7809LP datasheet(14/23 Pages) MAXWELL

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16-Bit Latchup Protected Analog to Digital Converter

7809LP

01.11.05 Rev 7

LPTTM Operation

Latchup Protection Technology (LPTTM) automatically detects an increase in the supply current of the 7809LP con-

verter due to a single event effect and internally cycles the power to the converter off, then on, which restores the

steady state operation of the device. A simplified block diagram of the 7809LP circuitry is shown in Figure 7. The

LPTTM circuitry consists of two power switch and current sensor blocks, an LPTTM controller block, a BIT current load

block, and an active input protection block.

Figure 7. 7809LP Simplified Block Diagram

The power switch/current sensor blocks sense the supply current drawn by the protected device on the analog and

digital supply pins. When a threshold level is exceeded on either supply line, indicating single event induced latchup of

the protected device, a signal is sent to the LPTTM controller block. The LPTTM controller then drives the power

switches to an off state which removes the power supplies from the protected device. At the same time, a signal is

sent to open the active input protection circuits and the LPSTATUS output pin is activated. After a period of time suffi-

cient to clear the latchup, the LPTTM controller drives the power switches and input protection back to the on state

restoring the operation of the protected device. The LPTBIT circuit is used during system test to electrically trigger the

latchup function by drawing current through the power switch/current sensor blocks sufficient to trigger the LPTTM pro-

tection.

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