TLC59283 Datasheet, PDF (17/25 Pages) Texas Instruments – 16-Channel, Constant-Current LED Driver with Pre-Charge FET

TLC59283
www.ti.com
SBVS199A – JUNE 2012 – REVISED JUNE 2012
Internal Pre-Charge FET
The internal pre-charge FET prevents ghosting of multiplexed LED modules. One cause of this phenomenon is
the parasitic capacitance charging current of the constant-current outputs (OUTn) and PCB wiring connected to
OUTn through the LED. One of the mechanisms is shown in Figure 23.
In Figure 23, the constant-current driver turns LED0-0 on at (1) and off at (2). After LED0-0 is turned off, the
OUT0 voltage is pulled up to V_CHG by LED0-0. This OUT0 node has some parasitic capacitance (such as the
constant-current driver output capacitance and the board layout capacitance shown as C0-2). After LED0-0 turns
off, SWPMOS0 is turned off, SWNMOS0 is turned on for COM0, and COM0 is pulled down to GND. Because
there is a parasitic capacitance between COM0 and OUT0, the OUT0 voltage is also pulled down to GND.
Afterwards, SWPMOS1 is turned on for the next common line (COM1). When SWPMOS1 turns on, the OUT0
voltage is pulled up from the ground voltage to V_LED – V_F. The charge current (I_CHRG) flows to the parasitic
capacitor (C0) through LED1-0, causing the LED to briefly turn on and creating a ghosting effect of LED1-0.
VLED
(LED Power-Supply)
SW
PMOS1
LED1-1
LED1-2
SW
NMOS1
LED1-0
VLED
C0
C1
SW
PMOS0
I_CHRG
COM1
¼
Parasitic Capacitor
C2
COM0
SW
NMOS0
LED0-0
LED0-1
LED0-2
OUT0
OUT1
¼
OUT2
Ordinal
LED Driver
OUT0
OUT1
OUT2
ON
ON
ON
¼
Constant-Current
Output
SW ^ON
PMOS0 _OFF
SW ^ON
NMOS0 _OFF
SW ^ON
PMOS1 _OFF
SW ^ON
NMOS1 _OFF
High
BLANK
Low
ON
OUT0
OFF
OUT0
VLED
Voltage
VLED - V_F
LED0-0
Current
LED1-0
Current
20 mA
0 mA
20 mA
0 mA
COM0 is VLED level.
COM0 is GND level.
COM1 is VLED level.
COM1 is GND level.
V_CHG
GND
(1) (2)
OUT0 voltage is pulled down to GND side
by the coupling with LED lamp capacitor
between COM0 and OUT0.
(3)
(4)
Ghost phenomenon is observed
when COM1 goes up to VLED.
Figure 23. LED Ghost-Lighting Phenomenon Mechanism
Copyright © 2012, Texas Instruments Incorporated
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