ac
RsADCIN0
Cp
10 pF
Ron
1 k
1.25 pF
Ch
Switch
Typical Values of the Input Circuit Components:
Switch Resistance (Ron): 1 k
Sampling Capacitor (Ch): 1.25 pF
Parasitic Capacitance (Cp): 10 pF
Source Resistance (Rs): 50
28x DSP
Source
Signal
ADC Power Up Delay ADC Ready for Conversions
PWDNBG
PWDNREF
PWDNADC
Request for
ADC
Conversion
td(BGR)
td(PWD)
SM320F2812-HT
www.ti.com
SGUS062A–JUNE 2009 –REVISED APRIL 2010

Figure 6-37. ADC Analog Input Impedance Model

6.29.4 ADC Power-Up Control Bit Timing

Figure 6-38. ADC Power-Up Control Bit Timing

Table 6-49. ADC Power-Up Delays(1) (2)
MIN TYP MAX UNIT
Delay time for band gap reference to be stable. Bits 6 and 5 of the ADCTRL3 register
td(BGR) 7 8 10 ms
(PWDNBG and PWDNREF) are to be set to 1 before the ADCPWDN bit is enabled.
20 50 ms
Delay time for power-down control to be stable. Bit 7 of the ADCTRL3 register (ADCPWDN)
td(PWD) is to be set to 1 before any ADC conversions are initiated. 1 ms
(1) These delays are necessary and recommended to make the ADC analog reference circuit stable before conversions are initiated. If
conversions are started without these delays, the ADC results shows a higher gain. For power down, all three bits can be cleared at the
same time.
(2) Not production tested.
Copyright © 2009–2010, Texas Instruments Incorporated Electrical Specifications 137
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