isl6236 Intersil Corporation, isl6236 Datasheet - Page 29

• Manufacturer Part Number: isl6236
• Description: High-efficiency, Quad-output, Main Power Supply Controllers For Notebook Computers
• Manufacturer: Intersil Corporation

controller continuously monitors the output for undervoltage
and overvoltage fault conditions.
Power-Up
Run
Overvoltage
Protection
Undervoltage
Protection
OUT-OF-BOUND CONDITION
When the output voltage is 5% above the set voltage, the
out-of-bound condition activates. LGATE turns on until
output reaches within regulation. Once the output is within
regulation, the controller will operate as normal. It is the
"first line of defense" before OVP. The output voltage
ripple must be sized low enough as to not nuisance trip
the OOB threshold. The equations in the Output Capacitor
Selection section on page 32 should be used to size the
output voltage ripple below 3% of the nominal output
voltage set point.
OVERVOLTAGE PROTECTION
When the output voltage of VOUT1 is 11% (16% for
VOUT2) above the set voltage, the overvoltage fault
protection activates. This latches on the synchronous
rectifier MOSFET with 100% duty cycle, rapidly
discharging the output capacitor until the negative current
limit is achieved. Once 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 Shutdown and
Output Discharge section below). 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.
MODE
PVCC < UVLO threshold.
EN LDO = high, EN1 or EN2
enabled.
Either output > 111% (VOUT1) or
116% (VOUT2) of nominal level.
Either output < 70% of nominal after
20ms time-out expires and output is
enabled.
29
CONDITION
TABLE 3. OPERATING-MODE TRUTH TABLE
Transitions to discharge mode after a VIN POR and after REF becomes valid. LDO,
VREF3, and REF remain active.
Normal operation
LGATE is forced high. LDO, VREF3 and REF active. Exited by a VIN POR, or by
toggling EN1 or EN2.
The internal 25Ω switch turns on. LDO, VREF3 and REF are active. Exited by a VIN
POR or by toggling EN1 or EN2.
ISL6236
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 ISL6236 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 ISL6236 in its
low-power shutdown state. The ISL6236 consumes only
20µA of quiescent current while in shutdown. When
shutdown mode activates, the 3.3V VREF3 remain on. 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.
THERMAL PROTECTION
The ISL6236 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 ISL6236 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.
COMMENT
June 28, 2007
FN6373.3