ISL8107 Datasheet, PDF (11/16 Pages) Intersil Corporation – Single-Phase Pulse-Width Modulation PWM Controller with Integrated High-Side Gate Drivers

ISL8107
If overcurrent is detected, the output immediately shuts off, it
cycles the soft-start function in a hiccup mode (4 dummy
soft-start time-outs, then up to one real one) to provide fault
protection. If the shorted condition is not removed, this cycle
will continue indefinitely.
V_OOUUTT
E_EN_NS_SS_S
I^IL^L
FIGURE 12. TYPICAL OVERCURRENT PROTECTION
ENSS
V^VOUUTT
ILL
FIGURE 13. TYPICAL HICCUP RECOVER
Thermal Protection
If the ISL8107 IC junction temperature reaches a nominal
temperature of +150°C, the controller will be disabled. The
ISL8107 will not be re-enabled until the junction temperature
drops below +110°C.
Power-Good
The PGOOD comparator monitors the voltage on the FB pin.
PGOOD is asserted (open drain) when the FB pin voltage is
within 14% of the reference voltage. The turn-on response of
the PGOOD circuit has a typical 3µs delay. The PGOOD is
deasserted under disable, overcurrent event, or
over-temperature event.
Component Selection Guidelines
Output Capacitor Selection
An output capacitor is required to filter the output and supply
the load transient current. The filtering requirements are a
function of the switching frequency and the ripple current.
The load transient requirements are a function of the slew
rate (di/dt) and the magnitude of the transient load current.
These requirements are generally met with a mix of
capacitors and careful layout.
For applications that have transient load rates above 1A/ns,
high frequency capacitors initially supply the transient and
slow the current load rate seen by the bulk capacitors. The
bulk filter capacitor values are generally determined by the
ESR (effective series resistance) and voltage rating
requirements rather than actual capacitance requirements.
High frequency decoupling capacitors should be placed as
close to the power pins of the load as physically possible. Be
careful not to add inductance in the circuit board wiring that
could cancel the usefulness of these low inductance
components. Consult with the manufacturer of the load on
specific decoupling requirements.
Use only specialized low-ESR capacitors intended for
switching-regulator applications for the bulk capacitors.
The bulk capacitor’s ESR will determine the output ripple
voltage and the initial voltage drop after a high slew-rate
transient. An aluminum electrolytic capacitor's ESR value is
related to the case size with lower ESR available in larger
case sizes. However, the equivalent series inductance
(ESL) of these capacitors increases with case size and can
reduce the usefulness of the capacitor to high slew-rate
transient loading. Unfortunately, ESL is not a specified
parameter. Work with your capacitor supplier and measure
the capacitor’s impedance with frequency to select a
suitable component. In most cases, multiple electrolytic
capacitors of small case size perform better than a single
large case capacitor.
Output Inductor Selection
The output inductor is selected to meet the output voltage
ripple requirements and minimize the converter’s response
time to the load transient. The inductor value determines the
converter’s ripple current and the ripple voltage is a function
of the ripple current. The ripple voltage and current are
approximated by Equation 7:
ΔI = ^V-----^I--^N-----^------^V----^O----^U-----^T- • ^V-----^O----^U----^T--
Fs x L
V_IN
ΔV_OUT = ΔI x ESR
(EQ. 7)
Increasing the value of inductance reduces the ripple current
and voltage. However, the large inductance values reduce
the converter’s response time to a load transient.
One of the parameters limiting the converter’s response to a
load transient is the time required to change the inductor
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FN6605.0
October 29, 2008