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ADP3191 Datasheet(PDF) 24 Page - Analog Devices |
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ADP3191 Datasheet(HTML) 24 Page - Analog Devices |
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24 / 28 page  ADP3191 Rev. 0 | Page 24 of 28 Because the ADP3191/ADP3191A turn off all of the phases (switches inductors to ground), there is no ripple voltage present during load release. Thus, headroom does not need to be added for ripple, allowing the load release, VTRANREL, to be larger than VTRAN1 by the amount of ripple and still meet specifications. If VTRAN1 and VTRANREL are less than the desired final droop, this implies that capacitors can be removed. When removing capaci- tors, also check the output ripple voltage to make sure it is still within specifications. REPLACING THE ADP3181 WITH THE ADP3191 Figure 17 shows the changes needed when replacing an existing ADP3181 design with the ADP3191. VIN 12V VIN RTN 370nH 18A VID4 VID3 VID2 VID1 VID0 VID5 FBRTN FB COMP PWRGD EN DELAY RT RAMPADJ VCC PWM1 PWM2 PWM3 PWM4 SW1 SW2 SW3 SW4 GND CSCOMP CSSUM CSREF ILIMIT 3 1 4 5 26 25 24 2 28 27 6 10 14 7 8 9 19 22 21 20 23 11 12 13 15 18 17 16 U1 ADP3191 1µF 100µF 2700µF/16V/3.3 A × 2 SANYO MV-WX SERIES + + 1N4148 + 240Ω 1206 1/4W ADP3191 357kΩ 1% R 1kΩ C 0.1µF Figure 17. Replacing the ADP3181 with the ADP3191 CHOOSING BETWEEN THE ADP3191 AND THE ADP3191A For existing designs using the ADP3181, the ADP3191 is the recommended replacement. For new designs, where 5 V system voltage is available, it is recommended to use the ADP3191A, as configured in Figure 18. For correct power sequencing, ensure that the 12 V rail is present before the 5 V VIN is applied to the ADP3191A. VIN 12V VIN RTN 370nH 18A VID4 VID3 VID2 VID1 VID0 VID5 FBRTN FB COMP PWRGD EN DELAY RT RAMPADJ VCC PWM1 PWM2 PWM3 PWM4 SW1 SW2 SW3 SW4 GND CSCOMP CSSUM CSREF ILIMIT 3 1 4 5 26 25 24 2 28 27 6 10 14 7 8 9 19 22 21 20 23 11 12 13 15 18 17 16 U1 ADP3191A 1µF 100µF 2700µF/16V/3.3 A × 2 SANYO MV-WX SERIES + + + 10Ω 0603 1/8W VIN 5V 357kΩ 1% R 1kΩ C 0.1µF Figure 18. Replacing the ADP3181 with the ADP3191A RAMPADJ FILTER It is recommended that a filter be placed on the RAMPADJ line. In designs using the ADP3181, the RAMPADJ and the VCC were typically both connected to the 12 V input supply. Therefore, the RAMPADJ could use the decoupled VCC line as its input. On the ADP3191, the VCC is 5 V, but the RAMPADJ still needs to be connected to the 12 V input supply. Therefore, the filter is needed to remove noise from the 12 V input supply. A 1 kΩ resistor and 0.1 μF cap are recommended for this filter. |
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