LMP7300

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SNOSAT7F – AUGUST 2007 – REVISED MARCH 2013

APPLICATION INFORMATION

GENERAL DESCRIPTION

The LMP7300 is a unique combination of micropower and precision. The open collector comparator has low

offset, high CMRR, high PSRR, programmable hysteresis and microamp supply current. The precision 2.048V

reference provides a DAC or ADC with an accurate binary divisible voltage. The comparator and reference

combination forms an ideal single IC solution for low power sensor or portable applications.

VOLTAGE REFERENCE

The reference output voltage is a band gap derived 2.048V that is trimmed to achieve typically 0.2% accuracy

over the full operating temperature range of

−40°C to 125°C. The trim procedure employs a curvature correction

algorithm to compensate for the base emitter thermal nonlinearity inherent in band gap design topologies. The

reference accuracy and the set resistor tolerance determine the magnitude and precision of the programmable

hysteresis. In situations where reference noise filtering is required a 5 µF capacitor in series with a 190

Ω resistor

to ground are recommended.

COMPARATOR

Output Stage

The comparator employs an open collector output stage that can switch microamp loads for micropower

precision threshold detection to applications requiring activating a solenoid, a lamp, or an LED. The wired-OR

type output easily interfaces to TTL, CMOS, or multiple outputs, as in a window comparator application, over a

range of 0.5V to 12V. The output is capable of driving greater than 10 mA output current and yet maintaining a

saturation voltage below 0.4V over temperature. The supply current increases linearly when driving heavy loads

so a pullup resistor of 100 k

Ω or greater is recommended for micropower applications.

Fault Detection Rate

The user’s choice of a pullup resistor and capacitive load determines the minimum response time and the event

detection rate. By optimizing overdrive, the pullup resistor and capactive load fault update rates of 200 kHz to

250 kHz or greater can be achieved.

HYSTERESIS

False triggering on noise coupled into the signal path is a common problem for comparator based threshold

detectors. One of the most effective solutions is to add hysteresis. Hysteresis is a circuit signal path

characteristic where an amplitude delay is introduced to the normal input. Positive hysteresis forces the signal to

pass the normal switch point before the output makes a low to high transition while negative hysteresis does the

opposite. This is a memory effect. The comparator behaves differently based on which direction the signal is

going.

The LM7300 has been designed with a unique way of introducing hysteresis. The set points are completely

independent of each other, the power supply, and the input or output conditions. The HYSTP pin sets positive

hysteresis and the HYSTN pin sets the negative hysteresis in a simple way using two resistors. The pins can be

tied together for the same hysteresis or tied to separate voltage taps for asymmetric hysteresis, or tied to the

reference for no hysteresis. When the precision reference is used to drive the voltage tap resistor divider precise,

stable threshold levels can be obtained. The maximum recommended hysteresis is about 130 mV. This places

negative input to keep the output off when the signal is above and on when it goes below this level. For a

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