LM5060Q1 National Semiconductor Corporation, LM5060Q1 Datasheet - Page 19

• Manufacturer Part Number: LM5060Q1
• Description: High-side Protection Controller With Low Quiescent Current
• Manufacturer: National Semiconductor Corporation

OVP, UVLO, and nPGD pins from harm, a larger bulk capac-
itor from VIN to GND may be needed to reduce the amplitude
of the voltage spikes. Protection diodes or surge suppressors
may also be used to limit the exposure of the LM5060 pins to
voltages below their maximum operating ratings.
THERMAL CONSIDERATIONS
In normal operation the LM5060 dissipates very little power
so that thermal design may not be very critical. The power
dissipation is typically the 2 mA input current times the input
voltage. If the application is driving a large capacitive load
application, upon shutdown of the LM5060, the load capacitor
may partially, or fully, discharge back through the LM5060
circuitry if no other loads consume the energy of the pre-
charged load capacitor. One application example where en-
ergy is dissipated by the LM5060 is a motor drive application
with a large capacitor load. When the LM5060 is turned off,
the motor might also turn off such that total residual energy in
the load capacitor is conducted through the OUT pin to
ground. The power dissipated within the LM5060 is deter-
mined by the discharge current of 80 mA and the voltage on
the load capacitor.
LARGE LOAD CAPACITANCE
Figure 12
C
at the same voltage as C
body diode of Q1 will not conduct any current and all the
charge on C
cuitry. The dotted line in
current flow. Initially the power dissipated by the LM5060 is
calculated with the formula:
Where I
In applications with a high input voltage and very large output
capacitance, the discharge current can be limited by an ad-
ditional discharge resistor R
shown in
threshold, so the value of R
In applications exposed to reverse polarity on the input and a
large load capacitance on the output, a current limiting resis-
tor in series with the OUT pin is required to protect the
LM5060 OUT pin from reverse currents exceeding 25 mA.
Figure 13
FIGURE 12. Discharge Path of Possible Load Capacitor
L
. Assume a worst case turn off scenario where Vin remains
GATE-FLT
Figure
shows an application with a large load capacitance
shows the resistor R
L
is dissipated through the LM5060 internal cir-
is the sink current of the LM5060 gate control.
13. This resistor will influence the current limit
P = I
GATE-FLT
L
Figure 12
and R
S
O
will need to be readjusted.
in series with the OUT pin as
O
in the trace to the OUT pin.
L
x V
is a high impedance. The
OUT
shows the path of this
30104240
19
If a R
will become less accurate since R
well as the current into the OUT pin. The OUT pin current is
specified in the
A R
pin and a maintaining V
See the
SISTOR
R
REVERSE POLARITY PROTECTION WITH DIODES
Figure 14
with reverse polarity protection. The second N-channel MOS-
FET Q2 is used to prevent the body diode of Q1 from con-
ducting in a reverse V
is used to limit
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 capaci-
tors with reverse polarity, a transorb circuit implemented with
D3 and D2 may be used. Diode D1 in
VIN pin in the event of reverse polarity. The resistor R1 pro-
tects 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 pre-
vent a slow turn off in fault conditions, D5 is added to bypass
the current limiting resistor R1. When Q1 and Q2 are turned
on, R1 does not cause any delay because the GATE pin is
driven with a 24 µA current source. D6, Q3 and R2 protect Q2
from V
Diodes D5 and D7 are only necessary if the output load is
highly capacitive. Such a capacitive load in combination with
a high reverse polarity input voltage condition can exceed the
power rating of the internal zener diode between OUT pin and
GATE pin as well as the internal diode between the OUT pin
and SENSE pin. External diodes D5 and D7 should be used
in reverse polarity protected applications with large capacitive
loads.
O
FIGURE 13. Current Limiting Resistor R
Operating Voltage Range
value.
O
O
resistor design compromise for protection of the OUT
GS
resistor in the OUT path is used, the current sensing
UVLO setting
REVERSE POLARITY PROTECTION WITH A RE-
Current max
OVP setting
for more details on how to calculate a reasonable
Figure 14 Example Circuit Specification
shows the LM5060 in an automotive application
damage in the event of reverse input polarity.
V
IN
Electrical Characteristics
voltage transients which will occur when Q1
IN
DS
polarity situation. The zener diode D3
sensing accuracy can be achieved.
Cases
O
has some variability as
Figure 14
27V typical
9V typical
9V – 24V
section as I
30A
O
for Special
www.national.com
protects the
OUT-EN
30104241
.