TPD4112K Toshiba Semiconductor, TPD4112K Datasheet - Page 12

• Manufacturer Part Number: TPD4112K
• Description: Intelligent Power Device High Voltage Monolithic Silicon Power IC
• Manufacturer: Toshiba Semiconductor

Description of Bootstrap Capacitor Charging and Its Capacitance
The bootstrap capacitor is charged by turning on the low-side IGBT of the same arm (approximately 1/5 of PWM
cycle) while the high-side IGBT controlled by PWM is off. (For example, to drive at 20 kHz, it takes approximately
10 ms per cycle to charge the capacitor.) When the VS voltage exceeds 3.8 V (55% duty), the low-side IGBT is
continuously in the off state. This is because when the PWM on-duty becomes larger, the arm is short-circuited
while the low-side IGBT is on. Even in this state, because PWM control is being performed on the high-side IGBT,
the regenerative current of the diode flows to the low-side FRD of the same arm, and bootstrap capacitor is charged.
Note that when the on-duty is 100%, diode regenerative current does not flow; thus, the bootstrap capacitor is not
charged.
When driving a motor at 100 % duty cycle, take the voltage drop at 100% duty (see the figure below) into
consideration to determine the capacitance of the bootstrap capacitor.
Capacitance of the bootstrap capacitor = Consumption current (max) of the high-side driver × Maximum drive time
/(V
Care must be taken for aging and temperature change of the capacitor.
Safe Operating Area
The IC uses bootstrapping for the power supply for high-side drivers.
CC
Note 1: The above safe operating areas are Tj = 135°C (Figure 1) and Tc = 95°C (Figure 2). If the temperature
Note 2: The above safe operating areas include the over current protection operation area.
Duty cycle 100% (V
V
V
Duty cyle 55% (V
F (BSD)
F (FRD)
− V
Duty cycle 0% (V
V
F (BSD)
PWM reference voltage
1.0
S
0
Range
A
B
C
exceeds thsese, the safe operation areas reduce.
VVsOFF (V
0
: Bootstrap diode forward voltage
: Flywheel diode forward voltage
Duty cycle 80%
+ V
Power supply voltage V
Figure 1 SOA at Tj = 135°C
F (FRD)
S
S
S
S
: 5.4 V)
: 3.8 V)
: 2.1 V)
: 1.3 V)
Both high- and low-side OFF.
Charging range. Low-side IGBT refreshing on the phase the high-side IGBT in PWM.
No charging range. High-side at PWM according to the timing chart. low-side no refreshing.
GND
Triangular wave
− 13.5) [F]
BB
(V)
Low-side ON
400
12
High-side duty ON
IGBT Operation
1.1
0
0
Power supply voltage V
Figure 2 SOA at Tc = 95°C
C
B
A
TPD4112K
BB
(V)
2005-11-04
400