Texas Instruments | Two Parallel, Synchronous, Four-Switch Buck-Boost Converters With Droop Method | Application notes | Texas Instruments Two Parallel, Synchronous, Four-Switch Buck-Boost Converters With Droop Method Application notes

Texas Instruments Two Parallel, Synchronous, Four-Switch Buck-Boost Converters With Droop Method Application notes
Application Report
SNVA794 – October 2017
Two Parallel, Synchronous, Four-Switch Buck-Boost
Converters With Droop Method for Higher Power
Hongjia Wu, Daniel Li, Kim Nielson, Vijay Choudhary, Gautam Hari
ABSTRACT
The synchronous, four-switch buck-boost controller LM5176 is widely used in automotive start-stop
systems, industrial personal computers (PC), and a variety of other applications. Paralleling two LM5176
converters is an appealing way to meet a larger power requirement while providing many other benefits,
such as enhanced modularity, design flexibility, minimized component ratings, and so forth. The benefits,
however, can only be effective if the load currents of each module are equally shared, which is the
fundamental difficulty of paralleling supplies.
In this application report, a droop method based current sharing architecture is presented. With a very
simple extra circuit, the effect of load sharing can be greatly improved. Test results show that with ±2%
voltage drop, the current error is within ±1.2% at full load while all the other indexes, including load
transient, startup and output ripple are satisfactory.
1
2
3
4
5
Contents
Introduction ................................................................................................................... 2
Droop and its Realization ................................................................................................... 3
Test Results .................................................................................................................. 6
Conclusion .................................................................................................................. 18
References .................................................................................................................. 18
List of Figures
1
LM5176 Converter as Power Supply ...................................................................................... 3
2
Equivalent Model (Single)
3
Output I-V Characteristic Curve of LM5176 Converter (Slope Exaggerated) ........................................ 3
4
Two Parallel LM5176 Converters as Power Supply..................................................................... 3
5
Equivalent Model (Two Parallel) ........................................................................................... 3
6
Output I-V Characteristic Curve of Two Parallel LM5176 Converters (Slope Exaggerated)....................... 4
7
Two Parallel Power Supplies With Droop (Slope Exaggerated) ....................................................... 4
8
Voltage Feedback Modulation With Output Current Information ...................................................... 5
9
Two Parallel LM5176 Converters With Extra Droop Circuit ............................................................ 6
10
Output I-V Curve of Board One Before Paralleling ...................................................................... 6
11
Output I-V Curve of Board Two Before Paralleling ...................................................................... 6
12
Output I-V Curve of Parallel Power
13
Load Distribution of Two Phases .......................................................................................... 7
14
Four Switch Nodes in 36-V Buck Region With 40-A Load ............................................................. 7
15
Inductor Current Waveforms in 36-V Buck Region With 40-A Load .................................................. 7
16
Four Switch Nodes in 12-V Buck-Boost Region With 40-A Load
17
18
19
20
..................................................................................................
.......................................................................................
.....................................................
Inductor Current Waveforms in 12-V Buck-Boost Region With 40-A Load ..........................................
Four Switch Nodes in 9-V Boost Region With 40-A Load ..............................................................
Inductor Current Waveforms in 9-V Boost Region With 40-A Load ...................................................
Load Transient in 36-V Buck Region With 20-A to 40-A Load Step ..................................................
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7
8
8
8
8
9
1
Introduction
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21
Load Transient in 36-V Buck Region With 0-A to 40-A Load Step .................................................... 9
22
Load Transient in 12-V Buck-Boost Region With 20-A to 40-A Load Step .......................................... 9
23
Load Transient in 12-V Buck-Boost Region With 0-A to 40-A Load Step ............................................ 9
24
Load Transient in 9-V Boost Region With 20-A to 40-A Load Step ................................................. 10
25
Load Transient in 9-V Boost Region With 0-A to 40-A Load Step ................................................... 10
26
Output Voltage Ripple in 36-V Buck Region With No Load
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
..........................................................
Output Voltage Ripple in 36-V Buck Region With 40-A Load ........................................................
Output Voltage Ripple in 12-V Buck-Boost Region With No Load...................................................
Output Voltage Ripple in 12-V Buck-Boost Region With 40-A Load ................................................
Output Voltage Ripple in 9-V Boost Region With No Load ...........................................................
Output Voltage Ripple in 9-V Boost Region With 40-A Load .........................................................
40-A Start-Up in 36-V Buck Region Total Output Current Waveform ...............................................
40-A Start-Up in 36-V Buck Region Two Phase Inductor Currents .................................................
40-A Start-Up in 12-V Buck-Boost Region Total Output Current Waveform .......................................
40-A Start-Up in 12-V Buck-Boost Region Two Phase Inductor Currents ..........................................
40-A Start-Up in 9-V Boost Region Total Output Current Waveform................................................
40-A Start-Up in 9-V Boost Region Two Phase Inductor Currents ..................................................
40-A Load Thermal Condition in 36-V Buck Region ...................................................................
40-A Load Thermal Condition in 12-V Buck-Boost Region ...........................................................
40-A Load Thermal Condition in 9-V Boost Region ...................................................................
Four Switch Node in 36-V Buck Region With 40-A Load .............................................................
Inductor Current Waveforms in 36-V Buck Region With 40-A Load.................................................
Four Switch Nodes in 12-V Buck-Boost Region With 40-A Load ....................................................
Inductor Current Waveforms in 12-V Buck-Boost Region With 40-A Load .........................................
Four Switch Nodes in 9-V Boost Region With 40-A Load ............................................................
Inductor Current Waveforms in 9-V Boost Region With 40-A Load .................................................
Output Voltage Ripple in 36-V Buck Region With No Load ..........................................................
Output Voltage Ripple in 36-V Buck Region With 40-A Load ........................................................
Output Voltage Ripple in 12-V Buck-Boost Region With No Load...................................................
Output Voltage Ripple in 12-V Buck-Boost Region With 40-A Load ................................................
Output Voltage Ripple in 9-V Boost Region With No Load ...........................................................
Output Voltage Ripple in 9-V Boost Region With 40-A Load .........................................................
10
10
11
11
11
11
12
12
12
12
13
13
14
14
15
15
15
16
16
16
16
16
16
17
17
17
17
List of Tables
1
Component Parameters for Droop Circuit ................................................................................ 6
Trademarks
All trademarks are the property of their respective owners.
1
Introduction
The LM5176 is a synchronous, four-switch, buck-boost DC/DC controller capable of regulating the output
voltage at, above, or below the input voltage. The wide input voltage range of 4 V to 55 V (60-V
maximum) makes the controller suitable for automotive start-stop systems, industrial PCs, battery backup
systems, point-of-sale (POS) terminals, and a variety of other applications.
One single LM5176 converter can deliver power greater than 200 W because of its synchronous switching
topology; however, at a higher power, the increased switching and conduction losses can eventually
overwhelm a single converter due to excessive board heating. This overheating makes it necessary to
parallel power stages to distribute heat sources, which at the same time provides many other benefits:
enhanced modularity, design flexibility, and minimized component ratings. These benefits, however, can
only be effective if the load currents of each module are equally shared.
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Different load sharing implementations are discussed in many literatures, and there is often a tradeoff
between complexity and accuracy. Active current sharing, which results in the most accurate load-sharing
results, relies on an elaborate negative feedback loop design. And when it comes to automatic masterslave selection, the circuit can be even more sophisticated. See Paralleling Power – Choosing and
Applying the Best Technique for Load Sharing (Balogh 2003) and Two Parallel, Synchronous Four-Switch
Buck-Boost Converters With Master Slave Method for Higher Power for further details.
In this application report, a droop method based current sharing architecture is presented. With a very
simple extra circuit, the load sharing can be greatly improved. Test results show that with ±2% voltage
drop, the current error is within ±1.2% at full load while all the other indexes, including load transient,
startup and output ripple are satisfactory.
2
Droop and its Realization
2.1
What Droop is and why Droop Helps
A power supply can be modeled as an ideal voltage source in series with a source impedance as shown
in Figure 1 and Figure 2. According to Figure 2, the output I-V characteristic curve of a LM5176 converter
is easily drawn as Figure 3, where Vo(0) represents the output voltage at no load and Vo(Ix) indicates the
output voltage when the load equals full load Ix.
Rs
Io
Iin
+
+
Vin
LM5176
+
VO (0)
Vo
+
±
-
-
Vo
Io
-
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Figure 1. LM5176 Converter as Power Supply
Figure 2. Equivalent Model (Single)
Vo(V)
Vo(0)
Vo(Io)=Vo(0)-Rs*Io
Vo(Ix)
0
Ix
Io(A)
Figure 3. Output I-V Characteristic Curve of LM5176 Converter (Slope Exaggerated)
Similarly, for two parallel LM5176 converters, the corresponding equivalence and I-V curve will be like
Figure 4, Figure 5, and Figure 6.
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Droop and its Realization
+
Iin1
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#1
LM5176
Vin1
+
-
Io
+
V01(0)
Vin
Vo1
±
+
+
Iin2
-
Io2
+
Vin2
-
#2
LM5176
Io
-
Vo
-
Io1
Io1
Vo1
-
Iin
Rs1
+
+
Rs2
Io2
Vo2
+
-
+
V02(0)
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Vo2
±
-
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Figure 4. Two Parallel LM5176 Converters as Power
Supply
Figure 5. Equivalent Model (Two Parallel)
Vo1(Vo2)
Vo1(0)
Vo1(Io1)=Vo1(0)-Rs1*Io1
Vo
Vo2(0)
Vo2(Io2)=Vo2(0)-Rs2*Io2
0
Ix
Io1(Io2)
¨I
Figure 6. Output I-V Characteristic Curve of Two Parallel LM5176 Converters (Slope Exaggerated)
Figure 6 explains clearly why loads are not equally shared if power supplies are simply stacked up. It can
be observed that although the difference between Vo1(0) and Vo2(0) is very small, the two I-V curves can
never completely overlap. Therefore, to achieve the same output voltage Vo, there will be two different
output currents and the gap between them are up to the slope of the curve, that is, the voltage drop from
no load to full load. Due to good load regulation performance, the slope is often very shallow, leading to a
considerable ∆I between two parallel supplies.
The droop method got its name from the fact that the output voltage is made to slightly decrease with
increasing load current. With careful design, a little sacrifice of load regulation can get equally-distributed
load currents in return. Figure 7 shows the output I-V curve of two parallel supplies with a steeper slope
and thus a narrowed ∆I.
Vo1(Vo2)
Vo1(0)
Vo2(0)
Vo1(Io1)=Vo1(0)-Rs1*Io1
Vo
Vo2(Io2)=Vo2(0)-Rs2*Io2
0
Ix
¨I
Io1(Io2)
Figure 7. Two Parallel Power Supplies With Droop (Slope Exaggerated)
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2.2
Schematic Realization
There are many different ways to implement a larger internal source resistor and a steeper slope. Simply
placing a resistor in series achieves this effect but is not practical because of the associated power loss.
A more flexible and attractive way is to sum the information of output current and output voltage and
compare the sum with a reference voltage through an error amplifier. While this approach can be
implemented in many different ways, Figure 8 illustrates an intuitive version.
Original On
Board
Internal
IC
Original On
Board
Vo
Io
R1
Rf
EA
+
R2
VS
INA194
R5
VFB
Rcs
Cf
VR
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Figure 8. Voltage Feedback Modulation With Output Current Information
As Figure 8 indicates, EA is located on the internal IC, R1 and R2 represent the resistor divider on the
board and Rcs is the current-sensing resistor that is also originally there if the average output current limit
function is activated for the LM5176. The only components added are the current-sense amplifier INA194,
the filter network RfCf, and a resistor R5.
The voltage across RCS is amplified by the INA194 current-sense amplifier and filtered by the RfCf filter to
eliminate switching frequency ripple. Using coupling resistor R5, a current is injected into the FB pin to
adjust the output voltage lower as output current is increased. Other gain values can also be selected by
choosing different kinds of current-sense amplifiers – the INA-series in particular has gain settings of 20
V/V, 50 V/V, and 100 V/V. Alternative gain values provide a wide selection for the current-sense resistor,
making it possible to minimize the power dissipation. The ratio of R1 and R2 sets the initial voltage
assuming zero current injection at the feedback node. The ratio of R1 and R5 sets the gain or level of
voltage adjustment for a given amount of current injection into the FB node.
According to Equation 1, the node current equation for the FB pin is:
V o - VR
R1
+
V s - VR
R5
=
VR
R2
(1)
And the voltage level of the output of INA is:
V s = A × R cs × I o
where
•
A is the gain of the current-sense amplifier.
(2)
Substituting Vs in Equation 1 with Equation 2, derives the final expression for Vo:
Vo = (1 +
R1
R2
+
R1
R5
) × VR -
R1
R5
× A × R cs ×I o
(3)
Given VR = 0.8 V, Rcs = 2 mΩ, and setting the voltages from no load to 20-A full load as 12.25 V and
11.75 V, the corresponding values can be calculated: R1 = 280 kΩ, R2 = 20 kΩ, R5 = 1.12 MΩ. Meanwhile,
choose Rf = 1 kΩ and Cf = 1µF to filter the high-frequency ripple in the output current. Table 1 lists all the
component parameters for the droop circuit.
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Table 1. Component Parameters for Droop Circuit
VR (V)
Rcs (mΩ)
Vo(0) (V)
Vo(20 A)
(V)
A (V/V)
R1 (kΩ)
R2 (kΩ)
R5 (MΩ)
Rf (kΩ)
Cf (µF)
0.8
2
12.25
11.75
50
280
20
1.12
1
1
Figure 9 shows the final architecture of two parallel LM5176 converters with an extra droop circuit.
VOUT
R1
R5
Rc
-
#1 LM5176
+
VIN
FB
C
R2
Rcs
INA194
LOAD
INA194
-
Rc
R5
Rcs
+
C
VIN
VOUT
VIN
R1
#2 LM5176
FB
R2
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Figure 9. Two Parallel LM5176 Converters With Extra Droop Circuit
3
Test Results
3.1
Output I-V Curve
Figure 10 and Figure 11 present the I-V curves of two separate boards before paralleling. Observe that
output voltage of each board drops from 12.25 V at no load to 11.75 V at 20-A full load, which is in
accordance with the calculation result. With different input voltages, the curves are slightly different.
Figure 10 and Figure 11 show the output I-V curves of two separate boards before paralleling.
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Output I-V Curve #2
12.3
12.3
12.2
12.2
12.1
VIN = 9 V
12
VIN = 12 V
11.9
VIN = 20 V
11.8
Output Voltage (V)
Output Voltage (V)
Output I-V Curve #1
12.1
VIN = 9 V
12
VIN = 12 V
11.9
VIN = 20 V
11.8
VIN = 36 V
VIN= 36 V
11.7
11.7
0
2
4
6
8
10
12
14
16
18
0
20
2
4
6
8
10
12
14
16
18
20
LOAD (A)
LOAD (A)
Figure 10. Output I-V Curve of Board One Before
Paralleling
Figure 11. Output I-V Curve of Board Two Before
Paralleling
Figure 12 shows the load regulation for the whole system after these two converters are in parallel, which
is almost the same as two separate curves. Figure 13 shows how load is distributed with increasing output
current. At 40-A full load, the gap between two phases is only 0.5 A, which indicates that with ±2% voltage
droop, the current error is within ±1.2%.
Figure 12 and Figure 13 show output I-V curve and load distribution of the parallel power.
Output Voltage (A)
Output I-V Curve
Load Distribution
12.3
12.25
12.2
12.15
12.1
12.05
12
11.95
11.9
11.85
11.8
11.75
11.7
11.65
11.6
VIN = 9 V
VIN = 12 V
VIN = 20 V
VIN = 36 V
0
4
8
12
16
20
24
28
32
36
40
Total Load (A)
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
-1
-2
VIN = 9 V, LOAD1
VIN = 9 V, LOAD2
VIN = 12 V, LOAD1
VIN = 12 V, LOAD2
VIN = 20 V, LOAD1
VIN = 20 V, LOAD2
VIN = 36 V, LOAD1
VIN = 36 V, LOAD2
0
4
8
12
16
20
24
28
32
36
40
Total Load (A)
Figure 12. Output I-V Curve of Parallel Power
3.2
Figure 13. Load Distribution of Two Phases
SYNC Operation
The RT/SYNC pin of the LM5176 can be used to synchronize the PWM controller to an external clock.
The clocks for two parallel LM5176 converters can be either in-phase or 180° out of phase. With in-phase
clocks, the current distribution condition will be more visualized.
Figure 14–Figure 17 show the 4 SW nodes and inductor current waveforms in 36-V buck, 12-V buck
boost, and 9-V boost region, respectively. Each operation region is stable and the inductor current
waveforms of the two phases nearly overlap, indicating equally-distributed load currents.
Figure 14 and Figure 15 show switch nodes and inductor currents in 36-V buck region with 40-A load.
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SW1 (#1)
IL1
IL2
SW2 (#1)
SW1 (#2)
SW1 (#1)
SW2 (#2)
Figure 14. Four Switch Nodes in 36-V Buck Region With
40-A Load
SW2 (#1)
Figure 15. Inductor Current Waveforms in 36-V Buck
Region With 40-A Load
Figure 16 and Figure 17 show switch nodes and inductor currents in 12-V buck-boost region with 40-A
load.
SW1 (#1)
IL1
IL2
SW2 (#1)
SW1 (#1)
SW1 (#2)
SW2 (#1)
SW2 (#2)
Figure 16. Four Switch Nodes in 12-V Buck-Boost
Region With 40-A Load
Figure 17. Inductor Current Waveforms in 12-V BuckBoost Region With 40-A Load
Figure 18 and Figure 19 show switch nodes and inductor currents in 9-V boost region with 40-A load.
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SW1 (#1)
IL1
IL2
SW1 (#1)
SW2 (#1)
SW1 (#2)
SW2 (#1)
SW2 (#2)
Figure 18. Four Switch Nodes in 9-V Boost Region With
40-A Load
Figure 19. Inductor Current Waveforms in 9-V Boost
Region With 40-A Load
Figure 20–Figure 23 show the load transient waveforms in 36-V buck, 12-V buck boost, and 9-V boost
region, respectively. Because output voltage is made to vary with load, there are visible voltage steps for
0-, 20-, and 40-A load conditions.
Figure 20 and Figure 21 show load transient in 36-V buck region with 20-A to 40-A and 0-A to 40-A load
step.
Io
Io
Vo1
Vo1
Vo2
Vo2
Figure 20. Load Transient in 36-V Buck Region With 20A to 40-A Load Step
Figure 21. Load Transient in 36-V Buck Region With 0-A
to 40-A Load Step
Figure 22 and Figure 23 show load transient in 12-V buck-boost region with 20-A to 40-A and 0-A to 40-A
load step.
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Io
Io
Vo1
Vo1
Vo2
Vo2
Figure 22. Load Transient in 12-V Buck-Boost Region
With 20-A to 40-A Load Step
Figure 23. Load Transient in 12-V Buck-Boost Region
With 0-A to 40-A Load Step
Figure 24 and Figure 25 show load transient in 9-V boost region with 20-A to 40-A and 0-A to 40-A load
step.
Io
Io
Vo1
Vo1
Vo2
Vo2
Figure 24. Load Transient in 9-V Boost Region With 20-A
to 40-A Load Step
Figure 25. Load Transient in 9-V Boost Region With 0-A
to 40-A Load Step
Figure 26–Figure 31 are the output ripple waveforms in 36-V buck, 12-V buck boost, and 9-V boost region,
respectively.
Figure 26 and Figure 27 show output voltage ripple in 36-V buck region with no load and 40-A load.
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Vo
Vo
Figure 26. Output Voltage Ripple in 36-V Buck Region
With No Load
Figure 27. Output Voltage Ripple in 36-V Buck Region
With 40-A Load
Figure 28 and Figure 29 show output voltage ripple in 12-V buck-boost region with no load and 40-A load.
Vo
Vo
Figure 28. Output Voltage Ripple in 12-V Buck-Boost
Region With No Load
Figure 29. Output Voltage Ripple in 12-V Buck-Boost
Region With 40-A Load
Figure 30 and Figure 31 show output voltage ripple in 9-V boost region with no load and 40-A load.
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Vo
Vo
Figure 30. Output Voltage Ripple in 9-V Boost Region
With No Load
Figure 31. Output Voltage Ripple in 9-V Boost Region
With 40-A Load
Figure 32–Figure 37 present the start-up waveforms in 36-V buck, 12-V buck boost, and 9-V boost region,
respectively. Because every two boards are not exactly the same, there is always sequential order during
startup, which explains the reason that for a certain period of the start-up process, the loads are not
equally distributed.
Figure 32 and Figure 33 show 40-A start-up in 36-V buck region.
Vin
Vin
Vo
Vo
Io
IL1
IL2
Figure 32. 40-A Start-Up in 36-V Buck Region Total
Output Current Waveform
Figure 33. 40-A Start-Up in 36-V Buck Region Two Phase
Inductor Currents
Figure 34 and Figure 35 show 40-A start-up in 12-V buck-boost region.
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Vin
Vin
Vo
Vo
Io
IL1
IL2
Figure 34. 40-A Start-Up in 12-V Buck-Boost Region
Total Output Current Waveform
Figure 35. 40-A Start-Up in 12-V Buck-Boost Region Two
Phase Inductor Currents
Figure 36 and Figure 37 show 40-A start-up in 9-V boost region.
Vin
Vin
Vo
Vo
Io
IL1
IL2
Figure 36. 40-A Start-Up in 9-V Boost Region Total
Output Current Waveform
Figure 37. 40-A Start-Up in 9-V Boost Region Two Phase
Inductor Currents
Due to the parallel structure of two LM5176 converters, the heat sources are also distributed. With
600CFM air flow, Figure 38–Figure 40 show the 40-A load thermal condition in 36-V buck, 12-V buck
boost, and 9-V boost, respectively.
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Figure 38. 40-A Load Thermal Condition in 36-V Buck Region
Figure 39. 40-A Load Thermal Condition in 12-V Buck-Boost Region
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Figure 40. 40-A Load Thermal Condition in 9-V Boost Region
3.3
Interleaved Operation
As previously mentioned, two LM5176 converters can also be configured as 180° out of phase, that is,
interleave architecture. Interleave architecture provides a better solution for smaller output voltage ripple.
To show the discrimination with in-phase operation, Figure 41– present the 4 SW nodes and inductor
current waveforms in 36-V buck, 12-V buck boost, and 9-V boost region, respectively.
Figure 41 and Figure 42 show switch nodes and inductor currents in 36-V buck region with 40-A load.
SW1 (#1)
IL1
IL2
SW2 (#1)
SW1 (#2)
SW1 (#1)
SW2 (#2)
Figure 41. Four Switch Node in 36-V Buck Region With
40-A Load
SW2 (#1)
Figure 42. Inductor Current Waveforms in 36-V Buck
Region With 40-A Load
Figure 43 and Figure 44 show switch nodes and inductor currents in 12-V buck-boost region with 40-A
load.
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Two Parallel, Synchronous, Four-Switch Buck-Boost Converters With Droop
Method for Higher Power
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Test Results
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IL1
SW1 (#1)
IL2
SW2 (#1)
SW1 (#2)
SW1 (#1)
SW2 (#1)
SW2 (#2)
Figure 43. Four Switch Nodes in 12-V Buck-Boost
Region With 40-A Load
Figure 44. Inductor Current Waveforms in 12-V BuckBoost Region With 40-A Load
Figure 45 and Figure 46 show switch nodes and inductor currents in 9-V boost region with 40-A load.
SW1 (#1)
IL1
IL2
SW1 (#1)
SW2 (#1)
SW1 (#2)
SW2 (#1)
SW2 (#2)
Figure 45. Four Switch Nodes in 9-V Boost Region With
40-A Load
Figure 46. Inductor Current Waveforms in 9-V Boost
Region With 40-A Load
Figure 47–Figure 52 show the output ripple in 36-V buck, 12-V buck boost, and 9-V boost region,
respectively. Compared with Figure 26–Figure 31, the amplitude of output voltage ripple is reduced while
the frequency is doubled.
Figure 47 and Figure 48 show output voltage ripple in 36-V buck region with no load and 40-A load.
16
Two Parallel, Synchronous, Four-Switch Buck-Boost Converters With Droop
Method for Higher Power
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Test Results
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Vo
Vo
Figure 47. Output Voltage Ripple in 36-V Buck Region
With No Load
Figure 48. Output Voltage Ripple in 36-V Buck Region
With 40-A Load
Figure 49 and Figure 50 show output voltage ripple in 12-V buck-boost region with no load and 40-A load.
Vo
Vo
Figure 49. Output Voltage Ripple in 12-V Buck-Boost
Region With No Load
Figure 50. Output Voltage Ripple in 12-V Buck-Boost
Region With 40-A Load
Figure 51 and Figure 52 show output voltage ripple in 9-V boost region with no load and 40-A load.
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Conclusion
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Vo
Vo
Figure 51. Output Voltage Ripple in 9-V Boost Region
With No Load
4
Figure 52. Output Voltage Ripple in 9-V Boost Region
With 40-A Load
Conclusion
Unequal load distribution is the fundamental difficulty of parallel power supplies. In this application report,
a droop method based current sharing architecture is presented. With a simple extra droop circuit, two
LM5176 converters can share equal currents with ±1.2% error at full load while the voltage drop is within
±2%. Experiment results for parallel LM5176 converters with 480-W capability were presented. This
provides an attractive solution for high-power applications.
5
References
1. Texas Instruments, LM5176 55-V Wide VIN Synchronous 4-Switch Buck-Boost Controller Data Sheet
2. Laszlo Balogh, Paralleling Power--Choosing and Applying the best technique for load sharing
18
Two Parallel, Synchronous, Four-Switch Buck-Boost Converters With Droop
Method for Higher Power
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