TLC59116-Q1 Datasheet, PDF (30/39 Pages) Texas Instruments – 16-Channel Constant-Current LED Sink Driver

TLC59116-Q1
SLDS223A – MARCH 2016 – REVISED MARCH 2016
10 Application and Implementation
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NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
10.1 Application Information
10.1.1 Constant Current Output
In LED display applications, TLC59116-Q1 provides nearly no current variations from channel to channel and
from device to device. While I_OUT ≤ 52 mA, the maximum current skew between channels is less than ±6% and
less than ±10% between devices.
10.1.2 Adjusting Output Current
TLC59116-Q1 scales up the reference current (I_ref) set by the external resistor (R_ext) to sink the output current
(I_out) at each output port. Table 13 shows the Configuration Code and discusses bits CM, HC, and CC[5:0]. The
following formulas can be used to calculate the target output current I_OUT,target in the saturation region:
V_REXT = 1.26 V × VG
(3)
I_ref = V_REXT/R_ext, if another end of the external resistor R_ext is connected to ground
(4)
I_OUT,target = I_ref × 15 × 3^{CM – 1}
(5)
Where R_ext is the resistance of the external resistor connected to the REXT terminal, and V_REXT is the voltage of
REXT, which is controlled by the programmable voltage gain (VG), which is defined by the Configuration Code.
The Current Multiplier bit (CM) sets the ratio I_OUT,target/I_ref to 15 or 5 (sets the exponent CM – 1 to either 0 or –1).
After power-on, the default value of VG is 127/128 = 0.992, and the default value of CM is 1, so that the ratio
I_OUT,target/I_ref = 15. Based on the default VG and CM:
V_REXT = 1.26 V × 127/128 = 1.25 V
(6)
I_OUT,target = (1.25 V/R_ext) × 15
(7)
Therefore, the default current is approximately 20 mA at 931 Ω. The default relationship after power-on between
I_OUT,target and R_ext is shown in Figure 24.
shows the output voltage versus the output current with several different resistor values on REXT. This shows
the minimum voltage required at the device to have full VF across the LED. The VLED voltage must be higher
than the VF plus the VOL of the driver. If the VLED is too high, more power will be dissipated in the driver. If this
is the case, a resistor can be inserted in series with the LED to dissipate the excess power and reduce the
thermal conditions on the driver.
If a single driver is used with LEDs that have different VF values, resistors can also be used in series with the
LED to remove the excess power from the driver. In cases where not all outputs are being used, the unused
outputs can be left floating without issue.
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