ISL6237 Datasheet, PDF (29/35 Pages) Intersil Corporation – High-Efficiency, Quad-Output, Main Power Supply Controllers for Notebook Computers

ISL6237
negative current limit is met, UGATE is turned on for a
minimum on-time, followed by another LGATE pulse until
negative current limit. This effectively regulates the
discharge current at the negative current limit in an effort to
prevent excessively large negative currents that cause
potentially damaging negative voltages on the load. Once an
overvoltage fault condition is set, it can only be reset by
toggling SHDN, EN_, or cycling VIN (POR).
UNDERVOLTAGE PROTECTION
When the output voltage drops below 70% of its regulation
voltage for at least 100µs, the controller sets the fault latch
and begins the discharge mode (see the following Shutdown
and Output Discharge sections). UVP is ignored for at least
20ms (typical), after start-up or after a rising edge on EN_.
Toggle EN_ or cycle VIN (POR) to clear the undervoltage
fault latch and restart the controller. UVP only applies to the
buck outputs.
THERMAL PROTECTION
The ISL6237 has thermal shutdown to protect the devices
from overheating. Thermal shutdown occurs when the die
temperature exceeds +150°C. All internal circuitry shuts
down during thermal shutdown. The ISL6237 may trigger
thermal shutdown if LDO_ is not bootstrapped from OUT_
while applying a high input voltage on VIN and drawing the
maximum current (including short circuit) from LDO_. Even if
LDO_ is bootstrapped from OUT_, overloading the LDO_
causes large power dissipation on the bootstrap switches,
which may result in thermal shutdown. Cycling EN_,
EN_LDO, or VIN (POR) ends the thermal-shutdown state.
Discharge Mode (Soft-Stop)
When a transition to standby or shutdown mode occurs, or
the output undervoltage fault latch is set, the outputs
discharge to GND through an internal 25Ω switch. The
reference remains active to provide an accurate threshold
and to provide overvoltage protection.
Shutdown Mode
The ISL6237 SMPS1, SMPS2 and LDO have independent
enabling control. Drive EN1, EN2 and EN_LDO below the
precise input falling-edge trip level to place the ISL6237 in its
low-power shutdown state. The ISL6237 consumes only
20µA of quiescent current while in shutdown. Both SMPS
outputs are discharged to 0V through a 25Ω switch.
Power-Up Sequencing and On/Off Controls (EN_)
EN1 and EN2 control SMPS power-up sequencing. EN1 or
EN2 rising above 2.4V enables the respective outputs. EN1
or EN2 falling below 1.6V disables the respective outputs.
Connecting EN1 or EN2 to REF will force its outputs off while
the other output is below regulation. The sequenced SMPS
will start once the other SMPS reaches regulation. The
second SMPS remains on until the first SMPS turns off, the
device shuts down, a fault occurs or PVCC goes into
undervoltage lockout. Both supplies begin their power-down
sequence immediately when the first supply turns off. Driving
EN_ below 0.8V clears the overvoltage, undervoltage and
thermal fault latches.
MODE
Power-Up
Run
Overvoltage
Protection
Undervoltage
Protection
Discharge
Standby
Shutdown
Thermal Shutdown
TABLE 3. OPERATING-MODE TRUTH TABLE
CONDITION
COMMENT
PVCC < UVLO threshold.
Transitions to discharge mode after a VIN POR and after REF becomes valid. LDO
and REF remain active.
EN_LDO = high, EN1 or EN2
enabled.
Normal operation
Either output > 111% (VOUT1) or
116% (VOUT2) of nominal level.
LGATE_ is forced high. LDO and REF are active. Exited by a VIN POR, or by toggling
EN1 or EN2.
Either output < 70% of nominal after The internal 25Ω switch turns on. LDO and REF are active. Exited by a VIN POR or
20ms time-out expires and output is by toggling EN1 or EN2.
enabled.
Either SMPS output is still high in
either standby mode or shutdown
mode
Discharge switch (25Ω) connects OUT_ to GND. One output may still run while the
other is in discharge mode. Activates when PVCC is in UVLO, or transition to UVLO,
standby, or shutdown has begun. LDO and REF active.
EN1, EN2 < startup threshold,
EN_LDO = High
LDO and REF are active.
EN1, EN2, EN_LDO = low
Discharge switch (25Ω) connects OUT_ to PGND. All circuitry off.
T_J > +150°C
All circuitry off. Exited by VIN POR or cycling EN_.
29
FN6418.4
March 18, 2008