Rainbow-electronics MAX149 Manual do Utilizador descarregar pdf (Página 15)

MAX148/MAX149

+2.7V to +5.25V, Low-Power, 8-Channel,

Serial 10-Bit ADCs

______________________________________________________________________________________ 15

delay and maximum sample rate. In external compensa-

tion mode, power-up time is 20ms with a 4.7µF compen-

sation capacitor when the capacitor is initially fully

discharged. From fast power-down, start-up time can be

eliminated by using low-leakage capacitors that do not

discharge more than 1/2LSB while shut down. In power-

down, leakage currents at VREF cause droop on the ref-

erence bypass capacitor. Figures 12a and 12b show

the various power-down sequences in both external and

internal clock modes.

SCLK

DIN

DOUT

S CONTROL BYTE 0

CONTROL BYTE 1S

CONVERSION RESULT 0

B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 S1 S0

CONVERSION RESULT 1

SSTRB

B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 S1 S0

CONTROL BYTE 2S

8 115 158 1

Figure 11a. External Clock Mode, 15 Clocks/Conversion Timing

SCLK

DIN

DOUT

1 8 16

CONTROL BYTE 0

CONTROL BYTE 1S

CONVERSION RESULT 0

B9 B8 B7 B6 B5 B4 B3 B2 B1 B0 S1 S0 B9 B8 B7 B6

CONVERSION RESULT 1

• • •

Figure 11b. External Clock Mode, 16 Clocks/Conversion Timing

POWERED UP

HARDWARE

POWER-

DOWN

POWERED UP

10 + 2 DATA BITS

INVALID

DATA

VALID

DATA

EXTERNAL

S X

X X X X

1 1 S 0 0

X XXXX X X X X X

S 1 1

SOFTWARE

POWER-DOWN

MODE

DOUT

DIN

CLOCK

MODE

SHDN

SETS EXTERNAL

CLOCK MODE

SETS EXTERNAL

CLOCK MODE

SETS SOFTWARE

POWER-DOWN

Figure 12a. Timing Diagram Power-Down Modes, External Clock

1 2 ... 10 11 12 13 14 15 16 17 18 19 20 ... 23 24

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