ISL6160 Datasheet, PDF (6/11 Pages) Intersil Corporation – InfiniBand +12V Bulk and +5V Auxiliary Power Controller

ISL6160
shutting down the VB supply. The length of this period is set by
the value of a capacitor between CTIM and VB_RET. See table
2 for CTIM value and resulting l current regulation period.
TABLE 2.
C_TIM CAPACITOR
0.001µF
NOMINAL CURRENT REGULATION
PERIOD
93µs
0.01µF
930µs
0.022µF
2ms
0.047µF
4.4ms
0.1µF
9.3ms
NOTE: Nominal time-out period in seconds = C_TIM x 93kΩ.
The programmed current level is held until either the OC event
passes or the time out period expires. If the former is the case
then the N-Channel MOSFET is fully enhanced and the CTIM
capacitor is discharged. Once CTIM charges to 1.87V, signaling
that the time out period has expired an internal latch is set
whereby the FET gate is quickly pulled to 0V turning off the N-
Channel MOSFET switch, isolating the faulty load. Monitor the
CTIM pin for an OC latch off indication. This pin will rise rapidly
from 1.9V to VB once the time out period expires. If no CTIM
capacitor is implemented the VB Secondary Rail will
immediately latch-off in an OC event.
The ISL6160 responds to a severe overcurrent load (defined as
a voltage across the sense resistor >150mV over the CR Vth
set point) by immediately, driving the N-Channel MOSFET gate
to 0V in ~1µs. The controlled gate voltage is then ramped up
turning on the N-Channel MOSFET to the programmed current
limit level. This is the start of the time out period.
The VB control circuitry is reset after an OC latch-off
condition by a low level on the VB _ON pin and is turned on
again by the VB_ON pin being driven high.
The DC-DC_EN pin is used to enable an accompanying DC-
DC converter on the IM when the VB Secondary Rail is within
specification. This pin pulls up to VB through a pull-up resistor
when the V_ISEN is > 10V. This pin can also be used as an
undervoltage (UV) signal as it will pull low once the V_ISEN falls
below 9.2V. This signal can also be passed to a system
controller chip or used to drive an LED for observation. The
state of this signal does not impact the VB current control
function.
For the VA supply the ISL6160 features fully integrated current
monitoring and regulation, an integrated 125mΩ N-channel
MOSFET power switch (Figure 13.) and a current limited delay
to latch-off for system protection. The current sense and limiting
circuitry sets the CR limit to a nominal 1A, making this device
well suited for the VA requirements. See Figure 14. for current
regulation performance. The ISL6160 provides VA OC fault
notification if needed, accurate current regulation and a
consistent timed latch-off thus isolating and protecting the
voltage bus in the presence of an OC event or short circuit. The
OC event to CR time is inversely related to the OC magnitude,
see Figure 15 and the 12mS time (Figure 16) to latch-off is
independent of thermal condition .
The ISL6160 VA_ENn pin provides on-off control over the
VA_IN supply when VA is greater than 2.5V. The switch is
asserted on and starts the soft start ramp once VA_ENn < 0.8V.
Once the VA is latched off due to an OC condition the
VA_Fltn pin will go low indicating the faulted state to a control
chip, indicator display or alarm.
The ISL6160 VB and VA control circuitries are isolated from
each other, thus there are no sequencing restrictions to be
considered.
Description of ISL6160 Operation in an
InfiniBand Module (IM)
On the IM the ISL6160 is necessarily paired with a DC-DC
converter to convert 12V to a lower usable voltage for the
application circuitry. Figure 2 shows a block diagram of a
complete IM power sequencer and power supply using the
ISL6160 and a HIP6006, single output PWM DC-DC converter.
Upon insertion, the InfiniBand (IB) backplane secondary side
connector sequences connections between the backplane
and the inserted module in the following order:
1. VA_Ret and VB_Ret
2. VA_In and VB_In
3. the 6 InfiniBand Module (IM) control signals and
4. VBx_En_L and IMxPRst due to the staggered lead lengths.
The ISL6160 VA undervoltage lockout feature prevents turn-on
of VA until VA_In > 2.5V. It then enables the VA soft start and
power up. The VA rising voltage output is a current limited ramp
so that both the inrush current and voltage slew rate are limited,
(Figure 18) independent of load. This reduces supply droop
due to surge and eliminates the need for additional external
EMI filters. During operation, once a VA OC condition is
detected the output current is limited to 1A for 12mS to allow
transient conditions to pass. If the IC is still in current limit mode
after the current limit period has elapsed, the output is then
latched off. The VA to the IM circuitry is latched off until reset by
the disconnection and reconnection of the IM from the chassis
backplane.
Once VB_In is connected, it is held off from the VB Secondary
Rail until the ISL6160 VB_On pin is signaled high. This is
accomplished through the exclusive OR of both the VBx_En_L
and the Local_Power_Enable being asserted. At that time the
ISL6160 turns on the VB in a soft start mode protecting the
primary supply rail from sudden in-rush current. During turn-on,
the external gate capacitor of the N-Channel MOSFET (VB
switch) is charged with a 20µA current source resulting in a
programmable ramp (soft start turn-on). An internal charge
pump supplies the gate drive for the 12V VB supply switch
driving the MOSFET gate to VB +5V. Once the VB Secondary
Rail ramps to 10V the DC-DC_En pin is pulled high thus
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