Through datasheet, we know that this is a single channel drive chip with current detection function. It is a high-end drive, i.e. the upper arm MOS tube drive, which requires an external bootstrap diode. Ir2121 is a low-end drive, i.e. the lower arm MOS tube drive, which does not require an external diode. Ir2125 and ir2121 are respectively configured to drive and control the upper axle arm and the lower axle arm. Because they have the same driving current up to 1a, while ir2127 has only 200mA. The matched lower axle arm drive chip is not found, so I use ir2127 as both the upper axle arm drive and the lower axle arm drive. Its typical application is shown in the figure below; Ir2128 is similar to ir2127, except that the direction of the output pulse is opposite to that of the input pulse.

It is non isolated and is generally used in low-voltage driving occasions. If it needs to be used in high-voltage driving, it must add an isolation circuit, although its VB and vs withstand voltage is as high as 625v The model ir2127 is used for motor drive. The voltage between VCC and com is generally between 12V and 20V. At first, the design voltage is about 12.5V. After passing through the bootstrap diode

The voltage to the VB terminal is less than vs+12v, which causes the chip to always detect the hardware overcurrent signal, so it cannot drive the MOS transistor normally. After the VCC voltage is increased to 13.5V, the drive chip is normal. The CS pin is used to detect the overcurrent signal. The principle is that when the input in pin is high, the output ho pin is high when the chip works normally, and the MOS tube behind it is driven to be on. When the current ID flowing through the MOS tube is larger, the uds=id*rd is larger. The voltage obtained by subtracting the voltage drop of the diode and passing through two resistance divider is the voltage of the CS pin. As long as the resistance value of the divider is adjusted, the maximum ID can be limited. If the voltage of the CS pin is greater than 0.25V, Then the maximum delay is 360ns to close the ho pin output, and the maximum delay is 510ns to set the fault pin. Note that this pin is an open drain output, and the external pull-up resistor needs to be connected. It is a high level in normal conditions, and the output is a low level after overcurrent alarm. You can see the internal block diagram of the driver chip as follows.

Then we can look at the chip logic sequence diagram. From the sequence diagram, we can know the difference between ir2127 and ir2128. When the ir2128 input is low, the output is high, and when the ir2127 input is high, the output is also high. Then we can look at the CS pin. When it is normal, it is normal, and the fault pin is high. Once overcurrent is detected, it is high, and the fault pin immediately becomes low. At the same time, the ho pin output is turned off, Protect the rear devices from being burnt out. When the chip works normally, the generation delay from input signal trigger to output signal is very short, and the maximum startup delay is ton+tr=200+130=330ns; The maximum shutdown delay is toff+tf=200+65=265ns It is worth noting that the chip starts the blanking time waveform, which is very important. When the chip is normally started, the CS pin will be pulled higher, and the fault pin will also be lowered at the same time. The maximum starting blanking time is tbl=950ns. MCU needs to avoid this period of time when detecting the fault pin, otherwise it will lead to system misoperation.

Start blanking time waveform

The floating channel can be used to drive an n-channel power MOSFET or IGBT in the high side or low side

Configuration which operates up to 600 v.). If it is used to design the lower bridge arm, since the lower bridge arm does not need a bootstrap diode, when designing the drive circuit, the other components are consistent with the upper bridge arm, but the bootstrap diode is replaced by a 0 ohm resistor. The circuit principle design is as follows.

After the actual circuit test, the improved circuit is stable and has been successfully applied in the product.

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