ADS8681_16 Datasheet, PDF (24/74 Pages) Texas Instruments – 16-Bit, High-Speed, Single-Supply, SAR ADC Data Acquisition System with Programmable, Bipolar Input Ranges

ADS8681, ADS8685, ADS8689
SBAS633B – FEBRUARY 2016 – REVISED DECEMBER 2016
www.ti.com
Feature Description (continued)
7.3.3 Input Protection Circuit
The device features an internal overvoltage protection (OVP) circuit on each of the analog inputs. Use the
internal protection circuit only as a secondary protection scheme. The external protection devices in the end
application are highly recommended to be used to protect against surges, electrostatic discharge (ESD), and
electrical fast transient (EFT) conditions. A conceptual block diagram of the internal OVP circuit is shown in
Figure 48.
AVDD
V_P+
R_FB
0V
ESD
AVDD
V_P-
R_S
AIN_P
R_S
AIN_GND
1 MŸ _D1p
D2p
AVDD
D1n
V_±
V₊
+
1 MŸ
D2n
R_DC
ESD
V_OUT
V_B
GND
Figure 48. Input Overvoltage Protection Circuit Schematic
As shown in Figure 48, the combination of the 1-MΩ (or, 1.2 MΩ for appropriate input ranges) input resistors
along with the PGA gain-setting resistors R_FB and R_DC 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 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 1. Input Overvoltage Protection Limits When AVDD = 5 V or Offers a Low Impedance of < 30 kΩ⁽¹⁾
INPUT CONDITION
(V_OVP = ±20 V)
CONDITION
RANGE
|V_IN| < |V_RANGE|
|V_RANGE| < |V_IN| < |V_OVP|
Within operating range
Beyond operating range but
within overvoltage range
|V_IN| > |V_OVP|
Beyond overvoltage range
TEST
CONDITION
ADC
OUTPUT
COMMENTS
All input
ranges
All input
ranges
All input
ranges
Valid
Device functions as per data sheet specifications.
Saturated
Saturated
ADC output is saturated, but device is internally protected
(not recommended for extended time).
This usage condition can cause irreversible damage to the
device.
(1) GND = 0 V, AIN_GND = 0 V, |V_RANGE| is the maximum input voltage for any selected input range, and |V_OVP| is the break-down voltage
for the internal OVP circuit. Assume that R_S is approximately 0 Ω.
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