LTC3815_15 Datasheet, PDF (10/42 Pages) Linear Technology – 6A Monolithic Synchronous DC/DC Step-Down Converter with Digital Power System Management

LTC3815
Pin Functions
R_T (Pin 1): Oscillator Frequency. This pin provides two
modes of setting the constant switching frequency. Con-
nect a resistor from R_T pin to ground to program the
switching frequency from 400kHz to 3MHz. Tying this
pin to V_IN enables the internal 1MHz oscillator frequency.
ASEL (Pin 2): Serial Bus Address Configuration Input.
Connect a ±1% resistor from this pin to ground in order
to select the 3 LSBs of the serial bus interface address.
(see Table 5).
MARGIN (Pin 3): Fast Margining Select. In the default
mode when this pin is floating, the reference voltage margin
offset is changed with MFR_VOUT_COMMAND through
the serial interface. If this pin is pulled high, the reference
voltage margin offset is immediately ramped to the value
pre-stored in the MFR_VOUT_MARGIN_HIGH register.
If this pin is pulled low, the reference voltage margin
offset is immediately ramped to the value pre-stored in
MFR_VOUT_MARGIN_LOW register.
WP (Pin 4): Write Protect Pin. Pulling this pin high disables
writes to MFR_VOUT_COMMAND, MFR_VOUT_MARGIN_
HIGH, and MFR_VOUT_MARGIN_LOW. When this pin is
grounded, there are no write restrictions.
ALERT (Pin 5): Open Drain Digital Output. Connect the
system SMBALERT interrupt signal to this pin. A pull-up
resistor is required in the application.
CLKOUT (Pin 6): Clock Out Signal for 2-Phase Operation.
The phase of this clock is 180° with respect to the internal
clock. Signal swing is from V_IN to GND.
SDA (Pin 7): Serial Bus Data Input and Output. A pull-up
resistor is required in the application.
SCL (Pin 8): Serial Bus Clock Input. A pull-up resistor is
required in the application.
MODE/SYNC (Pin 9): Mode Selection and External Clock
Input. If this pin is tied to V_IN, discontinuous mode is
enabled at light loads. If this pin is connected to ground,
forced continuous mode is selected. Driving the MODE/
SYNC pin with an external clock signal will synchronize
the switching frequency to the applied frequency. There
is an internal 20k resistor to ground on this pin.
SW (Pins 10, 11, 13, 14, 18, 19, 21, 22, 23): Switching
Node. This pin connects to the drains of the internal main
and synchronous power MOSFET switches.
NC (Pins 12, 20): No Connection. Can be connected to
ground or left open. This pin does not connect to any
internal circuitry.
PV_IN (Pins 15-17): Power Input Supply. PV_IN connects to
the source of the internal P-channel power MOSFET. This
pin is independent of V_IN and may be connected to the
same voltage or to a lower voltage supply.
PGOOD (Pin 29): Power Good. This open-drain output
is pulled down to SGND on start-up and while the output
voltage is outside the power good window set by the PGLIM
pin. If the output voltage increases and stays inside the
power good window for more than the delay programmed
at the PGFD pin, the PGOOD pin is released. If the output
voltage leaves the power good window for more than 16
switching cycles the PGOOD pin is pulled down.
V_IN (Pin 24): Signal Input Supply. Decouple this pin to
SGND with a capacitor. This pin powers the internal control
circuitry. This pin is independent of PV_IN and may be con-
nected to the same voltage or to a higher supply voltage.
PGFD (Pin 25): PGOOD Deglitch Filter Delay Select. The
voltage at this pin sets the delay that the output must be
in regulation before the PGOOD flag is asserted. The delay
can be programmed to one of seven discrete values where
t_DELAY = 200μs • 2^N (N = 0 to 5, 7).
RUN_MSTR (Pin 26): Master Run. The power up threshold
is set at 1V. When forced below 0.4V, all circuitry is shut
off and the IC is put into a low current shutdown mode
(I_Q < 1μA).
RUN_STBY (Pin 27): Standby Mode Off. The regulator
power up threshold is set at 1V. When forced below 0.4V,
only the voltage regulator is shut off while the ADC and
PMBus interface are still active. When shut off, the ADC
refresh rate is reduced to 1Hz and the IC quiescent current
is reduced to 120μA. This pin sources 2.5μA. Do not pull
up with a low impedance (<10kΩ).
3815p
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