DC1798A - Demo Manual

DEMO MANUAL DC1798A
LTC3869IGN-2
Dual, 2-Phase Synchronous
Step-Down DC/DC Controllers
DESCRIPTION
Demonstration circuit 1798A is a Dual Output, Dual
Phase 5A Synchronous Buck Converter featuring the
LTC3869IGN-2. The entire circuit, including the bulk output
capacitors, fit within a 1.04" × 0.94" area on all layers. The
package style for the LTC3869IGN-2 is a 28-lead narrow
plastic SSOP.
DC1798A-A has an on-board sense resistor for current
feedback, while the DC1798A-B is configured with a DCR
sense circuit that allows the converter to use the inductors
DCR as the sense element instead of the on-board sense
resistors to save cost and board space and improves
efficiency.
The main features of the board include rail tracking, an
internal 5V linear regulator for bias, RUN pins for each
output, a PGOOD signal and a mode selector that allows
the converter to run in CCM, pulse-skipping or Burst
Mode operation. Synchronization to an external clock is
also possible through some minor component changes.
Two versions of the board are available.
The input voltage range is 4.5V to 26V. The LTC3869 datasheet gives a complete description of the part, operation
and application information. The datasheet must be read
in conjunction with this demo manual for DC1798A.
PERFORMANCE SUMMARY
PARAMETER
Design files for this circuit board are available at
http://www.linear.com/demo
L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
(TA = 25°C)
CONDITIONS
VALUE
Minimum Input Voltage
4.5V
Maximum Input Voltage
26V
Output Voltage VOUT1
VIN = 6.5V to 26V, IOUT1 = 0A to 5A
3.3V±2%
Output Voltage VOUT2
VIN = 6.5V to 26V, IOUT2 = 0A to 5A
2.5V±2%
VIN = 26V, IOUT1 = 5A (20MHz BW)
<30mVP-P*
VIN = 26V, IOUT2 = 5A (20MHz BW)
<30mVP-P*
Typical Output Ripple VOUT
Nominal Switching Frequency
400kHz
DC1798A-A
DC1798A-B
Efficiency
VOUT1 = 3.3V, IOUT1 = 5A; VIN = 16V
90%** Typical
91.0%** Typical
See Figures 3 and 4 for efficiency
curves
VOUT2 = 2.5V, IOUT2 = 5A; VIN = 16V
87.5%* Typical
88.8%* Typical
*Measured at bulk output capacitor
**Optional Mosfet (Si4816BDY) will result in up to 0.4% improvement in efficiency at full load
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DEMO MANUAL DC1798A
QUICK START PROCEDURE
Demonstration circuit 1798A is easy to set up to evaluate
the performance of the LTC3869IGN-2. Refer to Figure 1
for proper measurement equipment setup and follow the
procedure below:
NOTE. When measuring the input or output voltage ripple,
care must be taken to avoid a long ground lead on the
oscilloscope probe. Measure the input or output voltage
ripple by touching the probe tip directly across the VIN or
VOUT and GND terminals. See Figure 2 for proper scope
probe technique.
1. Make sure jumpers are in the following positions:
JUMPER
POSITION
JP1
ON
JP2
ON
JP3
CCM
2. With power off, connect the input power supply to VIN
and GND. Connect active loads to outputs.
3. Turn on the power at the input.
NOTE. Make sure that the input voltage does not exceed
28V.
4. Check for the proper output voltages.
VOUT1 = 3.234V to 3.366V,
VOUT2 = 2.450V to 2.550V,
NOTE. If there is no output, temporarily disconnect the
load to make sure that the load is not set too high.
5. 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.
6. Different operating modes can be evaluated by changing
position of jumper JP3.
A
4
V
VOUT1
Load
V
A
POWER
SUPPLY
A
V
VOUT2
Load
Figure 1. Proper Measurement Equipment Setup
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DEMO MANUAL DC1798A
QUICK START PROCEDURE
Figure 2. Measuring Output Voltage Ripple
Rail Tracking
Demonstration circuit 1798A is set up for coincident rail
tracking where VOUT2 tracks VOUT1 and the ramp rate for
VOUT1 is determined by the value of the TRK/SS1 capacitor at C6.
This board can be modified on the bench for external rail
tracking or for independent turn-on of the rails. For the
latter case, the ramp-rate for VOUT1 and VOUT2 will be
determined by their respective TRK/SS capacitors. Refer
to Table 1 for tracking options and to the data sheet for
more details.
Inductor DCR Sensing and Resistor Sensing
The two different versions of the board offer either an
on-board sense resistor or an inductor DCR sense circuit for current feedback. The DCR sense circuit uses the
resistive voltage drop across the inductor to estimate the
current. In contrast to the traditional sense resistor current feedback, the DCR sensing circuit offers lower cost
and higher efficiency, but results in less accurate current
limit due to the large variation in the inductor resistance.
Furthermore, this indirect current sensing method cannot
detect inductor saturation and requires the use of ‘soft’
saturating inductors (such as powder iron) resulting in
increased core losses or ‘hard’ saturating inductors (such
as ferrite) with sufficiency high current ratings resulting
in increased inductor size. The demonstration circuit
1798A is intended to demonstrate the feasibility of a high
performance, high efficiency synchronous buck converter
using a ‘hard’ saturating ferrite inductor with DCR sensing.
The typical efficiency versus load current for each of the
outputs is given in Figure 3 and Figure 4 respectively. An
efficiency improvement of up to 1% is possible for the
DCR sensing version. If further improvement in efficiency
is required, the switching devices can be replaced by the
optional MOSFET Q3 and Q4.
Table 1. Output Tracking Options
TRACK 1 DIVIDER
TRK/SS1 CAPACITOR
TRACK 1 DIVIDER
TRK/SS1 CAPACITOR
CONFIGURATION
R10
R12
C
R1
R4
C
Soft Start Without Tracking
VOUT1
VOUT2
0Ω
OPEN
10nF
OPEN
OPEN
10nF
Coincident Tracking:
VOUT1 tracking External Ramp
VOUT2 tracking VOUT1
63.4kΩ
20.0kΩ
OPEN
43.2kΩ
20.0kΩ
OPEN
Ratiometric Tracking:
VOUT2 tracking VOUT1
OPEN
OPEN
OPEN
63.4kΩ
20.0kΩ
OPEN
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DEMO MANUAL DC1798A
QUICK START PROCEDURE
100
95
EFFICIENCY (%)
90
85
80
75
6.5VIN, 3.3VOUT, DCR SENSE, 400kHz
16VIN, 3.3VOUT, DCR SENSE, 400kHz
6.5VIN, 3.3VOUT, RSENSE, 400kHz
16VIN, 3.3VVOUT, RSENSE, 400kHz
70
65
0
1
1
2
2
3
3
4
4
5
5
LOAD CURRENT (A)
Figure 3. Typical Efficiency vs Load Current for A-A(RSENSE) and A-B(DCR SENSE) Boards, 3.3VOUT, 400kHz
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DEMO MANUAL DC1798A
100
95
EFFICIENCY (%)
90
85
80
75
6.5VIN, 2.5VOUT, DCR SENSE, 400kHz
16VIN, 2.5VOUT, DCR SENSE, 400kHz
6.5VIN, 2.5VOUT, RSENSE, 400kHz
16VIN, 2.5VOUT, RSENSE, 400kHz
70
65
0
1
1
2
2
3
3
4
4
5
5
LOAD CURRENT (A)
Figure 4. Typical Efficiency vs Load Current for A-A(RSENSE) and A-B(DCR SENSE) Boards, 3.3VOUT, 400kHz
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DEMO MANUAL DC1798A
PARTS LIST
ITEM
QTY
REFERENCE
PART DESCRIPTION
MANUFACTURER/PART NUMBER
Cap., X5R, 4.7μF, 50V, 20%, 1206
Cap., X5R, 4.7μF, 16V, 20%, 0805
Cap., OS-CON, 22μF, 35V, SMT
Cap., X5R, 22μF, 6.3V, 20%, 1206
Cap., POSCAP 220μF 4V 20%, D2E Size
Cap., NPO, 22pF, 50V, 10%, 0603
Cap., NPO, 1000pF, 25V, 10%, 0603
Cap., X7R, 0.1μF, 50V, 10%, 0603
Cap., X5R, 1μF, 16V, 10%, 0603
Cap., X7R, 0.01μF, 50V, 10%, 0603
Cap., NPO, 330pF, 25V, 10%, 0603
Cap., X7R, 2200pF, 50V, 10%, 0603
Cap., NPO, 220pF, 25V, 10%, 0603
Schottky Diode 30V, SOD323
Inductor, 2.4μH
Mosfet N-Ch.,Dual
Res., Chip, 0.006, 0.5W, 5%, 1206
Res., Chip, 63.4k, 1/16W, 1%, 0603
Res., Chip 0Ω 1/16W, 0603
Res., Chip, 10, 1/16W, 1%, 0603
Res., Chip, 20k, 1/16W, 1%, 0603
Res., Chip, 100k, 1/16W, 1%, 0603
Res., Chip, 90k, 1/16W, 1%, 0603
Res., Chip, 30.1k, 1/16W, 5%, 0603
Res., Chip, 10, 1/16W, 5%, 0603
Res., Chip, 100K,1/16W, 5%, 0603
Res., Chip, 13K, 1/16W, 5%, 0603
I.C.LTC3869IGN-2, SSOP, 28 PIN
Taiyo Yuden, UMK316BJ475ML-T
Taiyo Yuden, EMK212BJ475MG-T
SANYO, 35SVPD22M
AVX, 12066D226MAT2A
SANYO, 4TPE220MF
AVX, 06035A220KAT2A
AVX, 06033A102KAT2A
AVX, 06035C104KAT
AVX, 0603YD105KAT
TDK, C1608X7R1H103K
AVX, 06033A331KAT
AVX, 06035C222KAT
AVX, 06033A221KAT
Central Semi., CMDSH-3TR
Sumida, CDEP85NP-2R4MC-50
Fairchild Semi., FDS6982AS
IRC, LRC-LRF1206LF-01-R006-J
VISHAY, CRCW060363K4FKEA
VISHAY, CRCW06030000Z0EA (2rls)
VISHAY, CRCW060310R0FKEA
VISHAY, CRCW060320K0FKEA
VISHAY, CRCW0603100KFKEA
VISHAY, CRCW060390K0FKEA
VISHAY, CRCW060330K0JNEA
VISHAY, CRCW060310R0JNEA
VISHAY, CRCW0603100KJNEA
VISHAY, CRCW060313K0FKEA
LINEAR TECH., LTC3869IGN-2
Required Circuit Components
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
2
1
1
2
2
2
2
4
2
2
1
2
1
2
2
2
2
1
6
4
2
1
1
1
1
1
1
1
CIN1, CIN2
C13
CIN4
COUT2, COUT4
COUT1, COUT3
C3, C18
C7, C15
C4, C14, C19, C21
C5, C17
C1, C6
C12
C11, C9
C8,
D1, D3
L2, L1
Q1, Q2
RSNS1, RSNS2
R30
R10, R16, R18, R35, R36, R40
R11, R14, R26, R29
R19, R20
R7
R9
R15
R21
R33
R25
U1
Additional Circuit Components
1
0
CIN5, CIN6 (OPT)
Cap., 1206
2
0
C10, C16, C20 (OPT)
Cap., 0603
Cap., POSCAP, D2E size
3
0
COUT5, COUT6 (OPT)
4
0
R1, R4, R12, R24, R32, R34, R39, Res., Chip, 0603 (OPT)
R41, R6, R13, R17, R22, R23, R27
5
0
J1, J2 (OPT)
Res., Chip, 1206
6
0
Q3, Q4 (OPT)
Mosfet N-Ch.,Dual with Shottky Diode
1
13
E1-E13
Turret, Testpoint
Mill Max, 2501-2-00-80-00-00-07-0
2
2
JP1, JP2
0.079 SINGLE ROW HEADER, 3 PIN
SAMTEC, TMM-103-02-L-S
3
1
JP3
0.079 SINGLE ROW HEADER, 4 PIN
SAMTEC, TMM-104-02-L-S
4
3
JP1, JP2, JP3
SHUNT,
SAMTEC, 2SN-BK-G
5
4
STAND-OFF
STAND-OFF, NYLON 0.25" tall
KEYSTONE, 8831(SNAP ON)
Hardware
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DEMO MANUAL DC1798A
SCHEMATIC DIAGRAM
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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.
7
DEMO MANUAL DC1798A
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
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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,
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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.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation
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