irs20954s International Rectifier Corp., irs20954s Datasheet - Page 14

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

Since the sensed voltage of V
respect to COM for a trip level I
V
In order to neglect the input bias current of OCSET pin, it is recommended to use 10 k total for R4 and R5 to drain 0.5 mA
through the resistors.
For the positive load current, high side over-current sensing monitors over load condition by measuring V
pins and shutdown the operation. The CSH pin is to detect the drain-to-source voltage refers to the V
of the high side MOSFET. In order to neglect overshoot ringing at the switching edges, CSH sensing circuitry starts monitoring
after the first 300 ns the HO is on by blanking the signal from CSH pin.
In contrast to the low side current sensing, the threshold of CSH pin to engage OC protection is internally fixed at 1.2 V. An
external resistive divider R2 and R3 can be used to program a higher threshold.
An external reverse blocking diode, D1, is to block high voltage feeding into the CSH pin while high side is off. By subtracting a
forward voltage drop of 0.6 V at D1, the minimum threshold which can be set in the high side is 0.6 V across the drain to
source.
With the configuration in Fig. 14, the voltage in CSH is:
Since V
as:
The reverse blocking diode D1 is forward biased by a 10 k resistor R1 when the high side MOSFET is on.
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V
V
Where:
R
R
OCSET
CSH
CSH
2
3
V
VF
DS(HIGH SIDE)
(D1)
V
Vth
R
DS
= V
R
DS(HIGH SIDE)
2
is the forward drop voltage of D1
2

OCH
High Side Over-Current Sensing
R

R
3
V

DS(LOW SIDE)
R
3
F
R
3

3
˜
1
V
˜
is drain to source voltage of the high side MOSFET in its ON state
DS
R
DS
(
HIGHSIDE
is determined by the product of drain current I
(
ON
= I
)
˜
TRIP+
)
I
D

V

F
V
x R
(
D
F
TRIP+
) 1
S
(
D
DS(ON)
) 1
is compared with the voltages fed to the OCSET pin, the required voltage of OCSET with
is:
D
and R
DS(ON)
in the high side MOSFET. V
S
pin which is the source
CSH
DS
IRS20954S
with CSH and Vs
can be written
14