sc643 Semtech Corporation, sc643 Datasheet - Page 15

• Manufacturer Part Number: sc643
• Description: Light Management Unit With 4 Ldos And Sempulse Interface
• Manufacturer: Semtech Corporation

Applications Information (continued)
Shutdown Mode
The device is disabled when the SPIF pin is held low for
the shutdown time specifi ed in the electrical characteris-
tics section. All registers are reset to default condition at
shutdown. Typical current consumption is this mode is
0.1μA
Sleep Mode
When all backlights are off the charge pump is disabled,
and sleep mode is activated. This is a reduced current
mode that helps minimize overall current consumption.
In sleep mode, the SemPulse interface continues to
monitor its input for commands from the host. Typical
current consumption in this mode is 90μA.
Protection Features
The SC643 provides several protection features to safe-
guard the device from catastrophic failures. These features
include:
Output Open Circuit Protection
Over-Voltage Protection (OVP) at the OUT pin prevents
the charge pump from producing an excessively high
output voltage. In the event of an open circuit between
the OUT pin and all current sinks (no loads connected),
the charge pump runs in open loop and the voltage rises
up to the OVP limit. OVP operation is hysteretic, meaning
the charge pump will momentarily turn off until V
suffi ciently reduced. The maximum OVP threshold is 6.0V,
allowing the use of a ceramic output capacitor rated at
6.3V with no concern of over-voltage damage. Typical OVP
voltage is 5.7V.
Over-Temperature Protection
The Over-Temperature (OT) protection circuit prevents the
device from overheating and experiencing a catastrophic
failure. When the junction temperature exceeds 165 °C, the
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Output Open Circuit Protection
Over-Temperature Protection
Charge Pump Output Current Limit
LDO Current Limit
LED Float Detection
OUT
is
device goes into thermal shutdown with all outputs dis-
abled until the junction temperature is reduced. All
register information is retained during thermal shutdown.
Hysteresis of 30 °C is provided to ensure that the device
cools suffi ciently before re-enabling.
Charge Pump Output Current Limit
The device limits the charge pump current at the OUT pin.
When OUT is shorted to ground, the output current will
typically equal 300mA. The output current is also limited
to 300mA when over loaded resistively.
LDO Current Limit
The device limits the current at all LDO output pins. The
minimum limit is 200mA, so load current of greater than
the rated current can be used (with degraded accuracy)
without tripping the current limit.
LED Float Detection
Float detect is a fault detection feature of the LED back-
light outputs. If an output is programmed to be enabled
and an open circuit fault occurs at any backlight output,
that output will be disabled to prevent a sustained output
OVP condition from occurring due to the resulting open
loop. Float detect ensures device protection but does not
ensure optimum performance. Unused LED outputs must
be disabled to prevent an open circuit fault from
occurring.
Thermal Management
The device has the potential for peak power dissipation
equal to 2.7W when all outputs are simultaneously oper-
ating at maximum rated current and powered by a fully
charged Li-Ion cell equal to 4.2V. A calculation of the
maximum power dissipation of the device should be done
to identify if power management measures are needed to
prevent overheating. The MLP package is capable of dis-
sipating 1.85W when proper layout techniques are used.
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