7805ALPRPDK datasheet(9/18 Pages) MAXWELL

9 / 18 page

All data sheets are subject to change without notice

16-Bit Latchup Protected ADC

7805ALP

01.10.05 Rev 9

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.

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.

I/Os

POWER

SWITCH

PROTECTED

DEVICE

STATUS

OUTPUT

DECPLNG

VDIG

VANA

BYTE

ADS7805

7805ALPRP

DGND

AGND2

AGND1

CURRENT

SENSOR

STATUS

DRIVER

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