12

All data sheets are subject to change without notice

©2005 Maxwell Technologies

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16-Bit Latchup Protected ADC

7805ALP

01.10.05 Rev 9

Testing the 7805A Latchup Protection Circuitry

The DECPLNG pin provides direct access to the 7805ALP converter supply pins for attaching external decoupling

ground as shown in the test circuit in Figure 5 and as described in the LPT Operating Characteristics Table (Table 17)

and LPT Timing diagram (Figure 7). This test approximates the operation of the 7805A in response to a single event

latchup and recovery.

During the time that the power is cycled, output signals and data from the 7805A are invalid. The STATUS signal HIGH

indicates that power is removed from the ADS7805 die. All input pins must be driven low or tri-stated. When this signal

is low, power is applied to the ADS7805 die. The STATUS signal can be used to measure the supply recovery time.

The status signal can exhibit multiple transitions when power is re-applied and the decoupling capacitors are charged.

The duration and number of transitions is dependent on the amount of capacitance used. The supply recovery time

interval starts when the supply current rises (causing STATUS to go high) and ends when the STATUS signal stabi-

lizes low again.

Within the functional recovery time interval (typically 25 µ sec after the LPT circuit reapplies power), the normal func-

tional operation of the converter is restored with less than 5% full scale error. Additional settling time is then required to

return to full accurate operation. Defined recovery time intervals indicate that time to recover first is within 8-bit accu-

racy, then within 12 bit accuracy, and finally 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.

Supply threshold current - ITHR

56

77

99

mA

Protection time (IS Peak = .2A) - TPT

--

1

--

µ sec

Input tri-state time - TIOFF

--

--

100

nsec