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bq51013 Power Dissipation
Please teach the calculating formula of the Power Dissipation.
bq51013 Power Dissipation is Rectifying circuit loss+ LDO loss?
Even an electricity loss of LDO exceeds a permission loss at 400mA.
To improve efficiency and provide good load transient response voltage into the LDO (V-RECT) will change with output current. This will result in a change in efficiency as load changes, improving as load increases.
Also below 225mA the synchronous rectifier is operating in a half synchronous mode, but improving as load increases.
Figure 5 in data sheet will give the overall efficiency ( both LDO and Rectifier) as a function of output power.
Figure 4 in the data sheet provides rectifier efficiency as a function of output power.
Below is a breakdown of LDO voltage drop as a function of output current.
LDO input voltage (V-Rect) / LDO Voltage drop:
Less than 100mA – 7.08V / 2.08V
100mA to 200mA – 6.28V / 1.28V
200mA to 400mA – 5.53V / 0.53V
Greater than 400mA – 5.11V / 0.11V
In the case of an output current of 500A at 5V or 2.5W.
Rectifier efficiency is about 95% for a loss of 125mW (5% * 2.5W), see figure 4
LDO at that current will have a 0.11V drop for a loss of 55mW (0.11V * 0.5A).
Total loss is 180mW, this indicates an overall efficiency of about 93%.
Figure 5 indicates a total efficiency of about 93% at 2.5W
Bill Johns, Applications Engineer
bqTESLA Wireless Power Products
Texas Instruments Inc
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