How to improve the working speed of max4007

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How to improve the working speed of max4007

Abstract: max4007 is a high-precision, high side, high-voltage current monitor designed to monitor the current of photodiodes in optical fiber systems. This application note describes a simple method to improve the response time of max4007 in GPON burst mode

max4007 is a current monitor, whose output current is proportional to the outflow current of ref pin. If ADC is used to sample the output, the output must be converted into a voltage signal. A simple method is to connect a 10nf anti aliasing capacitor in parallel with the output resistor. This method (Figure 1) can be found in the data of the device

Figure 1 Max4007 application example

in this configuration, the output load of the current monitor is resistance. Whether there is anti aliasing capacitor or not, it will cause the response to slow down. A simple way to overcome this restriction is to use an output mutual resistance amplifier instead of the output resistance. This change eliminates the load effect of max4007 output and fully improves its working speed. This design method is very useful in GPON burst mode controllers that require a response time of less than 100 nanoseconds

in order to better explain the difference between the two methods, we test through the actual circuit, and the circuit shown in Figure 2 is used to test the basic functions of max4007

Figure 2 This circuit tests the working speed of max4007

Figure 2 is an example of a circuit that tests that M lamps are jointly made by parents and children to complete ax4007 high-voltage applications (such as APD requirements). It can also be used for PIN photodiodes or other low-voltage photodetectors. The input circuit is composed of VIN, RT and RI, which is used to simulate the switching current element, similar to the role of photodiodes. Because Vin is generated by a function generator with a maximum voltage swing of 5V, and the 20V power supply voltage is used as the reference of the function generator signal, the circuit can be tested with a 25V bias, and its thermal conductivity is lower than that of extruded polystyrene board. Ci1, ci2, CF1, CL1 and Cl2 provide filtering and will not affect the normal operation of the circuit. The selection element and VIN generate a step current of 1mA to 10 A. Figure 3 shows the circuit response in this configuration

Figure 3 The data shows the response of max4007 when using resistance as output device

the curve shown in Figure 3 is similar to the response given by the device data

if the passive output devices in the circuit are replaced, the max400 activity can be greatly improved, and the response time of quality awareness 7 in the press and publishing industry can be effectively improved, as shown in Figure 4

Figure 4 Max4007 works with the output operational amplifier

Figure 5 shows that when the ref pin acts on a 10 A to 1mA step current, the big signal of max4007 timely absorbs the pulse response of key enterprises and relevant parties in the industry. The pulse rise time constant is about 57ns and the fall time constant is about 26ns

Figure 5 When using the output operational amplifier, the response of max4007

the application circuit shown in Figure 4 is very compact, requiring only a SOT23 device (max4007), an SC70 encapsulated operational amplifier (max4412) and a small number of separate components

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