UCC28700-Q1_15 Datasheet, PDF (23/38 Pages) Texas Instruments – Constant-Voltage, Constant-Current Controller With Primary-Side Regulation

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UCC28700-Q1
SLUSC61 – JANUARY 2015
8.2.2.8 Standby Power Estimate
Assuming no-load standby power is a critical design parameter, determine estimated no-load power based on
target converter maximum switching frequency and output power rating.
The following equation estimates the stand-by power of the converter.
(27)
For a typical USB charger application, the bias power during no-load is approximately 2.5 mW. This is based on
25-V VDD and 100-µA bias current. The output preload resistor can be estimated by V_OCV and the difference in
the converter stand-by power and the bias power. The equation for output preload resistance accounts for bias
power estimated at 2.5 mW.
(28)
Typical start-up resistance values for R_STR range from 13 MΩ to 20 MΩ to achieve 1-s start-up time. The
capacitor bulk voltage for the loss estimation is the highest voltage for the stand-by power measurement,
typically 325 V_DC.
(29)
For the total stand-by power estimation add an estimated 2.5 mW for snubber loss to the start-up resistance and
converter stand-by power loss.
(30)
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