ISL81601 datasheet(44/54 Pages) RENESAS

44 / 54 page

FN9299 Rev.3.1

Page 44 of 53

May 27, 2021

ISL81601

6. Protection Circuits

6.3.3

Second Level Hiccup Peak Current Protection

To avoid any false trip in peak current-mode operation, a minimum on or blanking time is set to the PWM

signal. The first level pulse-by-pulse current limit circuit cannot further reduce the PWM duty cycle in the

minimum on-time. In output dead short condition especially at high VIN, the inductor current runs away with

the minimum on PWM duty. The ISL81601 integrates a second level hiccup type of peak current protection.

When the voltage drop on RS_IN reaches the set point VOCSET-CS-HIC (typical 100mV), the converter turns off

by turning off all four switches Q1, Q2, Q3, and Q4 for 50ms before a re-start up is issued. The second level

peak current protection set point IOCPP2 can be calculated by Equation 20.

6.3.4

Pulse-by-Pulse Negative Peak Current Limit

In cases of reverse direction operation and OVP protection, the inductor current goes to negative. The negative

current is sensed by the shunt resistor RS_OUT and op amp A2 shown in Figure 45. When the voltage drop on

RS_OUT reaches the set point VOCSET-ISEN (typical -59mV), Q2 and Q4 are turned off and Q1 and Q3 are turned

on. The negative peak current limit set point IOCPPN can be calculated by Equation 21.

The device can be damaged in negative peak current limit conditions. In these conditions, the energy flows from

output to input. If the impedance of the input source or devices is not low enough, the VIN voltage increases.

When VIN increases to higher than its maximum limit, the IC can be damaged.

6.4

Overvoltage Protection

The overvoltage set point is set at 114% of the nominal output voltage set by the feedback resistors. In the case of

an overvoltage event, the IC attempts to bring the output voltage back into regulation by keeping Q1 and Q3 turned

off and Q2 and Q4 turned on. If the OV condition continues, the inductor current goes negative to trip the negative

peak current limit. The converter reverses direction to transfer energy from the output end to the input end. Input

voltage is pushed high if the input source impedance is not low enough. The IC can be damaged if the input voltage

goes to higher than its maximum limit. If the overvoltage condition is corrected and the output voltage drops to the

nominal voltage, the controller resumes work in normal PWM switching. The OV pin is pulled high when output

OVP trips.

6.5

Over-Temperature Protection

The ISL81601 incorporates an over-temperature protection circuit that shuts the IC down when a die temperature

of +160°C is reached. Normal operation resumes when the die temperature drops below +145°C through the

initiation of a full soft-start cycle. During OTP shutdown, the IC consumes only 100µA current. When the

controller is disabled, thermal protection is inactive. This helps achieve a very low shutdown current of 5µA.

IOCPP2

VOCSET-CS-HIC

RS_IN

--------------------------------------------

(EQ. 20)

IOCPPN

VOCSET-ISEN

RS_OUT

--------------------------------------

(EQ. 21)

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