MB4053 Datasheet, PDF (12/17 Pages) Fujitsu Component Limited. – 6-Channel 8-BIT A/D Converter

MB4053
s APPLICATION EXAMPLES
Examples of analog voltage (0 to 5 V) A/D conversion with 10-bit resolution are shown in “PEAK LINEARITY
ERROR vs AMBIENT TEMPERATURE Ta” and “SUPPLY CURRENT vs AMBIENT TEMPERATURE”.
RB
Temperature
Sensor
To other
Sensor
RX
R1
3 kΩ
R2
5 kΩ
VCC = 8 V
5V
VCC
I1
RAMP
START
I2
RAMP
STOP
I3
A2
I4 _MB4053 A1
I5
A0
I6
CH
VREF
RREF
GND
IR
RREF
120 kΩ
20 kΩ
Control input/output from
MPU
CH = 5000 pF
Reference Voltage: VREF = ^R2 VCC ............ 7-1
R1 + R2
Ramp Current: IR =
R1
⋅¹
VCC ......... 7-2
R1 + R2 RREF
Input Voltage: = VIN =
RX
⋅ VCC ................ 7-3
RX + RB
Ramp Time: tR ^.=. VIN ⋅ ^CH
IR
=
RX
⋅ (1 + ^R2 ) ⋅ CH ⋅ RREF ................. 7-4
RX + RB
R1
VREF =
5 kΩ
×8V=5V
3 kΩ + 5 kΩ
IR =
tSL ≥
VCC - VREF
RREF
CH × VREF
IA(min) - IR
= ^{8 V - 5 V} = 25 µA
120 kΩ
= ^{5000 pF × (5 V + 0.7 V)} = 228 µs
150 µA - 25 µA
tRmax ^.=.
CH × VREF
IR
= ^{5000 pF × 5 V} = 1000 µs
25 µA
If the ramp time is counted with a 1 MHz clock, the following
resolution is obtained.
1000 µs
1 µs
=
1000 ^.=.
2¹⁰
As shown in this example, the voltage output of the sensor is
proportional to VCC (Eq. 7-3) and VREF is also proportional to VCC
(Eq. 7-1), the sensor output conversion results (Eq. 7-4) are not
influenced by power supply voltage fluctuation. Such a conversion
is called ratio metric conversion and is effective for minimizing the
effects of conversion error. Supply voltage fluctuations during
discharge do result in error, however.
12