ISL97675IRZ-TK Intersil, ISL97675IRZ-TK Datasheet - Page 15

• Manufacturer Part Number: ISL97675IRZ-TK
• Description: IC LED DVR PWM CTRL 4CH 20QFN
• Manufacturer: Intersil
• Type: Backlight, White LEDr

Specifications of ISL97675IRZ-TK

• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 4
• Internal Driver: Yes
• Type - Primary: Backlight
• Frequency: 600kHz, 1.2MHz
• Voltage - Supply: 4.5 V ~ 26 V
• Voltage - Output: 45V
• Mounting Type: Surface Mount
• Package / Case: 20-VQFN
• Operating Temperature: -40°C ~ 85°C
• Current - Output / Channel: 30mA
• Internal Switch(s): Yes
• Efficiency: 92%
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: ISL97675IRZ-TKTR

For systems with no master fault protection FET, the
inrush current will flow towards C
and it is determined by the ramp rate of V
values of C
Fault Protection and Monitoring
The ISL97675 features extensive protection functions to
cover all the perceivable failure conditions. The failure
mode of an 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 LED short circuit condition which causes the
FB voltage to rise to ~4V, will result in that channel
turning off. This does not affect any other channels.
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 ISL97675 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 3 for more details.
A fault condition that results in high input current due to
a short on V
result in a shutdown of all output channels. The control
device logic will remain functional.
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.
When an LED becomes shorted, the action taken is
described in Table 3. The short circuit threshold is 4V.
Open Circuit Protection (OCP)
When one of the LEDs becomes open circuit, it can
behave as either an infinite resistance or a gradually
increasing finite resistance. The ISL97675 monitors the
current in each channel such that any string which
reaches the intended output current is considered
“good”. Should the current subsequently fall below the
target, the channel will be considered an “open circuit”.
Furthermore, should the boost output of the ISL97675
reach the OVP limit or should the lower over-temperature
threshold be reached, all channels which are not “good”
will immediately be considered as “open circuit”.
Detection of an “open circuit” channel will result in a
time-out before disabling of the affected channel. This
time-out is run when the device is above the lower
over-temperature threshold in an attempt to prevent the
upper over-temperature trip point from being reached.
Some users employ special types of LEDs that have
zener diode structure in parallel with the LED for ESD
enhancement, thus enabling open circuit operation.
OUT
OUT
and boost inductor, L.
with master fault protection switch will
15
OUT
when V
IN
IN
and the
is applied
ISL97675
When this type of LED goes open circuit, the effect is as
if the LED forward voltage has increased, but no light is
emitted. Any affected string will not be disabled, unless
the failure results in the boost OVP limit being reached,
allowing all other LEDs in the string to remain
functional. Care should be taken in this case that the
boost OVP limit and SCP limit are set properly, to make
sure that multiple failures on one string do not cause all
other good channels to be faulted out. This is due to the
increased forward voltage of the faulty channel making
all other channels look as if they have LED shorts. See
Table 3 for details for responses to fault conditions.
Overvoltage Protection (OVP)
The integrated OVP circuit monitors the output voltage
and keeps the voltage at a safe level. The OVP threshold
is set as:
These resistors should be large to minimize the power
loss. For example, a 1MΩ R
OVP to 41.2V. Large OVP resistors also allow C
discharges slowly during the PWM Off time. Parallel
capacitors should also be placed across the OVP resistors
such that R
C
capacitors reduce the AC impedance of the OVP node,
which is important when using high value resistors.
Undervoltage Lockout
If the input voltage falls below the UVLO level of 3.1V, the
device will stop switching and be reset. Operation will
restart once the input voltage is back in the normal
operating range.
Master Fault Protection
During normal switching operation, the current through
the internal boost power FET is monitored. If the input
current exceeds the current limit due to output shorted
to ground or excessive loading, the internal switch will be
turned off. This monitoring happens on a cycle by cycle
basis in a self protecting way.
Additionally, the ISL97675 monitors the voltage at the LX
and OVP pins. At start-up, a fixed current is injected out
of the LX pins and into the output capacitor. The device
will not start up unless the voltage at LX exceeds 1.2V.
The OVP pin is also monitored such that if it rises above
and subsequently falls below 20% of the target OVP
level, the input protection FET will be switched off.
Over-Temperature Protection (OTP)
The ISL97675 includes two over-temperature thresholds.
The lower threshold is set to +130°C. When this
threshold is reached, any channel which is outputting
current at a level below the regulation target will be
treated as “open circuit” and disabled after a time-out
period. The intention of the lower threshold is to allow
bad channels to be isolated and disabled before they
cause enough power dissipation (as a result of other
OVP
UPPER
=
1.21V
value of at least 30pF is recommended. These
UPPER
×
(
R
UPPER
/R
LOWER
+
R
= C
LOWER
UPPER
LOWER
) R
⁄
and 30kΩ R
/C
LOWER
UPPER
. Using a
LOWER
OUT
May 19, 2010
(EQ. 12)
FN7630.0
sets