ADS8699IPWR datasheet(24/74 Pages) TI2

24 / 74 page

electrical fast transient (EFT) conditions. A conceptual block diagram of the internal OVP circuit is shown in

Figure 7-2.

VOUT

V+

V±

AVDD

GND

AIN_P

AIN_GND

1 MŸ

RDC

RFB

0 V

VP+

VP-

ESD

D1p

D2n

AVDD

D2p

D1n

ESD

Figure 7-2. Input Overvoltage Protection Circuit Schematic

As shown in Figure 7-2, the combination of the 1-MΩ (or, 1.2 MΩ for appropriate input ranges) input resistors

along with the PGA gain-setting resistors RFB and RDC limit the current flowing into the input pin. A combination

of anti-parallel diodes, D1 and D2 are added to protect the internal circuitry and set the overvoltage protection

limits.

Table 7-1 explains the various operating conditions for the device when powered on. This table indicates that

when the device is properly powered up (AVDD = 5 V) or offers a low impedance of < 30 kΩ, the internal

overvoltage protection circuit can withstand up to ±20 V on the analog input pins.

Table 7-1. Input Overvoltage Protection Limits When AVDD = 5 V (1)

INPUT CONDITION

(VOVP = ±20 V)

TEST

CONDITION

ADC

OUTPUT

COMMENTS

CONDITION

RANGE

|VIN| < |VRANGE|

Within operating range

All input

ranges

Valid

Device functions as per data sheet specifications.

|VRANGE| < |VIN| < |VOVP|

Beyond operating range but

within overvoltage range

All input

ranges

Saturated

ADC output is saturated, but device is internally protected

(not recommended for extended time).

|VIN| > |VOVP|

Beyond overvoltage range

All input

ranges

Saturated

This usage condition can cause irreversible damage to the

device.

(1)

GND = 0 V, AIN_GND = 0 V, |VRANGE| is the maximum input voltage for any selected input range, and |VOVP| is the break-down voltage

for the internal OVP circuit. Assume that RS is approximately 0 Ω.

The results indicated in Table 7-1 are based on an assumption that the analog input pin is driven by a very low

impedance source (RS is approximately 0 Ω). However, if the source driving the input has higher impedance, the

current flowing through the protection diodes reduces further, thereby increasing the OVP voltage range. Higher

source impedances result in gain errors and contribute to overall system noise performance.

Figure 7-3 shows the voltage versus current response of the internal overvoltage protection circuit when the

device is powered on. According to this current-to-voltage (I-V) response, the current flowing into the device

input pin is limited by the 1-MΩ (or 1.2 MΩ for appropriate input ranges) input impedance. However, for voltages

ADS8691, ADS8695, ADS8699

SBAS777B – DECEMBER 2016 – REVISED MARCH 2021

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