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Can DRV8833 work with TXB0106?
DRV8833 has four input control pins: AIN1, AIN2, BIN1, BIN2,
nSLEEP. According to ELECTRICAL
CHARACTERISTICS, AIN1, AIN2, BIN1, BIN2 require VIH > 2, and nSLEEP
require VIH > 2.5.
If a processor uses 1.8V I/O
voltage, then a voltage level translator is required. I found that TXB0106 which
has six pins on both A and B side might be an ideal choice.
However, TXB0106 is an auto-sensing translator which has
different architecture as traditional unidirectional translators. The primary
concern here is its weak output. It employs one-shot modules to translate
rising and falling edges with relatively strong current, but after a
short-period the one-shot modules would be shut off, and the high-or-low logic
level will be maintained weakly via 4K resistors
connected in parallel.
If DRV8833 detects rising/falling edges
as what is flip-flop does, then since at the
rising/falling edges one-shot module turns on T1 and T3 and there is very small
impedance, the current would then be strong enough to drive DRV8833 to trigger
the change. And also since flip-flops registers change only at edges, this
means the weak input through 4K resistor after one-shot has turned T1/T3 off
would have no impact on DRV8833, just as if there is without these 4K resistors.
However, if DRV8833 requires constant
input current to maintain input status, it might turns out that TXB0106 is not
a good idea after a short period the current would be limited by 4K resistors.
4K resistor limit the current to the extent that DRV8833 would fail to work?
From DRV8833's ELECTRICAL CHARACTERISTICS,
page 6, the input current is on the order of µA.
Assuming 3.3V VIH, this implies that there are equivalent resistor
of MΩ resistance internally at input pins to limit the current. Since MΩ >> 4K, it seems that this 4K resistor would
have little effect on the IIH AND IIL, and this suggests
that DRV8833 could work with TXB0106.
this reasoning correct? Could TI employees in this motor forum confirm with
people in the logic level translator group?
The DRV8833 has internal pull-down resistors on the inputs to nSLEEP and the other logic pins. On nSLEEP, the pull-down is ~500k which calculates back to 6.6uA of leakage (3.3V/500k). For the other logic pins, the resistance is nominally 150k, but can be as low as 100k which gives you the maximum value of 33uA.
In either case, the datasheet of the TXB0106 suggests a minimum pull-down impedance of 50kohm. Therefore, we are at least 2x this on the DRV8833 under the worst case process variation in terms of pull-down resistance.
Motor Drive Application Manager
I am still trying to understand this.
But a quick question: is this safe/OK to use TXB0106 with DRV8833?
I am no TXB0106 expert, but from the datasheet it looks to be OK for use with the DRV8833 based on the note of >50k impedance on the outputs.
I studied TXB0106 principle and agree with your answer.
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