irs20954s International Rectifier Corp., irs20954s Datasheet - Page 19

• Manufacturer Part Number: irs20954s
• Description: Protected Digital Audio Driver
• Manufacturer: International Rectifier Corp.

The high side bootstrap power supply can be charged up through a resistor from the positive supply bus to V
internal 20.8 V zener diode clamp between V
for the initial low-side ON.
To determine the requirement for Rcharge, following condition has to be met;
Where I
Note that Rcharge can drain floating supply charge during on state of high side, which limits maximum PWM modulation index
capability of the system. Rcharge should be large enough not to discharge the floating power supply during the high side ON.
The protection control block monitors the status of the power supply of V
Voltage Lockout threshold. The LO and HO of the IRS20954 are disabled by shutdown until the UVLO of V
released and CSD timer capacitor Ct is charged up. After the UVLO of V
time the voltage at CSD pin reached the release threshold, Vth1, shutdown logic enables LO and HO. The OC detection blocks
for the low side and high side are disabled until UVLO of V
www.irf.com
I
CHARGE
Start-up Sequence (UVLO)
I
!
CHARGE
QBS
Charging V
I
QBS
is high side quiescent current
is a required charging current through Rcharge
BS
Prior to start
PWM
VDD
CSD
OCSET
VSS
VREF
DT
IN
NC
Figure 19: Bootstrap Supply Pre-Charging
IRS20954S
CSD
VDD
VSS
VREF
OCSET
B
DT
IN
NC
and V
IRS20954S
Figure 18: Supplying V
10.4V
S
COM
CSH
VCC
. Advantage of this scheme is to eliminate the minimum duration required
NC
LO
HO
VS
VB
COM
CC
CSH
VCC
HO
NC
LO
VB
VS
and V
Rdd
BS
Rcharge
I
charge
are released.
DD
CC
DD
and V
is released, CSD pin resets power-on timer. At the
12V
+B
Vcc
-B
CC
whether the voltages are above the Under
12V
+B
Vcc
-B
IRS20954S
B
pin by utilizing an
CC
and V
DD
19
are