Covidien Force FX, Service Manual

Page: 89 / 246

Control Board
Principles of Operation
Force FX Electrosurgical Generator C Service Manual
4-9
Power Supply Supervisor Circuit
The controller assembly requires three different voltage levels, +5V, +3.3V and
+1.2V. These three power supply supervisory circuits use the Micrel
TM* MIC2776N-
YM5 IC, to provide under-voltage monitoring and power-on reset generation.
The voltage present at the IN pin is compared to the internal 300mV reference voltage. A
reset is triggered if and when V
IN
falls below V
REF
. The +5V Supervisory threshold is set to
trigger a reset signal at +4.69V, the +3.3V Supervisory circuit will trigger a reset signal at
+3.16V, and the +1.2V Supervisory circuit will initiate a reset signal at +1.15V.
A/D and D/A Conversion
Each 80C562 microcontroller (U5 and U11) contains an 8-channel multiplexed 8-bit A/D
converter. Resolution of voltage and current sense inputs is enhanced by incorporating
gain scaling relays in the sense circuits on the Power Supply/RF board and prescaling
based on the expected input voltage or current values.
An AD7226 quad 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 ASIC)
A dedicated Atmel TM* AT89C51 microcontroller (U9) generates the RF drive waveforms
(T_ON\) for the RF output amplifier on the Power Supply/RF board. The microcontroller
functions as an application-specific integrated circuit, or ASIC, performing an endless
series of repetitive tasks while enabled.
The feedback microcontroller (U11) holds the T_ON ASIC (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 ASIC from reset and communicates a
4-bit code that represents the generator mode to be activated. The acceptable
activation codes are listed below:
0:
Precise bipolar
1: Standard and Macro bipolar
2: Low and Pure Cut
3: Blend cut
7: Desiccate coag
8: LCF Fulgurate coag
9: Spray coag
11:Spark-controlled Blend
12:Fulgurate coag
Codes 4, 5, 6, 10 and A–F are unused.