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DRV8835: About RDS(ON) vs. temperature at power dissipation

Tao_2199
Genius 5770 points
Part Number: DRV8835
Other Parts Discussed in Thread: DRV8833

Hello,

 

Regarding to RDS(ON) on DRV8835, my customer is asking some question.

They will design power dissipation with RDS(ON).

 

Regarding to RDS(ON) on DRV8835, my customer is asking some question.

They will refer section 10.3.1 Power Dissipation (datasheet pagea6) and

will design it with RDS(ON).

 

(Question)

(1) About temperature in Figure 4 on datasheet.(RDS(ON) (High-Side + Low-Side))

Is it meaning the junction temperature?

If so, can they use real measured temperature of device package (top side) instead of junction temperature?

Or can they use 1ohm as total estimation RDS(ON)?

 


 

(2)Their conditions : motor current =0.4A , Vcc=7V, Vcm=11V, TA=35°C

In case of RDS(ON)(Hihg+Low) estimate to 1ohm,

Power = 0.4A^2 x 1ohm = 0.16W

TJ = TA + (PD × RθJA) = 35°C + (0.16 W × 47°C/W) = 42.5°C

 

Our understanding is correct?

 

Regards,

Tao2199

  • 0
    Genius 5770 points
    Hello,

    Additional question,
    They will design Vcc=2.8V VCM=7V.
    Do you have a RDS(ON) data at above condition?
    Or Is there other method for estimation RDS(ON)?
    (For example, it estimates 1 ohm as total.)

    Regards,
    Tao2199
  • 0 in reply to Tao_2199
    TI__Guru** 114905 points
    Hi Tao_2199,

    (1) About temperature in Figure 4 on datasheet.(RDS(ON) (High-Side + Low-Side))
    Is it meaning the junction temperature?
    If so, can they use real measured temperature of device package (top side) instead of junction temperature?
    Or can they use 1ohm as total estimation RDS(ON)?

    This is junction temperature. Using 1 Ohm is acceptable in the use case.

    (2)Their conditions : motor current =0.4A , Vcc=7V, Vcm=11V, TA=35°C
    In case of RDS(ON)(Hihg+Low) estimate to 1ohm,
    Power = 0.4A^2 x 1ohm = 0.16W
    TJ = TA + (PD × RθJA) = 35°C + (0.16 W × 47°C/W) = 42.5°C

    Your understanding is correct. Please note the 47C/W is based on a JEDEC standard board and may be different based on the board design.

    There is a thermal widget for the DRV8833 that is close to the DRV8835. It can also be used for rough calculations. The link is here: www.ti.com/.../midlevel.tsp