MAX8790 查看數據表（PDF） - Maxim Integrated

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MAX8790

Six-String White LED Driver with Active Current Balancing for LCD Panel Applications

Maxim Integrated 

MAX8790

Six-String White LED Driver with Active

Current Balancing for LCD Panel Applications

Fixed-Frequency Step-Up Controller

The MAX8790’s fixed-frequency, current-mode, step-up

controller automatically chooses the lowest active FB_

voltage to regulate the feedback voltage. Specifically, the

difference between the lowest FB_ voltage and the current

source-control signal plus an offset (VSAT) is integrated at

the CCV output. The resulting error signal is compared to

the external switch current plus slope compensation to

terminate the switch on-time. As the load changes, the

error amplifier sources or sinks current to the CCV output

to adjust the required peak inductor current. The slope-

compensation signal is added to the current-sense signal

to improve stability at high duty cycles.

At light loads, the MAX8790 automatically skips pulses

to improve efficiency and prevent overcharging the out-

put capacitor. In SKIP mode, the inductor current ramps

up for a minimum on-time of approximately 150ns, then

discharges the stored energy to the output. The switch

remains off until another pulse is needed to boost the

output voltage.

Internal 5V Linear Regulator VCC and UVLO

The MAX8790 includes an internal low-dropout linear

regulator (VCC). When VIN is higher than 5.5V and

SHDN is high, this linear regulator generates a 5V supply

to power an internal PWM controller, control logic, and

MOSFET driver. This linear regulator can deliver at least

10mA of total additional load current. If VIN is less than or

equal to 5.5V, VCC and IN can be connected together and

powered from an external 5V supply. There is an internal

diode from VCC to IN, so VIN must be greater than VCC

(see Figure 2).

The MAX8790 includes UVLO protection. The controller is

disabled until VCC exceeds the UVLO threshold of 4.25V

(typ). Hysteresis on UVLO is approximately 20mV.

The VCC pin should be bypassed to GND with a 1μF or

greater ceramic capacitor.

VIN

2.8V TO 5.5V

CIN

L1

0.9µH

SHDN

IN

EXT

EXTERNAL

5V SUPPLY

VCC

1µF

ENA

ISET

CS

BRT

FSET

GND

511kΩ

N.C.

OSC

MAX8790

OV

1.2kΩ

CCV

0.1µF

FB1

CPLL

FB2

0.1µF

FB3

FB4

EP

FB5

FB6

Figure 3. Low-Input-Voltage Application Circuit

D1

COUT

N1

RS

30mΩ

R1

1MΩ

R2

59kΩ

VOUT

UP TO 22V

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