TPS51285A
TPS51285B
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SLVSBX0 –APRIL 2013
TPS51285A and TPS51285B have a PGOOD open drain output. During the start-up, if the feedback voltages for
both CH1 and CH2 exceed 90% of the reference voltage, the PGOOD becomes high with defined PGOOD delay
time. During the operation, if the feedback voltage rise beyond 115%(typ) for either switching regulator, PGOOD
turns low. If the feedback voltage falls below 60%(typ), the PGOOD turns low.
Table 1. Enabling and PGOOD State (TPS51285A; Always-on VREG3)
EN1
OFF
ON
EN2
OFF
OFF
ON
VREG5
OFF
ON
VREG3
ON
CH1 (5Vout)
OFF
CH2 (3.3Vout)
VCLK
OFF
ON
PGOOD
Low
OFF
OFF
ON
ON
ON
Low
OFF
ON
ON
ON
OFF
OFF
ON
Low
ON
ON
ON
ON
ON
High
Table 2. Enabling and PGOOD State (TPS51285B; Always-on VREG3 and VREG5)
EN1
OFF
ON
EN2
OFF
OFF
ON
VREG5
ON
VREG3
ON
CH1 (5Vout)
OFF
CH2 (3.3Vout)
VCLK
OFF
ON
PGOOD
Low
OFF
OFF
ON
ON
ON
ON
Low
OFF
ON
ON
ON
OFF
OFF
ON
Low
ON
ON
ON
ON
ON
High
VIN-UVLO_threshold
VIN
VREG3
EN_threshold
EN1
VREG5-UVLO_threshold
VREG5
95% of VOUT
Soft-Start Time (t
)
SS
5-V VOUT
Soft-Start Time
(t
)
SS(ramp)
EN_threshold
EN2
95% of VOUT
3.3-V VOUT
Soft-Start Time
(t
)
SS(ramp)
Soft-Start Time (t
)
SS
PGOOD
PG start-up delay (t
)
PGDLY
Figure 4. TPS51285A Timing Diagram of Start-up
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