LTC3589 Linear Technology, LTC3589 Datasheet - Page 27

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

OPERATION
Table 13 shows command register and feedback divider
settings to enable slewing step-down switching regulator 1
between 1.2V and 1V in 70μs. The voltage ramp rate
control register bits VRRCR[1:0] are set to 10 which
selects a ramp rate of 1.75mV/μs at the DAC output.
The slew rate at the regulator output is a function of the
feedback resistor divider gain. In this example, the slew
is equal to 1.75 • (1 + 301/499) = 2.8mV/μs. Therefore, a
slew of 200mV will take 70μs. To initiate a change from
1.2V to 1V write 11 to voltage change control register bits
VCCR[1:0]. VCCR[1] selects target register B1DTV2 to
set the regulator reference input to 0.625V. VCCR[0] set
to 1 initiates the dynamic slew to go to the new voltage.
To slew back to 1.2V write 01 to command register bits
VCCR[1:0].
Table 13. Dynamic Slewing Example for Step-Down Switching
Regulator 1
COMMAND
REGISTER
VRRCR[1:0]
VCCR[1]
B1DTV1[4:0]
B1DTV2[4:0]
PUSHBUTTON OPERATION
State Event Diagram
Figure 5 shows the LTC3589 pushbutton state diagram.
Upon fi rst power application to V
reset circuit puts the pushbutton into power-down (PDN)
state and initiates a one second timer. Status pin RSTO is
pulled LOW until one second is timed out and the always-
alive LDO1 has indicated power good status. After the one
second interval the pushbutton circuit will transition to the
power-off (POFF) state. The pushbutton will not leave the
POFF state and enter the power-up state (PUP) until ON is
held LOW for at least 400ms (PB400ms) or until PWR_ON
V
OUT
10101
11111
01
=1.2V
0
V
OUT
10101
11111
01
=1V
1
IN
an internal power-on
Dynamic Slew Rate
Select DTV
Resistor Divider Shown
in Figure 3
R1 = 301kΩ
R2 = 499kΩ
PBSTAT Operation
PBSTAT goes LOW 50ms after the initial pushbutton ap-
plication (ON LOW) and will stay LOW for a minimum of
50ms. PBSTAT will go HIGH coincident with ON going
HIGH unless ON goes HIGH before the 50ms minimum
on-time.
is activated by the PWR_ON pin. When the controller enters
the PUP state the open drain WAKE pin releases HIGH.
The WAKE pin is typically used to enable the fi rst regulator
in a start-up sequence. The pushbutton state will stay in
PUP for fi ve seconds before transitioning to the power-on
(PON) state. Before leaving PUP , the PWR_ON pin must be
brought HIGH by the application to indicate that the system
rails are correct. If PWR_ON is not active at the end of fi ve
seconds the pushbutton controller will continue directly
through PON to the power-down (PDN) state and pull the
WAKE pin down. Three events will cause the pushbutton
to leave the PON state: 1) lowering the PWR_ON pin, 2)
forcing a hard reset by holding the ON pin LOW for fi ve
seconds, and 3) a fault condition is detected. Fault condi-
tions are low V
undervoltage of one of the regulator outputs. All regulator
enables, the ON input, and PWR_ON signals are inhibited
for one second while in the PDN state. After one second
in PDN the pushbutton controller returns to POFF .
Figure 5. Pushbutton Controller State Diagram
PB400ms OR
IN
PWR_ON
POFF
, device over temperature, or extended
1 SEC
POR
PUP
PDN
3589 F05
5 SEC
FAULT OR
PWR_ON
PON
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