MP1523 datasheet(4/7 Pages) MPS

4 / 7 page

MP1523 – PRECISION 6-LAMP WHITE LED DRIVER

INITIAL RELEASE

07/04, Rev. 1.6

www.MonolithicPower.com

OPERATION

The MP1523 is a step-up converter that

operates from an input voltage as low as 2.7V

and generates an output voltage up to 25V. The

0.5Ω internal N-Channel power MOSFET is

driven with a variable frequency, constant-peak-

current architecture for low operating current.

The 550ns minimum off time is extended to

1.6µs during start-up to yield a smooth glitch

free turn-on.

Variable Frequency Constant-Peak-Current

Operation

When the power MOSFET is turned on the

inductor current increases until the 0.45A

current limit is reached. The internal power

MOSFET is then turned off for a minimum of

550ns. At the end of this 550ns transition if the

FB pin is still lower than the 400mV threshold

the MOSFET will again be turned on, otherwise

the MP1523 waits until the voltage drops below

the threshold before turning on the MOSFET

again. This process allows for optimal use of

the inductor, while minimizing the output ripple

and size of the output capacitor and maintaining

low operating current.

Open Load Shutdown

Open load shutdown is implemented by

connecting the BIAS pin to the output. In the

fault condition where the connection to the LED

string is open, the output voltage will rise up, as

the FB pin has no voltage. Once the output

voltage exceeds 28V, the MP1523 will cease

operation until the EN pin is cycled off and on.

Connecting the BIAS pin to VIN disables open

load shutdown but reduces the chip power

consumption due to the quiescent current.

Figure 1—Functional Block Diagram

ERROR AMP.

CURRENT

450mA

CONTROL

LOGIC

INTERNAL

POWER

BIAS

GND

400mV

(2)

(3)

(1)

(5)

(4)

REGULATOR

Open Load

Shutdown

Comparator

1.23V

160K

17V

20K

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