SLUSEK7 September 2024 BQ25773
PRODUCTION DATA
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Output capacitor also should have enough ripple current rating to absorb output switching ripple current. The preferred ceramic capacitor is 35-V X7R or X5R for output capacitor. Minimum 7 pieces of 10-µF 0603 size capacitor is suggested to be placed as close as possible to Q3&Q4 half bridge (between Q4 drain and Q3 source terminal), when the power reaches 140 W/180 W 2 more 0603 MLCC are recommended at system output. Recommend to place minimum 2*10 µF after the charge current sense resistor for best stability. The overall minimum VSYS effective capacitance should be 50 μF including all the capacitance distributed along the VSYS output line like input capacitance on the next stage VRs referring to Table 8-7.
Ceramic capacitors show a dc-bias effect. This effect reduces the effective capacitance when a dc-bias voltage is applied across a ceramic capacitor, as on the output capacitor of a charger. The effect may lead to a significant capacitance drop, especially for high output voltages and small capacitor packages. See the manufacturer's data sheet about the derating performance with a dc bias voltage applied. It may be necessary to choose a higher voltage rating or nominal capacitance value in order to get the required capacitance value at the operating point.
OUTPUT CAPACITORS vs TOTAL INPUT POWER | 100 W | 140 W | 180 W |
---|---|---|---|
Minimum Effective Output Capacitance | 50 μF | 50 μF | 50 μF |
Minimum output capacitors at charger VSYS output terminal | 7*10 μF (0603 35 V MLCC) | 9*10 μF (0603 35 V MLCC) |
9*10 μF (0603 35 V MLCC) for VBUS<=28 V 9*10 μF (0805 50 V MLCC) for VBUS=36 V |
Minimum additional output capacitors along VSYS distribution line, input cap of next stage converter can also be counted. | 2*22 μF (2917 35 V POSCAP with <100 mΩ ESR for each) | 2*22 μF (2917 35 V POSCAP with <100 mΩ ESR for each) | 2*22 μF (2917 35 V POSCAP with <100 mΩ ESR for each) VBUS<=28 V 2*22 μF (2917 50 V POSCAP with <100 mΩ ESR for each) VBUS=36 V |
It is common under higher system power the total next stage (Vcore) input capacitance could be increased accordingly. These capacitance are also counted as charger system output capacitance. When these capacitance is too large it could also influence controller stability and maximum effective output capacitance are listed below for reference.
OUTPUT CAPACITORS vs TOTAL INPUT POWER | 100 W | 140 W | 180 W |
---|---|---|---|
Maximum Effective Output Capacitance | 500 μF | 800 μF | 800 μF |
Maximum output capacitors along VSYS distribution line, input cap of next stage converter can also be counted. | 5*100 μF (2917 35 V POSCAP with <100 mΩ ESR for each) | 8*100 μF (2917 35 V POSCAP with <100 mΩ ESR for each) |
8*100 μF (2917 35 V POSCAP with <100 mΩ ESR for each) VBUS<=28 V 8*100 μF (2917 50 V POSCAP with <100 mΩ ESR for each) VBUS=36 V |