7805ALP Datasheet, PDF (9/18 Pages) Maxwell Technologies – 16-Bit Latchup Protected ADC

16-Bit Latchup Protected ADC
7805ALP
steady state operation of the device. A simplified block diagram of 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.
VS
STATUS
OUTPUT
CURRENT
SENSOR
POWER
SWITCH
STATUS
DRIVER
PROTECTED
DEVICE
VDIG
VANA
ADS7805
BYTE
7805ALPRP
DECPLNG
I/Os
AGND1
AGND2
DGND
FIGURE 3. LATCHUP PROTECTION DIAGRAM
Differences Between the7805A and the ADS7805
Because the 7805A uses the ADS7805 die to perform the analog to digital conversion function its operation and per-
formance is very similar to the ADS7805 packaged part from Burr-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 from noise on the system digital
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 ceramic 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 diagram where 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 from the protected device. CAUTION: During the time that power is removed from the
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.
01.10.05 Rev 9
All data sheets are subject to change without notice 9
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