LTC3882_15 Datasheet, PDF (51/104 Pages) Linear Technology – Dual Output PolyPhase Step-Down DC/DC Voltage Mode Controller with Digital Power System Management

LTC3882
APPLICATIONS INFORMATION
V_OUT
(1V/DIV)
RUN
(5V/DIV)
200µs/DIV
3882 F31
Figure 31. Example of 1ms TON_RISE
1V/DIV
VOUT4
VOUT3
VOUT2
VOUT1
100ms/DIV
3882 F32
Figure 32. LTC3882 Time-Based Supply Sequencing
1V/DIV
VOUT4
VOUT3
VOUT2
VOUT1
100ms/DIV
3882 F33
Figure 33. LTC3882 Time-Based Coincident Supply Ramping
1V/DIV
VOUT4
VOUT3
VOUT2
VOUT1
greatly simplify actual system development because rails
can be re-sequenced without a hardware change as final
product requirements evolve. The LTpowerPlay GUI and
LTC3882 onboard EEPROM can be used for this task,
avoiding the need for firmware development to modify turn
on/off relationships between rails. Entire power systems
can then easily be scaled up or down, facilitating reuse of
proven hardware macro designs.
Voltage-Based Output Sequencing
The LTC3882 is capable of voltage-based output sequenc-
ing. For concatenated events between members of the
LTC388x family, it is possible to control one RUN pin from
a GPIO pin of a different controller as shown in Figure 35.
The GPIO output must be configured to only propagate
VOUT_UV_UF (MFR_GPIO_PROPAGATE programmed to
0x1000), and that IC must have MFR_GPIO_RESPONSE set
to ignore (0x00). This configuration hardware disables the
next downstream controller anytime the output is below the
specific UV threshold. Use of the unfiltered V_OUT UV fault
limit is recommended because there is less delay between
crossing the UV threshold and the GPIO pin releasing.
When this UV propagation is selected, there is a 250µs
deglitching filter on the GPIO output to assure the signal
does not toggle repeatedly at lower values of TON_RISE/
FALL due to noise on V_OUT. If unwanted transitions still
occur on GPIO due to noise or longer rise/fall settings,
place a capacitor to ground on the GPIO pin to filter the
waveform. The RC time-constant of the filter should be
low enough to assure no appreciable delay is incurred.
A value of 300μs to 500μs will provide some additional
filtering without significantly delaying the trigger event.
START
RUN 0
RUN 1
RUN 0
RUN 1
LTC3882
LTC3882
GPIO0 = V_{OUT0_UVUF}
GPIO1 = V_{OUT1_UVUF}
GPIO0 = V_{OUT0_UVUF}
GPIO1 = V_{OUT1_UVUF}
100ms/DIV
3882 F34
Figure 34. LTC3882 Time-Based Ratiometric Ramping
TO NEXT CHANNEL
IN THE SEQUENCE
3882 F35
Figure 35. Cascade Sequencing Configuration
3882f
For more information www.linear.com/LTC3882
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