DLPA3000 Datasheet, PDF (26/75 Pages) Texas Instruments – PMIC and High-Current LED Driver IC

DLPA3000
DLPS052 – OCTOBER 2015
www.ti.com
7.3.2.4.3 Transient Current Limit
Typically the forward voltages of the GREEN and BLUE diodes are close to each other (about 3 V to 5 V)
however the forward voltage of the red diode is significantly lower (2 V to 4 V). This can lead to a current spike in
the RED diode when the strobe controller switches from green or blue to red. This happens because V_LED is
initially at a higher voltage than required to drive the red diode. DLPA3000 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 register 0x02 (ILLUM_ILIM). In a typical application it is required only for the RED diode. The value for
ILLUM_ILIM should be set at least 20% higher than the DC regulation current. Register 0x02
(ILLUM_SW_ILIM_EN) contains three bits to select which switch employs the transient current limiting feature.
The effect of the transient current limit on the LED current is shown in Figure 10.
Current
overshoot
Transient current
limit active
ILLUM_ILIM
SW_IDAC
SW_IDAC
TIME
TIME
Figure 10. LED Current Without (Left) and With (Right) Transient Current Limit
7.3.2.5 Illumination Monitoring
The illumination block is continuously monitored for system failures to prevent damage to the DLPA3000 and
LEDs. Several possible failures are monitored, such as a broken control loop and a too high or too low output
voltage V_LED. The overall illumination fault bit is in register 0x0C (ILLUM_FAULT). If any of the below failures
occur, the ILLUM_FAULT bit may be set high:
• ILLUM_BC1_PG_FAULT
• ILLUM_BC1_OV_FAULT
Where PG is power good and OV is overvoltage.
7.3.2.5.1 Power Good
Both the Illumination driver and the Illumination LDO have a power good indication. The power good for the
driver indicates if the output voltage (V_LED) is within a defined window indicating that the LED current has
reached the set point. If, for some reason, the LED current cannot be controlled to the intended value, this fault
occurs. Subsequently, bit ILLUM_BC1_PG_FAULT in register 0x27 is set high. The illumination LDO output
voltage is also monitored. When the power good of the LDO is asserted, it implies that the LDO voltage is below
a pre-defined minimum of 80% (rising) or 60% (falling) edge. The power good indication for the LDO is in register
0x27 (V5V5_LDO_ILLUM_PG_FAULT).
7.3.2.5.2 Ratio Metric Overvoltage Protection
The DLPA3000 illumination driver LED outputs are protected against open circuit use. In case no LED is
connected and the PAD device is instructed to set the LED current to a specific level, the LED voltage
(ILLUM_A_FB) will quickly rise and potentially rail to VIN. This should be prevented. The OVP protection circuit
triggers once V_LED crosses a predefined level. As a result the DLPA3000 will be switched off.
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