NSC C1608C0G1E682J Evaluation board provides the design engineer with a fully functional Datasheet

National Semiconductor
Application Note 2066
Eric Lee
September 28, 2010
Introduction
ed to the J6 (OUT2+) and J5 (OUT2-/GND). Be sure to
choose the correct connector and wire size when attaching
the source power supply and the load.
The LM25119EVAL evaluation board provides the design engineer with a fully functional dual output buck converter, employing the LM25119 Dual Emulated Current Mode Synchronous Buck Controller. The evaluation board is designed
to provide both 3.3V and 1.8V outputs over an input range of
6.0V to 36V. Also the evaluation board can be easily configured for a single 3.3V, 16A regulator.
Performance of the Evaluation
Board
•
•
•
•
•
•
•
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Input Voltage Range: 6.0V to 36V
Output Voltage: 3.3V (CH1), 1.8V (CH2)
Output Current: 8A (CH1), 8A (CH2)
Nominal Switching Frequency: 230 KHz
Synchronous Buck Operation: Yes
Diode Emulation Mode: Yes
Hiccup Mode Overload Protection: Yes
External VCC Sourcing: No
SOURCE POWER
The power supply and cabling must present low impedance
to the evaluation board. Insufficient cabling or a high
impedance power supply will droop during power supply application with the evaluation board inrush current. If large
enough, this droop will cause a chattering condition during
power up. During power down, insufficient cabling or a high
impedance power supply will overshoot. This overshoot will
cause a non-monotonic decay on the output.
An additional external bulk input capacitor may be required
unless the output voltage droop/overshoot of the source power is less than 0.5V. In this board design, UVLO setting is
conservative while UVLO hysteresis setting is aggressive.
Minimum input voltage can goes down with an aggressive
design. Minimum operating input voltage depends on the output voltage droop/overshoot of the source power supply and
the forced off-time of the LM25119. Refer to the LM25119
datasheet for complete design information.
When applying power to the LM25119 evaluation board, certain precautions need to be followed. A misconnection can
damage the assembly.
LOADING
When using an electronic load, it is strongly recommended to
power up the evaluation board at light load and then slowly
increase the load. If it is desired to power up the evaluation
board at maximum load, resistor banks must be used. In general, electronic loads are best suited for monitoring steady
state waveforms.
PROPER BOARD CONNECTION
The input connections are made to the J1 (VIN) and J2 (RTN/
GND) connectors. The CH1 load is connected to the J3
(OUT1+) and J4 (OUT1-/GND) and the CH2 load is connect-
AIR FLOW
Prolonged operation with high input voltage at full power will
cause the MOSFETs to overheat. A fan with a minimum of
200LFM should be always provided.
Powering and Loading
Consideration
FIGURE 1. Typical Evaluation Setup
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301261
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30126101
LM25119 Evaluation Board
LM25119 Evaluation Board
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LOAD TRANSIENT
Figure 3 shows the transient response for a load of change
from 2A to 6A on 3.3V output. The upper waveform shows
output voltage droop and overshoot during the sudden
change in output current shown by the lower waveform.
QUICK START-UP PROCEDURE
STEP 1: Set the power supply current limit to at least 20A.
Connect the power supply to J1 and J2.
STEP 2: Connect one load with an 8A capacity between J3
and J4. Connect another load with an 8A capacity between
J6 and J5.
STEP 3: Set input voltage to 12V and turn it on.
STEP 4: Measure the output voltages. CH1 should regulate
at 3.3V and CH2 should regulate at 1.8V.
STEP 5: Slowly increase the load current while monitoring the
output voltages. The outputs should remain in regulation up
to full load current.
STEP 6: Slowly sweep the input voltage from 6.0V to 36V
while monitoring the output voltages. The outputs should remain in regulation.
Waveforms
SOFT START
When applying power to the LM25119 evaluation board a
certain sequence of events occurs. Soft-start capacitors and
other components allow for a linear increase in output voltages. The soft-start time of each output can be controlled
independently. Figure 2 shows the output voltage during a
typical start-up with a load of 0.5Ω on the 3.3V output, and
0.33Ω on the 1.8V output, respectively.
30126103
Conditions:
Input Voltage = 12VDC
Output Current 2A to 6A
Traces:
Top Trace: 3.3V Output Voltage, Volt/div = 100mV, AC coupled
Bottom Trace: Output Current Amp/Div = 2A
Horizontal Resolution = 0.5 ms/div
FIGURE 3. Load Transient Response
OVER LOAD PROTECTION
The evaluation board is configured with hiccup mode overload protection. The restart time can be programmed by C11.
Figure 4 shows hiccup mode operation in the event of an output short on CH1 output. One channel may operate in the
normal mode while the other is in hiccup mode overload protection.
30126102
Conditions:
Input Voltage = 12VDC
0.5Ω Load on 3.3V output
0.33Ω Load on 1.8V output
Traces:
Top Trace: 3.3V Output Voltage, Volt/div = 1V
Bottom Trace: 1.8V Output Voltage, Volt/div = 1V
Horizontal Resolution = 1 ms/div
FIGURE 2. Start-up with Resistive Load
30126104
Conditions:
Input Voltage = 12VDC
Output Short on 3.3V
Traces:
Top Trace: SW voltage on CH1, Volt/div = 10V
Bottom Trace: Inductor Current Amp/div = 10A
Horizontal Resolution = 20 ms/div
FIGURE 4. Short Circuit
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Performance Characteristics
Figure 7 shows the efficiency curves. The efficiency of the
power converter is 90% at 12V with full load current. Monitor
the current into and out of the evaluation board. Monitor the
voltage directly at the input and output terminals of the evaluation board.
30126105
Conditions:
Input Voltage = 12VDC
8A on 3.3V output
8A on 1.8V output
Traces:
Top Trace: SYNC pulse, Volt/div = 5V
Middle Trace: SW voltage on CH1, Volt/div = 10V
Bottom Trace: SW voltage on CH2, Volt/div = 10V
Horizontal Resolution = 1 µs/div
30126107
FIGURE 7. Typical Efficiency vs Load Current
FIGURE 5. Clock Synchronization
SHUTDOWN
Figure 6 shows the shutdown procedure by powering off the
source power. When UVLO pin voltage is less than 1.26V, the
switching stops and soft-start capacitors are discharged by
internal switches.
30126106
Conditions:
Input Voltage = 12VDC
0.5Ω Load on 3.3v output
Traces:
Top Trace: Input Voltage, Volt/div = 10V
Middle Trace1: 3.3V Output, Volt/div = 2V
Middle Trace2: VCC, Volt/div = 5V
Bottom Trace: SS voltage, Volt/div = 5V
Horizontal Resolution = 20 ms/div
FIGURE 6. Shutdown
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EXTERNAL CLOCK SYNCHRONIZATION
A TP1 (SYNC) test point has been provided on the evaluation
board in order to synchronize the internal oscillator to an external clock. Figure 5 shows the synchronized switching operation. Each channel operates 180 degrees out of phase
from the other.
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EXTERNAL VCC SUPPLY & VCC DISABLE
External VCC supply helps to reduce the temperature and the
power loss of the LM25119 at high input voltage. By populating D3 and D4, VCC can be supplied from an external power
supply. Use TP3 as an input of the external VCC supply with
0.1A current limit. R36, R35 and C45 should be populated
with proper value when the voltage of the external VCC is
smaller than 7V. The voltage at the VCCDIS pin can be monitored at TP2. To prevent a reverse current flow from VCC to
VIN through the internal diode, the external VCC voltage
should always be lower than VIN.
Board Configuration
INTERLEAVED BUCK OPERATION FOR SINGLE 3.3V
16A OUTPUT
The evaluation board is designed to be easily converted to a
3.3V, 16A single output regulator with the interleaved operation. Proper electronic load connection is shown in Figure 8.
Connecting the electronic load at the center of shorting bar is
recommended to prevent a voltage difference between CH1
and CH2 output. In order to produce a single 3.3V output with
16A maximum output current, populate R21 and R22 with
0Ω resistor and open R6, C15 and C14. The electronic load
should have over 16A capability to test the interleaved operation.
LOOP RESPONSE
TP5 and TP6 (TP7 and TP8) have been provided in order to
measure the loop transfer function of CH1 (CH2). Refer to
AN-1889 for detail information about the loop transfer function
measurement.
30126108
FIGURE 8. Load Connection for Single Output
30126109
FIGURE 9. Loop Response Measurement Setup
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Evaluation Board Schematic
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TABLE 1. Bill of Materials
Part
Value
Package
Part Number
Manufacturer
C1,C2,C3,C4,C5,C32,
C35,C36,C37,C38,C39
,C40,C41,C42
2.2 µF, 50V, X7R
1210
C3225X7R1H225K
TDK
TDK
C6,C7,C25,C29
1µF, 16V, X7R
0603
C1608X7R1C105K
C8,C10,C14,C16
100pF, 50V, C0G
0603
C1608C0G1H101J
TDK
C9
0.47µF, 50V, X7R
0805
UMK212B7474KG
Taiyo Yuden
C11,C18,C19
0.47µF, 25V, X7R
0603
GRM188R71E474KA12
Murata
C12,C13
0.047µF, 16V, X7R
0603
C1608X7R1C473K
TDK
C15,C17
6800pF, 25V, C0G
0603
C1608C0G1E682J
TDK
C20,C21
820pF, 50V, C0G
0603
C1608C0G1H821J
TDK
C22,C26
680µF, 6.3V
Φ10
APXA6R3ARA681MJC0G
NIPPON CHEMICON
C23,C24,C27,C28
22µF,10V, X7R
1210
C1210C226K8RAC
Kemet
C30,C31
1000pF, 50V, X7R
0603
C1608X7R1H102K
TDK
C33,C34
1000pF,100V, C0G
0805
C2012C0G2A102J
TDK
C43,C44,C45,C46,C47
NU
R1
3.9 ohm, 5%
0805
CRCW08053R90JNEA
Vishay
R2
52.3k, 1%
0805
MCR10EZHF5232
Rohm
R3
15k, 1%
0603
MCR03EZPFX1502
Rohm
R4
22.1k, 1%
0603
CRCW060322K1FKEA
Vishay
R5,R16,R21,R22,R35,
R36,R37
NU
R6,R7
36.5k, 1%
0603
CRCW060336K5FKEA
Vishay
R8,R9,
R23,R24,R29,R30,
R31, R32
10 ohm, 5%
0805
CRCW080510R0JNEA
Vishay
R10,R12
6.98k, 1%
0805
CRCW08056K98FKEA
Vishay
R11
2.21k, 1%
0805
MCR10EZHF2211
Rohm
R13
5.49k, 1%
0805
MCR10EZHF5491
Rohm
R14,R15
34k, 1%
0603
CRCW060334K0FKEA
Vishay
R17
0 ohm
0603
MCR03EZPJ000
Rohm
R18,R20
0.008 ohm, 1W, 1%
0815
RL3720WT-R008-F
Susumu
R25,R26
5.1 ohm, 1W, 1%
2512
ERJ-1TRQF5R1U
Panasonic-ECG
R27,R28
0 ohm, 5%
0805
MCR10EZPJ000
Rohm
D1,D2
60V, 1A
SOD123F
PMEG6010CEH
NXP
D3,D4
NU
L1,L2
6.8µH, 18.5A
18.2x18.3
7443556680
WE
Q1,Q2,Q3,Q4
40V, 58A
PowerPAK SO-8
SI7884BDP
Vishay
LLP32
LM25119
NSC
7693
Keystone
5002
Keystone
1040
Keystone
U1
J1,J2,J3,J4,J5,J6
TP1,TP2,TP3
15A
Φ10
TP5,TP6,TP7,TP8
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PCB Layout
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30126112
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30126114
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LM25119 Evaluation Board
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