LTC3589 Linear Technology, LTC3589 Datasheet - Page 17

• Manufacturer Part Number: LTC3589
• Description: 8-Output Regulator
• Manufacturer: Linear Technology

OPERATION
feature is to guarantee proper startup sequencing. This
feature and the 2k pull-down resistors may be overridden
by bit settings in command register SCR2.
To help reduce LDO power loss in the system, the regula-
tors have dedicated supply inputs that may be lower than
the main V
each of the output pins LDO2, LDO3, and LDO4.
LDO Regulator 2
One of the LTC3589 dynamic slewing DACs serves as the
reference input of LDO2. The output range of LDO2 is set
using an external resistor divider connected from LDO2 to
the feedback pin LDO2_FB as shown in Figure 2. Set the
output voltage of LDO2 using the following formula:
L2DTVx is the fi ve bit word contained in the LDO2 dynamic
target voltage 1 (L2DTV1) or the LDO2 dynamic target
voltage 2 (L2DTV2) command registers. The default value
of L2DTVx[4-0] is 11001 to output a reference voltage
of 0.675V. LDO2 is enabled by writing bit 4 in the output
voltage enable (OVEN) command register to 1 or driving
the LDO2_EN pin high. Whenever the command is given to
slew LDO2 DAC reference to a lower voltage an integrated
2k pull down resistor is connected to LDO2 output.
V
OUT
TO 0.75V
= 1+
0.3625V
IN
Figure 2. LDO2 Application Circuit
supply. Connect a low ESR 1μF capacitor to
R2
R1
• (0.3625 + L2DTVx • 0.0125)
DAC
EA
PV
IN
5
LDO2
3589 F02
FB
R1
R2
1μF
Table 1. Shows the I
to control LDO2.
Table 1. LDO 2 Command Register Settings
COMMAND
REGISTER[BIT]
OVEN[4]
SCR2[4]
VCCR[5]
VCCR[6]
VRRCR[7-6]
L2DTV1[4-0]
L2DTV1[5]
L2DTV1[7]
L2DTV2[4-0]
* Denotes Default Power-On Value
LDO Regulator 3
LDO3 is a fi xed 1.8V output regulator. LDO3 is enabled
by driving pin EN_LDO34 high or by writing command
register OVEN[5] to 1.
Table 2 shows the I
to control LDO3.
Table 2. LDO 3 Command Register Settings
COMMAND
REGISTER[BIT]
OVEN[5]
SCR2[5]
* Denotes Default Power-On Value
VALUE
VALUE
11001* DAC Dynamic Target Voltage V1
11001* DAC Dynamic Target Voltage V2
0*
0*
1
0*
1
0*
1
0*
1
0*
1
1
00*
01
10
11
0*
1
1
2
2
C command register settings used
C command register settings used
SETTING
Disable
Enable
Wait for Output Below 300mV Before Enable
Enable Immediately
SETTING
Disable
Enable
Wait for Output Below 300mV Before Enable
Enable Immediately
Select Register L2DTV1 (V1) Reference
Select Register L2DTV2 (V2) Reference
Initiate Dynamic Voltage Slew
Reference Slew Rate = 0.88mV/μs
Reference Slew Rate = 1.75mV/μs
Reference Slew Rate = 3.5mV/μs
Reference Slew Rate = 7mV/μs
Force PGOOD Low When Slewing
Normal PGOOD Operation When Slewing
Shutdown LDO2 Normally
Keep LDO2 Alive
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LTC3589
17
3589p