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PDF LTC3401EMS Data sheet ( Hoja de datos )
| Número de pieza | LTC3401EMS | |
| Descripción | 1A/ 3MHz Micropower Synchronous Boost Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Synchronous Rectification: Up to 97% Efficiency
s 1A Switch Current Rating
s Fixed Frequency Operation Up to 3MHz
s Wide Input Range: 0.5V to 5.5V (Operating)
s Very Low Quiescent Current: 38µA (Burst Mode®
Operation)
s 2.6V to 5.5V Adjustable Output Voltage
s 0.85V (Typ) Start-Up Voltage
s No External Schottky Diode Required (VOUT < 4.3V)
s Synchronizable Switching Frequency
s Burst Mode Enable Control
s Antiringing Control Reduces Switching Noise
s PGOOD Output
s OPTI-LOOP® Compensation
s Very Low Shutdown Current: < 1µA
s Small 10-Pin MSUOP Package
APPLICATIO S
s Pagers
s Handheld Instruments
s Cordless Phones
s Wireless Handsets
s GPS Receivers
s Battery Backup
s CCFL Backlights
LTC3401
1A, 3MHz Micropower
Synchronous Boost Converter
DESCRIPTIO
The LTC®3401 is a high efficiency, fixed frequency, step-
up DC/DC converter that operates from an input voltage
below 1V. The device includes a 0.16Ω N-channel MOSFET
switch and a 0.18Ω P-channel synchronous rectifier.
Switching frequencies up to 3MHz are programmed with
an external timing resistor and the oscillator can be
synchronized to an external clock. An external Schottky
diode is optional but will slightly improve efficiency.
Quiescent current is only 38µA in Burst Mode operation,
maximizing battery life in portable applications. Burst
Mode operation is user controlled and can be enabled by
driving the MODE/SYNC pin high. If the MODE/SYNC pin
has either a clock or is driven low, then fixed frequency
switching is enabled.
Other features include 1µA shutdown, antiringing control,
open-drain power good output, thermal shutdown and
current limit. The LTC3401 is available in the 10-lead
thermally enhanced MSOP package. Higher current appli-
cations should use the 2A rated LTC3402 synchronous
boost converter. Applications that require VOUT < 2.6V
should use the LTC3423.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATION
All-Ceramic-Capacitor 2-Cell to 3.3V at 500mA Step-Up Converter
VIN = 1.8V to 3V
L1
4.7µH
VOUT
3.3V
500mA
+
2
CELLS
C1
4.7µF
LTC3401
34
VIN SW
10
SHDN
7
VOUT
28
MODE/SYNC FB
6
PGOOD
1
Rt
9
VC
GND 5
Rt
30.1k
R2
909k
C3
470pF
R5
82k
C4 R1
4.7pF 549k
C2
22µF
0 = FIXED FREQUENCY
1 = Burst Mode OPERATION
C1: TAIYO YUDEN JMK212BJ475MG
C2: TAIYO YUDEN JMK325BJ226MM
L1: SUMIDA CD43-4R7M
3404 TA01
Efficiency
100
Burst Mode
90 OPERATION
80
70
60
1MHz
FIXED
FREQUENCY
50
40
30
20
10
VIN = 2.4V WITH SCHOTTKY
0
0.1 1
10
IOUT (mA)
100
1000
3401 TA02
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1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3401
EA FB Voltage
1.28
1.27
1.26
1.25
1.24
1.23
1.22
–55
–15 25
65
TEMPERATURE (°C)
PMOS RDS(ON)
0.30 VOUT = 3.3V
0.25
105 125
3401 G13
0.20
0.15
0.10
0.05
–55
–15 25
65
TEMPERATURE (°C)
PGOOD Threshold
–7.0
–7.5
–8.0
–8.5
–9.0
–9.5
–10.0
–10.5
–11.0
–11.5
–12.0
–55
–15 25
65
TEMPERATURE (°C)
105 125
3401 G16
105 125
3401 G19
Oscillator Frequency Accuracy
2.10
Rt = 15k
2.05
2.00
1.95
1.90
–55
–15 25
65
TEMPERATURE (°C)
Start-Up Voltage
1.1
105 125
3401 G14
1.0
0.9
0.8
0.7
0.6
–55
–15 25
65
TEMPERATURE (°C)
105 125
3401 G17
Burst Mode Operation Current
44
42
40
38
36
34
32
30
–55
–15 25
65
TEMPERATURE (°C)
105 125
3401 G20
NMOS RDS(ON)
0.30 VOUT = 3.3V
0.25
0.20
0.15
0.10
0.05
–55
–15 25
65
TEMPERATURE (°C)
Shutdown Threshold
1.10
1.05
1.00
0.95
0.90
0.85
0.80
0.75
0.70
0.65
0.60
–55
–15 25
65
TEMPERATURE (°C)
VOUT Turn-Off Voltage
2.50
2.45
2.40
2.35
2.30
2.25
2.20
2.15
2.10
2.05
2.00
–55
–15 25
65
TEMPERATURE (°C)
105 125
3401 G22
105 125
3401 G18
105 125
3401 G21
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5 Page 
LTC3401
APPLICATIO S I FOR ATIO
A logic level feed forward signal, VFF, is coupled through
components C5 and R6. The amount of feed forward
signal is attenuated with resistor R6 and is given by the
following relationship:
R6
≈
VFVFO•URT5••∆VIINOU•T1.5
–
R5
where ∆IOUT = load current change.
VIN
LTC3401
34
VIN SW
10
SHDN
7
VOUT
28
MODE/SYNC FB
6
PGOOD
1
Rt
9
VC
5
GND
C3
R5
LOAD FEED
FORWARD
SIGNAL
C5
R6 3.3nF
VFF
Figure 3
VOUT
3404 F03
Closing the Feedback Loop
The LTC3401 uses current mode control with internal
adaptive slope compensation. Current mode control elimi-
nates the 2nd order filter due to the inductor and output
capacitor exhibited in voltage mode controllers, and sim-
plifies it to a single-pole filter response. The product of the
modulator control to output DC gain plus the error amp
open-loop gain equals the DC gain of the system.
GDC = GCONTROLOUTPUT • GEA
GCONTROL
=
2 • VIN
IOUT
,
GEA
≈
2000
The output filter pole is given by:
fFILTERPOLE
=
π
•
IOUT
VOUT • COUT
Hz
where COUT is the output filter capacitor.
The output filter zero is given by:
fFILTERZERO
=
2
•
π
•
1
RESR
•
COUT
Hz
where RESR is the capacitor equivalent series resistance.
A troublesome feature of the boost regulator topology is
the right half plane zero (RHP) and is given by:
fRHPZ
=
VIN2 •RO
2 • π • L • VO2
Hz
At heavy loads this gain increase with phase lag can occur
at a relatively low frequency. The loop gain is typically
rolled off before the RHP zero frequency.
The typical error amp compensation is shown in Figure 4.
The equations for the loop dynamics are as follows:
fPOLE1
≈
2
•
π
•
20
1
• 106
•
Hz
CC1
which is extremelyclose to DC
fZERO1
=
2
•
π
1
• RZ
Hz
• CC1
fPOLE2
≈
2
•
π
•
1
RZ
•
CC2
Hz
+
ERROR
AMP
–
1.25V
FB
8
VC
9
CC1
RZ
VOUT
R1
R2
CC2
3401 F04
Figure 4
Refer to Application Note AN-76 for more closed loop
examples.
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11
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| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3401EMS.PDF ] | |
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