IRF IRDC3843A

IRDC3843A
SupIRBuck
TM
USER GUIDE FOR IR3843A EVALUATION BOARD
DESCRIPTION
Double Sided PCB
The IR3843A 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 IR3843A 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 startup, and pre-bias start-up.
This user guide contains the schematic and bill
of materials for the IR3843A evaluation board.
The guide describes operation and use of the
evaluation board itself. Detailed application
information for IR3843A is available in the
IR3843A data sheet.
BOARD FEATURES
• Vin = +12V (13.2V Max)
• Vcc=+5V (5.5V Max)
• Vout = +1.8V @ 0- 3A
• Fs=600kHz
• L= 2.2uH
• Cin= 1x10uF (ceramic 1206)
• Cout= 3x22uF (ceramic 0805)
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1
IRDC3843A
CONNECTIONS and OPERATING INSTRUCTIONS
A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum 3A 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.
IR3843A 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-.
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
LAYOUT
The PCB is a 4-layer board. All of layers are 2 Oz. copper. It is a double sided board with components
mounted on both sides.
Power supply decoupling capacitors, the Bootstrap capacitor and feedback components are located
close to IR3843A. 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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IRDC3843A
Connection Diagram
Vin
GND
Enable
GND
Seq
TOP SIDE
AGND
Vo
PGood
SS
Vcc GND
BOTTOM SIDE
Fig. 1: Connection diagram of IR384xA evaluation boards
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3
IRDC3843A
Fig. 2: Board layout, top overlay
Fig. 3: Board layout, bottom overlay (rear view)
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IRDC3843A
Fig. 4: Board layout, mid-layer I.
Fig. 5: Board layout, mid-layer II.
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5
1
PGood
1
Vcc-
N/S
VCC
R20
Seq.
R16
0
23.7K
R9
GND
SS
C10
0.1uF
R19
7.5K
7
6
5
4
3
2
1
C13
1uF
VCC
OCset
SS
Rt
AGnd1
COMP
FB
seq
U1
Enable
1
IR3843A
3.16k
R3
130
R4
C8
10
11
12
2200pF
4.99K
R2
PGnd
SW
Vin
49.9K
R18
A
20
R6
0.1uF
C24
R12
2.26K
B
1
C3
N/S
C2
10uF
1
1
Vin-
Vin+
Vin (+12V)
2.2uH
L1
C18
N/S
C17
22uF
Ceramic cap 16V 10uF 1206
C7
0.1uF
Fig. 6: Schematic of the IR3843A evaluation board
8.2nF
C26
180pF
2.74K
R1
C11
1
14
Enable
Vcc
9
1
R17
10.0K
Vcc+
1
PGood
8
1
13
Boot
AGnd2
15
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1
VCC
22uF
C16
22uF
C15
1
C14
0.1uF
1
Vout-
Vout+
Vout (+1.8V)
IRDC3843A
6
IRDC3843A
Bill of Materials
Ite
m
Quantit
y
1
1
C2
2
4
3
Description
Manufacturer
10uF
10uF,1206,16V, X7R, 20%
Panasonic - ECG
ECJ-3YX1C106K
C7 C14 C24 C10
0.1uF
0603, 25V, X7R, 10%
Panasonic
ECJ-1VB1E104K
1
C8
2200pF
0603,50V,X7R, 10%
Panasonic
ECJ-1VB1H222K
4
1
C11
180pF
50V, 0603, NP0, 5%
Murata
GRM1885C1H181JA01D
5
1
C13
1uF
16V, 0603, X5R, 10%
Murata
GRM188R61C105KA93B
6
3
C15 C16 C17
22uF
0805, 6.3V, X5R, 20%
Panasonic
ECJ-2FB0J226M
C3,C18
Not used
7
Part Reference
Value
Part Number
8
1
C26
8200pF
0603, 50V, X7R, 10%
Panasonic
ECJ-1VB1H822K
9
1
L1
2.2uH
7.05*6.6*4.8mm,12.5mΩ max
Cyntec
PCMB065T-2R2MS
10
1
R1
2.74k
0603,1/10W,1%
Rohm
MCR03EZPFX2741
11
1
R2
4.99k
0603,1/10W,1%
Rohm
MCR03EZPFX4991
12
1
R3
3.16k
0603,1/10W,1%
Rohm
MCR03EZPFX3161
13
1
R4
130
0603,1/10W,1%
Panasonic
ERJ-3EKF1300V
14
1
R6
20
0603,1/10 W,1%
Vishay/Dale
CRCW060320R0FKEA
15
1
R9
23.7K
0603,1/10W,1%
Rohm
MCR03EZPFX2372
16
1
R16
0
0603,1/10 W,5%
Vishay/Dale
CRCW06030000Z0EA
17
1
R12
2.26K
0603,1/10 W,1%
Rohm
MCR03EZPFX2261
18
1
R17
10K
0603,1/10 W,1%
Rohm
MCR03EZPFX1002
19
1
R18
49.9k
0603,1/10 W,1%
Rohm
MCR03EZPFX4992
20
1
R19
7.5k
0603,1/10W,1%
Rohm
MCR03EZPFX7501
R20
Not used
U1
IR3843A
3A SupIRBuck, PQFN 5x6mm
International
Rectifier
IR3843AMPbF
21
22
1
02/09/10
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IRDC3843A
TYPICAL OPERATING WAVEFORMS
Vin=12.0V, Vcc=5V, Vo=1.8V, Io=0-3A, Room Temperature, No Air Flow
Fig. 7. Start up at 3A Load
Ch1:Vin, Ch2:Vo, Ch3:Vss, Ch4:Enable
Fig. 8. Start up at 3A 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, 3A load
Ch2: Vo
Fig. 11. Inductor node at 3A load
Ch1:LX
Fig. 12. Short (Hiccup) Recovery
Ch2:Vo , Ch3:VSS
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IRDC3843A
TYPICAL OPERATING WAVEFORMS
Vin=12V, Vcc=5V, Vo=1.8V, Io=0-3A, Room Temperature, No Air Flow
Fig. 13. Transient Response, 1.5A to 3A step 2.5A/μs
Ch2:Vo
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IRDC3843A
TYPICAL OPERATING WAVEFORMS
Vin=12V, Vcc=5V, Vo=1.8V, Io=3A, Room Temperature, No Air Flow
Fig. 14. Bode Plot at 3A load shows a bandwidth of 83.8KHz and phase margin of 59.8°
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IRDC3843A
TYPICAL OPERATING WAVEFORMS
Vin=12V, Vcc=5V, Vo=1.8V, Io=0- 3A, Room Temperature, No Air Flow
IR3843A
92
90
Efficiency(%)
88
86
84
82
80
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
2.7
3
Iout(A)
Fig.15: Efficiency versus load current
IR3843A
0.700
Power Dissipation(W)
0.600
0.500
0.400
0.300
0.200
0.100
0.000
0.3
0.6
0.9
1.2
1.5
1.8
2.1
2.4
2.7
3
Iout(A)
Fig.16: Power loss versus load current
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11
IRDC3843A
THERMAL IMAGE
Vin=12V, Vcc=5V, Vo=1.8V, Io=3A, Room Temperature, No Air Flow
Fig. 17: Thermal Image at 3A load
Test points 1 and 2 are IR3843A and inductor, respectively.
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IRDC3843A
PCB Metal and Components Placement
Lead lands (the 11 IC pins) width should be equal to nominal part lead width. The minimum lead to
lead spacing should be ≥ 0.2mm to minimize shorting.
Lead land length should be equal to maximum part lead length + 0.3 mm outboard extension. The
outboard extension ensures a large and inspectable toe fillet.
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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IRDC3843A
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 misalignment.
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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IRDC3843A
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.
02/09/10
IRDC3843A
BOTTOM VIEW
IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (320) 252-7105
TAC Fax: (320) 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. 01/10
02/09/10