Rainbow-electronics MAX769 Manual de usuario descargar pdf (Pagina 10)

MAX769

2 or 3-Cell, Step-Up/Down,

Two-Way Pager System IC

10 ______________________________________________________________________________________

7-Bit ADC (CH0 Input and CH1, CH2)

Three analog channels are compared to a 7-bit, serially

programmed digital-to-analog converter (CH DAC). The

CH DAC voltage can be varied in 10mV steps from

200mV to V

REF

- 1LSB (or 1.27V) (Table 1). CH0 is an

external input, while CH1 and CH2 are signals internally

generated from the NICD and BATT pins. NICD and

BATT are internally divided by four before being com-

pared to CH DAC. The comparison threshold voltages

for each channel are described in the following equa-

tions:

(CH0: pin 9) = D x 10mV

(CH1: NICD) = D x 40mV

(CH2: BATT) = D x 40mV

where D is the decimal equivalent of the binary code

DAC0–DAC6 (Table 1). DAC0 is the LSB. A DAC code

of 1111111 equates to D = 127. When all zeros are pro-

grammed, the CH DAC and CH_ comparators turn off.

CH0, CH1, and CH2 comparison results reside in the

three MSB locations of the output serial data (Table 4).

The CH_ OUT data is delayed by one read cycle. In

other words, each CH_ OUT bit is the result of the com-

parison made against the CH DAC voltage programmed

during the previous serial-write operation.

An analog-to-digital (A/D) conversion can be performed

on a channel by using the system software to step

through a successive-approximation routine or, if the

input is partially known, by setting the CH DAC to a

voltage near the estimated point and checking succes-

sive CH_ OUT bits.

MAX769

2 OR 3-CELL

AA ALKALINE

BATTERY

BATT

OFS

0.1µF

3.0V

LOGIC

2.85V

ANALOG

1V RCVR

470k

1.3M

100k

3-CELL

NiCd

TO RF

OFS

, 15k

LX2

OUT

PGND

REG1

R2IN

OFS

REG2

68µH

MBR0520L

0.1µF

47µF

10µF

TO µC

RESET

1µF

22µF

SERIAL

I/O

A/D IN

270k

1.8Ω

DRIVERS

38.4kHz

C10

22nF

1µF

1nF

REG3

RSIN

RSO

NICD

AGND

LBI

250k

REG1

LBO

CH0

SCL

SDI

SDO

DR1

DR2

DR2IN

DRGND

SYNC

FILT

REF

LX1

10k

Figure 2. Standard Application Circuit

1 2 ... 5 6 7 8 9 10 11 12 13 14 15 16

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Rainbow-electronics MAX769 Manual de usuario Pagina 10

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