DEMO MANUAL DC143
NO DESIGN SWITCHER
DEMO MANUAL DC143
LTC1474/LTC1475
10µA I
Q
, High Efficiency,
Step-Down DC/DC
Converter
10µA (typical) is required to regulate the output. The parts
can be shut down to further reduce the supply current to
6µA (typical). In dropout, the internal P-channel MOSFET
is turned on continuously (100% duty cycle), providing
low dropout operation with V
OUT
≅
V
IN
. An onboard low-
battery detector allows the user to monitor the input
supply through an external resistive divider. This board is
intended for applications such as cellular phones, GSM
systems, 4mA to 20mA current-loop pirate supplies or any
portable battery-powered application.
Gerber files for this
circuit board are available. Call the LTC factory.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
DESCRIPTIO
This demonstration circuit is a step-down (buck) regulator
using the LTC
®
1474/LTC1475. The exclusive use of surface
mount components and the LTC1474/LTC1475 in the tiny
MSOP package results in a highly efficient application in a
small board space. This demo board highlights the
capabilities of the LTC1474/LTC1475, which use a current
mode, constant off-time architecture to switch an internal
P-channel power MOSFET. This results in a power supply
that has low ripple and fast transient response. At low
output currents the LTC1474/LTC1475 automatically
switch to Burst Mode
TM
operation to maintain high operating
efficiencies and minimize supply current. At no load,only
PERFORmANCE SU
SYMBOL
V
IN
V
OUT
PARAMETER
Input Voltage Range
Output Voltage
I
OUT
I
Q
Maximum Output Current
Typical Supply Current
TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO
Board A, B, D, E Efficiency
100
V
IN
= 5V
90
V
IN
= 10V
V
IN
= 15V
Demo Board A
EFFICIENCY (%)
80
70
60
L = 100µH
V
OUT
= 3.3V
R
SENSE
= 0Ω
3
30
0.3
LOAD CURRENT (mA)
300
DM143 TPC
50
0.03
DM143 DB A
U
WW
U W
U
ARY
CONDITIONS
V
OUT
= 3.3V
V
OUT
= 5V
LTC1474/LTC1475
LTC1474-3.3/LTC1475-3.3
LTC1474-5/LTC1475-5
R
SENSE
= 0Ω
R
SENSE
= 0.25Ω
V
IN
= 10V, I
LOAD
= 0
V
IN
= 10V, I
LOAD
= 0
U W
BOARD SUFFIX
A, B, D, E
C, F
A, D
B, E
C, F
ALL
ALL
A, B, C
D, E, F
VALUE
3.3V to 18V
5V to 18V
3.3V
±
0.10V
3.3V
±
0.10V
5V
±
0.15V
300mA
150mA
10µA
15µA
Demo Board D
DM143 DB D
1
DEMO MANUAL DC143
PERFORmANCE SU
SYMBOL
V
RIPPLE
∆V
OUT
PARAMETER
Typical Output Ripple
Typical Line Regulation
Typical Load Regulation
V
LBI
Low-Battery Trip Threshold
PACKAGE A D SCHE ATIC DIAGRA SM
TOP VIEW
V
IN
4V* TO 18V
C3
10pF
THIS NETWORK
IS PRESENT IN
BOARD A ONLY
C1
4.7µF
35V
+
R6
0Ω
R1
0.25Ω
C2
1000pF
6
SENSE
LBI
RUN
7
V
IN
C5
0.1µF
V
FB
LBO
SW
1
2
5
LBI
3
8
JP1
RUN
R7
100k
LTC1474
GND
4
*3.3V AT NO LOAD
Figure 1. LTC1474 Demo Board Schematic
TOP VIEW
V
IN
4V* TO 18V
C1
4.7µF
35V
+
R6
0Ω
R3
3.01M
R1
0.25Ω
C2
1000pF
6
SENSE
7
V
IN
C5
0.1µF
V
FB
1
LBI
R2
1M
SHDN
RUN
R7
100k
LTC1475
3
2
LBI/OFF
LBO
8
ON
SW
5
GND
4
*3.3V AT NO LOAD
Figure 2. LTC1475 Demo Board Schematic
2
W
WW
W
U
U W
ARY
CONDITIONS
I
OUT
= 100mA
4V < V
IN
< 18V, R
SENSE
= 0Ω, I
LOAD
= 100mA
4V < V
IN
< 18V, R
SENSE
= 0.25Ω, I
LOAD
= 100mA
4V < V
IN
< 18V, R
SENSE
= 0Ω, I
LOAD
= 100mA
4V < V
IN
< 18V, R
SENSE
= 0.25Ω, I
LOAD
= 100mA
6V < V
IN
< 18V, R
SENSE
= 0Ω, I
LOAD
= 100mA
6V < V
IN
< 18V, R
SENSE
= 0.25Ω, I
LOAD
= 100mA
0 < I
LOAD
< 300mA, R
SENSE
= 0Ω, V
IN
= 10V
0 < I
LOAD
< 150mA, R
SENSE
= 0.25Ω, V
IN
= 10V
BOARD SUFFIX
All
A, D
B, E
C, F
All
All
VALUE
50mV
35mV
25mV
20mV
10mV
20mV
10mV
10mV
10mV
1.23V
V
OUT
(V
FB
*)
LBO
LBI
GND
V
OUT
3.3V
300mA
1
2
3
4
8
7
6
5
RUN
V
IN
SENSE
SW
R5
+
R4
L1
100µH
MS8 PACKAGE
8-LEAD PLASTIC MSOP
*ADJUSTABLE OUTPUT VERSION
C4
100µF
6.3V
D1
MBR0530
LBO
DM143 F01
LTC1474CMS8
LTC1474CMS8-3.3
LTC1474CMS8-5
C3
10pF
THIS NETWORK
IS PRESENT IN
BOARD D ONLY
V
OUT
(V
FB
*)
LBO
LBI/OFF
GND
C4
100µF
6.3V
V
OUT
3.3V
300mA
1
2
3
4
8
7
6
5
ON
V
IN
SENSE
SW
R5
+
R4
L1
100µH
MS8 PACKAGE
8-LEAD PLASTIC MSOP
*ADJUSTABLE OUTPUT VERSION
D1
MBR0530
LBO
DM143 F02
LTC1475CMS8
LTC1475CMS8-3.3
LTC1475CMS8-5
DEMO MANUAL DC143
PARTS LIST
REFERENCE
DESIGNATOR
C1
C2
C3
C4
C5
D1
E1 to E6
JP1
L1
R1
R2
R3
R4
R5
R6
R7
S1, S2
U1
QUANTITY
1
1
1
1
1
1
6
1
1
1
1
1
1
1
1
1
2
1
PART NUMBER
TPSC475M035
080553102KAT2A
08055310KAT1A
TPSC107M006R0150
TPSC336M010R0375
08053E104ZAT1A
MBR0530
2501-02
2802S-02-G2
CDRH73-101
LR1206 01 R250 F0
CR21-105J-T
CR21-225J-T
WCR0805-1474-F-P-LT
CJ21-000J-T
WCR0805-2494-F-P-LT
CJ21-000J-T
CR21-104J-T
EVQ PJS05K
LTC1474CMS8
LTC1474CMS8-3.3
LTC1474CMS8-5
LTC1475CMS8
LTC1475CMS8-3.3
LTC1475CMS8-5
DESCRIPTION
4.7µF 35V 20% Tantalum Capacitor
1000pF 25V 10% X7R Capacitor
10pF 25V 10% NPO Capacitor (Boards B, C, E, F Only)
100µF 6.3V 20% Tantalum Capacitor (Boards A, B, D, E)
33µF 6.3V 20% Tantalum Capacitor (Boards C, F)
0.1µF 25V + 80% to – 20% Y5V Capacitor
0.5A 30V Schottky Diode
Terminal Turret
Connector Pin Header (Boards A, B, C)
100µH Inductor
0.25Ω 0.25W 1% Resistor
1M 0.1W 5% Resistor (Boards D, E, F Only)
2.2M 0.1W 5% Resistor (Boards D, E, F Only)
1.47M 0.1W 1% Resistor (Boards B, C, E, F Only)
0805 Shunt Resistor (Boards B, C, E, F)
2.49M 0.1W 1% Resistor (Boards A, D)
0805 Shunt Resistor
100k 0.1W 5% Resistor
Momentary Switch (Boards D, E, F)
8-Pin MSOP IC, LTC1474 (Board A)
8-Pin MSOP IC, LTC1474-3.3 (Board B)
8-Pin MSOP IC, LTC1474-5 (Board C)
8-Pin MSOP IC, LTC1475 (Board D)
8-Pin MSOP IC, LTC1475-3.3 (Board E)
8-Pin MSOP IC, LTC1475-5 (Board F)
VENDOR
AVX
AVX
AVX
AVX
AVX
Motorola
Mill Max
Comm Con
Sumida
IRC
AVX
AVX
IRC
AVX
IRC
AVX
AVX
Panasonic
LTC
TELEPHONE
(207) 282-5111
(803) 946-0362
(803) 946-0362
(207) 282-5111
(803) 946-0362
(602) 244-3576
(516) 922-6000
(818) 301-4200
(847) 956-0666
(512) 992-7900
(803) 946-0524
(803) 946-0524
(512) 992-7900
(803) 946-0524
(512) 992-7900
(803) 946-0524
(803) 946-0524
(201) 392-4511
(408) 432-1900
Table 1. Demo Board Version Cross Reference
BOARD SUFFIX
A
B
C
D
E
F
PART NUMBER
LTC1474
LTC1474-3.3
LTC1474-5
LTC1475
LTC1475-3.3
LTC1475-5
OUTPUT VOLTAGE
3.3V (Adjustable)
3.3V
5V
3.3V (Adjustable)
3.3V
5V
ON/OFF CONTROL
Jumper
Jumper
Jumper
Pushbutton
Pushbutton
Pushbutton
3
DEMO MANUAL DC143
QUICK START GUIDE
Demonstration Board DC143 is easy to set up for
evaluation of the LTC1474/LTC1475. Please follow the
procedure below for proper operation:
q
through a resistor network (the resistor divider is
present only on boards D, E and F).
q
Connect the input power supply to the V
IN
and GND
terminals.
The LBO pin is a current sinking pin. When the LBI pin
goes below 1.23V, the LBO pin will sink 0.7mA of
current.
The LBI pin is the low-battery detector input pin.
Normally, its input comes from the input voltage
q
Connect the load between the V
OUT
and GND terminals.
Refer to Figure 6 for proper measurement equipment
setup.
For board A, B or C, open jumper JP1 to turn on or short
the jumper to shut down. For Board C, D or E,
momentarily depress the RUN push-button to turn on
or momentarily depress the SHDN push-button to shut
down.
q
q
OPERATIO
The circuits shown in Figures 1 and 2 operate from input
voltages of 3.3V to 18V. The six different versions of the
demo board provide 3.3V or 5V, as specified in Table 1. For
output voltages other than 3.3V or 5V, use Board A or D
and change the resistive divider R4/R5 to the appropriate
ratio. For output voltages lower than 3V, input voltages as
low as 3V can be used. The demo boards provide two
on/off options — by opening or shorting jumper JP1
(Boards A, B and C) or push-button (Boards D, E and F).
Operation
The LTC1474/LTC1475 use a current mode, constant off-
time architecture shown in Figure 3. Current mode opera-
tion provides the well known advantages of clean start-up
and excellent line and load regulation. Constant off-time
adds to this list simplicity (neither an oscillator nor ramp
compensation is required) and inherent 100% duty cycle
in dropout.
The LTC1474/LTC1475 use Burst Mode operation to keep
the output capacitor charged to the proper output voltage
while minimizing quiescent current. Burst Mode operation
works by using short burst cycles to keep the output
capacitor charged, followed by a “sleep” mode where the
load current is supplied by the output capacitor and the
LTC1474/LTC1475 draw only 9µA of supply current.
Because of Burst Mode operation and the constant
off-time, the frequency changes with input voltage and
4
U
load. During sleep mode, the low quiescent current is
achieved by turning on only the voltage comparator and
voltage reference, which are needed to monitor the output
voltage, and the low-battery comparator. The low quies-
cent current and variable frequency minimize losses that
would normally dominate at light loads (DC supply current
losses and switching losses due to the MOSFET switch
gate charge). This results in the high efficiencies down to
extremely light loads and the ultralow supply current
required to maintain the output voltage at no load.
The LTC1474/LTC1475 also provide user-programmable
peak inductor current: the user can set the peak current to
any value between 10mA and 400mA with the appropriate
sense resistor. At the beginning of the burst cycle, the
internal P-channel MOSFET switch is turned on, causing
the inductor current to begin to increase. This current
flows through both an internal and an optional external
sense resistor. The internal current comparator monitors
the voltage drop across the sense resistors and, when the
voltage reaches 100mV, the current comparator trips and
turns the switch off, causing the inductor current to
decrease. At the end of the 4.75µs off-time, the switch
either turns back on or stays off (sleep mode), depending
on the status of the voltage comparator. Without an
external sense resistor (Pins 6 and 7 shorted), the peak
current defaults to the 400mA max due to the internal
sense resistor.
DEMO MANUAL DC143
OPERATIO
1µA
LTC1474: RUN 8
LTC1475: ON
4.75µs
1-SHOT
TRIGGER
V
FB
LBO
2
OUT
ON
SW
5
V
OUT
1×
25×
×
CONNECTION NOT PRESENT IN LTC1474 SERIES
CONNECTION PRESENT IN LTC1474 SERIES ONLY
The demo board includes two sense resistors; 0.25Ω R1
is shorted out with a 0Ω resistor (R6) to easily demonstrate
peak current programming. With the short in place (R
SENSE
= 0Ω), the peak current is the maximum 400mA providing
a maximum load of 300mA. With the short removed
(R
SENSE
= 0.25Ω), the peak current is reduced to 200mA
and the maximum load is 150mA.
Low-Battery Detector
The low-battery indicator senses the input voltage through
an external resistive divider. This divided voltage connects
to the (–) input of a voltage comparator (Pin 3), which is
compared with a 1.23V reference voltage. Because the
current going into Pin 3 is negligible, the following
expression is used for setting the trip point:
V
LBTRIP
= 1.23(1 + R3/R2)
R
SENSE
(Ω)
U
LBI/OFF
100mV
V
IN
7
R
SENSE
(OPTIONAL)
V
CC
SENSE
6
5Ω
–
×
C
ON
+
V
IN
+
–
V
ON
+
+
+
LB
–
READY
3
LTC1474: LBI
LTC1475: LBI/OFF
1.23V
1.23V
REFERENCE
4
GND
V
FB
1
DM143 F03
Figure 3. LTC1474/LTC1475 Block Diagram
5
4
3
2
1
0
0
250
100
150
200
50
MAXIMUM OUTPUT CURRENT (mA)
300
DM143 F04
Figure 4. R
SENSE
Selection
5
嵌入式系统
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