ISL81601 datasheet(28/54 Pages) RENESAS

28 / 54 page

FN9299 Rev.3.1

Page 28 of 53

May 27, 2021

ISL81601

5. Functional Description

5.4

Tracking Operation

The ISL81601 can track an external supply. To implement tracking, connect a resistive divider between the external

supply output and ground. Connect the center point of the divider to the SS/TRK pin of the ISL81601. The resistive

divider ratio sets the ramping ratio between the two voltage rails. To implement coincident tracking, set the

tracking resistive divider ratio exactly the same as the ISL81601 output resistive divider given by Equation 5 on

page 29. Make sure that the voltage at SS/TRK is greater than 0.8V when the master rail reaches regulation.

To minimize the impact of the 2µA soft-start current on the tracking function, Renesas recommends using resistors

less than 10kΩ for the tracking resistive divider.

When the SS/TRK pin voltage is pulled down to less than 0.3V by the external tracking source, the prebias startup

DE mode function is enabled again. The output voltage may not be able to be pull down if the load current is not

high enough.

When Overcurrent Protection (OCP) is triggered, the internal minimum soft-start circuit determines the 50ms OCP

soft-start hiccup off-time.

5.5

Control Loops

The ISL81601 is a current-mode controller that can provide an output voltage above, equal to, or below the input

voltage. Referring to Figure 2 on page 2 (Typical Application circuit) and Figure 6 on page 7 (Block Diagram), the

Renesas proprietary control architecture uses a current sense resistor in series with the buck upper FET to sense the

inductor current in Buck or Boost mode. The inductor current is controlled by the voltage on the COMP pin, which

is the lowest output of the error amplifiers Gm1 - Gm4. As the simplest example, when the output is regulated to a

constant voltage, the FB_OUT pin receives the output feedback signal, which is compared to the internal reference

by Gm1. Lower output voltage creates higher COMP voltage which leads to higher PWM duty cycle to push more

current to the output. Conversely, higher output voltage creates lower COMP voltage which leads to lower PWM

duty cycle to reduce the current to the output.

The ISL81601 has four error amplifiers (Gm1-4) which can control output voltage (Gm1), input voltage (Gm2),

input current (Gm3), and output current (Gm4). In a typical application, the output voltage is regulated by Gm1,

and the remaining error amplifiers are monitoring for excessive input or output current or an input undervoltage

condition. In other applications, such as a battery charger, the output current regulator (Gm4) implements constant

current charging until a predetermined voltage is reached, at which point the output voltage regulator (Gm1) takes

control.

ISL81601 Scheda tecnica(PDF) 28 Page - Renesas Technology Corp