Part Number: BQ40Z80
Other Parts Discussed in Thread: BQ40Z50
Hello, I am hoping you can help correct some conflicting information I have seen in the BQ40Z80 datasheet and EVM documents regarding the VCC, PACK, and BAT pins.
Datasheet: http://www.ti.com/lit/ds/slusbv4a/slusbv4a.pdf
EVM: http://www.ti.com/lit/ug/sluubz5/sluubz5.pdf
VCC ---------------------------------------------------------------------------------------------------------------
First, some relevant information I have collected on the VCC pin:
- Page 5 of datasheet: Pin 24 (P = Power Connection) Secondary power supply input. Connect to the middle of protection FETs though the series resistor
- Page 1 of the datasheet shows 100 Ohm series resistor
- Page 8 of datasheet has the following note: "A series 50-Ω or larger resistor is needed when voltage is applied beyond 28 V".
- Page 29 of datasheet shows 510 Ohm series resistor as well as 2 100pF caps to VSS
- Page 34 of datasheet (Section 9.2.2.4.3) says: "the VCC input uses a diode to guard against input transients and prevents misoperation of the date driver during short-circuit events"
- Page 22 of EVM document shows 510 Ohm series resistor as well as 2 100pF caps to VSS
So my questions about VCC are:
- Do we only need a series resistor in 28V+ systems? IE are 6s and lower systems safe to wire straight to the middle of the protection FETS with just the caps to VSS and no series resistor?
- If we do need the series resistor, what is the recommended value? Why is 510 ohm used instead of 100 ohm?
- What is the note on page 34 referring to? Is it referring to a built in diode? Or is it saying there should be one on the PCB?
PACK ---------------------------------------------------------------------------------------------------------------
First some relevant information I have collected on the PACK pin:
- Page 5 of datasheet: Pin 25 (AI = Analog Input) Pack sense input pin. Connect through the series resistor to PACK+
- Page 1 of the datasheet shows a 10k series resistor
- Page 8 of datasheet has the following note: "A series 50-Ω or larger resistor is needed when voltage is applied beyond 28 V"
- Page 29 of datasheet shows 1.1k Ohm series resistor as well as C6 unmarked capacitor to VSS
- Page 34 of datasheet (Section 9.2.2.4.3) says: " The PACK input uses a 100-Ω resistor"
- Page 22 of EVM document shows 1.1k Ohm series resistor as well as C6 unmarked cap to VSS
- I understand C6 should be removed due to it slowing down the turn off time of the DSG FET from this post and others:
So my questions about PACK are:
- Do we only need a series resistor in 28V+ systems? IE are 6s and lower systems safe to wire straight to the PACK output with no series resistor?
- If we do need the series resistor, should it be 1.1k, or 10k ohms? What effect do those different resistances have?
- What is the note on page 34 referring to? Is it saying there is a built in 100 Ohm resistor, or we should include a 100 ohm resistor in our PCBs? (Instead of the 1.1/10k?)
BAT ---------------------------------------------------------------------------------------------------------------
Similar to VCC and Pack above, does BAT only need the series resistor for 7s (28V+) systems? Is it safe with just the diode and no series resistor for 6s and lower packs?
