LTC3589_15 datasheet(21/50 Pages) LINER

21 / 50 page

LTC3589/LTC3589-1/

LTC3589-2

3589fg

For more information www.linear.com/LTC3589

and rectifier. Since the inductor current is allowed to be

negative in forced continuous operation the step-down

switching regulator has the ability to sink output current.

TheLTC3589automaticallyforcesthestep-downswitching

regulator into forced continuous mode when dynamically

slewing the DAC voltage reference down.

When the LTC3589 step-down switching regulators are in

Burst Mode operation, they automatically switch between

fixed frequency pulse-skipping operation and hysteretic

Burst Mode control as a function of the load current. At

light loads the step-down switching regulators control

the inductor current directly and use a hysteretic control

loop to minimize both noise and switching losses. While

in Burst Mode operation, the output capacitor is charged

to a voltage slightly higher than the regulation point. The

step-down switching regulator then goes into a low power

sleep mode during which the output capacitor provides

the load current. In sleep mode, most of the switching

regulator’s circuitry is powered off to conserve battery

power.Whentheoutputvoltagedropsbelowtheregulation

point the regulator’s circuitry is powered on and another

burst cycle begins. As the load current increases, the time

betweenburstcyclesdecreases.Abovealoadcurrentabout

one-quarter rated output load, the step-down switching

regulators will switch to low noise constant-frequency

PWM operation.

Set the mode of operation for the step-down switching

regulators by using the I2C command register SCR1. Each

of the three regulators has independent mode control.

A step-down switching regulator may enter a dropout

condition when its input voltage drops to near its

programmed output voltage. For example, a discharging

battery voltage of 3.4V dropping to the regulators

programmed output voltage of 3.3V. When this happens

thedutycycleoftheP-channelMOSFETswitchisincreased

until it turns on continuously with 100% duty cycle. In

dropout,theregulatorsoutputvoltageequalstheregulators

input voltage minus the voltage drops across the internal

P-channel MOSFET and the inductor DC resistance.

operaTion

Table 5, Table 6, and Table 7 show the I2C command

regulators.

Table 5. Step-Down Switching Regulator 1 Command Register

Settings

COMMAND

VALUE SETTING

SCR1[1-0]

00*

Pulse-Skipping Mode

Burst Mode Operation

Forced Continuous Mode

OVEN[0]

Disable

Enable

SCR2[0]

LTC3589/

LTC3589-1

Wait for Output Below 300mV Before Enable

Enable Immediately

SCR2[0]

LTC3589-2

Enable Immediately

Wait for Output Below 300mV Before Enable

VCCR[1]

Select Register B1DTV1 (V1) Reference

Select Register B1DTV2 (V2) Reference

VCCR[0]

Initiate Dynamic Voltage Slew

VRRCR[1-0]

11*

Reference Slew Rate = 0.88mV/µs

Reference Slew Rate = 1.75mV/µs

Reference Slew Rate = 3.5mV/µs

Reference Slew Rate = 7mV/µs

B1DTV1[5]

Force PGOOD Low When Slewing

Normal PGOOD Operation When Slewing

B1DTV1[4-0]

11001* DAC Dynamic Target Voltage V1

B1DTV2[4-0]

11001* DAC Dynamic Target Voltage V2

B1DTV2[5]

2.25MHz Switching Frequency

1.125MHz Switching Frequency

B1DTV2[6]

Switch on Clock Phase 1

Switch on Clock Phase 2

B1DTV2[7]

Shutdown Regulator 1 Normally

Keep Regulator 1 Alive

* Denotes Default Power-On Value

Soft-Start

Soft-start is accomplished by gradually increasing the

input reference voltage on each step-down switching

regulator from 0V to the dynamic reference DAC output

level at a rate of 0.8V/ms. This allows each output to

rise slowly, helping minimize inrush current required to

charge up the regulator output capacitor. A soft-start cycle

LTC3589 Datasheet(PDF) 21 Page - Linear Technology

LTC3589 Datasheet(HTML) 21 Page - Linear Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

Datasheet Download

Link URL