米6体育平台手机版

ZHCSL07C September 2019 – August 2021 TPS8802

PRODUCTION DATA

封装选项

机械数据 (封装 | 引脚)

DCP|38
- MPDS520B

散热焊盘机械数据 (封装 | 引脚)

DCP|38
- PPTD170A

订购信息

9.2.2.2 LED Driver Component Selection

The LED current depends on the TEMPCO bits, PDAC register and CSA and CSB resistors. Changing any of these values affects the LED current and temperature compensation. The following method selects the TEMPCO, PDAC, and CSA resistor value based on the required LED current and temperature compensation. The 100-mA LED current and 1 mA/°C temperature compensation is used as an example for LED A. Repeat the process for LED B.

Determine the room temperature current and temperature compensation required by the application.
- 100mA and 1mA/°C is required by the design.
Calculate the compensation in percentage per degree by dividing the compensation coefficient by the current and multiplying by 100.
- 1 mA/°C divided by 100 mA is 1%/°C.
Use Table 9-1 or Table 9-2 to select a TEMPCO setting which contains the required compensation. If the required compensation is in two ranges, use the range with a higher TEMPCO setting. If the required temperature coefficient is not in any of the ranges, choose the TEMPCO and PDAC setting closest to the required temperature coefficient, then go to step 5.
- 1%/°C is between the mimumum and maximum for TEMPCO = 11.
Calculate the target CSA voltage. Divide the driver temperature coefficient [mV/°C] by the desired temperature coefficient [%/°C] and multiply by 100.
- 1.040 mV/°C divided by 1 %/°C is 104 mV.
Calculate the CSA resistor by dividing the target CSA voltage by the required current and subtracting 0.1 Ω for internal resistance.
- 104 mV divided by 100 mA is 1.04 Ω. Subtract 0.1 Ω to get 0.94 Ω.
Select the closest available resistor and calculate the final CSA voltage by multiplying the required current by the total resistance (external and internal).
- Use a 0.92 Ω resistor. Multiply 100 mA and 1.02 Ω to get 102mV CSA voltage.
Calculate the PDAC value by subtracting the final CSA voltage by the specified CSA voltage at PDAC = 0x00 and dividing the result by 1.176 mV (the DAC LSB, equal to 300 mV divided by 255).
- 102 mV minus 79 mV is 23 mV, divided by 1.176 mV is 20. Write 0x14 to the PDAC register.
Calibrate the PDAC value. If using the LED A driver, read the CSA_BIN register bits and add 0x11 if CSA_BIN=00b, add 0x06 if CSA_BIN=01b, subtract 0x06 if CSA_BIN=10b, or subtract 0x11 if CSA_BIN=11b. The CSA_BIN value varies from unit to unit and must be read on each unit calibrated using this method. Alternatively, measure the CSA or CSB voltage using the MCU ADC and adjust PDAC accordingly.
- The microcontroller reads that a unit has CSA_BIN=01b. 0x20 is written to PDAC_A.

Table 9-1 Temperature Coefficients for Each TEMPCOA and DAC_A Setting

Register Setting	CSA Voltage [mV], T = 27°C	Temperature Coefficient [mV/°C]	Temperature Coefficient [%/°C]	Coefficient Information
TEMPCOA[1:0] = 11, PDAC_A = 0x00	79	1.040	1.316%	Max for TEMPCO = 11b
TEMPCOA[1:0] = 11, PDAC_A = 0xFF	376	1.040	0.277%	Min for TEMPCO = 11b
TEMPCOA[1:0] = 10, PDAC_A = 0x00	188	0.693	0.369%	Max for TEMPCO = 10b
TEMPCOA[1:0] = 10, PDAC_A = 0xFF	484	0.693	0.143%	Min for TEMPCO = 10b
TEMPCOA[1:0] = 01, PDAC_A = 0x00	277	0.416	0.150%	Max for TEMPCO = 01b
TEMPCOA[1:0] = 01, PDAC_A = 0xFF	572	0.416	0.073%	Min for TEMPCO = 01b
TEMPCOA[1:0] = 00, PDAC_A = 0x00	299	0.347	0.116%	Max for TEMPCO = 00b
TEMPCOA[1:0] = 00, PDAC_A = 0xFF	593	0.347	0.059%	Min for TEMPCO = 00b

Table 9-2 Temperature Coefficients for Each TEMPCOB and DAC_B Setting

Register Setting	CSB Voltage [mV], T = 27°C	Temperature Coefficient [mV/°C]	Temperature Coefficient [%/°C]	Coefficient Information
TEMPCOB[1:0] = 11, PDAC_B = 0x00	81	1.040	1.284%	Max for TEMPCO = 11b
TEMPCOB[1:0] = 11, PDAC_B = 0xFF	379	1.040	0.272%	Min for TEMPCO = 11b
TEMPCOB[1:0] = 10, PDAC_B = 0x00	189	0.693	0.369%	Max for TEMPCO = 10b
TEMPCOB[1:0] = 10, PDAC_B = 0xFF	486	0.693	0.143%	Min for TEMPCO = 10b
TEMPCOB[1:0] = 01, PDAC_B = 0x00	277	0.416	0.150%	Max for TEMPCO = 01b
TEMPCOB[1:0] = 01, PDAC_B = 0xFF	572	0.416	0.073%	Min for TEMPCO = 01b
TEMPCOB[1:0] = 00, PDAC_B = 0x00	299	0.347	0.116%	Max for TEMPCO = 00b
TEMPCOB[1:0] = 00, PDAC_B = 0xFF	594	0.347	0.059%	Min for TEMPCO = 00b

Use the same procedure for the blue LED, requiring 50 mA and 0.1 mA/°C, to calculate TEMPCOB = 10, RCSB = 6.8 Ω, VCSB = 345 mV, PDAC_B = 0x85 (before calibration).

The two drivers are identical, except for the CSA_BIN code to improve the accuracy of the LED_A driver for IR LEDs. Connect the IR LED to the LED A driver and the blue LED to the LED B driver in multi-wave systems.