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PDF LTC3201 Data sheet ( Hoja de datos )
| Número de pieza | LTC3201 | |
| Descripción | 100mA Ultralow Noise Charge Pump Led Supply | |
| Fabricantes | Linear Technology Corporation | |
| Logotipo |  |
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FEATURES
s Input Noise Filter Minimizes Supply Noise
s Constant Frequency Operation
s 3-Bit LED Current Control
s No Inductors
s Low Shutdown Current: IIN < 1µA
s Output Current: 100mA
s VIN Range: 2.7V to 4.5V
s 1.8MHz Switching Frequency
s Soft-Start Limits Inrush Current at Turn-On
s Short-Circuit and Overtemperature Protected
s Available in 10-Pin MSOP Package
U
APPLICATIO S
s White LED Backlighting
s Programmable Boost Current Source
, LTC and LT are registered trademarks of Linear Technology Corporation.
LTC3201
100mA Ultralow Noise
Charge Pump LED Supply
with Output Current Adjust
DESCRIPTIO
The LTC®3201 is an ultralow noise, constant frequency,
charge pump DC/DC converter specifically designed for
powering white LEDs. The part produces a low noise
boosted supply capable of supplying 100mA of output
current. LED current is regulated for accurate and stable
backlighting. A 3-bit DAC provides output current adjust
for brightness control.
Low external parts count (one small flying capacitor and
three small bypass capacitors) and small MSOP-10 pack-
age size make the LTC3201 ideally suited for space con-
strained applications. An input noise filter further reduces
input noise, thus enabling direct connection to the battery.
High switching frequency enables the use of small external
capacitors.
The LTC3201 contains overtemperature protection and
can survive an indefinite output short to GND. Internal
soft-start circuitry also prevents excessive inrush current
on start-up. A low current shutdown feature disconnects
the load from VIN and reduces quiescent current to less
than 1µA.
TYPICAL APPLICATIO
Ultralow Noise White LED Driver
with Adjustable Current Control
0.22µF
Input Current Ripple
IOUT = 100mA
IIN = 205mA
VIN = 3.6V
+
Li ION
1µF
LED
CURRENT
ADJUST
0.22µF
3
CM CP
VIN
FILTER
VOUT
LTC3201
D0-D2
GND
FB
UP TO
6-WHITE LEDs
1µF
•••
50mA/DIV
56Ω 56Ω
56Ω
3201 TA01a
100ns/DIV
3201 TA01b
3201f
1
1 page  
LTC3201
APPLICATIO S Iwww.DataSheet4U.com FOR ATIO
Operation (Refer to Simplified Block Diagram)
The LTC3201 is a switched capacitor boost charge pump
especially designed to drive white LEDs in backlighting
applications. The LTC3201’s internal regulation loop
maintains constant LED output current by monitoring the
voltage at the FB pin. The device has a novel internal filter
that, along with an external 0.22µF capacitor, significantly
reduces input current ripple. An internal 7-state DAC
allows the user to lower the regulation voltage at the FB
pin, thus lowering the LED current. To regulate the output
current, the user places a sense resistor between FB and
GND. The white LED is then placed between VOUT and FB.
The value at the FB pin is then compared to the output of
the DAC. The charge pump output voltage is then changed
to equalize the DAC output and the FB pin. The value of the
sense resistor determines the maximum value of the
output current.
When the charge pump is enabled, a two-phase
nonoverlapping clock activates the charge pump switches.
The flying capacitor is charged to VIN on phase one of the
clock. On phase two of the clock, it is stacked in series with
VIN and connected to VOUT. This sequence of charging and
discharging the flying capacitor continues at a free run-
ning frequency of 1.8MHz (typ) until the FB pin voltage
reaches the value of the DAC.
In shutdown mode all circuitry is turned off and the
LTC3201 draws only leakage current (<1µA) from the VIN
supply. Furthermore, VOUT is disconnected from VIN. The
LTC3201 is in shutdown when a logic low is applied to all
three D0:D2 pins. Note that if VOUT floats to >1.5V,
shutdown current will increase to 10µA max. In normal
operation, the quiescent supply current of the LTC3201
will be slightly higher if any of the D0:D2 pins is driven high
with a signal that is below VIN than if it is driven all the way
to VIN. Since the D0:D2 pins are high impedance CMOS
inputs, they should never be allowed to float.
Input Current Ripple
The LTC3201 is designed to minimize the current ripple at
VIN. Typical charge pump boost converters draw large
amounts of current from VIN during both phase 1 and
phase 2 of the clocking. If there is a large nonoverlap time
between the two phases, the current being drawn from VIN
can go down to zero during this time. At the full load of
100mA at the output, this means that the input could
potentially go from 200mA down to 0mA during the
nonoverlap time. The LTC3201 mitigates this problem by
minimizing the nonoverlap time, using a high (1.8MHz)
frequency clock, and employing a novel noise FILTER
network. The noise filter consists of internal circuitry plus
external capacitors at the FILTER and VIN pins. The filter
capacitor serves to cancel the higher frequency compo-
nents of the noise, while the VIN capacitor cancels out the
lower frequency components. The recommended values
are 0.22µF for the FILTER capacitor and 1µF for the VIN
capacitor. Note that these capacitors must be of the highest
possible resonant frequencies. See Layout Considerations.
3-Bit DAC for Output Current Control
Digital pins D0, D1, D2 are used to control the output
current level. D0 = D1 = D2 = VIN allows the user to program
an output LED current that is equal to 0.63V/RSENSE, where
RSENSE is the resistor connected to any single LED and
connected between FB and ground. Due to the finite
transconductance of the regulation loop, for a given diode
setting, the voltage at the FB Pin will decrease as output
current increases. All LEDs subsequently connected in
parallel should then have similar currents. The mismatch-
ing of the LED VF and the mismatching of the sense
resistors will cause a differential current error between
LEDs connected to the same output. Once the sense
resistor is selected, the user can then control the voltage
applied across that resistor by changing the digital values
at D0:D2. This in turn controls the current into the LED.
Note that there are only 7 available current states. The 8th
is reserved to shutdown. This is the all 0s code. Refer to
Table below.
D0
HIGH
HIGH
HIGH
HIGH
LOW
LOW
LOW
LOW
D1
HIGH
HIGH
LOW
LOW
HIGH
HIGH
LOW
LOW
D2
HIGH
LOW
HIGH
LOW
HIGH
LOW
HIGH
LOW
FB
0.63V
0.54V
0.45V
0.36V
0.27V
0.18V
0.09V
Shutdown
3201f
5
5 Page | ||
| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LTC3201.PDF ] | |
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