SI3233 datasheet(21/100 Pages) SILABS

21 / 100 page

Si3233

Preliminary Rev. 0.5

2.2.5. Power Monitoring and Line Fault Detection

In addition to reporting voltages and currents, the

ProSLIC continuously monitors the power dissipated in

each linefeed transistor. Realtime output power of any

one of the six linefeed transistors can be read by setting

the Power Monitor Pointer (direct Register 76) to point

to the desired transistor and then reading the Line

Power Output Monitor (direct Register 77).

The realtime power measurements are low-pass filtered

and compared to a maximum power threshold.

Maximum power thresholds and filter time constants are

software programmable and should be set for each

transistor pair based on the characteristics of the

transistors used. Table 22 describes the registers

associated with this function. If the power in any

external transistor exceeds the programmed threshold,

a power alarm event is triggered. The ProSLIC sets the

Power Alarm register bit, generates an interrupt (if

enabled), and automatically enters the Open state (if

AOPN = 1).

This

feature

protects

the

external

transistors from fault conditions and, combined with the

loop voltage and current monitors, allows diagnosis of

the type of fault condition present on the line.

The value of each thermal low-pass filter pole is set

according to the equation:

where

τ is the thermal time constant of the transistor

package, 4096 is the full range of the 12-bit register, and

800 is the sample rate in hertz. Generally

τ = 3 seconds

for SOT223 packages and

τ = 0.16 seconds for SOT23,

but check with the manufacturer for the package

thermal constant of a specific device. For example, the

power alarm threshold and low-pass filter values for Q5

and Q6 using a SOT223 package transistor are

computed as follows:

Thus,

indirect

should

set

2Ah x 27 = 1500h.

Note:

The power monitor resolution for Q3 and Q4 is different

from that of Q1, Q2, Q5, and Q6.

Thermal LPF Pole [12:0]

4096

800

------------------

PT56[7:0]

PMAX

Resolution

-------------------------------

1.28

0.0304

------------------

2Ah

Table 22. Associated Power Monitoring and Power Fault Registers

Parameter

Description/

Range

Resolution

Bits

Location*

Power Monitor Pointer

0 to 5 points to Q1

to Q6, respectively

N/A

PWRMP[2:0]

Direct Register 76

Line Power Monitor Output

0 to 7.8 W for Q1,

Q2, Q5, Q6

0 to 0.9 W for Q3,

30.4 mW

3.62 mW

PWROM[7:0]

Direct Register 77

Power Alarm Threshold, Q1 & Q2

0 to 7.8 W

30.4 mW

PPT12[7:0]

Indirect Register 19

Power Alarm Threshold, Q3 & Q4

0 to 0.9 W

3.62 mW

PPT34[7:0]

Indirect Register 20

Power Alarm Threshold, Q5 & Q6

0 to 7.8 W

30.4 mW

PPT56[7:0]

Indirect Register 21

Thermal LPF Pole, Q1 & Q2

see equation above

NQ12[12:0]

Indirect Register 24

Thermal LPF Pole, Q3 & Q4

see equation above

NQ34[12:0]

Indirect Register 25

Thermal LPF Pole, Q5 & Q6

see equation above

NQ56[12:0]

Indirect Register 26

Power Alarm Interrupt Pending

Bits 2 to 7 corre-

spond to Q1 to Q6,

respectively

N/A

QnAP[n+1],

where n = 1 to 6

Direct Register 19

SI3233 Datasheet(PDF) 21 Page - Silicon Laboratories

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