFT-START FUNCTION (ADP1715) For applications that require a controlled startup, the ADP1715 provides a programmable soft-start function. 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 1.2 μA current source charges this capacitor. The ADP1715 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 by TSS = VREF × (CSS/ISS) (1) where: TSS is the soft-start period. VREF is the 0.8 V reference voltage. CSS is the soft-start capacitance from SS to GND. ISS is the current sourced from SS (1.2 μA). When the ADP1715 is disabled (using EN), the soft-start capacitor is discharged to GND through an internal 100 Ω resistor. 2 1 EN OUT VIN = 5V VOUT = 3.3V COUT = 2.2µF CSS = 22nF ILOAD = 500mA TIME (4ms/DIV) Figure 27. OUT Ramp-Up with External Soft-Start Capacitor The ADP1715 adjustable version and the ADP1716 have no pins for soft start, so the function is switched to an internal soft- start capacitor. This sets the soft-start ramp-up period to approximately 24 μs. For the worst-case output voltage of 5 V, using the suggested 2.2 μF output capacitor, the resulting input inrush current is approximately 460 mA, which is less than the maximum 500 mA load current. 2 1 VIN =5V VOUT =1.6V COUT =2.2µF ILOAD = 10mA OUT EN TIME (20µs/DIV) Figure 28. OUT Ramp-Up with Internal Soft-Start |
Podobny numer części - ADP175ARMZ-0.9-R7 |
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Podobny opis - ADP175ARMZ-0.9-R7 |
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