DescriptionThe AP331A is a precision voltage comparators with an offset voltage specification as low as 8.0 mV max for comparator which were designed specifically to operate from a single power supply over a wide range of voltages. Operation from split power supplies is also possible and the low power supply current drain is independent of the magnitude of the power supply voltage. The comparator also have a unique characteristic in that the input common-mode voltage range includes ground, even though operated from a single power supply voltage.
Application areas include limit comparators, simple analog to digital converters; pulse, square wave and time delay generators; wide range VCO; MOS clock timers; multivibrators and high voltage digital logic gates. The AP331A is designed to directly interface with TTL and CMOS. When operated from both plus and minus power supplies, the AP331A will directly interface with MOS logic where their low power drain is a distinct advantage over standard comparators.
- Wide supply
Voltage range: 2.0V to 36V
Single or dual supplies: ±1.0V to ±18V
- Very low supply current drain (0.4mA) – independent of supply voltage
- Low input biasing current: 150nA
- Low input offset current: ±70nA
- Low input offset voltage: ±4mV
- Input common-mode voltage range includes ground
- Differential input voltage range equal to the power supply voltage
- Low output saturation voltage: 250mV at 4mA
- Output voltage compatible with TTL, DTL, ECL, MOS and CMOS logic systems
- SOT25 and SOT25R: Available in “Green” Molding Compound (No Br, Sb)
- Lead Free Finish/ RoHS Compliant
- High precision comparators
- Reduced VOS drift over temperature
- Eliminates need for dual supplies
- Allows sensing near ground
- Compatible with all forms of logic
- Power drain suitable for battery operation
The AP331A is high gain, wide bandwidth devices, like most comparators, can easily oscillate if the output lead is inadvertently allowed to capacitively couple to the inputs via stray capacitance. This shows up only during the output voltage transition intervals as the comparator change states. Power supply bypassing is not required to solve this problem. Standard PC board layout is helpful as it reduces stray input-output coupling. Reducing the input resistors to < 10kΩ reduces the feedback signal levels and finally, adding even a small amount (1.0 to 10 mV) of positive feedback (hysteresis) causes such a rapid transition that oscillations due to stray feedback are not possible. Simply socketing the IC and attaching resistors to the pins will cause input-output oscillations during the small transition intervals unless hysteresis is used. If the input signal is a pulse waveform, with relatively fast rise and fall times, hysteresis is not required. All input pins of any unused comparators should be tied to the negative supply.
The bias network of the AP331A establishes a drain current independent of the magnitude of the power supply voltage over the range of from 2.0 VDC to 30 VDC. It is usually unnecessary to use a bypass capacitor across the power supply line. The differential input voltage may be larger than V+ without damaging the device (Note 10). Protection should be provided to prevent the input voltages from going negative more than -0.3 VDC (at 25°C). An input clamp diode can be used as shown in the applications section.
The output of the AP331A is the uncommitted collector of a grounded-emitter NPN output transistor. Many collectors can be tied together to provide an output OR’ing function. An output pull-up resistor can be connected to any available power supply voltage within the permitted supply voltage range and there is no restriction on this voltage due to the magnitude of the voltage applied to the V+ terminal of the AP331A package. The output can also be used as a simple SPST switch to ground (when a pull-up resistor is not used). The amount of current the output device can sink is limited by the drive available (which is independent of V+) and the β of this device. When the maximum current limit is reached (approximately 16mA), the output transistor will come out of saturation and the output voltage will rise very rapidly. The output saturation voltage is limited by the approximately 60Ω rSAT of the output transistor. The low offset voltage of the output transistor (1.0 mV) allows the output to clamp essentially to ground level for small load currents.