LM9044: Short to Battery and short to gnd protection for INV and NON-INV inputs

Hi Sunney,

Please note that we have no measured information for the LMP9044 STG and STB conditions you are asking about and we have to rely on the very limited datasheet information.

Case 1: If during STB = 28V event occurs (inputs are clamped to 14V), the output will saturate to Vcc (i.e. 5V) as gain is 4.5. Please confirm

The LMP9044 input stage is a difference amplifier. If the +Vin input as seen in the first page circuit is forced to +14 V, the output of the input stage should follow and pull up against its maximum positive output swing. The G = +4.5 V output stage is a non-inverting amplifier so it too should swing to its maximum positive output which will be close to Vcc.

Case 2: If STG occurs, means input will be at 0 potential, output will be approx = 4.5 * some offset = ~200mV to 300mV  which happens to be the case in Lean mixture (or RICH)  also.

Since the common-mode range extends below 0 V the LMP9044 should be operating in its linear input operating range with 0 V applied.

The LMP9044 datasheet doesn't really indicate what level of voltage offset the input difference stage might have, but because of the wide difference between the two input bias currents the effective offset might be high. However, with an STG and an overall gain of +4.5 V/V the output looks like it would be indicating that the input is running in the lean condition.

The LMP9044 is a simple design so there aren't many options for detecting an STG. Possibly a way to detect an STG event is to characterize the output voltage range when the input is at 0 V (STG), and then when it is at the minimum lean (~100 mV) voltage level. If they are clearly different and distinguishable that may be a way to detect it. That would certainly require a lot of characterization.

Regards, Thomas

Precision Amplifiers Applications Engineering

Hi Thomas,

Thank you for replying.

1. Yes, you are right about STG, there will be very fine difference b/w LEAN and STG.

2. However I doubt STB detection as well because in datasheet for Rdiff & Ibias pos, the max value are 3 Meg ohm & 650nA respectively, which are used to calculate default output voltage when there is open connection at Vin+.

The output in this case Vout_OPEN_default_max = 4.5 * 650nA * 3 Meg = 8.775V [this may lead to confusion in STB detection as max output will be close to 5V in this case too]

where as nominal value is = 4.5*1.2 Meg * 380nA = 2.052V

Regards,

Sunney