MAX6870/MAX6871 Programmable Power Pin Function and Application Circuit

1 Features and Pin Functions MAX6870/MAX6871 pdf,MAX6870/MAX6871 datasheet 1.1 Features ●6 (MAX6870) or 4 (MAX6871) programmable input voltage detectors: 1 high-voltage input (+1.25 V to +7.625 V or +2.5 V to +13.2 V threshold); 1 bipolar voltage input (±1.25 V to ±7.625 V or ±2.5 V to ±15.25 V threshold); 4 (MAX6870) or 2 (MAX6871) positive voltage inputs (+0.5 V to +3.05 V or +1 V to +5.5 V threshold); ●4 general-purpose logic inputs; ●2 programmable watchdog timers; ● 8 (MAX6870) or 5 (MAX6871) programmable outputs: high active, low active, open drain, weak pull-up, push-pull, charge pump timing delay range of 25μs~1600ms; ● 10-bit internal ADC monitors input voltage, detector and two auxiliary inputs; ● Status control and manual reset control; ● Internal 1.25 V reference or external reference input; ● 4 KB internal user EEPROM; ● I2C/SMBus compatible serial programming/communication interface; ● ±1% threshold accuracy. 1.2 Pin Functions The MAX6870/MAX6871 uses a 32-pin thin QFN lead-free package. The functions of each pin are shown in Table 1.

2 Internal Structure and Working Principle
MAX6870 and MAX6871 have 6 inputs. As long as the voltage of any one of the inputs IN3-IN6 exceeds the minimum operating voltage of 2.7 V, or the voltage on IN1 exceeds 4 V, the circuit starts to work. There are two threshold levels for each of the 6 inputs. They can be set to both undervoltage detection states, or to one overvoltage detection state and one undervoltage detection state (i.e., window detector). The threshold level can be set through I2C and saved in the configuration EEPROM. The threshold level range of IN3-IN6 is 0.5 V~5.5 V. Depending on the selected threshold level, the step size can be 10mV or 20 mV. IN1 can detect voltages up to 13.2 V, so it is directly used to detect the system bus voltage of 12 V (or slightly lower). The
second input IN2 is used to detect another higher voltage or negative voltage.
The internal multiplexer of MAX6870 switches the 6 detector inputs and 2 auxiliary inputs to a 10-bit ADC with an accuracy of 1%. The ADC then digitizes the eight input voltages and writes them to the internal registers, which can be called up through the I2C interface. The two auxiliary inputs can be used to change the voltage values ​​of two additional inputs, such as the input voltage of a current sensing amplifier or the input voltage of a temperature sensor, to change the output state when the current or temperature is above a certain value.
The connection settings of the programmable logic array are changed according to the programming of the internal EEPROM. These six detector inputs and four common inputs (GPI) determine the state of the eight outputs. Similarly, by mixing inputs and outputs, some outputs can be controlled by other outputs of the device. The delay of each output can be set independently and stored in the EEPROM inside the circuit.
The outputs of the device can be set to internal pull-up open drain structure or external pull-up open drain structure, or it can be set to push-pull structure, and the output terminal can be directly connected to any supply voltage to be detected internally. All outputs can be set to either high level active or low level active. As mentioned above, the programmable logic array of the MAX6870 can be connected in many ways, and different combinations of inputs and outputs can be used to drive each output.
The MAX6870 also has a charge pump inside, allowing OUTl~OUT4 to be directly connected to an external N-channel switching device without the need for an additional power supply. The device also has two watchdog timers, and the watchdog timeout and start delay can be set by yourself. The watchdog generates a long start delay after the reset operation, allowing the system to initialize, upload memory data, and perform routine software testing during this period. The
manual reset input allows manual control of all outputs when testing the circuit. The MAX6870 also has configuration registers and configuration EEPROM. During the development phase, write the data to be modified into the configuration register, and the system configuration will change immediately. If you need to save these changes, you can write them to the configuration EEPROM later. If you need to re-load the data in the configuration EEPROM, you can restart the system by soft start or hard start. During the startup process, the system downloads the data from the EEPROM to the configuration register.

4 Application of MAX6870, MAX6871
The flexibility of MAX6870/MAX6871 lies in its programmable internal registers, and the register contents depend on the contents of EEPROM. After the system is powered on or soft-started, the configuration register information is downloaded from the EEPROM. Before powering on each input, the configuration signal should be written to the EEPROM through the I2C master device. The correct operation should be to quickly configure the registers using the write block protocol, then read the data to verify its correctness, and finally write the data to the EEPROM through the write word protocol. The register map address is shown in Figure 1. The 512-byte EEPROM from 8100h to 82ffh is available for users to save software or circuit board information.

The typical application circuit of MAX6870 is shown in Figure 2. The outputs monitor 12 V, 5 V, 3.3 V, 2.5 V, and 0.7 V respectively. Outputs 1 and 4 drive n-channel switching devices. The internal reference voltage is used. The auxiliary input is used as temperature detection. It communicates with the microprocessor through the I2C bus to realize the reading and writing of the internal EEPROM.

In order to reduce the impact of interference, a 0.1 μF capacitor is used to bypass high-frequency noise between the monitoring voltage and ground, and a 1 μF capacitor is used to bypass between ABP, DBP and ground. ABP and DBP are internally generated voltages and should not be used to power external circuits.