ISL81601 datasheet(43/54 Pages) RENESAS

43 / 54 page

FN9299 Rev.3.1

Page 43 of 53

May 27, 2021

ISL81601

6. Protection Circuits

Protection Circuits

The converter output and input are monitored and protected against overload, overvoltage, and undervoltage conditions.

6.1

Input Undervoltage Lockout

The ISL81601 includes input UVLO protection, which keeps the device in a reset condition until a proper

operating voltage is applied. UVLO protection shuts down the ISL81601 if the input voltage drops below 3.2V. The

controller is disabled when UVLO is asserted. When UVLO is asserted, PGOOD is valid and is deasserted. If the

input voltage rises above 3.5V, UVLO is deasserted to allow the start-up operation.

6.2

VCC5V Power-On Reset (POR)

The ISL81601 sets its VCC5V POR rising threshold at 4V and falling threshold at 3.5V when supplied by VIN.

EXTBIAS can kick in only after VCC5V reaches its POR rising threshold.

6.3

Overcurrent Protection (OCP)

6.3.1

Input and Output Average Overcurrent Protection

As described in “Input and Output Average Current Monitoring and Regulation Loops” on page 30, the

ISL81601 can regulate both input and output current with close loop control. This provides a constant current

type of overcurrent protection for both input and output average current. It can be set to a hiccup type of

protection by selecting a different value of the resistor connected between LG2/OC_MODE and GND.

The input and output constant or hiccup average OCP set points IINCC and IOUTCC can be calculated by

Equations 9 and 10 in Input and Output Average Current Monitoring and Regulation Loops.

The average OCP mode is set by a resistor connected from the LG2/OC_MODE pin to ground during the

initiation stage before soft-start. During the initiation stage, the LG2/OC_MODE pin sources out typical 10µA

current IMODELG2 to set the voltage on the pin. If the pin voltage is less than typical 0.3V, the OCP is set to

Constant Current-mode. Otherwise, the OCP is set to hiccup mode.

In hiccup OCP mode, after the average current is higher than the set point for 32 consecutive switching cycles

the converter turns off for 50ms before a restart-up is issued.

6.3.2

First Level Pulse-by-Pulse Peak Current Limit

As shown in Figure 45 on page 31 in Input and Output Average Current Monitoring and Regulation Loops, the

inductor peak current is sensed by the shunt resistor RS_IN and op amp A1. When the voltage drop on RS_IN

reaches the set point VOCSET-CS typical 82mV, Q1 is turned off in Buck mode or Q3 is turned off in Boost

mode. The first level peak current limit set point IOCPP1 can be calculated by Equation 19.

IOCPP1

VOCSET CS

–

RS_IN

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

(EQ. 19)

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