Reference Design - International Rectifier

IRDC3859
SupIRBuck
TM
USER GUIDE FOR IR3859 EVALUATION BOARD
DESCRIPTION
The IR3859 is a synchronous buck
converter, providing a compact, high
performance and flexible solution in a small
4mmx5mm Power QFN package.
Key features offered by the IR3859 include
programmable soft-start ramp, precision
0.7V reference voltage, Power Good,
thermal protection, over voltage protection,
programmable
switching
frequency,
synchronization to external clock, Sequence
input, Enable input, input under-voltage
lockout for proper start-up, and pre-bias
start-up.
An output over-current protection function is
implemented by sensing the voltage developed
across the on-resistance of the synchronous
rectifier MOSFET for optimum cost and
performance.
This user guide contains the schematic and bill
of materials for the IR3859 evaluation board.
The guide describes operation and use of the
evaluation board itself. Detailed application
information for IR3859 is available in the
IR3859 data sheet.
BOARD FEATURES
• Vin = +12V (13.2V Max)
• Vcc=+5V (5.5V Max)
• Vout = +1.8V @ 0- 9A
• Fs=600kHz
• L= 0.68uH
• Cin= 4x10uF (ceramic 1206) + 330uF (electrolytic)
• Cout= 6x22uF (ceramic 0805)
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IRDC3859
CONNECTIONS and OPERATING INSTRUCTIONS
A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum 9A load should be
connected to VOUT+ and VOUT-. The connection diagram is shown in Fig. 1 and inputs and outputs of the
board are listed in Table I.
IR3859 has two input supplies, one for biasing (Vcc) and the other as input voltage (Vin). Separate supplies
should be applied to these inputs. Vcc input should be a well regulated 4.5V-5.5V supply and it would be
connected to Vcc+ and Vcc-.
If single 12V application is required connect R7 (zero Ohm resistor) which enables the on board bias
regulator (see schematic). In this case there is no need of external Vcc supply.
The output can track a sequencing input at the start-up. For sequencing application, R16 should be
removed and the external sequencing source should be applied between Seq. and Agnd. The value of R14
and R28 can be selected to provide the desired ratio between the output voltage and the tracking input. For
proper operation of IR3859, the voltage at Seq. pin should not exceed Vcc.
Table I. Connections
Connection
Signal Name
VIN+
Vin (+12V)
VIN-
Ground of Vin
Vcc+
Vcc input
Vcc-
Ground for Vcc input
VOUT-
Ground of Vout
VOUT+
Vout (+1.8V)
Enable
Enable
Seq.
Sequence Input
PGood
Power Good Signal
SYNC
External Synchronization Clock
LAYOUT
The PCB is a 4-layer board. All of layers are 2 Oz. copper. The IR3859 SupIRBuck and all of the
passive components are mounted on the top side of the board.
Power supply decoupling capacitors, the Bootstrap capacitor and feedback components are located
close to IR3859. The feedback resistors are connected to the output voltage at the point of regulation
and are located close to the SupIRBuck. To improve efficiency, the circuit board is designed to
minimize the length of the on-board power ground current path.
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IRDC3859
Connection Diagram
Vin
GND
Enable
GND
Seq
AGND
Vout
SS
Vcc GND
PGood
Syc.
Fig. 1: Connection diagram of IR385x evaluation boards
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IRDC3859
Fig. 2: Board layout, top overlay
Single point
connection
between AGND
and PGND.
Fig. 3: Board layout, bottom overlay (rear view)
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IRDC3859
Fig. 4: Board layout, mid-layer I.
Fig. 5: Board layout, mid-layer II.
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1
PGood
1
1
R17
10K
R9
23.7K
R1
1.65k
C11
SS
C12
0.01uF
C10
0.1uF
Sy nc
6
5
8
3
1
U1
SS
Rt
PGood
COMP
FB
Vsns
seq
2.55k
R3
4.02k
R7
4.02K
130
R2
PGnd
Vcc
OCset
R4
IR3859
SW
Vin
0.1uF
C24
49.9K
R18
11
10
7
SW
PGND
B
C5
10uF
0
R50
L1
0.68uH
C7
0.1uF
C4
10uF
R11
N/S
N/S
Vin
C22
N/S
Ground and Signal ( “analog” ) Ground
D1
MM3Z5V6B
Vcc
N/S
N/S
22uF
Q1
MMBT3904-TP
+ C36
+ C35
C20
C14
0.1uF
1
1
1
1
Optional +5V supply for Vcc
C32
0.1uF
R8
3.30K
22uF
C21
C15
22uF
C16
Vout
22uF
Vin-
Vin-
Vin+
Vin+
C17
1
1
1
1
22uF 22uF
330uF
C1
Vin
C18
C2 +
10uF
C23
C3
10uF
Single point of connection between Power
A
C8
2200pF
R6
20
3.16k
C19
1uF
VCC
R12
12 N262216
13
0
R10
Fig. 6: Schematic of the IR3859 evaluation board
R5
2.55k
10000pF
270pF C26
2
16
R19
N/S 7.5k
C37
1
15
Enable
1
1
Vcc+ VCC
1
Vcc-
R28
N/S
1
AGnd1
4
Sync
9
14
Boot
Enable
17
AGnd2
R16
0
1
R14
N/S
1
1
VCC
1
Seq.
2
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1
AGND
C34
10uF
Vout-
Vout+
Vout-
Vout+
IRDC3859
6
IRDC3859
Bill of Materials
Item Quantity Part Reference
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
1
4
1
1
1
5
1
1
6
1
1
1
1
1
1
1
1
1
3
1
2
1
1
1
2
1
C1
C5 C4 C3 C2
C34
C19
C12
C7 C10 C14 C24 C32
C8
C11
C15 C16 C17 C18 C20 C21
C26
D1
L1
Q1
R8
R18
R4
R6
R9
R16 R10 R50
R12
R3 R5
R17
R19
R1
R2 R7
U1
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Value
Description
Manufacturer
Part Number
330uF
10uF
10uF
1uF
0.01uF
0.1uF
2200pF
270pF
22uF
10000pF
MM3Z5V6B
0.68uH
MMBT3904/SOT
3.3k
49.9k
130
20
23.7k
0
3.16k
2.55k
10.0k
7.50k
1.65k
4.02k
IR3859
SMD Elecrolytic, Fsize, 25V, 20%
1206, 25V, X5R, 20%
0805, 10V, X5R, 20%
0603, 16V, X7R, 10%
0603, 50V, X7R, 10%
0603, 25V, X7R, 10%
0603, 50V, NP0, 5%
0603, 50V, NP0, 5%
0805, 6.3V, X5R, 20%
0603, 25V, X7R, 10%
MM3Z5V6B,Zener, 5.6V
11.7x10x4mm, 20%, 1.5mOhm
NPN, 40V, 200mA, SOT-23
Thick Film, 0603,1/10W,1%
Thick Film, 0603,1/10W,1%
Thick Film, 0603,1/10W,1%
Thick Film, 0603,1/10 W,1%
Thick Film, 0603,1/10W,1%
Thick Film, 0603,1/10 W,5%
Thick Film, 0603,1/10 W,1%
Thick Film, 0603,1/10 W,1%
Thick Film, 0603,1/10W,1%
Thick Film, 0603,1/10W,1%
Thick Film, 0603,1/10W,1%
Thick Film, 0603,1/10W,1%
PQFN 4mmx5mm, 9A SupIRBuck
Panasonic
Murata
TDK
TDK
TDK
TDK
Murata
Murata
TDK
TDK
Fairchild
Panasonic
Fairchild
Rohm
Rohm
Panasonic - ECG
Vishey/Dale
Rohm
Vishay/Dale
Rohm
Rohm
Rohm
Rohm
Rohm
Rohm
International Rectifier
EEV-FK1E331P
GRM31CR61E106MA12L
C2012X5R1A106KB
C1608X7R1C105K
C1608X7R1H103K
C1608X7R1H104KB
GRM1885C1H222JA01D
GRM1885C1H271JA01D
C2012X5R0J226M
C1608X7R1E103K
MM3Z5V6B
ETQP4LR68XFC
MMBT3904/SOT
MCR03EZPFX3301
MCR03EZPFX4992
ERJ-3EKF1300V
CRCW060320R0FKEA
MCR03EZPFX2372
CRCW06030000Z0EA
MCR03EZPFX3161
MCR03EZPFX2551
MCR03EZPFX1002
MCR03EZPFX7501
MCR03EZPFX1651
MCR03EZPFX4021
IR3859MPbF
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IRDC3859
TYPICAL OPERATING WAVEFORMS
Vin=12.0V, Vcc=5V, Vo=1.8V, Io=0-9A, Room Temperature, No Air Flow
Fig. 7. Start up at 9A Load
Ch1:Vin, Ch2:Vo, Ch3:Vss, Ch4:Enable
Fig. 8. Start up at 9A Load,
Ch1:Vin, Ch2:Vo, Ch3:Vss, Ch4:VPGood
Fig. 9. Start up with 1.62V Pre Bias, 0A
Load, Ch2:Vo, Ch3:VSS
Fig. 10. Output Voltage Ripple, 9A load
Ch2: Vo
Fig. 11. Inductor node at 9A load
Ch2:Switch Node
Fig. 12. Short (Hiccup) Recovery
Ch2:Vo , Ch3:VSS
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IRDC3859
TYPICAL OPERATING WAVEFORMS
Vin=12V, Vcc=5V, Vo=1.8V, Io=0-9A, Room Temperature, No Air Flow
Fig. 13. Transient Response, 4.5A to 9A step 2.5A/μs
Ch2:Vo, Ch4:Io
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IRDC3859
TYPICAL OPERATING WAVEFORMS
Vin=12V, Vcc=5V, Vo=1.8V, Io=9A, Room Temperature, No Air Flow
Fig. 14. Bode Plot at 9A load shows a bandwidth of 86.4kHz and phase margin of 55.6 degrees
Fig. 15. Synchronization to External Clock
Ch1:Switch node, Ch2: Sync. Pin
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IRDC3859
TYPICAL OPERATING WAVEFORMS
Vin=12V, Vo=1.8V, Io=0- 9A, Room Temperature, No Air Flow
92.0
91.5
91.0
Efficiency (%)
90.5
90.0
89.5
89.0
88.5
88.0
87.5
87.0
86.5
86.0
10
20
10
20
30
40
50
60
70
Load Percentage (%)
Fig.16: Efficiency versus load current
80
90
100
80
90
100
2.25
2.00
Power Loss (W)
1.75
1.50
1.25
1.00
0.75
0.50
0.25
30
40
50
60
70
Load Percentage(%)
Fig.17: Power loss versus load current
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IRDC3859
THERMAL IMAGES
Vin=12V, Vo=1.8V, Io=9A, Room Temperature, No Air Flow
Fig. 18: Thermal Image at 9A load
Test points 1 and 2 are IR3859 and inductor, respectively.
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IRDC3859
Simultaneous Tracking at Power Up and Power Down
Vin=12V, Vo=1.8V, Io=9A, Room Temperature, No Air Flow
In order to run the IR3859 in the simultaneous tracking mode, the following steps should be
taken:
- Remove R16 from the board.
- Set the value of R14 and R28 as R2 (4.02K) and R3 (2.55K), respectively.
- Connect the controlling input across SEQ and AGND test points on the board. This voltage
should be at least 1.15 time greater than Vo. For the following test results a 0-3.3V source is
applied to SEQ input.
- The controlling input should be applied after the SS pin is clamped to 3.0V.
Fig. 19: Simultaneous Tracking a 3.3V input at power-up and shut-down
Ch1: SEQ (3.3V) Ch3:Vout (1.8V) Ch4: SS (1.8V)
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IRDC3859
PCB Metal and Components Placement
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IRDC3859
Solder Resist
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IRDC3859
Stencil Design
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IRDC3859
IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105
TAC Fax: (310) 252-7903
This product has been designed and qualified for the Consumer market
Visit us at www.irf.com for sales contact information
Data and specifications subject to change without notice. 07/10
07/21/10