First, fault phenomenon
MAX660MX starts and works perfectly when the ambient temperature is greater than 20℃;When the ambient temperature is between 0 and 20℃, there will be a power-on delay start, which works normally after starting, and the delay time is about 3~15 seconds.When the ambient temperature is lower than 0℃, the delay time of power-on starts becomes longer, and about 20% of power-on does not start.The input voltage of MAX660MX is DC5V. The input voltage drops to DC1.7V when the chip is not started or the input voltage drops to DC1.7V in the process of delayed start, which results in the meter cannot be started normally.
Second, circuit design
The circuit unit is to provide +5V and -5V DC power to the instrument control board CPU and the detection circuit.
Third, Circuit test results
Disconnect the power supply loop and connect the ammeter and fuse in series. The fuse specification (200mA) will be blown when there is a delay start.The replacement of MAX660ESA can start normally at low temperature -40℃, and will not blow the 200mA specification fuse.
Fourth. The MAX660MX batch specifications