Demonstration circuit 1185 is a dual phase/dual output
synchronous buck converter featuring the LTC3850EUF.
The demo board comes in two versions. The output volt
ages for version DC1185B-A are 2.0V/10A and 1.8V/10A.
The output voltages for version DC1185B-B are 1.5V/15A
and 1.2V/15A. The input voltage range is 6.5V to 14V for
both versions. For applications that have a 5V ±0.5V input,
the board has an optional resistor to tie the INTVCC pin
to the VIN pin.
The demo board uses a high density, 2-sided drop-in layout.
The power components excluding the bulk output and input
capacitors, fit within a 1.35" × 0.75" area on the top layer.
The control circuit resides in a 0.60" × 0.75" area on the
bottom layer. The package style for the LTC3850EUF is a
4mm × 4mm 28-lead QFN with an exposed ground pad.
PERFORMANCE SUMMARY
PARAMETERCONDITIONVALUE
Minimum Input Voltage6.5V
Maximum Input Voltage14V
Specifications are at TA = 25°C
The main features of the board include an internal 5V linear
regulator for bias, RUN pins for each output, an EXTVCC
-
pin and a PGOOD signal. The board can be configured
for either CCM (original setting), Burst Mode
skipping operation with the MODE jumper. The board
also has optional resistors for single output/dual phase
operation, rail tracking, DCR sensing and synchronization
to an external clock.
Design files for this circuit board are available at
http://www.linear.com/demo
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
Note: Q1-Q4 MOSFETs changed on September 10, 2013.
See Schematic Diagram.
®
, or pulse-
Version DC1185B-A
Output Voltage V
Output Voltage V
Nominal Switching Frequency500kHz
Full-Load Efficiency
(See Figure 3 for Efficiency Curves)
Version DC1185B-B
Output Voltage V
Output Voltage V
Nominal Switching Frequency400kHz
Full-Load Efficiency
(See Figure 4 for Efficiency Curves)
OUT1
OUT2
OUT1
OUT2
I
= 0A to 10A2.0V ±2%
OUT1
I
= 0A to 10A1.8V ±2%
OUT2
= 2.0V, I
V
OUT1
V
= 1.8V, I
OUT2
I
= 0A to 15A1.5V ±2%
OUT1
I
= 0A to 15A1.2V ±2%
OUT2
= 1.5V, I
V
OUT1
V
= 1.2V, I
OUT2
= 10A, VIN = 12V
OUT1
= 10A, VIN = 12V
OUT2
= 15A, VIN = 12V
OUT1
= 15A, VIN = 12V
OUT2
90.2%
89.5%
88.1%
86.5%
dc1185b-a/-bf
1
Page 2
DEMO MANUAL
DC1185B-A/-B
QUICK START PROCEDURE
Demonstration circuit 1185 is easy to set up to evaluate
the performance of the LTC3850EUF. Refer to Figure 1
for the proper measurement equipment setup and follow
the procedure below:
Note: When measuring the output or input voltage ripple,
care must be taken to avoid a long ground lead on the
oscilloscope probe. See Figure 2 for the proper scope
probe technique. Short, stiff leads need to be soldered
to the (+) and (–) terminals of an output capacitor. The
probe’s ground ring needs to touch the (–) lead and the
probe tip needs to touch the (+) lead.
Place jumpers in the following positions:
JP1 RUN1 ON
JP2 RUN2 ON
JP3 MODE CCM
With power off, connect the input power supply to VIN
and GND.
Turn on the power at the input.
Note: Make sure that the input voltage does not exceed 15V.
Check for the proper output voltages.
Version DC1158B-A:
V
V
Version DC1158B-B:
V
V
Once the proper output voltages are established, adjust
the loads within the operating range and observe the
output voltage regulation, ripple voltage, efficiency and
other parameters.
Note:
turrets. These turrets are only intended to Kelvin sense
the output voltage across COUT1 and COUT4. Heavy load
currents may damage the output voltage sense traces.
= 1.960V to 2.040V
OUT1
= 1.764V to 1.836V
OUT2
= 1.470V to 1.530V
OUT1
= 1.176V to 1.224V
OUT2
Do not apply load across the VOSn+ and VOSn –
2
Figure 1. Proper Measurement Equipment Setup
dc1185b-a/-bf
Page 3
DEMO MANUAL
VOUT
GND
COUT
+
-
DC1185B-A/-B
QUICK START PROCEDURE
Figure 2. Measuring Output Voltage Ripple
2.0V/10A and 1.8V/10A Efficiency at VIN = 12V and fSW = 500kHz1.5V/15A and 1.2V/15A Efficiency at VIN = 12V and fSW = 400kHz
95
90
85
80
EFFICIENCY (%)
QTOP: RJK030DPB
QBOTTOM: RJK0330DPB
75
L: TOKO FDU0650-R56M = P3
0.56µH, DCR = 2.45mΩ, 3.2mΩ MAX
R
70
0
= 3mΩ
SENSE
468
2
LOAD CURRENT (A)
2.0V
1.8V
1012
Figure 3. Efficiency Curves for the DC1185B-AFigure 4. Efficiency Curves for the DC1185B-B
SINGLE OUTPUT/DUAL PHASE OPERATION
A single output/dual phase converter may be preferred
for high output current applications. The benefits of
single output/dual phase operation is lower ripple current
through the input and output capacitors, improved load
step response and simplified thermal design. To implement
single output/dual phase operation, make the following
modifications:
1. Tie VOUT1 to VOUT2 by tying together the exposed
copper pads near J3 and J5 at the edge of the board.
Use a piece of heavy copper foil.
2. Tie ITH1 to ITH2 by stuffing 0Ω at R49.
3. Tie VFB1 to VFB2 by stuffing 0Ω at R50.
4. Tie TRK/SS1 to TRK/SS2 by stuffing 0Ω at R52.
5. Tie RUN1 to RUN2 by stuffing 0Ω at R55.
6. Remove the redundant ITH compensation network and
VFB divider.
Demonstration circuit 1185 is set up for independent
turn-on of VOUT1 and VOUT2. The ramp-rate for VOUT1 is
determined by the TRK/SS1 capacitor at C2 and the ramprate for VOUT2 is determined by the TRK/SS2 capacitor
at C47. The turn-on of one rail will not affect the other for
the original demo board.
Table 1. VOUT1 Tracking Options for a 1.5V Output
TRACK 1 DIVIDERTRK/SS1 CAPACITOR
CONFIGURATIONR3R2C2
Soft-Start without Tracking (Original Board)0ΩNot Stuffed0.1µF
This board can be modified on the bench to allow VOUT1
to track an external signal. It can also be modified to
allow VOUT
an
external signal. Tables 2 and 3 cover the rail tracking
2 to track VOUT1 or to allow VOUT2 to track
options for each rail, with the DC3850B-B version used
as an example.
TRACK 2 DIVIDERTRK/SS2 CAPACITOR
4
dc1185b-a/-bf
Page 5
INDUCTOR DCR SENSING
DEMO MANUAL
DC1185B-A/-B
Demonstration circuit 1185 provides an optional circuit
for DCR sensing. DCR sensing uses the DCR of the inductor to
sense
sense the inductor current instead of discrete
resistors. The advantages of DCR sensing are lower
cost, reduced board space and higher efficiency, but the
disadvantage is a less accurate current limit. If DCR sens
ing is used, be sure to select an inductor current with a
sufficiently
high saturation current or use an iron powder
type. Tables 3 and 4 show an example of how to modify
the DC1185 for DCR sensing using these parameters:
Table 3. V
CONFIGURATION RS1L1R29, R30C14R45 R47 R61
DCR SensingShort with Cu
Discrete R
(Original Board)
Configured as a 2.0V/10A Converter Using DCR Sensing and Discrete Sense Resistors
OUT1
DCR FILTER/DIVIDER RESISTORS
2.37kΩ6.49kΩ0Ω
SENSE
Strip or Very
Short and Thick
Piece of Wire
3mΩ
2010 Package
Toko
FDU0650-R56M=P3
Toko
FDU0650-R56M=P3
R
FILTER
SENSE
RESISTORS
Open0.1µF
100Ω1nFOpenOpenOpen
SENSE FIILTER
CAPACITOR
SENSE1– TO L1–
JUMPERTOPBOTTOM
Table 4. V
CONFIGURATION RS2L2R39, R40C15R51R53 R62
DCR SensingShort with Cu
Discrete R
(Original Board)
Configured as a 1.8V/10A Converter Using DCR Sensing and Discrete Sense Resistors
OUT2
DCR FILTER/DIVIDER RESISTORS
2.37kΩ6.49kΩ0Ω
SENSE
Strip or Very
Short and Thick
Piece of Wire
3mΩ
2010 Package
Toko
FDU0650-R56M=P3
Toko
FDU0650-R56M=P3
R
FILTER
SENSE
RESISTORS
Open0.1µF
100Ω1nFOpenOpenOpen
SENSE FIILTER
CAPACITOR
SENSE1– TO L1–
JUMPERTOPBOTTOM
dc1185b-a/-bf
5
Page 6
DEMO MANUAL
DC1185B-A/-B
SYNCHRONIZATION TO AN EXTERNAL CLOCK
The LTC3850 uses a phase-lock-loop which forces its
internal clock to be synchronized to an external clock.
Once synchronized, the rising edge of the top FET gate is
aligned to the rising edge of the external clock. The external
clock signal needs to be applied to the LTC3850’s MODE
pin which is tied to the turret labeled SYNC. The internal
phase lock loop is stabilized by a network on the FREQ pin
of the LTC3850. To set up the DC1185 for synchronization
to an external clock, follow the steps below.
1. Remove R7.
2. Stuff 10kΩ at R8.
3. Stuff 10nF at R10.
4. Leave 1nF at C12.
5. Float the MODE pin by placing the MODE jumper in the
BM position.
6. Apply the external clock from the turret la-beled SYNC
to GND.
6
dc1185b-a/-bf
Page 7
DEMO MANUAL
DC1185B-A/-B
PARTS LIST
ITEMQTYREFERENCEPART DESCRIPTIONMANUFACTURER/PART NUMBER
Required Circuit Components
13C11, C32, C36CAP, 0805 4.7µF 10% 6.3V X5RAVX 08056D475K AT
SET RSENSE FILTER TIME CONSTANT0.6nH/RSENSE FOR 2010 PACKAGE.
NOTE:
4
JP3
JP3
CCMBM
3
2
MODE
MODE
PS
1
R4
10.0KR410.0K
INTVCC
INTVCCVIN
C1
OPTC1OPT
R10R1
Linear Technology has made a best effort to
Linear Technology has made a best effort to
Linear Technology has made a best effort to
0
E1E1
R27
[1]
R27
[1]
C37
OPT
C37
OPT
R7
10.0KR710.0K
R26
OPT
R26
OPT
1
2
RUN1
ON
SYNC
and reliable operation in the actual application, Component
Applications Engineering for assistance.
and reliable operation in the actual application, Component
Applications Engineering for assistance.
and reliable operation in the actual application, Component
Applications Engineering for assistance.
Customer Notice:
Customer Notice:
Customer Notice:
design a circuit that meets customer-supplied specifications;
however, it remains the customer's responsibility to verify proper
substitution and printed circuit board layout may significantly
affect circuit performance or reliability. Contact Linear
This circuit is proprietary to Linear Technology and supplied
for use with Linear Technology parts.
design a circuit that meets customer-supplied specifications;
however, it remains the customer's responsibility to verify proper
substitution and printed circuit board layout may significantly
affect circuit performance or reliability. Contact Linear
This circuit is proprietary to Linear Technology and supplied
for use with Linear Technology parts.
design a circuit that meets customer-supplied specifications;
however, it remains the customer's responsibility to verify proper
substitution and printed circuit board layout may significantly
affect circuit performance or reliability. Contact Linear
This circuit is proprietary to Linear Technology and supplied
for use with Linear Technology parts.
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
VIN
4.7uF
4.7uF
CMDSH-3D1CMDSH-3
VINF
20
BG1
ITH1
C2
R2
0
D2
C11
C11
0.1uF
0.1uF
C17
C17
R18 2.2R18 2.2
INTVCC
19
18
17
VIN
BG2
INTVCC
ITH2
VFB2
VFB1
R32 20.0KR32 20.0K
R33 20.0KR33 20.0K
C43 100pFC43 100pF
C42
100pF
C42
100pF
R31
[1]
R31
[1]
0.1uFC20.1uF
OPTR2OPT
VOUT1
16
PGND
6
TRK/SS2
C44
C44
R35
R35
R34
R34
R250R25
15
9
RUN2
1nF
1nF
0
BOOST2
RUN2
OPT
OPT
CMDSH-3D2CMDSH-3
13
14
TG2
SW2
ILIM10EXTVCC11PGOOD
VIN
[1]
[1]
R36 0R36 0
E10E10
TRK/SS2
C21
C21
S2+
8
12
C47
C47
R37
R37
0.1uF
0.1uF
C15
C15
7
SENSE2+
0.1uF
0.1uF
OPT
OPT
SENSE2-
SGND
R38
R38
R40
100
R40
100
1nF
1nF
S2-
R39
100
R39
100
29
R43
[1]
R43
[1]
C49
OPT
C49
OPT
R44
OPT
R44
OPT
R42
OPT
R42
OPT
R41
OPT
R41
OPT
INTVCC
C48
OPT
C48
OPT
3
JP2JP2
OFF
E2E2
RUN2
OPT
OPT
1ON2
GND
INTVCC
EXTVCC
E3E3
R46
R46
C50
1uF
C50
1uF
EXTVCC
INTVCCVINF
R60
OPT
R60
OPT
STUFF R60 WITH 0 OHMS FOR
100K
100K
PGOOD
E4E4
PGOOD
4.6V<VIN<5.5V
NOTE:
D1
C20
0.1uF
C20
0.1uF
R30
100
R30
100
C14
1nF
C14
1nF
R90R90
S1+
S1-
R29
100
R29
100
27
23
28
22
21
TG1
SW1
BOOST1
SENSE1-
SENSE1+
U1
U1
LTC3850EUF
LTC3850EUF
TRK/SS11ITH12VFB13VFB24ITH25TRK/SS2
MODE24FREQ
RUN1
25
26
TRK/SS1
RUN1
C12
1nF
C12
1nF
0
[1]
[1]
R80R8
R10
R10
R28
OPT
R28
OPT
C38
OPT
C38
OPT
3
JP1JP1
OFF
C41 1nFC41 1nF
R30R3
E9E9
TRK/SS1
&
8.66K
5.9K
ITH1 ITH2
R43
25.5K
10.0K
4
30.1K
17.8K
VOUT1 VOUT2
TOP FEED BACK R
RENESAS RJK0330DPB
3
RENESAS RJK0305DPB RENESAS RJK0330DPB
RENESAS RJK0305DPB
0.4uH
2
TOKO FDU0650-R56M=P3
0.003
0.002VITEC 59PR9875
1.8V/10A
1.2V/15A
VOUT1
THESE ARE ONLY INTENDED TO KELVIN SENSE THE OUTPUT VOLTAGE ACROSS COUT1
AND COUT4.
ASSYVOUT2 RS1, RS2L1, 2Q1, 3Q2, 4R27R31, R35
2. FSW = 400kHz For Assy - B
3. DO NOT APPLY LOAD FROM THE VO1+ TO VO1- OR FROM THE VO2+ TO VO2- TURRETS.
1. FSW = 500kHz For Assy - A
2.0V/10A
- A
1.5V/15A
- B
1
[1]
dc1185b-a/-bf
9
Page 10
DEMO MANUAL
DC1185B-A/-B
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LT C ) 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 LT C 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 LT C 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. LT C assumes no liability for applications assistance,
customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.
LT C currently services a variety of customers for products around the world, and therefore this transaction is not exclusive.
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.