FAN4860 Fairchild Semiconductor, FAN4860 Datasheet - Page 12

• Manufacturer Part Number: FAN4860
• Description: The FAN4860 is a low-power boost regulator designed to provide a regulated 5V output from a single cell Li-Ion battery
• Manufacturer: Fairchild Semiconductor

© 2010 Fairchild Semiconductor Corporation
FAN4860 • Rev. 1.1.0
Fault State
The regulator enters the FAULT state under any of the
following conditions:
Once a fault is triggered, the regulator stops switching and
presents a high-impedance path between V
waiting 480 CLK counts, a re-start is attempted.
Soft-Start and Fault Timing
The soft-start timing for each state, and the fault times, are
determined by the fault clock, whose period is inversely
proportional to V
charge larger values of C
V
cycle in current limit.
The number of clock counts for each state is illustrated in
Figure 37.
IN
V
LIN state to SS state.
V
SS state to BST state.
Sustained (32 CLK counts) pulse-by-pulse current limit
during the BST state.
The regulator moves from BST to LIN state due to a short
circuit or output overload (V
, this also reduces power delivered to V
OUT
OUT
fails to achieve the voltage required to advance from
fails to achieve the voltage required to advance from
Figure 37.
IN
. This allows the regulator more time to
Fault Response into Short Circuit
OUT
when V
OUT
< V
IN
IN
-1V).
is lower. With higher
IN
OUT
and V
during each
OUT
. After
12
The fault clock period as a function of V
The V
in Figure 39.
Over-Temperature Protection (OTP)
The regulator shuts down when the thermal shutdown
threshold is reached. Restart, with soft-start, occurs when
the IC has cooled by about 30°C.
Over-Current Protection (OCP)
During boost-mode operation, the FAN4860 employs a
cycle-by-cycle peak current limit to protect switching
elements. Sustained current limit, for 32 consecutive fault
CLK counts, initiates a fault condition.
During an overload condition, as V
approximately
immediately switched off and a fault condition is declared.
Automatic restart occurs once the overload/short is removed
and the fault timer completes counting.
IN
-dependent LIN mode charging current is illustrated
Figure 38.
Figure 39.
V
IN
-1V,
Fault Clock Period vs. VIN
LIN Mode Current vs. V
the
synchronous
IN
is shown in Figure 38.
OUT
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collapses to
rectifier
IN
is