LP8860-Q1_17 Datasheet, PDF (27/110 Pages) Texas Instruments – Low-EMI Automotive LED Driver With Four 150-mA Channels

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LP8860-Q1
SNVSA21F – MAY 2014 – REVISED JULY 2017
8.3.2.7 PWM Calculation Data Flow for Display Mode
Figure 17 shows the PWM calculation data flow for display mode. In PWM direct control mode most of the blocks
are bypassed, and this flow chart does not apply.
HYSTERESIS
[1:0]
10
MHz
Clock
BRT_MODE[1:0]
External
Temp Sensor _{PWM_SLOPE[3:0]}
I_SLOPE[2:0] _DITHER[2:0]
EN_BRT_ADV_SLOPE
Current 12-bit
PWM Input
Signal
PWM
Detector
16-bit
00
01
10
16-bit
Temperature
Regulator
16-bit
Sloper
16-bit
Advanced ^16-bit
Slope
PWM &
Current
Control
PWM
16-bit
Dither
16-bit _PWM
Comparator
16-bit
11
11-bit
EN_PWM_I
PWM
freq
16-bit
Brightness
Register
Internal
Temp Sensor
GAIN_CTRL[2:0]
PWM
Counter
PWM_RESOLUTION
[1:0] _{PWM_FREQ[3:0]}
...
DISPLAY
MODE LED
CURRENT
SINKS
PLL Clock 5...40 MHz
Copyright © 2016, Texas Instruments Incorporated
Figure 17. PWM Data Flow Calculation
BLOCK NAME
PWM detector
Brightness register
Brightness mode control
Temperature regulator
External temperature sensor
Internal temperature sensor
Sloper
Advanced sloper
PWM and Current Control
Dither
PWM comparator
PWM counter
Table 8. PWM Calculation Blocks
DESCRIPTION
PWM detector block measures the duty cycle of the input PWM signal. Resolution depends on the
input signal frequency. Hysteresis selection sets the minimum allowable change to the input.
Smaller changes are ignored.
16-bit register for brightness setting <DISP_CL1_BRT[15:0]>
Brightness control block gets 16-bit value from the PWM detector, and also 16-bit value from the
brightness register <DISP_CL1_BRT[15:0]>. <BRT_MODE[1:0]> selects whether to use PWM input
duty cycle value, the brightness register value or multiplication.
Temperature regulator reduces LED PWM duty cycle depending on internal and external
temperature sensor.
See LED Current Dimming With Internal Temperature Sensor and LED Current Limitation With
External NTC Sensor for details
External NTC temperature sensor
Internal die temperature sensor
Sloper makes the smooth transition from one brightness value to another. Slope time can be
adjusted from 0 ms to 511 ms with <PWM_SLOPE[2:0]> EEPROM bits.
Advanced slope makes brightness changes smoother for eye; see Brightness Slope for details
Hybrid PWM and Current dimming improves the optical efficiency of the LEDs by using PWM
control with lower brightness values and current control with greater values. <EN_PWM_I>
EEPROM bit enables Hybrid PWM and Current control. PWM dimming range can be set 12.5 to
50% of the brightness range with <GAIN_CTRL[2:0]> EEPROM bits. Current slope can be adjusted
by using the <I_SLOPE[2:0]> EEPROM bits. See LED Dimming Methods for details
With dithering the output resolution can be further increased. This way the brightness change steps
are not visible to eye. The amount of dithering is 0 to 4 bits, and is selected with <DITHER[2:0]>
EEPROM bits.
PWM comparator compares the PWM counter output to the value received from the dither block.
Output of the PWM comparator directly controls the LED current sinks. If Phase Shift PWM
(PSPWM) mode is used, the PWM counter values for each LED output are modified by summing an
offset value to create different phases.
Overflowing 16-bit PWM counter creates new PWM cycle. Step for incrementation is defined by
<PWM_FREQ[3:0]> and <PWM_RESOLUTION[1:0]> bits, see Table 3.
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