ISL6111CRZA Ver la hoja de datos (PDF) - Renesas Electronics
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ISL6111CRZA Datasheet PDF : 16 Pages
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ISL6111
Introduction
The ISL6111, is an IC device designed to provide control and
protection of the four legacy PCI power supplies (+12V, -12V,
+5V and +3.3V) for a single PCI or PCI-X slot. Unlike the
widely used HIP1011, this device employs an active current
regulation (CR) method to provide system protection against
load faults.
Figure 1 illustrates the typical implementation of the ISL6111.
Key Feature Description and Operation
The ISL6111, 2 power MOSFETs and a few passive
components as configured in Figure 1, completes a power
control solution for the legacy supplies to a PCI slot. It provides
protection via a programmable maximum current regulation
(CR) level to the load for each supply. For the 3.3V and 5V
supplies, current monitoring is provided by sensing the voltage
across external current-sense resistors, and CR protection is
provided by active voltage modulation of external N-Channel
MOSFETs. For the +12V and -12V supplies, current monitoring
and CR protection are provided internally.
During initial power-up of the main bias supply pins (12VI), the
ENABLE input function is inhibited from turning on the
switches, this latch is held in the reset state until the bias
voltage is greater than 10V (POR rising). Additionally the
power good and fault reporting functions are also disabled at
this time and during the soft start duration.
During turn-on of the supplies onto their capacitive loads the
current limiting fail-safe is engaged, this limited current gives a
voltage ramp-up slew rate centered within the PCI specs. As
the startup is current-limited, the CRTIM timer is engaged
during the entire startup, as it should be. This eliminates the
otherwise destructive case of starting up into a dead short.
Depending on loading, the positive 3 supplies will start up and
exit current limiting in about 6ms -10ms. The -12V supply will
take much longer, as it has a fraction of the available charging
current into a potentially relatively very large load capacitance,
and the voltage has to slew to -12V. The -12V turn-on duration
can thus be several times as long extending to ~50ms for a
very capacitive (147µF) load in conjunction with a maximum
current load. In addition if the CR level is too low then it’s
possible that the load capacitance cannot fully charge in the
allowed for time, this is the consequence of the current
regulation limiting protection.
Once turned on, any subsequent over current (OC) condition
on any output results in the affected switch (external or
internal) to be put into its linear mode of operation, and the
current is regulated to the level determined by the choice of
external CRSET resistor value. An OC condition is defined as
a current level > the programmed CR level and that transitions
through the CR level with a quick ramp, <0.5µs. This CR level
is maintained until the OC condition passes or the CR duration
expires, whichever comes first. The CR duration is user
defined by the capacitor value on the CRTIM pin. Once in CR
mode, the CRTIM pin charges the capacitor with a 20µA
FN9146 Rev 1.00
Mar 2004
current until the voltage on CRTIM rises to ~2.8V, at which time
a turn-off latch is set on all 4 power FET switches. Also at this
time the open drain fault (FLTN) output is pulled low signalling
a latched off state. After a fault has been asserted and FLTN is
latched low, cycling ENABLE low will clear the FLTN latch.
On-chip references in the ISL6111 are used to monitor the +5V,
+3.3V and +12V outputs for under voltage (UV) conditions.
Once an UV condition is present the open drain power good
(PGOOD) output will pull low to indicate this.
Customizing Circuit Performance
Setting Current Regulation (CR) Level
The ISL6111 allows for easy and simultaneous custom
programming of the CR levels of all 4 supplies by simply
changing the resistor value between CRSET, (pin 18), and
ground. The RCRSET value and the CRSET 100A current
source create a reference voltage that is used in each of four
comparators. The IR voltages developed across the 3.3V and
5V sense resistors are applied to the inputs of their respective
comparators opposite this reference voltage. The +12V and -
12V currents are sensed internally with pilot devices. Because
of the internal current monitoring of the +12V and -12V
switches, their programming flexibility is limited to RCRSET
changes whereas the 3.3V and 5V over current regulation
levels depend on both RCRSET, and the value chosen for each
sense resistor.
See Table 1 to determine CR protection levels relative to
choice of RCRSET and RSENSE values.
Over current design guidelines and recommendations are as
follows:
1. For PCI applications, set RCRSET to 4.22k, and use 5m
1% sense resistors (see Figure 20). This RCRSET value
provides a nominal current trip level 110% to 130% higher
than the maximum specified current, to ensure full current
range use by the PCI load. The ISL6111 will trip off on a
slow increasing current ramp approximately 10% to 20%
lower than set CR level.
2. For non PCI specified applications, the following
precautions and limitations apply:
A. Do not exceed the maximum power of the integrated
NMOS and PMOS. High power dissipation must be coupled
with effective thermal management and prudent CR
durations. The integrated PMOS has an rDS(ON) of 0.35.
With 2.5A of steady load current on the PMOS device the
power dissipation is 2.2W. The thermal impedance of the
package is 31 degrees Celsius per watt, resulting in a 68°C
die temp rise thus limiting the average DC current on the
12V supply to about 2.5A maximum at +85°C ambient and
imposing an upper limit on the ROCSET resistor. Do not use
an RCRSET resistor greater than 15k.
The average current on the -12V supply should not exceed
0.8A. Since the thermal restrictions on the +12V supply are
more severe, the +12V supply restricts the use of the
ISL6111 to applications where the 12V supplies draw
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