pca9901 NXP Semiconductors, pca9901 Datasheet - Page 11

• Manufacturer Part Number: pca9901
• Description: One Wire Single Led Driver
• Manufacturer: NXP Semiconductors

NXP Semiconductors
PCA9901_1
Product data sheet
8.8.4 ‘Synchronization’ signal not generated after RUN ONCE command
8.10 Short-circuit and thermal protection
8.9 Current source generation
The PCA9901 is waiting for the ‘Synchronization’ signal (rising edge of CTRL) after a
RUN ONCE command has been issued.
The LED output contains a constant current driver that will source a current that is
determined by an external resistor connected between ISET pin and GND. The current
can be set using the following formula:
R
be programmed.
Remark: LED current accuracy is proportional to the accuracy and temperature
coefficient tolerance of R
When no external resistor is connected between the ISET pin and GND, the LED output is
able to source 5 mA through a fully internal current source. It is automatically shut down
when an external resistor is connected to ISET.
Remark: The LED current accuracy is proportional to the tolerance and temperature
coefficient of the resistor.
Remark: To save power, the current source generator is only enabled when the LED
needs to be turned on.
A short-circuit and thermal protection circuitry disables the LED output driver and the
current generator when a short occurs or when a high temperature condition has been
detected.
The circuitry is active during normal mode operation (Programing, RUN ONCE, RUN or
Bypass modes). When a fault condition is detected, the reference current circuitry (ISET)
and the LED output stage (LEDOUT) are automatically shut down. This will cause
LEDOUT to be OFF as long as the fault condition is present. The other analog blocks
(oscillator, voltage reference) are kept enabled as long as the PCA9901 is in normal mode
operation.
The PCA9901 goes automatically to Power-down mode when it exits the programming,
RUN ONCE, RUN or Bypass modes.
I
1. Once the RUN ONCE command has been decoded (end of the 1.5 ms window), a
2. The time-out counter counts until it reaches the maximum allowed ON value. The
3. If the maximum time-out value is reached, the RUN ONCE command is automatically
O
ext
=
time-out counter starts counting as long as CTRL stays LOW.
maximum allowed ON time is greater than or equal to 255 ms.
Remark: If CTRL goes HIGH before reaching the maximum counter value, the
time-out counter is reset and the PCA9901 runs the sequence once.
aborted and the PCA9901 goes to Shutdown mode.
can be chosen so that a maximum LED current value between 1 mA and 20 mA can
(
----------------------------- -
1.23
R
ext
×
400
)
Rev. 01 — 3 December 2009
ext
.
One wire single LED driver
PCA9901
© NXP B.V. 2009. All rights reserved.
11 of 27
(1)