LM5069_10 NSC [National Semiconductor], LM5069_10 Datasheet - Page 2

• Manufacturer Part Number: LM5069_10
• Description: Output Voltage Clamping Using the LM5069 Hot Swap Controller
• Manufacturer: NSC [National Semiconductor]

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The Solution
The solution presented here is to limit the voltage at V
a maximum value, rather than shut it off, when an over-volt-
In normal operation (when the over-voltage condition is not
present) the GATE pin of the LM5069 is approximately 12V
above the voltage at V
above the normal operating range, Q1’s gate voltage is
clamped by Z1. As V
V
duces to a level where Q1 limits the current to the load. Any
additional increase in V
additional increase in the voltage at V
The choice of zener voltage for Z1 depends not only on the
voltage at which V
OUT
is clamped when Q1’s gate-to-source voltage (V
OUT
IN
is to be clamped, but also on the spe-
OUT
continues to increase, the voltage at
IN
is absorbed by Q1 as there is no
. As the voltage at V
OUT
.
FIGURE 2. Zener Clamp Added to the Gate
IN
increases
GS
OUT
) re-
to
2
age condition appears at V
a zener diode at the GATE pin of the LM5069, as shown in
Figure 2.
cific MOSFET chosen for Q1 – more specifically, its V
characteristics. Typically Z1 should have a zener voltage ap-
proximately 2V to 5V above the desired clamping voltage at
V
MOSFET’s datasheet can provide an initial value for the dif-
ference between Z1’s voltage and the desired clamping volt-
age at V
experimentally.
OUT
. Using the Transfer Characteristics information in the
OUT
. The final selection for Z1 should be determined
IN
. This is accomplished by adding
30119202
GS