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PDF LTC1874EGN Data sheet ( Hoja de datos )
| Número de pieza | LTC1874EGN | |
| Descripción | Dual Constant Frequency Current Mode Step-Down DC/DC Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC1874
Dual Constant Frequency
Current Mode Step-Down
DC/DC Controller
FEATURES
s High Efficiency: Up to 94%
s High Output Currents Easily Achieved
s Wide VIN Range: 2.5V to 9.8V
s Constant Frequency 550kHz Operation
s Burst ModeTM Operation at Light Load
s Low Dropout: 100% Duty Cycle
s 0.8V Reference Allows Low Output Voltages
s Current Mode Operation for Excellent
Line and Load Transient Response
s Low Quiescent Current: 270µA (Each Controller)
s Separate Shutdown Pin for Each Controller
s Shutdown Mode Draws Only
8µA Supply Current (Each Controller)
s ±2.5% Reference Accuracy
s Available in 16-Lead Narrow SSOP
s Each Controller Functions Independent of the Other
U
APPLICATIO S
s 1- or 2-Cell Lithium-Ion-Powered Applications
s Personal Information Appliances
s Portable Computers
s Distributed 3.3V, 2.5V or 1.8V Power Systems
DESCRIPTIO
The LTC®1874 is a dual constant frequency current mode
step-down DC/DC controller with excellent AC and DC load
and line regulation. Each controller has an accurate
undervoltage lockout that shuts down the individual con-
troller when the input voltage falls below 2.0V.
The LTC1874 boasts ±2.5% output voltage accuracy and
consumes only 270µA of quiescent current per controller.
The LTC1874 is configured with Burst Mode operation,
which enhances efficiency at low output current for appli-
cations where efficiency is a prime consideration.
To further maximize the life of a battery source, each
external P-channel MOSFET is turned on continuously in
dropout (100% duty cycle). In shutdown, each controller
draws a mere 8µA. High constant operating frequency of
550kHz allows the use of small external inductors.
The LTC1874 is available in a small footprint 16-lead
narrow SSOP.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATION
VIN
3.5V
TO 9.5V
CIN
10µF
16V
×2
R1
0.04Ω
VOUT1
3.3V
1A
L1 M1
4.7µH
+
C1
47µF
D1
C1, C2: SANYO POSCAP 6TPA47M
CIN: TAIYO YUDEN CERAMIC
EMK325BJ106MNT (× 2)
249k
6V
D1, D2: MBRM120
L1, L2: COILCRAFT D01608C-472
80.6k
M1, M2: Si3443DV
R1, R2: DALE 0.25W
10k
220pF
1 LTC1874 8
VIN1 PVIN2
2 SENSE1–
7
PGATE2
3
GND1
6
PGND2
4
VFB1
5
ITH/RUN2
13
ITH/RUN1
12
VFB2
14
PGND1
11
GND2
15
PGATE1
SENSE2– 10
16
PVIN1
9
VIN2
10k
220pF
R2
0.04Ω
M2 L2
4.7µH
+
D2
Figure 1. LTC1874 3.5V-9.5V Input to 3.3V/1A and 1.8V/1A Dual Step-Down Converter
C2
47µF
6V
VOUT2
1.8V
1A
100k
80.6k
1874 TA01
1
1 page  
W
FUNCTIONAL DIAGRA
VIN1 SENSE1–
12
Controller #1
LTC1874
+
ICMP
–
SLOPE
OSC COMP
RS1
R
Q
SWITCHING
LOGIC AND
BLANKING
S CIRCUIT
PVIN1
16
PGATE1
15
PGND1
14
VIN
0.3V
GND1
3
FREQ
FOLDBACK
SHORT-CIRCUIT
DETECT
0.3V
0.15V
BURST
+ CMP
SLEEP
–
0.5µA
+
VIN
– 0.35V +
VOLTAGE
REFERENCE
VREF
0.8V
SHDN
CMP
SHDN
– UV
UNDERVOLTAGE
LOCKOUT
OVP
EAMP
+
VREF
–+
60mV
+
VREF
0.8V
–
VIN
VFB1
4
1.2V
GND2
11
VIN2 SENSE2–
9 10
13
ITH/RUN1
Controller #2
CONTROLLER #2 IS THE SAME AS CONTROLLER #1
5
ITH/RUN2
PVIN2
8
PGATE2
7
PGND2
6
VFB2
12
1874FD
5
5 Page 
LTC1874
APPLICATIO S I FOR ATIO
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
LTC1874. These items are illustrated graphically for a
single controller in the layout diagram in Figure 6. Check
the following in your layout:
1. Is the Schottky diode closely connected between power
ground (PGND) and the drain of the external MOSFET?
2. Does the (+) plate of CIN connect to the sense resistor
as closely as possible? This capacitor provides AC
current to the MOSFET.
3. Is the input decoupling capacitor (0.1µF) connected
closely between VIN and signal ground (GND)?
4. Connect the end of RSENSE as close to VIN as possible.
The VIN pin is the SENSE + of the current comparator.
5. Is the trace from SENSE– to the SENSE resistor kept
short? Does the trace connect close to RSENSE?
6. Keep the switching node PGATE away from sensitive
small signal nodes.
7. Does the VFB pin connect directly to the feedback
resistors? The resistive divider R1 and R2 must be
connected between the (+) plate of COUT and signal
ground.
8. PVIN must connect to VIN and PGND must connect to
GND. Isolate high current power paths from signal
power and signal ground where possible in the layout.
An unbroken ground plane is recommended.
VIN
+
CIN
VOUT
+
R2
L1 SW
COUT
D1
R1
RSENSE
1/2 LTC1874
1 16
M1
VIN PVIN
2 SENSE–
15
PGATE
0.1µF
3
14
GND PGND
4
VFB
13
ITH/RUN
RITH
CITH
BOLD LINES INDICATE HIGH CURRENT PATHS
1874 F06
Figure 6. LTC1874 Layout Diagram (See PC Board Layout Checklist)
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LTC1874EGN.PDF ] | |
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