SI3230 SILABS [Silicon Laboratories], SI3230 Datasheet - Page 23

• Manufacturer Part Number: SI3230
• Manufacturer: SILABS [Silicon Laboratories]

2.1.9. Linefeed Calibration
An internal calibration algorithm corrects for internal and
external component errors. The calibration is initiated by
setting the CAL bit in direct Register 96. Upon
completion of the calibration cycle, this bit is
automatically reset.
It is recommended that a calibration be executed
following system power-up. Upon release of the chip
reset, the Si3230 will be in the open state. After
powering up the dc-dc converter and allowing it to settle
for time (t
Additional calibrations may be performed, but only one
calibration should be necessary as long as the system
remains powered up.
During calibration, V
controlled by the calibration engine to provide the
correct external voltage conditions for the algorithm.
Calibration should be performed in the on-hook state.
RING or TIP must not be connected to ground during
the calibration.
2.2. Battery Voltage Generation and
Switching
The Si3230 integrates a dc-dc converter controller that
dynamically regulates a single output voltage. This
eliminates the need to supply large external battery
voltages. Instead, it converts a single positive input
voltage into the real-time battery voltage needed for any
given
parameters.
2.2.1. DC-DC Converter General Description
The dc-dc converter dynamically generates the large
negative voltages required to operate the linefeed
interface. The Si3230 acts as the controller for a buck-
boost dc-dc converter that converts a positive dc
voltage into the desired negative battery voltage. In
addition to eliminating external power supplies, this
allows the Si3230 to dynamically control the battery
voltage to the minimum required for any given mode of
operation.
Extensive design guidance can be obtained from
Application Note 45 (AN45) and from an interactive dc-
dc converter design spreadsheet. Both of these
documents are available on the Silicon Laboratories
website (www.silabs.com).
2.2.2. BJT/Inductor Circuit Using Si3230
The BJT/Inductor circuit, as defined in Figure 4, offers a
flexible, low-cost solution. Depending on selected L1
inductance value and the switching frequency, the input
voltage (V
dc-dc converter’s operation, peak and average input
currents can become large with small input voltages.
state
DC
settle
) can range from 5 V to 30 V. By nature of a
according
) the calibration can be initiated.
BAT
, V
TIP
to
, and V
programmed
RING
voltages are
Preliminary Rev. 0.96
linefeed
Consider this when selecting the appropriate input
voltage and power rating for the V
For this solution, a PNP power BJT (Q7) switches the
current flow through low ESR inductor L1. The Si3230
uses the DCDRV and DCFF pins to switch Q7 on and
off. DCDRV controls Q7 through NPN BJT Q8. DCFF is
ac coupled to Q7 through capacitor C10 to assist R16 in
turning off Q7. Therefore, DCFF must have opposite
polarity to DCDRV, and the Si3230 (not Si3230M) must
be used.
2.2.3. MOSFET/Transformer Circuit Option Using
The MOSFET/transformer circuit option, as defined in
Figure 5, offers higher power efficiencies across a larger
input voltage range. Depending on the transformers
primary inductor value and the switching frequency, the
input voltage (V
Therefore, it is possible to power the entire ProSLIC
solution from a single 3.3 V or 5 V power supply. By
nature of a dc-dc converter’s operation, peak and
average input currents can become large with small
input voltages. Consider this when selecting the
appropriate input voltage and power rating for the V
power supply (number of REN supported).
For this solution, an n-channel power MOSFET (M1)
switches the current flow through a power transformer
T1. T1 is specified in Application Note 45 (AN45), and
includes several taps on the primary side to facilitate a
wide range of input voltages. The Si3230M version of
the Si3230 must be used for the application circuit
depicted in Figure 5 because the DCFF pin is used to
drive M1 directly and therefore must be the same
polarity as DCDRV. DCDRV is not used in this circuit
option; connecting DCFF and DCDRV together is not
recommended.
2.2.4. DC-DC Converter Architecture
The control logic for a pulse width modulated (PWM) dc-
dc converter is incorporated in the Si3230. Output pins,
DCDRV and DCFF, are used to switch a bipolar
transistor or MOSFET. The polarity of DCFF is opposite
to that of DCDRV.
The dc-dc converter circuit is powered on when the
DCOF bit in the Power Down Register (direct
Register 14, bit 4) is cleared to 0. The switching
regulator
performance, pulse-width modulation controller. The
control pins are driven by the PWM controller logic in
the Si3230. The regulated output voltage (V
sensed by the SVBAT pin and is used to detect whether
the output voltage is above or below an internal
reference for the desired battery voltage. The dc
monitor pins SDCH and SDCL monitor input current and
Si3230M
circuit
DC
) can range from 3.3 V to 35 V.
within
the
DC
Si3230
power supply.
Si3230
is
a
BAT
high
) is
DC
23