DLPS052 October 2015 DLPA3000
The measurement system (Figure 24) 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 0x0A, 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 3 gain settings (1x, 9.5x, and 18x). The gain of the VGA can be set through register 0x0A, AFE_GAIN. The maximum input voltage of the VGA is 1.5 V. However, some of the internal voltages are too large to be handled by the VGA and are divided down first.
The multiplexer (MUX) connects to a wide range of nodes. Selection of the MUX input can be done through register 0x0A, AFE_SEL. Signals that can be selected:
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 DLPA3000. 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 0x18, 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 (VLED) is measured by sensing the feedback pin of the illumination driver (ILLUM_A_FB). Like 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 0x19, 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 by knowing the value of sense resistor RLIM 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 junction temperature of the chip: Temperature (°C) = 300 × VOTS (V) –270
For storage of trim bits, but also for the USER EEPROM bytes (0x30 to 0x35), the DLPA3000 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 ≈12 V.
LABB is a feature that stands for Local Area Brightness Boost. LABB locally increases the brightness 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:
Sampling of the signal can be done through one of the following methods:
ACMPR_IN_1,2,3 can measure external signals from for instance a light sensor or a temperature sensor. It should be ensured that the voltage on the input does not exceed 1.5 V.