General Description

The Maxim’s MAX8211 and MAX8212 are CMOS micropower voltage detectors that warn microprocessors (μPs) of power failures. Each contains a comparator, a 1.15V bandgap reference, and an open-drain n-channel output driver. Two external resistors are used in conjunction with the internal reference to set the trip voltage to the desired level. A hysteresis output is also included, allowing the user to apply positive feedback for noise-free output switching.
The MAX8211 provides a 7mA current-limited output sink whenever the voltage applied to the threshold pin is less than the 1.15V internal reference. In the MAX8212, a voltage greater than 1.15V at the threshold pin turns the output stage on (no current limit).
The CMOS MAX8211/MAX8212 are plug-in replacements for the bipolar ICL8211/ICL8212 in applications where the maximum supply voltage is less than 16.5V. They offer several performance advantages, including reduced supply current, a more tightly controlled bandgap reference, and more available current from the hysteresis output.

 

Applications

● μP Voltage Monitoring
● Undervoltage Detection
● Overvoltage Detection
● Battery-Backup Switching
● Power-Supply Fault Monitoring
● Low-Battery Detection

 

Features

● μP Power-Fail Warning
● Improved 2nd Source for ICL8211/ICL8212
● Low-Power CMOS Design
● 5μA Quiescent Current
● On-Board Hysteresis Output
● ±40mV Threshold Accuracy (±3.5%)
● 2.0V to 16.5V Supply-Voltage Range
● Define Output Current Limit (MAX8211)
● High Output Current Capability (MAX8212)

 

Compatibility with ICL8211/ICL8212

The CMOS MAX8211/MAX8212 are plug-in replacements for the bipolar ICL8211/ICL8212 in most applications. The use of CMOS technology has several advantages. The quiescent supply current is much less than in the bipolar parts. Higher-value resistors can also be used in the networks that set up the trip voltage, since the comparator input (THRESH pin) is a low-leakage MOSFET transistor. This further reduces system current drain. The tolerance of the internal reference has also been significantly improved, allowing for more precise voltage detection without the use of potentiometers.
The available current from the HYST output has been increased from 21μA to 10mA, making the hysteresis feature easier to use. The disparity between the HYST output and the voltage required at THRESH to switch the OUT pin has also been reduced in the MAX8211 from 8mV to 0.1mV to eliminate output “chatter” or oscillation.
Most voltage detection circuits operate with supplies of 15V or less; in these applications, the MAX8211/MAX8212 will replace ICL8211/ICL8212s with the performance advantages described above. However, note that the CMOS parts have an absolute maximum supply-voltage rating of 18V, and should never be used in applications where this rating could be exceeded.
Exercise caution when replacing ICL8211/ICL8212s in closed-loop applications such as programmable zeners. Although neither the ICL8211/ICL8212 nor the MAX8211/MAX8212 are internally compensated, the CMOS parts have higher gain and may not be stable for the external compensation-capacitor values used in lower-gain ICL8211/ICL8212 circuits.

 

Electrical Characteristics

The maximum output current of the MAX8211 is limited by design to 30mA under any operating condition. The output voltage may be sustained at any voltage up to +16.5V as long as the maximum power dissipation of the device is not exceeded.
The maximum output current of the MAX8212 is not defined, and systems using the MAX8212 must therefore ensure that the output current does not exceed 50mA and that the maximum power dissipation of the device is not exceeded.

 

Basic Voltage Detectors

Since the comparator inputs are very low-leakage MOSFET transistors, the MAX8211/MAX8212 can use much higher resistors values in the attenuator network than can the bipolar ICL8211/ICL8212.

 

Voltage Detectors with Hysteresis

To ensure noise-free output switching, hysteresis is frequently used in voltage detectors. For both the MAX8211 and MAX8212 the HYST output is on for threshold voltages greater than 1.15V.

 

Low-Voltage Detector for Logic Supply

The selected resistor values ensure that false undervoltage alarms will not be generated, even with worst-case threshold trip values and resistor tolerances.