TPD4122K TOSHIBA Semiconductor CORPORATION, TPD4122K Datasheet - Page 12

• Manufacturer Part Number: TPD4122K
• Description: Toshiba Intelligent Power Device High Voltage Monolithic Silicon Power Ic
• Manufacturer: TOSHIBA Semiconductor CORPORATION

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 μs per cycle to charge the capacitor.) When the V
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 the 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 = Current dissipation (max) of the high-side driver × Maximum drive time
/(V
Consideration must be made for aging and temperature change of the capacitor.
Safe Operating Area
The IC uses bootstrapping for the power supply for high-side drivers.
Duty cycle 100 % (V
CC
Duty cycle 55 % (V
V
V
Note: The above safe operating areas are at Tj = 135 °C (Figure 1).
F
F
− V
(BSD)
(FRD)
Duty cycle 0 % (V
V
F
PWM reference voltage
1.0
S
(BSD)
0
Range
A
B
C
VVsOFF (V
0
: Bootstrap diode forward voltage
: First recovery diode forward voltage
Duty cycle 80 %
+ V
Power supply voltage V
Figure 1 SOA at Tj = 135°C
F
S
S
(FRD)
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
− 13.5) [F]
Triangular wave
BB
(V)
Low-side ON
450
S
voltage exceeds 3.8 V (55 % duty), the low-side IGBT is
12
High-side duty ON
IGBT Operation
C
B
A
TPD4122K
2008-08-13