Valleylab LigaSure - A;D and D;A Conversion; Waveform Generation (T_ON); T_ON Average Check

Control Board
Principles of Operation
LigaSure Vessel Sealing Generator Service Manual 5-7
A/D and D/A Conversion
Each 80C562 microcontroller (U5 and U11) contains an 8-channel multiplexed 8-
bit analog-to-digital (A/D) converter. Incorporating fixed gain control in the sense
circuits on the RF board and prescaling based on the expected input voltage or
current values enhance the resolution of voltage and current sense inputs.
An MP7226 quad digital-to analog (D/A) converter (U15) provides 4-channel 8-
bit D/A capabilities for the feedback microcontroller to output 0 to 5 Vdc analog
voltages.
Waveform Generation (T_ON)
A dedicated 89C54 microcontroller (U9) generates the RF drive waveforms
(T_ON\) for the RF output amplifier on the RF board. The microcontroller
functions as an application-specific integrated circuit (ASIC), performing an
endless series of repetitive tasks while enabled.
The feedback microcontroller (U11) holds the T_ON microcontroller (U9) in a
reset state until the feedback microcontroller detects a valid activation request.
After validating the request, the feedback microcontroller releases the T_ON
microcontroller from reset and communicates a 4-bit code - 0 - that represents the
generator mode to be activated.
The code generates a unique waveform pattern to be delivered to the RF output
stage of the generator. The T_ON microcontroller reads and evaluates the code
and, if the code value is acceptable, repetitively generates the appropriate
waveform until the activation request ends. After the request ends, the feedback
microcontroller places the T_ON microcontroller back into reset.
If the code received by the T_ON microcontroller is not valid, the internal
program sets an error flag, deactivates all output signals, and remains in an error
state until the user resets the system.
T_ON Average Check
A capacitor filters the T_ON waveform generator output, returning it to the main
microcontroller as a DC voltage value called T_ON average. Each distinct output
mode of the T_ON waveform generator produces a different T_ON average. The
main microcontroller continually checks the T_ON average for compliance with
the calibrated value to ensure that the T_ON waveform generator is operating
properly.
The T_ON average signal rests at 5 V when the generator is not activated and
drops to the calibrated value when activation occurs. The main microcontroller
checks to make sure the T_ON average signal is within ± 15 counts of the
calibrated value.
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