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PDF LT1612 Data sheet ( Hoja de datos )
| Número de pieza | LT1612 | |
| Descripción | Synchronous/ Step-Down 800kHz PWM DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Operates from Input Voltage As Low As 2V
s Internal 0.7A Synchronous Switches
s Uses Ceramic Input and Output Capacitors
s 620mV Reference Voltage
s 800kHz Fixed Frequency Switching
s Programmable Burst Mode Operation
U
APPLICATIONS
s Portable Devices
s Lithium-Ion Step-Down Converters
s 5V to 3.3V Conversion
s 2-Cell Alkaline Step-Down Converters
Final Electrical Specifications
LT1612
Synchronous, Step-Down
800kHz PWM
DC/DC Converter
April 2000
DESCRIPTION
The LT®1612 is an 800kHz, synchronous step-down DC/
DC converter that operates from an input voltage as low
as 2V. Internal 0.45Ω switches deliver output currents up
to 500mA, and the 800kHz switching frequency allows the
use of small, low value ceramic input and output capaci-
tors. Input voltage ranges from 5.5V down to 2V and
output voltage can be set as low as the 620mV reference.
The device features Burst ModeTM operation, keeping
efficiency high at light loads. Burst Mode operation can be
defeated by pulling the MODE pin high, enabling constant
switching throughout the load range for low noise.
No-load quiescent current is 160µA and shutdown current
is less than 1µA. The device is available in 8-lead SO and
MSOP packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATION
VIN
2V
C1
10µF
0.1µF
VIN BOOST
SHDN
SW
LT1612
MODE
VC
FB
GND
33k
330pF
R2
232k
1%
L1
10µH
100pF
R1
215k
1%
VOUT
1.2V
500mA
C2
68µF
3.15V
C1: TAIYO-YUDEN JMK325BJ106MN
C2: PANASONIC EEFCDOF680R
L1: SUMIDA CD43-100
Figure 1. 2V to 1.2V Converter
1612 F01a
Efficiency for LT1612 vs Linear Regulator
VOUT = 1.2V
90
80 VIN = 2V
70 VIN = 3V
60
VIN = 2V (LINEAR)
50
40
30
10
VIN = 3V (LINEAR)
100
LOAD CURRENT (mA)
500
1612 • F01b
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.
1
1 page  
U
OPERATIO
Layout Hints
The LT1612 switches current at high speed, mandating
careful attention to layout for proper performance. You
will not get advertised performance with careless layouts.
Figure 2 shows recommended component placement for
a buck (step-down) converter. Follow this closely in your
PC layout. Note the direct path of the switching loops.
Input capacitor C1 must be placed close (< 5mm) to the IC
package. As little as 10mm of wire or PC trace from CIN to
VIN will cause problems such as inability to regulate or
oscillation.
The ground terminal of input capacitor C1 should tie close
to Pin 4 of the LT1612. Doing this reduces dI/dt in the
ground copper which keeps high frequency spikes to a
minimum. The DC/DC converter ground should tie to the
PC board ground plane at one place only, to avoid intro-
ducing dI/dt in the ground plane.
LT1612
consumption but also adds low frequency voltage ripple to
the output. Figure 3 shows switching waveforms for a 5V
to 3.3V converter running in Burst Mode operation. Output
voltage ripple is approximately 20mVP-P. If the MODE pin
is pulled high, Burst Mode operation will be inhibited and
the oscillator runs continuously with no low frequency
ripple at the output. See Figures 4 and 5.
VOUT
20mV/DIV
AC COUPLED
IL
200mA/DIV
5µs/DIV
Figure 3. Output Voltage Ripple is 20mVP-P for
the Circuit of Figure 1
1612 F03
R1 R2 RC
CC
1
8 SHDN
2 LT1612 7 MODE
36
VIN C1 4
5 C3
MULTIPLE
VIAs
GND
C2
L1
1612 F02
VOUT
Figure 2. Recommended Component Placement. Traces
Carrying High Current are Direct. Trace Area at FB Pin and VC
Pin Is Kept Low. Lead Length to Battery Should Be Kept Short
Burst Mode Operation Defeat
To maintain high efficiency at light loads, the LT1612 will
automatically shift into Burst Mode operation (MODE = 0V
or floating). In this mode of operation the oscillator and
switch drive circuitry is alternately turned on and off,
reducing quiescent current to 160µA. This reduces power
VOUT
200mV/DIV
AC COUPLED
IL
200mA/DIV
ILOAD
10mA TO 310mA
0.1ms/DIV
1612 F04
Figure 4. Transient Response for the Circuit of Figure 1
with the MODE Pin Tied to Ground or Floating
VOUT
200mV/DIV
AC COUPLED
IL
200mA/DIV
ILOAD
10mA TO 300mA
0.1ms/DIV
1612 F05
Figure 5. With the MODE Pin Tied High, Low
Frequency Output Voltage Ripple Is No Longer Present
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LT1612.PDF ] | |
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