M
9
All data sheets are subject to change without notice
2005 Maxwell Technologies
All rights reserved.
16-Bit Latchup Protected ADC
7805ALP
01.10.05 Rev 9
steady state operation of the device. A simplified block diagramof the 7805ALP circuitry is shown in Figure 1. The cir-
cuitry consists of a protected device, the ADS7805 die, a current sensor a power switch, and a status output driver.
F
IGURE
3. L
ATCHUP
P
ROTECTION
D
IAGRAM
Differences Between the7805A and the ADS7805
Because the 7805A uses the ADS7805 die to performthe analog to digital conversion function its operation and per-
formance is very simlar to the ADS7805 packaged part fromBurr-Brown. In general the operation and application will
be the same for both parts. There are two primary differences: the operation of the supply pins and the operation of the
BYTE and STATUS pins.
The ADS7805 provides separate analog and digital supply pins. The 7805A provides a single supply input V
S
pin in
place of the V
DIG
pin which powers both the analog and digital circuitry through the LPT
current sensor and power
switch. The V
S
power supply should be treated as an analog supply and isolated fromnoise on the systemdigital
power supply. The low side of the power switch connects to the ADS7805 die power pads and to the package DEC-
PLNG pin which replaces the VANA pin. The DECPLNG pin allows low ESR ceramc capacitors to directly decouple
the ADS7805 die. CAUTION: The DECPLNG pin must not be connected to the power supply since this will defeat the
LPT
power switch and could result in latchup of the device during operation in a radiation environment. Electrolytic
capacitors should not be connected to the DECPLNG pin because the large capacitance will increase the recovery
time of the 7805A.
The primary functional difference between the ADS7805 and the 7805A is that the BYTE signal of the ADS7805 is
internally grounded and the pin function is replaced by the STATUS output. Grounding the BYTE signal permanently
assigns the data output signal bits 15:0 as shown in the 7805A pinout diagramwhere bit15 is the MSB and bit 0 is the
LSB.
A high level STATUS signal indicates that a single event induced latchup current was detected by the LPT
circuitry
causing power to be removed fromthe protected device.
CAUTION:
During the time that power is removed fromthe
protected device, it is critical that external circuitry driving the device I/O pins does not backdrive the device supply.
Backdriving the supply could contribute to an extended or even a permanent latchup condition.
VS
I/Os
POWER
PROTECTED
STATUS
DECPLNG
VDIG
VANA
BYTE
ADS7805
7805ALPRP
DGND
AGND2
AGND1
CURRENT
STATUS