Texas Instruments LP8863EVM, Руководство пользователя

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Using the LP8863EVM
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24 SNVU558 – February 2017
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The LP8863EVM Evaluation Module
10 Using the LP8863EVM
The LP8863-Q1 automotive LED driver can be set or programmed to support optimal application
configuration for boost and LED driver control. A few basic settings such as boost switch frequency, PWM
output frequency, and LED string current can be controlled by external resistor options, and other settings
for preferences such as dimming option, brightness input selection, slope control, etc can be programmed
using LP8863-Q1 GUI software. This section shows how to set hardware conditions such as power
sequences, external resistor options, etc.
10.1 Power up/down sequence
Power up: Input V
IN
(generating VDD from on-board LDO) a few hundred µs earlier than EN. Input VBAT
and VDDIO earlier than EN.
Power down: V
IN
must be high for at least 400 ms after EN is low for correct discharge operation. VDDIO
and VBAT must be low after EN is low.
10.2 Enable
The EN pin controls boost enable/disable. If brightness input is 0% while EN is high, boost output voltage
stays at the initial voltage (approximately 46 V).
10.3 Setting Boost Switch Frequency
R59 between BST_FSET and GND sets boost switch frequency. The value can be selected from Table 2 .
The default switch frequency setting is 300 kHz.
Table 2.
R_FSET (k Ω ) BOOST SW FREQUENCY (kHz)
3.92 303
4.75 400
5.76 606
7.87 800
11 1000
17.8 1250
42.2 1667
140 2222
10.4 Setting PWM Output Frequency
R58 between PWM_FSET and GND sets PWM output frequency. The value can be selected from
Table 3 . The default PWM output frequency setting is 9.8 kHz.
Table 3.
R_FSET (k Ω ) BOOST SW FREQUENCY (kHz)
3.92 152
4.75 304
5.76 610
7.87 1221
11 2441
17.8 4883
42.2 9766
140 19531