Datasheet

LTC3589/LTC3589-1/
LTC3589-2
22
3589ff
For more information www.linear.com/3589
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
REGISTER[BIT]
VALUE SETTING
SCR1[3-2] 00*
01
10
Pulse-Skipping Mode
Burst Mode Operation
Forced Continuous Mode
OVEN[1] 0*
1
Disable
Enable
SCR2[1]
LTC3589/LTC3589-1
0*
1
Wait for Output Below 300mV Before Enable
Enable immediately
SCR2[1]
LTC3589-2
0*
1
Enable immediately
Wait for Output Below 300mV Before Enable
VCCR[3] 0*
1
Select Register B2DTV1 (V1) Reference
Select Register B2DTV2 (V2) Reference
VCCR[2] 1 Initiate Dynamic Voltage Slew
VRRCR[3-2] 00
01
10
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] 0*
1
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] 0*
1
2.25MHz Switching Frequency
1.125MHz Switching Frequency
B2DTV2[6] 0*
1
Switch on Clock Phase 1
Switch on Clock Phase 2
B2DTV2[7] 0*
1
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 I
2
C 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
REGISTER[BIT]
VALUE SETTING
SCR1[5-4] 00*
01
10
Pulse-Skipping Mode
Burst Mode Operation
Forced Continuous Mode
OVEN[2] 0*
1
Disable
Enable
SCR2[2]
LTC3589/LTC3589-1
0*
1
Wait for Output Below 300mV Before Enable
Enable Immediately
SCR2[2]
LTC3589-2
0*
1
Enable Immediately
Wait for Output Below 300mV Before Enable
VCCR[5] 0*
1
Select Register B3DTV1 (V1) Reference
Select Register B3DTV2 (V2) Reference
VCCR[4] 1 Initiate Dynamic Voltage Slew
VRRCR[5-4] 00
01
10
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] 0*
1
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] 0*
1
2.25MHz Switching Frequency
1.125MHz Switching Frequency
B3DTV2[6] 0*
1
Switch on Clock Phase 1
Switch on Clock Phase 2
B3DTV2[7] 0*
1
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
I
2
C 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-