DATASHEET

N OT R E
CO
RECOM MMENDED FO
ME N D E
R NEW
D REPL
DESIGN
ACEME
ISL9767
NT PAR S
1A or IS
TS
L97672
B
ISL97674
Features
The ISL97674 is a 6-Channel 45V dual dimming capable
LED driver that can be used with either SMBus/I2C or
PWM signal for dimming control. The ISL97674 drives 6
channels of LED to support 78 LEDs from 4.5V to 26V or
48 LEDs from a boost supply of 2.7V to 26V and a
separate 5V bias on the ISL97674 VIN pin.
• 6 Channels
The ISL97674 compensates for non-uniformity of the
forward voltage drops in the LED strings with its 6 voltage
controlled-current source channels. Its headroom control
monitors the highest LED forward voltage string for output
regulation, to minimize the voltage headroom and power
loss in a typical multi string operation.
• Extensive Dimming Control
• Frame Rate to Dimming Frequency Synchronization
• 4.5V to 26.5V Input
• 45V Output Max
• Up to 40mA LED Current per channel
- PWM/DPST Dimming, I2C 8-bit with equal phase
shift, and 0.007% Direct PWM dimming at 200Hz
• Optional Master Fault Protection
• PWM Dimming Linearity 0.4%~100% <30kHz
• 600kHz/1.2MHz selectable switching frequency
The ISL97674 features optional channel phase shift
control to minimize the input, output ripple
characteristics and load transients as well as spreading
the light output to help reduce the video and audio
interference from the backlight driver operation. The
phase shift can be programmed with equal phase angle
or adjustable in 7-bit resolution. In addition, the
ISL97674 also has a unique VSYNC function that accepts
30Hz ~ 120Hz frame signal and synchronizes it to the
dimming frequency to minimize panel to panel visual
interference variation. The dimming frequencies are
available from 200Hz to 30kHz and can be synchronized
from 140Hz to 1085Hz.
• Dynamic Headroom Control
• Protections with Flag Indication
- String Open/Short Circuit, VOUT Short Circuit,
Overvoltage and Over-Temperature Protections
- Optional Master Fault Protection
• Current Matching ±0.7%
• 20 Ld 4mmx3mm QFN Package
Applications
• Notebook Displays WLED or RGB LED Backlighting
• LCD Monitor LED Backlighting
• Automotive Displays LED Backlighting
Typical Application Circuit
VOUT = 45V*, 40mA PER STRING
VIN = 4.5~26.5V
ISL97674
1
FAULT
2 VIN
4
VDC
18 COMP
LX 20
OVP 16
PGND 19
7 SCL
6 SDA
3 EN/PWM
5 VSYNC
CH0 10
CH1 11
CH2 12
CH3 13
PLLC
CH4 14
17 RSET
CH5 15
8
AGND 9
*VIN > 12V
FIGURE 1. ISL97674 TYPICAL APPLICATION DIAGRAM
October 8, 2012
FN7634.2
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. 2010, 2012. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
ISL97674
6-Channel LED Driver with Phase Shift Control and
Frame Rate to Dimming Frequency
Synchronization
ISL97674
Block Diagram
45V*, 40mA
25mA per string
78 (6x13) LEDs
VIN = 4.5V~26.5V
10uH/3A
VIN
VDC
FAULT
REG
O/P Short
Bias
Σ=0
Imax
OVP
OVP
Fault/Status
Register
fsw
OSC &
RAMP
Comp
4.7uF/50V
LX
Boost SW
FET
Drivers
Logic
Segmentation
Slew Rate Ctrl
ILIMIT
PGND
pe
Open Ckt, Short Ckt
Detects
Fault/Status Control
GM
AMP
COMP
VSET
RSET
SCL
SDA
PLL
Fault/Status
Register
DAC1
1
+
-
PWM1
*V
> 12V
IN
* Vin
> 6V
Phase
Shift
Controller
DAC5
D AC5
PWM5
Controls
I2C
Control
Temp
Sensor
0
PWM0
DAC 1
PWM1
Controls
Dimming
Controller
PLLC
DAC0
PWM0
Controls
PWM
Ctrl Ckt
VSYNC
CH5
+
-
DAC0
REF_OVP
REF_VSC
GND
EN/PWM
REF
GEN
+
-
CH0
CH1
Highest VF
String Detect
+
-
5
PWM5
ISL97674
FIGURE 2. ISL97674 BLOCK DIAGRAM
2
FN7634.2
October 8, 2012
ISL97674
Pin Configuration
COMP
RSET
20 Ld 4x3 QFN L20.3x4
PGND
20
19
18
17
NOTES:
1. Add “-T” or “-TK” suffix for tape and reel. Please refer to
TB347 for details on reel specifications.
2. These Intersil Pb-free plastic packaged products employ
special Pb-free material sets, molding compounds/die
attach materials, and 100% matte tin plate plus anneal
(e3 termination finish, which is RoHS compliant and
compatible with both SnPb and Pb-free soldering
operations). Intersil Pb-free products are MSL classified at
Pb-free peak reflow temperatures that meet or exceed the
Pb-free requirements of IPC/JEDEC J STD-020.
FAULT
1
16 OVP
VIN
2
15 CH5
EN/PWM
3
14 CH4
VDC
4
13 CH3
VSYNC
5
12 CH2
3. For Moisture Sensitivity Level (MSL), please see device
information page for ISL97674. For more information on
MSL please see techbrief TB363.
Pin Descriptions
SDA 6
11 CH1
7
8
9
10
CH0
7674
ISL97674
(20 LD QFN)
TOP VIEW
PKG.
DWG. #
AGND
PACKAGE
(Pb-free)
PLLC
ISL97674IRZ
PART
MARKING
LX
PART NUMBER
(Notes 1, 2, 3)
SCL
Ordering Information
(I = Input, O = Output, S = Supply)
PIN NAME PIN NO. TYPE
DESCRIPTION
FAULT
1
O
Fault disconnect switch
VIN
2
S
Input voltage for the device and LED power
EN/PWM
3
I
Dual Functions: Enable pin and PWM brightness control pin. The device needs 4ms for initial
power-up Enable, then this pin can be applied with a PWM signal with off time no longer than
28ms.
VDC
4
S
De-couple capacitor for internally generated supply rail.
VSYNC
5
I
Frame Rate to Dimming Frequency Synchronization Input
SDA
6
I/O
SCL
7
I
SMBus/I2C serial clock input
PLLC
8
I
RC Components Setting Pin for Internal Phase Lock Loop
AGND
9
S
Analog Ground for precision circuits
CH0
10
I
Input 0 to current source, FB, and monitoring
CH1
11
I
Input 1 to current source, FB, and monitoring
CH2
12
I
Input 2 to current source, FB, and monitoring
CH3
13
I
Input 3 to current source, FB, and monitoring
CH4
14
I
Input 4 to current source, FB, and monitoring
CH5
15
I
Input 5 to current source, FB, and monitoring
OVP
16
I
Overvoltage protection input
RSET
17
I
Resistor connection for setting LED current, (see Equation 1 for calculating the ILEDpeak)
COMP
18
O
Boost compensation pin
PGND
19
S
Power ground
LX
20
O
Input to boost switch
SMBus/I2C serial data input and output
3
FN7634.2
October 8, 2012
ISL97674
Table of Contents
Typical Application Circuit .............................. 1
Block Diagram ................................................ 2
Pin Descriptions (I = Input, O = Output,
S = Supply).................................................. 3
Absolute Maximum Ratings ............................ 5
Thermal Information ...................................... 5
Operating Conditions ...................................... 5
Electrical Specifications ...............................5
Typical Performance Curves ........................... 8
Theory of Operation........................................ 10
PWM Boost Converter .....................................10
Enable and PWM ............................................10
Current Matching and Current Accuracy ............10
Dynamic Headroom Control .............................11
Dimming Controls ..........................................11
Maximum DC Current Setting .................. 11
DC Current Adjustment .......................... 11
PWM Control..................................................11
Phase Shift Control ................................ 12
VSYNC Frame Rate to Dimming Synchronization ..13
Switching Frequency.......................................13
5V Low Dropout Regulator...............................13
In-rush Control and Soft-Start .........................13
Fault Protection and Monitoring ........................13
Short Circuit Protection (SCP) ..........................14
Open Circuit Protection (OCP) ..........................14
Overvoltage Protection (OVP) ..........................14
4
Undervoltage Lockout .................................... 14
Input Overcurrent Protection........................... 14
Over-Temperature Protection (OTP) ................. 14
Write Byte ........................................................ 17
Read Byte ........................................................ 17
Slave Device Address......................................... 17
SMBus/I2C Register Definitions........................ 17
PWM Brightness Control Register (0x00)........... 19
Device Control Register (0x01)........................ 20
Fault/Status Register (0x02) ........................... 20
Si Revision Register (0x03) ............................. 20
DC Brightness Control Register (0x07) ............. 22
Configuration Register (0x08) ......................... 22
Output Channel Select and Fault Readout
Register (0x09) ........................................... 22
Phase Shift Control Register (0x0A) ................. 24
PLL Control Register (0x0B) ............................ 24
Components Selections ...................................24
Input Capacitor ............................................. 24
Inductor ....................................................... 25
Output Capacitors.......................................... 25
Channel Capacitor ......................................... 25
Output Ripple................................................ 25
Schottky Diode.............................................. 26
Applications ....................................................26
High Current Applications ............................... 26
Multiple Drivers Operation .............................. 26
Revision History ..............................................27
Products..........................................................27
Package Outline Drawing ................................ 28
FN7634.2
October 8, 2012
ISL97674
Absolute Maximum Ratings (TA = +25°C)
Thermal Information
VIN, EN/PWM. . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 28V
FAULT . . . . . . . . . . . . . . . . . . . . . VIN - 8.5V to VIN + 0.3V
VDC, COMP, RSET, OVP . . . . . . . . . . . . . . . . . -0.3V to 5.5V
SCL, SDA, VSYNC, PLLC . . . . . . . . . . . . . . . . -0.3V to 5.5V
CH0 - CH5, LX . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 45V
PGND, AGND . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +0.3V
Above voltage ratings are all with respect to AGND pin
ESD Rating
Human Body Model (Tested per JESD22-A114E) . . . . . 3kV
Machine Model (Tested per JESD22-A115-A) . . . . . . . 300V
Charged Device Model . . . . . . . . . . . . . . . . . . . . . . . 1kV
Thermal Resistance (Typical)
θJA (°C/W) θJC (°C/W)
20 Ld QFN Package (Notes 4, 5, 7).
Thermal Characterization (Typical)
40
2.5
PSIJT (°C/W)
20 Ld QFN Package (Note 6) . . . . . . . . . . . .
1
Maximum Continuous Junction Temperature . . . . . . +125°C
Storage Temperature . . . . . . . . . . . . . . . -65°C to +150°C
Operating Conditions
Temperature Range . . . . . . . . . . . . . . . . . . -40°C to +85°C
IMPORTANT NOTE: All parameters having Min/Max specifications are guaranteed. Typical values are for information purposes only. Unless
otherwise noted, all tests are at the specified temperature and are pulsed tests, therefore: TJ = TC = TA
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 in free air with the component mounted on a high effective thermal conductivity test board with “direct attach”
features. See Tech Brief TB379.
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.
7. Refer to JESD51-7 high effective thermal conductivity board layout for proper via and plane designs.
Electrical Specifications
PARAMETER
All specifications below are tested at TA = +25°C; VIN = 12V, EN/PWM = 5V, RSET = 20.1kΩ,
unless otherwise noted. Boldface limits apply over the operating temperature range,
-40°C to +85°C.
MAX
(Note 8)
UNIT
26.5
V
10
µA
4.5V < VIN ≤ 26V,
FSW = 600kHz
45
V
8.55V < VIN ≤ 26V,
FSW = 1.2MHz
45
V
VIN/0.19
V
3.3
V
DESCRIPTION
CONDITION
MIN
(Note 8)
TYP
GENERAL
VIN (Note 9)
IVIN_STBY
VOUT
Backlight Supply Voltage
≤13 LEDs per channel (3.2V/20mA
type)
4.5
VIN Shutdown Current
Output Voltage
4.5V < VIN ≤ 8.55V, FSW = 1.2MHz
VUVLO
Undervoltage Lock-out Threshold
VUVLO_HYS
Undervoltage Lock-out Hysteresis
2.6
275
mV
REGULATOR
LDO Output Voltage
VIN > 6V
Standby Current
EN/PWM = 0V
IVDC
Active Current
EN/PWM = 5V
VLDO
VDC LDO Droop Voltage
VIN > 5.5V, 20mA
VDC
IVDC_STBY
ENLow
Guaranteed Range for EN Input Low
Voltage
ENHi
Guaranteed Range for EN Input High
Voltage
tENLow
EN/PWM low time before shut-down
5
4.55
4.8
5
V
5
µA
5
20
1.8
mA
200
mV
0.5
V
V
30.5
ms
FN7634.2
October 8, 2012
ISL97674
Electrical Specifications
PARAMETER
All specifications below are tested at TA = +25°C; VIN = 12V, EN/PWM = 5V, RSET = 20.1kΩ,
unless otherwise noted. Boldface limits apply over the operating temperature range,
-40°C to +85°C. (Continued)
DESCRIPTION
CONDITION
MIN
(Note 8)
TYP
MAX
(Note 8)
UNIT
1.5
2.0
2.7
A
235
300
mΩ
BOOST
SWILimit
rDS(ON)
SS
Eff_peak
ΔIOUT/ΔVIN
Boost FET Current Limit
Internal Boost Switch ON-resistance
TA = +25°C
Soft-start
100% LED Duty Cycle
Peak Efficiency
7
ms
VIN = 12V, 72 LEDs, 20mA each,
L = 10µH with DCR 101mΩ,
TA = +25°C
92.9
%
VIN = 12V, 60 LEDs, 20mA each,
L = 10µH with DCR 101mΩ,
TA = +25°C
90.8
%
Line Regulation
0.1
%
DMAX
Boost Maximum Duty Cycle
FSW = 1, 600kHz
90
%
FSW = 0, 1.2MHz
81
DMIN
Boost Minimum Duty Cycle
FSW = 1, 600kHz
Lx Frequency High
FSW = 1, 600kHz
475
600
640
kHz
Lx Frequency Low
FSW = 0, 1.2MHz
0.97
1.14
1.31
MHz
Lx Leakage Current
LX = 45V, EN = 0
10
µA
4.3
V
9.5
FSW = 0, 1.2MHz
fOSC_hi
fOSC_lo
ILX_leakage
%
17
FAULT DETECTION
VSC
Channel Short Circuit Threshold
Reg0x08, SC[1:0] = 01
3.15
3.6
Reg0x08, SC[1:0] = 10
4.2
4.8
5.4
V
Reg0x08, SC[1:0] = 11
5.2
5.85
6.6
V
Temp_shtdwn
Temperature Shutdown Threshold
150
°C
Temp_Hyst
Temperature Shutdown Hysteresis
23
°C
VOVPlo
OVPfault
Overvoltage Limit on OVP Pin
1.19
OVP Short Detection Fault Level
1.25
400
V
mV
CURRENT SOURCES
IMATCH
IACC
Vheadroom
VRSET
ILEDmax
DC Channel-to-Channel Current
Matching
RSET = 20.1kΩ, Reg0x00 = 0xFF
(IOUT = 20mA)
Current Accuracy
±0.7
-1.5
Dominant Channel Current Source
Headroom at FBx Pin
ILED = 20mA
TA = +25°C
Voltage at RSET Pin
RSET = 20.1kΩ
Maximum LED Current per Channel
VIN = 12V, VOUT =45, TA = +25°C
±1.0
+1.5
500
1.20
%
%
mV
1.24
40
V
mA
PWM GENERATOR
VIL
Guaranteed Range for PWM Input
Low Voltage
VIH
Guaranteed Range for PWM Input
High Voltage
1.5
PWM Input Frequency Range
200
FPWM
PWMACC
FPWM
tMIN
PWM Input Accuracy
0.8
V
VDD
V
30,000
8
PWM Dimming Frequency Range
RFPWM = 660kΩ
Minimum On Time
Direct PWM Mode
Fault Pull-down Current
VIN = 12V
90
100
250
Hz
bits
110
Hz
350
ns
30
µA
FAULT PIN
IFAULT
6
12
21
FN7634.2
October 8, 2012
ISL97674
Electrical Specifications
PARAMETER
VFAULT
LXStart_thres
IlxStartup
All specifications below are tested at TA = +25°C; VIN = 12V, EN/PWM = 5V, RSET = 20.1kΩ,
unless otherwise noted. Boldface limits apply over the operating temperature range,
-40°C to +85°C. (Continued)
MIN
(Note 8)
TYP
MAX
(Note 8)
UNIT
6
7
8.3
V
1.3
1.4
1.5
V
1
3.5
5
mA
0.8
V
1.5
VDD
V
÷4 = 0
40
150
Hz
÷4 = 1
10
DESCRIPTION
Fault Clamp Voltage with Respect to
VIN
CONDITION
VIN = 12V, VIN - VFAULT
Lx Start-up Threshold
Lx Start-up Current
PLL
VIL
Guaranteed Range for VSYNC Input
Low Voltage
VIH
Guaranteed Range for VSYNC Input
High Voltage
fVSYNC
fPWM
VSYNC Input Frequency Range
Generated PWM Frequency
40
Hz
FVSYNC = 60Hz, ÷4 = 0,
DIVREG = 0x10
204
Hz
FVSYNC = 60Hz, ÷4 = 0,
DIVREG = 0x07F
1536
Hz
SMBus/I2C INTERFACE
VIL
VIH
Guaranteed Range for Data, Clock
Input Low Voltage
Guaranteed Range for Data, Clock
Input High Voltage
1.5
VOL
SMBus/I2C Output Data Line Logic
Low Voltage
IPULLUP = 4mA
ILEAK
Input Leakage On SDA/SCL
Measured at 4.8V
-10
0.8
V
VDD
V
0.17
V
10
µA
SMBus/I2C TIMING SPECIFICATIONS (Note 10)
tEN-SMBus/I2C
Minimum Time Between EN high and 1µF capacitor on VDC
SMBus/I2C Enabled
PWS
Pulse Width Suppression on SDA/SCL
fSCL
SCL Clock Frequency
t1
Bus Free Time Between Stop and
Start Condition
t2
tHD:STA Hold Time After (Repeated)
START Condition
2
0.15
After this Period, the First Clock is
Generated
ms
0.45
µs
400
kHz
1.3
µs
0.6
µs
tSU:STA
Repeated Start Condition Setup Time t5
0.6
µs
tSU:STO
Stop Condition Setup Time
0.6
µs
tHD:DAT
Data Hold Time
300
ns
tSU:DAT
Data Setup Time
100
ns
t3
Low Period of SCL Clock
1.3
µs
t4
High Period of SCL Clock
0.6
µs
tF
Clock/data Fall Time
300
ns
tR
Clock/data Rise Time
300
ns
NOTES:
8. Parameters with MIN and/or MAX limits are 100% tested at +25°C, unless otherwise specified. Temperature limits established
by characterization and are not production tested.
9. Independent from the numbers of LEDs, at minimum VIN of 4.5V, maximum VOUT is limited to 35V. And at maximum VIN of 26.5V,
minimum VOUT is limited 28V.
10. Limits established by characterization and are not production tested.
7
FN7634.2
October 8, 2012
ISL97674
100
100
90
90
80
80
70
24VIN
12VIN
60
EFFICIENCY (%)
EFFICIENCY (%)
Typical Performance Curves
5VIN
50
40
30
20
10
0
6P10S_30mA/CHANNEL
70
24VIN
12VIN
60
5VIN
50
40
30
20
10
0
5
10
15
20
0
25
0
5
10
ILED(mA)
FIGURE 3. EFFICIENCY vs up to 20mA LED CURRENT
(100% LED DUTY CYCLE) vs VIN
15
20
ILED(mA)
25
30
35
FIGURE 4. EFFICIENCY vs up to 30mA LED CURRENT
(100% LED DUTY CYCLE) vs VIN
100
100
80
70
580k
60
EFFICIENCY (%)
EFFICIENCY (%)
90
1.2MHz
50
40
30
20
80
60
1.2MHz
580k
40
20
10
0
0
5
10
15
20
25
0
0
30
5
10
15
FIGURE 5. EFFICIENCY vs VIN vs SWITCHING
FREQUENCY AT 20mA (100% LED DUTY
CYCLE)
30
0.40
CURRENT MATCHING(%)
90
80
EFFICIENCY (%)
25
FIGURE 6. EFFICIENCY vs VIN vs SWITCHING
FREQUENCY AT 30mA (100% LED DUTY
CYCLE)
100
70 +25°C
60
+85°C
-40°C
0°C
50
40
30
20
10
0
20
VIN
VIN
0
5
10
15
20
25
30
VIN
FIGURE 7. EFFICIENCY vs VIN vs TEMPERATURE AT
20mA (100% LED DUTY CYCLE)
8
0.30
0.20
0.10
0.00
4.5 VIN
-0.10
12 VIN
-0.20
-0.30
-0.40
0
21 VIN
1
2
3
4
5
6
7
CHANNEL
FIGURE 8. CHANNEL-TO-CHANNEL CURRENT
MATCHING
FN7634.2
October 8, 2012
ISL97674
Typical Performance Curves
(Continued)
1.2
0.60
+25°C
0.8
VHEADROOM (V)
CURRENT
1.0
4.5 VIN
0.6
12 VIN
0.4
-40°C
0.55
0.50
0°C
0.45
0.2
0
0
1
2
3
DC
4
5
6
FIGURE 9. CURRENT LINEARITY vs LOW LEVEL PWM
DIMMING DUTY CYCLE vs VIN
0.40
0
5
10
15
VIN (V)
20
25
30
FIGURE 10. VHEADROOM vs VIN AT 20mA
FIGURE 11. VOUT RIPPLE VOLTAGE, VIN = 12V, 6P12S
AT 20mA/CHANNEL
FIGURE 12. IN-RUSH and LED CURRENT AT VIN = 6V
FOR 6P12S AT 20mA/CHANNEL
FIGURE 13. IN-RUSH AND LED CURRENT AT VIN = 12V
FOR 6P12S AT 20mA/CHANNEL
FIGURE 14. LINE REGULATION WITH VIN CHANGE
FROM 6V TO 26V, VIN = 12V, 6P12S AT
20mA/CHANNEL
9
FN7634.2
October 8, 2012
ISL97674
Typical Performance Curves
(Continued)
FIGURE 15. LINE REGULATION WITH VIN CHANGE
FROM 26V TO 6V FOR 6P12S AT
20mA/CHANNEL
FIGURE 17. LOAD REGULATION WITH ILED CHANGE
FROM 100% TO 0% PWM DIMMING,
VIN = 12V, 6P12S AT 20mA/CHANNEL
Theory of Operation
PWM Boost Converter
The current mode PWM boost converter produces the
minimal voltage needed to enable the LED stack with the
highest forward voltage drop to run at the programmed
current. The ISL97674 employ 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 a
series of drained batteries or instantly change to an
AC/DC adapter without rendering a noticeable visual
nuisance. The number of LEDs that can be driven by
ISL97674 depend on the type of LED chosen in the
application. The ISL97674 are capable of boosting up to
45V and typically driving 13 LEDs in series for each of the
6 channels, enabling a total of 78 pieces of the
3.2V/20mA type of LEDs.
10
FIGURE 16. LOAD REGULATION WITH ILED CHANGE
FROM 0% TO 100% PWM DIMMING,
VIN = 12V, 6P12S AT 20mA/CHANNEL
FIGURE 18. ISL97671 SHUTS DOWN AND STOPS
SWITCHING ~ 30ms AFTER EN GOES LOW
Enable and PWM
The ISL97674 has EN/PWM pin that serves dual
purposes; it is used as an Enable signal and can be used
as a PWM input signal for dimming. If a PWM signal is
applied to this pin, the first pulse of minimum 4ms will be
used as an Enable signal. If there is no signal for longer
than 28ms, the device will enter shutdown.
Current Matching and Current Accuracy
Each channel of the LED current is regulated by the
current source circuit, as shown in Figure 19.
FN7634.2
October 8, 2012
ISL97674
MAXIMUM DC CURRENT SETTING
The initial brightness should be set by choosing an
appropriate value for RSET. This should be chosen to fix
the maximum possible LED current:
( 410.5 )
I LEDmax = ------------------R SET
(EQ. 1)
DC CURRENT ADJUSTMENT
+
-
Once RSET is fixed, the LED DC current can be adjusted
through Register 0x07 (BRTDC) as follows:
+
REF
I LED = 1.58x ( BRTDC ⁄ R SET )
RSET
(EQ. 2)
+
PWM DIMMING
DC DIMMING
FIGURE 19. SIMPLIFIED CURRENT SOURCE CIRCUIT
The LED peak current is set by translating the RSET
current to the output with a scaling factor of 410.5/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 1% tolerance resistor
is recommended.
Dynamic Headroom Control
The ISL97674 features a proprietary Dynamic Headroom
Control circuit that detects the highest forward voltage
string or effectively the lowest voltage from any of the
CH0-CH5 pins digitally. When the lowest channel 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 channel is at the target
headroom voltage. Since all LED stacks are connected to
the same output voltage, the other channel pins will have
a higher voltage, but the regulated current source circuit
on each channel will ensure that each channel has the
same current. The output voltage will regulate cycle-bycycle and it is always referenced to the highest forward
voltage string in the architecture.
Dimming Controls
The ISL97674 allow two ways of controlling the LED
current, and therefore, the brightness. They are:
1. DC current adjustment
2. PWM chopping of the LED current defined in Step 1.
There are various ways to achieve DC or PWM current
control, which will be described in the following.
where BRT is the PWM brightness level programmed in
the Register 0x00. BRT ranges from 0 to 255 in decimal
11
BRTDC can be programmed from 0 to 255 in decimal and
defaults to 255 (0xFF). If left at the default value, LED
current will be fixed at ILEDmax. BRTDC can be adjusted
dynamically on the fly during operation. BRTDC = 0
disconnects all channels.
For example, if the maximum required LED current
(ILED(max)) is 20mA, rearranging Equation 1 yields
Equation 3:
R SET = 410.5 ⁄ 0.02 = 20.52kΩ
(EQ. 3)
If BRTDC is set to 200 then:
I LED = 1.58 • 200 ⁄ 20100 = 15.7mA
(EQ. 4)
PWM Control
The ISL97674 provides two different PWM dimming
methods, as described in the following. Each of these
methods results in PWM chopping of the current in the
LEDs for all 6 channels to provide an average LED
current. During the On periods, the LED current will be
defined by the value of RSET and BRTDC, as described in
Equations 1 and 2. The source of the PWM signal can be
described as follows:
1. SMBus/I2C generated 256 level duty cycle
programmed through the SMBus/I2C.
2. External signal from PWM.
The default PWM dimming is in SMBus/I2C mode. In both
methods, the average LED current of each channel is
controlled by ILED and the PWM duty cycle in percent as:
I LED ( ave ) = I LED × PWM
(EQ. 5)
Method 1 (SMBus/I2C controlled PWM)
To use this mode, users need to set Register0x01 to 0x05
with EN/PWM in logic high.
The average LED current of each channel is controlled
by the SMBus/I2C setting as
I LED ( ave ) = I LED × ( BRT ⁄ 255 )
(EQ. 6)
and defaults to 255 (0xFF). BRT = 0 disconnects all
channels.
FN7634.2
October 8, 2012
ISL97674
Method 2 (External applied PWM)
To use this mode users need to set Register 0x01 to 0x03
PWMI
The average LED current of each channel can also be
controlled by an external PWM signal as:
ILED0
60%
40%
60%
40%
tD1
ILED1
(EQ. 7)
LILED ( ave ) = I LED × PWM
tD1
ILED2
tD1
PHASE SHIFT CONTROL
ILED3
The ISL97674 is capable of delaying the phase of each
current source to minimize load transients. By default,
phase shifting is disabled as shown in Figure 20 where
the channels PWM currents are switching uniformly. The
duty cycles can be controlled by the data in PWM
Brightness Control Register via the SMBus/I2C interface,
an external PWM signal with the frequency set by the
PLL, or by an external PWM signal with the frequency set
by the incoming signal.
tON
tD1
ILED5
tD2
tFPWM
ILED0
tON
tOFF
FIGURE 21. PHASE SHIFT WITH FIXED DELAY (6
CHANNELS)
PWMI
tFPWM
ILED0
tD1
ILED4
60%
40%
tOFF
ILED0
60%
40%
tD1
ILED1
ILED1
tD1
ILED2
ILED2
ILED3
ILED3
tD1
ILED4
ILED5
tFPWM
tD2
ILED0
FIGURE 20. NO DELAY (DEFAULT PHASE SHIFT
DISABLED)
When EqualPhase = 1, the phase shift evenly spreads
the channels switching across the PWM cycle, depending
on how many channels are enabled, as shown in
Figures 22 and 23. Such fixed delay can be calculated as
t FPWM 255
t D1 = ------------------- x ⎛ ----------⎞
255 ⎝ N ⎠
(EQ. 8)
t FPWM
255
t D2 = ------------------- x ⎛ 255 – ( N – 1 ) ⎛ ----------⎞ ⎞
⎝ N ⎠⎠
255 ⎝
(EQ. 9)
where (255/N) is rounded down to the nearest integer.
For example, if N = 6, (255/N) = 42, that leads to
tD1 = tFPWM x 42/255
tON
tOFF
FIGURE 22. PHASE SHIFT WITH FIXED DELAY (4
CHANNELS)
The ISL97674 allows the user to program the amount of
phase shift degree in 7-bit resolution, as shown in
Figure 24. To enable programmable phase shifting, the
user must write to the Phase Shift Control register with
EqualPhase = 0 and the desirable phase shift value of
PhaseShift[6:0]. The delay between CH5 and the
repeated CH0 is the rest of the PWM cycle.
tFPWM
ILED0
tON
tOFF
tPD
ILED1
tD2 = tFPWM x 45/255
tPD
where tFPWM is the sum of tON and tOFF. N is the number
of LED channels. The ISL97674 will detect the numbers
of operating channels automatically.
ILED2
tPD
ILED3
tPD
ILED4
tPD
ILED5
FIGURE 23. PHASE SHIFT WITH 7-BIT
PROGRAMMABLE DELAY
12
FN7634.2
October 8, 2012
ISL97674
VSYNC Frame Rate to Dimming
Synchronization
The ISL97674 features a VSYNC function that allows the
frame rate synchronized with the PWM dimming
frequency that minimizes the potential interference
generated by the mismatch between frame rate to PWM
dimming frequency. To use this function, users need to
configure the PLL filter network as shown in Figure 25
that sets the PLL loop stability. In addition the user must
provide a PWM dimming signal into the PWMI pin and a
video frame signal into the VSYNC pin. The incoming PWM
dimming duty cycle will be preserved but the frequency
will change as described below.
ISL97676
PLLC
Vsync
Cc1
Rc2
Rc1
FIGURE 24. PLL CONFIGURATION
The internal PLL locks the LED dimming PWM frequency
to the incoming frame frequency. The video frame signal
must be limited from 10Hz to 150Hz. If the video frame
signal is greater than 40Hz, then the PLLDIVBY4 bit
should be set low, and the generated PWM frequency is:
fPWM = fVSYNC * (PLLDIV + 1)/5. If the video frame signal
is less than 40Hz, then the PLLDIVBY4 bit should be set
high, and the generated PWM frequency is: fPWM = 4 *
fVSYNC * (PLLDIV + 1)/5. This allows LEDs to be dimmed
at 200Hz to 1kHz for any frame signal within the 10Hz to
150Hz range.
Switching Frequency
There are 2 levels of switching frequencies enable for the
boost regulator’s control of the LX pin: 600kHz or
1.2MHz. Each can be programmed in the Configuration
Register 0x08 bit 2. The default switching frequency is at
600kHz.
5V Low Dropout Regulator
A 5V LDO regulator is present at the VDC pin to develop
the necessary low voltage supply, which is used by the
chips internal control circuitry. Because VDC is an LDO
pin, it requires a bypass capacitor of 1µF or more for the
regulation. Low input voltage also limits higher output
voltage applications due to the maximum boost ratio
defined in “Components Selections” on page 24. The
VDC pin can be used as a coarse reference with a few
mA sourcing capability.
In-rush Control and Soft-Start
The ISL97674 has separately built in independent in-rush
control and soft-start functions. The in-rush control
13
function is built around the short circuit protection FET,
and is only available in applications, which include this
device. At start-up, the fault protection FET is turned on
slowly due to a 15µA pull-down current output from the
FAULT pin. This discharges the fault FET's gate-source
capacitance, turning on the FET in a controlled fashion.
As this happens, the output capacitor is charged slowly
through the weakly turned on FET before it becomes fully
enhanced. This results in a low in-rush current. This
current can be further reduced by adding a capacitor (in
the 1nF to 5nF range) across the gate-source terminals
of the FET.
Once the chip detects that the fault protection FET is
turned on hard, it is assumed that in-rush has
completed. At this point, the boost regulator will begin to
switch and the current in the inductor will ramp-up. The
current in the boost power switch is monitored and the
switching is terminated in any cycle where the current
exceeds the current limit. The ISL97674 includes a softstart feature where this current limit starts at a low value
(275mA). This is stepped up to the final 2.2A current
limit in 7 further steps of 275mA. These steps will
happen over at least 8ms, and will be extended at low
LED PWM frequencies if the LED duty cycle is low. This
allows the output capacitor to be charged to the required
value at a low current limit and prevents high input
current for systems that have only a low to medium
output current requirement.
For systems with no master fault protection FET, the
in-rush current will flow towards COUT when VIN is
applied and it is determined by the ramp rate of VIN and
the values of COUT and L.
Fault Protection and Monitoring
The ISL97674 features extensive protection functions to
cover all the perceivable failure conditions. The failure
mode of a LED can be either open circuit or as a short.
The behavior of an open circuited LED can additionally
take the form of either infinite resistance or, for some
LEDs, a zener diode, which is integrated into the device
in parallel with the now opened LED.
For basic LEDs (which do not have built-in zener diodes),
an open circuit failure of an LED will only result in the loss
of one channel of LEDs without affecting other channels.
Similarly, a short circuit condition on a channel that
results in that channel being turned off does not affect
other channels unless a similar fault is occurring. LED
faults are reported via the SMBus/I2C interface to
Register 0x02 (Fault/Status register). The controller is
able to determine which channels have failed via Register
0x09 (Output Masking register). The controller can also
choose to use Register 0x09 to disable faulty channels at
start-up, resulting in only further faulty channels being
reported by Register 0x02.
Due to the lag in boost response to any load change at its
output, certain transient events (such as LED current
steps or significant step changes in LED duty cycle) can
transiently look like LED fault modes. The ISL97674 uses
feedback from the LEDs to determine when it is in a
FN7634.2
October 8, 2012
ISL97674
stable operating region and prevents apparent faults
during these transient events from allowing any of the
LED stacks to fault out. See Table 1 for more details.
A fault condition that results in high input current due to
a short on VOUT will result in a shutdown of all output
channels. The control device logic will remain functional
such that the Fault/Status Register can be interrogated
by the system. The root cause of the failure will be
loaded to the volatile Fault/Status Register so that the
host processor can interrogate the data for failure
monitoring.
Short Circuit Protection (SCP)
The short circuit detection circuit monitors the voltage on
each channel and disables faulty channels which are
detected above the programmed short circuit threshold.
There are three selectable levels of short circuit threshold
(3.6V, 4.8V, and 5.85V) that can be programmed through
the Configuration Register 0x08. When an LED becomes
shorted, the action taken is described in Table 1. The
default short circuit threshold is 5.85V. The detection of
this failure mode can be disabled via Register 0x08.
Open Circuit Protection (OCP)
When one of the LEDs becomes open circuit, it can
behave as either an infinite resistance or a gradually
increasing finite resistance. The ISL97674 monitors the
current in each channel such that any string which
reaches the intended output current is considered
“good”. Should the current subsequently fall below the
target, the channel will be considered an “open circuit”.
Furthermore, should the boost output of the ISL97674
reaches the OVP limit or should the lower
over-temperature threshold be reached, all channels
which are not “good” will immediately be considered as
“open circuit”. Detection of an “open circuit” channel will
result in a time-out before disabling of the affected
channel. This time-out is run when the device is above
the lower over-temperature threshold in an attempt to
prevent the upper over-temperature trip point from
being reached.
Some users employ some special types of LEDs that
have zener diode structure in parallel with the LED for
ESD enhancement, thus enabling open circuit operation.
When this type of LED goes open circuit, the effect is as
if the LED forward voltage has increased, but no light is
emitted. Any affected string will not be disabled, unless
the failure results in the boost OVP limit being reached,
allowing all other LEDs in the string to remain
functional. Care should be taken in this case that the
boost OVP limit and SCP limit are set properly, so as to
make sure that multiple failures on one string do not
cause all other good channels to be faulted out. This is
due to the increased forward voltage of the faulty
channel making all other channel look as if they have
LED shorts. See Table 1 for details for responses to fault
conditions.
Overvoltage Protection (OVP)
The integrated OVP circuit monitors the output voltage
and keeps the voltage at a safe level. The OVP threshold
is set as:
OVP = 1.21V × ( RUPPER + R LOWER ) ⁄ R LOWER
(EQ. 10)
These resistors should be large to minimize the power
loss. For example, a 1MkΩ RUPPER and 30kΩ RLOWER sets
OVP to 41.2V. Large OVP resistors also allow COUT
discharges slowly during the PWM Off time. Parallel
capacitors should also be placed across the OVP resistors
such that RUPPER/RLOWER = CLOWER/CUPPER. Using a
CUPPER value of at least 30pF is recommended. These
capacitors reduce the AC impedance of the OVP node,
which is important when using high value resistors.
Undervoltage Lockout
If the input voltage falls below the UVLO level of 2.45V,
the device will stop switching and be reset. Operation will
restart only if the device is re-enabled through
SMBus/I2C interface once the input voltage is back in the
normal operating range.
Input Overcurrent Protection
During normal switching operation, the current through
the internal boost power FET is monitored. If the current
exceeds the current limit, the internal switch will be
turned off. This monitoring happens on a cycle by cycle
basis in a self protecting way.
Additionally, the ISL97674 monitors the voltage at the LX
and OVP pins. At startup, a fixed current is injected out of
the LX pins and into the output capacitor. The device will
not start up unless the voltage at LX exceeds 1.2V. The
OVP pin is also monitored such that if it rises above and
subsequently falls below 20% of the target OVP level, the
input protection FET will be switched off.
Over-Temperature Protection (OTP)
The ISL97674 includes two over-temperature thresholds.
The lower threshold is set to +130°C. When this
threshold is reached, any channel which is outputting
current at a level below the regulation target will be
treated as “open circuit” and disabled after a time-out
period. The intention of the lower threshold is to allow
bad channels to be isolated and disabled before they
cause enough power dissipation (as a result of other
channels having large voltages across them) to hit the
upper temperature threshold.
The upper threshold is set to +150°C. Each time this is
reached, the boost will stop switching and the output
current sources will be switched off. Hitting of the upper
threshold will also set the thermal fault bit of the
Fault/Status register 0x02. Unless disabled via the EN
pin, the device stays in an active state throughout,
allowing an external processor to interrogate the fault
condition.
For the extensive fault protection conditions, please refer
to Figure 25 and Table 1 for details.
14
FN7634.2
October 8, 2012
ISL97674
LX
VIN
FAULT
DRIVER
IMAX
ILIMIT
VOUT
O/P
SHORT
OVP
FET
DRIVER
LOGIC
CH0
VSC
CH5
VSET/2
REG
THRM
SHDN
REF
OTP
T2
TEMP
SENSOR
T1
VSET
+
Q0 VSET
PWM/OC0/SC0
FAULT/
STATUS
REGISTER
SMBus/I2C
CONTROL
LOGIC
+
Q5
-
-
PWM/OC5/SC5
DC CURRENT
FIGURE 25. SIMPLIFIED FAULT PROTECTIONS
TABLE 1. PROTECTIONS TABLE
CASE
FAILURE MODE
DETECTION MODE
VOUT
FAILED CHANNEL ACTION GOOD CHANNELS ACTION REGULATED BY
1
CH0 Short Circuit
CH0 ON and burns power.
Upper
Over-Temperature
Protection limit (OTP)
not triggered and CH0 <
4V
2
CH0 Short Circuit
Upper OTP triggered but All channels go off until chip Same as CH0
VCH0 < 4V
cooled and then comes back
on with current reduced to
76%. Subsequent OTP
triggers will reduce IOUT
further.
Highest VF of
CH1 through
CH5
3
CH0 Short Circuit
Upper OTP not
CH1 disabled after 6 PWM
triggered but CH0 > 4V cycle time-out.
CH1 through CH5 Normal
Highest VF of
CH1 through
CH5
4
CH0 Open Circuit
with infinite
resistance
Upper OTP not
VOUT will ramp to OVP. CH1
triggered and CH0 < 4V will time-out after 6 PWM
cycles and switch off. VOUT
will drop to normal level.
CH1 through CH5 Normal
Highest VF of
CH1 through
CH5
5
CH0 LED Open
Circuit but has
paralleled Zener
Upper OTP not
CH1 remains ON and has
triggered and CH0 < 4V highest VF, thus VOUT
increases.
CH1 through CH5 ON, Q1
through Q5 burn power
VF of CH0
6
CH0 LED Open
Circuit but has
paralleled Zener
Upper OTP triggered
but CH0 < 4V
15
CH1 through CH5 Normal
All channels go off until chip Same as CH0
cooled and then comes back
on with current reduced to
76%. Subsequent OTP
triggers will reduce IOUT
further
Highest VF of
CH1 through
CH5
VF of CH0
FN7634.2
October 8, 2012
ISL97674
TABLE 1. PROTECTIONS TABLE (Continued)
CASE
FAILURE MODE
VOUT
FAILED CHANNEL ACTION GOOD CHANNELS ACTION REGULATED BY
DETECTION MODE
VOUT increases, then CH-X VF of CH0
switches OFF after 6 PWM
cycles. This is an unwanted
shut off and can be
prevented by setting OVP at
an appropriate level.
7
CH0 LED Open
Circuit but has
paralleled Zener
Upper OTP not
CH0 remains ON and has
triggered but CHx > 4V highest VF, thus VOUT
increases.
8
Channel-toChannel
ΔVF too high
Lower OTP triggered
but CHx < 4V
Any channel at below the target current will fault out after Highest VF of
CH0 through
6 PWM cycles.
CH5
Remaining channels driven with normal current.
9
Channel-toChannel ΔVF too
high
Upper OTP triggered
but CHx < 4V
All channels go off until chip cooled and then comes back Highest VF of
on with current reduced to 76%. Subsequent OTP triggers CH0 through
will reduce IOUT further
CH5
10
Output LED stack
voltage too high
VOUT > VOVP
Any channel that is below the target current will time-out
after 6 PWM cycles, and VOUT will return to the normal
regulation voltage required for other channels.
11
VOUT/LX shorted
to GND at start-up
or VOUT shorted in
operation
LX current and timing The chip is permanently shutdown 31mS after power-up if
VOUT/Lx is shorted to GND.
are monitored.
OVP pins monitored for
excursions below 20%
of OVP threshold.
SCL
t3
Highest VF of
CH0 through
CH5
tF
tR
VIH
VIL
tHD:DAT
t2
t4
tSU:DAT
tSU:STA
tSU:STO
SDA
VIH
VIL
t1
P
S
P
S
NOTES:
SMBus/I2C Description
S = start condition
P = stop condition
A = acknowledge
A = not acknowledge
R/W = read enable at high; write enable at low
FIGURE 26. SMBus/I2C INTERFACE
1
7
1
1
8
1
8
1
1
S
Slave Address
W
A
Command Code
A
Data byte
A
P
Master to Slave
Slave to Master
FIGURE 27. WRITE BYTE PROTOCOL
16
FN7634.2
October 8, 2012
ISL97674
1
7
1
1
8
1
1
8
1
1
8
1
1
S
Slave Address
W
A
Command
Code
A
S
Slave Address
R
A
Data Byte
A
P
Master to Slave
Slave to Master
FIGURE 28. READ BYTE PROTOCOL
Write Byte
The Write Byte protocol is only three bytes long. The first
byte starts with the slave address followed by the
“command code,” which translates to the “register index”
being written. The third byte contains the data byte that
must be written into the register selected by the
“command code”. A shaded label is used on cycles during
which the slaved backlight controller “owns” or “drives”
the Data line. All other cycles are driven by the “host
master.”
controller class.” Bit 3 in the lower nibble of the Slave
Address byte is 1. Bit 0 is always the R/W bit, as
specified by the SMBus/I2C protocol. Note: In this
document, the device address will always be expressed
as a full 8-bit address instead of the shorter 7-bit address
typically used in other backlight controller specifications
to avoid confusion. Therefore, if the device is in the write
mode where bit 0 is 0, the slave address byte is 0x58 or
01011000b. If the device is in the read mode where bit 0
is 1, the slave address byte is 0x59 or 01011001b.
Read Byte
MSB
Slave Device Address
The slave address contains 7 MSB plus one LSB as R/W
bit, but these 8 bits are usually called Slave Address
bytes. As shown in Figure 29, the high nibble of the Slave
Address byte is 0x5 or 0101b to denote the “backlight
1
0
1
DEVICE
IDENTIFIER
1
0
0
DEVICE
ADDRESS
R/W
BI
T
0
LSB
RE
AD
/W
RI
TE
As shown in the Figure 28, the four byte long Read Byte
protocol starts out with the slave address followed by
the “command code” which translates to the “register
index.” Subsequently, the bus direction turns around
with the re-broadcast of the slave address with bit 0
indicating a read (“R”) cycle. The fourth byte contains
the data being returned by the backlight controller. That
byte value in the data byte reflects the value of the
register being queried at the “command code” index.
Note the bus directions, which are highlighted by the
shaded label that is used on cycles during which the
slaved backlight controller “owns” or “drives” the Data
line. All other cycles are driven by the “host master.”
FIGURE 29. SLAVE ADDRESS BYTE DEFINITION
SMBus/I2C Register Definitions
The backlight controller registers are Byte wide and
accessible via the SMBus/I2C Read/Write Byte
protocols. Their bit assignments are provided in the
following sections with reserved bits containing a
default value of “0”.
TABLE 2A. REGISTER LISTING
ADDRESS
REGISTER
DEFAULT SMBus/I2C
VALUE PROTOCOL
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
BRT7
BRT6
BRT5
BRT4
BRT3
BRT2
BRT1
BRT0
0xFF
Read & Write
EXT_PWM
BL_CTL
0x00
Read & Write
OV_CURR
THRM_SHDN
FAULT
0x00
Read Only
0x00
PWM
Brightness
Control
Register
0x01
Device Control
Register
Reserved
Reserved
Reserved Reserved Reserved SMBus/I2C_PWM
0x02
Fault/Status
Register
Reserved
Reserved
2_CH_SD 1_CH_SD BL_STAT
0x03
Si Revision
Register
1
1
0
0
1
REV2
REV1
REV0
0xC8
Read Only
0x07
DC Brightness
Control
Register
BRTDC7
BRTDC6
BRTDC5
BRTDC4
BRTDC3
BRTDC2
BRTDC1
BRTDC0
0xFF
Read & Write
17
FN7634.2
October 8, 2012
ISL97674
TABLE 2A. REGISTER LISTING (Continued)
ADDRESS
REGISTER
BIT 7
0x08
Configuration
Register
DsblPLL
0x09
Output Channel Reserved
Register
0x0A
Phase Shift Deg
0x0B
PLLC
BIT 6
BIT 5
BIT 4
DirectPWM PWMtoDC BstSlew
Rate1
DEFAULT SMBus/I2C
VALUE PROTOCOL
BIT 3
BIT 2
BIT 1
BIT 0
BstSlew
Rate0
FSW
VSC1
VSC0
0x1F
Read & Write
Reserved
CH5
CH4
CH3
CH2
CH1
CH0
0x3F
Read & Write
Equal
Phase
Phase
Shift6
Phase
Shift5
Phase
Shift4
Phase
Shift3
Phase
Shift2
Phase
Shift1
Phase
Shift0
0x00
Read & Write
PLLDivBy4
PLL
Divide6
PLL
Divide5
PLL
Divide4
PLL
Divide3
PLL
Divide2
PLL
Divide1
PLL
Divide0
0x10
Read & Write
TABLE 2B. DATA BIT DESCRIPTIONS
ADDRESS
REGISTER
DATA BIT DESCRIPTIONS
0x00
PWM Brightness Control
Register
BRT[7..0] = 256 steps of DPWM duty cycle brightness control
0x01
Device Control Register
SMBus/I2C_PWM = 1 selects SMBus/I2C controlled PWM dimming
EXT_PWM = 1 selects external applied PWM signal for PWM dimming
BL_CTL = BL On/Off (1 = On, 0 = Off), default = 0
0x02
Fault/Status Register
2_CH_SD = Two LED output channels are shutdown (1 = shutdown, 0 = OK)
1_CH_SD = One LED output channel is shutdown (1 = shutdown, 0 = OK)
BL_STAT = BL status (1 = BL On, 0 = BL Off)
OV_CURR = Input overcurrent (1 = Overcurrent condition, 0 = Current OK)
THRM_SHDN = Thermal Shutdown (1 = Thermal fault, 0 = Thermal OK)
FAULT = Fault occurred (Logic “OR” of all of the fault conditions)
0x03
Si Revision Register
REV[2..0] = Silicon rev (Rev 0 through Rev 7 allowed for silicon spins)
0x07
DC Brightness Control Register BRTDC[7..0] = 256 steps of DC brightness control
0x08
Configuration Register
DsblPLL = When 1, PLL is disabled and PWM frequency is set by resistor to ground on
PLLC pin.
DirectPWM = Forces the PWM input signal to directly control the current sources.
PWMtoDC = Switches current sources on and varies DC level rather than PWMing.
BstSlewRate = Controls strength of FET driver. 00 - 25% drive strength, 01 - 50% drive
strength, 10 - 75% drive strength, 11 - 100% drive strength.
FSW = Switching frequencies selection, FSW = 0 = 1.2MHz. FSW = 1 = 600kHz
VSC[1..0] = Short circuit thresholds selection, 0 = disabled, 1 = 3.6V, 2 = 4.8V, 3 = 5.8V
0x09
Output Channel Select and
Fault Readout Register
CH[5..0] = Output Channel Read and Write. In Write, 1 = Channel Enabled, 0 = Channel
Disabled. In Read, 1 = Channel OK, 0 = Channel Shutdown or Disabled
0x0A
Phase Shift Degree
EqualPhase = Controls phase shift mode - When 0, phase shift is defined by
PhaseShift<6:0>. When 1, phase shift is 360/N (where N is the number of channels
enabled).
PS[6..0] = 7-bit Phase shift setting - phase shift between each channel is
PhaseShift<6:0>/(255*PWMFreq). In direct PWM modes, phase shift between each
channel is PhaseShift<6:0>/12.8MHz. Note that user must not specify a value that gives
>360deg shift between first and last channels.
0x0B
VSYNC Dimming Frequency
Selection
PLLDivBy4 = VSYNC incoming frequency automatic scaling
PLLDivide[6..0] = 128 steps of synchronized dimming frequency selection
18
FN7634.2
October 8, 2012
ISL97674
PWM Brightness Control Register (0x00)
The Brightness control resolution has 256 steps of PWM
duty cycle adjustment. The bit assignment is shown in
Figure 30. All of the bits in this Brightness Control
Register can be read or write. Step 0 corresponds to the
minimum step. Steps 1 to 255 represent the linear steps
between 0.39% and 100% duty cycle with approximately
0.39% duty cycle adjustment per step.
• An SMBus/I2C Write Byte cycle to Register 0x00 sets
the PWM brightness level only if the backlight
controller is in SMBus/I2C mode (see Table 3
• An SMBus/I2C Read Byte cycle to Register 0x00
returns the programmed PWM brightness level.
• An SMBus/I2C setting of 0xFF for Register 0x00 sets
the backlight controller to the maximum brightness.
• An SMBus/I2C setting of 0x00 for Register 0x00 sets
the backlight controller to the minimum brightness
output.
• Default value for Register 0x00 is 0xFF.
PWM BRIGHTNESS CONTROL
REGISTER
REGISTER 0x00
BRT7
Operating Modes selected by Device Control Register
Bits 1 and 2).
BRT6
BRT5
BRT4
BRT3
BRT2
BRT1
BRT0
Bit 7 (R/W) Bit 6 (R/W) Bit 5 (R/W) Bit 4 (R/W) Bit 3 (R/W) Bit 2 (R/W) Bit 1 (R/W) Bit 0 (R/W)
BIT ASSIGNMENT
BIT FIELD DEFINITIONS
= 256 steps of PWM brightness levels
BRT[7..0]
FIGURE 30. DESCRIPTIONS OF BRIGHTNESS CONTROL REGISTER
REGISTER 0x01
DEVICE CONTROL REGISTER
RESERVED RESERVED RESERVED RESERVED RESERVED
SMBus/I2
C_PWM
EXT_PWM
BL_CTL
Bit 7 (R/W)
Bit 2 (R/W)
Bit 1 (R/W)
Bit 0 (R/W)
Bit 6 (R/W)
Bit 5 (R/W)
BIT ASSIGNMENT
SMBus/I2C_PWM
Bit 4 (R/W)
Bit 3 (R/W)
BIT FIELD DEFINITIONS
= PWM mode select bit (1 = absolute
brightness, 0 = % change) default = 0
EXT_PWM
= Brightness control select bit (1 = control
by PWM, 0 = control by SMBus/I2C) default
=0
BL_CTL
= BL On/Off (1 = On, 0 = Off) default = 0
FIGURE 31. DESCRIPTIONS OF DEVICE CONTROL REGISTER
19
FN7634.2
October 8, 2012
ISL97674
Device Control Register (0x01)
• This register has two bits that control either
SMBus/I2C controlled or external PWM controlled
PWM dimming and a single bit that controls the BL
ON/OFF state. The remaining bits are reserved. The
bit assignment is shown in Figure 31. All other bits in
the Device Control Register will read as low unless
otherwise written. Bits 7 and 6 are not implemented
and will always read low.
• All reserved bits return a “0” when read.
• All defined control bits return their current, latched
value when read.
• A value of 1 written to BL_CTL turns on the BL in 4ms
or less after the write cycle completes. The BL is
deemed to be on when Bit 3 BL_STAT of Register 0x02
is 1 and Register 0x09 is not 0.
• A value of 0 written to BL_CTL immediately turns off the
BL. The BL is deemed to be off when Bit 3 BL_STAT of
Register 0x02 is 0 and Register 0x09 is 0.
• The default value for Register 0x01 is 0x00.
Fault/Status Register (0x02)
This register has 6 status bits that allow monitoring of
the backlight controller’s operating state. Bit 0 is a logical
“OR” of all fault codes to simplify error detection. Not all
of the bits in this register are fault related (Bit 3 is a
simple BL status indicator). The remaining bits are
reserved and return a “0” when read. All of the bits in
this register are read-only, with the exception of bit 0,
which can be cleared by writing to it.
• A Read Byte cycle to Register 0x02 indicates the
current BL on/off status in BL_STAT (1 if the BL is on,
0 if the BL is off).
20
• A Read Byte cycles to Register 0x2 also returns
FAULT as the logical OR of THRM_SHDN, OV_CURR,
2_CH_SD, and 1_CH_SD should these events occur.
• 1_CH_SD returns a 1 if one or more channels have
faulted out.
• 2_CH_SD returns a 1 if two or more channels have
faulted out.
• A fault will not be reported in the event that the BL is
commanded on and then immediately off by the
system.
• When FAULT is set to 1, it will remain at 1 even if the
signal which sets it goes away. FAULT will be cleared
when the BL_CTL bit of the Device Control Register is
toggled or when written low. At that time, if the fault
condition is still present or reoccurs, FAULT will be
set to 1 again. BL_STAT will not cause FAULT to be
set.
• The default value for Register 0x02 is 0x00.
Si Revision Register (0x03)
The Si Revision register has 3 bits that allows up to 8
silicon revisions each. In order to keep the number of
silicon revisions low, the revision field will not be updated
unless the part will make it out to the user’s factory.
Thus, if during the first silicon engineering development
process, 2 silicon spins were needed, the revision
remains as 0. All of the bits in this register are read-only.
• The default value for Register 0x03 is 0xC8.
The initial value of REV shall be 0. Subsequent values of
REV will increment by 1.
FN7634.2
October 8, 2012
ISL97674
REGISTER 0x02
FAULT/STATUS REGISTER
RESERVE
D
RESERVE
D
2_CH_SD
1_CH_SD
BL_STAT
OV_CURR
THRM_SHDN
FAULT
Bit 7 (R)
Bit 6 (R)
Bit 5 (R)
Bit 4 (R)
Bit 3 (R)
Bit 2 (R)
Bit 1 (R)
Bit 0 (R)
BIT
BIT ASSIGNMENT
BIT FIELD DEFINITIONS
Bit 5
2_CH_SD
= Two LED output channels are shutdown (1 = shutdown, 0 = OK)
Bit 4
1_CH_SD
= One LED output channel is shutdown (1 = shutdown, 0 = OK)
Bit 3
BL_STAT
= BL Status (1 = BL On, 0 = BL Off)
Bit 2
OV_CURR
= Input Overcurrent (1 = Overcurrent condition, 0 = Current OK)
Bit 1
THRM_SHDN
Bit 0
FAULT
= Thermal Shutdown (1 = Thermal Fault, 0 = Thermal OK)
= Fault occurred (Logic “OR” of all of the fault conditions)
FIGURE 32. DESCRIPTIONS OF FAULT/STATUS REGISTER
REGISTER 0x03
ID REGISTER
LED
PANEL
MFG3
MFG2
MFG1
MFG0
REV2
REV1
REV0
Bit 7 = 1
Bit 6 (R)
Bit 5 (R)
Bit 4 (R)
Bit 3 (R)
Bit 2 (R)
Bit 1 (R)
Bit 0 (R)
BIT ASSIGNMENT
MFG[3..0]
REV[2..0]
BIT FIELD DEFINITIONS
= Manufacturer ID. See “Si Revision
Register (0x03)” on page 20.
data 0 to 8 in decimal correspond to other
vendors
data 9 in decimal represents Intersil ID
data 10 to 14 in decimal are reserved
data 15 in decimal Manufacturer ID is not
implemented
= Silicon rev (Rev 0 through Rev 7 allowed
for silicon spins)
FIGURE 33. DESCRIPTIONS OF ID REGISTER
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FN7634.2
October 8, 2012
ISL97674
REGISTER 0x07
BRTDC7
BRTDC6
DC BRIGHTNESS CONTROL
REGISTER
BRTDC5
BRTDC4
BRTDC3
BRTDC2
BRTDC1
BRTDC0
Bit 7 (R/W) Bit 6 (R/W) Bit 5 (R/W) Bit 4 (R/W) Bit 3 (R/W) Bit 2 (R/W) Bit 1 (R/W) Bit 0 (R/W)
BIT ASSIGNMENT
BRTDC[7..0]
BIT FIELD DEFINITIONS
= 256 steps of DC brightness levels
FIGURE 34. DESCRIPTIONS OF DC BRIGHTNESS CONTROL REGISTER
DC Brightness Control Register (0x07)
The DC Brightness Control Register 0x07 allows users to
have additional dimming flexibility by:
1. Effectively achieving 16-bits of dimming control when
DC dimming is combined with PWM dimming or,
2. Achieving visual or audio noise free 8-bit DC dimming
over potentially noisy PWM dimming.
The bit assignment is shown in Figure 34. All of the bits
in this Register can be read or write. Steps 0 to 255
represent the linear steps of current adjustment in DC on
the fly. It can also be considered as the peak current
factory calibration feature to account for various LED
production batch variations, but external EEPROM
settings storing and restoring are required.
• An SMBus/I2C Write Byte cycle to Register 0x07 sets
the brightness level in DC only.
• An SMBus/I2C Read Byte cycle to Register 0x07
returns the current DC brightness level.
• Default value for Register 0x07 is 0xFF.
Configuration Register (0x08)
The Configuration Register provides many extra functions
that users can explore in order to optimize the driver
performance at a given application.
A DsblPLL bit allows users to disable PLL mode. Instead
this pin is used to program the PWM dimming frequency
(up to 30kHz) by connecting a resistor to ground by
Equation 11:
7
6.66 ×10
F PWM = -----------------------RFPWM
function is to allow users to experiment the slew rate
with respect to EMI effect in the system. In general, the
slower the slew rate is, the lower the EMI interference to
the surrounding circuits; however, the switching loss of
the boost FET is also increased.
The FSW bit allows users to set the boost conversion
switching frequency between 1.2MHz and 600kHz.
The Vsc bits allow users to set 3 levels of channel
short-circuit thresholds or disable it.
The bit assignment is shown in Figure 35. The default
value for Register 0x08 is 0x1F.
Output Channel Select and Fault Readout
Register (0x09)
This register can be read or write; the bit position
corresponds to the channel. For example, bit 0
corresponds to Ch0 and bit 4 corresponds to Ch4 and so
on. Writing data to this register, it enables the channels
of interest. When reading data from this register, any
disabled channel and any faulted out channel will read as
0. This allows the user to determine which channel is
faulty and optionally not enabling it in order to allow the
rest of the system to continue to function. Additionally, a
faulted out channel can be disabled and re-enabled in
order to allow a retry for any faulty channel without
having to power-down the other channels.
The bit assignment is shown in Figure 36. The default for
Register 0x09 is 0x3F.
(EQ. 11)
A DirectPWM bit allows Direct PWM where the output
current follows the same input PWM signal.
A PWMtoDC bit allows users to provide convert PWM
input into average DC LED current output with the level
that is proportional to the input PWM duty cycle.
A BstSlewRate bit allows users to control the boost FET
slew rate (the rates of turn-on and turn-off). The slew
rate can be selected to four relative strengths when
driving the internal boost FET. The purpose of this
22
FN7634.2
October 8, 2012
ISL97674
REGISTER 0x08
CONFIGURATION REGISTER
DsblPLL
DirectPWM
PWMtoDC
BstSlewRate1
BstSlewRate0
FSW
VSC1
VSC0
Bit 7 (R/W)
Bit 6 (R/W)
Bit 5 (R/W)
Bit 4 (R/W)
Bit 3 (R/W)
Bit 2 (R/W)
Bit 1 (R/W)
Bit 0 (R/W)
BIT ASSIGNMENT
BIT FIELD DEFINITIONS
When 1, PLL is disabled and PWM frequency is set by resistor to ground on PLLC pin.
DsblPLL
DirectPWM
Forces the PWMI signal to directly control the current sources. Note that there is some
synchronous delay between PWMI and current sources.
PWMtoDC
Switches current sources on and varies DC level rather than PWMing.
Controls strength of FET driver. 00 - 25% drive strength, 01 - 50% drive strength,
10%-75% drive strength, 11 - 100% drive strength.
BstSlewRate[1:0]
FSW
2 levels of Switching Frequencies (0 = 1,200kHz, 1 = 600kHz)
3 levels of Short-Circuit Thresholds (0 = disabled, 1 = 3.6V, 2 = 4.8V, 3 = 5.8V)
VSC[1..0]
FIGURE 35. DESCRIPTIONS OF CONFIGURATION REGISTER
REGISTER 0x09
Reserved
OUTPUT CHANNEL REGISTER
Reserved
CH5
CH4
CH3
CH2
CH1
CH0
Bit 7 (R/W) Bit 6 (R/W) Bit 5 (R/W) Bit 4 (R/W) Bit 3 (R/W) Bit 2 (R/W) Bit 1 (R/W) Bit 0 (R/W)
BIT ASSIGNMENT
BIT FIELD DEFINITIONS
CH[5..0]
CH5 = Channel 5, CH4 = Channel 4 and so
on
FIGURE 36. DESCRIPTIONS OF OUTPUT CHANNEL REGISTER
REGISTER 0x0A
PHASE SHIFT CONTROL REGISTER
EqualPhase
PhaseShift6
PhaseShift5
PhaseShift4
PhaseShift3
PhaseShift2
PhaseShift1
PhaseShift0
Bit 7 (R/W)
Bit 6 (R/W)
Bit 5 (R/W)
Bit 4 (R/W)
Bit 3 (R/W)
Bit 2 (R/W)
Bit 1 (R/W)
Bit 0 (R/W)
BIT ASSIGNMENT
BIT FIELD DEFINITIONS
EqualPhase
Controls phase shift mode - When 0, phase shift is defined by PhaseShift<6:0>. When 1,
phase shift is 360/N (where N is the number of channels enabled).
PhaseShift[6..0]
7-bit Phase shift setting - phase shift between each channel is
PhaseShift<6:0>/(255*PWMFreq)
In direct PWM modes, phase shift between each channel is PhaseShift<6:0>/12.8MHz
Note that user must not specify a value that gives >360deg shift between first and last
channels.
FIGURE 37. DESCRIPTIONS OF PHASE SHIFT CONTROL REGISTER
23
FN7634.2
October 8, 2012
ISL97674
REGISTER 0x0B
PLL CONTROL REGISTER
PLLDivBy4 PLLDivide6 PLLDivide5 PLLDivide4 PLLDivide3 PLLDivide2 PLLDivide1 PLLDivide0
Bit 7 (R/W)
Bit 6 (R/W)
Bit 5 (R/W)
Bit 4 (R/W)
Bit 3 (R/W)
Bit 2 (R/W)
Bit 1 (R/W)
Bit 0 (R/W)
BIT ASSIGNMENT
BIT FIELD DEFINITIONS
PLLDivBy4
PLL input frequency range control bit.
PLLDivide[6..0]
Controls PLL divide setting:
If PLLDivBy4 = 0, Freq(PWM) = Freq(Vsync) * (1 + PLLDivide)/5
If PLLDivBy4 = 1, Freq(PWM) = 4 * Freq(Vsync) * (1 + PLLDivide)/5
FIGURE 38. DESCRIPTIONS OF PLL CONTROL REGISTER
Phase Shift Control Register (0x0A)
The Phase Shift Control register is used to set phase
delay between each channels. When bit 7 is set high, the
phase delay is set by the number of channels enabled
and the PWM frequency. The delay time is defined by the
Equation 12:
(EQ. 12)
t DELAY = ( t FPWM ⁄ N )
where N is the number of channels enabled, and tFPWM is
the period of the PWM cycle. When bit 7 is set low, the
phase delay is set by bits 6 to 0 and the PWM frequency.
The delay time is defined by Equation 13:
t DELAY = ( PS < 6, 0 > xt FPWM ⁄ ( 255 ) )
(EQ. 13)
where PS is an integer from 0 to 127, and tFPWM is the
period of the PWM cycle. By default, all the register bits
are set low, which sets zero delay between each channel.
Note that the user should not program the register to
give more than one period of the PWM cycle delay
between the first and last enabled channels.
PLL Control Register (0x0B)
The PLL Control register is used to set up the PLL. The
PWM frequency generated by the PLL is defined by
Equation 14:
( PLLDIV + 1 )
f PWM = ⎛ f VSYNC x -------------------------------------⎞
⎝
⎠
5
(EQ. 14)
where PLLDIVBY4 = 0
( PLLDIV + 1 )
f PWM = ⎛ 4xf VSYNC x -------------------------------------⎞
⎝
⎠
5
(EQ. 15)
where PLLDIVBY4 =1
where fVSYNC is the frequency of the incoming signal on
PLLDIV is an integer from 0 to 127. For incoming
frequencies less than 40Hz, the PLLDIVBY4 bit should be
set high. The default setting for this register is 0x10,
which gives a generated PWM frequency of 204 Hz with
an incoming frame rate of 60Hz.
24
Components Selections
According to the inductor Voltage-Second Balance
principle, the change of inductor current during the
switching regulator On time is equal to the change of
inductor current during the switching regulator Off time.
Since the voltage across an inductor is:
V L = L × ΔI L ⁄ Δt
(EQ. 16)
and ΔIL @ On = ΔIL @ Off, therefore:
( V I – 0 ) ⁄ L × D × tS = ( VO – VD – VI ) ⁄ L × ( 1 – D ) × tS
(EQ. 17)
where D is the switching duty cycle defined by the
turn-on time over the switching period. VD is Schottky
diode forward voltage that can be neglected for
approximation.
Rearranging the terms without accounting for VD gives
the boost ratio and duty cycle respectively as
Equations 18 and 19:
VO ⁄ VI = 1 ⁄ ( 1 – D )
(EQ. 18)
D = ( VO – VI ) ⁄ VO
(EQ. 19)
Input Capacitor
Switching regulators require input capacitors to deliver
peak charging current and to reduce the impedance of
the input supply. This reduces interaction between the
regulator and input supply, thereby improving system
stability. The high switching frequency of the loop causes
almost all ripple current to flow in the input capacitor,
which must be rated accordingly.
A capacitor with low internal series resistance should be
chosen to minimize heating effects and improve system
efficiency, such as X5R or X7R ceramic capacitors, which
offer small size and a lower value of temperature and
voltage coefficient compared to other ceramic capacitors.
In Boost mode, input current flows continuously into the
inductor; AC ripple component is only proportional to the
rate of the inductor charging, thus, smaller value input
capacitors may be used. It is recommended that an input
capacitor of at least 10µF be used. Ensure the voltage
FN7634.2
October 8, 2012
ISL97674
rating of the input capacitor is suitable to handle the full
supply range.
capacitor with low ESR and enough input ripple current
capability.
Inductor
The choice of X7R over Y5V ceramic capacitor is highly
recommend because X7R capacitor is less sensitive to
capacitance change overvoltage but the Y5V capacitor
exhibits very high capacitance coefficient as shown in
Figure 39. Y5V absolute capacitance can be reduced to
10~20% to its rated capacitance at maximum voltage.
In any case, Y5V type of ceramic capacitor should be
avoided.
The inductor’s maximum current capability must be
adequate enough to handle the peak current at the worst
case condition. If an inductor core is chosen with too low
a current rating, saturation in the core will cause the
effective inductor value to fall, leading to an increase in
peak to average current level, poor efficiency and
overheating in the core. The series resistance, DCR,
within the inductor causes conduction loss and heat
dissipation. A shielded inductor is usually more suitable
for EMI susceptible applications, such as LED
backlighting.
The peak current can be derived from the voltage across
the inductor during the Off period, as expressed in
Equation 20:
IL peak = ( V O × I O ) ⁄ ( 85% × V I ) + 1 ⁄ 2 [ V I × ( V O – V I ) ⁄ ( L × V O × f SW
(EQ. 20)
The choice of 85% is just an average term for the
efficiency approximation. The first term is the average
current, which is inversely proportional to the input
voltage. The second term is the inductor current change,
which is inversely proportional to L and fSW. As a result,
for a given switching frequency and minimum input
voltage on which the system operates, the inductor ISAT
must be chosen carefully. At a given inductor size,
usually the larger the inductance, the higher the series
resistance because of the extra winding of the coil. Thus,
the higher the inductance, the lower the peak current
capability. The ISL97674 current limit should also be
taken into account.
Output Capacitors
The output capacitor acts to smooth the output voltage
and supplies load current directly during the conduction
phase of the power switch. Output ripple voltage consists
of the discharge of the output capacitor for ILPEAK during
FET On and the voltage drop due to flowing through the
ESR of the output capacitor. The ripple voltage can be
shown as:
ΔV CO = ( I O ⁄ C O × D ⁄ f S ) + ( ( I O × ESR )
(EQ. 21)
The conservation of charge principle in Equation 21 also
brings up the fact that during the boost switch Off period,
the output capacitor is charged with the inductor ripple
current minus a relatively small output current in boost
topology. As a result, the user needs to select an output
25
Here are few recommendations at various applications:
For 20mA applications with VIN > 7V, 1x4.7µF (X7R type)
is sufficient.
For 20mA applications with VIN < 7V, 2x4.7µF (X7R type)
is required in some configurations.
3.0
CAPACITANCE (µF)
The selection of the inductor should be based on its
maximum current (ISAT) characteristics, power
dissipation (DCR), EMI susceptibility (shielded vs
unshielded), and size. Inductor type and value influence
many key parameters, including ripple current, current
limit, efficiency, transient performance and stability.
POLY. (CERAMIC X7R 2.2µF 50V CAP)
2.5
2.0
1.5
1.0
POLY. (CERAMIC Y5V 2.2µF 50V CAP)
0.5
0
0
5
10
15
20
25
30
APPLIED VOLTAGE (V)
35
40
45
FIGURE 39. X7R AND V5Y TYPES CERAMIC
CAPACITORS
Channel Capacitor
Recommend using at least 1.5nF capacitors from CH pins
to VOUT. Larger capacitors will reduce LED current ripple
at boost frequency, but will degrade transient
performance at high PWM frequencies. The best value is
dependant on PCB layout. Up to 4.7nF is sufficient for
most configurations.
Output Ripple
ΔVCo, can be reduced by increasing Co or fSW, or using
small ESR capacitors. In general, Ceramic capacitors are
the best choice for output capacitors in small to medium
sized LCD backlight applications due to their cost, form
factor, and low ESR.
A larger output capacitor will also ease the driver
response during PWM dimming Off period due to the
longer sample and hold effect of the output drooping.
The driver does not need to boost harder in the next On
period that minimizes transient current. The output
capacitor is also needed for compensation, and, in
general one to two 4.7µF/50V ceramic capacitors are
suitable for netbook to notebook display backlight
applications.
FN7634.2
October 8, 2012
ISL97674
Schottky Diode
Multiple Drivers Operation
A high speed rectifier diode is necessary to prevent
excessive voltage overshoot, especially in the boost
configuration. Low forward voltage and reverse leakage
current will minimize losses, making Schottky diodes the
preferred choice. Although the Schottky diode turns on
only during the boost switch Off period, it carries the
same peak current as the inductor, and therefore, a
suitable current rated Schottky diode must be used.
For large LCD panels where more than 6 channels of
LEDs are needed, multiple ISL97674s with each driver
having its own supporting components can be controlled
together with the common SMBus/I2C. While the
ISL97674 does not have extra pins strappable slave
address feature, but a separate EN signal can be applied
to each driver for asynchronous operation. A trade-off of
such scheme is that an exact faulty channel cannot be
identified since both ICs have the same I2C slave
address.
Applications
High Current Applications
Each channel of the ISL97674 can support up to 30mA.
For applications that need higher current, multiple
channels can be grouped to achieve the desirable
current. For example, the cathode of the last LED can be
connected to CH0 to CH2, this configuration can be
treated as a single string with 90mA current driving
capability.
V
VOUT
SCL
SCL
SDA
SDA
EN/PWM
EN/PWM
SCL
SDA
EN
FIGURE 41. MULTIPLE DRIVERS OPERATION
CH0
CH1
CH2
FIGURE 40. GROUPING MULTIPLE CHANNELS FOR
HIGH CURRENT APPLICATIONS
26
FN7634.2
October 8, 2012
ISL97674
Revision History
The revision history provided is for informational purposes only and is believed to be accurate, but not warranted. Please go to
web to make sure you have the latest Rev.
DATE
REVISION
CHANGE
August 1, 2012
FN7634.2
On page 11, changed 401.8 to 410.5 in Equations 1 and 3.
July 18, 2012
FN7634.1
Stamped page 1 “Not Recommended for New Designs”.
June 25, 2010
FN7634.0
Initial Release.
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27
FN7634.2
October 8, 2012
ISL97674
Package Outline Drawing
L20.3x4
20 LEAD QUAD FLAT NO-LEAD PLASTIC PACKAGE
Rev 1, 3/10
3.00
0.10 M C A B
0.05 M C
A
B
4
20X 0.25
16X 0.50
+0.05
-0.07
17
A
16
6
PIN 1
INDEX AREA
6
PIN 1 INDEX AREA
(C 0.40)
20
1
4.00
2.65
11
+0.10
-0.15
6
0.15 (4X)
A
10
7
VIEW "A-A"
1.65
TOP VIEW
+0.10
-0.15
20x 0.40±0.10
BOTTOM VIEW
SEE DETAIL "X"
0.10 C
C
0.9± 0.10
SEATING PLANE
0.08 C
SIDE VIEW
(16 x 0.50)
(2.65)
(3.80)
(20 x 0.25)
C
(20 x 0.60)
0.2 REF
5
0.00 MIN.
0.05 MAX.
(1.65)
(2.80)
DETAIL "X"
TYPICAL RECOMMENDED LAND PATTERN
NOTES:
1. Dimensions are in millimeters.
Dimensions in ( ) for Reference Only.
2. Dimensioning and tolerancing conform to AMSE Y14.5m-1994.
3. Unless otherwise specified, tolerance : Decimal ± 0.05
4. Dimension applies to the metallized terminal and is measured
between 0.15mm and 0.30mm from the terminal tip.
5. Tiebar shown (if present) is a non-functional feature.
6. The configuration of the pin #1 identifier is optional, but must be
located within the zone indicated. The pin #1 indentifier may be
either a mold or mark feature.
28
FN7634.2
October 8, 2012
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