The measurement system (Figure 7-18) is designed to sense internal and external nodes and convert them to digital by the implemented AFE comparator. The AFE can be enabled through register AFE_EN. The reference signal for this comparator, ACMPR_REF, is a low pass filtered PWM signal coming from the DLPC. To be able to cover a wide range of input signals a variable gain amplifier (VGA) is added with three gain settings (1x, 9.5x, and 18x). The gain of the VGA can be set through register AFE_GAIN. The maximum input voltage of the VGA is 1.5 V. Some of the internal voltage are too large though to be handled by the VGA and are divided down first.

Figure 7-18 Measurement System Schematic

The multiplexer (MUX) connects to a wide range of nodes. Selection of the MUX input can be done through register AFE_SEL. Signals that can be selected:

• System input voltage, SYSPWR
• LED anode cathode voltage, ILLUM_A_FB
• LED cathode voltage, CHx_SWITCH
• V_R_LIM to measure LED current
• Internal reference, VREF_1V2
• Die Temperature represented by voltage VOTS
• EEPROM programming voltage, VPROG1,2/12
• LABB sensor, V_LABB
• External sense pins, ACMPR_IN_1,2,3

The system input voltage SYSPWR can be measured by selecting the SYSPWR/xx input of the MUX. Before the system input voltage is supplied to the MUX the voltage needs to be divided. This is because the variable gain amplifier (VGA) can handle voltages up-to 1.5 V whereas the system voltage can be as high as 20 V. The division is done internally in the DLPA3005. The division factor selection (VIN division factor) is combined with the auto LED turn off functionality of the illumination driver and can be set through register ILLUM_LED_AUTO_OFF_SEL.

The LED voltages can be monitored by measuring both the common anode of the LEDs as well as the cathode of each LED individually. The LED anode voltage (V_LED) is measured by sensing the feedback pin of the illumination driver (ILLUM_A_FB). Likewise the SYSPWR, the LED anode voltage needs to be divided before feeding it to the MUX. The division factor is combined with the overvoltage fault level of the illumination driver and can be set through register VLED_OVP_VLED_RATIO. The cathode voltages CH1,2,3_SWITCH are fed directly to the MUX without division factor.

The LED current can be determined knowing the value of sense resistor R_LIM and the voltage across the resistor. The voltage at the top-side of the sense resistor can be measured by selecting MUX-input RLIM_K1. The bottom side of the resistor is connected to GND.

VOTS is connected to an on-chip temperature sensor. The voltage is a measure for the chip’s junction temperature: Temperature (°C) = 300 × VOTS (V) – 270

For storage of trim bits, but also for the USER EEPROM bytes, the DLPA3005 has two EEPROM blocks. The programming voltage of EEPROM block 1 and 2 can be measured through MUX input VPROG1/12 and VPROGR2/12, respectively. The EEPROM programming voltage is divided by 12 before it is supplied to the MUX to prevent a too large voltage on the MUX input. The EEPROM programming voltage is about 12 V.

LABB is a feature that is Local Area Brightness Boost. LABB increases the brightness locally while maintaining good contrast and saturation. The sensor needed for this feature should be connected to pin ACMPR_IN_LABB. The light sensor signal is sampled and held such that it can be read independently of the sensor timing. To use this feature it should be ensured that:

• The AFE block is enabled (AFE_EN = 1).
• The LABB input is selected (AFE_SEL<3:0>=3h).
• The AFE gain is set appropriately to have AFE_Gain × VLABB < 1.5 V (AFE_GAIN<1:0>).

Sampling of the signal can be done through one of the following methods:

1. Writing to register TSAMPLE_SEL by specifying the sample time window and set bit SAMPLE_LABB=1 to start sampling. The SAMPLE_LABB bit is automatically reset to 0 at the end of the sample period to be ready for a next sample request.
2. Use the input ACMPR_LABB_SAMPLE-pin as a sample signal. As long as this signal is high the signal on ACMPR_IN_LABB is tracked. Once the ACMP_LABB_SAMPLE is set low again the value at that moment will be held.

ACMPR_IN_1,2,3 can measure external signals from for instance a temperature sensor. It should be ensured that the voltage on the input does not exceed 1.5 V.