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参数资料
型号： SI3225DC0-EVB
厂商： Silicon Laboratories Inc
文件页数： 46/112页
文件大小： 0K
描述： DAUGHTER CARD W/SI3200 INTERFACE
标准包装： 1
系列： ProSLIC®
主要目的： 接口，模拟前端（AFE）
已用 IC / 零件： Si3225
已供物品： 板，CD
Si3220/25 Si3200/02
Rev. 1.3
39
Not
Recommended
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3.8.1. Transistor Power Equations
(Using Discrete Transistors)
When using the Si3220 or Si3225 with discrete bipolar
transistors, it is possible to control the total power of the
solution by individually regulating the power in each
discrete
transistor.
Figure 18
illustrates
the
basic
transistor-based linefeed circuit for one channel. The
power
dissipation
of
each
external
transistor
is
estimated based on the A/D sample values. The
approximate power equations for each external BJT are
as follows:
PQ1 VCE1 x IQ1 (|VTIP| + 0.75 V) x (IQ1)
PQ2 VCE2 x IQ2 (|VRING| + 0.75 V) x (IQ2)
PQ3 VCE3 x IQ3 (|VBAT| – R7 x IQ5) x (IQ3)
PQ4 VCE4 x IQ4 (|VBAT| – R6 x IQ6) x (IQ4)
PQ5 VCE5 x IQ5 (|VBAT| – |VRING| – R7 x IQ5) x (IQ5)
PQ6 VCE6 x IQ6 (|VBAT| – |VTIP| – R6 x IQ6) x (IQ6)
The maximum power threshold for each device is
software-programmable and should be set based on the
characteristics of the transistor package, PCB design,
and available airflow. If the peak power exceeds the
programmed threshold for any device, the power-alarm
bit is set for that device. Each external bipolar has its
own register bit (PQ1S–PQ6S bits of the IRQVEC3
register), which goes high on a rising edge of the
comparator output and remains high until the user
clears it. Each transistor power alarm bit is also
maskable by setting the PQ1E–PQ6E bits in the
IRQEN3 register.
3.8.2. Si3200/2 Power Calculation
When using the Si3200/2, it is also possible to detect
the thermal conditions of the linefeed circuit by
calculating the total power dissipated within the Si3200/
2. This case is similar to the transistor power equations
case, with the exception that the total power from all
transistor devices is dissipated within the same package
enclosure, and the total power result is placed in the
PSUM RAM location. The power calculation is derived
using the following equations:
PQ1 (|VTIP| + 0.75 V) x IQ1
PQ2 (|VRING| + 0.75 V) x IQ2
PQ3 (|VBAT |+ 0.75 V) x IQ3
PQ4 (|VBAT| + 0.75 V) x IQ4
PQ5 (|VBAT| – |VRING|) x IQ5
PQ6 (|VBAT| – |VTIP|) x IQ6
PSUM = total dissipated power = PQ1 + PQ2 + PQ3 +
PQ4 + PQ5 + PQ6
Note: The Si3200/2 THERM pin must be connected to the
THERM a/b pin of the Si3220/Si3225 in order for the
Si3200/2 power calculation method to work correctly.
3.8.3. Power Filter and Alarms
The power calculated during each A/D sample period
must be filtered before being compared to a user-
programmable maximum power threshold. A simple
digital low-pass filter is used to approximate the
transient thermal behavior of the package, with the
output of the filter representing the effective peak power
within the package or, equivalently, the peak junction
temperature.
For Q1, Q2, Q3, and Q4 in SOT23 and Q5 and Q6 in
SOT223 packages, the settings for thermal low-pass
filter poles and power threshold settings are (for an
ambient temperature of 70 °C) calculated as follows: If
the thermal time constant of the package is
thermal, the
decimal values of RAM locations PLPF12, PLPF34, and
PLPF56 are given by rounding to the next integer the
value given by the following equation:
Where 4096 is the maximum value of the 12-bit plus
sign RAM locations PLPF12, PLPF34, and PLPF56,
and 800 is the power calculation clock rate in Hz. The
equation is an excellent approximation of the exact
equation for
thermal = 1.25 ms
… 5.12 s. With the
above equations in mind, example values of the RAM
locations, PTH12, PTH34, PTH56, PLPF12, PLPF34,
and PLPF56, are as follows:
PTH12 = power threshold for Q1, Q2 = 0.3 W (0x25A)
PTH34 = power
threshold
for
Q3,
Q4 = 0.22 W
(0x1B5E)
PTH56 = power threshold for Q5, Q6 = 1 W (0x7D8)
PLPF12 = Q1/Q2 thermal LPF pole = 0x0012
(for SOT–89 package)
PLPF34 = Q3/Q4 thermal LPF pole = 0x008C
(for SOT–23 package)
PLPF56 = Q5/Q6 thermal LPF pole = 0x000E
(for SOT–223 package)
In the case where the Si3200/2 is used, thermal filtering
needs to be performed only on the total power reflected
in the PSUM RAM location. When the filter output
exceeds the total power threshold, an interrupt is
issued. The PTH12 RAM location is used to preset the
total power threshold for the Si3200/2, and the PLPF12
RAM location is used to preset the thermal low-pass
filter pole.
PLPFxx (decimal value)
4096
800
thermal
------------------------------------
2
3
=
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