DLPA2000
ZHCSCO5B –JUNE 2014–REVISED FEBRUARY 2018
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7.3.6 Transient Current Limiting
Typically the forward voltages of the green and blue diodes are close to each other (about 3 V to 4 V). However,
the forward voltage of the red diode is significantly lower (1.8 V to 2.5 V). This can lead to a current spike in the
red diode when the strobe controller switches from green or blue to red because VLED is initially at a higher
voltage than required to drive the RED diode. DLPA2000 provides transient current limiting for each switch to
limit the current in the LEDs during the transition. The transient current limit value is controlled through the
ILIM[3:0] bits in the IREG register. The same register also contains three bits to select which switch employs the
transient current limiting feature. In a typical application, the transient current limit will only apply to the RED
diode, and the ILIM[3:0] value will typically be set approximately 10% higher than the DC regulation current. The
effect that the transient current limit has on the LED current is shown in Figure 9.
1500
1200
900
600
300
0
1500
1200
900
600
300
0
Current overshoot due to
initially too high buck-boost
output voltage
Transient current
limit active
TIME
LED current with transient current limit.
Red LED current without transient current limit. The
current overshoots because the buck-boost voltage
starts at the (higher) level of the green or blue LED.
Figure 9. RED LED Current With and Without Transient Current Limit
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