IGBT｜Application
IGBT IPM: Protection Functions and Operation Sequences Fault Output（FO）of IGBT IPMs
2024.07.10
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.
This article concerns the fifth topic, “Fault Output (FO)”, in the explanations of “Protection Functions and Operation Sequence”.
- Short circuit current protection（SCP）
- Control power supply undervoltage lockout（UVLO）
- Thermal shutdown（TSD）
- Analog temperature output（VOT）
- Fault output （FO）
- Control inputs （HINU, HINV, HINW, LINU, LINV, LINW）
Fault Output（FO）
The FO pin is used for the fault output function, and provides notification to external devices of actuation of the equipped protection functions; for the protection of the IPM itself, it causes the IGBTs for all phases in the lower arm to be turned off.
As explained previously, this series of IGBT IPMs is equipped with SCP (short circuit current protection), UVLO (undervoltage lockout), and TSD as LVIC (low side IGBT gate driver) protection functions. As indicated in the explanations of the protection functions, when a protection function is actuated, the FO pin transitions from H level to L level.
Below is a block diagram that includes an example of connections with an MCU. The pin surrounded by red lines is the FO pin. The FO pin is configured as an IO pin; the output is an open-drain output, and the input is a Schmitt trigger buffer input. The FO pin input level is monitored, and while the input is at L level, the IGBTs for all phases in the lower arm are turned off. By connecting the FO pin to an external capacitor and resistor, the lower arm off time can be extended.
Moreover, the UVLO function is also provided in the HVIC (upper arm IGBT gate driver) section as well, but as indicated in the block diagram, it is unrelated to the FO output. Hence even when the HVIC UVLO is actuated, there is no change in the FO output voltage level. For details, please refer to “Control Power Supply Undervoltage Lockout (UVLO) Function“.
Below, the FO pin output functions and input functions are explained.
FO Pin Output Functions
As stated above, when an LVIC protection function is actuated, the FO pin voltage level transitions from H to L, providing notification of actuation of a protection function. This FO output is used to notify an MCU of the actuation of an IGBT IPM protection function, enabling proper countermeasures and event recording.
The FO output signal output time (L interval) differs depending on the type of protection actuated, as indicated by the table and timing chart below. This function is first provided in this series of devices, and by measuring the time duration of the signal, it is possible to discriminate the protection function that has been actuated. As a result, not only the occurrence of faults (protection function actuation), but the protection function that has been actuated can be identified and recorded. When the time over which a protection function is actuated is longer than the output time setting for the signal, L level is maintained throughout the interval.
The FO pin is an open-drain output, and so pull-up is necessary. The FO pin absolute maximum ratings are -0.5 V to VCC+0.5 V for an applied voltage VFO (FO to GND pins), and 1 mA for the sink current IFO. Hence the pull-up voltage and resistor must be determined within these ranges. IFO can be estimated from the pull-up power supply voltage divided by the pull-up resistor value. In addition to the absolute maximum ratings, the FO pin output specifications as well as the input specifications (VIL, VIH, etc.) of the connected MCU must also be considered. Below are shown the FO output specifications and the FO pin V-I characteristic.
For example, when pulling up to 5 V, a 10 kΩ pull-up resistor is recommended. In this case, the sink current is roughly half of the maximum rating, leaving an abundant margin, and the H level, which is affected by the leak current IFOLEAK, is also 5 V – 10 kΩ×10 µA = 4.9 V, which is sufficient as the logic level for a 5 V system.
FO Pin Input Functions
Because internally the FO pin is connected to an input to turn off the lower arm IGBTs for all phases, it has functions as an input. This can be utilized by connecting the FO pin to a resistor R2 and capacitor C2 and adjusting the charging time of C2 to extend the off interval of the lower arm IGBTs for all phases.
When the FO output is input to the MCU via a photocoupler or other isolating element, if the propagation delay time of the isolating element during output is longer than the shortest L level time (45 µs, for SCP) of the FO output, this feature can be used to extend the FO output time according to the signal propagation delay caused by the photocoupler (see the diagram and timing chart below).
The time constant of the connected RC circuit is adjusted referring to the FO pin input specifications. The threshold values and hysteresis given in the table below must be considered.
【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.
IGBT
Basic
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About IGBTs
- Applications Using IGBTs
- IGBT Structure
- Principles of Operation of IGBTs
- Range of Application of IGBTs
- IGBT Features: Comparisons with MOSFETs and Bipolar Transistors
- Selective Use of Power Devices in Motor Applications
- Short Circuit Withstand Time (SCWT) of IGBTs
- IGBTs Incorporating Fast Recovery Diodes (FRDs)
- About IGBT IPMs （Intelligent Power Modules）
Application
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IGBT IPM: Protection Functions and Operation Sequences
- Short Circuit Current Protection (SCP) Function of IGBT IPMs
- Control Power Supply Undervoltage Lockout（UVLO) Function of IGBT IPMs
- Thermal shutdown（TSD） Function of IGBT IPMs
- Analog Temperature Output（VOT）of IGBT IPMs
- Fault Output（FO）of IGBT IPMs
- Control inputs （HINU, HINV, HINW, LINU, LINV, LINW）of IGBT IPMs
- Protection Functions and Operation Sequences －Summary－
Product Information