EVAL-IH-R5IPB-A-V1 Evaluation board
User Guide
Experimental results
the other hand, when the INN voltage changes from low to high, the IGBT is turned off, with a typical propagation
delay of 2.2 µs. The larger propagation delay at turn-off is due to an increased filtering time to avoid spurious
turn-off events. As a consequence, the turn-off of the current in normal operation occurs with a delay, with
respect to the INN transition, from low to high. During normal operation, the high value of the voltage at pin INN
is typically equal to 2.5 V. Such a value corresponds to ‘normal’ condition of the IEWS20R5135IPB.
5.1.3
Operation in current limitation
Depending on the chosen setting of the maximum current, a current limitation can already be reached during
normal operation mode, especially at high power levels. When this happens, the 100 Hz envelope of the collector
current changes as shown in Figure 12a. In the single switching event, a strong current limitation can be identified
if the IGBT current switches off before the INN voltage changes from low to high, as shown in Figure 12b.The
operation in current limitation is still considered a ‘normal’ condition for the IEWS20R5135IPB and therefore no
change in the value of the off-state INN voltage is produced in this case. Nevertheless, it is important to mention
that when current limitation occurs during the operation, the input current of the overall system changes its
shape according to the envelope shown in Figure 12a. As a consequence, the total harmonic distortion (THD) of
the input current increases. For this reason, the current limitation features should be mainly used for protection,
and the limitation threshold should be set in a way that the current is not limited during the normal operation of
the system.
5.1.4
Operation in case of overtemperature warning and overtemperature
shutdown conditions
In case the temperature of the device exceeds 75°C, the status of the IEWS20R5135IPB changes to
‘overtemperature warning’ mode. In this condition, the high value of the INN voltage changes from 2.5 V to a
typical value of 4 V, as shown in Figure 13a. The MCU continuosly monitors the average value of the INN pin and
can therefore detect the status and react consequently. In particular, in ‘overtemperature warning’ mode:
•
The LED OTW on the board turns on.
•
The speed of the fan is increased.
As soon as the temperature of the device drops again below 75°C, the OTW LED switches off, and the speed of the
fan is again reduced. In case of significant power dissipation (e.g. strong hard switching turn-on at lower power),
the temperature of the IGBT can increase even more, and eventually reach the value of 150°C. When this happens,
the IEWS20R5135IPB enters ‘overtemperature shutdown’ mode. In this condition, the device stops operating and
keeps the INN voltage constantly at a value that is <0.5 V, as shown in Figure 13b. In this condition, the led OTS
(red) is turned on. The ‘overtemperature shutdown’ mode ceases as soon as the temperature of the IGBT drops
below 75°C; the OTS LED switches off, and the system restarts automatically, performing the vessel detection.
The fan speed is also reduced when the device restarts in ‘normal’ status. The circuit for detecting the INN status
is shown in Figure 13c whilst its operation is explained as follows:
•
The INN signal is split and fed into a peak-detector circuit consisted of the Schottky diode D3 and the
capacitor C10. The voltage across the capacitance is sensed by an A/D converter of the MCU. By means of
this circuit, the IEWS20R5135IPB status read can be performed in a relaxed time without the need to be
synchronized with PWM driving signal.
•
When the IEWS20R5135IPB enters overtemperature warning mode, the INN voltage increases to 4 V during
the off-state; the capacitance is therefore charged up to 3.8 V (considering the voltage drop across D3)
during roughly 100 ns because the charging current is mainly limited by the maximum output current of the
INN pin. Resistor R22 is instead used for allowing the discharge of the capacitance C10 when the
IEWS20R5135IPB is in shutdown mode, since it can’t be discharged by the INN current because of the diode
D3.
Application Note
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V 1.1
2019-11-25