Linear Technology DC1185B-A Quick setup guide

1
dc1185b-a/-bf
DEMO MANUAL
DC1185B-A/-B
DESCRIPTION
LTC3850EUF
Dual Phase/Dual Output
Synchronous Buck Converter
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.
Thedemoboardusesahighdensity,2-sideddrop-inlayout.
Thepowercomponentsexcludingthe 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.
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.
PERFORMANCE SUMMARY
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
®
, or pulse-
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
Specifications are at TA= 25°C
PARAMETER CONDITION VALUE
Minimum Input Voltage 6.5V
Maximum Input Voltage 14V
Version DC1185B-A
Output Voltage VOUT1 IOUT1 = 0A to 10A 2.0V ±2%
Output Voltage VOUT2 IOUT2 = 0A to 10A 1.8V ±2%
Nominal Switching Frequency 500kHz
Full-Load Efficiency
(See Figure 3 for Efficiency Curves)
VOUT1 = 2.0V, IOUT1 = 10A, VIN = 12V
VOUT2 = 1.8V, IOUT2 = 10A, VIN = 12V
90.2%
89.5%
Version DC1185B-B
Output Voltage VOUT1 IOUT1 = 0A to 15A 1.5V ±2%
Output Voltage VOUT2 IOUT2 = 0A to 15A 1.2V ±2%
Nominal Switching Frequency 400kHz
Full-Load Efficiency
(See Figure 4 for Efficiency Curves)
VOUT1 = 1.5V, IOUT1 = 15A, VIN = 12V
VOUT2 = 1.2V, IOUT2 = 15A, VIN = 12V
88.1%
86.5%

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dc1185b-a/-bf
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:Makesurethat the input voltage does not exceed 15V.
Check for the proper output voltages.
Version DC1158B-A:
VOUT1 = 1.960V to 2.040V
VOUT2 = 1.764V to 1.836V
Version DC1158B-B:
VOUT1 = 1.470V to 1.530V
VOUT2 = 1.176V to 1.224V
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: Do not apply load across the VOSn+ and VOSn–
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.
Figure 1. Proper Measurement Equipment Setup

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dc1185b-a/-bf
DEMO MANUAL
DC1185B-A/-B
QUICK START PROCEDURE
SINGLE OUTPUT/DUAL PHASE OPERATION
VOUT
GND
COUT
+
-
Figure 2. Measuring Output Voltage Ripple
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
stepresponseand 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.
LOAD CURRENT (A)
0
70
EFFICIENCY (%)
75
80
85
90
95
2.0V
1.8V
24 6 8 10 12
QTOP: RJK030DPB
QBOTTOM: RJK0330DPB
L: TOKO FDU0650-R56M = P3
0.56µH, DCR = 2.45mΩ, 3.2mΩ MAX
RSENSE = 3mΩ
LOAD CURRENT (A)
0
70
EFFICIENCY (%)
75
80
85
90
95
1.2V
36 9 12 15 18
QTOP: RJK030DPB
QBOTTOM: RJK0330DPB
L: VITEC 59PR9875
0.4µH, DCR = 0.47mΩ ±10%
RSENSE = 2mΩ
1.5V
2.0V/10A and 1.8V/10A Efficiency at VIN = 12V and fSW = 500kHz 1.5V/15A and 1.2V/15A Efficiency at VIN = 12V and fSW = 400kHz
Figure 3. Efficiency Curves for the DC1185B-A Figure 4. Efficiency Curves for the DC1185B-B

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dc1185b-a/-bf
DEMO MANUAL
DC1185B-A/-B
RAIL TRACKING
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 ramp-
rate 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.
This board can be modified on the bench to allow VOUT1
to track an external signal. It can also be modified to
allow VOUT2 to track VOUT1 or to allow VOUT2 to track
an external signal. Tables 2 and 3 cover the rail tracking
options for each rail, with the DC3850B-B version used
as an example.
Table 1. VOUT1 Tracking Options for a 1.5V Output
TRACK 1 DIVIDER TRK/SS1 CAPACITOR
CONFIGURATION R3 R2 C2
Soft-Start without Tracking (Original Board) 0Ω Not Stuffed 0.1µF
External Coincident Tracking 17.8kΩ 20.0kΩ Not Stuffed
Table 2. VOUT2 Tracking Options for a 1.2V Output
TRACK 2 DIVIDER TRK/SS2 CAPACITOR
CONFIGURATION R36 R34 R37 C47
Soft-Start without Tracking (Original Board) 0Ω Not Stuffed Not Stuffed 0.1µF
Coincident Tracking to VOUT1 (1.5V) 0Ω 10.0kΩ 20.0kΩ Not Stuffed
External Coincident Tracking 10.0kΩ Not Stuffed 20.0kΩ Not Stuffed

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dc1185b-a/-bf
DEMO MANUAL
DC1185B-A/-B
INDUCTOR DCR SENSING
Demonstration circuit 1185 provides an optional circuit
for DCR sensing. DCR sensing uses the DCR of the in-
ductor to sense the inductor current instead of discrete
sense 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:
VOUT1 = 2.0V/10A
VOUT2 = 1.8V/10A
VIN = 6.5V to 14V
fSW = 500kHz, typical
L1, L2 = Toko FDU0650-R56M=P3
(0.56µH, DCR = 2.45mΩ Typ, 3.2mΩ Max)
ILIM = Floating (R42, R44 = Open)
Table 3. VOUT1 Configured as a 2.0V/10A Converter Using DCR Sensing and Discrete Sense Resistors
RSENSE FILTER
RESISTORS
SENSE FIILTER
CAPACITOR
DCR FILTER/DIVIDER RESISTORS SENSE1– TO L1–
JUMPERTOP BOTTOM
CONFIGURATION RS1 L1 R29, R30 C14 R45 R47 R61
DCR Sensing Short with Cu
Strip or Very
Short and Thick
Piece of Wire
Toko
FDU0650-R56M=P3
Open 0.1µF 2.37kΩ 6.49kΩ 0Ω
Discrete RSENSE
(Original Board)
3mΩ
2010 Package
Toko
FDU0650-R56M=P3
100Ω 1nF Open Open Open
Table 4. VOUT2 Configured as a 1.8V/10A Converter Using DCR Sensing and Discrete Sense Resistors
RSENSE FILTER
RESISTORS
SENSE FIILTER
CAPACITOR
DCR FILTER/DIVIDER RESISTORS SENSE1– TO L1–
JUMPERTOP BOTTOM
CONFIGURATION RS2 L2 R39, R40 C15 R51 R53 R62
DCR Sensing Short with Cu
Strip or Very
Short and Thick
Piece of Wire
Toko
FDU0650-R56M=P3
Open 0.1µF 2.37kΩ 6.49kΩ 0Ω
Discrete RSENSE
(Original Board)
3mΩ
2010 Package
Toko
FDU0650-R56M=P3
100Ω 1nF Open Open Open

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dc1185b-a/-bf
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.

7
dc1185b-a/-bf
DEMO MANUAL
DC1185B-A/-B
PARTS LIST
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 3 C11, C32, C36 CAP, 0805 4.7µF 10% 6.3V X5R AVX 08056D475KAT
2 5 C12, C14, C15, C41, C44 CAP, 0603 1nF 10% 50V X7R AVX 06035C102KAT
3 5 C2, C17, C20, C21, C47 CAP, 0603 0.1µF 10% 25V X7R TDK C1608X7R1E104K
4 2 C43, C42 CAP, 0603 100pF 5% 25V X7R AVX 06033C101JAT
5 1 CIN1 CAP, 180µF 20% 16V OSCON SANYO OSCON 16SVP180MX
6 2 CIN2, CIN3 CAP, 1210 10µF 10% 16V X5R TAIYO YUDEN EMK325BJ106KN-T
7 2 COUT1, COUT4 CAP, 1210 47µF 20% 6.3V X5R TDK C3225X5R0J476MT
8 4 COUT2, COUT3, COUT5, COUT6 CAP, 7343 330µF 20% 2.5V POSCAP SANYO 2R5TPE330M9
9 2 D2, D1 DIODE, CMDSH-3 SOD323 CENTRAL CMDSH-3TR
10 2 L1, L2 IND, 0.56µH TOKO FDU0650-R56M=P3
11 2 Q1, Q3 XSTR, N-CHANNEL MOSFET RENESAS RJK0305DPB
12 2 Q2, Q4 XSTR, N-CHANNEL MOSFET RENESAS RJK0330DPB
13 1 R10 RES, 0603 3.16k 1% 1/10W VISHAY CRCW06033K16FKEA
14 1 R18 RES, 0603 2.2Ω 5% 1/10W VISHAY CRCW06032R20JNEA
15 1 R27 RES, 0603 30.1k 1% 1/10W VISHAY CRCW060330K1FKEA
16 4 R29, R30, R39, R40 RES, 0603 100Ω 5% 1/10W VISHAY CRCW0603100RJNEA
17 2 R31,R35 RES, 0603 8.66k 1% 1/10W VISHAY CRCW06038K66FKEA
18 2 R32,R33 RES, 0603 20k 1% 1/10W VISHAY CRCW060320KFKEA
19 1 R43 RES, 0603 25.5k 1% 1/10W VISHAY CRCW060325K5FKEA
20 1 R46 RES, 0603 100k 5% 1/10W VISHAY CRCW0603100KJNEB
21 2 R7, R4 RES, 0603 10k 1% 1/16W VISHAY CRCW060310K0FKEB
22 3 R8, R9, R25 RES, 0603 0Ω JUMPER PANASONIC ERJ3GEY0R00V
23 2 RS2, RS1 RES, 2010 0.003Ω 5% 1/2W VISHAY WSL20103L000FEA
24 1 U1 IC, LTC3850EUF LINEAR TECH. LTC3850EUF
Additional Circuit Components
1 0 CIN5, CIN4 CAP, 1210 OPTION OPTION
2 0 C1, C37, C38, C47, C48, C49 CAP, 0603 OPTION OPTION
3 1 C50 CAP, 0603 1µF 20% 16V X7R AVX 0603YC105MAT2A
4 0 D4, D3 DIODE, SCHOTTKY 40V 3A OPTION OPTION
5 0 Q5, Q6, Q7, Q8 DO NOT STUFF OPTION
6 3 R1, R3, R36 RES, 0603 0Ω JUMPER PANASONIC ERJ3GEY0R00V
7 0 R2, R26, R28, R34, R37, R38, R41, R42,
R44, R45, R47, R49, R50-R53, R55,
R60-R62
RES, 0603 OPTION OPTION
Hardware
1 12 E1-E6, E9-E14 TURRET MILL-MAX 2501-2-00-80-00-00-07-0
2 2 JP2, JP1 HEADER, 3-PIN, 2mm SAMTEC TMM-103-02-L-S
3 1 JP3 HEADER, 4-PIN SAMTEC TMM-104-02-L-S
4 6 J1, J2, J3, J4, J5, J6 JACK, BANANA KEYSTONE 575-4
5 3 JP1-JP3 SHUNT, 2mm SAMTEC 2SN-BK-G
(DC1185B-A)

8
dc1185b-a/-bf
DEMO MANUAL
DC1185B-A/-B
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 3 C11, C32, C36 CAP, 0805 4.7µF 10% 6.3V X5R AVX 08056D475KAT
2 5 C12, C14, C15, C41, C44 CAP, 0603 1nF 10% 50V X7R AVX 06035C102KAT
3 5 C2, C17, C20, C21, C47 CAP, 0603 0.1µF 10% 25V X7R TDK C1608X7R1E104K
4 2 C43, C42 CAP, 0603 100pF 5% 25V X7R AVX 06033C101JAT
5 1 CIN1 CAP, 180µF 20% 16V OSCON SANYO OSCON 16SVP180MX
6 2 CIN2, CIN3 CAP, 1210 10µF 10% 16V X5R TAIYO YUDEN EMK325BJ106KN-T
7 2 COUT1, COUT4 CAP, 1210 100µF 20% 6.3V X5R TDK C3225X5R0J107MT
8 4 COUT2, COUT3, COUT5, COUT6 CAP, 7343 330µF 20% 2.5V POSCAP SANYO 2R5TPE330M9
9 2 D2, D1 DIODE, CMDSH-3 SOD323 CENTRAL CMDSH-3TR
10 2 L1, L2 IND, 0.4µH VITEC 59PR9875
11 2 Q1, Q3 XSTR, N-CHANNEL MOSFET RENESAS RJK0305DPB
12 2 Q2, Q4 XSTR, N-CHANNEL MOSFET RENESAS RJK0330DPB
13 1 R10 RES, 0603 2.55k 1% 1/10W VISHAY CRCW06032K55FKEB
14 1 R18 RES, 0603 2.2Ω 5% 1/10W VISHAY CRCW06032R20JNEA
15 1 R27 RES, 0603 17.8k 1% 1/10W VISHAY CRCW060317K8FKEA
16 4 R29, R30, R39, R40 RES, 0603 100Ω 5% 1/10W VISHAY CRCW0603100RJNEA
17 2 R31, R35 RES, 0603 5.9k 1% 1/10W VISHAY CRCW06035K90FKEA
18 2 R32, R33 RES, 0603 20k 1% 1/10W VISHAY CRCW060320KFKEA
19 1 R43 RES, 0603 10.0k 1% 1/10W VISHAY CRCW060310K0FKEB
20 1 R46 RES, 0603 100k 5% 1/10W VISHAY CRCW0603100KJNEB
21 2 R7, R4 RES, 0603 10k 1% 1/16W VISHAY CRCW060310K0FKEB
22 3 R8, R9, R25 RES, 0603 0Ω JUMPER PANASONIC ERJ3GEY0R00V
23 2 RS2, RS1 RES, 2010 0.002Ω 5% 1/2W VISHAY WSL20102L000FEA
24 1 U1 IC, LTC3850EUF LINEAR TECH. LTC3850EUF
Additional Circuit Components
1 0 CIN5, CIN4 CAP, 1210 OPTION OPTION
2 0 C1, C37, C38, C47, C48, C49 CAP, 0603 OPTION OPTION
3 1 C50 CAP, 0603 1µF 20% 16V X7R AVX 0603YC105MAT2A
4 0 D4, D3 DIODE, SCHOTTKY 40V 3A OPTION OPTION
5 0 Q5, Q6, Q7, Q8 DO NOT STUFF OPTION
6 3 R1, R3, R36 RES, 0603 0Ω JUMPER PANASONIC ERJ3GEY0R00V
7 0 R2, R26, R28, R34, R37, R38, R41,
R42, R44, R45, R47, R49, R50-R53,
R55, R60-R62
RES, 0603 OPTION OPTION
Hardware
1 12 E1-E6, E9-E14 TURRET MILL-MAX 2501-2-00-80-00-00-07-0
2 2 JP2, JP1 HEADER, 3-PIN, 2mm SAMTEC TMM-103-02-L-S
3 1 JP3 HEADER, 4-PIN SAMTEC TMM-104-02-L-S
4 6 J1, J2, J3, J4, J5, J6 JACK, BANANA KEYSTONE 575-4
5 3 JP1-JP3 SHUNT, 2mm SAMTEC 2SN-BK-G
PARTS LIST
(DC1185B-B)

9
dc1185b-a/-bf
DEMO MANUAL
DC1185B-A/-B
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
1
1
2
2
3
3
4
4
5
5
6
6
7
7
8
8
A
A
B
B
C
C
D
D
VO1- VOUT1 VIN
TRK/SS1 EXTVCC
VOUT2 VO2- [1]
[1]
1
VO1+ GND VO2+ GND VIN+ VIN- GND
3 2
ON OFF
RUN1
3
RUN2
OFF
1
ON
2
PGOOD
GND SYNC
TRK/SS2
ASSY VOUT2 RS1, RS2 L1, 2 Q1, 3 Q2, 4 R27 R31, R35
2.0V/10A 1.5V/15A
VOUT1
1.8V/10A 1.2V/15A
0.003 0.002 VITEC 59PR9875
[1]
30.1K 17.8K
8.66K 5.9K
25.5K 10.0K
VOUT1 VOUT2 TOP FEED BACK R
ITH1 ITH2
OPTIONAL JUMPERS FOR
SINGLE OUTPUT/DUAL PHASE
OPERATION OPTIONAL DCR SENSING
NOTE: WHEN DCR SENSING IS
CCMBM
0.4uH
R43
- A
- B
R10 3.16K 2.55K FSW
NOTE:
RENESAS RJK0305DPB RENESAS RJK0330DPB
STUFF R60 WITH 0 OHMS FOR 4.6V<VIN<5.5V
COUT1/COUT4
47uF
100uF
TOKO FDU0650-R56M=P3
NOTE:
2010
2010
SET RSENSE FILTER TIME CONSTANT 0.6nH/RSENSE FOR 2010 PACKAGE.
RENESAS RJK0330DPB
Represents Tooling Holes
on PCB
<
&
REMOVE R30, R29, R40 & R39
2. FSW = 400kHz For Assy - B
CALCULATE R45, R47, C14 AND R51, R53 & C15 PER THE DATA SHEET. ALSO REFER TO QSG FOR EXAMPLE. STUFF R61 AND R62 WITH 0 OHMS. IMPLEMENTED, SHORT RSENSE1 & RSENSE2.
6.5V - 14V
PS
3. DO NOT APPLY LOAD FROM THE VO1+ TO VO1- OR FROM THE VO2+ TO VO2- TURRETS.
THESE ARE ONLY INTENDED TO KELVIN SENSE THE OUTPUT VOLTAGE ACROSS COUT1 AND COUT4.
1. FSW = 500kHz For Assy - A
1.1 CHANGE: Q1,Q2,Q3,Q4 08/04/13 MIKE S.
MIKE S.
MIKE S. 08/05/13
RENESAS RJK0305DPB
VSW2 VSW1
S1+ S1- S2+ S2-
TRK/SS1 ITH2 VFB2 VFB1 RUN2 RUN1
EXTVCC PGOOD
ITH1 TRK/SS2
ITH1 VFB1 VFB2
ITH2 TRK/SS2TRK/SS1 RUN2RUN1
VSW1 S1+
S1-
VSW2 S2+
S2-
VOUT1
VOUT2 VL1- VL2-
VOUT1
INTVCC
VIN
INTVCC
VIN
INTVCCVIN
VIN
INTVCC
VIN VIN
INTVCC
INTVCC
VINF
INTVCCVINF
VL1-
VL2-
REVISION HISTORY
DESCRIPTION DATE APPROVEDECO REV
PROD1 12/12/07
REVISION HISTORY
DESCRIPTION DATE APPROVEDECO REV
PROD1 12/12/07
REVISION HISTORY
DESCRIPTION DATE APPROVEDECO REV
PROD1 12/12/07
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
Applications Engineering for assistance.
This circuit is proprietary to Linear Technology and supplied for use with Linear Technology parts.
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
Applications Engineering for assistance.
This circuit is proprietary to Linear Technology and supplied for use with Linear Technology parts.
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
Applications Engineering for assistance.
This circuit is proprietary to Linear Technology and supplied for use with Linear Technology parts.
SIZE
SCALE:
CAGE CODE
DWG NO
REV
SHEET OF
FILENAME:
TITLE
CONTRACT NO.
APPROVALS
DATE
DRAWN CHECKED APPROVED ENGINEER DESIGNER
TECHNOLOGY
1630 McCarthy Blvd. Milpitas, CA 95035 Phone: [phone] Fax: [phone]
1
DC1185B
Tuesday, September 10, 2013
11
SCH, LTC3850EUF, DUAL OUTPUT SYNCHRONOUS
1185B-1.DSNNONE
MEI
10/31/06
BUCK CONVERTER
SIZE
SCALE:
CAGE CODE
DWG NO
REV
SHEET OF
FILENAME:
TITLE
CONTRACT NO.
APPROVALS
DATE
DRAWN CHECKED APPROVED ENGINEER DESIGNER
TECHNOLOGY
1630 McCarthy Blvd. Milpitas, CA 95035 Phone: [phone] Fax: [phone]
1
DC1185B
Tuesday, September 10, 2013
11
SCH, LTC3850EUF, DUAL OUTPUT SYNCHRONOUS
1185B-1.DSNNONE
MEI
10/31/06
BUCK CONVERTER
SIZE
SCALE:
CAGE CODE
DWG NO
REV
SHEET OF
FILENAME:
TITLE
CONTRACT NO.
APPROVALS
DATE
DRAWN CHECKED APPROVED ENGINEER DESIGNER
TECHNOLOGY
1630 McCarthy Blvd. Milpitas, CA 95035 Phone: [phone] Fax: [phone]
1
DC1185B
Tuesday, September 10, 2013
11
SCH, LTC3850EUF, DUAL OUTPUT SYNCHRONOUS
1185B-1.DSNNONE
MEI
10/31/06
BUCK CONVERTER
X2X2
1
C14 1nF C14 1nF
E2E2
R29 100 R29 100
+
COUT2 330uF 2.5V
+
COUT2 330uF 2.5V
+
COUT3 330uF 2.5V
+
COUT3 330uF 2.5V
R52
OPT
R52
OPT
E3E3
R61 OPT R61 OPT
J6J6
R34 OPT R34 OPT
CIN5 OPT CIN5 OPT
CIN2 10uF CIN2 10uF
R42 OPT R42 OPT
C17
0.1uF
C17
0.1uF
R41 OPT R41 OPT
E4E4
E14E14
R51 OPT R51 OPT
R55
OPT
R55
OPT
Q4 [1] Q4 [1]
4
5
6
7
8
3
1
2
E6E6
R62 OPTR62 OPT
C32 4.7uF 6.3V C32 4.7uF 6.3V
R43 [1] R43 [1]
R8
0
R8
0
CIN3 10uF CIN3 10uF
C12 1nF C12 1nF
C38 OPT C38 OPT
E12E12
R25
0
R25
0
C11
4.7uF
C11
4.7uF
U1
LTC3850EUF
U1
LTC3850EUF
TRK/SS1
1
ITH1
2
VFB1
3
VFB2
4
ITH2
5
TRK/SS2
6
SENSE2- 7
SENSE2+ 8
RUN2
9
BG2 17
INTVCC 18
PGND 16
BG1 20
BOOST1 21
TG1 22
SW1 23
MODE
24
FREQ
25
SENSE1- 28
VIN 19
ILIM
10
EXTVCC
11
PGOOD
12
SW2 13
TG2 14
BOOST2 15
RUN1
26
SENSE1+ 27
SGND
29
E1E1
R45
OPT
R45
OPT
CIN4 OPT CIN4 OPT
R39 100 R39 100
R32 20.0KR32 20.0K
RS2 [1] RS2 [1]
R26 OPT R26 OPT
Q7 OPT Q7 OPT
4
5
6
7
8
3
1
2
R33 20.0KR33 20.0K
R1 0 R1 0
E13E13
JP3
MODE
JP3
MODE
1
2
3
4
D2
CMDSH-3
D2
CMDSH-3
D4
OPT
D4
OPT
2 1
R46
100K
R46
100K
J5J5
C20 0.1uF C20 0.1uF
R40 100 R40 100
JP2JP2
R28 OPT R28 OPT
L1 [1]L1 [1]
C1
OPT
C1
OPT
R27 [1] R27 [1]
L2 [1]L2 [1]
C43 100pFC43 100pF
R9 0R9 0
Q3 [1] Q3 [1]
4
5
6
7
8
3
1
2
R49
OPT
R49
OPT
R44 OPT R44 OPT
R7
10.0K
R7
10.0K
C21 0.1uF C21 0.1uF
D3
OPT
D3
OPT
2 1
C2 0.1uF C2 0.1uF
J2J2
+
COUT5 330uF 2.5V
+
COUT5 330uF 2.5V
X1X1
1
R60 OPT R60 OPT
C41 1nFC41 1nF
R36 0R36 0
C36 4.7uF 6.3V C36 4.7uF 6.3V
E10E10
R2
OPT
R2
OPT
D1
CMDSH-3
D1
CMDSH-3
C48 OPT C48 OPT
R35 [1] R35 [1]
Q6 OPT Q6 OPT
4
5
6
7
8
3
1
2
C37 OPT C37 OPT
COUT1 {1} COUT1 {1}
C15 1nF C15 1nF
J1J1
R31 [1] R31 [1]
E9E9
C47 0.1uF C47 0.1uF
C42 100pF C42 100pF
E5E5
+
COUT6 330uF 2.5V
+
COUT6 330uF 2.5V
Q1 [1] Q1 [1]
4
5
6
7
8
3
1
2
Q2 [1] Q2 [1]
4
5
6
7
8
3
1
2
JP1JP1
R18 2.2R18 2.2
C49 OPT C49 OPT
C44
1nF
C44
1nF
E11E11
R53 OPT R53 OPT
RS1 [1] RS1 [1]
Q8 OPT Q8 OPT
4
5
6
7
8
3
1
2
R30 100 R30 100
Q5 OPT Q5 OPT
4
5
6
7
8
3
1
2
J4J4
R47 OPT R47 OPT
R4
10.0K
R4
10.0K
C50 1uF C50 1uF
J3J3
R37
OPT
R37
OPT
R50
OPT
R50
OPT
COUT4 {1} COUT4 {1}
R3 0 R3 0
+
CIN1
180uF
16V
+
CIN1
180uF
16V
12
R10
[1]
R10
[1]
R38 OPT R38 OPT

10
dc1185b-a/-bf
DEMO MANUAL
DC1185B-A/-B
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2013
LT 1213 • PRINTED IN USA
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 LT C applica-
tion engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation

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