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PDF SC623 Data sheet ( Hoja de datos )
| Número de pieza | SC623 | |
| Descripción | LED Light Management Unit Charge Pump | |
| Fabricantes | Semtech Corporation | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de SC623 (archivo pdf) en la parte inferior de esta página. Total 21 Páginas | ||
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POWER MANAGEMENT
Features
Input supply voltage range — 3.0V to 5.5V
Charge pump modes — 1x, 1.5x and 2x
Four programmable current sinks with 32 steps from
0.5mA to 25mA
Flash LED — 400mA max in flash mode, 250mA max
continuous for spotlight
Charge pump frequency — 250kHz
SemWireTM single wire interface — up to 75kbit/s
Backlight current accuracy ±1.5% typical
Backlight current matching ±0.5% typical
Programmable fade-in/fade-out for main backlight
External flash control pin to sync with camera
Optional 1s flash time out
Automatic sleep mode (LEDs off ) — I = 100μA
Q
Low shutdown current — 0.1μA (typical)
Ultra-thin package — 3mm x 3mm x 0.6mm
Fully WEEE and RoHS compliant
Applications
Cellular phone backlighting and flash
PDA backlighting and flash
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SC623
LED Light Management Unit
Charge Pump, 4 LEDs, 400mA Flash LED,
and SemWireTM Interface
Description
The SC623 is a high efficiency charge pump LED driver
using Semtech’s proprietary mAhXLifeTM technology.
Performance is optimized for use in single-cell Li-ion
battery applications.
The charge pump provides backlight current in
conjunction with four matched current sinks. It also can
supply continuous or bursted current to a flash LED using
the dedicated flash driver current sink. The load and
supply conditions determine whether the charge pump
operates in 1x, 1.5x, or 2x mode. An optional fading
feature that gradually adjusts the backlight current is
provided to simplify control software. A flash-timeout
feature disables the flash if active for longer than 1
second.
The SC623 uses the proprietary SemWireTM single wire
interface. The interface controls all functions of the device,
including backlight and flash currents. The single wire
implementation minimizes microcontroller and interface
pin counts. The flash/spotlight output is triggered via
either the SemWire interface or a dedicated pin.
In sleep mode, the device reduces quiescent current to
100μA while continuing to monitor the serial interface.
Total current reduces to 0.1μA in shutdown.
Typical Application Circuit
VBAT
CIN
2.2μF
SemWire
Interface
Flash
Control
VIN VOUT
SWIF
FLEN SC623
GREF
AGND
PGND
BL1
BL2
BL3
BL4
FL
C1+ C1- C2+ C2-
C1
2.2μF
C2
2.2μF
COUT
4.7μF
June 27, 2007
© 2007 Semtech Corporation
MAIN BACKLIGHT
FLASH
US Patents: 6,504,422; 6,794,926
1
1 page  
SC623
Electrical Characteristics (continued)
Parameter
Symbol
Conditions
Min Typ Max Units
Digital I/O Electrical Specifications (FLEN, SWIF)
Input High Threshold
V
IH
V = 5.5V
IN
1.6
V
Input Low Threshold
V
IL
V = 3.0V
IN
0.4 V
Input High Current
I
IH
V = 5.5V
IN
-1 +1 μA
Input Low Current
I
IL
V = 5.5V
IN
-1 +1 μA
SemWire Bit Rate
f
SWIF
10 75 kbit/s
SemWire Start-up Time(5)
t
EN
1 ms
SemWire Disable Time(6)
t
DIS
10 ms
SemWire Data Latch Delay(7)
D
DL
5 bit
Notes:
(1) ΔV is the voltage difference between any two LEDs.
F
(2) Once tripped, flash output will remain disabled until FLEN pin is cycled or reset via serial interface.
(3) Current matching equals ± [I - I ] / [I + I ].
BL(MAX) BL(MIN
BL(MAX) BL(MIN)
(4) Test voltage is VOUT = 4.0V — a relatively extreme LED voltage — to force a transition during test. Typically VOUT = 3.2V for white LEDs.
(5) The SemWire start-up time is the minimum period that the SWIF pin must be held high to enable the part before commencing
communication.
(6) The SemWire disable time is the minimum period that the SWIF pin must be pulled low to shut the part down.
(7) The SemWire data latch delay is the maximum duration after communication has ended before the register is updated.
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5
5 Page 
SC623
Applications Information
General Description
This design is optimized for handheld applications
supplied from a single Li-Ion cell and includes the
following key features:
• A high efficiency fractional charge pump that
supplies power to all LEDs
• Four matched current sinks that control LED
backlighting current, with 0.5mA to 25mA per
LED
• An LED flash output that provides up to 400mA
of momentary current or up to 250mA of
continuous spotlight current
• A SemWire single wire interface that provides
control of all device functions
High Current Fractional Charge Pump
The backlight and flash outputs are supported by a high
efficiency, high current fractional charge pump output
at the VOUT pin. The charge pump multiplies the input
voltage by 1, 1.5, or 2 times. The charge pump switches
at a fixed frequency of 250kHz in 1.5x and 2x modes
and is disabled in 1x mode to save power and improve
efficiency.
The mode selection circuit automatically selects the
1x, 1.5x or 2x mode based on circuit conditions. Circuit
wwcwo.nDdatiatSiohneest4suU.cchomas low input voltage, high output current,
or high LED voltage place a higher demand on the charge
pump output. A higher numerical mode may be needed
momentarily to maintain regulation at the VOUT pin
during intervals of high demand, such as the high current
of an LED flash or the droop at the VIN pin during a supply
voltage transient. The charge pump responds to these
momentary high demands, setting the charge pump to
the optimum mode (1x, 1.5x or 2x), as needed to deliver
the output voltage and load current while optimizing
efficiency. Hysteresis is provided to prevent mode
toggling.
The charge pump requires two bucket capacitors for
low ripple operation. One capacitor must be connected
between the C1+ and C1- pins and the other must be
connected between the C2+ and C2- pins as shown in
the typical application circuit diagram. These capacitors
should be equal in value, with a minimum capacitance of
2.2μF to support the charge pump current requirements.
The device also requires a 2.2μF capacitor on the VIN
pin and a 4.7μF capacitor on the VOUT pin to minimize
noise and support the output drive requirements.
Capacitors with X7R or X5R ceramic dielectric are
strongly recommended for their low ESR and superior
temperature and voltage characteristics. Y5V capacitors
should not be used as their temperature coefficients
make them unsuitable for this application.
LED Backlight Current Sinks
The backlight current is set via the SemWire interface.
The current is regulated to one of 32 values between
0.5mA and 25mA. The step size varies depending upon
the current setting. Between 0.5mA and 12mA, the
step size is 0.5mA. The step size increases to 1mA for
settings between 12mA and 15mA and 2mA for settings
greater than 15mA. This feature allows finer adjustment
for dimming functions in the low current setting range
and coarse adjustment at higher current settings where
small current changes are not visibly noticeable in LED
brightness.
All backlight current sinks have matched currents, even
when there is variation in the forward voltages (ΔV )
F
of the LEDs. A ΔV of 1.2V is supported when the input
F
voltage is at 3.0V. Higher ΔVFLED mis-match is supported
when V is higher than 3.0V. All current sink outputs are
IN
compared and the lowest output is used for setting the
voltage regulation at the VOUT pin. This is done to ensure
that sufficient bias exists for all LEDs, including the flash
LED.
The backlight LEDs default to the off state upon power-
up. For backlight applications using less than four LEDs,
any unused output must be left open and the unused
LED driver must remain disabled. When writing to the
Backlight Enable Control register, a zero (0) must be
written to the corresponding bit of any unused output.
11
11 Page | ||
| Páginas | Total 21 Páginas | |
| PDF Descargar | [ Datasheet SC623.PDF ] | |
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