Toshiba TCK401G, Reference Manual, Page: 6 / 15

RD002-RGUIDE-01
2018-03-07
Rev. 1
6 / 15
© 2018
Toshiba Electronic Devices & Storage Corporation
The TCK401G has slew rate control circuit which limits inrush current during switch-on transitions.
Figure 3.1.3 shows an example of switching waveforms of back-to-back MOSFETs using TCK401G.
Figure 3.1.3 Example of switching waveforms of back-to-back MOSFETs with TCK401G
As shown in Figure 3.1.3, reducing the rising slew rate helps suppress inrush current and reduce
ringing and EMI.
Note that delay time may happens from V
CT
signal applied to the TCK401G to activate the driver
stage of the TCK401G. This delay is caused by the time required for signal processing in the TCK401G.
The V
GATE
output of the TCK401G drives the MOSFET gate inputs and the V
GATE
ON time (t
ON
) is
specified in the datasheet. Note that in actual circuit, ON time (t
ON
) is not a specification that defines
the switching time of external MOSFETs. In actual circuit, the turn-on time of the MOSFETs depends
on their gate capacitance and threshold voltage (V
th
). The TCK401G specifies V
GATE
ON time (t
ON
) at
a gate capacitance of 2000pF. The assumption comes from the TCK401G being used to drive two
back-to-back MOSFETs and each gate capacitance has roughly 1000pF. When the TCK401G drives
MOSFETs with lower gate capacitance, V
GATE
ON time is less than the number in the datasheet. This
means the switching time of external MOSFETs becomes faster. On the other hand, when the
TCK401G drives MOSFETs with higher gate capacitance, the MOSFET switching time becomes slower
because of a longer V
GATE
ON time. When MOSFETs with a high threshold voltage (V
th
) are used, it
is recommended to use the TCK401G at an input voltage (V
IN
) with high as possible in order to raise
the V
GATE
voltage. For a details of the specification on the V
GATE
ON time, see Section 4, “Design
considerations.”
Figure 3.1.4 and Figure 3.1.5 show examples of switching waveforms of back-to-back MOSFETs
driven by the TCK401G at -40°C and 85°C.
Test conditions:
V
IN
= 5V
V
CT
= 0 ⇔ 5V
Output current= 5 A
C
OUT
＝
4.7μF
T
a
= 25°C
V
CT
(5V/div)
Output current
(5A/div)
Output voltage
(5V/div)
200μs/div