ZHCSTD7A December 2021 – November 2023 BQ79631-Q1
PRODUCTION DATA
Related Pins | Components | Value | Description |
---|---|---|---|
VPWR | Filter resistor | 30 Ω | Single-ended RC filter, recommended values must be used for hot-plug performance. |
Filter capacitor | 10 nF/20 V |
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NPNB | NPN (Q1) | Collector–emitter breakdown voltage 15 V to 20 V, Power rating ≥ 1 W Gain > 80 at the expected load current Current handling >100 mA |
The external NPN is used to form a pre-regulation circuit to
provide a 6-V (typical) input to the LDOIN pin. The voltage rating of the NPN can be optimized by the following equation: NPN voltage rating = Max VPWR – Min VLDOIN + Margin Where: Max VPWR = supply of the device Min VLDOIN = minimum spec of the VLDOIN parameter Margin = system transient voltage + design margin per application requirement |
Resistor on external NPN collector (RNPN) | Various based on module voltage | The resistor has a couple of purposes: (a) For an RC filter for the NPN pre-regulation circuit (b) Share the thermal dissipation with the NPN |
|
Capacitor on external NPN collector | 0.22 nF/100 V Can use lower voltage rating based on module size |
The capacitor forms the RC filter for the NPN
pre-regulation circuit The capacitor rating is based on the peak voltage spike seen on the module. For a smaller module size, <100-V rated capacitor can be used. System designer selects the optimized voltage-rated capacitor per their system tolerance and requirements. |
To reduce the power rating needed for the external NPN (Q1), the system designer can put power resistors on the NPN collector to create IR drop from the VPWR. Figure 9-10 shows the current paths to power the BQ79631-Q1 device.
To ensure there is sufficient headroom to maintain a 6-V (typical) regulated voltage on the LDOIN pin, the system designer ensures VCollector has ≥ 8 V at any time with the assumption of about 2-V drop across the NPN.
Hence, maximum allowable RNPN value = ((Min VPWR) – (VCollector)) / (Max peak current)
Where:
VCollector: 8 V with the assumption of about 2-V drop across NPN
Max peak current: highest operation current, which is the active current with all functions turned on. Note that different communication isolation components (for example, capacitor isolation versus transformer, or the type of transformer) contribute different loading to the total power consumption.