ISL6232 Datasheet, PDF (18/25 Pages) Intersil Corporation – High Efficiency System Power Supply Controller for Notebook Computers

ISL6232
includes its own internal digital soft-start circuit. In shutdown
or standby mode, the soft-start output is reset to zero.
Fault Protection
Undervoltage Protection
When the output undervoltage is detected at below 75%
(typ) of the regulation output for 20ms blanking time, it enters
the discharge mode by discharging the output through the
internal 20Ω switch connected from PHASE to PGND. When
the output voltage drops below 0.3V, the external low side
MOSFET is latched on to discharge the output to ground.
When either output is in UVP, both outputs are latched off
through soft-discharge. The latches can be reset by toggling
V_IN, SHDN#, or EN.
Overvoltage Protection
When either output voltage is above 113% (typ) of the
regulation point, both outputs are latched off by turning on
the low side MOSFET and turning off the high side MOSFET.
Discharging the output capacitors through the inductor and
low-side MOSFET causes negative output voltage. For loads
that cannot tolerate a negative voltage, place a 1A power
Schottky diode across the output to act as a reverse-polarity
clamp. If the overvoltage is due to a short in the high side
MOSFET, the battery fuse will be blown and isolated from
the output.
Overcurrent Protection
The output current is continuously monitored through either
an accurate sensing resistor or the DCR of the inductor.
When the inductor peak current reaches the overcurrent limit
threshold, it immediately turn off the high side MOSFET and
turn on the low side MOSFET. This peak current limiting
prevents inductor saturation. If the overcurrent or short
circuit condition is detected for more than 20ms (typ), the
high side MOSFET is latched off and the output is
discharged through the internal 20Ω switch connected from
PHASE to PGND. When the output voltage drops below
0.3V, the low side MOSFET is latched on to discharge the
output to ground. When either output is latched off due to
overcurrent, the other output is also latched off through
soft-discharge.
Thermal Protection
Thermal-overload protection limits total power dissipation in
the device. When the junction temperature exceeds +150°C,
a thermal sensor forces most of the internal circuitry into
shutdown mode, thus allowing the device to cool down. The
thermal sensor turns the device on again after the junction
temperature drops by +25°C, causing a pulsed output during
continuous overload conditions. The digital soft-start
sequence begins after the thermal shutdown condition is
removed.
Power-Up Sequence
EN3 and EN5 control the power-up sequencing of buck
controllers. Setting EN above 2.4V enables the outputs, and
setting EN below 0.8V disables the outputs. Connecting EN3
or EN5 to REF forces the respective output off until the other
output reaches 90% of the regulation point and soft-start
cycle has ended. One of the buck controllers can remain on
even though the other buck controller turns off. Table 2
shows the power sequence selection.
TABLE 2. POWER-UP SEQUENCE TABLE
3.3V
SHDN# EN3 EN5 LDO3 LDO5 5V BUCK BUCK
Low
x
x
OFF OFF
OFF
OFF
High Low Low ON ON
OFF
OFF
High Low High ON ON
ON
OFF
High High Low ON ON
OFF
ON
High High High ON ON
ON
ON
High High REF ON ON ON after ON
3.3V up
High REF High ON ON
ON ON after
5V up
SHUTDOWN MODE
When SHDN# is set below 0.8V, the part is completely shut
down with a 5µA (typ) shutdown V_IN current. When SHDN#
is set above 2.4V, both LDO outputs and REF are active.
This is prerequisite for enabling buck controllers. For
automatic shutdown and startup, SHDN# can be tied to V_IN.
Table 3 is the summary of various operation modes.
18
FN9116.1
April 20, 2009