TI-LP8864S-Q1：汽车LED背光驱动器，高效能与精准调光

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"TI-LP8864S-Q1.pdf" TI-LP8864S-Q1是一款专为汽车应用设计的高效LED背光驱动器，它符合AEC-Q100标准，适用于温度等级1的环境，能够在-40°C至+125°C的温度范围内稳定工作，并具有二级人体模型ESD保护和C4B级设备ESD保护。这款驱动器在3V至48V的输入电压范围内工作，提供了四个独立的150mA电流阱，每个通道的电流匹配度为1%。通过152Hz的LED输出PWM频率，可以实现高达32000:1的调光比，而使用I2C或PWM输入时，LED调光分辨率可达16位。 LP8864S-Q1的亮点之一是其自动移相PWM调光功能，这有助于优化LED的亮度控制和能效。此外，还支持12位模拟调光，提供了更细腻的亮度调整选项。该驱动器内置一个最高48V的升压或SEPIC直流/直流控制器，开关频率在100kHz到2.2MHz之间可调，且具备升压扩频功能以减少电磁干扰。升压同步输入允许用户通过外部时钟来设定升压开关频率，而在禁用升压模式时，输出电压会自动放电。在故障诊断方面，LP8864S-Q1具备多种功能，确保了系统可靠性和安全性。此驱动器特别适合用于汽车信息娱乐系统、汽车仪表组、智能车镜和抬头显示屏（HUD）等应用场景的背光照明。其升压控制器具有自适应输出电压控制，可根据LED电流阱的余量电压动态调整，以降低功耗。宽范围的可调频率设计可以避免AM无线电频段的干扰，同时，混合PWM调光和模拟电流调光功能则有助于降低电磁干扰，延长LED寿命，提升光学效率。封装选项包括HTSSOP（38引脚）和QFN（32引脚），其中QFN封装为5mm×5mm的紧凑设计，适合空间有限的应用。用户可以根据数据表末尾的可订购产品附录查看所有可用封装。简化的原理图展示了随着亮度和升压电压变化的效率曲线，强调了LP8864S-Q1在不同工作条件下的高效性能。此器件是汽车电子领域中LED背光解决方案的理想选择，兼顾性能、可靠性和能效。

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VDD

ISNSGND

OUT

ISNS

C1N

C1P

CPUMP

PGND

OUT

VSENSE_P

VSENSE_N

3 to 48V

VDD

PUMP

图 7-2. Charge Pump Disabled Circuit

If the charge pump is enabled, the CPCAP_STATUS bit shows whether a fly capacitor was detected and the

CP_STATUS bit shows status of any charge pump faults and generates an INT signal. The CP_INT_EN bit can

be used to prevent the charge-pump fault from causing an interrupt on the INT pin.

7.3.6 Boost Controller

The LP8864S-Q1 current-mode-controlled boost DC/DC controller generates the anode voltage for the LEDs.

The boost is a current-mode-controlled topology with a cycle by cycle current limit. The boost converter senses

the switch current and across the external sense resistor connected between ISNS and ISNSGND. A 20-m

sense resistor results in a 10-A cycle by cycle current limit. The sense resistor value could vary from 15 mΩ to

50 m

Ω depending on the application. Maximum boost voltage is configured with external FB-pin resistor divider

connected between V

OUT

and FB. The FB-divider equation is described in

节

7.3.6.3.

MUX

ADC

R Q

Adaptive

voltage

control

VREF

BOOST OSCILLATOR

OFF/BLANK TIME

PULSE GENERATOR

CURRENT RAMP

GENERATOR



COMP

OVP

OCP

TSD

OUT

PGND

ISNS

ISNSGND

CPUMP

BST_FSET

BST_SYNC

OUT

图 7-3. Boost Controller Block Diagram

The boost switching frequency is adjustable from 100 kHz to 2.2 MHz via an external resistor at BST_FSET (see

表 7-1). Resistor with 1% accuracy is needed to ensure proper operation.

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LP8864S-Q1

ZHCSLM4A – AUGUST 2020 – REVISED FEBRUARY 2021

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表 7-1. Boost Frequency Selection

R_BST_FSET (kΩ)

BOOST FREQUENCY (kHz)

3.92 400

4.75 200

5.76 303

7.87 100

11 500

17.8 1818

42.2 2000

124 2222

7.3.6.1 Boost Cycle-by-Cycle Current Limit

The voltage between ISNS and ISNSGND is used for both boost DC/DC controller's current sensing and cycle-

by-cycle current limit settings. When the cycle-by-cycle current limit is reached, the controller will turn off the

switching MOSFET immediately and turn on it again in next siwtching cycle. This cycle-by-cycle current limit

could be used as a common protection for all related DC/DC components (inductor, schottky diode and switching

MOSFET) to avoid current running over their max limit. Cycle-by-Cycle current limit won't trigger any faults of the

device.

CYCLE _ LIMIT

ISNS

SENSE

I =

(1)

where

• V

ISNS

= 200 mV

7.3.6.2 Controller Min On/Off Time

The device boost DC/DC controller has minimum on/off time as below table. Minimum off time should be

specially taken care in system design. The SW node rising time plus falling time should be higher than minimum

off time to avoid controller not turning off the MOSFET.

表 7-2. Controller Minimum On/Off Time

Frequency (kHz) Minimum Switch OFF Time (ns) Minimum Switch ON Time (ns)

100 to 500 150 150

1818 to 2222 40 110

7.3.6.3 Boost Adaptive Voltage Control

The LP8864S-Q1 boost DC/DC converter generates the anode voltage for the LEDs. During normal operation,

boost output voltage is adjusted automatically based on the LED current sink headroom voltages. This is called

adaptive boost control. The number of used LED outputs is set by LED_SET pin and only the active LED outputs

are monitored to control the adaptive boost voltage. Any LED strings with open or short faults are also removed

from the adaptive voltage control loop. The LED driver pin voltages are periodically monitored by the control loop

and the boost voltage is raised if any of the LED outputs falls below the V

HEADROOM

threshold. The boost voltage

is lowered until any of the LED outputs touch the V

HEADROOM

threshold. See 图 7-4 for how the boost voltage

automatically scales based on the OUTx-pin voltage, V

HEADROOM

and V

HEADROOM_HYS

LP8864S-Q1

ZHCSLM4A – AUGUST 2020 – REVISED FEBRUARY 2021

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Maximum boost voltage can be calculated with Equation 2. The maximum boost voltage can be reached during

OPEN string detection or if all LED strings are left disconnected.

§ ·

u   u

¨ ¸

BOOST _ MAX SEL _ MAX 1 REF

V I R 1 V

(2)

where

• V

REF

= 1.21 V

• I

SEL_MAX

= 38.7 µA

• R

/ R

normal recommended range is 7~15

The minimum boost voltage must be less than the minimum LED string voltage. Minimum boost voltage is

calculated with Equation 3:

BOOST_MIN REF

V = +1 V

§ ·

¨ ¸

(3)

where

• V

REF

= 1.21 V

When the boost OVP_LOW level is reached, the boost controller stops switching the boost FET and the

BSTOVPL_STATUS bit is set. The LED drivers are still active during this condition, and the boost resumes

normal switching operation once the boost output level falls. The boost OVP low voltage threshold changes

dynamically with current boost voltage. It is calculated in Equation 4:

( )

§ ·

¨ ¸



BOOST_OVPL BOOST FB_OVPL REF

V = V + +1 V V

(4)

where

• V

FB_OVPL

= 1.423 V

• V

REF

= 1.21 V

When the boost OVP_HIGH level is reached the boost controller enters fault recovery mode, and the

BSTOVPH_STATUS bit is set. The boost OVP high-voltage threshold also changes dynamically with current

boost voltage and is calculated in Equation 5:

( )

§ ·

¨ ¸



BOOST_OVPH BOOST FB_OVPH REF

V = V + +1 V V

(5)

where

• V

FB_OVPH

= 1.76 V

• V

REF

= 1.21 V

When the boost UVP level is reached the boost controller starts a 110-ms OCP counter. The LP8864S-Q1

device enters the fault recovery mode and sets the BSTOCP_STATUS bit if the boost voltage does not rise

above the UVP threshold before the timer expires. The boost UVP voltage threshold also changes dynamically

with current boost voltage and is calculated in Equation 6:

LP8864S-Q1

ZHCSLM4A – AUGUST 2020 – REVISED FEBRUARY 2021

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TI-LP8864S-Q1：汽车LED背光驱动器，高效能与精准调光

TI-LP8864-Q1.pdf

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