SI3215MPPQX-EVB Silicon Laboratories Inc, SI3215MPPQX-EVB Datasheet - Page 30

• Manufacturer Part Number: SI3215MPPQX-EVB
• Description: BOARD EVAL W/DISCRETE INTERFACE
• Manufacturer: Silicon Laboratories Inc
• Series: ProSLIC®r

Specifications of SI3215MPPQX-EVB

• Main Purpose: Interface, Analog Front End (AFE)
• Utilized Ic / Part: Si3215
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Si3215
2.3.2. BJT/Inductor Circuit Option Using Si3215
The BJT/Inductor circuit option, as defined in Figure 10
on page 17, offers a flexible, low-cost solution.
Depending on selected L1 inductance value and the
switching frequency, the input voltage (V
from 5 V to 30 V. 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
For this solution, a PNP power BJT (Q7) switches the
current flow through low ESR inductor L1. The Si3215
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 Si3215 (not Si3215M) must
be used.
2.3.3. MOSFET/Transformer Circuit Option Using
The MOSFET/transformer circuit option, as defined in
Figure 11, offers higher power efficiencies across a
larger
transformers primary inductor value and the switching
frequency, the input voltage (V
to 35 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 “AN45: Design Guide for the
Si3210 DC-DC Converter” and includes several taps on
the primary side to facilitate a wide range of input
voltages. The Si3215M must be used for the application
circuit depicted in Figure 11 on page 19 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 Si3215. Output pins,
DCDRV and DCFF, are used to switch a bipolar
transistor or MOSFET. The polarity of DCFF is opposite
that of DCDRV.
The dc-dc converter circuit is powered on when the
DCOF
Register 14, bit 4) is cleared to 0. The switching
30
Si3215M
input
DC
bit
power supply.
in
voltage
the
Powerdown
range.
DC
) can range from 3.3 V
Depending
Register
DC
) can range
on
(direct
the
Rev. 0.92
DC
regulator
performance, pulse-width modulation controller. The
control pins are driven by the PWM controller logic in
the Si3215. The regulated output voltage (V
sensed by the SVBAT pin and 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 period to prevent damage to external
components. It is important that the proper value of R18
be selected to ensure safe operation. Guidance is given
in 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
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.
Because the Si3215 dynamically regulates its own
battery supply voltage using the dc-dc converter
controller, the battery voltage (V
negative-most terminal by a programmable voltage
(V
signals.
As mentioned previously, the Si3215 dynamically
adjusts V
illustrate this, the behavior of V
shown in Figure 17. In the active state, the TIP-to-RING
open circuit voltage is kept at V
voltage region while the 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
BAT
OV
) to allow voltage headroom for carrying audio
= V
CM
BAT
circuit
+ V
PWM
to suit the particular circuit requirement. To
OC
+ V
within
Pulse
OV
.
the
Width
BAT
BAT
Si3215
in the active state is
OC
) is offset from the
LOOP
register
in the constant
. As the TIP
is
LIM
a
, the dc
BAT
(direct
high-
) is