• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 689 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BAT protect net

Matt Mitchell46
Intellectual 560 points
Other Parts Discussed in Thread: LM2903

Hi,

In HPA-603 there are some questionswith the protector.

  1. Although R32=R34, R35=750k < R33. These resistors connects to net driving U4:A sleep mode comparator. Yet there is 1M R29 connecting with 3.3V VREF complicating voltage comparison. What is expected U4:A pin 3 voltage of the design?
  2. BAT connects to through R10, R28, R31 to VREF, but as in first question the net is also connects to U4:A pin 3 via R29.

 

These are not simple voltage divider. How should we calculate them?

Also on the lower right sheet format fields (with TI brand, title, Date) in the schematic the EVM is labeled as HV 48V; J2 header labeled as VOUT 0-50.4V; J1 header Vin is labeled 36-57V. Yet in 1.1 Introduction the evm is said for 8-cell battery.

We are unclear on the exact battery count suitable for the EVM. Also as we change input and battery count within the range the resistor values above needs to be updated. Please give us guide lines on how to calculate the values (we are aware of the spreadsheet for calculating components for bq2461x, just this network is a bit complex and wish to get guidance).

 

 Matt

  • 0
    Intellectual 560 points
    Hello,

    Could someone explain the circuit?
  • 0
    TI__Expert 5565 points
    R28 and R29 are weak pull-up resistors to provide positive feedback so that there are no oscillations. Since the LM2903 are open collectors, we want the outputs of the op amp pulled high when the positive terminals at input are greater than the negative terminals. Since there is very little current going through R28 and R29 (they are tied to a 3.3V reference), the inputs to U4:A are driven by the resistor dividers (R33/R32 and R34/R35). C27 and C29 form low pass filters for noise immunity.

    The max DC input voltage is driven by the IC chosen for U6 (60V for HPA603), and the max DC battery voltage is driven by the IC chosen for U2.
  • 0 in reply to Smriti B
    Intellectual 560 points

    Hi,

    1. The sleep mode is then actually qualified VIN < 1.11*VBAT, from (866+232)/(750+232)? So this disables CHEGN when buck converter cycle goes above 90%? And this should be adjustable?
    2. The low BAT does make much sense as VBAT is compared against 3.3V VREF, and this only works for one cell? But for multiple cells it is also difficult to generate high voltage reference to compare with the full battery pack stack voltage.
    3. Can we compare VREF against a divided VBAT (like 1/2,1/3,1/4)? Even if the linear divider series uses large resistors there are small current leakage. But as LM2903 ds show, they are on the order of nA and small than battery self-discharge current. Can we use a divider? And should we do additional cell-balancing?
    4. For the part consisting of D5, U5A, C14 and R3, could they be viewed as a biasing and filtering network?

     

    Matt