SLVAEG2A August   2019  – May 2021 LM10011 , TPS53515 , TPS53915 , TPS543B20 , TPS543C20A , TPS54424 , TPS544B20 , TPS546D24 , TPS546D24A , TPS54824 , TPS548A20 , TPS549A20 , TPS549B22 , TPS549D22 , TPS54A24

 

  1.   Trademarks
  2. 1Suggested DC/DC Converters
  3. 2Adaptive Voltage Scaling
  4. 3High Efficiency and Thermal Performance
  5. 4Current Sharing
  6. 5Voltage Regulation Accuracy
  7. 6Conclusion
  8. 7Resources
  9. 8Revision History

5 Voltage Regulation Accuracy

As semiconductor process technology advances, processors require tighter voltage accuracy and lower operating voltages. The processor data sheet specifies the voltage tolerance as either a percentage or value in mV, which includes DC, AC and ripple variations over the entire operating temperature range. Designers must also consider the tolerance of the resistor divider used by the DC/DC converter, the routing and trace losses of the circuit board, and variations in the application. These include input voltage variations, temperature swings, and fast changes in the load.

It is important to check the feedback voltage accuracy of the DC/DC converter in the data sheet rather than the front page. Table 5-1 shows the regulated feedback voltage specification of the TPS543820, which is a 4 to 18-V, 8-A converter, and shows that the reference accuracy is ±2.5mV, or ±0.5%, over input voltage and temperature variations. The total output voltage accuracy is improved by choosing tighter tolerance resistors. If more headroom is needed, designers can choose 0.1% or 0.5% resistors (2), even though they may cost a little bit more. The additional headroom will allow the total ±3% or ±5% output voltage variation during load transients to be met with less bulk and bypass capacitance.

Table 5-1 TPS543820 Feedback Voltage Regulation
ParameterTest ConditionMin.Typ.Max.Unit
Feedback Voltage

VFB

TJ = -40°C to 150°C, VIN = 4 V to 18 V497.5500502.5mV

Often, layout constraints, connectors, and board density requirements affect the total output voltage accuracy. A remote-sense feature of a DC/DC converter compensates for voltage drops from long-trace lines to accommodate processors that need high-accuracy output voltage. This feature is especially useful when routing higher currents, as the voltage drop can be a large portion of the overall DC error. Figure 5-1 shows the TPS543B20 using the remote-sense feature with voltage feedback resistors used to program the output voltage. Figure 5-2 shows the TPS543B20 using the remote-sense feature, without voltage feedback resistors, when the VSEL pin selects the reference voltage. The RSP and RSN pins are extremely high-impedance input terminals of a true-differential, remote-sense amplifier.

GUID-67D51B0B-4EB7-48F9-8570-3A881266239B-low.gif Figure 5-1 Remote Sense Without Feedback Resistors
GUID-00C9839F-5541-4188-AB32-DB218C56D59C-low.gif Figure 5-2 Remote Sense With Feedback Resistors