ISL78171

6-Channel, 50mA Automotive LED Driver with Ultra-high Dimming Ratio and Phase Shift Control

OVERVIEW

The ISL78171 is a 6-channel, 50mA, LED driver capable of very high dynamic range dimming. It offers an integrated boost converter, six high precision, adjustable current sinks and a SMBus/I2 C interface for digital programmability and extensive diagnostics. These features provide the ISL78171 with the capabilities to design a compact, highly versatile LED backlight for a wide variety of ambient lighting conditions.

The integrated peak current mode PWM boost converter operates with a constant frequency and can boost an input voltage range of 4.5V - 26.5V to an output up to 40V and supply six strings of LEDs with up to 50mA each. A dynamic headroom control circuit detects and regulates the highest voltage string to improve efficiency in multistring configurations.

The six high precision adjustable current sinks offer typical current matching better than ±1% and a dimming ratio capable of exceeding 60,000:1. The dimming ratio can be adjusted with either or both the I2 C/SMBus and an external PWM signal. They also feature an optional channel phase shift control which helps to reduce the input and output capacitance and ripple, to improve efficiency and to prevent audible noise.

The SMBus/I2 C interface offers a wide range of programmability that includes the boost FET slew rate control, individual string enabling, and converter switching frequency selections. It offers a wide range of protection features and diagnostics that cover all perceivable faults, enabling the system to self-diagnose the functioning of the backlight and react to such conditions as failed LEDs. The ISL78171 is offered in a compact and thermally efficient 20 Ld QFN package with an ambient temperature range of -40°C to +105°C.

KEY FEATURES

  • 6 channels at 50mA maximum per channel
  • Input voltage: 4.5V to 26.5V, output voltage: 40V max
  • Bootstrap operation Input:3V to 21V output: 26.5V max
  • PWM dimming with phase shift control
  • SMBus/I2C controlled PWM or DC dimming
  • Direct PWM dimming
  • Internal PWM dimming mode linearity: 0.4% to 100%, dimming frequency <30kHz
  • Direct PWM dimming duty cycle linearity: 0.007% to 100% at a dimming frequency of 200Hz
  • Current matching ±0.7% typ
  • 600kHz/800kHz/1.2MHz selectable switching frequency
  • Dynamic headroom control
  • Fault protection
  • String open/short-circuit, OVP, OTP and optional output short-circuit fault protection
  • AEC-Q100 qualified

BLOCK DIAGRAM

 Block Diagram

PARAMETRICS

Parameters
ISL78171
Basic Information
Production Status
Mass Production
# of Devices/ Channels
6
Total Current for DC/DC Lighting (mA)
300
Output Current Max/Channel (mA)
50
Output Voltage Max (V)
40
Brightness Control
SMBus, PWM or DC
Bus/Output Interface
SMBus/I2C
Input Voltage Max (V)
26.5
Input Voltage Min (V)
4.5
Backlight for LCD Size (min) (in)
0
Backlight for LCD Size (max) (in)
17
Qualification Level
Automotive
Peak Efficiency (%)
92.9
# of LEDs (max)
72
Frequency
0.6/1.2 MHz
IQ (max)
5 µA
ISW (typ) (mA)
2000
Integrated Diode
No
Over Voltage Protection
Yes
Fault Switch
Yes
Topologies
Inductor Boost
Input Voltage Range (V)
4.5 to 26.5
Backlight for LCD Size
up to 17
Can Sample
YES
Temperature Range
-40 to +105

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