ISL97682IRTZ-TK Intersil, ISL97682IRTZ-TK Datasheet - Page 13

• Manufacturer Part Number: ISL97682IRTZ-TK
• Description: 2 Channel LED Driver, 16LD TQFN 3X3, 1K T&R
• Manufacturer: Intersil
• Series: -r

Specifications of ISL97682IRTZ-TK

• Constant Current: -
• Constant Voltage: -
• Topology: PWM, Step-Up (Boost)
• Number Of Outputs: 2
• Internal Driver: Yes
• Type - Primary: Backlight
• Type - Secondary: -
• Frequency: 500kHz ~ 650kHz, 900kHz ~ 1.1MHz
• Voltage - Supply: 4 V ~ 26.5 V
• Voltage - Output: 45V
• Mounting Type: Surface Mount
• Package / Case: 16-WFQFN Exposed Pad
• Operating Temperature: -40°C ~ 85°C
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Fault Protection and Monitoring
The ISL97682, ISL97683, ISL97684 feature 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 also 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.
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 ISL97682, ISL97683, ISL97684 use 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.
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 4.4V.
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 ISL97682, ISL97683, ISL97684 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 ISL97682, ISL97683, ISL97684 reach the OVP
limit, 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.
13
ISL97682, ISL97683, ISL97684
Some users employ some special types of LEDs that have zener
diode structure in parallel with the LED for ESD enhancement, thus
enabling open circuit operation. 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, in order to assure 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 Equation 9:
These resistors should be large to minimize the power loss. For
example, a 1MkΩ R
Large OVP resistors also allow C
PWM Off time. Parallel capacitors should also be placed across
the OVP resistors such that R
Using a 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 2.5V, the device
will stop switching and be reset. Operation will restart only if the
device is re-powered and re-enabled once the input voltage is
back in the normal operating range.
Over-Temperature Protection (OTP)
The ISL97682, ISL97683, ISL97684 over-temperature protection
threshold is set to +150°C. Each time this is reached, the boost
will stop switching and the output current sources will be
switched off.
For the extensive fault protection conditions, please refer to
Figure 25 and Table 3 for details.
OVP
=
1.22V
UPPER
×
(
R
value of at least 30pF is recommended. These
UPPER
UPPER
+
R
and 30kΩ R
LOWER
UPPER
OUT
) R
⁄
/R
discharges slowly during the
LOWER
LOWER
LOWER
= C
sets OVP to 41.2V.
LOWER
March 11, 2011
/C
FN7689.0
UPPER
(EQ. 9)
.