ISL97635AIRZ-T Intersil, ISL97635AIRZ-T Datasheet - Page 12

• Manufacturer Part Number: ISL97635AIRZ-T
• Description: IC LED DRVR WHT/RGB BCKLGT 24QFN
• Manufacturer: Intersil
• Type: Backlight, White LED, RGBr

Specifications of ISL97635AIRZ-T

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 6
• 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

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 ILED is guaranteed to be
<10µA 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 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 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:
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 Register 0x01 to 0x05 with EN/PWMI in
logic high.
R
I
I
I
LED
LED ave
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
(
(
LED
=
=
2.87 ∗ 200 36600
and BRTDC, as described in Equations 1 and 2. The
733 0.02
)
)
is guaranteed to be <10µA in this state.
=
=
⁄
I
I
LED
LED
LED
⁄
×
×
=
and the PWM duty cycle in percent as
PWM
(
BRT 255
36.6kΩ
LEDmax
=
⁄
15.7mA
12
)
. BRTDC can be adjusted
LEDmax
(EQ. 3)
(EQ. 4)
(EQ. 5)
(EQ. 6)
ISL97635A
)
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 follows:
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 the external PWM signal.
The DPST mode PWM frequency is adjusted by a capacitor
at the FPWM pin. Also, a C
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 C
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
I
I
PWM
I
LED ave
LED ave
LED ave
(
(
(
DPST
)
)
)
=
=
=
=
I
I
I
LED
LED
LED
BRT 255
xPWM
×
×
⁄
PWMI
BRT 255
DPST
×
⁄
PWMI
FPWM
PWMO
×
PWMI
in Equation 10) and the
capacitor is also needed,
December 22, 2008
(EQ. 10)
(EQ. 7)
(EQ. 8)
(EQ. 9)
FN6564.2