ISL62381_11 Datasheet, PDF (15/23 Pages) Intersil Corporation – High-Efficiency, Quad or Triple-Output System Power Supply Controller for Notebook Computers

ISL62381, ISL62382, ISL62383, ISL62381C, ISL62382C, ISL62383C
1.5ms
tSOFTSTART
2.75ms
PGOOD Delay
VOUT
VCC and LDO5
EN
FB
PGOOD
FIGURE 24. SOFT-START SEQUENCE FOR ONE SMPS
The PGOOD pin indicates when the converter is capable of
supplying regulated voltage. It is an undefined impedance if V_IN
is not above the rising POR threshold or below the POR falling
threshold. When a fault is detected, these controllers will turn
on the open-drain NMOS, which will pull PGOOD low with a
nominal impedance of 63 or 95 This will flag the system
that one of the output voltages is out of regulation.
Separate enable pins allow for full soft-start sequencing.
Because low shutdown quiescent current is necessary to
prolong battery life in notebook applications, the LDO5 5V LDO
is held off until any of the three enable signals (EN1, EN2 or
LDO3EN) is pulled high. Soft-start of all outputs will only start
until after LDO5 is above the 4.2V POR threshold. In addition to
user-programmable sequencing, these controllers include a
pre-programmed sequential SMPS soft-start feature. Table 1
shows the SMPS enable truth table.
TABLE 1. SMPS ENABLE SEQUENCE LOGIC
EN1
EN2
START-UP SEQUENCE
0
0
Both SMPS outputs OFF simultaneously
0
Float
Both SMPS outputs OFF simultaneously
Float
0
Both SMPS outputs OFF simultaneously
Float
Float
Both SMPS outputs OFF simultaneously
0
1
SMPS1 OFF, SMPS2 ON
1
0
SMPS1 ON, SMPS2 OFF
1
1
Both SMPS outputs ON simultaneously
Float
1 SMPS1 enables after SMPS2 is in regulation
1
Float SMPS2 enables after SMPS1 is in regulation
VCC1
The VCC1 nominal operation voltage is 5V. If EN1, EN2 and
LDO3EN are all logic low, the VCC1 start-up voltage is 3.6V
when VIN is applied on these controllers. LDO5 is held off
until any of the three enable signals (EN1, EN2 or LDO3EN)
is pulled high. When LDO5 is above the 4.2V VCC1 POR
threshold, VCC1 will switchover to LDO5 internally.
After VIN is applied, the VCC1 start-up 3.6V voltage can be
used as the logic high signal of any of EN1, EN2 and LDO3EN
to enable PVCC if there is no other power supply on the board.
MOSFET Gate-Drive Outputs LGATE and UGATE
These controllers have internal gate-drivers for the high-side
and low-side N-Channel MOSFETs. The low-side gate-drivers
are optimized for low duty-cycle applications where the low-side
MOSFET conduction losses are dominant, requiring a low
r _DS(ON) MOSFET. The LGATE pull-down resistance is small in
order to clamp the gate of the MOSFET below the V_GS(th) at
turn-off. The current transient through the gate at turn-off can
be considerable because the gate charge of a low r _DS(ON)
MOSFET can be large. Adaptive shoot-through protection
prevents a gate-driver output from turning on until the opposite
gate-driver output has fallen below approximately 1V. The
dead-time shown in Figure 25 is extended by the additional
period that the falling gate voltage stays above the 1V
threshold. The typical dead-time is 21ns. The high-side
gate-driver output voltage is measured across the UGATE and
PHASE pins while the low-side gate-driver output voltage is
measured across the LGATE and PGND pins. The power for
the LGATE gate-driver is sourced directly from the LDO5 pin.
The power for the UGATE gate-driver is sourced from a “boot”
capacitor connected across the BOOT and PHASE pins. The
boot capacitor is charged from the 5V LDO5 supply through a
“boot diode” each time the low-side MOSFET turns on, pulling
the PHASE pin low. These controllers have integrated boot
diodes connected from the LDO5 pins to BOOT pins.
t_LGFUGR
UGATE
LGATE
50%
50%
t_UGFLGR
FIGURE 25. LGATE AND UGATE DEAD-TIME
Diode Emulation
FCCM is a logic input that controls the power state of these
controllers. If forced high, these controllers will operate in
forced continuous-conduction-mode (CCM) over the entire
load range. This will produce the best transient response to
all load conditions, but will have increased light-load power
loss. If FCCM is forced low, these controllers will
automatically operate in diode-emulation-mode (DEM) at
light load to optimize efficiency in the entire load range. The
15
FN6665.5
May 13, 2011