FP7122-LED Driver with Average-Mode Constant Current Control에 대한 고찰

 

 

오늘은 FP7122-LED Driver with Average-Mode Constant Current Control에 대한 고찰을 해 보겠습니다.

FP7122은 Switching FET 내장형 LED Driver로 아래와 같은 특성을 지니고 있습니다.

 

 

The FP7122 is an average current mode control LED driver IC operating in a constant off-time
mode. FP7122 does not produce a peak-to-average error, and therefore greatly improves accuracy,
line and load regulation of the LED current without any need for loop compensation or high-side
current sensing. 

The output LED current accuracy is ±3%.
The FP7122 can be powered from an 8.0 - 100V supply. 

A PWM & linear dimming input is provided that accepts an external control TTL compatible signal. 

The output current can be programmed by an internal 250mV reference. or controlled externally through a 0.2 – 1.5V dimming
input.

 

 

• Fast Average Current Control

• Internal 8 to 100V Linear Regulator

• Linear and PWM Dimming Capability

• Output Short Circuit Protection with Skip Mode

• Requires Few External Components for Operation

• Internal 100V/6A N-MOSFET

 

Function Description

Input Voltage Regulator
The FP7122 can be powered directly from its VIN pin and can work from 8.5 - 100VDC at its VIN pin. 

When a voltage is applied at the VIN pin, the FP7122 maintains a constant 7.5V at the VDD pin.
This voltage is used to power the IC and any external resistor dividers needed to control the IC. 

The VDD pin must be bypassed by a low ESR capacitor to provide a low impedance path for the high
frequency current of the internal driver.

The FP7122 can also be operated by supplying a voltage at the VDD pin greater than the internally regulated voltage. 

This will turn off the internal linear regulator of the IC and the FP7122 will operate directly off the voltage supplied at the VDD pin. 

Please note that this external voltage at the VDD pin should not exceed 8.5V.

 

Average Current Control
The LED current is detected using a sense resistor at the CS pin. 

The feedback operates in a fast open-loop mode. No compensation is required.

When the voltage at the DIM input VDIM ≥ 1.5V It is a good practice to design the inductor such that the switching ripple current in it is 25% of its average peak-to-peak, full load, DC current.

 

 

Output Short Circuit Protection
The short circuit protection comparator trips when the voltage at CS exceeds 0.55V. When this
occurs, the GATE off-time THICCUP = 550μs is generated to prevent stair-casing of the inductor current
and potentially its saturation due to insufficient output voltage.

 

 

Linear Dimming
When the voltage at DIM falls below 1.5V, the internal 250mV reference to the constant-current
feedback becomes overridden by VDIM • 0.185. 

As long as the current in the inductor remains continuous, the LED current is given by the equation above. 

However, when VDIM falls below 200mV, the internal MOSFET output becomes disabled. 

The internal MOSFET signal recovers, when VDIM exceeds 250mV. 

This is required in some applications to be able to shut the LED lamp off with the same signal input that controls the brightness.

 

 

PWM Dimming
Due to the fast open-loop response of the average-current control loop of the FP7122, its PWM
dimming performance nearly matches that of the FP7171.

 

 

The rising and falling edges are limited by the current slew rate in the inductor. 

The first switching cycle is terminated upon reaching the 250mV (VDIM • 0.167) level at CS. 

The circuit is further reaching its steady-state within 1 switching cycles regardless of the switching frequency.

 

 

 

예로서 아래와 같은 Application이 있습니다.

In=60V, Out=42V / 0.7A=0.35Ax2ch, 0 to 10 PWM Dimming, PWM=1KHz

 

 

 

 

 

아래는 spec sheet의 응용 회로도입니다.

 

 

FP7122V061-G1-FET내장-100V6A.pdf

0.36MB