6

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.

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 ~1

µs. 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

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 125m

Ω 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 20

µA 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

TABLE 2.

NOMINAL CURRENT REGULATION

PERIOD

0.001

µF93µs

0.01

µF930µs

0.022

µF2ms

0.047

µF4.4ms

0.1

µF9.3ms

ISL6160