LM3464 Datasheet, PDF (14/33 Pages) National Semiconductor (TI) – 4 Channel LED Driver Evaluation Board

LM3464, LM3464A
SNVS652F – APRIL 2010 – REVISED MAY 2013
www.ti.com
Figure 18. Linear LED Current Regulator
The driving currents of the LED strings are defined by the values of R_ISNS1 to R_ISNS4 individually. The LED current
and the value of R_ISNSx are related by the following equation:
I_LED
=
200
R_ISNSx
mA
(10)
Since the accuracy of the LED currents are dependent on the tolerance of R_ISNSx, the R_ISNSx to recommended to
be thick carbon file resistors with no more than 1% tolerance and adequate rated power to the desired LED
current.
Figure 19. LED Current vs R_ISNSx
RESPONSE OF THE LM3464/64A DRIVER STAGE
In order to ensure good operation stability of the entire system, the response of the LM3464/64A circuitry must
be set slower than the primary power supply. The response of the LM3464/64A is decided by the value of the
capacitor, C_DHC. In general, a higher capacitance C_DHC will result in slower response of the LM3464/64A driver
stage.
Generally, a first order integrator that consists of C_DHC and a transconductance amplifier with g_m = 76umho and
+/– 15uA current limit as shown in Figure 20 defines the frequency response of the LM3464/64A driver stage.
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