Analog Devices DC2851A Manuel utilisateur

DC2851A User Guide

LT7200S

Quad 18V, ±5A Synchronous

Monolithic Step-Down Regulator

Rev 0; 10/22

One A n al o g Way, Wilmi ngt on, MA 01887 U.S .A. | Te l: 7 81.329.4700 | © 2 02 2 A n a lo g D evic es, I nc . All r ig hts r es erv ed .

General Description

Evaluation kit DC2851A is a quad-channel synchronous

step-down regulator featuring the LT®7200S. The

LT7200S is ideal for high step-down ratio applications

that operate at high frequency while demanding fast

transient response thanks to its constant frequency,

current-mode architecture, and phase-lockable controlled

on-time. The DC2851A operates from an input voltage

range of 2.9V to 18V, with each regulator capable of

delivering ±5A of output current. The evaluation kit is

designed for 1.2V, 1.8V, 3.3V, and 5V outputs with

switching frequency set at 1MHz. The DC2851A provides

LT7200S-based different multichannel combinations for

flexible output current rating.

The LT7200S features independent soft-start, output

tracking and power good for each output to simplify the

complex design of quad-output converters. The output

tracking and soft-start pins allows to control the rise time

and ramp rate of the output voltage. Each output can be

independently disabled into the low quiescent current

shutdown mode with its own TRACK or RUN pin.

A user-selectable MODE/SYNC pin on the evaluation kit

allows the part to operate in either discontinuous mode

for higher efficiency at light load currents, or forced

continuous mode for lower output ripple at the expense of

light load efficiency. The MODE/SYNC pin can also be

used to synchronize the switching frequency to an

external clock. The switching frequency for all regulators

can be programmed either through the oscillator resistor

or external clock over a 400kHz to 3MHz range. At all

frequencies, a 180° phase shift is maintained between

channel 1 and channel 2, channel 3 and channel 4 when

PHMODE pin is low, reducing the input peak current and

voltage ripple.

The DC2851A has an EMI filter installed on the bottom

layer. The conducted and radiated EMI performance of

the board is shown in Figure 4. The red line in Figure 4 is

the CISPR25 Class 5 peak limit. The figure shows that

the circuit passes the test with a wide margin. To achieve

EMI/ EMC performance as shown in Figure 4, the input

EMI filter is required, and the input voltage should be

applied at VEMI turret.

The LT7200S data sheet gives a complete description of

the part operation and application information. Read the

data sheet in conjunction with this quick start guide for

DC2851A. The LT7200S is assembled in a 5mm × 6mm

LQFN package with exposed pads for low thermal

resistance. Proper board layout is essential for both low

EMI operation and best thermal performance.

DC2851A User Guide

LT7200S

Quad 18V, ±5A

Synchronous Monolithic

Step-Down Regulator

www.analog.com

Analog Devices | 2

Performance Summary Specifications are at TA= 25°C

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

VIN1, VIN2,

VIN3, VIN4

Input Voltage Range

2.9

VOUT1

Default Output Voltage

VIN = 12V, IOUT = 0A to 5A per Channel

1.15

1.2

1.25

VOUT2

Default Output Voltage

VIN = 12V, IOUT = 0A to 5A per Channel

1.73

1.8

1.87

VOUT3

Default Output Voltage

VIN = 12V, IOUT = 0A to 5A per Channel

3.17

3.3

3.43

VOUT4

Default Output Voltage

VIN = 12V, IOUT = 0A to 5A per Channel

4.8

5.2

IOUT1, IOUT2,

IOUT2,IOUT4

Maximum Continuous

Output Current per Channel

VIN = 12V

fsw

Switching Frequency

0.9

1.1

MHz

Eff

Efficiency

VIN = 12V, fSW = 1MHz, VOUT1 = 1.2V,

VOUT2 = 1.8V, VOUT3 = 3.3V, VOUT4 = 5V,

IOUT1 = IOUT2 = IOUT3 = IOUT4 = 5A

DC2851A User Guide

LT7200S

Quad 18V, ±5A

Synchronous Monolithic

Step-Down Regulator

www.analog.com

Analog Devices | 3

Quick Start Procedure

The evaluation kit DC2851A is easy to set up to evaluate

the performance of the LT7200S. See Figure 1 for proper

measurement equipment setup and follow this procedure.

1. With power off, place the jumpers in the following

positions:

JP1

JP2

JP3

JP4

JP5

JP6

RUN1

RUN2

RUN3

RUN4

MODE/

SYNC

PHMODE

FCM

LOW

2. With power off, connect the input power supply to

VEMI+ and VEMI-.

3. With power off, connect the loads from VOUT1,

VOUT2, VOUT3, and VOUT4 to GND.

4. Place the voltmeters across the output terminals to get

accurate output voltage measurements.

5. Turn on the power at the input.

NOTE: Make sure that the input voltage does not exceed

18V and VIN > VOUT.

6. Check for proper output voltages. Regulate the output

at 1.2V (±4%), 1.8V (±4%), 3.3V (±4%), and 5.0V (±4%).

NOTE: If there is no output, temporarily disconnect the

load to make sure the load is not set too high.

7. Once the proper output voltage is established, adjust

the load within the operating ranges and observe the

output voltage regulation, ripple voltage, efficiency, and

other parameters.

NOTE: When measuring the input or output voltage

ripple, take care to avoid a long ground lead on the

oscilloscope probe. Measure the output voltage ripple by

touching the probe tip directly across the output capacitor.

See Figure 2 for the proper scope technique.

8. Add an external clock to the SYNC terminal when SYNC

function is used (JP5 on the CLKIN position). Make sure t

choose the R50 resistor to set the LT7200S switching

frequency close to the synchronization frequency.

9. (Option) 4-Phase 20A Output Circuit Configuration:

DC2851A can be configured as a 4-Phase 20A output

regulator.

The following simple modifications are required:

1. Tie VIN1, VIN2, VIN3, and VIN4 together with 0Ω

resistors (R29, R30, R31).

2. Tie RUN1, RUN2, RUN3, and RUN4 together with 0Ω

resistors (R33, R34, R48).

3. Tie TRACK1, TRACK2, TRACK3, and TRACK4

together with 0Ω resistors (R58, R59, R60).

4. Tie FB1, FB2, FB3, and FB4 together with 0Ω resistors

(R55, R56, and R57). Keep the resistor divider network on

one of the 4 channels to program the desired output

voltage and remove the resistor divider networks of other

3 channels.

5. Tie ITH1, ITH2, ITH3, and ITH4 together with 0Ω

resistors (R62, R63, R64).

6. Tie 4 channel outputs together at the exposed copper

strips on the top of the board. Connect the load from VOUT

to GND.

7. Calculate and insert the inductors needed for L1, L2, L3,

and L4 (L1=L2=L3=L4).

8. Place the PHMODE jumper (JP6) to LOW.

9. Place RUN1, RUN2, RUN3, and RUN4 jumpers to ON.

DC2851A User Guide

LT7200S

Quad 18V, ±5A

Synchronous Monolithic

Step-Down Regulator

www.analog.com

Analog Devices | 4

Figure 1. Proper Measurement Equipment Setup

DC2851A User Guide

LT7200S

Quad 18V, ±5A

Synchronous Monolithic

Step-Down Regulator

www.analog.com

Analog Devices | 5

Figure 2. Scope Probe Placement for Measuring Input or Output Voltage Ripple

Typical Performance Characteristics

Figure 3. DC2851A Efficiency vs Load Current

(VIN = 12V, 1MHz Switching Frequency, DCM Mode)

DC2851A User Guide

LT7200S

Quad 18V, ±5A

Synchronous Monolithic

Step-Down Regulator

www.analog.com

Analog Devices | 6

DC2851A User Guide

LT7200S

Quad 18V, ±5A

Synchronous Monolithic

Step-Down Regulator

www.analog.com

Analog Devices | 7

Figure 4. DC2851A EMI Performance in CISPR25 Conducted and Radiated Emission Tests

(VEMI = 14V, VOUT1 = 1.2V, VOUT2 = 1.8V, VOUT3 = 3.3V, VOUT4 = 5V,

IOUT1 = IOUT2 = IOUT3 = IOUT4 = 5A, 1MHz Switching Frequency)

DC2851A User Guide

LT7200S

Quad 18V, ±5A

Synchronous Monolithic

Step-Down Regulator

www.analog.com

Analog Devices | 8

Bill of Materials

ITEM

QTY

REFERENCE

PART DESCRIPTION

MANUFACTURER/PART NUMBER

Required Evaluation Kit Components

C2,C5,C10,C14

CAP.,10uF, X5R,25V,10%,0805

MURATA,

GRM21BR61E106KA73L

C3,C6,C11,C15

CAP.,1uF, X5R,25V,10%,0402

MURATA, GRM155R61E105KA12D

C12

CAP.,4.7uF,

X5R,6.3V,20%,0402

Taiyo Yuden, JMK105BBJ475MVHF

C16

CAP.,1uF, X5R,25V,10%,0603

AVX, 06033D105KAT2A

C19,C20,C21,C22,C23,

C24,C25,C26,C56

CAP.,47uF, X5R,10V,20%,1206

TDK, C3216X5R1A476M160AB

C34,C37,C40,C43

CAP.,470pF, X7R,50V,10%,

0603

MURATA, GRM188R71H471KA01D

C35,C38,C41,C44

CAP.,4.7pF,C0G/NP0,50V,0603

MURATA, GRM1885C1H4R7CA01D

C36,C39,C42,C45

CAP.,1uF, X5R,10V,10%,0603

TAIYO YUDEN, LMK107BJ105KA-T

C46,C47,C48,C49,C66,

C67,C68,C69

CAP.,4.7uF,

X5R,10V,10%,0402

TDK, C1005X5R1A475K050BC

C50,C51,C52,C53

CAP.,100pF, C0G,50V,5%,0603

TDK, CGA3E2C0G1H101J080AA

C58

CAP.,100uF, ALUM

ELECT,25V,20%, CE-BS Series

SUN ELECTRONIC INDUSTRIES

CORP, 25CE100BS

L1,L2

IND.,0.6uH, XEL5030

COILCRAFT, XEL5030-601MEB

L3,L4

IND.,1.5uH, XEL5030

COILCRAFT, XEL5030-152MEB

XSTR., MOSFET, N-

CH,40V,14A, DPAK (TO-252)

VISHAY, SUD50N04-8M8P-4GE3

R1,R9,R13,R14,R17,R

18,R23,R24

RES.,0 OHM,1/10W,0603,AEC-

Q200

VISHAY, CRCW06030000Z0EA

R3,R4,R5,R6,R50

RES.,100k

OHMS,1%,1/10W,0603

VISHAY, CRCW0603100KFKEA

RES.,2.2

OHMS,5%,1/10W,0603

VISHAY, CRCW06032R20JNEA

R8,R10,R15,R16

RES.,1M OHM,1%,1/10W,0603

VISHAY, CRCW06031M00FKEA

R19,R22,R25,R28,R41

RES.,10k

OHMS,1%,1/10W,0603

VISHAY, CRCW060310K0FKEA

R29,R30,R31

RES.,0 OHM,1/4W,1206

VISHAY, CRCW12060000Z0EA

R40

RES.,20k

OHMS,1%,1/10W,0603

VISHAY, CRCW060320K0FKEA

R42

RES.,15k

OHMS,1%,1/10W,0603

VISHAY, CRCW060315K0FKEA

DC2851A User Guide

LT7200S

Quad 18V, ±5A

Synchronous Monolithic

Step-Down Regulator

www.analog.com

Analog Devices | 9

R43

RES.,4.99k

OHMS,1%,1/10W,0603

VISHAY, CRCW06034K99FKEA

R51

RES.,26.1k

OHMS,1%,1/10W,0603

VISHAY, CRCW060326K1FKEA

R52

RES.,56.2k

OHMS,1%,1/10W,0603

VISHAY, CRCW060356K2FKEA

R53

RES.,14k

OHMS,1%,1/10W,0603

VISHAY, CRCW060314K0FKEA

R54

RES.,90.9k

OHMS,1%,1/10W,0603

VISHAY, CRCW060390K9FKEA

R71

RES.,10k

OHMS,1%,1/10W,0603

VISHAY, CRCW060310K0FKEA

R72

RES.,0.01OHM,1%,1W,2512,

PWR, METAL,SENSE

VISHAY, WSL2512R0100FEA

IC,18V,±5A, Synch. Buck

Regulator, LQFN-48

ANALOG DEVICES,

LT7200SAV#PBF

Additional Evaluation Kit Components

FB1

IND.,100 OHMS@100MHz,

FERRITE

BEAD,25%,8A,6mOHMS,1812

WURTH ELEKTRONIK,

74279226101

C59

CAP.,1uF, X5R,25V,10%,0402

MURATA, GRM155R61E105KA12D

C60,C61,C64,C65

CAP.,0.22uF,

X5R,25V,10%,0402

MURATA, GRM155R61E224KE01D

C62,C63

CAP.,22uF, X7R,25V,10%,1210

MURATA, GRM32ER71E226KE15L

IND.,0.33uH, PWR, SHIELDED,

SMD

WURTH ELEKTRONIK,

744373360033

C8,C13,C17,C18,C55

(OPT)

CAP., OPTION, 0603

C57 (OPT)

CAP., OPTION, 1206

R2,R33,R34,R48,R55,

R56,R57,R58,R59,R60,

R62,R63,R64,R65,R66,

R67,R68,R69,R70

(OPT)

RES., OPTION, 0603

R32,R47 (OPT)

RES., OPTION, 1206

Hardware for Evaluation Kit Only

E2,E3,E4,E5,E6,E12,E

14,E15,E16,E17,E18,E

19,E20,E21,E27,E28

TEST POINT, TURRET,0.094"

MTG. HOLE, PCB 0.062" THK

MILL-MAX, 2501-2-00-80-00-00-07-0

E8,E9,E10,E11,E13,E2

2,E23,E24,E25,E26,E2

TEST POINT, TURRET,0.064"

MTG. HOLE,PCB 0.062" THK

MILL-MAX, 2308-2-00-80-00-00-07-0

DC2851A User Guide

LT7200S

Quad 18V, ±5A

Synchronous Monolithic

Step-Down Regulator

www.analog.com

Analog Devices | 10

9,E30,E31,E32,E33,E3

4,E35,E36,E37

J1,J2

CONN., BANANA JACK,

FEMALE, THT, NON-

INSULATED, SWAGE,0.218"

KEYSTONE, 575-4

JP1,JP2,JP3,JP4,JP6

CONN.,

HDR,MALE,1x3,2m0000m,VER

T,ST,THT

WURTH ELEKTRONIK,

62000311121

JP5

CONN.,

HDR,MALE,2x3,2mm,VERT,ST,

THT

WURTH ELEKTRONIK,

62000621121

MP1,MP2,MP3,MP4

STANDOFF, NYLON,SNAP-

ON,0.50"

KEYSTONE, 8833

XJP1,XJP2,XJP3,XJP4,

XJP5,XJP6

CONN., SHUNT, FEMALE, 2-

POS,2mm

WURTH ELEKTRONIK,

60800213421

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