16-Bit Latchup Protected Analog to Digital Converter
7809LP
Testing the 7809LPRP Latchup Protection Circuitry
The LPVANA and LPVDIG pins provide direct access to the 7809LP converter supply pins for attaching external
decoupling capacitors to ground. These pins can also be used to test the LPTTM operation and threshold level by sink-
ing a pulsed current load to ground as shown in the test circuit in Figure 8. The most accurate threshold current mea-
surements are made with the ADS7809 in its lowest power state (PWRD = 5V).
The LPTTM operation and device recovery times are most easily measured using the LPBIT input to trigger protection
and recovery. Applying a 10 µsec high duration TTL level to the LPBIT pin causes internal test currents sufficient to
trigger the LPTTM circuit to be drawn through both the analog and digital supply sense circuits.
LPTTM operating characteristics are summarized in Table 16 according to the timing diagram shown in Figure 9. Dur-
ing the time that the power is cycled, output signals and data from the 7809LP are invalid. The LPSTATUS signal high
indicates that power is removed from the ADS7809 die. When this signal is low, power is applied to the ADS7809 die.
The LPSTATUS signal is used to measure the supply recovery time. The supply recovery time interval starts when the
supply current rises (causing LPSTATUS to go high) and ends when the LPSTATUS signal stabilizes low again.
Within the functional recovery time interval (~25 µsec after the LPTTM circuit reapplies power), the normal functional
operation of the converter is restored with less than 5% full scale error. Additional settling time is then required to
return to full accuracy operation. Recovery time intervals are defined which indicate the time to recover first to within 8
bit accuracy, then to within 12 bit accuracy, and finally to full 16 bit accuracy. These recovery times are primarily due to
the single event and power cycling effects on the reference circuits and the settling times of their respective filter
capacitors.
TABLE 16. 7809LP LPTTM OPERATING CHARACTERISTICS
PARAMETER
SYMBOL
CONDITIONS
TYP
UNIT
Supply Threshold Current
Protection Time
ITHR
TPT
PWRD = 5V
75
mA
µsec
µsec
µsec
µsec
msec
LPBIT = 2.4V for 5 µs
LPBIT = 2.4V for 5 µs
LPBIT = 2.4V for 5 µs
LPBIT = 2.4V for 5 µs
LPBIT = 2.4V for 5 µs
10
Supply Recovery Time
TSR
TFR
T8R
50
Functional Recovery Time
8-bit Accuracy Recovery Time
Full Accuracy Recovery Time
TSR + 25
80
5
TFAR
01.11.05 Rev 7
All data sheets are subject to change without notice 17
©2005 Maxwell Technologies
All rights reserved.
MAXWELL [ MAXWELL TECHNOLOGIES ]
