LP3942 Datasheet, PDF (8/20 Pages) National Semiconductor (TI) – The Dual RGB LED Controller with 1.5x/2x Charge Pump and SPI Interface

Start-Up Sequence of LP3942
The LP3942 start-up sequence can be triggered in the following way: V_DD power is connected to the device and NRST pin is ‘0’
(or floating) and NSTBY is set to ‘1’ via SPI.
The LP3942 activates first internal oscillator and waits for appr. 0.8 ms. Then, if CP_ON bit is set to ‘1’, LP3942 enables internal
soft-start circuitry to start-up the charge pump smoothly. Soft-start sequence takes appr. 200 µs. After this start-up sequence,
P_OUT is settled to correct value and RGB outputs can be enabled via SPI.
Modes of Operation
RESET:
In the RESET mode all the internal registers are reset to the default values. Reset is entered always if input
NRST is LOW or internal Power On Reset is active.
STANDBY:
The STANDBY mode is entered if the register bit NSTBY is HIGH and Reset is not active. This is the low
power consumption mode, when all circuit functions are disabled. Registers can be written in this mode and
the control bits are effective immediately after power up.
STARTUP:
INTERNAL STARTUP SEQUENCE powers up all the needed internal blocks. To ensure the correct oscillator
initialization, a 0.8 ms delay is generated by the internal state-machine. Thermal shutdown (T_SHD) stops the
chip operation and Startup mode is entered. Normal mode is entered after the device has cooled down.
NORMAL/CP OFF During NORMAL MODE WITH CHARGE PUMP OFF all LED controls can be used but the charge pump is
not active.
NORMAL/CP ON In NORMAL MODE WITH CHARGE PUMP ON all the chip functions are active.
Internal Start-Up Sequence
www.national.com
20129207
8