ISL97635IRZ-TK Intersil, ISL97635IRZ-TK Datasheet - Page 12

• Manufacturer Part Number: ISL97635IRZ-TK
• Description: IC LED DRVR WHT/RGB BCKLGT 24QFN
• Manufacturer: Intersil
• Type: Backlight, White LED, RGBr

Specifications of ISL97635IRZ-TK

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 8
• Internal Driver: Yes
• Type - Primary: Automotive, Backlight
• Type - Secondary: RGB, White LED
• Frequency: 600kHz, 1.2MHz
• Voltage - Supply: 6 V ~ 24 V
• Voltage - Output: 34.5V
• Mounting Type: Surface Mount
• Package / Case: 24-VQFN
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 35mA
• Internal Switch(s): Yes
• Efficiency: 91%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

MAXIMUM DC CURRENT SETTING
The initial brightness should be set by choosing an
appropriate value for R
maximum possible LED current, as shown in Equation 1:
DC CURRENT ADJUSTMENT
Once R
through Register 0x07 (BRTDC), as shown in Equation 2:
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 I
dynamically on the fly during operation. BRTDC = 0
disconnects all channels and I
at this state.
For example, if the maximum required LED current (I
is 20mA, rearranging Equation 1 yields Equation 3:
If BRTDC is set to 200 then:
PWM CONTROL
The ISL97635 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 8 channels to provide an average LED current. During
the On periods, the LED current will be defined by the value
of R
source of the PWM signal can be described as follows:
The default PWM dimming is in DPST mode. In all four
methods, the average LED current of each channel is
controlled by I
shown in Equation 5:
I
I
R
I
I
LEDmax
LED
LED
LED ave
1. Internally generated 256 step duty cycle programmed
2. External signal from PWMI.
3. DPST mode. Internally generated signal with a duty cycle
4. DC-to-PWM control.
SET
through the SMBus.
defined by the product of the external PWMI and SMBus
programmed PWM at the internal setting frequency.
SET
(
=
=
=
SET
2.87
2.87 200 36600
and BRTDC, as described in Equations 1 and 2. The
733 0.02
)
=
=
-------------- -
R
is fixed, the LED DC current can be adjusted
×
•
733
⁄
I
SET
LED
BRTDC R
LED
×
⁄
=
and the PWM duty cycle in percent, as
PWM
36.6kΩ
⁄
SET
LEDmax
SET
=
. This should be chosen to fix the
15.4mA
12
LED
. BRTDC can be adjusted
is guaranteed to be <10µA
LEDmax
(EQ. 1)
(EQ. 2)
(EQ. 3)
(EQ. 4)
(EQ. 5)
ISL97635
)
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:
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 I
To use only the SMBus controlled PWM brightness control,
users need to set Register0x01 to 0x05 with EN/PWMI in
logic high.
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:
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:
Where:
Therefore:
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 external PWM signal.
The DPST mode PWM frequency is adjusted by a capacitor at
the FPWM pin. A C
I
I
I
PWM
I
LED ave
LED ave
LED ave
LED ave
(
(
(
(
LED
DPST
)
)
)
)
is guaranteed to be <10µA in this state.
=
=
=
=
=
I
I
I
I
LED
LED
LED
LED
BRT 255
xPWM
×
×
×
⁄
(
PWMI
BRT 255
PWMO
BRT 255
DPST
×
⁄
⁄
PWMI
capacitor, is also needed in the
×
)
PWMI
December 22, 2008
(EQ. 10)
FN6434.2
(EQ. 6)
(EQ. 7)
(EQ. 8)
(EQ. 9)