ISL97671AIRZ-T Intersil, ISL97671AIRZ-T Datasheet - Page 12

• Manufacturer Part Number: ISL97671AIRZ-T
• Description: IC LED DRVR 6-CH BACKLIGHT 20QFN
• Manufacturer: Intersil
• Series: -r

Specifications of ISL97671AIRZ-T

• Constant Current: -
• Constant Voltage: -
• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 6
• Internal Driver: Yes
• Type - Primary: Automotive, Backlight
• Type - Secondary: RGB
• Frequency: 475kHz ~ 640kHz, 970kHz ~ 1.31MHz
• Voltage - Supply: 4.5 V ~ 26.5 V
• Voltage - Output: 45V
• Mounting Type: Surface Mount
• Package / Case: 20-VFQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: ISL97671AIRZ-TTR

The ISL97671A allows two ways of controlling the LED current,
and therefore, the brightness. They are:
There are various ways to achieve DC or PWM current control,
described in the following.
MAXIMUM DC CURRENT SETTING
The initial brightness should be set by choosing an appropriate
value for R
possible LED current:
Once R
Register 0x07 (BRTDC) as follows:
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
during operation. BRTDC = 0 disconnects all channels.
For example, if the maximum required LED current (I
20mA, rearranging Equation 2 yields Equation 4:
If BRTDC is set to 200 then:
PWM DIMMING CONTROL
The ISL97671A provides multiple 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
Equations 2 and 3. The source of the PWM signal can be
described as follows:
The default PWM dimming is in DPST mode. In all of the
methods, the average LED channel current is controlled by I
and the PWM duty cycle in percent, as shown in Equation 6:
Method 1 (Internal Mode, SMBus/I
The average LED channel current is controlled by the internally
generated PWM signal, as shown in Equation 7:
I
I
R
I
I
I
LEDmax
LED
LED
LED ave
LED ave
1. DC current adjustment
2. PWM chopping of the LED current defined in Step 1.
1. Internally generated 256 step duty cycle programmed
2. External signal from PWM.
3. DPST mode. Internally generated signal with a duty cycle
SET
through the SMBus/I
defined by the product of the external PWM and SMBus/I
programmed PWM at the internal setting frequency.
(
(
=
=
=
SET
1.58x BRTDC R
1.58 200 20100
401.8 0.02
)
)
=
=
=
SET
is fixed, the LED DC current can be adjusted through
401.8
-------------- -
LEDmax
R
•
I
I
LED
LED
(
SET
. This should be chosen to fix the maximum
⁄
×
×
⁄
. BRTDC can be adjusted dynamically on the fly
PWM
(
BRT 255
=
⁄
20.1kΩ
SET
⁄
2
=
C.
)
15.7mA
)
12
SET
and BRTDC, as described in
2
C controlled PWM)
LED(max)
ISL97671A
(EQ. 2)
(EQ. 3)
(EQ. 4)
(EQ. 5)
(EQ. 6)
(EQ. 7)
) is
LED
2
C
LILED ave
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.
To use only the SMBus/I
users need to set Register 0x01 to 0x05.
The PWM dimming frequency is adjusted by a resistor at the
FPWM pin.
Method 2 (External Mode)
The average LED channel current can also be controlled by an
external PWM signal, as shown in Equation 8:
The PWM dimming frequency can be set or applied up to 30kHz
with duty cycles from 0.4% to 100%. The PWM dimming off time
cannot be longer than 28ms or else the driver will enter
shutdown.
To use externally applied PWM signal only for brightness control,
users need to set Register 0x01 to 0x03.
Method 3 (DPST Mode)
The average LED channel current can also be controlled by the
product of the SMBus/I
signals as:
Where:
PWM
Therefore:
Where BRT is the value held in Register 0x00 (default setting
0xFF) controlled by SMBus/I
incoming PWM 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 an external PWM signal.
The DPST mode PWM dimming frequency is adjusted by a resistor
at the FPWM pin.
For example, if the SMBus/I
dimming at 200Hz (see Equation 12) and the external PWM duty
cycle is 60% dimming at 1kHz, the resultant PWM duty cycle is
48% dimming at 200Hz.
PWM Dimming Frequency Adjustment
The PWM dimming frequency is set by an external resistor at the
FPWM pin as:
where F
R
The PWM dimming frequency can be set or applied up to 30kHz
with duty cycle from 0.4% to 100%.
I
I
F
LED ave
LED ave
PWM
FPWM
(
(
(
DPST
=
is the setting resistor.
PWM
)
)
)
6.66
------------------------
RFPWM
=
=
=
=
I
I
I
LED
LED
LED
is the desirable PWM dimming frequency and
BRT 255
×10
xPWM
×
7
×
⁄
PWMI
BRT 255
DPST
×
⁄
2
2
C controlled PWM and the external PWM
PWMI
C controlled PWM brightness control,
×
2
2
C controlled PWM duty is 80%
C and PWM is the duty cycle of the
PWMI
March 24, 2011
FN7709.1
(EQ. 10)
(EQ. 11)
(EQ. 12)
(EQ. 8)
(EQ. 9)