International Rectifier IR3821 Manuale utente

IRDC3821

Rev 0.1

01/07/2008 1

USER GUIDE FOR IR3821 EVALUATION BOARD

DESCRIPTION

The IR3821 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 IR3821 include

programmable soft-start ramp, precision

0.6V reference voltage, programmable

Power Good,thermal protection, fixed

600kHz switching frequency requiring no

external component, 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 IR3821 evaluation board.

The guide describes operation and use of the

evaluation board itself. Detailed application

information for IR3821 is available in the

IR3821 data sheet.

BOARD FEATURES

•Vin = +12V (13.2V Max)

•Vout = +1.8V @ 0- 7A

•L=1.0uH

•Cin=3x10uF (ceramic 1206) + 330uF (electrolytic)

•Cout=6x22uF (ceramic 0805)

SupIRBuckTM

IRDC3821

Rev 0.1

01/07/2008 2

A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum 7A 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.

IR3821 has two input supplies, one for biasing (Vcc) and the other as input voltage (Vin). These inputs are

connected on the board with a zero ohm resistor (R15). Separate supplies can be applied to these inputs.

Vcc input cannot be connected unless R15 is removed. Vcc input should be a well regulated 5V-12V supply

and it would be connected to Vcc+ and Vcc-.

CONNECTIONS and OPERATING INSTRUCTIONS

LAYOUT

The PCB is a 4-layer board. All of layers are 2Oz. copper. The IR3821 SupIRBuck and all of the

passive components are mounted on the top side of the board.

Power supply decoupling capacitors, the charge-pump capacitor and feedback components are located

close to IR3821. The feedback resistors are connected to the output voltage at the point of regulation

and are located close to SupIRBuck.

To improve efficiency, the circuit board is designed to minimize the length of the on-board power ground

current path.

Table I. Connections

Ground for Optional Vcc inputVcc-

Optional Vcc inputVcc+

Vout (+1.8V)VOUT+

Power Good SignalP_Good

Ground of Vout

VOUT-

Ground of Vin

VIN-

Vin (+12V)VIN+

Signal NameConnection

IRDC3821

Rev 0.1

01/07/2008 3

Fig. 1: Connection diagram of IR3821 evaluation board

Vin= +12v GROUND

Connection Diagram

VCC+

GROUND

PGood

VOUT = +1.8v

GROUND

IRDC3821

Rev 0.1

01/07/2008 4

Fig. 2: Board layout, top overlay

Fig. 3: Board layout, bottom overlay (rear view)

IRDC3821

Rev 0.1

01/07/2008 5

Fig. 4: Board layout, mid-layer I

Fig. 5: Board layout, mid-layer II

Single point

connection

between AGND

and PGND.

AGND

Plain PGND

Plain

IRDC3821

Rev 0.1

01/07/2008 6

Fig. 6: Schematic of the IR3821 evaluation board

Single point of connection between Power

Ground and Signal ( “analog” ) Ground

Vout-

C21

N/S

C22

N/S

Vin

C14

0.1uF

Vcc-

C10

0.22uF

PGND

C12

0.1uF

C24

560pF

C23

Open

BAT54S

C26

1000pF

C13

1uF

Vout

Vcc+

10uF

N/S

R1 21k

R10

Open

10uF

30.1K

1.96K

60.4k

10uF

C15

22uF

R6 20

C16

22uF

C25

0.1uF

C17

22uF

R12

6.98K

Open

C18

22uF

C19

22uF

C20

22uF

Open

R18

Open

330uF

1.0uH

VCC

180pF

0.1uF

R15

Agnd

Vin+

Vin-

Vout+

Vout-

IR3821

Vc 14

Hg 13

AGnd3

AGnd2

SW 11

PGood

COMP

OCset

7PGnd 10

Vsns

AGnd1

Vcc

Vin 12

R17

10K

PGood

C11

22pF

N/S

VCC

Vin+

R16

3.09k

Vin-

R14

10.0k

Vout+

IRDC3821

Rev 0.1

01/07/2008 7

Item Quantity Designator Value Description Size Manufacturer Mfr. Part Number

1 1 C1 330uF SMD Electrolytic, 25V, 20% SMD Panasonic EEV-FK1E331P

2 3 C2 C3 C4 10uF Ceramic, 16V, X7R, 10% 1206 Panasonic ECJ-3YX1C106K

34 C7 C12 C14

C25 0.1uF Ceramic, 50V, X7R, 10% 0603 Panasonic ECJ-1VB1H104K

4 1 C10 0.22uF Ceramic, 10V, X5R, 10% 0603 Panasonic ECJ-1VB1A224K

5 1 C8 180pF Ceramic, 50V, NPO, 5% 0603 Murata GRM1885C1H181JA01

6 1 C11 22pF Ceramic, 50V, NPO, 5% 0603 Murata GRM1885C1H220JA01

7 1 C13 1uF Ceramic, 16V, X5R, 10% 0603 Panasonic ECJ-1VB1C105K

86 C15 C16 C17

C18 C19 C20 22uF Ceramic, 6.3V, X5R, 20% 0805 Panasonic ECJ-2FB0J226M

9 1 C24 560pF Ceramic, 50V, NPO, 5% 0603 Murata GRM1885C1H561JA01

10 1 C26 1000pF Ceramic, 50V, NPO, 5% 0603 Murata GRM1885C1H102JA01

11 1 D1 BAT54S Diode Schottky ,40V, 200mA SOT-23 Fairchild BAT54S

12 1 L1 1.0uH SMT Inductor, 2.3mOhm,

20%

11.5x

10mm Delta MPL105-1R0

13 1 R1 21.0K Thick film, 1/10W, 1% 0603 Vishey/Dale CRCW060321K0FKEA

14 1 R3 30.1K Thick film, 1/10W, 1% 0603 Vishey/Dale CRCW060330K1FKEA

15 1 R2 60.4K Thick film, 1/10W, 1% 0603 Vishey/Dale CRCW060360K4FKEA

16 1 R4 1.96K Thick film, 1/10W, 1% 0603 Vishey/Dale CRCW06031K96FKEA

17 1 R6 20 Thick film, 1/10W, 1% 0603 Vishey/Dale CRCW060320R0FKEA

18 2 R9 R15 0 Thick film, 1/10W, 1% 0603 Vishey/Dale CRCW06030000Z0EA

19 1 R12 6.98K Thick film, 1/10W, 1% 0603 Vishey/Dale CRCW06036K98FKEA

20 2 R14, R17 10K Thick film, 1/10W, 1% 0603 Vishey/Dale CRCW060310K0FKEA

21 1 R16 3.09K Thick film, 1/10W, 1% 0603 Vishey/Dale CRCW06033K09FKEA

22 1 U1 IR3821 600kHz, 7A, SupIRBuck

Module 5x6mm International

Rectifier IR3821

23 2 - - Banana Jack, Insulated

Solder Terminal, Black -Johnson

Components 105-0853-001

24 1 - - Banana Jack- Insulated

Solder Terminal, Red -Johnson

Components 105-0852-001

25 1 - - Banana Jack- Insulated

Solder Terminal, Green -Johnson

Components 105-0854-001

Bill of Materials

IRDC3821

Rev 0.1

01/07/2008 8

TYPICAL OPERATING WAVEFORMS

Vin=Vcc=12.0V, Vo=1.8V, Io=0-7A, Room Temperature, No Air Flow

Fig. 10: Output Voltage Ripple, 7A load

Ch3: Vout ,Ch4: Iout

Fig. 11: Inductor node at 7A load

Ch1:LX, Ch4:Iout

Fig. 12: Short (Hiccup) Recovery

Ch2:VSS , Ch3:Vout

Fig. 9: Pre-Bias Start up, 0A Load

Ch1:Vin, Ch2:VSS, Ch3:Vout

Fig. 8: Start up at 7A Load,

Ch1:Vin, Ch2:VSS, Ch3:Vout, Ch4:VPGood

Fig. 7: Start up at 7A Load

Ch1:Vin, Ch2:VSS, Ch3:Vout, Ch4:Iout

Vin

Vss

Vout

Iout

Vin

Vss

Vout

PGood

IRDC3821

Rev 0.1

01/07/2008 9

TYPICAL OPERATING WAVEFORMS

Vin=Vcc=12V, Vo=1.8V, Io=3.5A-7A, Room Temperature, No Air Flow

Fig. 13: Transient Response, 3.5A to 7A step

Ch3:Vout, Ch4:Iout

IRDC3821

Rev 0.1

01/07/2008 10

TYPICAL OPERATING WAVEFORMS

Vin=Vcc=12V, Vo=1.8V, Io=7A, Room Temperature, No Air Flow

Fig. 14: Bode Plot at 7A load shows a bandwidth of 62 kHz and phase margin of 51 degrees

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