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PDF LTC3523-2 Data sheet ( Hoja de datos )
| Número de pieza | LTC3523-2 | |
| Descripción | Synchronous 600mA Step-Up And 400mA Step-Down DC/DC Converters | |
| Fabricantes | Linear Technology Corporation | |
| Logotipo |  |
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LTC3523/LTC3523-2
Synchronous 600mA Step-Up
and 400mA Step-Down
DC/DC Converters
FEATURES
DESCRIPTION
■ Dual High Efficiency DC/DC Converters:
Step-Up (VOUT = 1.8V to 5.25V, ISW = 600mA)
Step-Down (VOUT = 0.615V to 5.5V, IOUT = 400mA)
■ 1.8V to 5.5V Input Voltage Range
www.DataSh■eetU4Up.ctoom94% Efficiency
■ Pin Selectable Burst Mode® Operation
■ 45μA Quiescent Current in Burst Mode Operation
■ 1.2MHz (LTC3523) or 2.4MHz (LTC3523-2)
Switching Frequency
■ Independent Power Good Indicator Outputs
■ Integrated Soft-Start
■ Thermal and Overcurrent Protection
■ <2μA Quiescent Current in Shutdown
■ Small 16-Lead 3mm × 3mm × 0.75mm QFN Package
APPLICATIONS
■ Digital Cameras
■ Medical Instruments
■ Industrial Handhelds
■ GPS Navigators
The LTC®3523/LTC3523-2 combine a 600mA step-up
DC/DC converter with a 400mA synchronous step-down
DC/DC converter in a tiny 3mm × 3mm package. The
1.2MHz/2.4MHz switching frequencies minimize the
solution footprint while maintaining high efficiency. Both
converters feature soft-start and internal compensation,
simplifying the design.
Both the step-up and step-down converters are current
mode controlled and utilize an internal synchronous rec-
tifier for high efficiency. The step-up supports 0% duty
cycle operation and the step-down converter supports
100% duty cycle operation to extend battery run time.
If the MODE pin is held high, both converters automati-
cally transition between Burst Mode operation and PWM
operation improving light load efficiency. Fixed, low noise
1.2MHz/2.4MHz PWM operation is selected when MODE
is grounded.
The LTC3523/LTC3523-2 provide a sub-2μA shutdown
mode, overtemperature shutdown and current limit pro-
tection on both converters. The LTC3523/LTC3523-2 are
housed in a 16-lead 3mm × 3mm × 0.75mm QFN package.
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
VIN
1.8V TO 3.2V
+
2-CELL
ALKALINE
VOUT1
STEP-UP
OUTPUT
3.3V
200mA
10μF
47μF
4.7μH
VIN1 VIN2 VBAT
SW1 SW2
4.7μH
634k
365k
VOUT
FB1
LTC3523
FB2
MODE
PGOOD1
PGOOD2
SHDN1
SHDN2
GND1 GND2 GND3
VIN
10pF 511k
511k
OFF ON
OFF ON 3523 TA01a
VOUT2
STEP-DOWN
OUTPUT
10μF
1.2V
200mA
LTC3523 Efficiency and Power
Loss vs Load Current
100 1000
90
80
EFFICIENCY
70
100
60
50 P0WER LOSS
10
40
30
20
10
0
0.1
VIN = 2.4V
VOUT1 = 3.3V
VOUT2 = 1.2V
fOSC = 1.2MHz
1
STEP-UP
STEP-DOWN
0.1
1 10 100 1000
LOAD CURRENT (mA)
3523 TA01b
3523f
1
1 page  
LTC3523/LTC3523-2
TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise noted)
Normalized RDS(ON) vs
Temperature
1.3
1.2
1.1
1.0 PMOS
0.9
www.DataSheet40.U8 .com
NMOS
0.7
0.6
0.5
–45 –25
–5 15 35 55
TEMPERATURE (°C)
75
3523 G10
Step-Up No-Load Input Current
vs VIN
500
450
400
VOUT = 5V
350
300
250
200
VOUT = 3.3V
150
100
50 VOUT = 2.8V
0
1.5 2 2.5 3 3.5 4 4.5 5
INPUT VOLTAGE (V)
3523 G11
Mode Transition Response
VOUT_BST
50mV/DIV
VOUT_BCK
20mV/DIV
MODE
2V/DIV
VOUT1 = 3.3V 200μs/DIV
VOUT2 = 1.2V
VIN = 2.4V
IOUT1 = 20mA
IOUT2 = 25mA
COUT1 = COUT2 = 10μF
L1 = L2 = 4.7μH
3523 G12
Maximum IOUT vs VIN for the
Step-Up Converter
500
450 VOUT = 3.3V
400 VOUT = 2.5V
VOUT = 5V
350
300
250
200
150
100
50
0
12345
INPUT VOLTAGE (V)
3523 G13
Maximum IOUT vs VIN for the
Step-Down Converter
450
VOUT = 1.8V
400
350 VOUT = 1.2V
VOUT = 2.5V
300
250
200
150
100
50
0
1 1.5 2 2.5 3 3.5 4 4.5 5
INPUT VOLTAGE (V)
3523 G14
PIN FUNCTIONS
FB1 (Pin 1): Step-Up Converter Feedback Input to the Er-
ror Amplifier. Connect resistor divider tap to this pin. The
output voltage can be adjusted from 1.8V to 5.25V by:
VOUT(STEP-UP)
=
1.2V
•
⎛⎝⎜1+
R1⎞
R2⎠⎟
See Block Diagram.
VIN1 (Pin 2): Step-Up Converter Power Voltage Input. This
pin can be connected to a different supply than VIN2. This
pin must be connected to a valid supply voltage.
PGOOD1 (Pin 3): Step-Up Converter Power Good Com-
parator Output. This open-drain output is pulled low when
VFB1 < –9% of its regulation voltage.
VOUT (Pin 4): Step-Up Converter Output Voltage Sense Input
and Drain of the Internal Synchronous Rectifier MOSFET.
Driver bias is derived from VOUT. PCB trace length from
VOUT to the output filter capacitor(s) should be as short
and wide as possible.
3523f
5
5 Page 
LTC3523/LTC3523-2
APPLICATIONS INFORMATION
will increase loop bandwidth resulting in a faster transient
response. Maximum capacitance values will produce lower
ripple. Table 3 shows a list of several ceramic capacitor
manufacturers. Consult the manufacturers directly for
detailed information on their entire selection of ceramic
parts.
Table 2. Step-Down Output Capacitor Range vs Programmed
Output Voltage
www.DataSheeVtO4UUT.coMmINIMUM CAPACITANCE (μF) MAXIMUM CAPACITANCE (μF)
0.8 8.4
33.6
1.2 5.6
22.4
1.5 4.5
17.9
1.8 3.7
14.9
2.5 2.7
10.7
5 1.3
5.4
Table 3. Capacitor Vendor Information
SUPPLIER
PHONE
AVX (803) 448-9411
Murata
(714) 852-2001
Taiyo-Yuden
(408) 573-4150
WEBSITE
www.avxcorp.com
www.murata.com
www.t-yuden.com
STEP-UP VIN > VOUT OPERATION
The LTC3523/LTC3523-2 step-up converters will maintain
voltage regulation when the input voltage is above the
output voltage. Since this mode will dissipate more power,
the maximum output current is limited in order to maintain
an acceptable junction temperature and is given by:
( )IOUT(MAX)
=
136
•
⎡⎣
250 – TA
VIN + 1.5
–
VOUT ⎤⎦
T
where TA = ambient temperature.
For example, at VIN = 4.5V, VOUT = 3.3V and TA = 85°C, the
maximum output current is limited to 449mA.
SHORT-CIRCUIT PROTECTION
The LTC3523/LTC3523-2’s step-up output disconnect
feature allows output short circuit while maintaining
a maximum internally set current limit. However, the
LTC3523/LTC3523-2 also incorporate internal features
such as current limit foldback and thermal shutdown for
protection from an excessive overload or short circuit.
During a prolonged short circuit of VOUT less than 950mV,
the current limit folds back to 2/3 the normal current limit.
This 2/3 current limit remains in effect until VOUT exceeds
1V, at which time the normal internal set current limit is
restored.
When the LTC3523/LTC3523-2 step-down converters out-
put is shorted to ground, the step-down uses a comparator
to limit the current through the synchronous rectifying
N-channel switch to 650mA. If this limit is exceeded, the
P-channel switch is inhibited from turning on until the
current through the synchronous rectifying N-channel
switch falls below 650mA.
THERMAL CONSIDERATIONS
To deliver the LTC3523/LTC3523-2’s full-rated power, it is
imperative that a good thermal path be provided to dis-
sipate the heat generated within the package. This can be
accomplished by taking advantage of the large thermal pad
on the underside of the LTC3523/LTC3523-2. It is recom-
mended that multiple vias in the printed circuit board be
used to conduct heat away from the LTC3523/LTC3523-2
and into the copper plane with as much area as possible.
In the event that the junction temperature gets too high,
the LTC3523/LTC3523-2 will go into thermal shutdown
and all switching will cease until the internal temperature
drops to a safe level at which point the soft-start cycle
will be initiated.
3523f
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3523-2.PDF ] | |
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