TLC5922 Datasheet, PDF (6/16 Pages) Texas Instruments – LED DRIVER

TLC5922
SLVS486 – SEPTEMBER 2003
PARAMETER MEASUREMENT INFORMATION
SOUT
15 pF
Figure 4. Test Circuit for Tr0, Tf1, Td0, Td1
OUTn
51 Ω
15 pF
Figure 5. Test Circuit for Tr1, Tf1, Td2, Td3, Td5, Td6
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470 kΩ
XDOWN
Figure 6. Test Circuit for Td4
PRINCIPLES OF OPERATION
Setting Constant-Current Value
The maximum programmable output current for all 16 outputs is set by a single resistor, R_(IREF), which is placed
between IREF and GND. The current flowing through R_(IREF) is sampled by the TLC5922 and multiplied by a
scaling factor of 40 to set the maximum output current for all outputs. The voltage on IREF is set by an internal
band gap with a nominal value of 1.22V. The maximum programmable output current is set by Equation 1:
IMAX
+
VIREF
RIREF
40
(1)
where:
V_IREF = 1.22V
R_IREF = User selected external resistor (R_IREF should not be smaller than 600Ω)
Setting Dot-Correction
The TLC5922 has the capability to adjust the brightness of each channel, OUT0,...,OUT15. This capability is
called dot-correction. The external processor programs each of the 16 channels of the TLC5922 with a 7 bit word
that adjusts each respective output from 0% to 100% of the maximum output current, Imax. The 7 bits provides
2⁷ (= 128) programmable current values. Equation 2 below determines the output current for each output:
IOutn
+
IMAX
127
DCn
(2)
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