MP4012 datasheet(11/17 Pages) MPS

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MP4012 ─ HIGH-VOLTAGE, HIGH-CURRENT ACCURACY WLED CONTROLLER

MP4012 Rev. 1.12

www.MonolithicPower.com

10/12/2013

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

APPLICATION INFORMATION

Switching Frequency Set

An external resistor RT on RT pin can be used to

set the switching frequency through the following

equation:

55.6 10

LED Current Set

Choose an external current sense resistor (RFB)

to set the LED current.

ISET

LED

Here, VISET is LED current reference on ISET pin,

which is set by a resistor divider from REF pin to

GND. It is recommended to add a 0.1uF ceramic

capacitor on ISET pin to avoid noise injection.

Over Voltage Protection Set

Choose a voltage divider (ROVP1, ROVP2 in typical

application) from the output to set the over

voltage protection threshold:

OVP1

OVP2

OVP

OVP2

V4.95V

=×

Slope Compensation

MP4012 employs peak current mode control

which need slope compensation to avoid sub-

harmonic oscillation when duty cycle exceeds

50%. To ensure current loop stability, choosing a

slope compensation which is at least half of the

down slope of inductor current.

The slope compensation is set by two external

resistors RSL and RSC. The slope compensation

resistor can be calculated as:

DOWN

=×

SDOWN (A/μs) is the down slope of the inductor

current.

DOWN

Where VL is the voltage across the inductor, and

L is the inductor value.

TS is the switching period, which is set by the

frequency set resistor RT.

RCS is the current sense resistor which senses

the switch current. It is recommended that the

current sense resistor RCS can be chosen to

provide 200mV current sense signal (also need

take

the

power

consumption

into

consideration).

The RSL is the slope resistor on SL pin, its value

is limited by the maximum source current of SL

pin. The minimum value of RSL is 25kΩ. 25kΩ –

50kΩ of slope resistor value is recommended.

Current Limit

Current limit value can be set by a resistor divider

from REF pin to GND. The voltage of CL can be

set as:

4.5 R

V1.2 I

≥×

Here, IPK is peak current of inductor.

The VCL value should NOT be greater than

450mV, NO capacitor should be connected

between CL pin and GND.

Hiccup Timer

If the fault conditions are detected (either short

circuit or open circuit), the COMP pin is

disconnected from the internal EA and the Gate

and Fault pins are pulled down to disable the

LED controller. Once the fault condition is

cleared, the COMP pin is charged by an internal

5μA current source until it reaches 5V, then the

COMP is discharged by an internal 5μA current

source. When it reaches 1V, the current source is

disconnected from COMP pin and the internal EA

is reconnected to it, the Fault pin starts to go high

and the Gate pin is allowed to switch. The hiccup

timer can be programmed by R -C network (RZ,

CZ in series and parallel with CC) on COMP pin.

The delay time of Startup (Figure 2) can be

approximately calculated as:

hiccup

t(C

C )

≈

In most case the voltage drop on RZ can be

neglected.

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