KTB8331

December 2021

– Revision 04b

Page 11 of 25

Kinetic Confidential

Functional Description

The KTB8331 is a highly efficient, high-performance, small buck regulator that operates from an input voltage of

2.7V to 5.5V and can output up to 3A. It integrates the main switch, synchronous rectifier switch, PWM control

circuitry, VOUT setting DAC, various protection features, and an I2C serial interface to configure the output voltage,

dynamic voltage scaling (DVS), control modes, and interrupts.

Control Scheme

The KTB8331 uses a proprietary adaptive on-time (AOT) PWM control scheme to maintain a nearly constant

switching frequency as input voltage and output voltage vary. Compared to typical current-mode PWM schemes,

the AOT control scheme provides quick response to line and load transients with excellent stability and wide

bandwidth, thereby minimizing output voltage droop and soar for dynamic loads, even with minimal output

capacitance. The adaptive on-time approximates fixed-frequency switching without using a fixed clock oscillator,

which eliminates the need to wait for the next clock before responding to a load transient.

The KTB8331 feedback loop also adds a proprietary, internally-compensated, integrating error amplifier to

remove the output voltage offset normally associated with other AOT, constant on-time (COT), and hysteretic

architectures.

Shutdown Mode

When the EN pin is low, the KTB8331 buck is in shutdown mode and draws very little current. In shutdown, the

I2C is still active, allowing read and write commands, as long as VIN is above VUVLO. Similarly, register contents

are retained during shutdown (and even when VIN is a little below VUVLO), as long as VIN is above VPOR=1.8V.

Hardware Enable

The KTB8331 buck regulator is turned on and off via hardware enable using the EN pin or via software enable

using I2C commands. The default register settings allow simple hardware control. For hardware enable, drive the

EN pin high. For hardware disable, drive the EN pin low.

Software Enable

For software enable/disable control, first write 0 into the EN0 bit (B7) of the VSEL0 configuration register (0x00),

and/or write 0 into the EN1 bit (B7) of the VSEL1 configuration register (0x01). The VSEL pin determines which

register is used. Then bring the EN pin high. After that, write 1 into the corresponding EN0 or EN1 bit to enable

the buck, and write 0 to disable the buck.

Soft-Start

The KTB8331 buck contains soft-start circuitry to ramp up VOUT slowly in order to reduce inrush current at VIN and

prevent the inductor current from reaching the peak current limit (ILX_PEAK) during startup. The soft-start ramp

rates are I2C programmable using the SLEW[2:0] bits (B6:4) in the CONTROL configuration register (0x02).

The default register setting provides the slowest ramp rate to accommodate cold startup with certain processor

cores. Once the processor is warm, faster ramps may be used. The slower rates are also better for applications

with large amounts of total output capacitance.

The inductor’s average current during soft-start is given by:

������������_������������ = ������������������������ × (������������ ������������������������) + ������������������������������_������������

⁄

where dV/dtSS is the soft-start ramp rate and ILOAD_SS is the load current during soft-start. Choose a ramp rate that

keeps the inductor current average below 3A, or even lower. As an example, if ILOAD_SS = 0, the fastest ramp rate

of dV/dtSS = 30mV/µs is still slow enough for IL_SS

≤ 3A with COUT ≤ 100µF. But if ILOAD_SS = 1.5A and COUT =

300µF, choose a dV/dtSS < 5mV/µs.

Setting the Output Voltage

The KTB8331 has two independent output voltage ranges. The low range is VOUT = 0.6V to 1.39375V in 6.25mV

steps. The high range is VOUT = 1.44V to 3.345V in 15mV steps. The range is I2C programmable using the

RANGE bit (B3) in the CONTROL configuration register (0x02). The default range setting is factory trimmed to

match the default output voltage setting

– see the Ordering Information section.