ISL81601 datasheet(31/54 Pages) RENESAS

31 / 54 page

FN9299 Rev.3.1

Page 31 of 53

May 27, 2021

ISL81601

5. Functional Description

Figure 45. Input and Output Average Current Monitoring and Regulation Loops

By connecting resistor RIM_IN and RIM_OUT on the IMON_IN and IMON_OUT pins, the ICS and IISEN current

signals are transferred to voltage signals. The RC networks on the IMON_IN and IMON_OUT pins

RIM_IN1/CIM_IN1/CIM_IN2 and RIM_OUT1/CIM_OUT1/CIM_OUT2 are needed to remove the AC content in the ICS

and IISEN signals and ensure stable loop operation. The average voltages at the IMON_IN and IMON_OUT

pins are regulated to 1.2V by Gm3 and Gm4 for constant input and output current control.

The input constant current loop set point IINCC is calculated by Equation 9. Refer to VAVOCP_CS on page 19 in

the Electrical Specifications table to estimate the set point tolerance.

The output constant current loop set point IOUTCC is calculated by Equation 10. Refer to VAVOCP_ISEN on

page 19 in the Electrical Specifications table on to estimate the set point tolerance.

Similar to the voltage control loops, the average current loop stability can be affected by many different factors

such as VIN, VOUT, switching frequency, inductor value, output and input capacitance, and the RC network on

the IMON_IN or IMON_OUT pin. Due to the high AC content in ICS and IISEN, large CIM_IN1 and CIM_OUT1

are needed. Larger CIM_IN1 and CIM_OUT1 can also make the loop more stable by giving a larger phase margin,

but the loop bandwidth is lower. For most applications 47nF is a good value for CIM_IN1 and CIM_OUT1.

CIM_IN2 and CIM_OUT2 are typically 1/10th to 1/30th of CIM_IN1 and CIM_OUT1 to filter high frequency noise.

RIM_IN1 and RIM_OUT1 are needed to boost the phase margin. A good starting value for RIM_IN1 and RIM_OUT1

is 5k. Optimize the final compensation network with iSim simulation and bench testing.

CS+

IMON_OUT

CS-

COMP

ISEN+

ISEN-

1.2V

Gm3

Gm4

IMON_IN

VIN

VOUT

RS_IN

RS_OUT

UG1

LG1

UG2

LG2

PH1

PH2

1.2V

RIM_IN

RIM_OUT

RIM_IN1

CIM_IN1

CIM_IN2

CIM_OUT2

CIM_OUT1

RIM_OUT1

RS_IN1

RS_IN2

CS_IN1

CS_IN2

CS_OUT1

CS_OUT2

RS_OUT1

RS_OUT2

VCS_OFFSET

VISEN_OFFSET

Ics

IISEN

IINCC

1.2 ICSOFFSET

–

xRIM_IN

RIM_INxRS_INxGmCS

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

(EQ. 9)

IOUTCC

1.2 IISENOFFSET

–

xRIM_OUT

RIM_OUTxRS_OUTxGmISEN

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

(EQ. 10)

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