Datasheet

POWER DOWN MODES
Global Power Down
Channel Standby
Input Clock Stop
POWER SUPPLY SEQUENCING
ADS6425
www.ti.com ......................................................................................................................................................... SLWS197B – MARCH 2007 – REVISED JUNE 2009
Table 20. Minimum Clock Amplitude Across Gains
CLOCK BUFFER GAIN MINIMUM CLOCK AMPLITUDE SUPPORTED, mV (pp differential)
Gain 0 (minimum gain) 800
Gain 1 (default gain) 400
Gain 2 300
Gain 3 200
Gain 4 150
Gain 5 (highest gain) 100
The ADS6425 has three power down modes – global power down, channel standby and input clock stop.
This is a global power down mode in which almost the entire chip is powered down, including the four ADCs,
internal references, PLL and LVDS buffers. As a result, the total power dissipation falls to about 77 mW typical
(with input clock running). This mode can be initiated by setting the register bit < PDN GLOBAL> (Table 11 ). The
output data and clock buffers are in high impedance state.
The wake-up time from this mode to data becoming valid in normal mode is 100 µ s.
In this mode, only the ADC of each channel is powered down and this helps to get very fast wake-up times. Each
of the four ADCs can be powered down independently using the register bits < PDN CH> (Table 11 ). The analog
power dissipation varies from 1115 mW (only one channel in standby) to 245 mW (all four channels in standby).
The output LVDS buffers remain powered up.
The wake-up time from this mode to data becoming valid in normal mode is 200 clock cycles.
The converter enters this mode:
• If the input clock frequency falls below 1 MSPS or
• If the input clock amplitude is less than 400 mV (pp, differential with default clock buffer gain setting) at any
sampling frequency.
All ADCs and LVDS buffers are powered down and the power dissipation is about 235 mW. The wake-up time
from this mode to data becoming valid in normal mode is 100 µ s.
Table 21. Power Down Modes Summary
AVDD POWER LVDD POWER
POWER DOWN MODE WAKE UP TIME
(mW) (mW)
In power-up 1360 297 –
Global power down 65 12 100 µ s
1 Channel in standby 1115 297 200 Clocks
2 Channels in standby 825 297 200 Clocks
3 Channels in standby 532 297 200 Clocks
4 Channels in standby 245 297 200 Clocks
Input clock stop 200 35 100 µ s
During power-up, the AVDD and LVDD supplies can come up in any sequence. The two supplies are separated
inside the device. Externally, they can be driven from separate supplies or from a single supply.
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