ISL97671IRZ-T Intersil, ISL97671IRZ-T Datasheet - Page 11

• Manufacturer Part Number: ISL97671IRZ-T
• Description: IC LED DVR PWM CTRL 6CH 20QFN
• Manufacturer: Intersil

Specifications of ISL97671IRZ-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: 4.5 V ~ 26.5 V
• Mounting Type: Surface Mount
• Package / Case: 20-VFQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 40mA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -

For example, if 10 LEDs are used with the worst case
V
level is set at 40V, then the V
between 25.6V and 40V. If the requirement is changed to
a 6 LEDs 21V V
be reduced and users should follow V
~100%) OVP requirement. Otherwise, the headroom
control will be disturbed such that the channel voltage
can be much higher than expected and sometimes it can
prevent the driver from operating properly.
The ratio of the OVP capacitors should be the inverse of
the OVP resistors. For example, if R
then C
C
Current Matching and Current Accuracy
Each channel of the LED current is regulated by the
current source circuit, as shown in Figure 20.
The LED peak current is set by translating the R
to the output with a scaling factor of 401.8/R
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. On the
other hand, the absolute accuracy is additionally
determined by the external R
tolerance will be contributed by the current setting
resistor. A 1% tolerance resistor is therefore
recommended.
Dynamic Headroom Control
The ISL97671 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. When this lowest channel voltage is lower
than the short circuit threshold, V
used as the feedback signal for the boost regulator. The
OUT
LOWER
FIGURE 20. SIMPLIFIED CURRENT SOURCE CIRCUIT
of 35V. If R
UPPER
= 3.3nF.
RSET
RSET
PWM DIMMING
/C
DC DIMMING
LOWER
OUT
+
-
1
and R
REF
REF
application, then the OVP level must
= 1/33 with C
2
11
are chosen such that the OVP
+
+
-
-
SET
OUT
, and therefore, additional
SC
is allowed to operate
UPPER
UPPER
, such voltage will be
+
+
-
-
OUT
/R
= 100pF and
= (64%
LOWER
SET
SET
. The
= 33/1,
current
ISL97671
boost makes the output to the correct level such that the
lowest channel pin 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
programmed current. The output voltage will regulate
cycle-by-cycle and is always referenced to the highest
forward voltage string in the architecture.
Dimming Controls
The ISL97671 provides SMBus/I
dimming where the users need to turn the LEDs on
through the SMBus/I
“SMBus/I
hand, the ISL97671 also provides PWM dimming by
external PWM signal where the SMBCLK and SMBDAT
pins need to pull low or grounded.
The ISL97671 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, which will be described in the following.
MAXIMUM DC CURRENT SETTING
The initial brightness should be set by choosing an
appropriate value for R
the maximum possible LED current:
Once R
through 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
dynamically on the fly during operation. BRTDC = 0
disconnects all channels.
For example, if the maximum required LED current
(I
Equation 4:
If BRTDC is set to 200 then:
PWM CONTROL
The ISL97671 provides three 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 6channels to provide an average LED
current. During the On periods, the LED current will be
defined by the value of R
I
I
R
I
1. DC current adjustment
2. PWM chopping of the LED current defined in Step 1.
LEDmax
LED
LED
SET
LED(max)
=
=
=
1.58x BRTDC R
1.58 200 20100
SET
401.8 0.02
=
2
) is 20mA, rearranging Equation 2 yields
C Communications” section). On the other
-------------- -
R
401.8
is fixed, the LED DC current can be adjusted
•
SET
(
⁄
⁄
=
⁄
20.1kΩ
2
C communications (see the
SET
=
SET
LEDmax
15.7mA
SET
)
. This should be chosen to fix
and BRTDC, as described in
. BRTDC can be adjusted
2
C controlled PWM or DC
June 24, 2010
FN7631.0
(EQ. 2)
(EQ. 3)
(EQ. 4)
(EQ. 5)