Texas Instruments | Eliminate the Voltage Drop and Save Power: An Ideal Diode (Rev. A) | Application notes | Texas Instruments Eliminate the Voltage Drop and Save Power: An Ideal Diode (Rev. A) Application notes

Texas Instruments Eliminate the Voltage Drop and Save Power: An Ideal Diode (Rev. A) Application notes
Eliminate the Voltage Drop and Save Power: An Ideal
Diode
Emily Roth
Texas Instruments' LM66100 Integrated Ideal Diode
provides reverse current blocking and reverse polarity
protection with a low forward voltage drop, leading to
significant power dissipation savings. The key
advantages of using the LM66100 ideal diode over
discrete diode solutions, as shown in Table 1, are
highlighted in this tech note.
Dual Ideal Diode
ORing Solution
Power Dissipation Savings
The LM66100 device intelligently controls a P-channel
MOSFET to behave as an ideal diode, removing the
forward voltage drop found on discrete diode solutions.
This integration into a single device results in a lower
Ron and greater power dissipation savings as
compared to a discrete diode. In a discrete diode, the
normal 0.4 V–0.7 V forward voltage drop increases the
power dissipation in conduction mode, which results in
a shortened battery life and lower system efficiency.
For example, if a battery system requires an input
voltage above 2.5 V, the full capacity of the battery
cannot be used due to the diode drop across the
voltage rail. Figure 2 shows that the LM66100 results
in a more than 90% power dissipation reduction as
compared to discrete diodes. This reduction in heat
can be advantageous in small form factor products.
0.4
0.35
Power Dissipation (W)
Today, discrete diodes are commonly used in power
system designs to protect against reverse current and
reverse polarity events. In certain applications such as
smart eMeters or thermostats, redundant power
supplies or backup batteries are used to prevent
system downtime. The system needs to prevent the
main rail that is powering the downstream load from
flowing back into the secondary supply and potentially
damaging the system. A typical application with ideal
diodes is shown in Figure 1. Using a discrete diode to
block this unwanted reverse current may be a simple
fix, however, discrete diodes have high reverse
leakage current, which results in higher power
dissipation. In addition, the forward voltage drop of a
diode leads to a shortened battery life and lower
system efficiency.
LM66100
Discrete Diode 1
Discrete Diode 2
0.3
0.25
0.2
0.15
0.1
0.05
0
0.15
VIN1
+
-
LM66100
CL
VBAT
0.2
0.25
0.3
Current (A)
0.35
0.4
powe
Figure 2. Power Dissipation vs. Load Current
RL
LM66100
Downstream Load
+ Lower Power Dissipation
+ Lower Leakage Current
+ Robust Protection
Figure 1. Typical ORing Application
Table 1. LM66100 Ideal Diode vs Discrete Diodes
Feature
Discrete
Diode
Advantages
✓
Reduced amount of heat in
small form factor products
✓
Lower reverse leakage
current results in higher
system efficiency
✓
✓
Prevent damage to
downstream loads from
miswiring input supply
✓
✓
Provides protection in a
smaller integrated package
Low Power
Dissipation
Low Reverse
Leakage Current
Reverse Polarity
Protection
Small Solution Size
Figure 3. Discrete Diode 1
at 400 mA, Tj (111C)
LM66100
SLVAEA8A – April 2019 – Revised July 2019
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Figure 4. LM66100 at 400
mA, Tj (30C)
Reverse Current Blocking and Reverse Polarity
Protection
The LM66100 integrates a fast comparator that
disables the device in a reverse current scenario.
When the output voltage is higher than the input
voltage, the device turns off in 40 µs as shown in
Figure 5. Integrated reverse polarity protection
Eliminate the Voltage Drop and Save Power: An Ideal Diode
Copyright © 2019, Texas Instruments Incorporated
Emily Roth
1
www.ti.com
provides additional protection without the need for
external components. When a negative voltage is seen
at the input, such as when a battery is inserted
backwards, the LM66100 responds by disabling the
device within 4 µs to prevent any damage to
downstream loads. This behavior can be seen in
Figure 6.
Table 2. LM66100 Reverse Leakage Current
Comparison
Vin
Discrete Diode
1
Discrete
Diode 2
LM66100
Unit
1.5 V
0.91
100
0.082
µA
3V
1.05
120
0.214
µA
5V
1.30
150
0.339
µA
5.5 V
1.50
180
0.423
µA
ORing Power Supplies
Figure 5. Reverse Current Blocking
There are applications which rely on some form of
backup power via a battery or supercap to provide
alternate power to the system. A traditional solution is
a simple dual diode configuration as shown in
Figure 1, allowing the highest voltage supply to
provide power to the system while the other diode is
reverse biased. When used in an ORing configuration,
the LM66100 provides a fast switchover response and
includes a status pin to notify which power supply is
providing power. This switchover response can be
seen in Figure 7.
Figure 7. LM66100 Switchover from IN1 to IN2
Figure 6. Reverse Polarity Protection
Conclusion
Low Reverse Leakage
Along with the advantages of low power dissipation,
the LM66100 has low reverse current leakage when
compared to a discrete diode. Reverse current can
damage a nonrechargable battery. Therefore, in an
ORing scenario, it is important to reduce reverse
leakage to prevent damaging the battery. This reverse
current can damage a nonrechargable battery. Table 2
shows that compared to the discrete diode solutions,
the LM66100 has a 65% reduction in leakage current,
therefore, preventing excessive charge from flowing
back to the battery. The leakage values below were
taken at 85°C and only increase as temperature rises,
adding to the lost efficiency.
2
Eliminate the Voltage Drop and Save Power: An Ideal Diode
Input power protection such as reverse polarity
protection and reverse current blocking, are crucial in
many systems. Traditional discrete diodes are a
simple solution but lead to undesirable power
dissipation and reduced system efficiency due to their
non-ideal characteristics. TI’s LM66100 Ideal Diode
with an integrated P-Channel MOSFET provides
protection against reverse battery, reverse current, and
other fault events without the drawbacks of a discrete
diode. The LM66100 also has a status pin that can be
used to notify when the power sources have switched
adding optional diagnostics to a system. Key features
such as low forward conduction loss, fast reverse
voltage recovery, and reduced leakage current of the
LM66100 result in an efficient, robust solution as
compared to discrete diodes.
Emily Roth
Copyright © 2019, Texas Instruments Incorporated
SLVAEA8A – April 2019 – Revised July 2019
Submit Documentation Feedback
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