7

Using the ISL6118EVAL1 Platform

Upon proper bias the PPTC, F1, has a nominal 400mA load

current passing through it which is the hold current rating for

that particular device. Removal of the PPTC is necessary to

isolate the ISL6118 as the PPTC load current is common to

the ISL6118EVAL1 bias connections.

By enabling either or both of the ISL6118H switches by

signaling TP3 and/or TP4 high (>2.4V) these switches are

also loaded with a nominal 400mA current.

Provided test points enable the evaluation of voltage loss

across the PPTC (TP9 - TP10) and likewise across the

ISL6118 enabled switches (TP9 - TP6 and TP7). Expect to

see 100% - 300% greater voltage loss across the PPTC than

the ISL6118 (see Figure 11 for ISL6118 vs PPTC voltage

loss comparison).

An overcurrent (OC) condition can be invoked on both the

ISL6118 and the PPTC by driving TP11 to +6V, causing SW1

to close and a nominal 0.94mA load is imposed. This

represents a current overload to the ISL6118 and is thus

quickly current regulated to the 600mA limit. If the OC

duration extends beyond the nominal 12ms of the internal

ISL6118 timer then the output is latched off and the fault

output is asserted by being pulled low turning on the

appropriate FAULT LED. (Please note: the labeling for the

FAULT-1 and FAULT-2 is reversed.) The eval board is

designed to only invoke a OC condition on channel 2 (TP4)

so that a channel to channel isolation evaluation in the

presence of a OC condition can be evaluated.

The primary function of any OC protection device is to

quickly isolate the voltage bus from a faulty load. Unlike the

PPTC and other vendor available IC products, the ISL6118

internal timer that starts upon OC detection provides

consistent protection that is independent of temperature.

Figures 11 through 13 illustrate the comparative efficiency

and effectiveness of the ISL6118 vs the PPTC in protecting

and isolating a faulty load capable from drooping the system

bus in that system.

FIGURE 11. ISL6118 vs PPTC INTO 8.2

Ω LOAD

FIGURE 12. ISL6118 vs PPTC INTO 3.5

Ω LOAD

FIGURE 13. ISL6118 vs PPTC WITH EXTENDED 3.5

Ω LOAD

VOLTAGE (0.5V/DIV)

3.32V

ISL6118

3.29V (0.075

Ω)

0.4A HOLD

CURRENT PPTC

2.93V (1.1

Ω)

GND

VOLTAGE (0.5V/DIV)

TIME (4ms/DIV)

VIN

ISL6118 CR

12ms PERIOD

0.4A HOLD CURRENT PPTC OUT

ISL6118 OUT

VOLTAGE (0.5V/DIV)

TIME (4s/DIV)

ISL6118 OUT

0.4A HOLD CURRENT PPTC OUT

VIN

2.3V AT 10s

1.5V AT 30s

ISL6118