LTC3815_15 Datasheet, PDF (15/42 Pages) Linear Technology – 6A Monolithic Synchronous DC/DC Step-Down Converter with Digital Power System Management

LTC3815
Operation
above the reference voltage, tracking is disabled and the
feedback voltage will regulate to the reference voltage. Ei-
ther concurrent or ratiometric tracking can be implemented
by connecting the track voltage to either the I_REF pin or the
TRACK/SS pin as described in the applications section.
Output Power Good
When the LTC3815’s output voltage is within the its power
good window of the regulation point, the output voltage is
good and the PGOOD pin is pulled high with an external
resistor. Otherwise, an internal open-drain pull-down
device (40Ω) will pull the PGOOD pin low. This window
is programmed by the PGLIM pin by connecting it to a
resistive divider to the REF pin. This allows the the PGOOD
window to be programmed as a percentage of the output
voltage reference. If PGLIM is tied to V_IN, the PGOOD
window defaults to ±10%.
The PGOOD Filter Delay pin provides a user program-
mable delay from output voltage good to the rising edge
of PGOOD. A wide range of delays from 200μs to 25ms
can be user programmed by a configuration resistor
connected to the PGFD pin. To prevent unwanted PGOOD
glitches during transients or dynamic V_OUT changes, the
LTC3815’s PGOOD falling edge includes a blanking delay
of approximately 16 switching cycles.
Continuous operation is forced during OV and UV condition
except during start-up when the TRACK/SS pin is ramping
up to the internal reference voltage.
Master Shutdown and Standby Modes
There are three different ways to shut down the LTC3815:
RUN_MSTR pin, RUN_STBY pin, and the ON bit of the
OPERATION command.
Pulling the RUN_MSTR pin low forces the LTC3815 into a
master shutdown state, turning off both power MOSFETs,
the internal control circuitry, the ADC converter, and the
PMBus interface. Also, all data written to the internal
registers, such as the margin register, will be reset to the
power-on state. Supply current in this mode is typically
less than 1μA.
Pulling RUN_STBY pin low or clearing the ON bit in the
OPERATION register puts the LTC3815 in a standby mode
where the regulator is off but the ADC and PMBus are still
active. In standby mode the LTC3815 will still respond to
the PMBus host but will only refresh the telemetry data
at 1Hz rate instead of 25Hz. In standby mode the supply
current is 120μA. Exiting standy mode with the rising
edge of the ON bit resets all faults and the ALERT pin. All
data written to the internal registers, such as the margin
registers, is not affected by this shutdown mode, so when
RUN_STBY is re-asserted, the V_OUT will power back up
to the last value written prior to shutdown (as long as no
change to the margin registers or MARGIN pin was made
during shutdown).
For the switcher to run and provide output regulation all
three must be asserted, i.e. RUN_MSTR and RUN_STBY
pins high and OPERATION ON bit set. At power on or
master shutdown, the ON bit is automatically set in the
OPERATION register. Pulling RUN_MSTR low overrides
the standby controls and puts the LTC3815 in master
shutdown.
Table 2. Shutdown Modes
INPUT CONDITIONS
ON/OFF STATES
RUN_MSTR RUN_STBY ON BIT V_OUT PMBus ADC
I_Q
High
X
0 OFF ON 1Hz Refresh 120μA
(see Note)
Low
X
X OFF OFF
OFF
<1μA
High
High
1 ON ON
25Hz
5mA
Refresh
High
Low
X OFF ON 1Hz Refresh 120μA
(see Note)
Note: Only V_IN, V_OUT and temperature telemetry are refreshed.
Short Circuit Protection
The LTC3815 has a precision cycle-by-cycle current limit
to prevent inductor saturation in a short circuit condition.
The valley of the inductor current is guaranteed to not
exceed 6A ±10%. The maximum cycle-by-cycle inductor
current is therefore limited to 6A + 10% + ΔI_L, where ΔI_L
depends on the inductor valley and operating frequency but
is typically ~2A. Internal control circuitry also guarantees
smooth recovery with no output voltage overshoot once
the short is removed.
For more information www.linear.com/LTC3815
3815p
15