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PDF SC658 Data sheet ( Hoja de datos )
| Número de pieza | SC658 | |
| Descripción | Backlight Driver | |
| Fabricantes | Semtech | |
| Logotipo |  |
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POWER MANAGEMENT
Features
Input supply voltage range — 2.9V to 5.5V
Very high efficiency charge pump driver system with
three modes — 1x, 1.5x and 2x
Four programmable current sinks — 0mA to 25mA
Up to three LED grouping options
Fade-in/fade-out feature for main LED bank
Charge pump frequency — 250kHz
SemPulse single wire interface
Backlight current accuracy — ±1.5% typical
Backlight current matching — ±0.5% typical
LED float detection
Automatic sleep mode (LEDs off ) — IQ = 60µA (typ.)
Shutdown current — 0.1µA (typical)
Ultra-thin package — 2 x 2 x 0.6 (mm)
Fully WEEE and RoHS compliant
Applications
Cellular phones, smart phones, and PDAs
LCD modules
Portable media players
Digital cameras
Personal navigation devices
Display/keypad backlighting and LED indicators
SC658
Backlight Driver for 4 LEDs
with SemPulseTM Interface
Description
The SC658 is a high efficiency charge pump LED driver
using Semtech’s proprietary charge pump technology.
Performance is optimized for use in single-cell Li-ion
battery applications.
The charge pump provides backlight current utilizing four
matched current sinks. 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.
The SC658 uses the proprietary SemPulseTM single wire
interface to control all functions of the device, including
backlight currents. The single wire interface minimizes
microcontroller and interface pin counts. The four LEDs
can be grouped in up to three separate banks that can be
independently controlled.
The SC658 enters sleep mode when all the LED drivers are
disabled. In this mode, the quiescent current is reduced
while the device continues to monitor the SemPulse
interface.
With a 2 x 2 (mm) package and four small capacitors, the
SC658 provides a complete LED driver solution with a
minimal PCB footprint.
Typical Application Circuit
VBAT = 2.9 to 5.5V
CIN
2.2µF
From
Microprocessor
IN OUT
SC658
SPIF
BL1
BL2
BL3
BL4
COUT
2.2µF
April 3, 2009
GND
C1+ C1- C2+ C2-
C1
2.2µF
C2
2.2µF
© 2009 Semtech Corporation
US Patents: 6,504,422; 6,794,926
1 page  
SC658
Electrical Characteristics (continued)
Parameter
Symbol
Conditions
Min Typ Max Units
SemPulse Interface
Input High Threshold
VIH
VIN = 5.5V
1.6
V
Input Low Threshold
VIL
VIN = 2.9V
0.4 V
Input High Current
IIH
VIN = 5.5V
-1 +1 µA
Input Low Current
IIL
VIN = 5.5V
-1 +1 µA
Start up Time(5)
tSU
Only required when leaving shutdown mode
1
ms
Bit Pulse Duration(6)
tHI
0.75 250 µs
Duration Between Pulses(6)
Hold Time - Address(6)
Hold Time - Data(6)
Bus Reset Time (6)
tLO
tHOLDA
tHOLDD
tBR
Software limit — SPIF must be held high for this
amount of time to latch the data
Software limit — SPIF must be held high for this
amount of time to latch the address
Software Limit — SPIF must be held high for this
amount of time to force a bus system reset
0.75
550
550
12
250
5000
µs
µs
µs
ms
Shutdown Time (7)
tSD
Software Limit — SPIF must be held low for this
amount of time to disable device
10
ms
Notes:
(1) Capacitors are MLCC of X5R type. Production tested with higher value capacitors than the application requires
(2) SPIF is high for more than 10ms to place serial bus in standby mode
(3) Current matching is defined as ± [IBL(MAX) - IBL(MIN] / [IBL(MAX) + IBL(MIN)].
(4) Test voltage is VOUT = 4.2V — a relatively extreme LED voltage — to force a transition during test. Typically VF = 3.2V for white LEDs.
(5) The SemPulse start-up time is the minimum time that the SPIF pin must be held high to enable the part before starting communication.
(6) The source driver used to provide the SemPulse Output must meet these limits.
(7) The SemPulse shutdown time is the minimum time that the SPIF pin must be pulled low to shut the part down.
5 Page 
SC658
Applications Information (continued)
Backlight Quiescent Current
The quiescent current required to operate all backlights is
reduced when the backlight current is set to 4.0mA or less.
This feature results in higher efficiency under light-load
conditions. Further reduction in quiescent current will
result from using fewer than the maximum number of
LEDs.
LED Banks
The LEDs can be grouped in up to three independently
controlled LED banks. Using the SemPulse interface, the
four LED drivers can be grouped as described in the
Backlight Grouping Configuration subsection. The banks
can be used to provide up to three different current
options. This can be useful for controlling keypad, display,
and auxiliary backlight operation from one SC658 device.
The LED banks provide versatility by allowing backlights
to be controlled independently. For example, applications
that have a main and sub display may also need to supply
an indicator LED. The three bank option allows the SC658
to control each function with different current settings.
Another application involves backlighting two displays
and a keypad, each requiring different brightness settings.
A third scenario requires supplying different brightness
levels to different types of LEDs (such as RGB) to create
display effects. In all applications, the brightness level for
each LED can be set independently.
Backlight Fade-in / Fade-out Function
The SC658 contains bits that control the fade state of the
main bank. When enabled, the fade function causes the
backlight settings to step from their current state to the
next programmed state as soon as the new state is stored
in its register. For example, if the backlight is set at 25mA
and the next setting is the off state, the backlight will step
from 25mA down to 0mA using all settings at the fade rate
specified by the bits in register 04h. The same is true when
turning on or increasing the backlight current — the
backlight current will step from the present level to the
new level at the step rate defined in register 04h. This
process applies to the main display only.
The fade rate may be changed dynamically when a fade
operation is active by writing new values to the fade reg-
ister. When a new backlight level is written during an
ongoing fade operation, the fade will be redirected to the
new value from the present state. An ongoing fade opera-
tion may be cancelled by disabling fade which will result
in the backlight current changing immediately to the final
value. If fade is disabled, the current level will change
immediately without the fade delay.
The state diagram in Figure 1 describes the fade opera-
tion. More details can be found in the Register Map
section.
No change
Write FADE=0
FADE=0
Immediate
change to new
bright level
Write new
bright level
FADE=0
Write
FADE=1
Immediate
change to
new bright
level
Write
FADE=0 FADE=1
FADE=1
No
change
Write
FADE=1
Fade=0
Write new
bright
level
Fade
ends
Fade
begins
No
change
Fade
processing(1)
Write
Fade=1
Fade is redirected
toward the new value
from current state
Write new
bright level
Continue
fade using
new rate
Write
new fade
rate
Note:
(1) When the data in backlight
enable register 00h is not 00h
Figure 1 — State Diagram for Fade Function
Fade-In from Off State
When the initial state of the main backlight current regis-
ter is 00h (the data value for 0mA), fading to an on state is
accomplished by following the steps listed in Table 1.
Following these steps explicitly will ensure that the fade-
in operation will proceed with no interruption at the rate
specified in the Main Fade register (04h). This procedure
11
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| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet SC658.PDF ] | |
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