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IRDC3841
SupIRBuck
DESCRIPTION
TM
USER GUIDE FOR IR3841 EVALUATION BOARD
The IR3841 is a synchronous buck converter, providing a compact, high performance and flexible solution in a small 5mmx6mm Power QFN package. Key features offered by the IR3841 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.
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 IR3841 evaluation board. The guide describes operation and use of the evaluation board itself. Detailed application information for IR3841 is available in the IR3841 data sheet.
BOARD FEATURES * Vin = +12V (13.2V Max) * Vcc=+5V (5.5V Max) * Vout = +1.8V @ 0- 8A * Fs=600kHz * L= 1.0uH * Cin= 4x10uF (ceramic 1206) + 330uF (electrolytic) * Cout= 6x22uF (ceramic 0805)
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IRDC3841
CONNECTIONS and OPERATING INSTRUCTIONS
A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum 8A 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. IR3841 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 IR3841, the voltage at Seq. pin should not exceed Vcc. Table I. Connections
Connection VIN+ VINVcc+ VccVOUTVOUT+ Enable Seq. P_Good Signal Name Vin (+12V) Ground of Vin Vcc input Ground for Vcc input Ground of Vout Vout (+1.8V) Enable Sequence Input Power Good Signal
LAYOUT
The PCB is a 4-layer board. All of layers are 2 Oz. copper. The IR3841 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 IR3841. 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. 02/02/2009
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IRDC3841
Connection Diagram
Vin
GND
Enable
GND
Seq AGND Vo
PGood
SS
Vcc
GND
Fig. 1: Connection diagram of IR384x evaluation boards
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IRDC3841
Fig. 2: Board layout, top overlay
Fig. 3: Board layout, bottom overlay (rear view)
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IRDC3841
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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1
1
C26 R1 3.01K 10000pF U1 En Seq1 Boot Seq Vin 12 FB COMP AGnd Rt PGND PGnd 1 10 C30 N/S SS Vcc OCset 8 9 VCC 15 R12 3.09k L1 1.0uH C29 N/S C28 N/S C27 N/S C20 22uF 2 Agnd 3 4 1
14
13
1
PGood
R9 23.7K 7 C10 0.1uF
AGnd1
1
1
1
1
1
4.02K R3 2.55K A B
2
0
Optional +5V supply for Vcc
Single point of connection between Power Ground and Signal ( "analog" ) Ground
IRDC3841
Fig. 6: Schematic of the IR3841 evaluation board
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Vin 1 Enable R18 1 4.99K C25 N/S C7 0.1uF C5 10uF C2 10uF C3 10uF C4 10uF C6 N/S Vin+ Vin+ R19 750 + C1 330uF Vin1 1 C24 C11 150pF 0.1uF VinVout 1 Vout+ Vout+
Seq.
VCC
R14 N/S
R16 0
R28 N/S
IR3841
SW
11
1 C14 0.1uF C19 22uF C18 C17 C16 22uF 22uF 22uF C15 22uF 1
5 SS 6
Vout-
Vcc-
Vcc+
Vout1
VCC
R17 10K
C13 0.1uF Vin R7 N/S C8 2200pF R2 R6 20
+ C21 N/S C22 N/S C35 N/S
+ C36 N/S
PGood
R4 130
Q1 MMBT3904-TP R5 3.30K
Vcc
R*
C32 0.1uF
D1 MM3Z5V6B
C34 10uF
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IRDC3841
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 23 24
1 1 4 6 1 1 6 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
C1 C34 C3 C4 C5 C2 C7 C10 C13 C14 C24 C32 C8 C11 C15 C16 C17 C18 C19 C20 C26 D1 L1 Q1 R5 R18 R4 R6 R9 R16 R12 R17 R19 R1 R2 R3 U1
330uF 10uF 10uF 0.1uF 2200pF 150pF 22uF 10000pF MM3Z5V6B 1.0uH MMBT3904/SOT 3.3k 4.99k 130 20 23.7k 0 3.09k 10.0k 750 3.01k 4.02k 2.55k IR3841
SMD Elecrolytic, Fsize, 25V, 20% 0805, 10V, X5R, 20% 1206, 16V, X5R, 20% 0603, 25V, X7R, 10% 0603, 50V, NP0, 5% 0603, 50V, NP0, 5% 0805, 6.3V, X5R, 20% 0603, 50V, X7R, 10% MM3Z5V6B,Zener, 5.6V 11.5x10x4mm, 20%, 3mOhm 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, 0603,1/10W,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 6mmx5mm, 8A SupIRBuck
Panasonic Panasonic - ECG Panasonic - ECG Panasonic - ECG Murata Panasonic- ECG Panasonic- ECG Panasonic - ECG Fairchild Delta Fairchild Rohm Rohm Panasonic - ECG Vishey/Dale Rohm Vishay/Dale Rohm Rohm Rohm Rohm Rohm Rohm International Rectifier
EEV-FK1E331P ECJ-GVB1A106M ECJ-3YB1C106M ECJ-1VB1E104K GRM1885C1H222JA01D ECJ-1VC1H151J ECJ-2FB0J226M ECJ-1VB1H103K MM3Z5V6B MPO104-1R0IR MMBT3904/SOT MCR03EZPFX3301 MCR03EZPFX4991 ERJ-3EKF1300V CRCW060320R0FKEA MCR03EZPFX2372 CRCW06030000Z0EA MCR03EZPFX3091 MCR03EZPFX1002 MCR03EZPFX7500 MCR03EZPFX3011 MCR03EZPFX4021 MCR03EZPFX2551 IR3841MPbF
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IRDC3841
TYPICAL OPERATING WAVEFORMS Vin=12.0V, Vcc=5V, Vo=1.8V, Io=0-8A, Room Temperature, No Air Flow
Fig. 7: Start up at 8A Load Ch1:Vin, Ch2:Vout, Ch3:Vss, Ch4:Enable
Fig. 8: Start up at 8A Load, Ch1:Vin, Ch2:Vout, Ch3:Vss, Ch4:VPGood
Fig. 9: Start up with 1.62V Pre Bias, 0A Load, Ch2:Vout, Ch3:VSS
Fig. 10: Output Voltage Ripple, 8A load Ch2: Vout
Fig. 11: Inductor node at 8A load Ch3:LX
Fig. 12: Short (Hiccup) Recovery Ch2:Vout , Ch3:Vss
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IRDC3841
TYPICAL OPERATING WAVEFORMS Vin=12V, Vcc=5V, Vo=1.8V, Io=0-8A, Room Temperature, No Air Flow
Fig. 13: Transient Response, 4A to 8A step 2.5A/us Ch1:Vout, Ch4:Iout
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IRDC3841
TYPICAL OPERATING WAVEFORMS Vin=12V, Vcc=5V, Vo=1.8V, Io=8A, Room Temperature, No Air Flow
Fig. 14: Bode Plot at 8A load shows a bandwidth of 127kHz and phase margin of 50 degrees
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IRDC3841
TYPICAL OPERATING WAVEFORMS Vin=12V, Vo=1.8V, Io=0- 8A, Room Temperature, No Air Flow
92.5 92.0 91.5 91.0 90.5 Efficiency (%) 90.0 89.5 89.0 88.5 88.0 87.5 87.0 86.5 86.0 85.5 10 20 30 40 50 60 70 80 90 100 Load Percentage (%)
Fig.15: Efficiency versus load current
1.6 1.5 1.4 1.3 1.2 Power Loss (W) 1.1 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 10 20 30 40 50 60 70 80 90 100 Load Percentage (%)
Fig.16: Power loss versus load current
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IRDC3841
THERMAL IMAGES Vin=12V, Vo=1.8V, Io=8A, Room Temperature, No Air Flow
Fig. 17: Thermal Image at 8A load Test points 1 and 2 are IR3841 and inductor, respectively.
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IRDC3841
Simultaneous Tracking at Power Up and Power Down Vin=12V, Vo=1.8V, Io=8A, Room Temperature, No Air Flow
In order to run the IR3841 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 pin. - 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: SEQ Ch3:Vout Ch4: SS
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IRDC3841
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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IRDC3841
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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IRDC3841
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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IRDC3841
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 02/02/2009

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