ISL97673IRZ Intersil, ISL97673IRZ Datasheet - Page 14

• Manufacturer Part Number: ISL97673IRZ
• Description: IC LED DVR PWM CTRL 6CH 20QFN
• Manufacturer: Intersil

Specifications of ISL97673IRZ

• 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
• Voltage - Output: *
• 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

The ISL97673 allows the user to program the amount of
phase shift degree in 7-bit resolution, as shown in
Figure 24. To enable programmable phase shifting, the
user must write to the Phase Shift Control register with
EqualPhase = 0 and the desirable phase shift value of
PhaseShift[6:0]. The delay between CH5 and the
repeated CH0 is the rest of the PWM cycle.
Switching Frequency
There are 2 levels of switching frequencies enable for the
boost regulator’s control of the LX pin: 600kHz or
1.2MHz. Each can be programmed in the Configuration
Register 0x08 bit 2. The default switching frequency is at
600kHz.
5V Low Dropout Regulator
A 5V 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. Low input voltage also allows only lower
output voltage applications only with the maximum
boost ratio defined in “Components Selections” on
page 24. The VDC pin can be used as a coarse reference
with a few mA sourcing capability.
In-rush Control and Soft-start
The ISL97673 has separately built in independent in-rush
control and soft-start functions. The in-rush 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 15µA 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 in-rush has
completed. At this point, the boost regulator will begin to
switch and the current in the inductor will ramp-up. The
FIGURE 23. PHASE SHIFT WITH 7-BIT
ILED0
ILED1
ILED2
ILED3
ILED4
ILED5
t
PD
PROGRAMMABLE DELAY
t
PD
t
PD
t
ON
t
PD
t
t
FPWM
PD
t
OFF
14
ISL97673
current in the boost power switch is monitored and the
switching is terminated in any cycle where the current
exceeds the current limit. The ISL97673 includes a
soft-start feature where this current limit starts at a low
value (275mA). This is stepped up to the final 2.2A
current limit in 7 further steps of 275mA. These steps will
happen over at least 8ms, and will be extended at low
LED PWM frequencies if the LED duty cycle is low. 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
inrush current will flow towards C
and it is determined by the ramp rate of VIN and the
values of C
Fault Protection and Monitoring
The ISL97673 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. LED
faults are reported via the SMBus/I
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 ISL97673 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 2 for more details.
A fault condition that results in high input current due to
a short on V
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.
OUT
OUT
and L.
will result in a shutdown of all output
OUT
2
C interface to
when VIN is applied
June 24, 2010
FN7633.0