Datasheet

GND
OUT
SENSE
GATE
Q1
Fault
OFF
LM5060
R
S
R
O
C
L
R
L
V
OUT
V
IN
I
GATE-FLT
80 mA
GND
OUT
SENSE
GATE
Q1
Fault
OFF
LM5060
R
S
C
L
R
L
V
IN
V
OUT
I
GATE-FLT
80 mA
LM5060
www.ti.com SNVS628F –OCTOBER 2009–REVISED APRIL 2013
Figure 32. Discharge Path of Possible Load Capacitor
In applications exposed to reverse polarity on the input and a large load capacitance on the output, a current
limiting resistor in series with the OUT pin is required to protect the LM5060 OUT pin from reverse currents
exceeding 25 mA. Figure 33 shows the resistor R
O
in the trace to the OUT pin.
Figure 33. Current Limiting Resistor R
O
for Special Cases
If a R
O
resistor in the OUT path is used, the current sensing will become less accurate since R
O
has some
variability as well as the current into the OUT pin. The OUT pin current is specified in the Electrical
Characteristics section as I
OUT-EN
. A R
O
resistor design compromise for protection of the OUT pin and a
maintaining V
DS
sensing accuracy can be achieved. See the REVERSE POLARITY PROTECTION WITH A
RESISTOR for more details on how to calculate a reasonable R
O
value.
REVERSE POLARITY PROTECTION WITH DIODES
Figure 34 shows the LM5060 in an automotive application with reverse polarity protection. The second N-channel
MOSFET Q2 is used to prevent the body diode of Q1 from conducting in a reverse V
IN
polarity situation. The
zener diode D3 is used to limit V
IN
voltage transients which will occur when Q1 and Q2 are shut off quickly. In
some applications the inductive kick is handled by input capacitors and D3 can be omitted. In reverse polarity
protected applications, the input capacitors will see the reverse voltage. To avoid stressing input capacitors with
reverse polarity, a transorb circuit implemented with D3 and D2 may be used. Diode D1 in Figure 34 protects the
VIN pin in the event of reverse polarity. The resistor R1 protects the GATE pin from reverse currents exceeding
25 mA in the reverse polarity situation. This GATE resistor would slow down the shutdown of Q1 and Q2
dramatically. To prevent a slow turn off in fault conditions, D5 is added to bypass the current limiting resistor R1.
Copyright © 2009–2013, Texas Instruments Incorporated Submit Documentation Feedback 23
Product Folder Links: LM5060