Datasheet

EN
V
GS
Status
nPGD
V
TIMER
Fault Latch
V
GS
6 PA
V
TRMRH
GATE pin will be
discharged to GND
at 80 mA rate
V
GATE-TH
OFF
ON
Fault
V
TRMRL
V
GS
< 5V
LM5060
SNVS628F –OCTOBER 2009–REVISED APRIL 2013 www.ti.com
Figure 23. Voltages During Startup with V
GS
Gate Leakage Condition
V
DS
FAULT CONDITION
The LM5060 includes a V
DS
Fault Comparator that senses the voltage difference between the SENSE pin and
the OUT pin. If the voltage at the OUT pin falls lower than the voltage at the SENSE pin, the V
DS
Fault
Comparator will trip and switch the nPGD pin to a high impedance state. It will also initiate charging of the
capacitor on the TIMER pin with a 6 µA (typical) current source if V
GS
is less than than 5V, or a 11 µA (typical)
current source if V
GS
is higher than 5V. If the voltage on the TIMER pin reaches the typical 2V fault threshold, the
gate of the N-Channel MOSFET is pulled low with a 80 mA (typical) sink current. Figure 24 illustrates a V
DS
fault
condition during start-up. The nPGD pin never switches low because the V
DS
fault comparator detects excessive
V
DS
voltage throughout the entire sequence.
OVER-CURRENT FAULT
The V
DS
Fault Comparator can be used to implement an Over-Current shutdown function. The V
DS
Fault
Comparator monitors the voltage difference between the SENSE pin and the OUT pin. This is, essentially, the
same voltage that is across the N-Channel MOSFET R
DS(ON)
less the threshold voltage that is set by the series
resistor on the SENSE pin. The value of capacitor on the TIMER pin, the capacitor charge current (I
TIMERH
, 11 uA
typical), along with the TIMER pin fault threshold (V
TMRH
) will determine the how long the N-Channel MOSFET
will be allowed to conduct excessive current before the MOSFET is turned-off. When this delay time expires, the
gate is discharged at a 80 mA rate.
The LM5060 is intended for applications where precise current sensing is not required, but some level of fault
protection is needed. Examples are applications where inductance or impedance in the power path limits the
current rise in a short circuit condition.
The Safe Operating Area (SOA) of the external N-Channel MOSFET should be carefully considered to ensure
the peak drain-to-source current and the duration of the fault delay time is within the SOA rating of the MOSFET.
Also note that the R
DS(ON)
variations of the external N-Channel MOSFET will affect the accuracy of the Over-
Current detection.
RESTART AFTER OVER-CURRENT FAULT EVENT
When a V
DS
fault condition has occurred and the TIMER pin voltage has reached 2V, the LM5060 latches off the
external MOSFET. In order to initiate a restart, either the EN pin, the VINpin, or the UVLO pin must be toggled
low and then high.
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