R34DS0022EU0102 Rev.1.02

Page 27

Feb 15, 2023

ISL73847SEH Datasheet

5.15 Fault Handling

5.15.1

Cycle-by-Cycle Current Limit

The current flowing through the inductor is monitored through the current-sense inputs using a sense resistor or

DCR sensing. When the input reaches the current limit threshold (VPCL), the PWM pulse is terminated to limit the

peak current. A single cycle-by-cycle current limit event does not trigger hiccup but if there are four current limit

events in an eight clock cycle window, the ISL73847SEH enters hiccup.

5.15.2

Inductor Peak Overcurrent Protection

If the output current increases even after triggering the cycle-by-cycle current limit, the ISL73847SEH has a

second overcurrent protection (VPOC and VNOC). If triggered, it drives the PWM outputs to mid-level (tri-state the

power stage) and enters hiccup. If the initial fault continues to persist or another fault occurs during the next

soft-start, the cycle repeats indefinitely and stays in hiccup. The overcurrent protection protects against both

positive and negative overcurrent conditions.

5.15.3

Overvoltage and Undervoltage Fault

The ISL73847SEH has overvoltage and undervoltage protection that is triggered when V(FB, OV) or V(FB, UV) are

exceeded. If the V(FB, OV) or V(FB, UV) levels are reached, the part enters hiccup.

5.15.4

FLT Pin

The FLT pin is a bi-directional communication pin between the ISL73847SEH controller and the ISL73041SEH

driver. On the ISL73847SEH, the FLT pin is low and is an I/O when the part is not ready (during startup) or when it

encounters a fault. The ISL73041SEH uses this pin to communicate if it is not ready to accept input or

encountered a fault on its end. In either case, if the FLT pin is pulled low by the ISL73041SEH, the ISL73847SEH

tri-states the output (mid level) and enters hiccup. The FLT pin is an input while switching (during and after

startup).

5.15.5

Oscillator and Sync Input Fault

If the FS pin is inadvertently shorted to ground, this causes a fault in the controller and switching would be

inhibited.

The ISL73847SEH has the ability to synchronize to an external frequency. If the external clock is not present or if

the internal clock frequency is not less than 15% of the required external clock frequency, the part reverts to the

internal oscillator and continues operation. When the external sync input returns or if the internal clock frequency

is less than 15% of the required external clock frequency, the ISL73847SEH immediately switches back to the

external clock, as shown in Figure 46.

Figure 46. Switching between Internal Oscillator and External Oscillator on SYNC-I

(External clock frequency changed from 1MHz to 1.15MHz)