−120

−100

−80

−60

−40

−20

0

0.1

10

1k

G067

1

100

AVDD3V

DVDD3V

AVDD5V

ADS5484

ADS5485

Power Supplies and Sleep Modes

The ADS548x uses three power supplies. For the analog portion of the design, a 5-V and 3.3-V supply (AVDD5

and AVDD3) are used, while the digital portion uses a 3.3-V supply (DVDD3). The use of low-noise power

supplies with adequate decoupling is recommended. Linear supplies are preferred to switched supplies; switched

supplies generate more noise that can be coupled to the ADS548x. However, the PSRR value and plot shown in

Figure 46 were obtained without bulk supply decoupling capacitors. When bulk (0.1-

μF) decoupling capacitors

are used near the supply pins, the board-level PSRR is much higher than the stated value for the ADC. The user

may be able to supply power to the device with a less-than-ideal supply and still achieve good performance. It is

not possible to make a single recommendation for every type of supply and level of decoupling for all systems. If

the noise characteristics of the available supplies are understood, a study of the PSRR data for the ADS548x

may provide the user with enough information to select noisy supplies if the performance is still acceptable within

the frequency range of interest. The power consumption of the ADS548x does not change substantially over

clock rate or input frequency.

Figure 46. PSRR versus Supply Injected Frequency

Two separate sleep modes are offered. They are differentiated by the amount of power consumed and the time it

takes for the ADC to wake-up from sleep. The light sleep mode consumes 605 mW and can be used when

wake-up of less than 600

μs is required. Deep sleep consumes 70 mW and requires 6 ms to wake-up. See the

wake-up characteristic in Figure 27. For directions on enabling these modes, see Table 5. The input clock can be

in either state when the power-down modes are enabled. The device can enter power-down mode whether using

an internal or external reference. However, the wake-up time from light sleep enabled to external reference mode

is dependent on the external reference voltage and is not necessarily 0.6 ms, but should be noticeably faster

than deep sleep wake-up. No specific power sequences are required.

Table 5. Power-Down and Reference Modes

MODE

PDWNF PIN

PDWNS PIN

POWER CONSUMPTION

WAKE-UP TIME

ADC On - Internal reference

Low

Low

2.16 W

On

ADC On - External reference

High

High

2.16 W

On

Light sleep

High

Low

600 mW when enabled

0.6 ms

Deep sleep

Low

High

70 mW when enabled

6 ms

Copyright © 2008–2009, Texas Instruments Incorporated

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Product Folder Link(s): ADS5484 ADS5485