Datasheet

DEVICE INFORMATION
Digital Inputs
Limiter
I =I
INmax LIM
5V
I
LIM
I
IN
IPx
R
LIM
I Mirror
n=72
LIM
I
REF
1.25V
REF
LIM
LIM
90 V 90 V
R = = = 36 kΩ
I 2.5 mA
Debounce Filter
SN65HVS885
SLAS638 – JANUARY 2009 ............................................................................................................................................................................................... www.ti.com
Figure 10. Digital Input Stage
Each digital input operates as a controlled current sink limiting the input current to a maximum value of I
LIM
. The
current limit is derived from the reference current via I
LIM
= n × I
REF
, and I
REF
is determined by I
REF
= V
REF
/R
LIM
.
Thus, changing the current limit requires the change of R
LIM
to a different value via: R
LIM
= n × V
REF
/I
LIM
.
Inserting the actual values for n and V
REF
gives: R
LIM
= 90 V / I
LIM
.
While the device is specified for a current limit of 3.6 mA, (via R
LIM
= 25 k Ω ), it is easy to lower the current limit
to further reduce the power consumption. For example, for a current limit of 2.5 mA simply calculate:
The HVS885 applies a simple analog/digital filtering technique to remove unintended signal transitions due to
contact bounce or other mechanical effects. Any new input (either low or high) must be present for the duration
of the selected debounce time to be latched into the shift register as a valid state.
The logic signal levels at the control inputs, DB0 and DB1 of the internal Debounce-Select logic determine the
different debounce times listed in the following truth table.
Table 1. Debounce Times
DB1 DB0 FUNCTION
Open Open 3 ms delay
Open GND 1 ms delay
0 ms delay
GND Open
(Filter bypassed)
GND GND Reserved
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Product Folder Link(s): SN65HVS885