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PDF LTC3406B-2 Data sheet ( Hoja de datos )
| Número de pieza | LTC3406B-2 | |
| Descripción | 600mA Synchronous Step-Down Regulator | |
| Fabricantes | Linear | |
| Logotipo |  |
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FEATURES
■ High Efficiency: Up to 96%
■ 600mA Output Current at VIN = 3V
■ 2.5V to 5.5V Input Voltage Range
■ 2.25MHz Constant Frequency Operation
■ No Schottky Diode Required
■ Low Dropout Operation: 100% Duty Cycle
■ Low Quiescent Current: 350µA
■ 0.6V Reference Allows Low Output Voltages
■ Shutdown Mode Draws < 1µA Supply Current
■ Current Mode Operation for Excellent Line and
Load Transient Response
■ Overtemperature Protected
■ Low Profile (1mm) SOT-23 Package
U
APPLICATIO S
■ Cellular Telephones
■ Personal Information Appliances
■ Wireless and DSL Modems
■ Digital Still Cameras
■ MP3 Players
■ Portable Instruments
LTC3406B-2
2.25MHz, 600mA
Synchronous Step-Down
Regulator in ThinSOTTM
DESCRIPTIO
The LTC®3406B-2 is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. Supply current with no load is 350µA,
dropping to <1µA in shutdown. The 2.5V to 5.5V input
voltage range makes the LTC3406B-2 ideally suited for
single Li-Ion battery-powered applications. 100% duty
cycle capability provides low dropout operation, extend-
ing battery life in portable systems. PWM pulse skipping
mode operation provides very low output ripple voltage for
noise sensitive applications.
The switching frequency is internally set at 2.25MHz, allow-
ing the use of tiny surface mount inductors and capacitors.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with the 0.6V feedback
reference voltage. The LTC3406B-2 is available in a low pro-
file (1mm) SOT-23 package. Refer to LTC3406 for appli-
cations that require Burst Mode® operation.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
ThinSOT is a trademark of Linear Technology Corporation.
Protected by U.S. Patents, including 6580258, 5481178.
TYPICAL APPLICATIO
VIN
2.7V
TO 5.5V
High Efficiency Step-Down Converter
4.7µF
CER
VIN SW
LTC3406B-2
RUN VFB
GND
2.2µH*
22pF
1M
10µF
CER
VOUT
1.8V
600mA
499k
3406B TA01a
Efficiency vs Load Current
100
VOUT = 1.8V
90 TA = 25°C
80
70
60 VIN = 3.6V
50
VIN = 2.7V
40
30
20
10
0.1
VIN = 4.2V
1 10 100
OUTPUT CURRENT (mA)
1000
3406B TA01b
sn3406b2 3406b2fs
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a Except for the Resistive Divider Resistor Values)
LTC3406B-2
Load Step
VOUT
100mV/DIV
AC COUPLED
IL
500mA/DIV
ILOAD
500mA/DIV
VIN = 3.6V
20µs/DIV
VOUT = 1.8V
ILOAD = 100mA TO 600mA
3406B G19
Load Step
VOUT
100mV/DIV
AC COUPLED
IL
500mA/DIV
ILOAD
500mA/DIV
VIN = 3.6V
20µs/DIV
VOUT = 1.8V
ILOAD = 200mA TO 600mA
3406B G20
PI FU CTIO S
RUN (Pin 1): Run Control Input. Forcing this pin above
1.5V enables the part. Forcing this pin below 0.3V shuts
down the device. In shutdown, all functions are disabled
drawing <1µA supply current. Do not leave RUN floating.
GND (Pin 2): Ground Pin.
SW (Pin 3): Switch Node Connection to Inductor. This pin
connects to the drains of the internal main and synchro-
nous power MOSFET switches.
VIN (Pin 4): Main Supply Pin. Must be closely decoupled
to GND, Pin 2, with a 2.2µF or greater ceramic capacitor.
VFB (Pin 5): Feedback Pin. Receives the feedback voltage
from an external resistive divider across the output.
sn3406b2 3406b2fs
5
5 Page 
LTC3406B-2
APPLICATIO S I FOR ATIO
A second, more severe transient is caused by switching in
loads with large (>1µF) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with COUT, causing a rapid drop in VOUT. No regulator can
deliver enough current to prevent this problem if the load
switch resistance is low and it is driven quickly. The only
solution is to limit the rise time of the switch drive so that
the load rise time is limited to approximately (25 • CLOAD).
Thus, a 10µF capacitor charging to 3.3V would require a
250µs rise time, limiting the charging current to about
130mA.
PC Board Layout Checklist
When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
LTC3406B-2. These items are also illustrated graphically
in Figures 5 and 6. Check the following in your layout:
1. The power traces, consisting of the GND trace, the SW
trace and the VIN trace should be kept short, direct and
wide.
2. Does the VFB pin connect directly to the feedback
resistors? The resistive divider R1/R2 must be con-
nected between the (+) plate of COUT and ground.
3. Does the (+) plate of CIN connect to VIN as closely as
possible? This capacitor provides the AC current to the
internal power MOSFETs.
4. Keep the switching node, SW, away from the sensitive
VFB node.
5. Keep the (–) plates of CIN and COUT as close as possible.
–
VOUT
+
COUT
L1
1
RUN
5
VFB
LTC3406B-2
2
GND
3 SW
VIN 4
CIN
R2
BOLD LINES INDICATE HIGH CURRENT PATHS
R1
CFWD
+
VIN
–
3406B F05
Figure 5. LTC3406B-2 Layout Diagram
VIA TO GND
VOUT
VIA TO VIN
PIN 1
L1 SW
LTC3406B-2
R1
R2
CFWD
VIN
VIA TO VOUT
COUT
GND
CIN
Figure 6. LTC3406B-2 Suggested Layout
3406B F06
sn3406b2 3406b2fs
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3406B-2.PDF ] | |
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