ISL6534 Intersil Corporation, ISL6534 Datasheet - Page 23

• Manufacturer Part Number: ISL6534
• Description: Dual PWM
• Manufacturer: Intersil Corporation

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10. Other variables that may contribute to a lesser degree
11. Adding external circuitry to sense a fault may be possible,
So the recommendations are as follows:
6. In general, the faster the rise time of the output current
7. The load current at the time of the short can affect the
8. The compensation components are chosen to stabilize
9. The output capacitance and its ESR can affect how
1. If there is a specific fault condition that needs protection,
2. Compare the short circuit resistance to the nominal load
3. Check the rise time of the short circuit current, and what
4. From the waveform of the COMP pin, see if the values
5. Note that the linear output has no protection at all.
will get a clean shutdown; see also #6. In addition, the
higher VOUT for a given VIN will give a higher UGATE
duty cycle, and the average COMP voltage is higher, so it
doesn’t have as far to go to trip.
during the short, the more current will be allowed on the
initial peak, and the better chance the COMP pin will have
a sharp rise as well. A low resistance short (#4) and a
higher output voltage (#5) both help. However, if the
current ramps too fast, then a false trip is also possible
(shutting down at a current level still within the expected
load range).
results; the response of a short can be different at no load
versus full load.
the regulation loop; however, if they unnecessarily load
the COMP output, that could affect the trip point
response.
quickly the current ramps up during a short.
include variations in the COMP comparator and filter, the
inductor L and DCR, the r
resistor dividers, the error amp reference voltage, the
oscillator frequency, switching noise, VCC voltage,
ambient temperature and airflow, and the layout of the
PCB.
but subject to the usual limitations of those circuits. For
example, sensing the output or FB voltage doesn’t always
directly correlate with output current.
try it out first under controlled conditions, either on an
EVAL board, the final circuit, or something close to it,
along with the power supply that will also be used.
Monitor VCC12 and VCC (to be sure they aren’t tripping
POR), the output and the COMP pin. A current probe
monitoring the output current is also very useful.
resistance; if they are too close, the circuit may not work
well. Calculate how long the FETs can sit at the higher
current. Is the short more likely from zero load or full
load?
happens if when the short is released.
can be optimized for the short condition. Within the
constraints of the stability criteria, smaller caps (in
general) may give a quicker response.
23
DS(ON)
of the FET, the FB
ISL6534
PCB Layout Considerations
General Layout Considerations
As in any high frequency switching converter, layout is very
important. Switching current from one power device to
another can generate voltage transients across the
impedances of the interconnecting bond wires and circuit
traces. These interconnecting impedances should be
minimized by using wide, short printed circuit traces. The
critical components should be located as close together as
possible using ground plane construction or single point
grounding.
Figure 21 shows the critical power components of the
converter, for either output channel. To minimize the voltage
overshoot the interconnecting wires indicated by heavy lines
should be part of ground or power plane in a printed circuit
board. The components shown in Figure 21 should be
located as close together as possible. Please note that the
capacitors C
capacitors. Locate the ISL6534 within 1-2 inches (or even
less, if possible) of the MOSFETs, Q1 and Q2. The circuit
traces for the MOSFETs’ gate and source connections from
the ISL6534 must be sized to handle up to 1.5A peak
current.
Figure 22 shows the circuit traces that require additional
layout consideration. Use single point and ground plane
construction for the circuits shown. Minimize any leakage
current paths on each of the SS pins and locate the
capacitors, C
current source is only 30µA. Provide local V
between VCC12 and PGND pins, as well as the VCC and
GND pins. Locate the capacitor, C
to the BOOT pin and PHASE node. Note that the PGND pins
are used only for the gate drivers and other output circuitry
(including the VCC12 decoupling capacitor); the GND pins
are used by the VCC pin, and the control circuitry. They
should be joined at a common point.
FIGURE 21. PRINTED CIRCUIT BOARD POWER AND
ISL6534
UGATE
LGATE
PGND
IN
ss
GROUND PLANES OR ISLANDS
and C
close to the SS pin because the internal
O
each represent numerous physical
V
Q2
Q1
RETURN
IN
BOOT
C
as close as practical
IN
L
CC12
O
C
O
decoupling
V
OUT
FN9134.1