General Questions:
Q: What types of DDR does TPS51200 support?
A: TPS51200 supports DDR, DDR2, DDR3, DDR3L, LP DDR3 (Low power DDR3) and DDR4.
Q: How to calculate the power dissipation on TPS51200.
A: TPS51200 is a linear regulate, the VLDOIN current is equal to VO current. The power dissipation on TPS51200 device can be calculated as: (VLDOIN-VO)*Iout.
Take DDR4 application as example. VDDQ voltage is 1.2V, VTT is 0.6V, the VTT current is 1A, so the power dissipation on TPS51200 is (1.2V-0.6V)*1A=0.6W.
Q: TPS51200 is a 3A LDO regulator, can I use TPS51200 to support continuous 3A DC current?
A: We don’t suggest using TPS51200 to support continuous 3A DC load for long time. With large power dissipation, the device will be heated up and VO voltage deviation may out of DDR spec. Refer to load regulation curves on datasheet page 7 for a safe DC load current.
Q: What is REFOUT tolerance?
A: The REFOUT tolerance is +/-12mV with +/-1mA current. This spec is available on datasheet spec table.
Q: Can EN pin voltage be higher than VIN voltage?
A: No, the EN pin voltage should be equal or lower than VIN voltage at any time. This information is available on datasheet section 9 (power supply recommendation).
Schematic Related Questions:
Q: How to check if my schematic is correct?
A: We suggest to follow the reference designs provided on datasheet section 8 (application and implementation). Below are key things to follow.
- Use minimum 20uF capacitors for VLDOIN and minimum 30uF capacitors for VO. There is no maximum limitation for VLDOIN and VO capacitor values.
- Use a capacitor between 1uF and 4.7uF for VIN pin.
- A 0.1uF capacitor is suggested for REFOUT pin. If REFOUT (VREF) capacitor is needed at DDR side, keep the total capacitance below 1uF.
Q: Should a RC filter be added between VOSNS pin and output?
A: If VOSNS trace in layout is very long in layout, it is suggested to add a RC filter (or placeholder) between VOSNS pin and output to filter potential noised coupled to the trace. If VOSNS trace in layout is short and away from noise, RC filter is not needed.
Q: Can REFOUT pin be open if REFOUT signal will not be used?
A: No, REFOUT pin can not be open. With REFOUT pin is open, the VO voltage may not be stable. A 0.1uF capacitor is suggested for REFOUT pin.
Q: Is there an internal pull-up or pull-down resistor on EN pin?
A: There is no internal pull-up or pull-down resistor on EN pin. EN pin can not be floating, it must be pulled down externally to turn off the part or pulled high externally to turn on the part.
Q: How to deal with PGOOD pin if the PGOOD signal will not be used?
A: PGOOD pin is an open drain pin and it is not recommended to leave it open. Connecting to VIN via pull-up resistor is suggested. Connecting to ground is allowed.
Q: Should I strictly follow the start-up and shut down timing in datasheet figure 19 and 20?
A: The timings in datasheet figure 19 and 20 are suggested. In figure 19, it is also allowed to turn on VLDOIN earlier than VIN during power on, and turn off VIN earlier than VLDOIN during power off. Keep in mind that EN pin voltage should not exceed VIN voltage at any time.
Layout Related Questions:
Q: Is layout guideline available on datasheet?
A: Yes, the layout guideline is available on datasheet section 10. Please follow the guideline for better performance and to avoid any unexpected issue.
Q: How to connect TPS51200 thermal pad, AGND pin and PGND pin in layout?
A: The thermal pad is used to dissipate heat on TPS51200. It is suggested to connect thermal pad to power ground copper plane via multiple vias. Connect AGND pin and PGND pin to the thermal pad directly.
Q: Where should VTT capacitors be located in layout?
A: At least one 10uF capacitor needs to be placed close to TPS51200 VO pin. Other VTT capacitors can be placed at either TPS51200 side or DIMM side.