Fluke 123B/S Service Manual - Page 41

Slow ADC, BATCUR, BATVOLT, BATTEMP, BATIDENT Battery current, - voltage

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3 Circuit Descriptions 3.3 Detailed Circuit Descriptions An internal current source supplies a current to R559. The resulting voltage is a reference for the maximum allowable primary current (IMAXFLY). The voltage across the sense resistor (FLYSENSP) is compared to the IMAXFLY voltage. If the current exceeds the set limit, FET V554 will be turned off. Another internal current source supplies a current to R558. This resulting voltage is a reference for the maximum allowable output voltage (VOUTHI). The -3V3A output voltage (M3V3A) is attenuated and level shifted in the P-ASIC, and then compared to the VOUTHI voltage. If the -3V3A voltage exceeds the set limit, FET V554 will be turned off. The FREQPS control signal is converted to appropriate voltage levels for the FET switch V554 by the BOOST circuit. The voltage VBAT supplies the BOOST circuit power via V553 and R561. The FREQPS signal is also supplied to the D-ASIC, in order to detect if the Fly Back converter is running well. V551 and C552 limit the voltage on the primary winding of T552 when the FET V554 is turned of. The signal SNUB increases the FLYGATE high level to decreases ONresistance of V554 (less power dissipation in V554). VBAT V553 T552 R561 FLYBOOST SNUB C551 C552 V551 48 47 BOOST 49 FLYGATE 63 FREQPS COSC 43 C553 CONTROL 55 FLYSENSP 57 IMAXFLY 52 VCOIL 58 -3V3A 51 VOUTHI 54 VSENS 62 PWRONOFF 72 REFP (1.23V) POWER ASIC V554 R551 R559 R558 V561 V562 V563 V564 +5VA +3V3A -3V3A -30VD R570 R552 R554 R553 Figure 3-6. Fly-Back Converter Block Diagram Slow ADC (Refer to Figure 9-7) The Slow ADC enables the D-ASIC to measure the following signals: BATCUR, BATVOLT, BATTEMP, BATIDENT (Battery current, - voltage, temperature, - type ), DACTEST-A, DACTEST-B, and DACTEST-T (test output of the C-ASIC's and the T-ASIC). De-multiplexer D531 supplies one of these signals to its output, and to the input of comparator N531 TP536). The D-ASIC supplies the selection control signals SELMUX0-2. The Slow ADC works according to the successive approximation principle. The D-ASIC changes the SADCLEV signal level, and thus the voltage level 3-13

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Circuit Descriptions
3.3 Detailed Circuit Descriptions
3
3-13
An internal current source supplies a current to R559. The resulting voltage is a
reference for the maximum allowable primary current (IMAXFLY).
The voltage across
the sense resistor (FLYSENSP) is compared to the IMAXFLY voltage.
If the current
exceeds the set limit, FET V554 will be turned off.
Another internal current source supplies a current to R558. This resulting voltage is a
reference for the maximum allowable output voltage (VOUTHI).
The -3V3A output
voltage (M3V3A) is attenuated and level shifted in the P-ASIC, and then compared to
the VOUTHI voltage.
If the -3V3A voltage exceeds the set limit, FET V554 will be
turned off.
The FREQPS control signal is converted to appropriate voltage levels for the FET switch
V554 by the BOOST circuit.
The voltage VBAT supplies the BOOST circuit power via
V553 and R561.
The FREQPS signal is also supplied to the D-ASIC, in order to detect
if the Fly Back converter is running well.
V551 and C552 limit the voltage on the primary winding of T552 when the FET V554 is
turned of.
The signal SNUB increases the FLYGATE high level to decreases ON-
resistance of V554 (less power dissipation in V554).
-30VD
+5VA
PWRONOFF
VSENS
VOUTHI
-3V3A
VCOIL
FLYGATE
FLYBOOST
REFP (1.23V)
VBAT
FLYSENSP
IMAXFLY
FREQPS
R558
SNUB
COSC
T552
V551
V553
R561
C551
C552
+3V3A
-3V3A
V561
V562
V563
V564
BOOST
CONTROL
R559
R570
R551
R553
R552
R554
POWER ASIC
C553
48
47
49
63
55
57
52
62
51
54
58
43
V554
72
Figure 3-6. Fly-Back Converter Block Diagram
Slow ADC
(Refer to Figure 9-7)
The Slow ADC enables the D-ASIC to measure the following signals:
BATCUR, BATVOLT, BATTEMP, BATIDENT (Battery current, - voltage, -
temperature, - type ), DACTEST-A, DACTEST-B, and DACTEST-T (test output of the
C-ASIC’s and the T-ASIC).
De-multiplexer D531 supplies one of these signals to its output, and to the input of
comparator N531 TP536).
The D-ASIC supplies the selection control signals
SELMUX0-2.
The Slow ADC works according to the successive approximation
principle.
The D-ASIC changes the SADCLEV signal level, and thus the voltage level