Datasheet

OUT
SENSE GATE
VIN
LM5060
Q1
R
S
V
IN
V
OUT
C1
OUTSENSE GATE
VIN
LM5060
Q1
R
S
V
IN
V
OUT
I
DSTH
=
V
DSTH
R
DS(ON)
LM5060
www.ti.com SNVS628F –OCTOBER 2009–REVISED APRIL 2013
APPLICATION INFORMATION
V
DS
FAULT DETECTION and SELECTING SENSE PIN RESISTOR R
S
The LM5060 monitors the V
DS
voltage of the external N-Channel MOSFET. The drain to source voltage threshold
(V
DSTH
), which is set with the resistor R
S
, is shown in Figure 27;
V
DSTH
= (R
S
x I
SENSE
) - V
OFFSET
(1)
The MOSFET drain to source current threshold is:
where
• R
DS(ON)
is the resistive drop of the pass element Q1 in Figure 27
• V
OFFSET
is the offset voltage of the V
DS
comparator
• I
SENSE
(16 µA typical) is the threshold programming current (2)
Figure 27. Setting the V
DS
Threshold
TURN-ON TIME
To slow down the output rise time a capacitor from the GATE pin to GND may be added. The turn on time
depends on the threshold level of the N-Channel MOSFET, the gate capacitance of the MOSFET as well as the
optional capacitance from the GATE pin to GND. Figure 28 shows the slow down capacitor C1. Reducing the
turn-on time allows the MOSFET (Q1), to slowly charge a large load capacitance. Special care must be taken to
keep the MOSFET within its safe operating area. If the MOSFET turns on too slow, the peak power losses may
damage the device.
Figure 28. Turn-On Time Extension
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