NXP Semiconductors
PCU9955
16-channel UFm I 2 C-bus 57 mA constant current LED driver
7.3.15 Overtemperature protection
If the PCU9955 chip temperature exceeds its limit (T th(otp) , see Table 19 ), all output
channels will be disabled until the temperature drops below its limit minus a small
hysteresis (T hys , see Table 19 ). Once the die temperature reduces below the
T th(otp) ? T hys , the chip will return to the same condition it was prior to the overtemperature
event.
7.4 Power-on reset
When power is applied to V DD , an internal power-on reset holds the PCU9955 in a reset
condition until V DD has reached V POR . At this point, the reset condition is released and the
PCU9955 registers and I 2 C-bus state machine are initialized to their default states (all
zeroes) causing all the channels to be deselected. Thereafter, V DD must be pulled lower
than 1 V and stay LOW for longer than 20 ? s. The device will reset itself, and allow 2 ms
for the device to fully wake up.
7.5 Hardware reset recovery
When a reset of PCU9955 is activated using an active LOW input on the RESET pin, a
reset pulse width of 2.5 ? s minimum is required. The maximum wait time after RESET pin
is released is 1.5 ms.
7.6 Software reset
The Software Reset Call (SWRST Call) allows all the devices in the I 2 C-bus to be reset to
the power-up state value through a specific formatted I 2 C-bus command.
The maximum wait time after software reset is 1 ms.
The SWRST Call function is defined as the following:
1. A START command is sent by the I 2 C-bus master.
2. The reserved General Call address ‘0000 000’ with the W bit set to ‘0’ (write) is sent
by the I 2 C-bus master.
3. Since PCU9955 is a UFm I 2 C-bus device, no acknowledge is returned to the I 2 C-bus
master.
4. Once the General Call address has been sent, the master sends 1 byte with 1 specific
value (SWRST data byte 1): Byte 1 = 06h.
If more than 1 byte of data is sent, they will be ignored by the PCU9955.
5. Once the correct byte (SWRST data byte 1) has been sent, the master sends a STOP
command to end the SWRST function: the PCU9955 then resets to the default value
(power-up value) and is ready to be addressed again within the specified bus free
time (t BUF ).
PCU9955
Product data sheet
All information provided in this document is subject to legal disclaimers.
Rev. 2 — 2 October 2012
? NXP B.V. 2012. All rights reserved.
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