LPV7215

SNOSAI6I – SEPTEMBER 2005 – REVISED APRIL 2013

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APPLICATION INFORMATION

Low supply current and fast propagation delay distinguish the LPV7215Q from other low power comparators.

INPUT STAGE

The LPV7215Q has rail-to-rail input common mode voltage range. It can operate at any differential input voltage

within this limit as long as the differential voltage is greater than zero. A differential input of zero volts may result

in oscillation.

The differential input stage of the comparator is a pair of PMOS and NMOS transistors, therefore, no current

flows into the device. The input bias current measured is the leakage current in the MOS transistors and input

protection diodes. This low bias current allows the comparator to interface with a variety of circuitry and devices

with minimal concern about matching the input resistances.

The input to the comparator is protected from excessive voltage by internal ESD diodes connected to both supply

rails. This protects the circuit from both ESD events, as well as signals that significantly exceed the supply

voltages. When this occurs the ESD protection diodes will become forward biased and will draw current into

these structures, resulting in no input current to the terminals of the comparator. Until this occurs, there is

essentially no input current to the diodes. As a result, placing a large resistor in series with an input that may be

exposed to large voltages, will limit the input current but have no other noticeable effect.

OUTPUT STAGE

The LPV7215Q has a MOS push-pull rail-to-rail output stage. The push-pull transistor configuration of the output

keeps the total system power consumption to a minimum. The only current consumed by the LPV7215Q is the

less than 1 µA supply current and the current going directly into the load. No power is wasted through the pull-up

resistor when the output is low. The output stage is specifically designed with deadtime between the time when

one transistor is turned off and the other is turned on (break-before-make) in order to minimize shoot through

currents. The internal logic controls the break-before-make timing of the output transistors. The break-before-

make delay varies with temperature and power condition.

OUTPUT CURRENT

Even though the LPV7215Q uses less than 1 µA supply current, the outputs are able to drive very large currents.

The LPV7215Q can source up to 17 mA and can sink up to 19 mA, when operated at 5V supply. This large

current handling capability allows driving heavy loads directly.

RESPONSE TIME

Depending upon the amount of overdrive, the propagation delay will be typically 6 to 30 µs. The curves showing

propagation delay vs. overdrive in the TYPICAL PERFORMANCE CHARACTERISTICS section shows the delay

time when the input is preset with 100 mV across the inputs and then is driven the other way by 10 mV to 500

mV.

The output signal can show a step during switching depending on the load. A fast RC time constant due to both

small capacitive and resistive loads will show a significant step in the output signal. A slow RC time constant due

to either a large resistive or capacitive load will have a clipped corner on the output signal. The step is observed

more prominently during a falling transition from high to low.

The plot in Figure 32 shows the output for single 5V supply with a 100 k

Ω resistor. The step is at 1.3V.

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