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PDF LTC3410B Data sheet ( Hoja de datos )
| Número de pieza | LTC3410B | |
| Descripción | 2.25MHz/ 300mA Synchronous Step-Down Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
■ High Efficiency: Up to 96%
■ 300mA Output Current at VIN = 3V
■ 380mA Minimum Peak Switch Current
■ 2.5V to 5.5V Input Voltage Range
■ 2.25MHz Constant Frequency Operation
■ No Schottky Diode Required
■ Low Dropout Operation: 100% Duty Cycle
■ Stable with Ceramic Capacitors
■ 0.8V Reference Allows Low Output Voltages
■ Shutdown Mode Draws < 1µA Supply Current
■ ±2% Output Voltage Accuracy
■ Current Mode Operation for Excellent Line and
Load Transient Response
■ Overtemperature Protected
■ Available in Low Profile SC70 Package
U
APPLICATIO S
■ Cellular Telephones
■ Personal Information Appliances
■ Wireless and DSL Modems
■ Digital Still Cameras
■ MP3 Players
■ Portable Instruments
LTC3410Bwww.DataSheet4U.com
2.25MHz, 300mA
Synchronous Step-Down
Regulator in SC70
DESCRIPTIO
The LTC®3410B is a high efficiency monolithic synchro-
nous buck regulator using a constant frequency, current
mode architecture. The device is available in adjustable
and fixed output voltage versions. Supply current during
operation is only 200µA, dropping to <1µA in shutdown.
The 2.5V to 5.5V input voltage range makes the LTC3410B
ideally suited for single Li-Ion battery-powered applica-
tions. 100% duty cycle provides low dropout operation,
extending battery life in portable systems. PWM pulse
skipping mode operation provides very low output ripple
voltage for noise sensitive applications.
Switching frequency is internally set at 2.25MHz, allowing
the use of small surface mount inductors and capacitors.
The LTC3410B is specifically designed to work well with
ceramic output capacitors, achieving very low output
voltage ripple and a small PCB footprint.
The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with the 0.8V feed-
back reference voltage. The LTC3410B is available in a
tiny, low profile SC70 package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All
other trademarks are the property of their respective owners. Protected by U.S. Patents,
including 5481178, 5994885, 6580258, 6304066, 6127815, 6498466, 6611131.
TYPICAL APPLICATIO
VIN
2.7V
TO 5.5V
CIN
2.2µF
CER
VIN SW
LTC3410B
RUN
VFB
GND
4.7µH
10pF
232k
464k
3410 TA01
VOUT
1.2V
COUT
2.2µF
CER
100
90
80
70
60
50
40
30
20
20
0
1
Efficiency and Power Loss
vs Output Current
EFFICIENCY
1
0.1
0.01
POWER LOSS
0.001
VIN = 2.7V
VIN = 3.6V
VIN = 4.2V 0.0001
10 100 1000
OUTPUT CURRENT (mA)
3410 TA01b
3410bfa
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1 Except for the Resistive Divider Resistor Values)
LTC3410Bwww.DataSheet4U.com
Switch Leakage vs Input Voltage
600
550
500
450
400
350 MAIN
300 SWITCH
250
200
150
100 SYNCHRONOUS
50 SWITCH
0
01 2 3 4 56
INPUT VOLTAGE (V)
3410 G12
Pulse Skipping
VOUT
10mV/DIV
AC COUPLED
SW
2V/DIV
IL
100mA/DIV
VIN = 3.6V
VOUT = 1.8V
ILOAD = 2mA
1µs/DIV
Load Step
Start-Up from Shutdown
RUN
2V/DIV
VOUT
1V/DIV
IL
200mA/DIV
3410 G13
VIN = 3.6V
VOUT = 1.8V
ILOAD = 128mA
100µs/DIV
3410 G14
Load Step
VOUT
100mV/DIV
AC COUPLED
IL
200mA/DIV
ILOAD
200mA/DIV
VIN = 3.6V
4µs/DIV
VOUT = 1.8V
ILOAD = 0mA TO 300mA
3410 G15
VOUT
100mV/DIV
AC COUPLED
IL
200mA/DIV
ILOAD
200mA/DIV
VIN = 3.6V
4µs/DIV
VOUT = 1.8V
ILOAD = 30mA TO 300mA
3410 G16
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5 Page 
LTC3410Bwww.DataSheet4U.com
APPLICATIO S I FOR ATIO
Thermal Considerations
In most applications the LTC3410B does not dissipate
much heat due to its high efficiency. But, in applications
where the LTC3410B is running at high ambient
temperature with low supply voltage and high duty
cycles, such as in dropout, the heat dissipated may
exceed the maximum junction temperature of the part. If
the junction temperature reaches approximately 150°C,
both power switches will be turned off and the SW node
will become high impedance.
To avoid the LTC3410B from exceeding the maximum
junction temperature, the user will need to do some
thermal analysis. The goal of the thermal analysis is to
determine whether the power dissipated exceeds the
maximum junction temperature of the part. The tempera-
ture rise is given by:
TR = (PD)(θJA)
where PD is the power dissipated by the regulator and
θJAis the thermal resistance from the junction of the die to
the ambient temperature.
The junction temperature, TJ, is given by:
TJ = TA + TR
where TA is the ambient temperature.
As an example, consider the LTC3410B in dropout at an
input voltage of 2.7V, a load current of 300mA and an
ambient temperature of 70°C. From the typical perfor-
mance graph of switch resistance, the RDS(ON) of the
P-channel switch at 70°C is approximately 1.0Ω.
Therefore, power dissipated by the part is:
PD = ILOAD2 • RDS(ON) = 90mW
For the SC70 package, the θJA is 250°C/ W. Thus, the
junction temperature of the regulator is:
TJ = 70°C + (90)(250) = 92.5°C
which is well below the maximum junction temperature
of 125°C.
Note that at higher supply voltages, the junction tempera-
ture is lower due to reduced switch resistance (RDS(ON)).
Checking Transient Response
The regulator loop response can be checked by looking at
the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to (∆ILOAD • ESR), where ESR is the effective series
resistance of COUT. ∆ILOAD also begins to charge or
discharge COUT, which generates a feedback error signal.
The regulator loop then acts to return VOUT to its steady-
state value. During this recovery time VOUT can be moni-
tored for overshoot or ringing that would indicate a stability
problem. For a detailed explanation of switching control
loop theory, see Application Note 76.
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.
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3410B.PDF ] | |
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