PCA9922BS NXP [NXP Semiconductors], PCA9922BS Datasheet - Page 8

• Manufacturer Part Number: PCA9922BS
• Description: 8-channel constant current LED driver with output error detection
• Manufacturer: NXP [NXP Semiconductors]

NXP Semiconductors
PCA9922_1
Product data sheet
7.2.2 Short-circuit detection principle
7.2.3 Entering error detect mode
Table 4.
[1]
The LED short-circuit detection compares the effective voltage level (V
shorted-load detection threshold voltages V
V
V
as an error status code in the Special mode. For short-circuit error detection, a channel
must be on.
Table 5.
Entering the error detect mode consists of a 5-clock sequence involving CLK, OE and LE
as shown in
detailed
noted that the act of driving LE HIGH around the rising edge of clock 4 opens the latch in
the current control register block and data captured in the shift register at that point in time
is moved into the output control register. It should also be noted that the output logic was
enabled for a brief period of time while OE is LOW around the rising edge of clock 2. The
outputs LED[7:0] will glitch during this period.
State of
output port
off
on
State of
output port
off
on
Fig 6.
th(det)sc
th(norm)
I
th(det)
inTable 10
threshold, no error is detected or error bit is reset. This error status can be read
threshold, the PCA9922 detects a shorted-load condition. If V
= 0.5
Timing for ‘Enter Error Detect Mode’ command
Open-circuit detection
Shorted-load detection
Figure
I
O
(target) (typical).
Condition of
output current
I
I
I
Condition of
output voltage
I
V
V
O
O
O
O
8-channel constant current LED driver with output error detection
O
O
to guarantee proper operation of the error detect circuitry. It should be
6. The user must meet the set-up and hold times for OE and LE as
= 0 mA
< I
= 0 mA
< V
I
Rev. 01 — 15 January 2009
th(det)
th(det)
V
th(det)sc
th(norm)
[1]
[1]
CLK
OE
LE
Error status code
0
1
channel n error status bit 0
Error status code
0
1
channel n error status bit 0
th(det)sc
and V
002aad204
th(norm)
. If V
Meaning
detection not possible
open circuit
normal
Meaning
detection not possible
short circuit
normal
O
PCA9922
is above the
O
O
© NXP B.V. 2009. All rights reserved.
) with the
is below the
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