Linear Technology LTC3126UFD User manual

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dc2215af
DEMO MANUAL DC2215A
Description
LTC3126UFD
42V, 2.5A Synchronous Step-Down
Regulator with Lossless PowerPath
Demonstration Circuit 2215A, features the LT C
®
3126, a
synchronous buck converter with an integrated lossless
input PowerPath™. Pin selectable (JP2) ideal diode-OR
and priority input modes, with programmable undervolt-
age lockout thresholds provide control over the transi-
tion between input sources. The unique all N-channel
architecture provides efficient operation from either of
two input sources to a programmable output voltage.
In this application the valid input voltage range is set
to be from 4.3V to 42V on VIN1 and from 6V to 8.4V on
VIN2 providing flexibility and voltage margin for a variety
of applications and power sources. VIN2 can operate to
42V. Other input voltage ranges are possible by adjusting
VSET1/2 accordingly.
The LTC3126 uses a low noise, current mode architec-
ture and a resistor programmable (R13) PWM oscillator
frequency which is also synchronizable from 200kHz to
2.2MHz. This minimizes the solution footprint while ensur-
ing high efficiency. For higher efficiency at light loads, the
user can select Burst Mode
®
operation (JP1).
Typical efficiencies for both PWM mode (JP1 = PWM)
and Burst Mode operation (JP1 = BURST) are shown
in Figure1. Burst Mode operation allows the automatic
transition to PWM operation if the load current increases.
This is shown in Figure 5. More information on Burst Mode
operation and PWM mode can be found in the data sheet.
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
and PowerPath is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
In some applications the efficiency can be improved by
setting the EXTVCC jumper (JP3) to VOUT. This allows the
converter to operate from the fixed VOUT voltage. Typical
performance in response to a transient load is shown in
Figure 4.
The system can be monitored through VALID1, VALID2,
PRIORITY and PGOOD indicators. There are accurate
VSET1 and VSET2 comparators to program independent
UVLO thresholds. Consult the data sheet for information
on start-up and shutdown thresholds. Other features
include a 1μA shut-down current (ENA pin JP4 = OFF),
short-circuit protection, soft-start, inductor current limit
and thermal overload protection.
The LTC3126 data sheet has detailed information about
the operation, specifications, and applications of the part.
The data sheet should be read in conjunction with this
Quick Start Guide.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2215A
Input Voltage Range VIN1 4.3V to 42.0V
Input Voltage Range VIN2 6.0V to 8.4V (Operational to 42V)
VOUT 3.3V
IOUT 2.5A

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DEMO MANUAL DC2215A
Figure 1. Typical Efficiency as a Function
of Input Voltage and Load Current
Figure 2. Demonstration of Priority Operation Where the
Source of the Converter’s Power Is Switched to VIN1 When
VIN1 Exceeds the Preset Threshold
LOAD CURRENT(A)
0.0001
0
10
20
30
PERCENTAGE (%)
40
50
100
90
80
70
60
0.001 0.01 0.1 1 10
DC2215A F01
Burst Mode OPERATION
VIN = 4.5V
VIN = 12V
VIN = 25V
PWM MODE
2ms/DIV DC2215A F02
VIN2 = 2V/DIV
VIN2
TRANSITION
VIN1
TRANSITION
VIN1 = 2V/DIV
PRIORITY MODE OPERATION
VOUT = 1V/DIV
LOAD = 5Ω

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DEMO MANUAL DC2215A
Figure 3. The LTC3126 Monitors the Voltage on VIN1 and VIN2
and Selects the Higher of These Voltages in Ideal Diode
Figure 4. Typical 2.2A to 45mA to 2.2A Load Transient on
a 3.3V Output with VIN = 12V
2ms/DIV DC2215A F03
VOUT = 1V/DIV
VIN2 = 2V/DIV
VIN1 = 2V/DIV
TRANSITION
TO VIN1
TRANSITION
TO VIN2
IDEAL DIODE MODE OPERATION
LOAD = 5Ω
2ms/DIV DC2215A F04
45mA
2.2A
3.3V
OUTPUT
CURRENT
200mV/DIV
OUTPUT
VOLTAGE
1A/DIV

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DEMO MANUAL DC2215A
Figure 5. Output Ripple and Transients in Burst Mode Operation
and Transitioning from and into Burst Mode Operation
2ms/DIV DC2215A F05
PWM OPERATION 100mV/DIV Burst Mode
RIPPLE
AUTOMATIC
TRANSITION FROM
Burst Mode TO PWM
AUTOMATIC
TRANSITION FROM
PWM TO Burst Mode
OUTPUT VOLTAGE
OUTPUT CURRENT 500mA/DIV
600mA
100mA
Burst Mode
OPERATION

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DEMO MANUAL DC2215A
Quick start proceDure
Using short twisted pair leads for any power connections
and with all loads and power supplies off, refer to Figure6
for the proper measurement and equipment setup. The
power supplies should not be connected to the circuit until
told to do so in the procedure below.
When measuring the input or output voltage ripple, care
must be taken to avoid a long ground lead on the oscil-
loscope probe.
The indicators for PRIORITY, VALID1 and VALID2 are
negative logic while the indicator for PGOOD is positive
logic. PGOOD indicates the output voltage is good if it is
pulled to VCC and VALID1 and VALID2 indicate that the
input voltage on the respective sources are good if the
pins are pulled to ground. With the unit enabled (JP4,
(ENA = ON) and JP2 (DIODE = PRIORITY)) the unit is
operating in PRIORITY mode. This means that if there is
enough voltage on VIN1 then VIN1 will be supplying power
to the converter independent of the voltage on VIN2 and
VALID1 will be low.
If JP2 (DIODE) is connected to IDEAL DIODE the unit is
operating in IDEAL DIODE mode and power will be drawn
from whichever source has enough voltage to be enabled
and is the higher voltage. Both VALID1 and VALID2 will be
low if VIN1 and VIN2 are above their operating thresholds.
Turrets
Left side of board:
VIN1:4.3V to 42V supply input: do not exceed +42V.
GND: Ground connection for input supply.
VIN2:6V to 8.4V supply input: operational to +42V.
Right side of board:
GND: Ground connection for LOAD.
VOUT:3.3V/2.5A first of two terminals in parallel.
VOUT:3.3V/2.5A second of two terminals in parallel.
GND: Ground connection for LOAD.
Jumpers
JP1/PWM/SYNCH:Selects PMWorBurstMode opera-
tion. Leaving the jumper open and applying a square
wave signal to the SYNC pin allows the converter to
be synchronized. Default position is PWM which puts
the unit in fixed frequency PWM operation.
JP2/DIODE: Selects PRIORITY or DIODE-OR mode.
JP3/EXTVCC:connects EXTVCC to VOUT through a
diode or leaves EXTVCC open. If EXTVCC is open, the
LTC3126 derives bias from VIN. The default position
is VOUT.
JP4/ENA: Selects ENA =ON/OFF. The default position
is “ON”.
1. JP1 through JP4 settings to start:
JP1 PWM/SYNC =PWM
JP2 DIODE = PRIORITY
JP3 EXTVcc =VOUT
JP4 ENA =ON
2. With the power supplies (VIN1, VIN2) OFF connect them
as shown inFigure 6.If accurate currentmeasurements
are desired (for efficiency calculations for example)
then connect the ammeters in series with the supplies
as shown. The ammeters, however, are not required.
3. Connect the load, set at 5Ω, (660mA) toVOUT as shown
in Figure 6. Again, connect an ammeter if accurate
current measurement or monitoring is desired.
4. Turn on the Power Supply, VIN1, and increase the volt-
age. The converter will start at approximately 4.3V.
5. Verify VOUT is ~3.3V.
6. VIN1 can now be varied between 4.3V and 42V. VOUT
will remain in regulation for load currents up to 2.5A.
7. Set VIN1 to 0V and turn off VIN1.

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DEMO MANUAL DC2215A
8. Repeat steps 4 to 6 with VIN2. With VIN1 off increase
VIN2 from 0V to 8.4V. The part will turn on when VIN2
is approximately 6V. Once on, VIN2 can be varied
between 6V and 8.4V. 8.4V symbolizes a 2-cell Li-Ion
battery range. However, VIN2 is rated for operation up
to 42V.
9. Set the load to 5.0Ω (660mA).
10. Set VIN2 to 7.5V and turn on VIN1 slowly increasing
the VIN1 voltage from 0V to 10V. Note that VIN1 starts
to supply the power as the voltage of VIN1 exceeds its
turn on set point of 4.3V (see Figure 2).
Quick start proceDure
11. By adjusting the voltage on VIN1 from 10V to 0V and
back the converter operates from VIN1 while VIN1 is
above approximately 4.3V and when VIN1 is below ap-
proximately 4.2V it operates from VIN2. (See Figure2).
12. Change JP2 to “DIODE”. By adjusting the voltage on
VIN1 from 10V to 0V and back the converter operates
from VIN1 while VIN1 is above approximately 7.5V and
from VIN2 when VIN1 is below approximately 7.5V.
(See Figure. 3).

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DEMO MANUAL DC2215A
Figure 6. Measurement Setup
Quick start proceDure

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DEMO MANUAL DC2215A
parts List
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 3 C1, C2, C8 CAP CER 0.1µF 50V 10% X7R 0805 MURATA, GRM21BR71H104KA01L
2 2 C3, C4 CAP CER 10µF 50V 10% X7R 1210 MURATA, GRM32ER71H106KA12L
3 2 C7, C15 CAP CER 47µF 10V 10% X7R 1210 MURATA, GRM32ER71A476KE15L
4 1 C10 CAP CER 10pF 50V 5% NP0 0402 MURATA, GRM1555C1H100JA01D
5 2 C11, C12 CAP CER 0.1µF 16V 10% X7R 0402 MURATA, GRM155R71C104KA88D
6 1 C13 CAP CER 4.7µF 10V 10% X7R 0805 MURATA, GRM21BR71A475KA73K
7 1 L1 INDUCTOR, 4.7µH COILCRAFT, XAL4030-472ME
8 1 R1 RES 51Ω 1% 1/10W 0402 PANASONIC, ERJ-2RKF51R0X
9 5 R2, R5, R6, R7, R8 RES 1MΩ 1% 1/10W 0402 PANASONIC, ERJ-2RKF1004X
10 1 R3 RES 324kΩ 1% 1/10W 0402 PANASONIC, ERJ-2RKF3243X
11 1 R4 RES 0Ω 1% JUMPER 1/10W 0402 PANASONIC, ERJ-2GE0R00X
12 1 R9 RES 787kΩ 1% 1/10W 0402 PANASONIC, ERJ-2RKF7873X
13 1 R10 RES 215kΩ 1% 1/10W 0402 PANASONIC, ERJ-2RKF2153X
14 1 R11 RES 732kΩ 1% 1/10W 0402 PANASONIC, ERJ-2RKF7323X
15 1 R12 RES 309kΩ 1% 1/10W 0402 PANASONIC, ERJ-2RKF3093X
16 1 R13 RES 44.2kΩ 1% 1/10W 0402 PANASONIC, ERJ-2RKF4422X
17 1 U1 42V, 2.5A SYNCHRONOUS BUCK WITH LOSSLESS
POWERPATH
LINEAR TECH;, LTC3126EUFD #TRBPF
Additional Demo Board Circuit Components
18 0 C5, C6 CAP CER 10µF 50V 10% X7R 1210 MURATA, GRM32ER71H106KA12L
19 0 C9 CAP CER 47µF 10V 10% X7R 1210 MURATA, GRM32ER71A476KE15L
20 0 C14 CAP CER 4.7µF 10V 10% X7R 0805 MURATA, GRM21BR71A475KA73K
21 0 R14 RES 0Ω 1% JUMPER 1/10W 0402 PANASONIC, ERJ-2GE0R00X
Hardware: For Demo Board Only
22 8 E1-E7, E9 TURRET, 0.09 DIA MILL-MAX, 2501-2-00-80-00-00-07-0
23 5 E8, E10-E13 TURRET, 0.061 DIA MILL-MAX, 2308-2-00-80-00-00-07-0
24 4 JP1, JP2, JP3, JP4 JMP, 3-PIN 1 ROW .079CC Wurth Elektronik, 62000311121
25 4 XJP1, XJP2, XJP3, XJP4 SHUNT, .079" CENTER Wurth Elektronik, 60800213421
26 4 STAND OFF STAND-OFF, NYLON 0.375" TALL Wurth Elektronik, 702933000

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DEMO MANUAL DC2215A
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
schematic Diagram
5 5
4 4
3 3
2 2
1 1
D D C C B B A A
PWM
BURST
EXTVcc
OPEN VOUT ON
OFF
PRIORITY
IDEAL DIODE
3. INSTALL SHUNTS AS SHOWN.
NOTE: UNLESS OTHERWISE SPECIFIED 1. ALL RESISTORS ARE IN OHMS, 0402.
PIN 8 (QUIET GROUND) MUST BE CONNECTED TO PINS 18 , 19 AND 29 (POWER GROUND) DIRECTLY UNDER THE LTC3126. COMPONENTS CONNECTED TO THE QUIET GROUND PIN8 (R4, R7, R9, R12, C9, C14, JP1-3, JP2-3, JP4-3) SHOULD BE ON THE QUIET GROUND PLANE WHICH SHOULD ALSO BE UNDER R1, R2, R5, R6, R8, AND JP3.
REGULATOR WITH LOSSLESS POWERPATH
OPT
OPT
XAL4030-472ME
DIODE
PWM / SYNC
ENA
OPT
0805
0805
0805
2. ALL CAPACITORS ARE 0402 UNLESS OTHERWISE NOTED
OPT
DNP
VOUT
VOUT
VCC
VCC
VCC
VCC
Vref Vref
Vref
VEXTVcc
VEXTVcc
DIODE
DIODE
PRIORITY
PRIORITY
VCC
Vref
PGOOD PGOOD
PGOOD
SIZE DATE:
IC NO. REV.
SHEET OF
TITLE:
APPROVALS
PCB DES.
APP ENG.
TECHNOLOGY Fax: [phone]
Milpitas, CA 95035 Phone: [phone] McCarthy Blvd. LTC Confidential-For Customer Use Only
CUSTOMER NOTICE
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS; HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL APPLICATION. COMPONENT SUBSTITUTION AND PRINTED CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT PERFORMANCE OR RELIABILITY. CONTACT LINEAR TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE. THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND
SCHEMATIC
SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
SCALE = NONE
www.linear.com
2
DEMO CIRCUIT 2215A
11
N/A LTC3126UFD
NC
JB
5 - 29 - 15
42V, 2.5A SYNCHRONOUS STEP-DOWN
SIZE DATE:
IC NO. REV.
SHEET OF
TITLE:
APPROVALS
PCB DES.
APP ENG.
TECHNOLOGY Fax: [phone]
Milpitas, CA 95035 Phone: [phone] McCarthy Blvd. LTC Confidential-For Customer Use Only
CUSTOMER NOTICE
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS; HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL APPLICATION. COMPONENT SUBSTITUTION AND PRINTED CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT PERFORMANCE OR RELIABILITY. CONTACT LINEAR TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE. THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND
SCHEMATIC
SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
SCALE = NONE
www.linear.com
2
DEMO CIRCUIT 2215A
11
N/A LTC3126UFD
NC
JB
5 - 29 - 15
42V, 2.5A SYNCHRONOUS STEP-DOWN
SIZE DATE:
IC NO. REV.
SHEET OF
TITLE:
APPROVALS
PCB DES.
APP ENG.
TECHNOLOGY Fax: [phone]
Milpitas, CA 95035 Phone: [phone] McCarthy Blvd. LTC Confidential-For Customer Use Only
CUSTOMER NOTICE
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS; HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL APPLICATION. COMPONENT SUBSTITUTION AND PRINTED CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT PERFORMANCE OR RELIABILITY. CONTACT LINEAR TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE. THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND
SCHEMATIC
SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
SCALE = NONE
www.linear.com
2
DEMO CIRCUIT 2215A
11
N/A LTC3126UFD
NC
JB
5 - 29 - 15
42V, 2.5A SYNCHRONOUS STEP-DOWN
REVISION HISTORY
DESCRIPTION DATEAPPROVEDECO REV
JBPRODUCTION FAB- 2 5 - 29 - 15
REVISION HISTORY DESCRIPTION DATEAPPROVEDECO REV
JBPRODUCTION FAB- 2 5 - 29 - 15
REVISION HISTORY DESCRIPTION DATEAPPROVEDECO REV
JBPRODUCTION FAB- 2 5 - 29 - 15
E3
GND
R2
1.00M
U1
LTC3126UFD
VALID2 1
Vcc
2
PVcc
3
EXTVcc
4
Vset1
5
Vset2
6
Vref
7
GND
8
FB 9
RT
10
PGOOD
11
PRIORITY
12
PVin2
13
ENA 14
BST2 15
COM2 16
SW 17
PGND
18
PGND
19
SW 20
COM1 21
BST1 22
DIODE
23
PVIN1
24
Vin1
25
Vin2
26
PWM/SYNC 27
VALID1 28
PGND
29
E6
GND
C2 0.1 uF
C14
4.7 uF
0805 JP4
1 2 3
JP2
1 2 3
C1 0.1 uF
R5
1.00M
E5
VOUT
3.3V / 2.5A
E7
GND
C3
10 uF
1210
JP3
1 2 3
C7
47uF
1210
R8 1.00M
R3
324K
R10
215K
C12
0.1 uF
C5
10uF
1210
R7
1.00M
E2
VIN2
6 V - 8.4V
R6
1.00M C13
4.7 uF
0805
E13
SYNC
E9
EXTVcc
R9
787K
L1
4.7 uH
C10 10 pF
E8
PGOOD
C6
10uF 1206
JP1
1 2 3
C9 47uF
1210
E11
VALID2
E12
VALID1
R12
309K
R14
0.0
R1 51
C4
10 uF 1210
R11
732K
E4
VOUT
3.3V / 2.5A
R4 0.0
C11
0.1 uF
C15
47uF
1210
E1
VIN1
4.3V - 42.0V
E10
PRIORITY
R13 44.2K
C8
0.1 uF

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dc2215af
DEMO MANUAL DC2215A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2016
LT 0916 • PRINTED IN USA
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:
This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT
OR EVALUATION PURPOSES ONLY and is not provided by LTC for commercial use. As such, the DEMO BOARD herein may not be complete
in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety
measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union
directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.
If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date
of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU
OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS
FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR
ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.
The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LTC from all claims
arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all
appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or
agency certified (FCC, UL, CE, etc.).
No License is granted under any patent right or other intellectual property whatsoever. LTC assumes no liability for applications assistance,
customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.
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Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and
observe good laboratory practice standards. Common sense is encouraged.
This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LTC application
engineer.
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Copyright © 2004, Linear Technology Corporation

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