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AP7173-FNG-13 Datasheet(PDF) 11 Page - Diodes Incorporated |
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AP7173-FNG-13 Datasheet(HTML) 11 Page - Diodes Incorporated |
11 / 15 page AP7173 1.5A LOW DROPOUT LINEAR REGULATOR WITH PROGRAMMABLE SOFT-START AP7173 Rev. 4 11 of 15 MARCH 2008 www.diodes.com © Diodes Incorporated Application Note BIAS VOLTAGE VVCC DROPOUT VOLTAGE The AP7173 is a low VIN, low dropout regulator that uses an NMOS pass FET. The VCC pin must be connected to a DC bias supply VVCC for the internal control circuitry and the gate drive of the pass FET to function properly and to obtain low dropout. The VVCC needs to be equal to or higher than the VIN and in the range of 2.7V-5.5V. Figure 27 illustrates the typical application circuit for the AP7173. EN PG VCC IN OUT FB SS GND AP7173 R1 R2 R3 C1 C2 C3 VOUT VIN +5V CSS Figure 27. Typical Application Circuit for AP7173 ADJUSTABLE OUTPUT VOLTAGE With an external voltage divider, the AP7173 can provide output voltage from 0.8V to 3.3V. R1 and R2 can be calculated for any output voltage using the following equation, where VREF=0.8 is the AP7173’s internal reference voltage. Refer to Table 1 for resistor combinations for commonly used output voltages. For maximum voltage accuracy, R2 should be ≤ 5kΩ. VOUT = VREF x (1 + R1/R2) INPUT VIN AND BIAS VVCC CAPACITORS It is important to keep the IN and VCC pins clear of large ripples, glitches and other noises by connecting capacitors to the IN and VCC pins. The required capacitance on these pins is strongly dependent on source and wiring impedance of the supplies. To provide good decoupling for the input power supply VIN, it is recommended that a ceramic capacitor with capacitance of at least 1 μF is connected between the IN and GND pins at a location as close to them as possible. High quality, low ESR capacitors should be used for better performance. It is critical to provide good decoupling to the VCC pin for the AP7173’s internal control circuitry to function properly. The minimum recommended capacitance for the VVCC is 1μF when the VVCC and VIN are separate supplies. If the VIN and VVCC are connected to the same supply, the recommended minimum capacitance for VVCC is 4.7μF. Again good quality, low ESR capacitors should be used for optimum performance. OUTPUT CAPACITOR The output capacitor affects the stability and transient response of the LDO. The AP7173 is designed to be stable for all types of output capacitors ≥ 2.2μF, single or multiple in parallel. Using high-quality, low ESR capacitors and placing them close to the OUT and GND pins can improve perfomance. The very low dropout makes the AP7173 well suited for high-current, low VIN/low VOUT applications. To achieve the specified low-dropout performance for such applications, the VCC pin should be connected to a separate supply of at least 3.25V higher than VOUT. Figure 28 shows an application circuit where VVCC is 5V and VOUT is 1.2V. Vref VCC IN FB AP7173 OUT R1 R2 C2 (1.2V) IOUT VVCC (5V) + _ (1.5A) VOUT VIN (1.5V) Figure 28. Typical Application Circuit for AP7173 Using Separate VCC and IN Rails For applications where low dropout is not required or a separate VVCC supply is not available, the IN and VCC pins can be tied together. In this situation, a voltage difference of at least 1.7V between the VVCC and VOUT has to be maintained for the VVCC to provide enough gate drive to the pass FET. Therefore, the VOUT needs to be 1.7V or more below VIN, as shown in Figure 29. Vref VCC IN FB AP7173 OUT R1 R2 C2 VOUT (1.2V) VIN (3.0V) + _ IOUT (1.5A) Figure 29. Typical Application Circuit for AP7173 Without an Auxiliary VCC Rail PROGRAMMABLE SOFT-START The AP7173 features a voltage-controlled soft-start that is programmable with an external capacitor (CSS). The AP7173 achieves a monotonic soft-start by tracking the voltage ramp of the external soft-start capacitor until the ramp voltage reaches the internal reference voltage. The relationship between the soft-start time and the soft-start charging current (ISS), soft-start capacitance (CSS), and the internal reference voltage (VREF) is tSS = (VREF x CSS) / ISS Refer to Table 2 for suggested soft-start capacitor values. |
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Similar Description - AP7173-FNG-13 |
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