TLV1570

2.7 V TO 5.5 V 8-CHANNEL 10-BIT 1.25-MSPS

SERIAL ANALOG-TO-DIGITAL CONVERTER

SLAS169B – DECEMBER 1997– REVISED OCTOBER 2000

8

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

initialization-software sequence (continued)

The TLV1570 interfaces to a DSP over five lines: CS, SCLK, SDOUT, SDIN, and FS, and interfaces to a

µC over

four lines: CS, SCLK, SDOUT, and SDIN. The FS input should be pulled high in

µC mode. The device is in 3-state

and power-down mode when CS is high. After CS falls, the TLV1570 checks the FS input at the CS falling edge

to determine the operation mode. If FS is low, DSP mode is set, otherwise

µC mode is set.

CS

SCLK

FS

SDIN

SDOUT

XF

CLKX

CLKR

FSX

FSR

DX

DR

TLV1570

TMS320

CS

SCLK

FS

SDIN

SDOUT

I/O Terminal

SCLK

DX

DR

TLV1570

µC

DVDD

Figure 3. DSP to TLV1570 Interface

Figure 4.

µC to TLV1570 Interface

grounding and decoupling considerations

General practices should apply to the PCB design to limit high frequency transients and noise that are fed back

into the supply and reference lines (see Figure 5). This requires that the supply and reference pins be sufficiently

bypassed. In most cases 0.1

µF ceramic chip capacitors are adequate to keep the impedance low over a wide

frequency range. Since their effectiveness depends largely on the proximity to the individual supply pin. They

should be placed as close to the supply pins as possible.

To reduce high frequency and noise coupling, it is highly recommended that digital and analog ground be

shorted immediately outside the package. This can be accomplished by running a low impedance line between

DGND and AGND, under the package.

AVDD

AGND

REF

TLV1570

100 nF

100 nF

DVDD

DGND

100 nF

Figure 5. Placement of Decoupling Capacitors

power supply ground layout

Printed-circuit boards that use separate analog and digital ground planes offer the best system performance.

Wire-wrap boards do not perform well and should not be used. The two ground planes should be connected

together at the low-impedance power-supply source. The best ground connection may be achieved by

connecting the ADC AGND terminal to the system analog ground plane making sure that analog ground

currents are well managed.