Analog Devices DC2897A Quick setup guide

1
DEMO MANUAL
DC2897A
Rev. 0
DESCRIPTION
LTC7819
Low IQ, Triple Output
Synchronous Step-Down Supply
Demonstration circuit 2897A is a low IQ, triple output,
synchronous step-down supply featuring the LTC
®
7819.
The circuit is optimized for high efficiency. It provides
outputs of 3.3V at 12A, 8.5V at 10A and 5.0V at 12A over
an input voltage range of 10V to 36V with a switching
frequency of 380kHz. Each rail uses a 3mΩ sense resis-
tor to sense the current and provides optional footprints
for DCR sensing. Typical applications include automotive,
transportation, industrial, military and avionics systems.
Features of the DC2897A include pin selectable light
load operating modes of forced continuous mode,
All registered trademarks and trademarks are the property of their respective owners.
BOARD PHOTO
pulse-skipping and Burst Mode
®
operation. Optional
spread spectrum modulation to reduce EMI, a PLLIN pin
to synchronize to an external clock, optional DCR sensing
footprints, an EXTVCC pin to reduce losses in the controller
and optional footprints to parallel two or three channels.
The LTC7819 data sheet provides a complete description
of the part, operational details, and applications infor-
mation. DC2897A must be read in conjunction with the
datasheet.
Design files for this circuit board are available.

2
DEMO MANUAL
DC2897A
Rev. 0
QUICK START PROCEDURE
Demonstration circuit 2897A is easy to setup for eval -
uating the LTC7819. Please refer to Figure 1 for the
proper measurement equipment setup and follow the
procedurebelow.
1. Connect the input power supply to VIN (10V – 36V)
and GND (input return).
2. Preset the load for each output to 0A and the input
supply to 0V.
3. Place jumpers in the following positions:
JP4: RUN1 ON
JP2: RUN2 ON
JP1: RUN3 ON
JP3: MODE FCC
JP5: SPREAD SPECTRUM NO
4. Set the input voltage to within the specified range and
check VOUT1, VOUT2 and VOUT3.
5. Once the proper output voltages have been confirmed,
observe the output voltage ripple, efficiency, and
otherparameters.
PERFORMANCE SUMMARY
Specifications are at TA= 25°C
PARAMETER CONDITIONS MIN TYP MAX UNITS
Input Voltage Range 10 36 V
Output Voltage #1, VOUT1 VIN = 10V to 36V, IOUT1 = 0A – 12A 3.3 V
Output Voltage #2, VOUT2 VIN = 10V to 36V, IOUT2 = 0A – 10A 8.5 V
Output Voltage #3, VOUT3 VIN = 10V to 36V, IOUT3 = 0A – 12A 5.0 V
Maximum Output Current, IOUT1 VIN = 10V to 36V, VOUT1 = 3.3V 12 A
Maximum Output Current, IOUT2 VIN = 10V to 36V, VOUT2 = 8.5V 10 A
Maximum Output Current, IOUT3 VIN = 10V to 36V, VOUT3 = 5.0V 12 A
Switching Frequency 380 kHz
Efficiency (fSW = 380kHz) VIN = 12V, VOUT1 = 3.3V, IOUT1 = 12A
VIN = 12V, VOUT2 = 8.5V, IOUT2 = 10A
VIN = 12V, VOUT3 = 5.0V, IOUT3 = 12A
94.9
97.9
96.4
%
%
%
LIGHT LOAD OPERATION, SYNCHRONIZATION TO AN
EXTERNAL CLOCK AND SPREAD SPECTRUM
To synchronize the LTC7819 to an external clock, place
the SPREAD SPECTRUM jumper (JP5) in the EXT CLK
position and apply an external clock between the PLLIN
turret and GND. The phase-lockable frequency range is
100kHz to 3MHz. The low clock level should be 0.5V or
lower and the high clock level should be 2.2V or higher.
For spread spectrum, place the jumper in the YES posi-
tion. With spread spectrum enabled, the frequency will be
modulated between 100% and 120% of the programmed
frequency (380kHz to 456kHz). This will help reduce the
peak emission levels. To allow the converter to free run
at is programmed frequency (380kHz), place the jumper
in the NO position which is the default setting.
Demonstration circuit 2897A can be programmed to
operate in either forced continuous conduction mode
(FCC), pulse-skipping mode (PS) or Burst Mode opera-
tion (BURST) at no load or light load with JP3. Forced
continuous mode (default setting) provides the clean-
est output voltage ripple. Pulse-skipping mode provides
higher efficiency at light load, but the output voltage ripple
is less regular. Burst Mode operation provides the highest
light load efficiency, but the output voltage ripple is the
least regular and highest of the three modes.

3
DEMO MANUAL
DC2897A
Rev. 0
OPTIONAL DCR SENSING
Demonstration circuit 2897A has optional footprints for
DCR sensing. The benefit of DCR sensing is a lower parts
count and high efficiency but at the expense of a less
accurate current sensing and current limit. To imple-
ment DCR sensing refer to Table1 and the Applications
Information section of the data sheet. Be sure to stuff a
0mΩ copper shunt or a short, thick piece of copper at
RS1, RS2 and/or RS3.
EXTVCC BIAS OPTION
The EXTV
CC
pin of the LTC7819 on the standard demo
board is connected to the 5V output (VOUT3) to reduce
the losses in the controller and improve efficiency. If nec-
essary, the EXTVCC pin can be tied to an external supply
by following these steps:
1. Remove the 0Ω jumper at R20.
2. Connect a DC voltage from the EXTVCC turret to a GND
turret. The DC voltage should be between 5V and 30V.
PARALLELING CHANNELS
For higher power, two or more channels of demonstra-
tion circuit 2897A can be paralleled. Given that the chan-
nels operate 120 degrees out of phase with each other,
paralleling channels provides the benefit of ripple cur-
rent cancelation in the output and input capacitors. This
in turn provides lower output voltage and input voltage
ripple. Another benefit of interleaved channels is a faster
load step response. When paralleling phases channel 1
is always the master and channels 2 and 3 are slaves.
In addition, each phase should have the same inductor,
sense resistor–if used and MOSFETs. Detailed instruc-
tions are below:
Parallel Channel 1 with Channel 2:
nStuff 0Ω jumpers at R11, R12 and R15.
nStuff a 0mΩ jumper or short, thick piece of copper
atR19.
Parallel Channel 1 with Channel 3:
nStuff 0Ω jumpers at R10, R13 and R14.
nStuff a 0mΩ jumper or short, thick piece of copper
atR18.
Parallel Channel 1 with Channel 2 and Channel 3:
n
Stuff 0Ω jumpers at R11, R10, R12, R13, R15 and R14.
nStuff a 0mΩ jumper or short, thick piece of copper at
R19 and R18.
Notes
1. When measuring the output voltage or input voltage
ripple do not use the long ground lead on the oscillo-
scope probe. See Figure2 for the proper scope probe
technique. Short, stiff leads need to be soldered to the
(+) and (–) terminals of the output or input capacitor.
The probe’s ground ring needs to contact the (–) lead
and the probe tip needs to contact the (+) lead.
2. When powering the board, first connect the input sup-
ply to the demo board as written above. Next, turn-on
the input supply. Do not hot plug. This could cause
large input voltage transients that may damage the
converter, especially at high VIN.
3. When using electronic loads which are rated to pro-
vide full current with a voltage of 0V, make sure the
load is off before turning off the rail. Otherwise, the
load could pull VOUT below ground. This may damage
theconverter.
QUICK START PROCEDURE
Table1. Optional Inductor DCR Sensing
CONFIGURATION
CHANNEL 1 RS1 R30 R29 C14 R45 R47 R61
CHANNEL 2 RS2 R52 R54 C56 R50 R49 R46
CHANNEL 3 RS3 R40 R39 C15 R51 R53 R62
RSENSE (DEFAULT) 3mΩ 0Ω 0Ω 1nF Open Open Open
DCR SENSING 0mΩ Cu Open Open Refer to Data Sheet 0Ω

4
DEMO MANUAL
DC2897A
Rev. 0
dc2897a F01
VOUT2
LOAD
IOUT2
+
–
+
–
+
–
+
–
VOUT1
LOAD +–
VOUT2
VOUT3
LOAD
IOUT3
VOUT3
+
–
IIN
IOUT1
+
–
VOUT1
VIN SUPPLY
+
–
VIN
NOTE FOR ACCURATE EFFICIENCY MEASUREMENTS:
MONITOR VOUT1, VOUT2 AND VOUT3 ACROSS COUT1, COUT7 AND COUT4, RESPECTIVELY.
MONITOR VIN ACROSS EITHER CIN7 (CH1), CIN9 (CH2) OR CIN5 (CH3).
Figure1. Proper Measurement Equipment Setup
+ –
VOUT GND
COUT
dc2897a F02
Figure2. How to Measure the Output or Input Voltage Ripple
QUICK START PROCEDURE

5
DEMO MANUAL
DC2897A
Rev. 0
QUICK START PROCEDURE
Figure3. Efficiency of the 3.3V/12A Rail (VOUT1) Over the
Input Voltage Range, the Other Two Rails Were Disabled, No
Voltage Was Applied to the EXTVCC Pin and the PGOOD Pull-Ups
WereRemoved
Figure4. Efficiency of the 8.5V/10A Rail (VOUT2) Over the
Input Voltage Range, the Other Two Rails Were Disabled, No
Voltage Was Applied to the EXTVCC Pin and the PGOOD Pull-Ups
WereRemoved
Figure5. Efficiency of the 5V/12A Rail (VOUT3) Over the Input
Voltage Range, the Other Two Rails Were Disabled, the 5V Output
was Tied to the EXTVCC Pin and the PGOOD Pull-Ups Were Removed
f
SW
= 380kHz
MODE = FCM
V
IN
= 12V
V
IN
= 24V
V
IN
= 36V
LOAD CURRENT (A)
0
1
2
3
4
5
6
7
8
9
10
11
12
75
80
85
90
95
100
EFFICIENCY (%)
dc2897a F03
Efficiency, VOUT = 3.3V
f
SW
= 380kHz
MODE = FCM
V
IN
= 12V
V
IN
= 24V
V
IN
= 36V
LOAD CURRENT (A)
0
1
2
3
4
5
6
7
8
9
10
75
80
85
90
95
100
EFFICIENCY (%)
dc2897a F04
Efficiency, VOUT = 8.5V
f
SW
= 380kHz
MODE = FCM
V
IN
= 12V
V
IN
= 24V
V
IN
= 36V
LOAD CURRENT (A)
0
1
2
3
4
5
6
7
8
9
10
11
12
75
80
85
90
95
100
EFFICIENCY (%)
dc2897a F05
Efficiency, VOUT = 5V

6
DEMO MANUAL
DC2897A
Rev. 0
QUICK START PROCEDURE
Figure6. Efficiency of the 3.3V/12A Rail (VOUT1) at 12VIN for the
Three Light Load Operating Modes, the Other Two Rails Were
Disabled, No Voltage Was Applied to the EXTVCC Pin and the
PGOOD Pull-Ups Were Removed
Figure8. Efficiency of the 5V/12A Rail (VOUT3) for the Three Light
Load Operating Modes, the Other Two Rails Were Disabled, the
5V Output Was Tied to the EXTVCC Pin and the PGOOD Pull-Ups
Were Removed
f
SW
= 380kHz
Burst Mode
PULSE SKIP
FCM
LOAD CURRENT (A)
0.001
0.01
0.1
1
10
1
10
100
EFFICIENCY (%)
dc2897a F07
f
SW
= 380kHz
Burst Mode
PULSE SKIP
FCM
LOAD CURRENT (A)
0.001
0.01
0.1
1
10
100
1
10
100
EFFICIENCY (%)
dc2897a F08
f
SW
= 380kHz
Burst Mode
PULSE SKIP
FCM
LOAD CURRENT (A)
0.001
0.01
0.1
1
10
100
1
10
100
EFFICIENCY (%)
dc2897a F06
Efficiency, VOUT = 3.3V, VIN = 12V
Figure7. Efficiency of the 8.5V/10A Rail (VOUT2) at 12VIN for the
Three Light Load Operating Modes, the Other Two Rails Were
Disabled, No Voltage Was Applied to the EXTVCC Pin and the
PGOOD Pull-Ups Were Removed
Efficiency, VOUT = 8.5V, VIN = 12V
Efficiency, VOUT = 5V, VIN = 12V

7
DEMO MANUAL
DC2897A
Rev. 0
Figure9. Thermal Image with Full Load on Each Rail at 12VIN,
fSW = 380kHz, No Airflow, TA= 23°C, Markers Show the Hot Spot
for Each Channel
Figure10. Thermal Image with Full Load on Each Rail at 36VIN,
fSW = 380kHz, No Airflow, TA= 23°C, Markers Show the Hot Spot
for Each Channel
Figure11. 50% to 100% Load Step Response of the 3.3V/12A
Rail (VOUT1)
Figure12. 50% to 100% Load Step Response of the 8.5V/10A
Rail (VOUT2)
Figure13. 50% to 100% Load Step Response of the
5.0V/12A Rail (VOUT3)
50µs/DIV
dc2897a F11
VOUT (AC)
100mV/DIV
LOAD
CURRENT
5A/DIV
100µs/DIV
dc2897a F12
VOUT (AC)
200mV/DIV
LOAD
CURRENT
5A/DIV
50µs/DIV
VOUT (AC)
100mV/DIV
LOAD
CURRENT
5A/DIV
dc2897a F13
QUICK START PROCEDURE

8
DEMO MANUAL
DC2897A
Rev. 0
PARTS LIST
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 5 C1, C14, C15, C43, C56 CAP., 1000pF, C0G, 50V, 10%, 0603 AVX, 06035A102KAT2A
2 1 C11 CAP., 4.7μF, X5R, 10V, 10%, 0805 KEMET, C0805C475K8PACTU
MURATA, GRM21BR61A475KA73L
SAMSUNG, CL21A475KPFNNNF
TDK, C2012X5R1A475K125AA
3 8 C2, C4, C20, C21, C47, C52,
C61, C74
CAP., 0.1μF, X7R, 50V, 10%, 0603 AVX, 06035C104KAT2A
KEMET, C0603C104K5RAC7867; C0603C104K5RACTU
TDK, C1608X7R1H104K080AA
4 1 C41 CAP., 2200pF, X7R, 50V, 10%, 0603 AVX, 06035C222KAT2A
MURATA, GRM188R71H222KA01D
SAMSUNG, CL10B222KB8NFNC
5 2 C42, C44 CAP., 47pF, X7R, 50V, 10%, 0603 AVX, 06035C470KAT2A
KEMET, C0603C470K5RACTU
6 1 C53 CAP., 0.01μF, C0G, 50V, 5%, 0603 MURATA, GRM1885C1H103JA01D
TDK, C1608C0G1H103J080AA
7 1 C54 CAP., 220pF, X7R, 50V, 10%, 0603 AVX, 06035C221KAT2A
KEMET, C0603C221K5RACTU
NIC, NMC0603X7R221K50TRPF
8 2 C69, C70 CAP., 1μF, X7R, 10V, 10%, 0603 AVX, 0603ZC105KAT2A
KEMET, C0603C105K8RACTU
MURATA, GRM188R71A105KA61D
TDK, C1608X7R1A105K080AC
9 1 CIN1 CAP., 220μF, ALUM ELECT, 50V, 20%,
10mm × 10.2mm, RADIAL, SMD,
AEC-Q200
PANASONIC, EEEFK1H221GP
CORNELL DUBILIER, AFK227M50G24T-F
10 8 CIN3, CIN4, CIN5, CIN6,
CIN7, CIN8, CIN9, CIN10
CAP., 4.7μF, X7R, 50V, 10%, 1210 AVX, 12105C475KAT2A
KEMET, C1210C475K5RACTU
MURATA, GRM32ER71H475KA88L
YAGEO, CC1210KKX7R9BB475
11 6 COUT1, COUT2, COUT4,
COUT5, COUT7, COUT8
CAP., 47μF, X7R, 10V, 10%, 1210 AVX, 1210ZC476KAT2A
MURATA, GRM32ER71A476KE15L
TAIYO YUDEN, LMK325B7476KM-PR; LMK325B7476KM-TR
12 2 COUT10, COUT11 CAP., 470μF, TANT, POSCAP, 6.3V, 20%,
7343, 10mΩ, TCF
PANASONIC, 6TCF470MAH
13 1 COUT12 CAP., 150μF, TANT. POSCAP, 10V, 20%,
7343, D3L
PANASONIC, 10TPF150ML
14 3 D1, D2, D6 DIODE, SCHOTTKY, 100V, 1A,
POWERDI-123, AEC-Q101
DIODES INC., DFLS1100Q-7
15 2 L1, L3 IND., 2.2μH, PWR., 20%,
11.8mm × 10.5mm SMD, AEC-Q200
COILCRAFT, XAL1010-222MEB; XAL1010-222MED
16 1 L2 IND., 3.3μH, PWR., 20%, 25A, 4.10mΩ,
11.8mm × 10.5mm, XAL1010, AEC-Q200
COILCRAFT, XAL1010-332MEB; XAL1010-332MED
17 3 Q1, Q3, Q5 XSTR., MOSFET, N-CH, 40V, 59A,
TDSON-8 FL
INFINEON, BSC059N04LS6; BSC059N04LS6ATMA1
18 3 Q2, Q4, Q6 XSTR., MOSFET, N-CH, 40V, 100A,
TDSON-8 FL
INFINEON, BSC022N04LS6; BSC022N04LS6ATMA1
19 16 R1, R3, R4, R5, R9, R25,
R27, R29, R30, R39, R40,
R44, R52, R54, R83, R84
RES., 0Ω, 1/10W, 0603, AEC-Q200 VISHAY, CRCW06030000Z0EA; CRCW06030000Z0EB
NIC, NRC06ZOTRF

9
DEMO MANUAL
DC2897A
Rev. 0
PARTS LIST
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
20 1 R20 RES., 0Ω, 1/4W, 1206, AEC-Q200 VISHAY, CRCW12060000Z0EA
PANASONIC, ERJ8GEY0R00V
NIC, NRC12ZOTRF
21 3 R26, R38, R55 RES., 1M, 1%, 1/10W, 0603, AEC-Q200 NIC, NRC06F1004TRF
PANASONIC, ERJ3EKF1004V
VISHAY, CRCW06031M00FKEA
22 1 R31 RES., 10k, 1%, 1/10W, 0603, AEC-Q200 PANASONIC, ERJ3EKF1002V
VISHAY, CRCW060310K0FKEA; CRCW060310K0FKEB
KOA SPEER, RK73H1JTTD1002F
23 2 R33, R35 RES., 20k, 1%, 1/10W, 0603 NIC, NRC06F2002TRF
VISHAY, CRCW060320K0FKEA
PANASONIC, ERJ3EKF2002V
YAGEO, RC0603FR-0720KL
24 1 R43 RES., 105k, 1%, 1/10W, 0603, AEC-Q200 VISHAY, CRCW0603105KFKEA
NIC, NRC06F1053TRF
25 1 R57 RES., 133k, 1%, 1/10W, 0603 BOURNS, CR0603-FX-1333ELF
YAGEO, RC0603FR-07133KL
26 1 R58 RES., 13.7k, 1%, 1/10W, 0603,
AEC-Q200
VISHAY, CRCW060313K7FKEA
PANASONIC, ERJ3EKF1372V
27 1 R6 RES., 1k, 5%, 1/10W, 0603, AEC-Q200 PANASONIC, ERJ3GEYJ102V
28 1 R60 RES., 4.99k, 1%, 1/10W, 0603 PANASONIC, ERJ3EKF4991V
YAGEO, RC0603FR-074K99L
29 4 R7, R34, R37, R63 RES., 100k, 1%, 1/10W, 0603, AEC-Q200 VISHAY, CRCW0603100KFKEA
NIC, NRC06F1003TRF
PANASONIC, ERJ3EKF1003V
30 3 R8, R36, R59 RES., 10Ω, 1%, 1/10W, 0603 VISHAY, CRCW060310R0FKEA
NIC, NRC06F10R0TRF
PANASONIC, ERJ3EKF10R0V
ROHM, MCR03EZPFX10R0
YAGEO, RC0603FR-0710RL
31 3 RS1, RS2, RS3 RES., 0.003, 0Ω, 1%, 2W, 2010 LONG-
SIDE TERM, METAL, SENSE, AEC-Q200
SUSUMU, KRL5025E-C-R003-F-T1
32 1 U1 IC, SYN. STEP-DOWN CONVERTER,
40-PIN QFN
ANALOG DEVICES, LTC7819RUJ#PBF; LTC7819RUJ#TRPBF
Additional Circuit Components
1 0 C38, C48, C60, C62, C63,
C64, C65, C66, C67, C68,
C71, C72, C73
CAP., OPTION, 0603
2 0 CIN2 CAP., OPTION, ALUM. ELECT., SMD
3 0 COUT13, COUT14, COUT15 CAP., OPTION, 1210
4 0 COUT3, COUT6, COUT9 CAP., OPTION, 7343
5 0 Q7, Q10, Q11, Q12, Q13, Q14 XSTR., OPTION, MOSFET N-CH,
PG-TDSON-8
6 0 R18, R19 RES., OPTION, 2010
7 0 R2, R10, R11, R12, R13,
R14, R15, R21, R22, R23,
R28, R32, R41, R42, R45,
R46, R47, R49, R50, R51,
R53, R56, R61, R62
RES., OPTION, 0603

10
DEMO MANUAL
DC2897A
Rev. 0
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Hardware: For Demo Board Only
1 19 E1, E2, E3, E4, E5, E6, E7,
E8, E9, E10, E11, E12, E13,
E14, E15, E16, E17, E18, E19
TEST POINT, TURRET, 0.094" MTG.
HOLE, PCB 0.062" THK
MILL-MAX, 2501-2-00-80-00-00-07-0
2 8 J1, J2, J3, J4, J5, J6, J7, J8 CONN., BANANA JACK, FEMALE, THT,
NON-INSULATED, SWAGE, 0.218"
KEYSTONE, 575-4
3 3 JP1, JP2, JP4 CONN., HDR, MALE, 1×3, 2mm, VERT,
ST, THT, NO SUBS. ALLOWED
WURTH ELEKTRONIK, 62000311121
4 2 JP3, JP5 CONN., HDR, MALE, 2×3, 2mm, VERT,
ST, THT
WURTH ELEKTRONIK, 62000621121
5 8 MP1, MP2, MP3, MP4,
MP5, MP6, MP7, MP8
STANDOFF, NYLON, SNAP-ON, 0.625"
(5/8"), 15.9mm
KEYSTONE, 8834
6 3 XJP1, XJP2, XJP4 CONN., SHUNT, FEMALE, 2-POS, 2mm WURTH ELEKTRONIK, 60800213421
PARTS LIST