LTC3589 datasheet(22/50 Pages) LINER

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LTC3589/LTC3589-1/

LTC3589-2

3589fe

while powering up following a fault condition. A soft-start

cycle is not triggered by a change of operating modes or

a dynamic voltage slew. During soft-start the converter is

forced to pulse-skipping mode regardless of the settings

in the SCR1 command register.

Table 6. Step-Down Switching Regulator 2 Command Register

Settings

COMMAND

VALUE SETTING

SCR1[3-2]

00*

Pulse-Skipping Mode

Burst Mode Operation

Forced Continuous Mode

OVEN[1]

Disable

Enable

SCR2[1]

LTC3589/LTC3589-1

Wait for Output Below 300mV Before Enable

Enable immediately

SCR2[1]

LTC3589-2

Enable immediately

Wait for Output Below 300mV Before Enable

VCCR[3]

Select Register B2DTV1 (V1) Reference

Select Register B2DTV2 (V2) Reference

VCCR[2]

Initiate Dynamic Voltage Slew

VRRCR[3-2]

11*

Reference Slew Rate = 0.88mV/μs

Reference Slew Rate = 1.75mV/μs

Reference Slew Rate = 3.5mV/μs

Reference Slew Rate = 7mV/μs

B2DTV1[5]

Force PGOOD Low When Slewing

Normal PGOOD Operation When Slewing

B2DTV1[4-0]

11001* DAC Dynamic Target Voltage V1

B2DTV2[4-0]

11001* DAC Dynamic Target Voltage V2

B2DTV2[5]

2.25MHz Switching Frequency

1.125MHz Switching Frequency

B2DTV2[6]

Switch on Clock Phase 1

Switch on Clock Phase 2

B2DTV2[7]

Shutdown Regulator 2 Normally

Keep Regulator 2 Alive

* Denotes Default Power-On Value

Switching EMI Control

The step-down switching regulators contain new pat-

ent pending circuitry to limit the edge rate of the switch

nodes SW1, SW2, and SW3. This new circuitry controls

the transition of the switch node over a period of a few

nanoseconds, signiﬁcantly reducing radiated EMI and

conducted supply noise while maintaining high efﬁciency.

OPERATION

Since slowing the slew rate of the switch nodes causes

efﬁciency loss, the slew rate of the step-down switching

regulators is adjustable using the I2C command register

B1DTV1 bits 6 and 7. Optimize efﬁciency or EMI as neces-

sary with four different slew rate settings. The power-on

default is the fastest slew rate, highest efﬁciency setting.

Table 7. Step-Down Switching Regulator 3 Command Register

Settings

COMMAND

VALUE SETTING

SCR1[5-4]

00*

Pulse-Skipping Mode

Burst Mode Operation

Forced Continuous Mode

OVEN[2]

Disable

Enable

SCR2[2]

LTC3589/LTC3589-1

Wait for Output Below 300mV Before Enable

Enable Immediately

SCR2[2]

LTC3589-2

Enable Immediately

Wait for Output Below 300mV Before Enable

VCCR[5]

Select Register B3DTV1 (V1) Reference

Select Register B3DTV2 (V2) Reference

VCCR[4]

Initiate Dynamic Voltage Slew

VRRCR[5-4]

11*

Reference Slew Rate = 0.88mV/μs

Reference Slew Rate = 1.75mV/μs

Reference Slew Rate = 3.5mV/μs

Reference Slew Rate = 7mV/μs

B3DTV1[5]

Force PGOOD Low When Slewing

Normal PGOOD Operation When Slewing

B3DTV1[4-0]

11001* DAC Dynamic Target Voltage V1

B3DTV2[4-0]

11001* DAC Dynamic Target Voltage V2

B3DTV2[5]

2.25MHz Switching Frequency

1.125MHz Switching Frequency

B3DTV2[6]

Switch on Clock Phase 1

Switch on Clock Phase 2

B3DTV2[7]

Shutdown Regulator 3 Normally

Keep Regulator 3 Alive

* Denotes Default Power-On Value

Operating Frequency

The switching frequency of each of the LTC3589 step-

down switching regulators may be independently set using

I2C command register bits B1DTV2[5], B2DTV2[5] and

B3DTV2[5]. The power-on default frequency is 2.25MHz.

Writing bit BxDTV2[5] HIGH will reduce the switching fre-

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