FAN48610BUC50X データシートの表示（PDF） - Fairchild Semiconductor
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FAN48610BUC50X Datasheet PDF : 11 Pages
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Circuit Description
FAN48610 is a synchronous boost regulator, typically
operating at 2.5 MHz in Continuous Conduction Mode
(CCM), which occurs at moderate to heavy load current and
low VIN voltages. The regulator’s Pass-Through Mode
automatically activates when VIN is above the boost
regulator’s set point.
Table 2. Operating Modes
Mode
Description
Invoked When:
LIN
SS
BST
PT
Linear Startup
Boost Soft-Start
Boost Operating Mode
Pass-Through Mode
VIN > VOUT
VIN < VOUT < VOUT(TARGET)
VOUT= VOUT(TARGET)
VIN > VOUT(TARGET)
Boost Mode Regulation
The FAN48610 uses a current-mode modulator to achieve
excellent transient response and smooth transitions between
CCM and DCM operation. During CCM operation, the device
maintains a switching frequency of about 2.5 MHz. In light-
load operation (DCM), frequency is naturally reduced to
maintain high efficiency.
Shutdown and Startup
When EN is LOW, all bias circuits are off and the regulator is
in Shutdown Mode. During shutdown, current flow is
prevented from VIN to VOUT, as well as reverse flow from
VOUT to VIN. It is recommended to keep load current draw
below 500 mA until the devices successfully executes
startup. The following table describes the startup sequence.
Table 3. Boost Startup Sequence
Start
Mode
Entry
Exit
End Timeout
Mode (µs)
LIN1
LIN2
SS
VIN > VUVLO,
EN=1
VOUT > VIN-
300 mV
TIMEOUT
SS
LIN2
LIN1 Exit
VOUT > VIN-
300 mV
TIMEOUT
SS
FAULT
LIN1 or LIN2
Exit
VOUT=VOUT(TARG
ET)
OVERLOAD
TIMEOUT
BST
FAULT
512
1024
64
LIN Mode
When EN is HIGH and VIN > VUVLO, the regulator first
attempts to bring VOUT within 300 mV of VIN by using the
internal fixed-current source from VIN (Q2). The current is
limited to the LIN1 set point.
If VOUT reaches VIN-300 mV during LIN1 Mode, the SS Mode
is initiated. Otherwise, LIN1 times out after 512 µs and LIN2
Mode is entered.
In LIN2 Mode, the current source is incremented to 1.6 A. If
VOUT fails to reach VIN-300 mV after 1024 µs, a fault
condition is declared and the device waits 20 ms to attempt
an automatic restart.
Soft-Start (SS) Mode
Upon the successful completion of LIN Mode (VOUT>VIN-
300 mV), the regulator begins switching with boost pulses
current limited to 50% of nominal level.
During SS Mode, if VOUT fails to reach regulation during the
SS ramp sequence for more than 64 µs, a fault is declared. If
large COUT is used, the reference is automatically stepped
slower to avoid excessive input current draw.
Boost (BST) Mode
This is a normal operating mode of the regulator.
Pass-Through (PT) Mode
In normal operation, the device automatically transitions from
Boost Mode to Pass-Through Mode if VIN goes above the
target VOUT. In Pass-Through Mode, the device fully
enhances Q2 to provide a very low impedance path from
VIN to VOUT. Entry to the Pass-Through Mode is triggered
by condition where VIN > VOUT and no switching has occurred
during the past 5 µs. To soften the entry into Pass-Through
Mode, Q2 is driven as a linear current source for the first
5 µs. Pass-Through Mode exit is triggered when VOUT
reaches the target VOUT voltage. During Automatic Pass-
Through Mode, the device is short-circuit protected by a
voltage comparator tracking the voltage drop from VIN to
VOUT; if the drop exceeds 300 mV, a fault is declared.
Fault State
The regulator enters Fault State under any of the following
conditions:
VOUT fails to achieve the voltage required to advance
from LIN Mode to SS Mode.
VOUT fails to achieve the voltage required to advance
from SS Mode to BST Mode.
Boost current limit triggers for 2 ms during BST Mode.
VIN – VOUT > 300 mV; this fault can occur only after
successful completion of the soft-start sequence.
VIN < VUVLO.
Once a fault is triggered, the regulator stops switching and
presents a high-impedance path between VIN and VOUT.
After waiting 20 ms, an automatic restart is attempted.
Over-Temperature
The regulator shuts down if the die temperature exceeds
150°C. Restart occurs when the IC has cooled by
approximately 20°C.
© 2013 Fairchild Semiconductor Corporation
FAN48610 • Rev. 1.0.0 •
9
www.fairchildsemi.com
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