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ADP1706ARDZ-2.5-R7 数据表(PDF) 10 Page - Analog Devices |
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ADP1706ARDZ-2.5-R7 数据表(HTML) 10 Page - Analog Devices |
10 / 20 page ADP1706/ADP1707/ADP1708 Rev. 0 | Page 10 of 20 THEORY OF OPERATION The ADP1706/ADP1707/ADP1708 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 a small 4.7 μF ceramic output capacitor. All devices operate from a 2.5 V to 5.5 V input rail and provide up to 1 A of output current. Supply current in shutdown mode is typically 100 nA. SOFT START REFERENCE CURRENT LIMIT THERMAL PROTECT SHUTDOWN GND OUT SENSE ADJ/ TRK/ SS IN EN Figure 27. Internal Block Diagram Internally, the ADP1706/ADP1707/ADP1708 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 ADP1706/ADP1707 are available in 16 fixed output voltage options between 0.75 V and 3.3 V. The ADP1706 allows for connection of an external soft start capacitor, which controls the output voltage ramp during startup. The ADP1707 features a TRK pin that allows the output voltage to follow the voltage at this pin. The ADP1708 is available in an adjustable version with an output voltage that can be set to between 0.8 V and 5.0 V by an external voltage divider. All devices are controlled by an enable pin (EN). SOFT START FUNCTION (ADP1706) For applications that require a controlled startup, the ADP1706 provides a programmable soft start function. The programma- ble soft start is useful for reducing inrush current upon startup and for providing voltage sequencing. To implement a soft start, connect a small ceramic capacitor from SS to GND. Upon startup, a 1.2 μA current source charges this capacitor. The ADP1706 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 ADP1706 is disabled (using EN), the soft start capacitor is discharged to GND through an internal 100 Ω resistor. TIME (2ms/DIV) VIN = 5V VOUT = 3.3V COUT = 4.7μF CSS = 10nF ILOAD = 1A 1 2 EN OUT Figure 28. OUT Ramp-Up with External Soft Start Capacitor The ADP1707 and ADP1708 have no pins for soft start; therefore, the function is switched to an internal soft start capacitor, which sets the soft start ramp-up period to approxi- mately 48 μs. Note that the ramp-up period is the time it takes OUT to go from 0% to 90% of the nominal value and is different from the start-up time in Table 1, which is the time between the rising edge of EN to OUT being at 90% of the nominal value. For the worst-case output voltage of 5 V, using the suggested 4.7 μF output capacitor, the resulting input inrush current is approximately 490 mA, which is less than the maximum 1 A load current. TIME (20µs/DIV) VIN = 5V VOUT = 1.6V COUT = 4.7μF ILOAD = 10mA 1 2 EN OUT Figure 29. OUT Ramp-Up with Internal Soft Start |
类似零件编号 - ADP1706ARDZ-2.5-R7 |
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类似说明 - ADP1706ARDZ-2.5-R7 |
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