ISL97673IRZ-TK Intersil, ISL97673IRZ-TK Datasheet - Page 15

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

Specifications of ISL97673IRZ-TK

• 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

There are three selectable levels of short circuit threshold
(3.6V, 4.8V, and 5.85V) that can be programmed through
the Configuration Register 0x08. When an LED becomes
shorted, the action taken is described in Table 2. The
default short circuit threshold is 5.85V. The detection of
this failure mode can be disabled via Register 0x08.
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 ISL97673 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 ISL97673
reaches 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 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, so as 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 channel look as if they have
LED shorts. See Table 2 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 1MkΩ 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.
OVP
UPPER
=
1.21V
value of at least 30pF is recommended. These
UPPER
×
(
R
UPPER
/R
LOWER
+
R
= C
LOWER
15
UPPER
LOWER
) R
⁄
and 30kΩ R
/C
LOWER
UPPER
. Using a
LOWER
OUT
(EQ. 12)
sets
ISL97673
Undervoltage Lockout
If the input voltage falls below the UVLO level of 2.45V,
the device will stop switching and be reset. Operation will
restart only if the device is re-enabled through the
SMBus/I
operating range. In non-SMBus/I
will automatically restart once the input voltage clears
the UVLO threshold with the part already enabled.
Input Overcurrent Protection
During normal switching operation, the current through
the internal boost power FET is monitored. If the current
exceeds the current limit, the internal switch will be
turned off. This monitoring happens on a cycle by cycle
basis in a self protecting way.
Additionally, the ISL97673 monitors the voltage at the LX
and OVP pins. At startup, 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 ISL97673 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
channels having large voltages across them) to hit the
upper temperature threshold.
The upper 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. Hitting of the upper
threshold will also set the thermal fault bit of the
Fault/Status register 0x02. Unless disabled via the EN
pin, the device stays in an active state throughout,
allowing an external processor to interrogate the fault
condition.
For the extensive fault protection conditions, please refer
to Figure 24 and Table 2 for details.
2
C interface once the input voltage is back in the
2
C applications, the part
June 24, 2010
FN7633.0