Analog Devices DC2851A User manual

DC2851A User Guide
LT7200S
Quad 18V, ±5A Synchronous
Monolithic Step-Down Regulator
Rev 0; 10/22
© 2022 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners.
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
12
18
V
VOUT1
Default Output Voltage
VIN = 12V, IOUT = 0A to 5A per Channel
1.15
1.2
1.25
V
VOUT2
Default Output Voltage
VIN = 12V, IOUT = 0A to 5A per Channel
1.73
1.8
1.87
V
VOUT3
Default Output Voltage
VIN = 12V, IOUT = 0A to 5A per Channel
3.17
3.3
3.43
V
VOUT4
Default Output Voltage
VIN = 12V, IOUT = 0A to 5A per Channel
4.8
5
5.2
V
IOUT1, IOUT2,
IOUT2,IOUT4
Maximum Continuous
Output Current per Channel
VIN = 12V
5
A
fsw
Switching Frequency
0.9
1
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
90
%

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
ON
ON
ON
ON
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
1
4
C2,C5,C10,C14
CAP.,10uF, X5R,25V,10%,0805
MURATA,
GRM21BR61E106KA73L
2
4
C3,C6,C11,C15
CAP.,1uF, X5R,25V,10%,0402
MURATA, GRM155R61E105KA12D
3
1
C12
CAP.,4.7uF,
X5R,6.3V,20%,0402
Taiyo Yuden, JMK105BBJ475MVHF
4
1
C16
CAP.,1uF, X5R,25V,10%,0603
AVX, 06033D105KAT2A
5
9
C19,C20,C21,C22,C23,
C24,C25,C26,C56
CAP.,47uF, X5R,10V,20%,1206
TDK, C3216X5R1A476M160AB
6
4
C34,C37,C40,C43
CAP.,470pF, X7R,50V,10%,
0603
MURATA, GRM188R71H471KA01D
7
4
C35,C38,C41,C44
CAP.,4.7pF,C0G/NP0,50V,0603
MURATA, GRM1885C1H4R7CA01D
8
4
C36,C39,C42,C45
CAP.,1uF, X5R,10V,10%,0603
TAIYO YUDEN, LMK107BJ105KA-T
9
8
C46,C47,C48,C49,C66,
C67,C68,C69
CAP.,4.7uF,
X5R,10V,10%,0402
TDK, C1005X5R1A475K050BC
10
4
C50,C51,C52,C53
CAP.,100pF, C0G,50V,5%,0603
TDK, CGA3E2C0G1H101J080AA
11
1
C58
CAP.,100uF, ALUM
ELECT,25V,20%, CE-BS Series
SUN ELECTRONIC INDUSTRIES
CORP, 25CE100BS
12
2
L1,L2
IND.,0.6uH, XEL5030
COILCRAFT, XEL5030-601MEB
13
2
L3,L4
IND.,1.5uH, XEL5030
COILCRAFT, XEL5030-152MEB
14
1
Q1
XSTR., MOSFET, N-
CH,40V,14A, DPAK (TO-252)
VISHAY, SUD50N04-8M8P-4GE3
15
8
R1,R9,R13,R14,R17,R
18,R23,R24
RES.,0 OHM,1/10W,0603,AEC-
Q200
VISHAY, CRCW06030000Z0EA
16
5
R3,R4,R5,R6,R50
RES.,100k
OHMS,1%,1/10W,0603
VISHAY, CRCW0603100KFKEA
17
1
R7
RES.,2.2
OHMS,5%,1/10W,0603
VISHAY, CRCW06032R20JNEA
18
4
R8,R10,R15,R16
RES.,1M OHM,1%,1/10W,0603
VISHAY, CRCW06031M00FKEA
19
5
R19,R22,R25,R28,R41
RES.,10k
OHMS,1%,1/10W,0603
VISHAY, CRCW060310K0FKEA
20
3
R29,R30,R31
RES.,0 OHM,1/4W,1206
VISHAY, CRCW12060000Z0EA
21
1
R40
RES.,20k
OHMS,1%,1/10W,0603
VISHAY, CRCW060320K0FKEA
22
1
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
23
1
R43
RES.,4.99k
OHMS,1%,1/10W,0603
VISHAY, CRCW06034K99FKEA
24
1
R51
RES.,26.1k
OHMS,1%,1/10W,0603
VISHAY, CRCW060326K1FKEA
25
1
R52
RES.,56.2k
OHMS,1%,1/10W,0603
VISHAY, CRCW060356K2FKEA
26
1
R53
RES.,14k
OHMS,1%,1/10W,0603
VISHAY, CRCW060314K0FKEA
27
1
R54
RES.,90.9k
OHMS,1%,1/10W,0603
VISHAY, CRCW060390K9FKEA
28
1
R71
RES.,10k
OHMS,1%,1/10W,0603
VISHAY, CRCW060310K0FKEA
29
1
R72
RES.,0.01OHM,1%,1W,2512,
PWR, METAL,SENSE
VISHAY, WSL2512R0100FEA
30
1
U1
IC,18V,±5A, Synch. Buck
Regulator, LQFN-48
ANALOG DEVICES,
LT7200SAV#PBF
Additional Evaluation Kit Components
1
1
FB1
IND.,100 OHMS@100MHz,
FERRITE
BEAD,25%,8A,6mOHMS,1812
WURTH ELEKTRONIK,
74279226101
2
1
C59
CAP.,1uF, X5R,25V,10%,0402
MURATA, GRM155R61E105KA12D
3
4
C60,C61,C64,C65
CAP.,0.22uF,
X5R,25V,10%,0402
MURATA, GRM155R61E224KE01D
4
2
C62,C63
CAP.,22uF, X7R,25V,10%,1210
MURATA, GRM32ER71E226KE15L
5
1
L5
IND.,0.33uH, PWR, SHIELDED,
SMD
WURTH ELEKTRONIK,
744373360033
6
0
C8,C13,C17,C18,C55
(OPT)
CAP., OPTION, 0603
7
0
C57 (OPT)
CAP., OPTION, 1206
8
0
R2,R33,R34,R48,R55,
R56,R57,R58,R59,R60,
R62,R63,R64,R65,R66,
R67,R68,R69,R70
(OPT)
RES., OPTION, 0603
9
0
R32,R47 (OPT)
RES., OPTION, 1206
Hardware for Evaluation Kit Only
1
16
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
2
19
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
3
2
J1,J2
CONN., BANANA JACK,
FEMALE, THT, NON-
INSULATED, SWAGE,0.218"
KEYSTONE, 575-4
4
5
JP1,JP2,JP3,JP4,JP6
CONN.,
HDR,MALE,1x3,2m0000m,VER
T,ST,THT
WURTH ELEKTRONIK,
62000311121
5
1
JP5
CONN.,
HDR,MALE,2x3,2mm,VERT,ST,
THT
WURTH ELEKTRONIK,
62000621121
6
4
MP1,MP2,MP3,MP4
STANDOFF, NYLON,SNAP-
ON,0.50"
KEYSTONE, 8833
7
6
XJP1,XJP2,XJP3,XJP4,
XJP5,XJP6
CONN., SHUNT, FEMALE, 2-
POS,2mm
WURTH ELEKTRONIK,
60800213421

DC2851A User Guide
LT7200S
Quad 18V, ±5A
Synchronous Monolithic
Step-Down Regulator
www.analog.com
Analog Devices | 11
Schematic Diagram

DC2851A User Guide
LT7200S
Quad 18V, ±5A
Synchronous Monolithic
Step-Down Regulator
www.analog.com
Analog Devices | 12
Schematic Diagram (continued)

DC2851A User Guide
LT7200S
Quad 18V, ±5A Synchronous
Monolithic Step-Down
Regulator
Revision History
DC2851A
User Guide
REVISION
DATE
DESCRIPTION
PAGES
CHANGED
0
10/22
Initial release
—
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is
assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that
may result from its use. Specifications subject to change without notice. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the
property of their respective owners.
w w w . a n a l o g . c o m
Analog Devices | 13