Electronic – Help understanding purpose of this schottky diode and resistors in MAXIM DS2777 typical configuration

circuit analysisintegrated-circuit

I am looking to design a pack-side gauge/protection IC and so am looking at the MAXIM DS2777 IC (datasheet).

In their datasheet page 10 is the typical application circuit. I lack understanding with parts of the circuit and was hoping for someone to provide an explanation:

  1. What is the purpose of the Schottky Diode on pin PLS?
  2. What is the purposes of the 1k resistor on the PLS, as a resistor for a internal voltage divider?
  3. What is the purpose of the 1k resistor on Vin2 and Vin1? I don't see what they do at all, the input resistance of these pins are 15Mohm so the 1k here won't really achieve anything (negligible impact to current flow and also very low voltage drop)
  4. Whats the purpose of the 150ohm resistor on Vdd? That doesn't seem to be necessary either..

Thanks in advance!

Typical application circuit

Best Answer

  • What is the purpose of the Schottky Diode on pin PLS?

    • V_PLS has absolute maximum rating of -0.3V to 18V. The shottky is there to protect the pin. Without it, the PLS input may see too negative of an input under some circumstances, for example if connector is not plugged in all the way so that PK- is disconnected, and both FETs are open, and there are 5V pull-ups on SDA and SCL.

  • What is the purposes of the 1k resistor on the PLS, as a resistor for a internal voltage divider?

    • This limits current when the batter is very discharged: "When a charger is detected and VPLS > VIN2, the DS2775–DS2778 provide a current-limited recovery charge path (IRC) from PLS to VDD to gently charge severely depleted cells.". Plus protection (see below).

  • What is the purpose of the 1k resistor on Vin2 and Vin1?

    • Battery protection. If chip fails or goes to latch-up mode for some reason such that Vin is connected to ground/Vcc, the whole thing will not catch fire. It also protects from shorted pins, for example due to tin whiskers.

  • Whats the purpose of the 150ohm resistor on Vdd?

    • Same reason. If pass transistor in internal regulator fails, the whole thing will not catch fire.
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