PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
1
2
3
4
5
6
7
8
TC514
USING THE TC510/514
Design Example
Negative Supply Voltage Converter (TC510, TC514)
Given: Required Resolution: 16 Bits (65,536 counts).
Maximum VIN:
Power Supply Voltage: +5V
60Hz System
±2V
A capacitive charge pump is employed to invert the
voltage on VDD for negative bias within the TC510/514. 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
fromanon-boardoscillator. Duringthefirstphase, capacitor
CF 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 100kHz to
ensure minimum output ripple. This frequency can be re-
duced by placing a capacitor from OSC to VDD. The relation-
ship between the capacitor value is shown in the typical
characteristics curves at the end of this data sheet.
Step 1: Pick integration time (tINT) as a multiple of the
line frequency:
1/60Hz = 16.6msec. Use 4x line frequency = 66msec
Step 2: Calculate RINT
RINT (in MΩ) = VINMAX/20 = 2/20 = 100kΩ
Step 3: Calculate CINT for maximum (4V) integrator
output swing:
Analog Input Multiplexer (TC514)
CINT (in µF) = (tINT) (20 x 10 –6) / (VS – 0.9)
= (.066) (20 x 10 –6) / (4.1)
The TC514 is equipped with a four input differential
analogmultiplexer. Inputchannelsareselectedusingselect
inputs (A1, A0). These are high-true control signals
(i.e., channel 0 is selected when (A1, A0 = 00).
= .32µF (use closest value: 0.33µF)
NOTE: TelCom recommended capacitor:
WIMA p/n: MK12 .33/63/10
EVALUATION KIT (TC500EV)
The TC500EV consists of a pre-assembled, 4 inch by 6
inch printed circuit board that connects to the serial port of
any PC or dumb terminal. Design software is also included.
TC500EV helps reduce design time and optimize converter
performance.PleasecontactyourlocalTelComrepresenta-
tive for more information.
Step 4: Choose CREF and CAZ based on conversion rate
:
Conversions/sec
= 1/(tAZ + tINT + 2 tINT + 2msec)
= 1/(66msec + 66msec +132msec+2msec)
= 3.7 conversions/sec
From which CAZ = CREF = 0.22µF (see Table 1)
NOTE: TelCom recommended capacitor:
WIMA p/n: MK12 .22/63/10
Step 5: Calculate VREF
VREF (in Volts) = (VS – 0.9) (CINT) (RINT
)
2(tINT
)
= (4.1) (0.33 x 10 –6) (105) / 2(.066)
= 1.025V
TELCOM SEMICONDUCTOR, INC.
3-31
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
