DATASHEET

ISL97635A
®
Data Sheet
December 22, 2008
SMBus 6-Channel LED Driver
Features
The ISL97635A is a digitally controlled LED driver that
controls 6 channels of LED current for LCD backlight
applications. The ISL97635A is capable of driving typically
54 (6x9) pieces of 3.5V/30mA or 60 (6x10) pieces of
3.2V/20mA LEDs. The ISL97635A contains 6 channels of
voltage controlled current sources with typical currents
matching of ±1%, which compensate for the non-uniformity
effect of forward voltages variance in the LED stacks. To
minimize the voltage headroom and power loss in the typical
multi-strings operation, the ISL97635A features a dynamic
headroom control that monitors the highest LED forward
voltage string and uses its feedback signal for output
regulation.
• 6 Channels
The LED dimming control can be achieved through a
SMBus, an external PWM, or a variable DC (analog light
sensor) input. SMBus controlled dimming allows 256 levels
each of PWM and DC current adjustments. The SMBus
PWM dimming frequency can be adjusted from 100Hz to
5kHz by an external capacitor. External PWM input allows up
to 20kHz audio noise free PWM dimming. The SMBus PWM
setting and an external PWMI signal can also be combined
to provide a dynamic PWM dimming that complies with
Intel’s DPST (Display Power Saving Technology)
requirement.
One or more channels can be selected sequentially in any
order allowing scrolling in RGB LED backlighting
applications.
FN6564.2
• 6V to 24V Input
• 34.5V Output Max
• Drive Maximally 54 (3.5V/30mA each) or 60 (3.2V/20mA
each) LEDs
• Current Matching ±1% Typ
• Dynamic Headroom Control
• Dimming Controls
- SMBus 8-Bit PWM Current Control
- SMbus 8-Bit DC Current Control
- External PWM Input up to 20kHz Dimming
- SMBus and External PWM DPST Dimming Control
- DC-to-PWM Dimming Control
• Protections
- String Open Circuit Detection
- String Short Circuit Detection with Selectable
Thresholds
- Over-Temperature Protection
- Overvoltage Protection
- Input Overcurrent Protection with Disconnect Switch
• 600kHz/1.2MHz Selectable fSW
• Selectable Channels Allows Scrolling Backlight
• 24 Ld (4mmx4mm) QFN Package
The ISL97635A features extensive protection functions that
include string open and short circuit detections, OVP, OTP,
thermal shutdown and an optional input overcurrent
protection with master fault disconnect switch. The fault
conditions will be recorded in the Fault/Status register. There
are selectable short-circuit thresholds and the switching
frequency can be programmed between 600kHz and
1.2MHz.
• Pb-Free (RoHS Compliant)
Available in the 24 Ld 4mmx4mm QFN, the ISL97635A
operates from -40°C to +85°C with input voltage ranging
from 6V to 24V for high LEDs count applications.
Ordering Information
Applications
• Notebook Displays WLED or RGB LED Backlighting
• LCD Monitor LED Backlighting
• Automotive Displays LED Backlighting
• Automotive or Traffic Lighting
PART
NUMBER
(Note)
ISL97635AIRZ*
PART
MARKING
976 35AIRZ
PACKAGE
(Pb-Free)
24 Ld 4x4 QFN
PKG.
DWG. #
L24.4x4D
*Add “-T” or “-TK” suffix for tape and reel. Please refer to TB347 for
details on reel specifications
NOTE: 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.
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. 2008. All Rights Reserved
All other trademarks mentioned are the property of their respective owners.
ISL97635A
Typical Application Circuit
VBL+ = 6V TO 24V
VOUT = 34.5V, 30mA PER STRING
ISL97635A
21 FAULT
LX 19
LX 20
23 VIN
24 VDC
OVP 16
PGND 17
PGND 18
22 COMP
IIN0 15
1 SMBCLK IIN1 14
2 SMBDAT IIN2 13
6 PWMI/EN IIN3 12
4 PWMO
IIN4 10
11 RSET
IIN5 9
3 FPWM
5 GND
2
FN6564.2
December 22, 2008
ISL97635A
Block Diagram
34.5V, 30mA PER STRING
(6 x 9 = 54 WHITE LEDS)
VBL+ = 6V TO 24V
FAULT
VIN
VDC
LX
ISL97635A
REG
OVP
FAULT/STATUS
REGISTER
OSC AND
RAMP
COMP
fPWM
Σ =0
FET
DRIVER
LOGIC
IMAX ILIMIT
LED PWM
CONTROL
PGND
IIN0
COMP
RSET
GND
GM
AMP
REFERENCE
GENERATOR
HIGHEST VF
STRING
DETECT
OC, SC
DETECT
IIN5
+
-
+
-
OC, SC
DETECT
FAULT/STATUS
REGISTER
TEMP
SENSOR
REGISTERS
SMBCLK
SMBDAT
PWMI
PWMO
SMBUS
INTERFACE
INTERFACE
PWM BRIGHTNESS CONTROL
DEVICE CONTROL
PWM/OC/SC
FAULT/STATUS
IDENTIFICATION
AM
DC BRIGHTNESS CONTROL
CONFIGURATION
+
FAULT/STATUS
REGISTER
FIGURE 1. ISL97635A BLOCK DIAGRAM
3
FN6564.2
December 22, 2008
ISL97635A
Absolute Maximum Ratings (TA = +25°C)
Thermal Information
VIN, FAULT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 24V
VDC, COMP, RSET . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 6.5V
SMBCLK, SMBDAT, FPWM, PWMO, EN/PWM . . . . . -0.3V to 6.5V
OVP, IIN0 - IIN5 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 28V
LX. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to 36V
PGND. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . -0.3V to +0.3V
Above voltage ratings are all with respect to GND pin
Thermal Resistance (Typical, Notes 1, 2)
Operating Conditions
θJA (°C/W)
24 Ld QFN . . . . . . . . . . . . . . . . . . . . . .
Thermal Characterization (Typical, Note 3)
39
θJC (°C/W)
2
PSIJT (°C/W)
24 Ld QFN . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
~0.7
Maximum Continuous Junction Temperature . . . . . . . . . . . . +125°C
Storage Temperature . . . . . . . . . . . . . . . . . . . . . . .-65°C to +150°C
Pb-free Reflow Profile . . . . . . . . . . . . . . . . . . . . . . . . .see link below
http://www.intersil.com/pbfree/Pb-FreeReflow.asp
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:
1. 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.
2. For θJC, the “case temp” location is the center of the exposed metal pad on the package underside assumed under ideal case temperature.
3. PSIJT is the junction-to-top thermal resistance. 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.
4. Limits established by characterization and are not production tested.
Electrical Specifications
All specifications below are tested at TA = -40°C to +85°C; VIN = 12V, EN = 5V, RSET = 36.6kΩ, unless
otherwise noted. 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.
PARAMETER
DESCRIPTION
CONDITION
MIN TYP MAX UNIT
GENERAL
VIN
Backlight Supply Voltage
IVIN_STBY
VIN Shutdown Current
VOUT
Output Voltage
VUVLO
Undervoltage Lockout Threshold
VUVLO_HYS
Undervoltage Lockout Hysteresis
≤ 9 LEDs per channel (3.5V/30mA type)
6
2.45
24
V
5
µA
34.5
V
2.8
V
300
mV
REGULATOR
VDC
LDO Output Voltage
VIN >6V
5.0
5.5
V
IVDC_STBY
Standby Current
EN/PWM = 0V
20
µA
IVDC
Active Current
EN/PWM = 5V
10
VLDO
VDC LDO Dropout Voltage
VIN > 5.5V, 30mA
30
SS
Soft-Start
1
ms
ENmin
Minimum Enable Signal
40
µs
mA
200
mV
BOOST
SWILimit
rDS(ON)
Boost FET Current Limit
Internal Boost Switch ON-Resistance
4
TA = +25°C
2.3
TA = -40°C to +85°C
2.2
3.2
A
A
130
260
mΩ
FN6564.2
December 22, 2008
ISL97635A
Electrical Specifications
All specifications below are tested at TA = -40°C to +85°C; VIN = 12V, EN = 5V, RSET = 36.6kΩ, unless
otherwise noted. 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. (Continued)
PARAMETER
Eff_peak
DESCRIPTION
Peak Efficiency
CONDITION
MIN TYP MAX UNIT
VIN = 18V, 54 LEDs, 20mA each, L = 8.2µH
with DCR 106mΩ, TA = +25°C
91
%
VIN = 12V, 54 LEDs, 20mA each, L = 8.2µH
with DCR 106mΩ, TA = +25°C
88
%
VIN = 6V, 54 LEDs, 20mA each, L = 8.2µH
with DCR 106mΩ, TA = +25°C
86
%
0.1
%
ΔIOUT/ΔVIN
Line Regulation
Dmax
Boost Maximum Duty Cycle
Dmin
Boost Minimum Duty Cycle
FOSC_hi
LX Frequency
Register 0x08, fSW = 1
1.0
1.2
1.3
MHz
FOSC_lo
LX Frequency
Register 0x08, fSW = 0
550
600
650
kHz
ILX_leakage
LX Leakage Current
VLX = 36V, EN = 0
10
µA
IMATCH
Channel-to-Channel Current Matching
IOUT = 30mA, BRT = 255
+3.5
%
IACC
Current Accuracy
82
%
7
%
REFERENCE
-3.5
±1
±3
%
FAULT DETECTION
VSC
Short Circuit Threshold
Reg0x08 = 0x0F or 0x0B Reg0x00 = 0xFF
7.8
8
8.8
V
Reg0x08 = 0x0E or 0x0A Reg0x00 = 0xFF
2.8
3.1
3.8
V
°C
Vtemp_acc
Over-Temperature Threshold Accuracy
5
VOVPlo
Overvoltage Limit on OVP Pin
OVPhys
OVP Hysteresis
20
mV
OVPfault
OVP Short Detection Fault Level
300
mV
1.17
1.2
1.23
V
SMBus INTERFACE
VIL
Guaranteed Range for Data, Clock Input Low
Voltage
VIH
Guaranteed Range for Data, Clock Input High
Voltage
VOL
SMBus Data Line Logic Low Voltage with 1.1kΩ
Series Resistor from Data Bus to SMBDAT pin
SMBus Data Line Logic Low Voltage without Series
Resistor from Data Bus to SMBDAT Pin
ILEAK
Input Leakage on SMBData/SMBClk
VDD
Nominal Bus Voltage
0.8
V
VDD
V
IPULLUP = 350µA
0.4
V
IPULLUP = 4mA
0.17
V
-1
1
µA
2.7
5.5
V
100
kHz
2.1
3V to 5V ±10%
SMBus TIMING SPECIFICATIONS (Note 4)
fSMB
SMBus Clock Frequency
10
tBUF
Bus Free Time between STOP and START Condition
4.7
µs
tHD:STA
Hold Time after (Repeated) START Condition. After
this Period, the First Clock is Generated.
4.0
µs
tSU:STA
Repeated Start Condition Setup Time
4.7
µs
tSU:STO
Stop Condition Setup Time
4.0
µs
tHD:DAT
Data Hold Time
300
ns
5
FN6564.2
December 22, 2008
ISL97635A
Electrical Specifications
All specifications below are tested at TA = -40°C to +85°C; VIN = 12V, EN = 5V, RSET = 36.6kΩ, unless
otherwise noted. 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. (Continued)
PARAMETER
DESCRIPTION
CONDITION
MIN TYP MAX UNIT
tSU:DAT
Data Setup Time
250
ns
tLOW
Clock Low Period
4.7
µs
tHIGH
Clock High Period
4.0
tF
tR
50
µs
Clock/Data Fall Time
300
ns
Clock/Data Rise Time
1000
ns
GENERAL TIMING SPECIFICATIONS (Note 4)
t1
Minimum Setup Time Between VIN Rising above
VUVLO with EN = 1 and SMBus Communications
EN = 1, TA = +25°C, VDC capacitor < 10µF
80
µs
t2
Minimum Setup Time Between EN Going High with
VIN above VUVLO and SMBus Communications
VIN > VUVLO, TA= +25°C,
VDC capacitor < 10µF
80
µs
t3
Minimum Time Between VIN Rising above VUVLO
with EN = 1 to SMBus BL CTRL On
EN = 1, TA = +25°C
4.5
ms
t4
Minimum Time Between EN Going High with VIN
above VUVLO to SMBus BL CTRL On
VIN > VUVLO, TA = +25°C
4.5
ms
t5
Minimum Time for LED Output to Respond to SMBus
Data at any Levels
VIN > VUVLO, EN = 1, TA = +25°C
5
µs
t6
Response Time Between Backlight CTRL Off with
Boost Not Switching to Backlight CTRL On with
Boost Switching
VIN > VUVLO, EN = 1, TA = +25°C
5
µs
t7
Response Time Between Backlight CTRL On with
Boost Switching to Backlight CTRL Off with Boost
Not Switching
VIN > VUVLO, EN = 1, TA = +25°C
5
µs
t8
LED Channel Short Circuit Fault Detection to Status
Register Data Ready
VIN > VUVLO, EN = 1, TA = +25°C, LEDs
Active
6
ms
t9
VOUT-GND Short Circuit Detection During Operation
to Status Register Data Ready
VIN > VUVLO, EN = 1, TA = +25°C, Fault
FET used
5
µs
t10
Time Between VIN Rising Above VUVLO with
EN = 1 and VOUT-GND Short being Reported in
Status Register
EN = 1, VDC capacitor < 10µF, TA = +25°C,
Fault FET used.
30
ms
t11
Time Between EN Going High with VIN Above
VUVLO and a VOUT-GND Short being Reported in
Status Register
VIN > VUVLO, VDC capacitor < 10µF,
TA = +25°C, Fault FET used.
30
ms
100
mV
CURRENT SOURCES
Vheadroom
Dominant Channel Current Source Headroom at IIN
Pin
ILED = 20mA, TA = +25°C
VRSET
Voltage at RSET Pin
RSET = 36.6kΩ
ILEDmax
Maximum LED Current Per Channel
RSET = 20.9kΩ
35
mA
680
700
720
mV
PWM GENERATOR (Note 4)
FPWM
Generated PWM Frequency
CFPWM = 27nF, CPWMO = 220nF
200
Hz
DPWM
Duty Cycle of Generated PWM (DC-to-PWM)
VPWMO = 0.3V CFPWM = 27nF
90
%
VPWMO = 1.1V CFPWM = 27nF
10
%
EN/PWMI toggles
28
ms
tMAX_PWM_OFF
Maximum PWMI Off-Time Before Shutdown
6
FN6564.2
December 22, 2008
ISL97635A
Electrical Specifications
All specifications below are tested at TA = -40°C to +85°C; VIN = 12V, EN = 5V, RSET = 36.6kΩ, unless
otherwise noted. 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. (Continued)
PARAMETER
DESCRIPTION
CONDITION
MIN TYP MAX UNIT
FAULT PIN
IFAULT
Fault Pull-down Current
VIN = 12V
10
VFAULT
FAULT Clamp Voltage With Respect to VIN
VIN = 12, VIN - VFAULT
IlxStart-up
LX Start-up Current
VDC = 5.2V
18
30
7.5
1
µA
V
2.7
7
mA
Typical Performance Curves
92
90
90
88
88
86
86
EFFICIENCY (%)
84
7S6P - 18V
82
7S6P - 12V
80
9S6P - 12V
9S6P - 18V
78
7S6P - 6V
76
74
72
EFFICIENCY (%)
92
68
82
7S6P - 18V
78
20
40
60
80
IO (mA)
100
7S6P - 6V
74
L = 10µH
IHLP-2525BD-01
DCR = 129mΩ
ISAT = 2.5A
68
120
0
140
FIGURE 2. EFFICIENCY, L = 8.2µH WITH DCR = 106mΩ,
CO = 4x4.7µF/50V
1.2
L = 10µH
DCR ~ 500mΩ
88 <1mm HEIGHT
1.0
90
CURRENT VARIATION (%)
9S6P - 18V
84
7S6P - 12V
9S6P - 12V
80
7S6P - 18V
76
9S6P - 6V
74
72
7S6P - 6V
70
60
80
IO (mA)
100
120
140
0.6
0.4
0.2
20mA
0.0
-0.2
-0.4
-0.6
-0.8
-1.0
68
66
40
0.8
86
78
20
FIGURE 3. EFFICIENCY, L = 10µH WITH DCR = 129mΩ,
CO = 4x4.7µF/50V
92
82
9S6P - 12V
76
66
0
9S6P - 6V
9S6P - 18V
80
70
66
EFFICIENCY (%)
84
72
L = 8.2µH
IHLP-2525BD-01
DCR = 106mΩ
ISAT = 3A
9S6P - 6V
70
7S6P - 12V
0
20
40
60
80
IO (mA)
100
120
140
FIGURE 4. 3 EFFICIENCY, L = 10µH WITH DCR = 500mΩ,
1mm, CO = 4x4.7µF/50V
7
-1.2
4
6
8
10
12
14 16
VIN (V)
18
20
22
24
26
FIGURE 5. CURRENT REGULATION
FN6564.2
December 22, 2008
ISL97635A
Typical Performance Curves (Continued)
1.0
0.020
6P9S = 54 LEDs
VIN = 12V
0.015
CURRENT MATCHING (%)
CURRENT MATCHING
12V/1mA
0.010
12V/20mA
0.005
0
-0.005
6V/20mA
-0.010
6V/1mA
0.9
20kHz
0.8
0.7
200Hz
0.6
10kHz
-0.015
-0.020
Ch 0
Ch 1
Ch 2
Ch 3
CHANNELS
Ch 4
1kHz
100Hz
0.5
Ch 5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0
PWM DUTY CYCLE
FIGURE 6. CHANNEL-TO-CHANNEL CURRENT MATCHING
FIGURE 7. CURRENT MATCHING vs DUTY CYCLE vs
DIMMING FREQUENCY
180
TOTAL OUTPUT CURRENT (mA)
160
6 CHANNELS
9 LEDs PER CHANNEL
VIN = 12V
140
120
VIN = 6V
100
80
60
40
VIN = 18V
20
0
0
10
20
30
40
50
60
70
PWM DUTY CYCLE (%)
80
90
100
FIGURE 8. PWM DIMMING LINEARITY
FIGURE 9. LX, IIN, IL AND LO
FIGURE 10. IL AT 50% PWM DIMMING
FIGURE 11. IL ZOOM IN AT PWM DIMMING ZOOM IN
8
FN6564.2
December 22, 2008
ISL97635A
Typical Performance Curves (Continued)
FIGURE 12. ILED AT 50% PWM DIMMING
FIGURE 13. LX AT 50% PWM DIMMING
FIGURE 14. LX ZOOM IN AT 50% DIMMING
FIGURE 15. RIPPLE VOLTAGE
FIGURE 16. RIPPLE VOLTAGE ZOOM IN
9
FN6564.2
December 22, 2008
ISL97635A
Pinout
VDC
VIN
COMP
FAULT
LX
LX
ISL97635A
(24 LD QFN)
TOP VIEW
24
23
22
21
20
19
17
PGND
FPWM
3
16
OVP
PWMO
4
15
IIN0
GND
5
14
IIN1
PWMI/EN
6
13
IIN2
7
8
9
10
11
12
IIN3
2
RSET
SMBDAT
IIN4
PGND
IIN5
18
NC
1
NC
SMBCLK
Pin Descriptions (I = Input, O = Output, S = Supply)
PIN
NAME
TYPE
DESCRIPTION
1
SMBCLK
I
2
SMBDAT
I/O
3
FPWM
I
Connect a capacitor between FPWM and GND to set the DPWM frequency. FPWM = 5.4µ/CFPWM
If SMBus PWM or DPST mode is used, connect CFPWM to GND to set the dimming frequency. Also,
connect CPWMO between VPWMO and GND pins for DPST operation. If DC-to-PWM mode is used,
connect CFPWM to set the dimming frequency and apply a 0.21V to 1.21V at VPWMO.
4
PWMO
I/O
PWMI buffered output. If one connects a capacitor between PWMO and GND, it forms a lowpass filter
with an internal 40kΩ resistor to filter the PWMI signal for DPST operation when Reg 0x01 = 0x01. If
one applies a 0.2V to 1.2V DC input voltage, the output will be PWM with duty cycle proportional to
the DC input.
5
GND
S
Analog GND and LED power return
6
PWMI/EN
I
Dual Functions: Enable Pin and PWM brightness control pin or DPST control input. DO NOT let
PWMI/EN floating. 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.
7, 8
NC
-
No Connect. Can be floating or grounded
9
IIN5
I
Input 5 to current source, FB, and monitoring
10
IIN4
I
Input 4 to current source, FB, and monitoring
11
RSET
I
Resistor connection for setting LED current, (see Equation 1 for calculating the ILEDmax)
12
IIN3
I
Input 3 to current source, FB, and monitoring
13
IIN2
I
Input 2 to current source, FB, and monitoring
14
IIN1
I
Input 1 to current source, FB, and monitoring
15
IIN0
I
Input 0 to current source, FB, and monitoring
SMBus serial clock input
SMBus serial data input and output
16
OVP
I
Overvoltage protection input
17, 18
PGND
S
Power ground (LX Power return)
19, 20
LX
I
Input to boost switch
21
FAULT
O
Fault disconnect switch
22
COMP
O
Boost compensation pin
23
VIN
S
Input voltage for the device and LED power
24
VDC
S
De-couple capacitor for internally generated supply rail. If 2.7V < VBL+ < 5.5V, apply VDC directly with
a supply voltage of 2.7V to 5.5V
10
FN6564.2
December 22, 2008
ISL97635A
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 ISL97635A employes 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 applications where the power can be a series of
drained batteries or instantly changed to an AC/DC adapter
without rendering a noticeable visual nuisance. The number
of LEDs that can be driven by ISL97635A depends on the
type of LED chosen in the application. The ISL97635A is
capable of boosting up to 34.5V and typically driving 9 LEDs
in series for each of the 6 channels, enabling a total of 54
pieces of the 3.5V/30mA type of LEDs.
+
-
+
REF
RSET
+
PWM DIMMING
DC DIMMING
FIGURE 17. SIMPLIFIED CURRENT SOURCE CIRCUIT
Dynamic Headroom Control
Enable and PWMI
The EN/PWMI pin serves dual purposes; it is used as an
enable signal and can be used for PWM input signal for
dimming. If a PWM signal is applied to this pin, the first pulse of
minimum 40µs will be used as an Enable signal. If there is no
signal for longer than 28ms, the device will enter shutdown.
The EN/PWMI pin cannot be floating, thus, a 10kΩ pull-down
resistor may need to be added.
Current Matching and Current Accuracy
Each channel of the LED current is regulated by the current
source circuit, as shown in Figure 17.
The LED peak current is set by translating the RSET current
to the output with a scaling factor of 733/RSET. The source
terminals of the current source MOSFETs are designed as
100mV to minimize the power loss. The sources of errors of
the channel-to-channel current matching come from the
op amp’s offset, internal layout, reference, and current
source resistors. These parameters are optimized for current
matching and absolute current accuracy. On the other hand,
the absolute accuracy is additionally determined by the
external RSET, and therefore, additional tolerance will be
contributed by the current setting resistor. A 1% tolerance
resistor is therefore recommended.
The ISL97635A features a proprietary Dynamic Headroom
Control circuit that detects the highest forward voltage string
or effectively the lowest voltage from any of the IIN 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 IIN pin is at the target
headroom voltage. Since all LED stacks are connected to
the same output voltage, the other IIN 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 it is always referenced to the highest forward
voltage string in the architecture.
Dimming Controls
The ISL97635A allows 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.
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, as shown in Equation 1:
733
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 shown in Equation 2:
I LED = 2.87 × BRTDC ⁄ R SET
11
(EQ. 2)
FN6564.2
December 22, 2008
ISL97635A
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 and ILED is guaranteed to be
<10µA at this state.
For example, if the maximum required LED current (ILEDmax)
is 20mA, rearranging Equation 1 yields Equation 3:
R SET = 733 ⁄ 0.02 = 36.6kΩ
(EQ. 3)
If BRTDC is set to 200, then:
I LED = 2.87∗ 200 ⁄ 36600 = 15.7mA
(EQ. 4)
PWM CONTROL
The ISL97635A provides four 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. Internally generated 256 step duty cycle programmed
through the SMBus.
The SMBus controlled PWM frequency is adjusted by a
capacitor at the FPWM pin, which will be described in “PWM
Dimming Frequency Adjustment” on page 13.
Method 2 (External Mode)
The average LED current of each channel can also be
controlled by an external PWMI signal, as shown in Equation 7:
I LED ( ave ) = I LED × PWMI
(EQ. 7)
The PWM dimming frequency can be for example 20kHz but
there are a minimum on and off time requirements such that
the dimming will be in the range of 10% to 99.5%. If the
dimming frequency is below 5kHz, the dimming range can
be 1% to 99.5%.
The PWM dimming off time cannot be longer than 28ms or
else the driver will enter shutdown.
To use PWMI only brightness control, users need to set
Register 0x01 to 0x03.
Method 3 (DPST Mode)
The average LED current of each channel can also be
controlled by the product of the SMBus controlled PWM and
the external PWMI signals as follows:
I LED ( ave ) = I LED xPWM DPST
(EQ. 8)
2. External signal from PWMI.
3. DPST mode. Internally generated signal with a duty cycle
defined by the product of the external PWMI and SMBus
programmed PWM at the internal setting frequency.
4. DC-to-PWM control.
The default PWM dimming is in DPST mode. In all four
methods, the average LED current of each channel is
controlled by ILED and the PWM duty cycle in percent as
shown in Equation 5:
I LED ( ave ) = I LED × PWM
(EQ. 5)
Method 1 (Internal Mode, SMBus controlled PWM)
The average LED current of each channel is controlled by the
internally generated PWM signal as shown in Equation 6:
I LED ( ave ) = I LED × ( BRT ⁄ 255 )
(EQ. 6)
where BRT is the PWM brightness level programmed in the
register 0x00. BRT ranges from 0 to 255 in decimal and
defaults to 255 (0xFF). BRT = 0 disconnects all channels
and ILED is guaranteed to be <10µA in this state.
To use only the SMBus controlled PWM brightness control,
users need to set Register 0x01 to 0x05 with EN/PWMI in
logic high.
Where:
PWM DPST = BRT ⁄ 255 × PWMI
(EQ. 9)
Therefore:
I LED ( ave ) = I LED × BRT ⁄ 255 × PWMI
(EQ. 10)
Where BRT is the value held in register 0x00 (default setting
0xFF) controlled by SMBus and PWMI is the duty cycle of
the incoming PWMI signal. In this way, the users can change
the PWM current in ratiometric manner to achieve DPST
compliance backlight dimming.
To use the DPST mode, users need to set register 0x01 to
0x01 with the external PWM signal.
The DPST mode PWM frequency is adjusted by a capacitor
at the FPWM pin. Also, a CPWMO capacitor is also needed,
which will be described in “PWM Dimming Frequency
Adjustment” on page 13.
For example, if the SMBus controlled PWM duty is 80%
dimming at 200Hz (see CFPWM in Equation 10) and the
external PWMI duty cycle is 60% dimming at 1kHz, the
resultant PWM duty cycle is 48% dimming at 200Hz.
Method 4 (Analog Mode, DC-to-PWM Mode)
By overdriving the PWMO pin with a DC voltage between
0.21V and 1.21V, the average LED current of each channel
12
FN6564.2
December 22, 2008
ISL97635A
is controlled by the internally generated PWM signal as
shown in Equation 11:
I LED ( ave ) = I LED × BRT ⁄ 255 × ( 1 – ( V ( PWMO ) – 0.21 ) )
(EQ. 11)
Where BRT is the value held in register 0x00 (default setting
0xFF). The PWMO pin is internally driven to 0.21V via a
40kΩ resistor when the PWMI/EN pin is in logic high, any
overdrive circuit will need to be able to drive up to 40µA in
order to overcome this.
The DC-to-PWM controlled PWM frequency is adjusted by a
capacitor at the FPWM pin, which will be described in “PWM
Dimming Frequency Adjustment” on page 13.
For example, if PWMO is applied with a DC voltage ≥1.21V,
the output will be zero. On the other hand, if the PWMO is
applied with a DC voltage ≤ 0.21V, the PWM duty cycle will
be at its maximum. If the PWMO pin is applied with a DC
voltage of 0.31V, the PWM duty cycle will be at 90% at
200Hz if CFPWM = 27nF.
PWM Dimming Frequency Adjustment
(Applicable to SMBus controlled PWM, DPST, and
DC-to-PWM Modes)
Except for the external PWM dimming mode where the
frequency follows the external signal’s, the dimming
frequencies of the other modes are set by an external
capacitor CFPWM at the FPWM pin as shown in Equation 12:
C FPWM = 5.4μ ⁄ F PWM
(EQ. 12)
where FPWM is the desirable PWM dimming frequency.
For example, if FPWM = 200Hz, CFPWM = 5.4µ/200 = 27nF
The PWM dimming frequency can be for example 20kHz but
there are a minimum on and off time requirements such that
the dimming will be in the range of 10% to 99.5%. If the
dimming frequency is below 5kHz, the dimming range can
be 1% to 99.5%.
In the DPST and DC-to-PWM modes, a CPWMO capacitor is
also needed. An internal 40kΩ and an external CPWMO at the
PWMO pin form a low pass network to filter the PWMI to an
averaged DC. As a result, the time constant of the 40kΩ and
CPWMO should be significantly larger than the external PWMI
period, t, such that:
(EQ. 13)
40kΩ x C PWMO >t
For example, if FPWM is 200Hz and external PWMI is 1kHz
or above, a 220nF CPWMO can be chosen that allows the
external PWMI signal to be filtered as an averaged DC. Also,
the FPWM frequency in the DPST mode should be limited
between 100Hz to 2kHz and at least five times smaller than
the external PWMI frequency when DPST mode is used.
13
Switching Frequency
An internal clock of 1.2MHz is used for the boost regulator
control of the LX pin in default. There are 2 levels of
switching frequencies: 600kHz or 1.2MHz. Each can be
programmed in the Configuration Register 0x08 bit 2. The
default switching frequency is at 1.2MHz.
5V Low Dropout Regulator
A 5.2V 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. For applications with an input voltage ≤ 5.5V, the
VIN and VDC pins can be connected together. The VDC pin
can be used as a coarse reference with few mA sourcing
capability.
In-rush Control and Soft-start
The ISL97635A has separately built-in independent inrush
control and soft-start functions. The inrush control 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
30µA 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 inrush is complete. 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 terminated in any cycle
where the current exceeds the current limit. The ISL97635A
includes a soft-start feature where this current limit starts at a
low value (375mA). This is stepped up to the final 3A current
limit in seven further steps of 375mA. These steps will
happen over a 1ms total time, such that after 1ms the final
limit will be reached. 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.
FN6564.2
December 22, 2008
ISL97635A
Fault Protection and Monitoring
The ISL97635A 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. All LED faults are reported
via the SMBus 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 ISL97635A uses feedback
from the LEDs to determine when it is in a 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 an input current that exceeds
the devices electrical limits 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 two selectable levels of short circuit threshold
(3.1V and 8.0V) that can be programmed through the
Configuration Register 0x08 bit 0. When an LED becomes
shorted, the action taken is described in Table 1. The default
short circuit threshold is 8V. The detection of this failure
mode can be disabled via register 0x08 bit 1 if required.
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 ISL97635A monitors the current in each
channel such that any string which reaches at least 75% of
the intended output current is considered “good”. Should the
current subsequently fall below 50% of the target, the
14
channel will be considered an “open circuit”. Furthermore,
should the boost output of the ISL97635A reach 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 sped up 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 and enabling open circuit operation. When
this type of LED is open circuited, the effect is as if the LED
forward voltage has increased but no lighting. 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 channels look as if they have LED shorts. See
Table 1 for details regarding 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 Equation 14:
OVP = 1.21V × ( RUPPER + R LOWER ) ⁄ R LOWER
(EQ. 14)
These resistors should be large to minimize the power loss.
For example, a 1MΩ RUPPER and 39kΩ RLOWER sets OVP
to 32.2V. Large OVP resistors also allow COUT discharges
slowly during the PWM off time.
Undervoltage Lockout
If the input voltage falls below the UVLO level of 2.45V, the
device will stop switching and reset. Operation will restart
when the voltage comes back into the 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 ISL97635A monitors the voltage at the LX
and OVP pins. At start-up, 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. Furthermore,
should the voltage at LX not rise above this threshold during
any subsequent period where the power FET is not switched
on, it will immediately disable the input protection FET. The
OVP pin is also monitored such that if it rises above and
FN6564.2
December 22, 2008
ISL97635A
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. Once the device has cooled to
approximately +100°C, the device will restart with the DC
LED current level reduced to 77% of the initial setting. If the
dissipation problem persists, subsequent hitting of the limit
will cause identical behavior, with the current reduced in
steps to 53% and finally 30%. 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, allows the external processor to
interrogate the fault condition.
subsequently falls below 20% of the target OVP level, the
input protection FET will also be switched off.
Over-Temperature Protection (OTP)
The ISL97635A 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
significantly below the regulation target will be treated as
“open circuit” and disabled after a time-out period. This
time-out period is also reduced to 800µs when it is above the
lower threshold. 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.
For the extensive fault protection conditions, please refer to
Figure 18 and Table 1 for details.
LX
VIN
VOUT
LX
FAULT
O/P
SHORT
DRIVER
OVP
IMAX
ILIMIT
LOGIC
FET
DRIVER
IIN0
VSC
IIN5
VSET/2
REG
THRM
SHDN
REF
OTP
T2
TEMP
SENSOR
T1
+
VSET
Q0 VSET
PWM/OC0/SC0
FAULT/
STATUS
REGISTER
SMBUS
CONTROL
LOGIC
+
Q5
-
-
PWM/OC5/SC5
DC CURRENT
FIGURE 18. SIMPLIFIED FAULT PROTECTIONS
15
FN6564.2
December 22, 2008
ISL97635A
TABLE 1. PROTECTIONS TABLE
CASE
FAILURE MODE
DETECTION
MODE
FAILED CHANNEL ACTION
GOOD CHANNELS ACTION
VOUT
REGULATED BY
1
CH0 Short Circuit
CH0 ON and burns power
Upper
Over-Temperature
Protection limit
(OTP) not
triggered and
VIIN0 < VSC
CH1 through CH5 Normal
Highest VF of CH1
through CH5
2
CH0 Short Circuit
CH0 goes off until chip cooled and
Upper OTP
triggered but VIN0 then comes back on with current
reduced to 76%. Further OTP
< VSC
triggers result in reduction to 53%,
then 30%. Thermal event reported
in Fault/Status Register.
Same as CH0
Highest VF of CH1
through CH5
3
CH0 Short Circuit
Upper OTP not
triggered but
VIIN0 > VSC
CH1 through CH5 Normal
CH0 doubled after 6ms time-out.
Time-out reduced to 420µs if above
lower OTP limit
Highest VF of CH1
through CH5
4
CH0 Open Circuit
with infinite
resistance
Upper OTP not
triggered and
VIIN0 < VSC
VOUT will ramp to OVP. CH0 will
time-out after 6ms (800µs if above
lower OTP limit) 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
triggered and
VIIN0 < VSC
CH0 remains ON and has 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
VIIN0 < VSC
CH0 goes off until chip cooled and
then comes back on with current
reduced to 76%. Further OTP
triggers result in reduction to 53%,
then 30%. Thermal event reported
in Fault/Status Register.
Same as CH0
VF of CH0
7
CH0 LED Open
Circuit but has
paralleled Zener
Upper OTP not
triggered but
VIIN0 > VSC
CH0 OFF
CH1 through CH5 Normal
Highest VF of CH1
through CH5
CH0 remains ON and has highest
Upper OTP not
triggered but VIINx VF, thus VOUT increases.
> VSC
VF of CH0
VOUT increases then CH-X
switches OFF. This is an unwanted
shut off and can be prevented by
setting OVP and/or VSC at an
appropriate level.
8
Any channel at below 50% of the target current will fault out after 400µs.
Channel-to-Channel Lower OTP
ΔVF too high
triggered but VIINx Remaining channels driven with normal current.
< VSC
Highest VF of CH0
through CH5
9
All channels switched off until chip cooled and then comes back on with Highest VF of CH0
Channel-to-Channel Upper OTP
ΔVF too high
triggered but VIINx current reduced to 76%. Further OTP triggers result in reduction to 53%, through CH5
then 30%. Thermal event reported in Fault/Status Register.
< VSC
10
Output LED stack
voltage too high
VOUT > VOVP
Driven with normal current. Any channel that is below 50% of the target
current will time-out after 6ms.
11
VOUT/LX shorted to LX current and
GND
timing are
monitored.
Fault switch disabled and system shutdown until fault goes away, VOUT
is checked at startup with a low current from LX to check for presence of
short before the fault switch is enabled.
Highest VF of CH0
through CH5
OVP pin
monitored for
excursions below
20% of OVP
threshold
16
FN6564.2
December 22, 2008
ISL97635A
SMBCLK
tF
tR
tLOW
VIH
VIL
tHD:DAT
tHD:STA
tHIGH
tSU:STA
tSU:DAT
tSU:STO
SMBDAT
VIH
VIL
tBUF
P
S
P
S
NOTES:
SMBus Description
S = start condition
P = stop condition
A = acknowledge
A = not acknowledge
R/W = read enable at high; write enable at low
FIGURE 19. SMBUS 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 20. WRITE BYTE PROTOCOL
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 21. READ BYTE PROTOCOL
17
FN6564.2
December 22, 2008
ISL97635A
Write Byte
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.
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.”
The backlight controller may sense the state of the pins at POR
or during normal operation—the pins will not change state while
the device is in operation.
MSB
LSB
Read Byte
1
0
1
DEVICE
IDENTIFIER
1
0
DEVICE
ADDRESS
0
R/W
EB
IT
0
RE
AD
/W
R IT
As shown in the Figure 21, the 4 byte long Read Byte protocol
starts out with the slave address followed by the “command
code” which translates to the “register index.” Then 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 22. SLAVE ADDRESS BYTE DEFINITION
SMBus Register Definitions
The backlight controller registers are Byte wide and
accessible via the SMBus Read/Write Byte protocols. Their
bit assignments are provided in the following sections with
reserved bits containing a default value of “0”.
Slave Device Address
The slave address contains in 7 MSB plus one LSB as R/W bit
but these 8 bits are usually called slave address byte. As
shown in Figure 22, the high nibble of the slave address byte is
0x5 or 0101b to denote the “backlight 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 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
TABLE 2A. REGISTER LISTING
ADDRESS
REGISTER
BIT 7
BIT 6
BIT 5
BIT 4
BIT 3
BIT 2
BIT 1
BIT 0
DEFAULT
VALUE
SMBUS
PROTOCOL
0x00
PWM
Brightness
Control Register
BRT7
BRT6
BRT5
BRT4
BRT3
BRT2
BRT1
BRT0
0xFF
Read and Write
0x01
Device Control
Register
Reserved
Reserved
Reserved
Reserved
Reserved
PWM_MD
PWM_SEL
BL_CTL
0x00
Read and Write
0x02
Fault/Status
Register
Reserved
Reserved
2_CH_SD 1_CH_SD
BL_STAT
OV_CURR
THRM_SHDN
FAULT
0x00
Read Only
0x03
Identification
Register
LED
PANEL
MFG3
MFG2
MFG1
MFG0
REV2
REV1
REV0
0xC8
Read Only
0x07
DC Brightness
BRTDC7
Control Register
BRTDC6
BRTDC5
BRTDC4
BRTDC3
BRTDC2
BRTDC1
BRTDC0
0xFF
Read and Write
0x08
Configuration
Register
Reserved
Reserved
Reserved
Reserved
Reserved
FSW
VSC1
VSC0
0xXF
Read and Write
0x09
Output Channel
Register
Reserved
Reserved
CH5
CH4
CH3
CH2
CH1
CH0
0xFF
Read and Write
18
FN6564.2
December 22, 2008
ISL97635A
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
PWM_MD = PWM mode select bit (1 = absolute brightness, 0 = % change), default = 0
PWM_SEL = Brightness control select bit (1 = control by PWMI, 0 = control by SMBus), default = 0
BL_CTL = BL On/Off (1 = On, 0 = Off), default = 0
PWM_MD PWM_SEL
MODE
X
1
PWMI Mode
1
0
SMBus Mode
0
0
SMBus and PWMI mode with DPST
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
Identification Register
MFG[3..0] = Manufacturer ID (16 vendors available. Intersil is vendor ID 9)
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
VSC[1..0] = Short circuit thresholds selection
FSW[2] = Switching frequencies selection
VSC1
VSC0
0
X
No VSC error detection
1
0
VSC = 3.1V ±15%
1
1
VSC = 8V ±15%
FSW
0x09
Output Channel Mask / Fault
Readout Register
OPERATION
0
FSW = 600kHz
1
FSW = 1.2MHz
CH[5..0] = Output Channel Read and Write. In Write, 1 = Channel Enabled, 0 = Channel Disabled.
In Read, 1 = Channel OK, 0 = Channel Not OK/Channel disabled
PWM Brightness Control Register (0x00)
The Brightness control resolution has 256 steps of PWM
duty cycle adjustment. The bit assignment is shown in
Figure 23. All of the bits in this Brightness Control Register
can be read or write. Step 0 corresponds to the minimum
step where the current is less than 10µA. Step1 to step 255
represent the linear steps between 0.39% and 100% duty
cycle with approximately 0.39% duty cycle adjustment per
step.
• An SMBus Write Byte cycle to register 0x00 sets the PWM
brightness level only if the backlight controller is in SMBus
19
OPERATION
mode (see Table 3 Operating Modes selected by Device
Control Register Bits 1 and 2).
• An SMBus Read Byte cycle to register 0x00 returns the
programmed PWM brightness level regardless of the
value of PWM_SEL.
• An SMBus setting of 0xFF for register 0x00 sets the
backlight controller to the maximum brightness.
• An SMBus setting of 0x00 for register 0x00 sets the
backlight controller to the minimum brightness output in
which the LED current is guaranteed to be less than 10µA.
• Default value for register 0x00 is 0xFF.
FN6564.2
December 22, 2008
ISL97635A
Device Control Register (0x01)
This register has two bits that control the operating mode of
the backlight controller and a single bit that controls the BL
ON/OFF state. The remaining bits are reserved. The bit
assignment is shown in Figure 24. 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.
TABLE 3. OPERATING MODES SELECTED BY DEVICE
CONTROL REGISTER BITS 1 AND 2
PWM_MD PWM_SEL
1
PWMI Mode
1
0
SMBus Mode
0
0
SMBus and PWMI Mode with DPST
The PWM_SEL bit determines whether the SMBus or PWMI
input should drive the output brightness in terms of PWM
dimming. When PWM_SEL bit is 1, the PWMI drives the
output brightness regardless of what the PWM_MD is.
When the PWM_SEL bit is 0, the PWM_MD bit selects the
manner in which the PWM dimming is to be interpreted;
when this bit is 1, the PWM dimming is based on the SMBus
brightness setting. When this bit is 0, the PWM dimming
reflects a percentage change in the current brightness
REGISTER 0x00
DPST Brightness = Cbt × PWMI
(EQ. 15)
Where:
Cbt = Current brightness setting from SMBus register 0x00
without influence from the PWMI
PWMI = is the percent duty cycle of the PWMI
MODE
X
programmed in the SMBus register 0x00, i.e. DPST (Display
Power Saving Technology) mode as shown in Equation 15:
For example, the Cbt = 50% duty cycle programmed in the
SMBus register 0x00 and the PWM frequency is tuned to be
200Hz with an appropriate capacitor at the FPWM pin. On the
other hand, PWMI is fed with a 1kHz 30% high PWM signal.
When PWM_SEL = 0 and PWM_MD = 0, the device is in DPST
operation where DPST brightness = 15% PWM dimming at
200Hz.
• All reserved bits return a “0” when read.
• All reserved bits have no functional effect when written.
• 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
PWM BRIGHTNESS CONTROL REGISTER
BRT7
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
BRT[7..0]
BIT FIELD DEFINITIONS
= 256 steps of PWM brightness levels
FIGURE 23. DESCRIPTIONS OF BRIGHTNESS CONTROL REGISTER
REGISTER 0x01
DEVICE CONTROL REGISTER
RESERVED RESERVED RESERVED RESERVED RESERVED
PWM_MD
PWM_SEL
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 4 (R/W)
Bit 3 (R/W)
BIT ASSIGNMENT
BIT FIELD DEFINITIONS
PWM_MD
= PWM mode select bit (1 = absolute brightness,
0 = % change) default = 0
PWM_SEL
= Brightness control select bit (1 = control by
PWMI, 0 = control by SMBus) default = 0
BL_CTL
= BL On/Off (1 = On, 0 = Off) default = 0
FIGURE 24. DESCRIPTIONS OF DEVICE CONTROL REGISTER
20
FN6564.2
December 22, 2008
ISL97635A
when Bit 3 BL_STAT of register 0x02 is 1 and register 0x09
is not 0. See Figures 23 and 24.
• 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. See Figures 23 and 24.
• ** Note that the behavior of register 0x00 (Brightness
Control Register) is affected by certain combinations of the
control bits, as shown in Table 3 “Operating Modes
Selected by Device Control Register Bits 1 and 2.”
• When an SMBus mode is selected, register 0x00 reflects
the last value written to it. But, when any non-SMBus
mode is selected, register 0x00 reflects the current
brightness value based on the current mode of operation,
with the exception of SMBus mode with DPST, where
PWM_MD = 0 and PWM_SEL = 0.
• When SMBus mode with DPST is selected, register 0x00
reflects the last value written to it from SMBus.
• When a write to register 0x01 (Device Control Register)
causes the backlight controller to transition to an SMBus
mode, the brightness of the BL does not change. On the
other hand, when a write to register 0x01causes the
backlight controller to transition to a non-SMBus mode,
the brightness of the BL changes as appropriate for the
new mode.
• The default value for register 0x01 is 0x00.
Fault/Status Register (0x02)
This register has six 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 and
ignore the bit value when written. 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 fault will not be reported in the event the BL is
commanded on and 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 controller will not indicate a fault if the VBL+ goes
away, whether or not the LEDs were on at the time of the
power loss. This can occur if there is some hang condition
that causes the user to force the system off by holding the
power button down for 4s.
Default value for register 0x02 is 0x00.
Identification Register (0x03)
The ID register contains three bit fields to denote the LED
driver (always set to 1), manufacturer and the silicon revision
of the controller IC. The bit field widths allow up to 16 vendors
with up to eight 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 engineering development process three
Silicon spins were needed, the next available revision ID
would be used for all three spins until that same ID made it to
the factory. Except Bit 7 which has to be 1, all of the bits in this
register are read-only.
• Vendor ID 9 represents Intersil Corp.
• Default value for register 0x03 is 0xC8.
The initial value of REV shall be 0. Subsequent values of
REV will increment by 1.
• 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).
• 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.
21
FN6564.2
December 22, 2008
ISL97635A
REGISTER 0x02
RESERVED RESERVED
Bit 7 (R)
Bit 6 (R)
FAULT/STATUS REGISTER
2_CH_SD
1_CH_SD
BL_STAT
OV_CURR
THRM_SHDN
FAULT
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
Bit 1
THRM_SHDN
= Thermal Shutdown (1 = Thermal Fault, 0 = Thermal OK)
Bit 0
FAULT
= Fault occurred (Logic “OR” of all of the fault conditions)
= Input Overcurrent (1 = Overcurrent condition, 0 = Current OK)
FIGURE 25. 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
BIT FIELD DEFINITIONS
MFG[3..0]
= Manufacturer ID. See “Identification Register
(0x03)” on page 21.
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
REV[2..0]
= Silicon rev (Rev 0 through Rev 7 allowed for
silicon spins)
FIGURE 26. DESCRIPTIONS OF ID REGISTER
22
FN6564.2
December 22, 2008
ISL97635A
REGISTER 0x07
DC BRIGHTNESS CONTROL REGISTER
BRTDC7
BRTDC6
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 27. DESCRIPTIONS OF DC BRIGHTNESS CONTROL REGISTER
DC Brightness Control Register (0x07)
The DC Brightness Control Register 0x07 allows users to
have additional dimming flexibility as:
1. Achieving effectively 16-bit of dimming control when
combined DC dimming 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 27. 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 batches
variations but external EEPROM settings storing and
restoring are required.
• An SMBus Write Byte cycle to register 0x07 sets the
brightness level in DC only.
• An SMBus Read Byte cycle to register 0x07 returns the
current DC brightness level.
• Default value for register 0x07 is 0xFF.
users to set the boost conversion switching frequency
between 1.2MHz and 600kHz.
The bit assignment is shown in Figure 28. Default value for
register 0x08 is 0xFF
Output Channel Mask/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 5 corresponds to Ch5 and so on. When
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 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 29. Default for register
0x09 is 0xFF.
Configuration Register (0x08)
The Configuration Register allows users to set 2 levels of
channel Short-Circuit thresholds or disable it. It also allows
REGISTER 0x08
CONFIGURATION REGISTER
RESERVED RESERVED RESERVED RESERVED RESERVED
Bit 7 (R/W)
Bit 6 (R/W)
Bit 5 (R/W)
Bit 4 (R/W)
Bit 3 (R/W)
FSW
VSC1
VSC0
Bit 2 (R/W)
Bit 1 (R/W)
Bit 0 (R/W)
BIT ASSIGNMENT
BIT FIELD DEFINITIONS
VSC[1..0]
2 levels of Short-Circuit Thresholds (1 = 8V, 0 = 3.1V, accuracy ±15%)
FSW[2]
2 levels of Switching Frequencies (1 = 1,200kHz, 0 = 600kHz)
FIGURE 28. DESCRIPTIONS OF CONFIGURATION REGISTER
23
FN6564.2
December 22, 2008
ISL97635A
REGISTER 0x09
RESERVED RESERVED
Bit 7 (R/W)
Bit 6 (R/W)
OUTPUT CHANNEL REGISTER
CH5
CH4
CH3
CH2
CH1
CH0
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 29. OUTPUT CHANNEL REGISTER
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
of the input capacitor is suitable to handle the full supply
range.
Inductor
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.
Its maximum current capability must be adequate 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 fact that the
voltage across the inductor during the Off-period can be
shown as Equation 20:
IL peak = ( V O × I O ) ⁄ ( 85% × V I ) + 1 ⁄ 2 [ V I × ( V O – V I ) ⁄ ( L × V O × f S ) ]
(EQ. 20)
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, 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, with an AC ripple component proportional to the
rate of inductor charging only and smaller value input
capacitors may be used. It is recommended that an input
capacitor of at least 10µF be used. Ensure the voltage rating
24
The choice of 85% is just an average term for the efficiency
approximation. The first term is average current that is
inversely proportional to the input voltage. The second term
is inductor current change that is inversely proportional to L
and fS. As a result, for a given switching frequency and
minimum input voltage 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 ISL97635A current limit may also have to 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
FN6564.2
December 22, 2008
ISL97635A
and the voltage drop due to flowing through the ESR of the
output capacitor. The ripple voltage can be shown as
Equation 21:
ΔV CO = ( I O ⁄ C O × D ⁄ f S ) + ( ( I O × ESR )
.
VOUT
(EQ. 21)
The conservation of charge principle in Equation 19 also
brings up a 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 users need to select an output capacitor with
low ESD and with a enough input ripple current capability.
IIN0
IIN1
IIN2
FIGURE 30. GROUPING MULTIPLE CHANNELS FOR HIGH
CURRENT APPLICATIONS
Output Ripple
ΔVCo can be reduced by increasing CO or fS, 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 respond
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 2x4.7µF/50V ceramic
capacitors are suitable for the notebook display backlight
applications.
Multiple Drivers Operation
For large LCD panels where more than 6 channels of LEDs
are needed, multiple ISL97635As with each driver having its
own supporting components can be controlled together with
the common SMBus. While the ISL97635A does not have
extra pins strappable slave address feature, 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 if the EN/PWMI signal is
common to all drivers.
SMBCLK
Schottky Diode
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’s, and therefore, a suitable current
rated Schottky diode must be used.
SMBCLK
SMBDAT
SMBDAT
EN/PWMI
EN/PWMI
SMBCLK
SMBDAT
EN1
EN2
FIGURE 31. MULTIPLE DRIVERS OPERATION
16-Bit Dimming
Applications
High Current Applications
Each channel of the ISL97635A can support up to 35mA.
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
IIN0 to IIN2; this configuration can be treated as a single
string with 105mA current driving capability.
25
The SMBus controlled PWM and DC dimmings can be
combined to effectively provide 16 bits of dimming capability,
which can be valuable for automotive and avionics display
applications. Figure 32 illustrates one programming example
where 256 steps of PWM dimming can be programmed
between each DC dimming steps or vice versa.
FN6564.2
December 22, 2008
ISL97635A
Compensation
STEP 255 PWM CONTROL
STEP 0~255 DC CONTROL
STEP 254 PWM CONTROL
STEP 1 PWM CONTROL
STEPS 0~255 DC
STEP 0 PWM CONTROL
FIGURE 32. 16-BIT DIMMING ILLUSTRATION
RGB LED Backlight or Scrolling Backlight
Operation
The SMBus control features of PWM dimming, DC dimming,
and random channels selection have offered many driving
possibilities. For example, red, green, and blue LEDs can be
arranged in Ch0 and Ch1, Ch2 and Ch3, Ch4 and Ch5
respectively such that each group can be controlled
independently in sequential order for RGB LED backlighting
applications.
The ISL97635A has two main elements in the system; the
Current Mode Boost Regulator and the op amp based
multi-channel current sources. The ISL97635A incorporates
a transconductance amplifier in its feedback path to allow
the user some levels of adjustment on the transient
response and better regulation. The ISL97635A uses current
mode control architecture, which has a fast current sense
loop and a slow voltage feedback loop. The fast current
feedback loop does not require any compensation. The slow
voltage loop must be compensated for stable operation. The
compensation network is a series Rc, Cc1 network from
COMP pin to ground and an optional Cc2 capacitor
connected to the COMP pin. The Rc sets the high frequency
integrator gain for fast transient response and the Cc1 sets
the integrator zero to ensure loop stability. For most
applications, Rc is in the range of 200Ω to 3kΩ and Cc1 is in
the range of 27nF to 37nF. Depending upon the PCB layout,
a Cc2, in range of 100nF, may be needed to create a pole to
cancel the output capacitor ESR’s zero effect for stability.
The ISL97635A evaluation board is configured with Rc1 of
500Ω, Cc1 of 33nF, and Cc2 of 0, which achieves stability. In
the actual applications, these values may need to be tuned
empirically but the recommended values are usually a good
starting point.
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.
Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without
notice. Accordingly, the reader is cautioned to verify that data sheets are current before placing orders. Information furnished by Intersil is believed to be accurate and
reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
from its use. No license is granted by implication or otherwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com
26
FN6564.2
December 22, 2008
VIN
4
C1
10µ/25V
C2
0.1µ/25V
L1 : IHLP-2525BD-01 Vishay Inductor,
D1 D1 : SS15 - Vishay Schottky Diode, 5
Q1
1
2
5
6
3
L1
8.2µH
C4
10µ/25V
C6
4.7µ/50V
SS15
C7
4.7µ/50V
FDMA530PZ
SMBCLK
1
SMBCLK
SMBDAT
2
SMBDAT
3
FPWM
19
PWMO
IIN0
15
IIN1
14
IIN2
13
8
7
LED19
LED28
LED37
LED46
LED2
LED11
LED20
LED29
LED38
LED47
R2
36.6k
OVP
LED3
LED12
LED21
LED30
LED39
LED48
LED4
LED13
LED22
LED31
LED40
LED49
LED5
LED14
LED23
LED32
LED41
LED50
LED6
LED15
LED24
LED33
LED42
LED51
LED7
LED16
LED25
LED34
LED43
LED52
LED8
LED17
LED26
LED35
LED44
LED53
LED9
LED18
LED27
LED36
LED45
LED54
R4
39k
FN6564.2
December 22, 2008
NOTES:
FOR 2 LAYERS BOARD, LAYOUT
PGND (NOISY GROUND) ON TOP
LAYER AND AGND (QUIET GROUND)
ON BOTTOM LAYER. TIE PGND AND
AGND ONLY AT ONE POINT BY DOING
THIS: BRIDGE U1 PGND (PINS 18 AND 19)
AND AGND (PIN 5) TO THE PACKAGE
THERMAL PAD. PUT MULTIPLE VIAS ON THE
THERMAL PAD THAT CONNECTS TO THE
BOTTOM SIDE AGND.
FIGURE 33. TYPICAL APPLICATION CIRCUIT
ISL97635A
U1
12 IIN3
PWMI/EN
RSET
6
11
PWMI/EN
NC
GND
NC
5
LED10
LX
20
LX
21
16
GND
LED1
18
OVP
ISL97635A
10 IIN4
C14 4
PGND
17
IIN5
220n/6.3V
C13
R3
1M
PGND
9
27n/6.3V
FAULT
VIN
VDC
27
C11
1µ/10V
23
C12
0.1µ/10V
R5
10k
24
R6
10k
C20
COMP
VLOGIC
22
C10
33n
R7
500
JP26
ISL97635A
Package Outline Drawing
L24.4x4D
24 LEAD QUAD FLAT NO-LEAD PLASTIC PACKAGE
Rev 2, 10/06
4X 2.5
4.00
A
20X 0.50
B
PIN 1
INDEX AREA
PIN #1 CORNER
(C 0 . 25)
24
19
1
4.00
18
2 . 50 ± 0 . 15
13
0.15
(4X)
12
7
0.10 M C A B
0 . 07
24X 0 . 23 +- 0
. 05 4
24X 0 . 4 ± 0 . 1
TOP VIEW
BOTTOM VIEW
SEE DETAIL "X"
0.10 C
C
0 . 90 ± 0 . 1
BASE PLANE
( 3 . 8 TYP )
SEATING PLANE
0.08 C
SIDE VIEW
(
2 . 50 )
( 20X 0 . 5 )
C
0 . 2 REF
5
( 24X 0 . 25 )
0 . 00 MIN.
0 . 05 MAX.
( 24X 0 . 6 )
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 b 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 identifier may be
either a mold or mark feature.
28
FN6564.2
December 22, 2008