ISL6112 Datasheet, PDF (14/31 Pages) Intersil Corporation – Dual Slot PCI-Express Power Controller

3V_GATE
3I_OUT
ISL6112
VAUX
C_FILTER
3V_OUT
IAUX
C_FILTER
FIGURE 11. 3VMAIN WOC SHUT-DOWN
The VAUX outputs have a different isolation protection
function. The VAUX isolation circuit does not incorporate a
fast-trip detector, instead they regulate the output current
into a fault to avoid exceeding their operating current limit.
The protection circuit will trip due to an overcurrent on VAUX
when the programmable CR duration timer, t_FILTER expires.
This use of the t_FILTER timer prevents the circuit from
tripping prematurely due to brief current transients. See
Figures 12 and 13 for illustrations of the VAUX protection
performance into a slight OC and more severe OC condition
respectively. The ISL6112 AUX current control responds
proportionally to the severity of the OC condition resulting in
faster VAUX pull-down and current regulation until t_FILTER
has expired.
VAUX
C_FILTER
IAUX
FIGURE 12. VAUX OC REGULATION AND SHUT-DOWN
FIGURE 13. VAUX WOC REGULATION AND SHUT-DOWN
Following a fault condition, the outputs can be turned on
again via the ON inputs (if the fault occurred on one of the
MAIN outputs), via the AUXEN inputs (if the fault occurred
on the AUX outputs), or by cycling both ON and AUXEN (if
faults occurred on both the MAIN and AUX outputs). A fault
condition can alternatively be cleared under SMI control of
the ENABLE bits in the CNTRL registers (See “Control
Register Bits D[1:0]” on page 19). When the circuit
protection trips, FAULT will be asserted if the outputs were
enabled through the Hot-Plug Interface inputs. If SMI is
enabled, INT will be asserted (unless interrupts are
masked). Note that INT is deasserted by writing a Logic 1
back into the respective fault bit position(s) in the STAT
register or the “Common Status Register (CS) 8-Bits,
Read/Write” on page 23.
The ISL6112 current regulation duration (t_FILTER) is
individually set for each slot by an external capacitor at the
CFILTER pin to GND. Once the CR mode is entered, the
external cap is charged with a 2.5µA current source to
1.25V. Once this threshold has been reached, the IC then
turns-off only the related faulted output(s), either both of the
MAIN (external FETs) and or the AUX (internal FET) and
sets the FAULT output low. For a desired t_FILTER, the value
for C_FILTER is given by Equation 4:
C_FILTER
=
-ⁿ---^o---^m-----ⁱ-ⁿ----^a---^l---^t--^F----^I--^L---^T----^E---^R---
500 k Ω
(EQ. 4)
where 500kΩ is the nominal V_FILTER/nominal I_FILTER and
where t_FILTER is the desired response time with the values
for I_FILTER and V_FILTER being found in the “Electrical
Specifications Table” on page 6. See Table 2 for nominal
t_FILTER times for given C_FILTER cap values.
14
FN6456.0
September 28, 2007