Reference Design - IRDC3843W

IRDC3843W
SupIRBuck
TM
USER GUIDE FOR IR3843W EVALUATION BOARD
DESCRIPTION
The IR3843W is a synchronous buck
converter, providing a compact, high
performance and flexible solution in a small
5mmx6mm Power QFN package.
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.
Key features offered by the IR3843W
include programmable soft-start ramp,
precision 0.7V reference voltage, Power
Good, thermal protection, programmable
switching frequency, Sequence input,
Enable input, input under-voltage lockout for
proper start-up, and pre-bias start-up.
This user guide contains the schematic and bill
of materials for the IR3843W evaluation board.
The guide describes operation and use of the
evaluation board itself. Detailed application
information for IR3843W is available in the
IR3843W data sheet.
BOARD FEATURES
• Vin = +12V (13.2V Max)
• Vcc=+5V (5.5V Max)
• Vout = +1.8V @ 0- 2A
• Fs=600kHz
• L= 3.3uH
• Cin= 1x10uF (ceramic 1206) + 330uF (electrolytic)
• Cout= 2x22uF (ceramic 0805)
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IRDC3843W
CONNECTIONS and OPERATING INSTRUCTIONS
A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum 2A 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.
IR3843W 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 IR3843W, 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
P_Good
Power Good Signal
LAYOUT
The PCB is a 4-layer board. All of layers are 2 Oz. copper. The IR3843W 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 IR3843W. 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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IRDC3843W
Connection Diagram
Vin
GND
Enable
GND
Seq
AGND
Vo
PGood
SS
Vcc
GND
Fig. 1: Connection diagram of IR384xW evaluation boards
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IRDC3843W
Fig. 2: Board layout, top overlay
Fig. 3: Board layout, bottom overlay (rear view)
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IRDC3843W
PGND
Plane
Single point
connection
between AGND
and PGND.
AGND
Plane
Fig. 4: Board layout, mid-layer I.
Fig. 5: Board layout, mid-layer II.
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5
Vcc-
PGood
1
1
R17
10K
Vcc+
R14
N/S
1
VCC
R28
N/S
R16
0
C11
180pF
Agnd
C26
R1
2.74k 8.2nF
R9
23.7K
1
SS
C10
0.1uF
7
6
5
4
3
2
Seq1
R19
7.5k
1
IR3843W
4.99K
R2
R3
3.16K ohm
158ohm
R4
C13
0.1uF
VCC
PGnd
SW
Vin
49.9K
R18
10
11
12
PGND
A
B
0
R*
L1
3.3uH
IHLP2525EZ-01 3.3uH
Vin
C30
N/S
R7
N/S
C29
N/S
C7
0.1uF
Ground and Signal ( “analog” ) Ground
Single point of connection between Power
R6
20
C8
2200pF
R12
1.54K
0.1uF
C24
1
1
Fig. 6: Schematic of the IR3843W evaluation board
OCset
SS
Rt
AGnd
COMP
FB
Seq
U1
C25
N/S
13
Boot
14
En
PGood
8
Vcc
9
AGnd1
15
1
Enable
1
VCC
1
Seq.
C21
N/S
C28
N/S
C19
N/S
C18
N/S
C4
N/S
C17
N/S
C3
N/S
+
+
C36
N/S
Optional +5V supply for Vcc
D1
MM3Z5V6B
Q1
MMBT3904-TP
C35
N/S
2X22uF,0805,6.3V
C20
N/S
C5
N/S
C32
0.1uF
R5
3.30K
C22
N/S
C27
N/S
C6
N/S
2
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1
Vcc
C16
22uF
C2
10uF
C34
1uF
C15
22uF
+
C1
330uF
1
1
1
1
1
1
1
1
C14
0.1uF
Vout
Vin
Vout-
Vout-
Vout+
Vout+
Vin-
Vin-
Vin+
Vin+
IRDC3843W
6
IRDC3843W
Bill of Materials
Item
Quantity
Part Reference
Value
Description
Manufacturer
Part Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
1
1
6
1
1
2
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
C2
C1
C7 C14 C24 C10 C13 C32
C8
C11
C15 C16
C26
L1
R1
R2
R3
R4
R6
R9
R16
R12
R17
R18
R19
R5
C34
D1
10uF
330uF
0.1uF
2200pF
180pF
22uF
8200pF
3.3uH
2.74k
4.99k
3.16k
158
20
23.7K
0
1.54K
10K
49.9k
7.5k
3.3k
1uF
MM3Z5V6B
1206,16V, X7R, 20%
SMD Elecrolytic, Fsize, 25V, 20%
0603, 25V, X7R, 10%
2200pF,0603,50V,X7R
50V, 0603, NP0, 5%
0805, 6.3V, X5R, 20%
0603, 50V, X7R, 10%
6.9x6.5x5mm, 8A,20%
0603,1/10W,1%
0603,1/10W,1%
0603,1/10W,1%
0603,1/10W,1%
0603,1/10 W,1%
0603,1/10W,1%
0603,1/10 W,5%
0603,1/10 W,1%
0603,1/10 W,1%
0603,1/10 W,1%
0603,1/10W,1%
0603,1/10W,1%
1uF, 10V, X5R,0805
Zener,5.6V
Panasonic - ECG
Panasonic
Panasonic
Panasonic
Panasonic
Panasonic
Panasonic
Vishay/Dale
Rohm
Rohm
Rohm
Panasonic
Vishay/Dale
Rohm
Vishay/Dale
Rohm
Rohm
Rohm
Rohm
Rohm
Panasonic
Fairchild
ECJ-3YX1C106K
EEV-FK1E331P
ECJ-1VB1E104K
ECJ-1VB1H222K
ECJ-1VC1H181J
ECJ-2FB0J226M
ECJ-1VB1H822K
IHLP2525EZ-01 3.3uH
MCR03EZPFX2741
MCR03EZPFX4991
MCR03EZPFX3161
ERJ-3EKF1580V
CRCW060320R0FKEA
MCR03EZPFX2372
CRCW06030000Z0EA
MCR03EZPFX1541
MCR03EZPFX1002
MCR03EZPFX4992
MCR03EZPFX7501
MCR03EZPFX3301
ECJ-2FB1C105K
MM3Z5V6B
23
24
1
1
Q1
U1
MMBT3904/SOT
IR3843W
NPN, 200mA, 40V, SOT23
2A SupIRBuck. PQFN 5x6mm
Fairchild
International Rectifier
MMBT3904/SOT
IR3843WMPbF
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IRDC3843W
TYPICAL OPERATING WAVEFORMS
Vin=12.0V, Vcc=5V, Vo=1.8V, Io=0-2A, Room Temperature, No Air Flow
Fig. 17. Start up at 2A Load
Ch1:Vin, Ch2:Vo, Ch3:Vss, Ch4:Enable
Fig. 18. Start up at 2A Load,
Ch1:Vin, Ch2:Vo, Ch3:Vss, Ch4:VPGood
Fig. 19. Start up with 1.62V Pre Bias, 0A
Load, Ch2:Vo, Ch3:VSS
Fig. 20. Output Voltage Ripple, 2A load
Ch2: Vo
Fig. 21. Inductor node at 2A load
Ch2:LX
Fig. 22. Short (Hiccup) Recovery
Ch2:Vo , Ch3:VSS
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IRDC3843W
TYPICAL OPERATING WAVEFORMS
Vin=12V, Vcc=5V, Vo=1.8V, Io=0-2A, Room Temperature, No Air Flow
Fig. 23. Transient Response, 1A to 2A step 2.5A/s
Ch1:Vo, Ch4:Io
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IRDC3843W
TYPICAL OPERATING WAVEFORMS
Vin=12V, Vcc=5V, Vo=1.8V, Io=2A, Room Temperature, No Air Flow
Fig. 24. Bode Plot at 2A load shows a bandwidth of 85.54kHz and phase margin of 55.509
degrees
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IRDC3843W
TYPICAL OPERATING WAVEFORMS
Vin=12V, Vo=1.8V, Io=0- 2A, Room Temperature, No Air Flow
93
91
89
Efficiency (%)
87
85
83
81
79
77
75
10
20
30
40
50
60
70
80
90
100
Load Percentage (%)
Fig.15: Efficiency versus load current
0.45
0.4
Power Loss (W)
0.35
0.3
0.25
0.2
0.15
0.1
0.05
0
10
20
30
40
50
60
70
80
90
100
Load Percentage (%)
Fig.16: Power loss versus load current
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IRDC3843W
THERMAL IMAGES
Vin=12V, Vo=1.8V, Io=2A, Room Temperature, No Air Flow
Fig. 17: Thermal Image at 2A load
Test points 1 and 2 are IR3843W and inductor, respectively.
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IRDC3843W
Simultaneous Tracking at Power Up and Power Down
Vin=12V, Vo=1.8V, Io=2A, Room Temperature, No Air Flow
In order to run the IR3843W 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 (4.99K) and R3 (3.16K), 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. 18: Simultaneous Tracking a 3.3V input at power-up and shut-down
Ch2: Vout Ch3:SS Ch4: Seq
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IRDC3843W
PCB Metal and Components Placement
The lead lands (the 11 IC pins) width should be equal to the nominal part lead width. The minimum
lead to lead spacing should be ≥ 0.2mm to minimize shorting.
Lead land length should be equal to the maximum part lead length + 0.3 mm outboard extension. The
outboard extension ensures a large and inspectable toe fillet.
The pad lands (the 4 big pads other than the 11 IC pins) length and width should be equal to
maximum part pad length and width. However, the minimum metal to metal spacing should be no less
than 0.17mm for 2 oz. Copper; no less than 0.1mm for 1 oz. Copper and no less than 0.23mm for 3 oz.
Copper.
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IRDC3843W
Solder Resist
It is recommended that the lead lands are Non Solder Mask Defined (NSMD). The solder resist
should be pulled away from the metal lead lands by a minimum of 0.025mm to ensure NSMD
pads.
The land pad should be Solder Mask Defined (SMD), with a minimum overlap of the solder resist
onto the copper of 0.05mm to accommodate solder resist mis-alignment.
Ensure that the solder resist in between the lead lands and the pad land is ≥ 0.15mm due to the
high aspect ratio of the solder resist strip separating the lead lands from the pad land.
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IRDC3843W
Stencil Design
•
•
The Stencil apertures for the lead lands should be approximately 80% of the area of the
lead lads. Reducing the amount of solder deposited will minimize the occurrences of lead
shorts. If too much solder is deposited on the center pad the part will float and the lead
lands will be open.
The maximum length and width of the land pad stencil aperture should be equal to the
solder resist opening minus an annular 0.2mm pull back to decrease the incidence of
shorting the center land to the lead lands when the part is pushed into the solder paste.
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IRDC3843W
BOTTOM VIEW
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. 11/07
10/27/2009