MAX16820ATT-T 데이터 시트보기 (PDF) - Maxim Integrated

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MAX16820ATT-T

2MHz High-Brightness LED Drivers with High-Side Current Sense and 5000:1 Dimming

Maxim Integrated 

2MHz High-Brightness LED Drivers with

High-Side Current Sense and 5000:1 Dimming

Undervoltage Lockout (UVLO)

The MAX16819/MAX16820 include a 4.5V undervoltage

lockout (UVLO) with 500mV hysteresis. When VIN falls

below 4.5V, DRV goes low, turning off the external n-chan-

nel MOSFET. DRV goes high once VIN is 5V or higher.

5V Regulator

VCC is the output of a 5V regulator capable of sourcing

10mA. Bypass VCC to GND with a 1µF capacitor.

DIM Input

The MAX16819/MAX16820 allow dimming with a PWM

signal at the DIM input. A logic level below 0.6V at DIM

forces the MAX16819/MAX16820’s DRV output low,

turning off the LED current. To turn the LED current on,

the logic level at DIM must be at least 2.8V.

Applications Information

Selecting RSENSE to Set the LED Current

The MAX16819/MAX16820 feature a programmable LED

current using a resistor connected between IN and CSN.

Use the following equation to calculate the sense resistor:

RSENSE (Ω)

=

1

2

(VSNSHI + VSNSLO)(V)

ILED (A )

For the values of VSNSHI and VSNSLO, see the Electrical

Characteristics.

Current Regulator Operation

The MAX16819/MAX16820 regulate the LED output

current using an input comparator with hysteresis

(Figure 1). As the current through the inductor ramps

up and the voltage across the sense resistor reaches

the upper threshold, the voltage at DRV goes low, turn-

ing off the external MOSFET. The MOSFET turns on

again when the inductor current ramps down through

the freewheeling diode until the voltage across the

sense resistor equals the lower threshold. Use the fol-

lowing equation to determine the operating frequency:

( ) fSW =

VIN − n × VLED × n × VLED × RSENSE

VIN × ∆V × L

where n = number of LEDs, VLED = forward voltage

drop of one LED, and ∆V = (VSNSHI - VSNSLO).

For proper component selection, please use the design

tool available at: http://www.maxim-ic.com/MAX16819-

20-Tool.

HYSTERETIC MODE

ILED

AVG. LED

CURRENT

TSW

=

1

fSW

VDIM

∆I

t

t

Figure 1. Current Regulator Operation

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