IGBT｜Application

IGBT IPM: Protection Functions and Operation SequencesProtection Functions and Operation Sequences　－Summary－

2024.07.24

Protection Functions and Operation Sequences　－Summary－

In six sections of this series, we have explained the protection functions and operation sequences of the IGBT IPMs listed below, using as examples the BM6437x series of ROHM 3rd-generation IGBT IPMs. In addition, we have also shown how to calculate the values of external components. These articles should prove useful for design.

If these protection functions were to be provided through external circuits based on discrete (individual) IGBTs, considerably complex and sophisticated circuit design, numerous components and a large amount of circuit board area, as well as enormous amounts of labor for verification tests and evaluations. This cannot in fact be regarded as a pragmatic option. IPMs are provided with the basic functions required in applications, all in a compact package; this is an enormous advantage gained by using IPMs.

To summarize, below is a list of the BM6437x series products used in the examples, with links to the product data sheets. The application note on which the above articles are based, together with the URL for downloading same, are also provided.

Series Part Number Rating
Temperature Output function
Thermal Shutdown function		 BM64374S-VA 15A/600V
BM64375S-VA 20A/600V
BM64377S-VA 30A/600V
BM64378S-VA 35A/600V

■600V IGBT Gen.3 Intelligent Power Module (IPM) BM6437*S Series Application Note
https://fscdn.rohm.com/en/products/databook/applinote/discrete/ipm/gen3_igbt-ipm_bm64x_series_an-e.pdf

Below is a list of the key points explained in the articles of this section.

IGBT IPM: Protection Functions and Operation Sequences

Key Points of This Article

・The protection functions and operation sequences of IGBT IPMs are explained, using as examples the BM6437x series.

・In addition to understanding protection functions, the operation sequences, method of calculating the values of external components, and other matters must be understood.

Short Circuit Current Protection (SCP) Function of IGBT IPMs

Key Points of This Article

・The short circuit current protection (SCP) function is implemented by connecting an external shunt resistor to an IPM and feeding back the voltage appearing across the resistor to the CIN pin.

・The CIN pin requires an RC filter to prevent malfunctions.

・Short circuit current protection operates only for the lower arm.

・When the short circuit current protection is actuated, operation must immediately be halted to avoid an anomalous state.

・The shunt resistor value and the RC filter time constant are set to close to recommended values that are based on equations provided, and are ultimately finalized by confirming operation of actual equipment.

Control Power Supply Undervoltage Lockout（UVLO) Function of IGBT IPMs

Key Points of This Article

・The control power supply undervoltage lockout (UVLO) circuit is activated if the control power supply voltage falls to a predetermined voltage or lower.

・This function is provided for both the HVIC (High Side Gate Driver) and the LVIC (Low Side Gate Driver), but an FO signal (error output) is output only when the LVIC UVLO is activated.

Thermal shutdown（TSD）Function of IGBT IPMs

Key Points of This Article

・The BM6437x series is provided with a thermal shutdown (TSD) circuit that monitors the LVIC (low side gate driver) temperature; if the Tj of an LVIC chip rises above a specific value, the thermal shutdown circuit is actuated, IGBTs for all phases of the lower arm are turned off, and an FO signal is output.

・If TSD is actuated, the Tj of an IGBT has exceeded the absolute maximum rating of 150°C; hence the IPM must be replaced.

・The value Tj being monitored by this function is a property of an LVIC chip. Because rapid temperature increases of an IGBT chip cannot be followed, the TSD cannot effectively function in the case of a sharp increase in Tj, and so proper caution is required.

Analog Temperature Output（VOT）of IGBT IPMs

Key Points of This Article

・The LVIC section temperature is converted into an analog voltage and output as the VOT output; the purpose of this function is mainly temperature monitoring in order to provide protection should the temperature rise higher than anticipated.

・For high-precision monitoring of the temperature of an IGBT IPM, a thermistor is generally used. However, the BM6437x series of devices achieve precision on a par with that of thermistors, and so in some cases can be used in place of a thermistor.

・The VOT output indicates the temperature of the LVIC section, and cannot track sudden increases in the temperatures of IGBT or FWD chips.

・Hence it is recommended that the VOT function be used for purposes and in methods similar to when a thermistor is mounted on a heat sink and used, that is, for limiting output in such cases as temperature increases due to cooling fan malfunctions or continuous overloading.

・In cases where a low-voltage microcontroller is used to process the VOT output, a clamp circuit should be added so that the VOT voltage does not exceed the microcontroller power supply voltage.

・When a design is required in which the VOT voltage can exceed the microcontroller power supply voltage, a method of resistive dividing of the VOT output can be used.

Fault Output（FO）of IGBT IPMs

Key Points of This Article

・The FO pin is a fault output function pin. It provides notification to an external device of the actuation of an onboard protection function, and causes lower arm IGBTs for all phases to be turned off in order to protect the IPM itself.

・The FO signal output time duration differs depending on the type of protection actuated. Hence the type of protection that has been actuated can be discriminated. This function was first added to these products.

・As a FO pin input function, by connecting an RC circuit to the FO pin and adjusting the time constant, the off interval for the lower arm IGBTs for all phases can be extended.

・Thus, when the FO output is input to an MCU via an isolating element, if the propagation delay time due to the isolating element is longer than the shortest L level time of the FO output, the FO output time can be extended according to the delay time.

Control inputs （HINU, HINV, HINW, LINU, LINV, LINW）of IGBT IPMs

Key Points of This Article

・The control pins HINU, HINV, HINW are control inputs for high side IGBTs, and the control pins LINU, LINV, LINW are control inputs for low side IGBTs, for the U, V, and W phases respectively.

・When an RC filter is inserted to avoid noise and prevent malfunctions, internal pulldown resistors must be considered, and the RC values must be set so as to satisfy the control pin input specifications.

・The control input pins HINU, HINV, HINW are provided with a proprietary ROHM function to indicate different resistance values according to the part number when there is no power at HVCC. Hence even after board mounting, the part number can be identified, so that erroneous mounting etc. can be checked.

・The resistance for part number identification is measured using a specific measurement method.

【Download Documents】 Basics of IGBTs

IGBTs are one of the typical power devices and are used in a wide range of applications including motor drives. This handbook provides a basic understanding of IGBTs, including their application scope and application picture based on their features, their structure and principle of operation, and how they compare with and use other power devices.

Protection Functions and Operation Sequences　－Summary－
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