u4091bm-r ATMEL Corporation, u4091bm-r Datasheet - Page 23

• Manufacturer Part Number: u4091bm-r
• Description: Programmable Telephone Audio Processor
• Manufacturer: ATMEL Corporation

13. Analog-to-Digital Converter (ADC)
4872A–CORD–08/05
This circuit is a 7-bit successive-approximation analog-to-digital converter in switched capacitor
technique. An internal band gap circuit generates a 1.25-V reference voltage which is the equiv-
alent of 1 MSB (1 LSB = 19.5 mV). The possible input voltage at ADIN is 0V to 2.48V.
The ADC needs an SOC (Start Of Conversion) signal. In the High phase of the SOC signal, the
ADC is reset. Then, 50 µs after the beginning of the Low phase of the SOC signal, the ADC gen-
erates an EOC (End Of Conversion) signal which indicates that the conversion is finished. The
rising edge of EOC generates an interrupt at the INT output. The result can be read out by the
serial bus.
Voltages higher than 2.45V have to be divided. The signal connected to the ADC is determined
by 4 bits: ADC0, ADC1, ADC2 and ADC3. TLDR/TLDT measuring is possible relative to a pre-
ceding reference measurement. The current range of IL can be doubled by ADCR. If ADCR is
High, S has the value 0.5, otherwise S = 1.
The source impedance at ADIN must be lower than 250 k .
Accuracy: 1 LSB + 3%
Figure 13-1. Timing of ADC
Figure 13-2. ADC Input Selection
IL x 20 mV/(1 mA x S )
EOC
SOC
8 x (TLDR - REF)
8 x (TLDT - REF)
0.4 x VMP S
0.4 x S AO1
0.4 x OFF1
0.4 x OFF2
0.4 x OFF3
0.4 x VMP
0.4 x VB
ADIN
50
s
ADC
S OC
EOC
MS B
BIT5
BIT4
BIT3
BIT2
BIT1
LS B
U4091BM-R
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