Understanding Max Current Specifications for VNH motor driver family

[joshlian]

Hi, 

I'm trying to spec a fully integrated H-bridge for driving a small motor taking up to 6A nominal, with spikes up to 12A (looking at the VNHD7012AY, VNHD7070AY, and the VNH7100BAS). There are a lot of numbers for current limitation on the ST datasheets that I've come across and I haven't been able to find an explanation for. How should I interpret all of these, and how are each of these numbers obtained?

Specifically, I'm looking at:

- Continuous maximum output current I_max

- High-side current limitation I_lim_h

- Shutdown low-side current I_sd_ls

- Output saturation current I_out_sat (under Current Sense)

[Peter BENSCH · Accepted solution]

Welcome @joshlian, to the community!

Let me try to explain these values:

• Continuous maximum output current Imax
  Sometimes also called Iout. Maximum output current, but is monitored internally and limited if necessary. As this current limitation depends on the chip load and temperature, no value is specified, only ‘Internal Limited’.
• High-side current limitation Ilimh
  The data sheet for the VNHD7012AY, for example, section 3.3, states that:
  ‘In case of short circuit, overload or during load power-up, the output current is clamped to a safety level, ILIMH, by operating the output power MOSFET in the active region.’
  In other words: the current is limited to the value that the resulting power loss does not lead to impermissible overheating. (In this state, the device looks completely unimpressed - but please do NOT touch it, it's become a little warm!)
• Shutdown low-side current Isd_ls
  This is the low-side current at which the driver is switched to shutdown. This also includes the time tsd_ls, which specifies the time for this.
• Output saturation current Iout_sat (under Current Sense)
  Iout_sat (output saturation current) is the guaranteed range of Isense vs Iout. The specified ratio (usually K0, K1, etc) is therefore guaranteed up to this output current.

Does it answer your question?
Regards
/Peter

[joshlian]

It does thank you very much! 

[hahaxiaodehouzi]

So how about 12A and 15A mean in the VNH7100BAS  datasheet?

[Peter BENSCH]

With a fully protected H-bridge driver, it is somewhat difficult to make a concrete statement regarding the current, which is why I have attempted to break it down a little above. Also consider the resulting power loss of up to P = (12A)²*120mohms = 17.28W, which in the case of the high-side driver (depending on the test environment with 32K/W or 40.7K/W) would result in a temperature difference of up to 703K during static operation. For this reason, this current of 12A can only flow when the driver is under very short-term load.