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PDF ISL97678 Data sheet ( Hoja de datos )
| Número de pieza | ISL97678 | |
| Descripción | 8-Channel 45V 50mA LED Driver | |
| Fabricantes | Intersil Corporation | |
| Logotipo |  |
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8-Channel 45V 50mA LED Driver
ISL97678
The ISL97678 is an 8-channel PWM dimming LED driver
for LCD backlight applications. The ISL97678 is capable
of driving up to 96 pieces of 3.4V/50mA LEDs but larger
numbers of LEDs is possible if the LED forward voltage
combined is less than 45V. The ISL97678 has 8 channels
of voltage controlled current sources with typical currents
matching to ±1%, which compensate for the
non-uniformity effect of forward voltages variance in the
LED strings. To minimize the voltage headroom and
power loss in the typical multi-string operation, the
ISL97678 features dynamic headroom control that
monitors the highest LED forward voltage string and uses
its feedback signal for output regulation.
The ISL97678 features PWM dimming up to 30kHz with
0.8%~100% duty cycle and maintains ±1% current
matching across all ranges. The PWM dimming frequency
can be adjusted between 100Hz and 30kHz. The boost
switching frequency can also be adjusted between
600kHz and 1.5MHz.
The ISL97678 features extensive protection functions
that include string open and short circuit detections, OVP,
and OTP.
ISL97678 is available in the 32 Leads QFN 5mmx5mm
and operate from -40°C to +85°C with input voltage
ranges from 4.75V to 26V.
Features
• 8 Channels
• 4.75V ~ 26V Input
• 45V Maximum Output
• Drive Typically 96 LEDs (3.4V/50mA each)
• External PWM Input up to 25kHz Dimming
• Dimming range 0.8%~100% up to 30kHz
• Current Matching ±0.7%
• Protections
- String Open Circuit and Short Circuit Detections,
OVP, and OTP
• Adjustable Dimming Frequency
• Adjustable Switching Frequency
• 32 Ld (5mmx5mm) QFN Package
Applications
• Notebook Displays WLED or RGB LED Backlighting
• LCD Monitor LED Backlighting
www.DataSheet4U.com
November 5, 2009
FN6998.1
1 CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures.
1-888-INTERSIL or 1-888-468-3774 | Intersil (and design) is a registered trademark of Intersil Americas Inc.
Copyright Intersil Americas Inc. 2009. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
1 page  
ISL97678
Absolute Maximum Ratings
Voltage ratings are all with respect to AGND pin
VIN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 27V
EN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 27V
VLOGIC . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 2.75V
VDC, PWM . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 5.75V
COMP, RSET, FPWM, FSW . . . . . . . . . . . . . . . . -0.3V to min
. . . . . . . . . . . . . . . . . . . . . . . . . . . . (VDC + 0.3V, 5.75V)
CH1 - CH8, LX, OVP . . . . . . . . . . . . . . . . . . . . -0.3V to 45V
PGND, AGND . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +0.3V
Recommended Operating Conditions
Temperature Range . . . . . . . . . . . . . . . . . . -40°C to +85°C
Thermal Information
Thermal Resistance (Typical)
θJA (°C/W) θJC (°C/W)
32 Ld QFN (Notes 4, 5) . . . . . . . . . 31
3
Thermal Characterization (Typical, Note 6)
PSIJT (°C/W)
32 Ld QFN . . . . . . . . . . . . . . . . . . . . . . . . . 0.2
Maximum Continuous Junction Temperature . . . . . . +125°C
Storage Temperature . . . . . . . . . . . . . . . -65°C to +150°C
Power Dissipation
TA < +25°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2W
TA < +70°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.8W
TA < +85°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.3W
TA < +100°C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.8W
Pb-Free Reflow Profile . . . . . . . . . . . . . . . . . .see link below
http://www.intersil.com/pbfree/Pb-FreeReflow.asp
CAUTION: Do not operate at or near the maximum ratings listed for extended periods of time. Exposure to such conditions may adversely impact
product reliability and result in failures not covered by warranty.
NOTES:
4. θJA is measured with the component mounted on a high effective thermal conductivity test board in free air. See Tech Brief
TB379 for details.
5. For θJC, the “case temp” location is the center of the exposed metal pad on the package underside.
6. PSIJT is the PSI junction-to-top thermal characterization parameter. If the package top temperature can be measured with
this rating then the die junction temperature can be estimated more accurately than the θJC and θJC thermal resistance
ratings.
5E. lectrical Specifications
All specifications below are characterized at TA = -40°C to +85°C; VIN = 12V, /SHUT = 5V,
ISET = 36kΩ, unless otherwise noted. Boldface limits apply over the operating
temperature range, -40°C to +85°C.
PARAMETER
DESCRIPTION
CONDITION
MIN
MAX
(Note 7) TYP (Note 7) UNIT
GENERAL
VIN Backlight Supply Voltage
4.75
26
(Note 8)
V
IVIN_SHDN
VIN Shutdown Current
VOUT
Output Voltage
www.DVaUtaVSLOheet4U.com
VUVLO_HYS
Undervoltage Lockout Threshold
Undervoltage Lockout Hysteresis
LINEAR REGULATOR
/SHUT = 0
5
45
2.9 3.3
300
µA
V
V
mV
VDC
5V Analog Bias Regulator
VDC_DROP
VDC LDO Dropout Voltage
IVDC
Active Current
VLOGIC
2.5V Logic Bias Regulator
VLOGIC_DROP
VLOGIC LDO Dropout Voltage
BOOST SWITCHING REGULATOR
VIN > 6V
IVDC = 30mA
/SHUT = 5V, R = 33kΩ
VIN > 6V
IVLOGIC = 30mA
4.8
2.3
5 5.1
71 100
10
2.4 2.5
31 100
V
mV
mA
V
mV
SS Soft-Start
16 ms
SWILimit
rDS(ON)
Boost FET Current Limit
Internal Boost Switch ON-Resistance
TA = +25°C to +85°C
3.0 4.7
130
A
mΩ
5 FN6998.1
November 5, 2009
5 Page 
ISL97678
Typical Performance Curves (Continued)
VO (20V/DIV)
EN (5V/DIV)
IIN (1A/DIV)
ILED (50mA/DIV)
FIGURE 23. DISABLE PROFILE
Theory of Operation
PWM Boost Converter
The current mode PWM boost converter produces the
minimal voltage needed to enable the LED string with the
highest forward voltage drop to run at the programmed
current. The ISL97678 employs current mode control
boost architecture that has a fast current sense loop and
a slow voltage feedback loop. Such architecture achieves
a fast transient response that is essential for the
notebook backlight application where the power can be
several Li-ion cell batteries or instantly change to an
AC/DC adapter without rendering a noticeable visual
nuisance. The number of LEDs that can be driven by
ISL97678 depends on the type of LED chosen in the
application. The ISL97678 is capable of boosting up to
45V and drive 8 channels of LEDs at maximum of 45mA
per channel.
www.CDautarSrheenett4UM.coamtching and Current Accuracy
Each channel of the LED current is regulated by the
current source circuit, as shown in Figure 24.
The LED peak current is set by translating the RSET
current to the output with a scaling factor of 707.9/RSET.
The source terminals of the current source MOSFETs are
designed to run at 500mV to optimize power loss versus
accuracy requirements. The sources of errors of the
channel-to-channel current matching come from the
op amps offset, internal layout, reference, and current
source resistors. These parameters are optimized for
current matching and absolute current accuracy.
However, the absolute accuracy is additionally
determined by the external RSET. A 0.1% tolerance
resistor is recommended.
.
+- REF
RSET
+
-
PWM DIMMING
+
-
FIGURE 24. SIMPLIFIED CURRENT SOURCE CIRCUIT
Dynamic Headroom Control
The ISL97678 features a proprietary Dynamic Headroom
Control circuit that detects the highest forward voltage
string or effectively the lowest voltage from any of the
CH pins. When this lowest IIN voltage is lower than the
short circuit threshold, VSC, such voltage will be used as
the feedback signal for the boost regulator. The boost
makes the output to the correct level such that the
lowest CH pin is at the target headroom voltage. Since all
LED strings are connected to the same output voltage,
the other CH pins will have a higher voltage, but the
regulated current source circuit on each channel will
ensure that each channel has the same programmed
current. The output voltage will regulate cycle-by-cycle
and is always referenced to the highest forward voltage
string in the architecture.
11 FN6998.1
November 5, 2009
11 Page | ||
| Páginas | Total 18 Páginas | |
| PDF Descargar | [ Datasheet ISL97678.PDF ] | |
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