TMC603 DATA SHEET (V. 1.06 / 26. Mar. 2009)
The slope time tSLOPE can be calculated as follows:
14
Whereas QMILLER is the charge the power transistor needs for the switching event, and IGATE is the
driver current setting of the TMC603.
Taking into account, that a slow switching event means high power dissipation during switching, and,
on the other side a fast switching event can cause EMV problems, the desired slope will be in some
ratio to the switching (chopper) frequency of the system. The chopper frequency is typically slightly
outside the audible range, i.e. 18 kHz to 40 kHz. The lower limit for the slope is dictated by the reverse
recovery time of the MOSFET internal diodes, unless additional Schottky diodes are used in parallel to
the MOSFETs source-drain diode. Thus, for most applications a switching time between 100ns and
750ns is chosen.
The required slope control resistor RSLP can be calculated as follows:
Example:
A circuit using the transistor from the diagram above shall be designed for a slope time of
200ns. The miller charge of the transistor is about 6nC.
The nearest available resistor value is 330 k . It sets the gate driver current to roughly 30 mA.
This is well within the minimum and maximum RSLP resistor limits.
5.2.5 Reverse capacity (QGD) protection
The principle of slope control often is realized by gate series resistors with competitor’s products, but,
as latest MOSFET generations have a fairly high gate-drain charge (QGD), this approach is critical for
safe bridge operation. If the gate is not held in the off state with a low resistance, a sudden raise of the
voltage at the drain (e.g. when switching on the complementary transistor) could cause the gate to be
pulled high via the MOSFETs gate drain capacitance. This would switch on the transistor and lead to a
bridge short circuit.
The TMC603 provides for safe and reliable slope controlled operation by switching on a low resistance
gate protection transistor (see figure).
Vgate
Ion
QGD
D
on
Slope
controlled
G
S
QGS
off
Ioff
full, safe off
TMC603 QGD protected
driver stage
External
MOSFET
figure 9: QGD protected driver stage
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TRINAMIC [ TRINAMIC MOTION CONTROL GMBH & CO. KG. ]
