SC908 View Datasheet(PDF) - Semtech Corporation
Part Name
Description
MFG CO.
'SC908' PDF : 30 Pages View PDF
SC908
Applications Information (continued)
fied current and voltage limits of the Li-Ion cell. The output
current is constant at the CC limit, then decreases abruptly
when the output voltage steps from the overshoot voltage
to the regulation voltage at the transition to CV control.
This can be compared to voltage and current trajectories
for other monolithic charger devices to show the softness
of the linear crossover. This explains the charge-time
advantage of the SC908 logical crossover method.
Input Over-Voltage Protection
The VAD input is protected from adapter over-voltage to
at least 28V above V . When V exceeds its OVP rising
DGND
VAD
threshold VAD the charger turns off its output while
OVP-R
the charge timer continues to run, and the FLTB status
indicator is asserted. When V subsequently falls below
VAD
the VAD OVP falling threshold VAD , charging continues
OVP-F
normally and FLTB is released.
Charger Protection Features
The protection features are:
• Short Circuit Protection
• Over Current and Max Temperature Protection
• Input Overvoltage Protection
• Thermal Protection
Short Circuit Protection
The BAT output can tolerate an indefinite short circuit to
ground. The current into a ground short will be equal to
the precharge current.
The ITERM pin voltage prior to termination, and the IPRGM
pin voltage while in CC mode, are regulated to 1.5V.
Precharge current and termination current are propor-
tional to the resulting ITERM current, and CC current is
proportional to the resulting IPRGM current. High battery
current is prevented by pinshort detectors on both pro-
gramming pins. Pinshort detection asynchronously forces
the charger into reset, turning off the output and clearing
the charge timer. When the pinshort condition is removed,
the charger begins normal operation automatically.
Over Current and Max Temperature Protection
Over current protection is provided in all modes of opera-
tion. When the device is in the charge mode the output is
current-limited to either the programmed pre-charge
current or the programmed fast charge current, depend-
ing on the voltage at the output. Junction over-temperature
protection allows operation with maximum power dissi-
pation by disabling the charger output current when the
die temperature reaches the maximum operating tem-
perature. This results in operation as a pulse charger in
extreme power dissipation applications, delivering the
maximum allowable output current while limiting the
internal die temperature to a safe level.
Thermal Protection
The charger’s internal over-temperature (OT) threshold is
set to approximately 145°C. If the temperature exceeds
this threshold prior to termination, the charger output is
turned off. All other functions remain active, the charger
logical state is preserved, and no fault is indicated. This
allows thermal pulse charging in conditions of high power
dissipation. Following termination, a charger OT condi-
tion will be indicated as a fault. Refer to the Indicator Flags
subsection for more information.
A second high OT threshold is set to approximately 165°C.
Should the die temperature exceed this threshold, all
SC908 functions are disabled, and the status outputs indi-
cate an exceptional condition fault. Refer to the Indicator
Flags subsection for more information.
Low Battery Detector Operation
The low battery detector provides two low battery detec-
tion voltage thresholds: a fixed warning threshold and a
resistor programmable detection (shutdown request)
threshold. The low battery detector is enabled when
either the buck converter is enabled (SEN is high) or the
LDO regulator is enabled (LEN is high). The warning and
shutdown request are provided by the status output pins
FLTB and LBATB, as described in the Status Outputs sub-
section. When a charging adapter is present (V >
VAD
VAD ), the FLTB and LBATB outputs are redefined to
UVLO-x
reflect the interaction of battery voltage and charging
state.
The low battery detector warning threshold is fixed at
3.28V ± 70mV. The battery voltage fault threshold is pro-
grammable, with a resistor from the RLBAT pin to ground,
20
Share Link: 
