Rainbow-electronics MAX17061 Bedienungsanleitung PDF herunterladen (Seite 12)

MAX17061

The MAX17061 includes a 5V linear regulator that pro-

vides the internal bias and gate drive for the step-up

controller. When an external 5V is available, the internal

LDO can be overdriven to decrease power dissipation.

Otherwise, connect the IN pin to an input greater than 5.5V.

Fixed-Frequency Step-Up Controller

The MAX17061’s fixed-frequency, current-mode, step-

up controller automatically chooses the lowest active

FB_ voltage to regulate the output 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 determine the switch on-time. As the

load changes, the error amplifier sources or sinks cur-

rent to the CCV output to deliver the required peak-

inductor current. The slope-compensation signal is

added to the current-sense signal to improve stability at

high duty cycles.

When the input voltage is close to the output voltage, the

MAX17061 automatically skips pulses to prevent over-

charging the output capacitor. In SKIP mode, the induc-

tor current ramps up for a minimum on-time of

approximately 90ns, and 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

and UVLO

The MAX17061 includes an internal low-dropout linear

regulator (V

). When V

is higher than 5.5V, this lin-

ear regulator generates a 5V supply to power internal

PWM controller, control logic, and MOSFET driver. The

voltage drops to 4.35V in shutdown. If V

is less

than or equal to 5.5V, V

and IN can be tied together

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

internal diode from V

to IN, so V

must be greater

than V

(see Figure 3).

8-String White LED Driver with

SMBus for LCD Panel Applications

12 ______________________________________________________________________________________

FB1

FSET

PGND2

PGND1

7V TO 21V

LX2

FB2

FB3

FB4

FB5

FB6

FB7

FB8

10μH

0.1μF

1μF

4.7μF

OSC

GND

PWMIPWM

ISET

OUT

LX1

MAX17061

OUT

UP TO 45V

220pF

464kΩ

0.022μF

5.1kΩ

CCV

SCLCLK

SDADATA

PWMO

61.9kΩ

2μF

2.21MΩ

Figure 1. Typical Operating Circuit

1 2 ... 7 8 9 10 11 12 13 14 15 16 17 ... 25 26

MAX17061 1

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