Start-Up; Start-Up: Swen Pin - Linear Technology Analog Devices LT8708-1 Datasheet

OPERATION
In addition, all LT8708-1s' V
nected to the LT8708's V
See the Quick-Start Multiphase Setup Guidelines section
in the Applications Information for a step-by-step design
procedure to add LT8708-1s to your system.

START-UP

Figure 3 illustrates the start-up sequence for the LT8708-1.

Start-Up: SWEN Pin

The LT8708-1 and LT8708's SWEN pins share the same
functionality. Refer to Start-Up: SWEN Pin of the LT8708
• SS CHARGES UP
and V should be con-
IN OUT
and V , respectively.
IN OUT
SHDN < 1.181V OR
V < 2.5V OR
INCHIP
T > 165°C
JUNCTION
CHIP OFF
• SWITCHER OFF
• LDOs OFF
• SWEN PULLED LOW
ICP AND ICN < 510mV
SOFT-START 2
SS > 0.8V
Figure 3. Start-Up Sequence (All Values are Typical)
For more information
data sheet for more details. SWEN is internally pulled
down by the LT8708 and/or LT8708-1(s) when the respec-
tive switching regulator is unable or not ready to operate
(see CHIP OFF and SWITCHER OFF 1 states in Figure 3).
In a multiphase system, the SWEN pins are connected
between all phases. Due to the internal SWEN pull-down
on the LT8708 and LT8708-1, the external pull-up for
the common SWEN node should always have a current
limiting resistor. Typically, the common SWEN node is
pulled up, through a resistor, to the LT8708's LDO33 pin.
In other cases, the common SWEN node can be digitally
driven through a current limiting resistor.
T < 160°C AND SHDN > 1.221V AND V
JUNCTION
((INTV AND GATEV
CC CC
OR LDO33 < 3.04V)
SWITCHER OFF 1
• SWITCHER DISABLED
• INTV AND LDO33 OUTPUTS ENABLED
CC
• SWEN AND SS PULLED LOW
(INTV
CC
LDO33 > 3.075V AND SWEN < 0.8V
SWITCHER OFF 2
• SWITCHER DISABLED
• INTV AND LDO33 OUTPUTS ENABLED
CC
• SS PULLED LOW
(INTV
CC
LDO33 > 3.075V AND SWEN > 1.208V
INITIALIZE
• SS PULLED LOW
• V FORCED TO COMMAND NEAR ZERO
C
CURRENT LIMIT
SS < 50mV
SOFT-START 1
• SS CHARGES UP
ICP OR ICN > 510mV
SOFT-START 3
• SS CHARGES UP
• SWITCHER ENABLED
• M1, M4 ON-TIME SOFT-START
• V IS FREE TO SLEW
C
SS > 1.8V
NORMAL MODE
• NORMAL OPERATION
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LT8708-1
> 2.5V AND
INCHIP
< 4.65V)
AND GATEV > 4.81V) AND
CC
AND GATEV > 4.81V) AND
CC
87081 F02
Rev 0
17