LTC3883 Datasheet, PDF (59/112 Pages) Linear Technology – Single Phase Step-Down DC/DC Controller with Digital Power System Management

LTC3883/LTC3883-1
Applications Information
V_IN
LTC
100k 100k
CONTROLLER
HEADER
V_IN
ISOLATED
3.3V
SDA
TP0101K
V_DD33 V_DD25
1µF
LTC3883
1µF
SCL
10k
SDA
10k
SCL
WP SGND
TO LTC DC1613
USB TO I²C/SMBus/PMBus
CONTROLLER
V_IN
TP0101K
V_DD33 V_DD25
1µF
1µF
LTC3883
SDA
VGS MAX ON THE TP0101K IS 8V IF V_IN > 16V
CHANGE THE RESISTOR DIVIDER ON THE PFET GATE
SCL
WP SGND
3883 F29
Figure 29. LTC Controller Connection
V_DD node because this will interfere with bus communica-
tion in the absence of system power. If V_IN is applied the
dongle will not supply the LTC3883s on the board. It is
recommended the RUN pins be held low to avoid providing
power to the load until the part is fully configured.
The LTC controller I²C connections are optoisolated from
the PC USB. The 3.3V from the controller and the LTC3883
V_DD33 pin must be driven to each LTC3883 with a separate
PFET. If V_IN is not applied, the V_DD33 pins can be in parallel
because the on-chip LDO is off. The controller 3.3V cur-
rent limit is 100mA but typical V_DD33 currents are under
15mA. The V_DD33 does back drive the INTV_CC/EXTV_CC pin.
Normally this is not an issue if V_IN is open.
Inductor DCR Auto Calibration
Using the DC resistance of the inductor as a current shunt
element has several advantages—no additional power
loss, lower circuit complexity and cost. However any error
between the specified nominal inductor DCR value and
the actual DCR value will cause a proportional error in the
peak current limit, as well as the output current read-back
value. The LTC3883 can calibrate the inductor DCR value
to compensate for the tolerance from its typical value.
Setting bit 3 of the MFR_PWM_MODE_3883 command
will start the calibration procedure. To successfully
complete the calibration procedure, the PWM must be
enabled, the DUTY_CYCLE value must be at least 3%, the
READ_IIN value must be at least 10mA, and the calibrated
IOUT_CAL_GAIN must be with ±30% of the uncalibrated
IOUT_CAL_GAIN value. If any of the above conditions are
not met, bit 0 of the STATUS_CML command will be set,
and the value of IOUT_CAL_GAIN will not be changed.
During the inductor DCR calibration the supply voltage,
output voltage, and load current must be in a steady state
condition for 180ms during the command execution to
ensure accurate calibration. The load current should be
sufficiently large to create at least a 6mV average signal
across the R_IINSNS sense resistor as well as 6mV across
the output current sense network in order to ensure that
the READ_IIN and READ_IOUT values used in the DCR
calibration calculation are within 1% TUE. The inductor
DCR is calibrated by multiplying the measured READ_IIN
value by the measured READ_DUTY_CYCLE value to obtain
a calculated output current. The LTC3883 then updates the
IOUT_CAL_GAIN value so that the measured READ_IOUT
value matches the calculated output current value that is
based on power stage input current and duty cycle, so
that READ_IOUT • DUTY_CYCLE = READ_IIN.
3883f
59