SI3201-X-FS SILABS [Silicon Laboratories], SI3201-X-FS Datasheet - Page 24

• Manufacturer Part Number: SI3201-X-FS
• Manufacturer: SILABS [Silicon Laboratories]

Si3233
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).
In this circuit, 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 Si3233M version of
the Si3233 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.
2.3.4. DC-DC Converter Architecture
The control logic for a pulse width modulated (PWM) dc-
dc converter is incorporated in the Si3233. 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 Si3233. 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
voltage to the dc-dc converter external circuitry. If an
overload condition is detected, the PWM controller will
turn off the switching transistor for the remainder of a
PWM
components. It is important that the proper value of R18
be selected to ensure safe operation. Guidance is given
in Application Note 45 (AN45).
The PWM controller operates at a frequency set by the
dc-dc Converter PWM register (direct Register 92).
During a PWM period the outputs of the control pins
DCDRV and DCFF are asserted for a time given by the
read-only
Register 94).
The dc-dc converter must be off for some time in each
cycle to allow the inductor or transformer to transfer its
stored energy to the output capacitor, C9. This minimum
off time can be set through the dc-dc Converter
Switching Delay register, (direct Register 93). The
24
period
circuit
PWM
to
within
Pulse
prevent
the
Width
damage
Si3233
register
to
is
Preliminary Rev. 0.5
a
external
BAT
(direct
high
) is
DC
number of 16.384 MHz clock cycles that the controller is
off is equal to DCTOF (bits 0 through 4) plus 4. If the dc
Monitor pins detect an overload condition, the dc-dc
converter interrupts its conversion cycles regardless of
the register settings to prevent component damage.
These inputs should be calibrated by writing the DCCAL
bit (bit 7) of the dc-dc Converter Switching Delay
register, direct Register 93, after the dc-dc converter
has been turned on.
The most negative terminal (V
from the battery voltage (V
overlead voltage (V
audio signals.
The dc-dc converter can be made to adjust more quickly
to voltage changes by setting DCSU = 1 (Direct
Register 108, bit 5). Audio band noise can optionally be
reduced using an audio band filter by setting DCFIL = 1
(Direct Register 108, bit 1).
2.3.5. DC-DC Converter During Forward Active
The Si3233 dynamically adjusts V
requirements of the loop and line state. The behavior of
the tracking dc-dc converter in the active state is shown
in Figure 10.
In the active state, the TIP-to-RING open circuit voltage
is kept at V
regulator output voltage, V
When the loop current attempts to exceed I
line driver circuit enters constant current mode allowing
the TIP to RING voltage to track R
terminal is kept at a constant voltage, it is the RING
terminal voltage that tracks R
|V
= I
the VOC/I
continue to track R
tracking mechanism is stopped when |V
(TRACK = 0). The former case is the more common
application
dissipation savings. In principle, the regulator output
voltage can go as low as |V
significant power savings.
When TRACK = 0, |V
V
to decrease with decreasing R
dissipation on the NPN bipolar transistor driving the
RING terminal can become large and may require a
higher power rating device. The non-tracking mode of
operation is required by specific terminal equipment
which, in order to initiate certain data transmission
modes, goes briefly on-hook to measure the line voltage
to determine whether there is any other off-hook
terminal equipment on the same line. TRACK = 0 mode
BATL
BAT
LIM x
| voltage will also track R
. The RING terminal voltage, however, continues
R
LOOP
LIM
OC
and
+ V
mark, the regulator output voltage can
in the constant voltage region while the
CM
OV
provides
LOOP
+V
) to allow sufficient headroom for
OV
BAT
BAT
(TRACK = 1), or the R
. As R
| will not decrease below
BAT
LOOP
BAT
= V
LOOP
the
RING
) by a programmable
| = V
LOOP
CM
. In this state, |V
and, as a result, the
LOOP
BAT
maximum
+ V
CM
LOOP
or V
decreases below
+ V
OC
. The power
BAT
to match the
. As the TIP
TIP
+ V
OV
LIM
| = |V
) is offset
, offering
OV
, the dc
power
.
LOOP
BATL
BAT
|
|