TC500_06 Datasheet, PDF (14/34 Pages) Microchip Technology – Precision Analog Front Ends

TC500/A/510/514
S
S
S
30V
N_TH
Low V_REF
N_TH
Normal V_REF
N_TH
High V_REF
Slope (S) = ^VREF
R_INT C_INT
N_TH = Noise Threshold
FIGURE 8-1:
Noise Threshold.
8.6 Integrator Output Zero Phase
The comparator delay and the controller’s response
latency may result in overshoot, causing charge
buildup on the integrator at the end of a conversion.
This charge must be removed or performance will
degrade. The integrator output zero phase should be
activated (AB = 00) until CMPTR goes high. It is
absolutely critical that this phase be terminated
immediately so that overshoot is not allowed to occur in
the opposite direction. At this point, it can be assured
that the integrator is near zero. Auto-zero should be
entered (AB = 01) and the TC5XX held in this state until
the next cycle is begun (see Figure 8-2).
Integrator
Output
Zero
Crossing
Comparator
Output Comp
Integrate
Phase
FIGURE 8-2:
Overshoot
De-integrate Phase
Integrator
Zero Phase
Overshoot.
8.7 Using the TC510/TC514
8.7.1
NEGATIVE SUPPLY VOLTAGE
CONVERTER (TC510, TC514)
A capacitive charge pump is employed to invert the
voltage on V_DD for negative bias within the TC510/
TC514. This voltage is also available on the V_OUT- pin
to provide negative bias elsewhere in the system. Two
external capacitors are required to perform the
conversion.
Timing is generated by an internal state machine driven
from an on-board oscillator. During the first phase,
capacitor C_F is switched across the power supply and
charged to V_S+. This charge is transferred to capacitor
C_OUT- during the second phase. The oscillator normally
runs at 100 kHz to ensure minimum output ripple. This
frequency can be reduced by placing a capacitor from
OSC to V_DD. The relationship between the capacitor
value is shown in Section 2.0 “Typical Performance
Curves”.
8.7.2
ANALOG INPUT MULTIPLEXER
(TC514)
The TC514 is equipped with a four-input differential
analog multiplexer. Input channels are selected using
select inputs (A1, A0). These are high-true control
signals (i.e., channel 0 is selected when (A1, A0 = 00).
DS21428D-page 14
© 2006 Microchip Technology Inc.