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PDF LTC3527 Data sheet ( Hoja de datos )
| Número de pieza | LTC3527 | |
| Descripción | 1.2MHz/2.2MHz Synchronous Step-Up DC/DC Converters | |
| Fabricantes | Linear Technology Corporation | |
| Logotipo |  |
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LTC3527/LTC3527-1
FEATURES
Dual 800mA/400mA,
1.2MHz/2.2MHz Synchronous
Step-Up DC/DC Converters
DESCRIPTION
■ Dual Synchronous Step-Up DC/DC Converters
■ Delivers 3.3V at 200mA/100mA from one Alkaline/
NiMH Cell, or 3.3V at 400mA/200mA from Two Cells
■ VIN Start-Up Voltage: 700mV
www.DataSh■eet04U.5.cVomto 5V VIN Range after Start-Up
■ 1.6V to 5.25V VOUT Range
■ Output Disconnect in Shutdown
■ VIN > VOUT Operation
■ 1.2MHz or 2.2MHz Operation
■ Up to 94% Efficiency
■ 12µA Quiescent Current in Burst Mode® Operation
■ Inrush Current Limiting and Soft-Start
■ Internal Synchronous Rectifiers
■ Logic-Controlled Shutdown (< 2µA)
■ Quick VOUT Discharge (LTC3527-1)
■ 16-Lead, 0.75mm × 3mm × 3mm QFN Package
APPLICATIONS
■ MP3/Personal Media Players
■ Noise Canceling/Bluetooth Headsets
■ Wireless Mice
■ Portable Medical Instruments
The LTC®3527/LTC3527-1 are dual high efficiency,
step-up DC/DC converters in a space saving 16-lead 3mm
× 3mm QFN package. Battery life is maximized with a
700mV start-up voltage and operation down to 500mV
once started. The ⎯S⎯H⎯D⎯N and PGOOD pins enable the
converters to be sequenced or started together.
The LTC3527/LTC3527-1 limit inrush current during start-
up. Selectable 1.2MHz or 2.2MHz operation provides a
choice between the highest efficiency or smallest solu-
tion footprint. The current mode PWM design is internally
compensated reducing external parts count. Burst Mode
operation or fixed frequency operation is selectable via the
MODE pin. Anti-ring circuitry reduces EMI in discontinuous
mode. This device also features thermal shutdown.
True output disconnect allows the output to be completely
open in shutdown. The LTC3527-1 actively discharges
VOUT1 or VOUT2 when its respective ⎯S⎯H⎯D⎯N goes low. Qui-
escent current in shutdown is less than 2µA.
, 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
Two-Cell Alkaline to 3.3V/1.8V Synchronous Boost Converters
+ 1.6V to 3.2V
VIN
4.7µF
4.7µH
VIN1 VIN VIN2
VOUT
3.3V
150mA
4.7µF 1.78M
ON
OFF
1M
SW1
VOUT1
LTC3527
SW2
VOUT2
FB1 FB2
PGOOD1
PGOOD2
SHDN1
SHDN2
MODE GND FSEL
ON
OFF
4.7µH
619k
1.21M
35271 TA01
VOUT
1.8V
150mA
4.7µF
1.2MHz Efficiency and Power Loss
100
BURST
90 EFFICIENCY
80
1000
100
70
60 10
50 FIXED
FREQUENCY
40
1
30
POWER
20 LOSS
0.1
10
BURST
0
VIN = 2.4V
VOUT1 = 3.3V
0.01
0.01 0.1 1 10 100 1000
LOAD CURRENT (mA)
35271 TA01b
35271f
1
1 page  
LTC3527/LTC3527-1
TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C, unless otherwise noted)
No-Load Input Current vs VIN
180
160
140
VOUT = 5V
120
100
80
www.DataSheet4U.com
60
40
20 VOUT =
1.8V
0
0.5 1 1.5
VOUT =
2.4V
VOUT = 3.3V
2 2.5 3 3.5 4 4.5
VIN (V)
35271 G09
Maximum Output Current
vs VIN for Converter 1
800
700
VOUT =
2.5V
VOUT = 3.3V
600 VOUT =
1.8V
500
400
300 VOUT = 5V
200
100
0
0.5 1 1.5 2 2.5 3 3.5 4 4.5
VIN (V)
35271 G10
Maximum Output Current
vs VIN for Converter 2
500
450
400 VOUT = 3.3V
VOUT =
350 2.5V
300 VOUT =
1.8V
250
200
150 VOUT = 5V
100
50
0
0.5 1 1.5 2 2.5 3 3.5
VIN (V)
4 4.5
35271 G11
Minimum Load Resistance During
Start-Up vs VIN
1000
CONVERTER 2
100
CONVERTER 1
10
0.635 0.685 0.735 0.785 0.835 0.885 0.935
VIN (V)
35271 G12
Burst Mode Threshold Current
vs VIN for VOUT1 = VOUT2 = 1.8V
45
40
35
30
CONVERTER 1
LEAVE BURST
25
20
15
CONVERTER 2
ENTER BURST
10
5
0
0.7
CONVERTER 2
CONVERTER 1
0.8 0.9 1 1.1 1.2 1.3
VIN (V)
1.4 1.5
35271 G13
Burst Mode Threshold Current
vs VIN for VOUT1 = VOUT2 = 3.3V
60
50
CONVERTER 1
LEAVE BURST
40
30
ENTER BURST
20 CONVERTER 2
10 CONVERTER 2
CONVERTER 1
0
1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6 2.8 3
VIN (V)
35271 G14
Burst Mode Threshold Current
vs VIN for VOUT1 = VOUT2 = 5V
70
60 CONVERTER 1
50 LEAVE BURST
40
30
CONVERTER 2 ENTER BURST
20
10
0
1
CONVERTER 2
CONVERTER 1
1.5 2 2.5 3 3.5 4 4.5
VIN (V)
35271 G15
Oscillator Frequency
vs Temperature
2.50
FSEL = 3.3V
2.00
VIN = 1.2V
VOUT = 3.3V
1.50
FSEL = 0V
1.00
–45 –30 –15 0 15 30 45 60 75 90
TEMPERATURE (°C)
35271 G16
35271f
5
5 Page 
LTC3527/LTC3527-1
OPERATION
limit the minimum and maximum error amp output volt-
ages for improved large-signal transient response. Power
converter control loop compensation is provided internally.
An external resistive voltage divider from VOUT1 (VOUT2)
to ground programs the respective output voltage via FB1
(FB2) from 1.6V to 5.25V.
VOUT1
www.DataSheet4U.com
=
1.2
0V
•
⎡⎣⎢1+
R1
R2
⎤
⎦⎥
VOUT2
=
1.20V
•
⎣⎢⎡1+
R3
R4
⎤
⎦⎥
(See Block Diagram)
Current Sensing: Lossless current sensing converts the
peak current signal of each N-channel MOSFET switch
into a voltage which is summed with its corresponding
internal slope compensation. The summed signals are
compared to their respective error amplifier outputs to
provide individual peak current control commands for the
PWM of each converter.
Current Limit: The current limit comparators shut off
the N-channel MOSFET switches once their threshold
is reached. Each current limit comparator delay time to
output is typically 60ns. Peak switch current is limited
to approximately 900mA for converter 1 and 500mA for
converter 2, independent of input or output voltage. If
VOUT1 or VOUT2 falls below 1V, its respective current limit
is cut in half.
Zero Current Comparator: The zero current comparators
monitor the inductor current to the outputs and shut off
the synchronous rectifiers when the current reduces to ap-
proximately 30mA. This prevents the inductor current from
reversing in polarity, improving efficiency at light loads.
Synchronous Rectifier: To control inrush current and
to prevent the inductor currents from running away when
VOUT1 or VOUT2 is close to VIN, the P-channel MOSFET
synchronous rectifiers are only enabled when their respec-
tive VOUT > (VIN + 0.24V).
Anti-Ringing Control: The anti-ringing control connects a
resistor across the inductor to prevent high frequency ring-
ing on the SW1 (SW2) pins during discontinuous current
mode operation. Although the ringing of the resonant circuit
formed by the inductors and CSW (capacitance on SW1 or
SW2 pins) is low energy, it can cause EMI radiation.
Output Disconnect: The LTC3527/LTC3527-1 are
designed to allow true output disconnect by eliminating
body diode conduction of the internal P-channel MOSFET
rectifiers. This allows VOUT1 and VOUT2 to go to zero volts
during shutdown, drawing no current from the input source.
It also allows for inrush current limiting at turn-on, mini-
mizing surge currents seen by the input supply. Note that
to obtain the advantages of output disconnect, there must
not be external Schottky diodes connected between the
SW1 (SW2) pins and VOUT1 (VOUT2). The output discon-
nect feature also allows VOUT1 or VOUT2 to be pulled high,
without any reverse current into a battery on VIN.
Thermal Shutdown: If the die temperature exceeds
160°C, the device will go into thermal shutdown. All
switches will be turned off and the soft-start capacitors
will be discharged. The device will be enabled again when
the die temperature drops by about 15°C.
Burst Mode Operation
To realize the efficiency benefits of Burst Mode operation,
both VOUT1 and VOUT2 must be under a light load current
condition, if they are both enabled. If one channel is shut
down, then Burst Mode operation is enabled on the other
channel. With the MODE pin low, the LTC3527/LTC3527-1
will automatically enter Burst Mode operation at light load
and return to fixed frequency PWM mode when the load
increases. Refer to the Typical Performance Characteristics
to see the Output Load Burst Mode Threshold Current vs
VIN. The load current at which Burst Mode operation is
entered can be changed by adjusting the inductor value.
Raising the inductor value will lower the load current at
which Burst Mode is operation entered.
In Burst Mode operation, the LTC3527/LTC3527-1 still
switches at a fixed frequency of 1.2MHz (FSEL = 0) or
2.2MHz (FSEL = 1), using the same error amplifier and
loop compensation for peak current mode control. This
control method eliminates the output transient when
switching between modes. In Burst Mode operation,
energy is delivered to the output until it reaches the
nominal regulation value, then the LTC3527/LTC3527-1
transitions to sleep mode where the outputs are off and
the LTC3527/LTC3527-1 consumes only 12µA of quies-
cent current from the higher of VOUT1 or VOUT2. When
35271f
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3527.PDF ] | |
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