Time (µs)

Noise Margin

Noise Margin

GND

VDD

Pulse

Count

Signal

17

LMT01-SP

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Figure 26. Pulse Count Signal Amplitude Variation

8.2.1.2.1

Setting the MSP430 Threshold and Hysteresis

The comparator hysteresis determines the noise level that the signal can support without causing the comparator

to trip falsely and resulting in an inaccurate pulse count. The comparator hysteresis is set by the precision of the

MSP430 and what thresholds it is capable of. For this case, as the input signal transitions high, the comparator

threshold is dropped by 77 mV. If the noise on the signal is kept below this level as it transitions, the comparator

will not trip falsely. In addition, the MSP430 has a digital filter on the COMP_B output that can be used to further

filter output transitions that occur too quickly.

8.2.1.3 Application Curves

Amplitude = 200 mV/div

Δy at cursors = 500 mV

Time Base = 10 µs/div

Δx at cursors = 11.7 µs

Figure 27. MSP430 COMP_B Input Signal No Capacitance

Load

Amplitude = 200 mV/div

Δy at cursors = 484 mV

Time Base = 10 µs/div

Δx at cursors = 11.7 µs

Figure 28. MSP430 COMP_B Input Signal 100-pF

Capacitance Load

8.3 System Examples

The LMT01-SP device can be configured in a number of ways. Transistor level shifting can be used so that the

output pulse of the device can be read with a GPIO (see Figure 29). Multiple LMT01-SP devices can be

controlled with GPIOs and read by a single comparator input as shown in Figure 30. Lastly, the LMT01-SP

device can be configured to have a common ground with a high side signal (see Figure 31).