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LTC3589/LTC3589-1/

LTC3589-2

3589fe

Table 13. Slewing DAC Command Register Control Summary

COMMAND

FUNCTION

VCCR[0], VCCR[2],

VCCR[4], VCCR[6]

Voltage Change Control Register

G0 / Slew

Write a 1 to Initiate a Slew to the Voltage

Selected in VCCR[1], VCCR[3], VCCR[5],

VCCR[7] Respectively.

Bits are Reset to 0 at the End of the Slew

Operation.

VCCR[1], VCCR[3],

VCCR[5], VCCR[7]

Voltage Change Control Register

Dynamic Target Select

Write a 0 to Select Voltage V1 Stored in

Registers B1DTV1[4-0], B2DTV1[4-0],

B3DTV1[4-0], L2DTV1[4-0].

Write a 1 to Select Voltage V2 in

Registers B1DTV2[4-0], B2DTV2[4-0],

B3DTV2[4-0], L2DTV2[4-0].

B1DTV1[4-0], B2DTV1[4-0],

B3DTV1[4-0], L2DTV1[4-0]

Dynamic Target Voltage 1

Five Bits Corresponding to V1 Output

from Each DAC.

B1DTV1[5], B2DTV1[5],

B3DTV1[5], L2DTV1[5]

PGOOD Mask

Write a 1 to Continue Normal PGOOD

Operation When Slewing.

Write a 0 to Force PGOOD to Pull Low

During Slew.

B1DTV2[4-0], B2DTV2[4-0],

B3DTV2[4-0], L2DTV2[4-0]

Dynamic Target Voltage 2

Five Bits Corresponding to V2 Output

from Each DAC.

VRRCR[1-0], VRRCR[3-2],

VRRCR[5-4], VRRCR[7-6]

Voltage Ramp Rate Control

Two Bits That Set the DAC Output Slew

Rate for Step-Down Switching Regulator

and LDO2.

Setting and Slewing the DAC Outputs

The 5-bit word in dynamic target voltage command reg-

isters B1DTV1, B2DTV1, B3DTV1, and L2DTV1 programs

reference voltage V1. The 5-bit word in command regis-

ters B1DTV2, B2DTV2, B3DTV2, and L2DTV2 programs

reference voltage V2. A resistor divider network on the

output and feedback pins of the regulators set their

output voltage.

Capacitor Selection

Low ESR ceramic capacitors should be used at both the

output and input supply of the buck-boost switching

regulator. Only X5R or X7R ceramic capacitors should

be used because they retain their capacitance over wider

voltage and temperature ranges than other ceramic types.

A 22μF capacitor is sufficient for the buck-boost switch-

ing regulator output. For good transient response and

stability the output capacitor should retain at least 10μF of

capacitance over operating temperature and bias voltage.

Place at least 4.7μF decoupling capacitance as close as

possible to PVIN4 pin. Refer to Table 12 for recommended

ceramic capacitor manufacturers.

Table 12. Ceramic Capacitor Manufacturers

AVX

www.avxcorp.com

Murata

www.murata.com

Taiyo Yuden

www.t-yuden.com

Vishay Siliconix

www.vishay.com

TDK

www.tdk.com

SLEWING DAC REFERENCE OPERATION

Controlling the DAC References

The three LTC3589 step-down switching regulators and

linear regulator LDO2 have programmable DAC reference

inputs. Each DAC is programmable from 0.3625V to 0.75V

in 12.5mV steps:

VOUT = 1+

• (0.3625+BxDTVx • 0.0125)(V)

The DAC references may be commanded to independently

slew between two voltages at one of four selectable slew

rates. Table 13 summarizes the command registers used

to control slewing DAC operation.

OPERATION

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