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PDF LTC3552-1 Data sheet ( Hoja de datos )
| Número de pieza | LTC3552-1 | |
| Descripción | Standalone Linear Li-Ion Battery Charger and Dual Synchronous Buck Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3552-1
FEATURES
Standalone Linear Li-Ion
Battery Charger and Dual
Synchronous Buck Converter
DESCRIPTIO
■ Programmable Charge Current Up to 950mA
■ Complete Linear Charger and Dual DC/DC
Regulator
■ Dual Fixed Outputs:
1.8V at 800mA
1.575V at 400mA
■ No MOSFET, Sense Resistor or Blocking Diode
Required
■ Thermal Regulation Maximizes Charge Rate
Without Risk of Overheating*
■ Charges Directly from a USB Port
■ Programmable Charge Current Termination
■ Preset 4.2V Charge Voltage with ±1% Accuracy
■ Charge Current Monitor Output for Gas Gauging*
■ Automatic Recharge
■ Charge Status Output
■ “Power Present” Output
■ Soft-Start Limits Inrush Current
■ Low Quiescent Current Buck Converter (40µA)
■ Current Mode Operation, Constant Frequency (2.25MHz)
■ Low Profile (5mm × 3mm × 0.75mm) DFN Package
U
APPLICATIO S
■ Cellular Telephones, PDAs, MP3 Players
■ Bluetooth Applications
The LTC®3552-1 is a complete constant-current/constant-
voltage linear charger and dual fixed output DC/DC con-
verter for single cell lithium-ion batteries. Its DFN package
and low external component count make the LTC3552-1
ideally suited for portable applications. Furthermore,
the LTC3552-1 is designed to work within USB power
specifications.
No external sense resistor or external blocking diode are
required due to the internal MOSFET architecture. The
charge voltage is fixed at 4.2V and the charge current is
programmed with a resistor. The charge cycle terminates
when the charge current drops below the programmed
termination threshold after the final float voltage is
reached. When the input supply (wall adapter or USB
supply) is removed, the LTC3552-1 enters a low current
state dropping the battery drain current to less than 2µA.
Thermal regulation maximizes charge rate without risk
of overheating.
The synchronous step-down switching regulators
generate fixed output voltages of 1.8V and 1.575V.
The switching frequency is set at 2.25MHz, allowing the
use of small surface mount inductors and capacitors.
, LTC and LT are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
*Protected by U.S. patents, including 6522118, 6700364, 5481178, 6580258, 6304066,
6127815, 6498466, 6611131.
TYPICAL APPLICATIO
Single Cell Li-Ion Battery Charger with
C/5 Termination and Dual DC/DC Converter
VIN
4.5V TO
6.5V
VOUT2
1.575V/
400mA
1µF
619Ω 1.24k
4.7µH
COUT2
10µF
CER
CFF2
330pF
VIN
ITERM
PROG
RUN1
RUN2
CHRG
BAT
PWR LTC3552-1 VCC
EN
SW2 SW1
VOUT2
VOUT1
VFB2 GND VFB1
800mA
+
10µF
2.2µH
CFF1
330pF
4.2V
1-CELL
Li-Ion
BATTERY
VOUT1
1.8V/
800mA
COUT1
10µF
CER
35521 TA01
Efficiency Curve/
Power Loss of Regulators
100
1000
95
90 VOUT1 = 1.8V
85
VOUT2 = 1.575V
100
80
CHANNEL 1
75
70 CHANNEL 2
10
1
65 VIN = 3.6V
Burst Mode OPERATION
60 0.1
1 10 100 1000
LOAD CURRENT (mA)
35521 TAO1b
35521f
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LTC3552-1
TYPICAL PERFOR A CE CHARACTERISTICS TA = 25°C Unless Otherwise Specified.
Battery Charger
Charge Current vs Supply Voltage
600
RPROG = 2k
500
400
VBAT = 4V
300 θJA = 40°C/W
200
RPROG = 10k
100
Charge Current
vs Ambient Temperature
600
ONSET OF THERMAL REGULATION
500
RPROG = 2k
400
VIN = 5V
300 VBAT = 4V
θJA = 40°C/W
200
RPROG = 10k
100
0
4 4.5 5 5.5 6 6.5 7 7.5 8
VIN (V)
35521 G10
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
35521 G11
Power FET “On” Resistance
vs Temperature
700
VIN = 4.2V
650
IBAT = 100mA
RPROG = 2k
600
550
500
450
400
350
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
35521 G12
Recharge Threshold Voltage
vs Temperature
4.16
VIN = 5V
RPROG = 10k
4.14
4.12
4.10
4.08
4.06
4.04
–50 –25
0
25 50
TEMPERATURE (°C)
75 100
35521 G13
35521f
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U
OPERATIO
Thermal Limiting
An internal thermal feedback loop reduces the pro-
grammed charge current if the die temperature attempts
to rise above a preset value of approximately 120°C. This
feature protects the charger from excessive temperature
and allows the user to push the limits of the power handling
capability of a given circuit board without risk of damag-
ing the charger. The charge current can be set according
to typical (not worst case) ambient temperature with the
assurance that the charger will automatically reduce the
current in worst-case conditions. DFN package power
considerations are discussed further in the Applications
Information section.
Undervoltage Lockout (UVLO)
An internal undervoltage lockout circuit monitors the in-
put voltage and keeps the charger in shutdown mode
until VIN rises above the undervoltage lockout threshold.
The UVLO circuit has a built-in hysteresis of 200mV.
Also, to protect against reverse current in the power
MOSFET, the UVLO circuit keeps the charger in shutdown
mode if VIN falls to within 30mV of the BAT voltage. If the
UVLO comparator is tripped, the charger will not come
out of shutdown mode until VIN rises 100mV above the
BAT voltage.
Manual Shutdown
At any point in the charge cycle, the charger can be put
into shutdown mode by driving the ⎯E⎯N pin high. This re-
duces the battery drain current to less than 2µA and the
VIN supply current to less than 50µA. When in shutdown
mode, the ⎯C⎯H⎯R⎯G pin is in the high impedance state. A new
charge cycle can be initiated by driving the ⎯E⎯N pin low. An
internal resistor pull-down on this pin forces the charger
to be enabled if the pin is allowed to float.
DUAL SWITCHING REGULATOR
The regulators use a current mode architecture with a con-
stant operating frequency of 2.25MHz. Both regulators share
the same clock and run in-phase. The output voltages are
fixed at 1.8V for regulator 1 and at 1.575V for regulator 2.
The resistive divider feedback networks are integrated inside
the LTC3552-1. An error amplifier compares the divided
LTC3552-1
output voltage (VFB) with a reference voltage of 0.6V and
adjusts the peak inductor current accordingly.
Main Regulator Control Loop
During normal operation, the top power switch (P-channel
MOSFET) is turned on at the beginning of a clock cycle
when the VOUT feedback voltage is below the reference
voltage. The current flows into the inductor and the load in-
creases until the current limit is reached. The switch turns
off and energy stored in the inductor flows through the
bottom switch (N-channel MOSFET) into the load until the
next clock cycle. The peak inductor current is controlled
by the internally compensated ITH voltage, which is the
output of the error amplifier. This amplifier compares the
VFB to the 0.6V reference (see Block Diagram). When the
load current increases, the VFB voltage decreases slightly
below the reference. This decrease causes the error ampli-
fier to increase the ITH voltage until the average inductor
current matches the new load current. The main control
loop is shut down by pulling the RUN pin to ground.
Low Load Current Operation
When the load is relatively light, the regulator automati-
cally switches into Burst Mode operation, where the PMOS
switch operates intermittently based on load demand with
a fixed peak inductor current. By running cycles periodi-
cally, the switching losses which are dominated by the gate
charge losses of the power MOSFETs are minimized. The
main control loop is interrupted when the output voltage
reaches the desired regulated value. A voltage comparator
trips when ITH is below 0.35V, shutting off the switch and
reducing the power. The output capacitor and the induc-
tor supply the power to the load until ITH exceeds 0.65V,
turning on the switch and the main control loop which
starts another cycle.
Dropout Operation
When the VCC input supply voltage decreases approach-
ing the output voltage, the duty cycle increases to 100%
which is the dropout condition. In dropout, the PMOS
switch is turned on continuously with the output voltage
being equal to the input voltage minus the voltage drops
across the internal P-channel MOSFET and the inductor.
An important design consideration is that the RDS(ON) of
35521f
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| PDF Descargar | [ Datasheet LTC3552-1.PDF ] | |
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