IRF IRAUDAMP5, Manual

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IRAUDAMP5 REV 3.1
.
OCREF
OCREF
5.1V
CSD
O
C
SET
+
.
LO
VS
VCC
VB
CSH
R4
1
R2
5
D1
BAV19
LP Filter
R18
HO
OCSET COM
10R
R30
CSD
R43
1.2V
+B
R19
10R
R32
-B
IRF6645
Q4
IRF6645
Q3
Simplified Functional Block Diagram of High-Side and Low-Side Current Sensing (CH1)
Fig 15
High-Side Current Sensing (Fig15)
The high-side MOSFET is protected from an overload condition and will shutdown the switching
operation if the load current exceeds a preset trip level. High-side over-current sensing monitors
detect an overload condition by measuring the high side MOSFET’s drain-to-source voltage
(V
DS
) through the CSH and VS pins. The CSH pin detects the drain voltage with reference to the
VS pin, which is the source of the high-side MOSFET. In contrast to the low-side current sensing,
the threshold of CSH pin to engage OC protection is internally fixed at 1.2V. An external
resistive divider R43+R25 and R41 (for Ch1) can be used to program a higher threshold. An
additional external reverse blocking diode (D1 for CH1) is required to block high voltage feeding
into the CSH pin during low-side conduction. By subtracting a forward voltage drop of 0.6V at
D1, the minimum threshold which can be set for the high-side is 0.6V across the drain-to-source.
For IRAUDAMP5, the high-side over-current trip level is set to 0.6V across the high-side
MOSFET. For the IRF6645 MOSFETs with a nominal R
DS-ON
of 28 mOhms at 25
°
C, this results
in a ~21A maximum trip level. Since the R
DS-ON
is a function of temperature, the trip level is
reduced to ~14A at 100
°
C.
For a complete description of calculating and designing the over-current trip limits, please refer to
the IRS2092S datasheet.
Positive and Negative Side of Short Circuit, versus switching output shut down:
The plots below show the speed that the IRS2092S responds to a short circuit condition. Notice
that the envelope behind the sine wave output is actually the switching frequency ripple. Bus
pumping naturally affects this topology.