TLC5924 Datasheet, PDF (9/23 Pages) Texas Instruments – 16-CHANNEL LED DRIVER WITH DOT CORRECTION AND PRE-CHARGE FET

TLC5924
www.ti.com
SLVS626 – JUNE 2006
PRINCIPLES OF OPERATION (continued)
Output Enable
When BLANK = H, TLC5924 switches off the sink current of all OUTn with each output delay, then switches on
the pre-charge FET of all OUTn. When BLANK = L, the TLC5924 switches off the pre-charge FETs, and enables
the sink current set by input data. See "Delay Between Outputs" section for more detail on the output delay.
Table 1. BLANK Signal Truth Table
BLANK
LOW
HIGH
OUT0 - OUT15
Normal condition
VUP
Setting Channel On/Off Status
All OUTn channels of TLC5924 can be switched on or off independently. Each of the channels can be
programmed with a 1-bit word. On/Off data are entered for all channels at the same time. The complete On/Off
data format consists of 16 x 1-bit words, which form a 16-bit wide data packet. The channel data is put one after
another. All data is clocked in with MSB first. Figure 8 shows the On/Off data format.
MSB
15
On/Off On/Off On/Off
OUT15 OUT14 OUT13
On/Off Data
On/Off
OUT2
On/Off
OUT1
LSB
0
On/Off
OUT0
Figure 8. On/Off Data Format
To input On/Off data into On/Off register MODE must be set to low. The internal input shift register is then set to
16 bit width. After all serial data is clocked in, a rising edge of XLAT is used to latch data into the On/Off
register. The ON/OFF register is an edge-triggered latch of XLAT signal. BLANK signal does not need to be high
to latch in new data. Figure 16 shows the On/Off data input timing chart.
Delay Between Outputs
The TLC5924 has graduated delay circuits between outputs. These delay circuits can be found in the constant
current block of the device (see Functional Block Diagram). The fixed delay time is 20 ns (typical), OUT0 has no
delay, OUT1 has 20 ns delay, OUT2 has 40 ns delay, etc. This delay prevents large inrush currents, which
reduce power supply bypass capacitor requirements when the outputs turn on. The delay works during switch on
and switch off of each output channel. LEDs that have not turned on before BLANK is pulled high will still turn on
and off at the determined delayed time regardless of the state of BLANK. Therefore, every LED will be
illuminated for the amount of time BLANK is low.
Pre-Charge FET On/Off Timing
The pre-charge FETs turn on at the same time; and, they turn on at the time the last output that is on turns off.
All pre-charge FETs turn off just after BLANK signal becomes low level, regardless of on/off data of each output.
Figure 9 shows the example of BLANK and OUTn timing.
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