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ADP2380AREZ-R7 数据表(PDF) 18 Page - Analog Devices |
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ADP2380AREZ-R7 数据表(HTML) 18 Page - Analog Devices |
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18 / 28 page ![]() ADP2380 Data Sheet Rev. 0 | Page 18 of 28 PROGRAMMING INPUT VOLTAGE UVLO The internal voltage divider from PVIN to GND sets the default start/stop values of the input voltage to achieve undervoltage lockout (UVLO) performance. The default rising/falling threshold of PVIN and UVLO are listed in Table 9. For a more accurate, externally adjustable UVLO, these default values can be replaced by using an external voltage divider, as shown in Figure 32. Lower values of the external resistors are recommended to obtain a high accuracy UVLO threshold because the values of the internal 320 kΩ and 125 kΩ resistors may vary by as much as 20%. Table 9. Default Rising/Falling Voltage Threshold Pin Rising Threshold (V) Falling Threshold (V) PVIN 4.28 3.92 UVLO 1.2 1.1 PVIN VIN R1 R2 UVLO 320kΩ 125kΩ ADP2380 Figure 32. External Programmable UVLO A 1 kΩ resistor is an appropriate choice for R2. Use the following equation to obtain the value of R1 for a chosen input voltage rising threshold: ( ) V 2 . 1 V 2 . 1 _ R2 V R1 RISING IN × − = where VIN_RISING is the rising threshold of VIN. The falling threshold of VIN can be determined by V 1 . 1 V 1 . 1 _ + × = R2 R1 V FALLING IN where VIN_FALLING is the falling threshold of VIN. COMPENSATION DESIGN The ADP2380 uses a peak current mode control architecture for excellent load and line transient response. For peak current mode control, the power stage can be simplified as a voltage controlled current source, supplying current to the output capacitor and load resistor. It consists of one domain pole and one zero contributed by the output capacitor ESR. The control to output transfer function is given by P Z VI COMP OUT VD f s f s R A s V s V s G × × + × × + × × = = π π 2 1 2 1 ) ( ) ( ) ( OUT ESR Z C R f × × × = π 2 1 OUT ESR P C R R f × + × × = ) ( 2 1 π where: AVI = 8.7 A/V. R is the load resistance. COUT is the output capacitance. RESR is the equivalent series resistance of the output capacitor. The external voltage loop is compensated by a transconductance amplifier with a simple external RC network placed either between COMP and GND or between COMP and FB, as shown in Figure 33 and Figure 34, respectively. Compensation Network Between COMP and GND Figure 33 shows the simplified peak current mode control, small signal circuit with a compensation network placed between COMP and GND. RESR R + – g m RC CCP COUT CC RTOP RBOT – + AVI VOUT VCOMP VOUT ADP2380 GND COMP FB Figure 33. Small Signal Circuit with Compensation Network Between COMP and GND The RC and CC compensation components contribute a zero, and the optional CCP and RC contribute an optional pole. The closed-loop transfer function is as follows: ) ( 1 1 ) ( s G s C C C C R s s C R C C g R R R s T VD CP C CP C C C C CP C m TOP BOT BOT V × × + × × + × × × + × + − × + = |
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