I am trying to select an IR receiver for a remote controlled unit, from this table. Here is one example, but all of the parts exhibit the same seemingly contradictory specification.
Having a look inside TSOP75438's datasheet, we immediately notice the promising:
IR Receiver Modules for Remote Control Systems
Recommended for NEC code: yes
Cool. However, moments later, there is:
For bursts greater than: 70 cycles
a minimum gap time in the data stream is needed of: 4 x burst length
Hmmm. Here is a NEC example message:
With carrier frequency 38kHz, the initial 9ms pulse consists of 342 impulses, much more than 70, and the pause of 4.5 ms is much less than 4*9 ms.
Here is some more data, from an application note:
Note that 70 cycles @ 38kHz equals approximately 1.8 ms.
I understand that the above restriction is posed by the Automatic Gain Control unit, in order to distinguish between data and long monotonous sequences of IR noise form e.g. fluorescent lamp or LED backlight. However, my understanding MUST be flawed, as 1) the part is actually recommended for this protocol and 2) I just tested it with a scope and it works perfectly.
So what am I missing?