DC621A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 621
1.25MHZ TRIPLE DC/DC CONVERTER
LT1941
DESCRIPTION
Demonstration circuit 621 is a 1.25MHz triple DC/DC
switching converter using the LT1941. The LT1941 features fast switching speed, three internal power
switches, and a wide input voltage range, making it a
versatile and powerful IC that fits easily into spaceconstrained applications and removes the need for three
separate DC/DC converters in triple output applications.
The constant 1.1MHz switching frequency allows for the
use of tiny, surface mount external components. The
current-mode control topology yields fast transient response and good loop stability, requiring a minimum
number of external compensation components and allowing the use of ceramic input and output capacitors.
The anti-phase switching and single-IC solution reduces
the input capacitance requirements from three separate
capacitors to only two. The low resistance internal
power switches maintain high efficiencies (typically 80%
to 85%) over a wide range of input voltages and loads.
Its 260µA shutdown current (activated by grounding all
three of the RUN/SS pins) extends battery life. All three
outputs have external adjustable soft-start capacitors to
limit inrush current during turn-on. The wide VIN range
of the LT1941 allows step-down, SEPIC, and boost configurations with up to 25V input. Power good terminals
provide diagnostics for each output voltage (within 10%
of final value) and the input voltage (within 10% of 5V
and 12V).
This board is designed for applications that require three
outputs (two step-down supplies and a SEPIC or boost)
with high load current in a small board space with low
cost and low parts count as well as simple circuit design. The high current, on-board, triple monolithic
switches eliminate the need for external switches. The
use of ceramic capacitors in this circuit not only demonstrates small size and low cost, but the advantage of
current-mode control in step-down, SEPIC, and boost
applications with a simple compensation network for
good stability and transient response.
For optional adjustments in the output voltage, compensation, ripple, power good diagnostics, run/soft-start,
and other aspects of LT1941 design, please consult the
datasheet. With three outputs and internal power
switches, this design can start to heat up under maximum load current and high ambient temperature conditions. Please consult the datasheet for thermal considerations, especially when altering the output voltage for
much higher power DC/DC converters.
Design files for this circuit board are available. Call
the LTC factory.
LT is a trademark of Linear Technology Corporation
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 621
1.25MHZ TRIPLE DC/DC CONVERTER
Table 1. Typical Performance Summary (TA = 25°C)
Parameter
Conditions
Value
VIN
4.7V to 14V
VOUT1
1.8V
VOUT2
3.3V
VOUT3
-12V
VOUT1 Maximum Load Current
2.4A
VOUT2 Maximum Load Current
1.4A
VOUT3 Maximum Load Current
VIN = 12V
550mA
VIN = 5V
240mA
VIN = 12V, IOUT1 = 1.2A, IOUT2 = 700mA, IOUT3 = 275mA
79%
VIN = 5V, IOUT1 = 1.2A, IOUT2 = 700mA, IOUT3 = 120mA
82.5%
VOUT1 ripple
VIN = 12V, IOUT1 = 2.4A, IOUT2 = 0A, IOUT3 = 0A
25mV pk-pk
VOUT2 ripple
VIN = 12V, IOUT1 = 0A, IOUT2 = 1.4A, IOUT3 = 0A
10mV pk-pk
VOUT3 ripple
VIN = 12V, IOUT1 = 0A, IOUT2 = 0A, IOUT3 = 550mA
15mV pk-pk
Zero-Load Quiescent Current
IOUT1 = IOUT2 = IOUT3 = 0A, VIN = 12V
8mA
Shutdown Quiescent Current
RUN/SS1 = RUN/SS2 = RUN/SS3 = GND, VIN = 12V
260µA
Efficiency
100
100
95
80
12V IN
V O U T2 @ 700m A
V O U T3 @ 275m A
75
70
5V IN
V O U T1 @ 1200m A
V O U T3 @ 120m A
90
E F F IC IE N C Y (%)
85
EFFICIENCY (%)
95
5V IN
V O U T2 @ 700m A
V O U T3 @ 120m A
90
65
85
80
75
65
60
60
55
55
50
12V IN
V O U T1 @ 1200m A
V O U T3 @ 275m A
70
50
0
500
1000
1500
2000
2500
VOUT1 LOAD CURRENT (mA)
Figure 1. Typical Efficiency of Demo Circuit 621 LT1941 with varying load current on VOUT1
0
250
500
750
1000 1250 1500
V O U T 2 LO A D C U R R E N T (mA )
Figure 2. Typical Efficiency of Demo Circuit 621 LT1941 with varying load current on VOUT2
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 621
1.25MHZ TRIPLE DC/DC CONVERTER
100
95
E F F IC IE N C Y (%)
90
5V IN
85
80
12V IN
75
70
65
V O U T1 @ 1200m A
V O U T2 @ 700m A
60
55
50
0
100
200
300
400
500
600
V O U T 3 LO A D C U R R E N T (mA )
Figure 4. Proper Measurement Equipment Setup
OPTIONS
Figure 3. Typical Efficiency of Demo Circuit 621 LT1941 with
varying load current on VOUT3
QUICK START PROCEDURE
Demonstration circuit 621 is easy to set up to evaluate
the performance of the LT1941. Refer to Figure 5 for
proper measurement equipment setup and follow the
procedure below:
1. Connect
the 4.7V–14V input power supply to the
VIN and GND terminals.
2. After
all connections are made, turn on input power
and verify that the output voltages are 3.3V, 1.8V,
and -12V.
3. The RUN/SS
and Power Good functions are optional
and their terminals can be left floating (disconnected) if their functions are not being used. Connecting a RUN/SS terminal to the GND terminal will
disable the corresponding output. Connecting
RUN/SS2 to the GND terminal will disable VOUT3 as
well as VOUT2.
POWER GOOD TERMINALS
The power good terminals indicate the state of the
three outputs and the input voltage. PGOOD1,
PGOOD2, and PGOOD3 indicate when VOUT1, VOUT2,
and VOUT3 are within 10% of their final values.
PGOOD1 is pulled up to VIN and both PGOOD2 and
PGOOD3 are pulled up to VOUT2. PGOOD3 is therefore dependent upon the state of VOUT2.
5GOOD and 12GOOD indicate when the input voltage
is within 10% of 5V and 12V. Each has a pull-up resistor to VIN.
The power good terminals are not valid if the input
voltage is below 3.5V or if all three of the RUN/SS
terminals are pulled low and the LT1941 is in shutdown.
RUN / SOFT-START TERMINALS
The run/soft-start terminals (RUN/SS1, RUN/SS2,
RUN/SS3) are used to disable or enable the three outputs and to adjust soft-start for each output. C2, C4,
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 621
1.25MHZ TRIPLE DC/DC CONVERTER
and C5 (1500pF) provide soft-start to all three outputs
and can be easily adjusted.
For normal operation (RUN), the terminals are left
floating. In order to disable, or shutdown, an output
stage, the RUN/SS terminal for that stage must be
pulled to GND. If all three of the RUN/SS terminals are
pulled to GND, the LT1941 enters micropower shutdown and the quiescent current drops to only 260µA
at 12V input.
Table 2. RUN/SS Terminal Logic Table
RUN/SS1
RUN/SS2
RUN/SS3
VOUT1
VOUT2
VOUT3
n/c
n/c
n/c
1.8V
3.3V
-12V
GND
n/c
n/c
0V
3.3V
-12V
n/c
GND
n/c
1.8V
0V
0V
n/c
n/c
GND
1.8V
3.3V
0V
GND
GND
n/c
0V
0V
0V
n/c
GND
GND
1.8V
0V
0V
GND
n/c
GND
0V
3.3V
0V
GND
GND
GND
0V
0V
0V
R15 / R16 BIAS2 SOURCE
The BIAS2 pin supplies the current to the driver of
SW3. This pin is tied to the lowest available voltage
source above 2.5V (VOUT2) for highest efficiency. R15
(0Ω) provides a direct connection from BIAS2 to
VOUT2.
BIAS2 can be tied directly to VIN if VOUT2 is not guaranteed to be available or if VOUT2 can be in shutdown
when VOUT3 is required. By removing R15 and installing R16 (0Ω), BIAS2 is tied directly to VIN. R16 and
R15 must never be installed simultaneously. Installing
R16 will change the logic in Table 2 to reflect a direct
correlation between RUN/SS3 and VOUT3; RUN/SS2
no longer affects VOUT3.
4
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 621
1.25MHZ TRIPLE DC/DC CONVERTER
5
5
4
3
2
ECO
REV
DESCRIPTION
DATE
PROTO
4
D
APPROVED
02/23/04
D
VIN
TP3
TP4
PGOOD1
TP5
C13
0.1uF
VOUT1
VOUT1
TP1
1.8V @2.4A
GND
25
Pgood3
21
Pgood1
12Good
16
5
BOOST1
Pgood2
9
0.22uF
R8
13.7k
1%
33uF
6.3V
5Good
6
BOOST2
D3
SW1
4
SW1
SW2
TP9
R6 2.2k C1
R7
7.32k
1%
3300pF
8
FB1
7
Vc1
12
TP14
C2
23
11
Vc2
10
RUN/SS2
13
L3 22uH
B
VOUT3
TP12
-12V
[email protected]
[email protected]
L4 22uH
C12
10uF
16V
C11
1uF
35V
R10
133k
1%
D5
B130
27
SW3
19
NFb
BIAS1
15
BIAS2
28
VC3
18
TP7
D2
R9
13.7k
1%
RUN/SS3
20
GND
TP11
D4
UPS120
0.22uF
TP2
VOUT2
R14 10.7k 1%
C10
R13
2.49k
1%
C
3.3V @1.4A
22uF
6.3V
GND
TP10
RUN/SS2
1500pF
TP15
R15 0
C3
22nF
R11 1.5k
VIN
R16
B
OPT
RUN/SS3
14
TP16
C4
FB3
12GOOD
PGOOD2
VOUT2
L1 3.3uH
C6 1000pF R12 10k
PGOOD3
1500pF
26
TP13
CMDSH-3
C14 15pF
GND
VIN
RUN/SS1
1500pF
R3
100k
TP6
C5
RUN/SS1
R2
130k
C7
FB2
B220A
VOUT2
24
LT1941EFE
3
VIN
R1
100k
17
C8
L2 3.0uH
C9
U1
VIN3
5GOOD
R4
100k
2
R5
100k
CMDSH-3
VIN2
D1
VOUT2
22
VOUT1
VIN1
TP8
GND
CIN2
4.7uF
16V
1
CIN1
10uF
16V
4.7V to 14V
VIN0
VIN
C
1
REVISION HISTORY
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 customers 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.
UNLESS OTHERWISE SPECIFIED
DIMENSIONS ARE IN INCHES
TOLERANCE ON ANGLE - - 2 PLACES - - - 3 PLACES - - INTERPRET DIM AND TOL
PER ASME Y14.5M -1994
A
THIRD ANGLE PROJECTION
CONTRACT NO.
APPROVALS
DRAWN MEI
DATE
10/24/02
CHECKED
TECHNOLOGY
TITLE
DC/DC CONVERTER
ENGINEER
SIZE CAGE CODE
Custom
DO NOT SCALE DRAWING
5
4
3
Monday, April 19, 2004
A
SCH, LT1941EFE 1.1MHz TRIPLE OUTPUT
APPROVED
DESIGNER
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900
Fax: (408)434-0507
SCALE:NONE
2
DWG NO
REV
4
DC621A
FILENAME: 621A-4.DSN
SHEET
1
1
OF
1
Linear Technology Corporation
LT1941EFE
Item
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
29
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31
32
33
34
Qty
1
1
1
3
1
1
2
1
1
1
1
1
1
2
1
1
1
1
1
2
4
1
1
1
2
1
1
1
1
1
1
0
16
1
Parts List
Ref
CIN1
CIN2
C1
C2,C4,C5
C3
C6
C8,C7
C9
C10
C11
C12
C13
C14
D2,D1
D3
D4
D5
L1
L2
L3,L4
R1,R3,R4,R5
R2
R6
R7
R9,R8
R10
R11
R12
R13
R14
R15
R16
TP1-TP16
U1
Desc
CAP, X5R 10uF 16V 20% 1210
CAP, X5R 4.7uF 16V 10% 1206
CAP, X7R 3300pF 50V 10% 0402
CAP, X7R 1500pF 50V 5% 0402
CAP, X7R 22nF 25V 10% 0402
CAP, X7R 1000pF 10V 10% 0402
CAP, X5R 0.22uF 16V 20% 0603
CAP, X5R 33uF 6.3V 20% 1210
CAP, X5R 22uF 6.3V 20% 1206
CAP, X7R 1uF 35V 10% 1206
CAP, X7R 10uF 16V 20% 1206
CAP, X5R 0.1uF 10V 10% 0402
CAP, NPO 15pF 50V 5% 0402
DIODE,CMDSH-3 SOD323
DIODE, B220A SCHOTTKY RECTIFIER 2A
DIODE, SCHOTTKY 20V 1A
DIODE, B130 SCHOTTKY RECTIFIER 1.0A
IND, 3.3uH
IND, 3.0uH
IND, 22uH
RES, 100K OHMS 5% 1/16W 0402
RES, 130K OHMS 5% 1/16W 0402
RES, 2.2K OHMS 5% 1/16W 0402
RES, 7.32K OHMS 1% 1/16W 0402
RES, 13.7K OHMS 1% 1/16W 0402
RES, 133K OHMS 1% 1/16W 0402
RES, 1.5K OHMS 5% 1/16W 0402
RES, 10K OHMS 1% 1/16W 0402
RES, 2.49K OHMS 1% 1/16W 0402
RES, 10.7K OHMS 1% 1/16W 0402
RES, 0 OHM JUMPER 0402
OPTION
TURRET
IC, LT1941EFE
1 of 1
DC621A Rev 4
6/17/2005
Manufacturer / Part #
TAIYO YUDEN EMK325BJ106MN-T
TAIYO YUDEN EMK316BJ475KL
AVX 04025C332KAT
AVX 04025C152JAT
TDK C1005X7R1E223K
AVX 0402ZC102K
AVX 0603YD224MAT
TDK C3225X5R0J336ML
TAIYO YUDEN JMK316BJ226KL
TAIYO YUDEN GMK316BJ105KL
TDK C3216X7R1C106M
AVX 0402ZD104KAT
AVX 04025A150JAT2A
CENTRAL CMDSH-3-LTC
DIODES INC. B220A
MICROSEMI UPS120
DIODES INC. B130
SUMIDA CDRH5D28R-3R3
SUMIDA CDRH6D28-3R0
SUMIDA CDRH5D28-220
AAC CR05-104JM
AAC CR05-134JM
AAC CR05-222JM
KOA RK73H1E7321F
AAC CR05-1372FM
AAC CR05-1333FM
AAC CR05-152JM
AAC CR05-1002FM
AAC CR05-2491FM
AAC CR05-1072FM
AAC CJ05-000M
OPTION
MILL-MAX-2501-2
LINEAR TECH LT1941EFE
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