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TPS61088: Frequency and current limit

Weinan Ji
Intellectual 265 points
Part Number: TPS61088

Hi

I have two questions for using this device

1. Since the switching frequency is programmable, what will be the optimal frequency provided that I am using this device to power brushless dc motors (continuous current 1A, peak current 3A)?

2. The switch peak current limit is also programmable, but what is the purpose of doing this? And since I am boosting up from 3.7V battery to 9V to drive the motor, which limit would you suggest to set?

Thank you!

  • 0
    TI__Mastermind 40080 points

    Hi,

    You input/output condition is just what the EVM board defined. So you can choose fsw=500k-600kHz for a balance of efficiency and size.

    In your application , please let Rlim=100k. 

    The current limit pin for for some application like 3.7Vin, 9V/1A/500mA . Because in those application, the output power is low, the customer   will choose a small inductor instead of a big inductor. So limit the peak inductor current (also the peak switch current) can protect the inductors from destroyed.

  • 0 in reply to Helen chen
    Intellectual 265 points
    Hi Helen,

    Thank for your reply.

    The output from the booster is to supply the brushless dc motor driver, and the motor speed is controlled by PWM with 100kHz frequency. Does 500k-600kHz a bit small for this?

    Could I ask about the trade-offs when people tune the switching frequency higher than lower?

    Thanks.

    Best regards
    Weinan
  • 0 in reply to Weinan Ji
    TI__Mastermind 40080 points

    500-600kHZ operation frequency is already several times higher than the Motor frequency, so its OK. Please choose the fsw no higher than 1MHz considering the conversion efficiency. 500- 750kHz is a good choice. When use fsw=750kHz, you can choose a 1uH inductor, which is easy to choose. if fsw=600k, L=1.2uH as what is the EVM board shows.