MP3313 Rev.1.0

www.MonolithicPower.com

17

8/2/2017

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© 2017 MPS. All Rights Reserved.

5. LED current multiplied by the input PWM

duty, LED slope step controlled by the

internal register only: When the brightness

control mode bits are set to 100, the LED

current is dimmed by the input PWM

dimming duty, and slope step is controlled

by the internal brightness register only.

In linear mode, the LEDs can be calculated

with Equation (30) and Equation (31):

ILED0

PWM0

I

(40.806 A 12.195 A Code0) D



 

 



(30)

ILED1

PWM1

I

(40.806 A 12.195 A Code1) D



 

 



(31)

In exponential mode, the LEDs can be

calculated with Equation (32) and Equation

(33):

Code0

ILED0

PWM0

I

51.1 A 1.003040572

D



 



(32)

Code1

ILED1

PWM1

I

51.1 A 1.003040572

D



 



(33)

The ramp time in either mode can be

calculated with Equation (34):

RAMP

t

RAMP | Code1 Code0 1|









(34)

Cycle-by-Cycle Current Limit

To prevent the external components from

exceeding the current stress rating, the MP3313

uses a cycle-by-cycle current limit protection.

The limit value can be selected by the register

bit CL1:0. When the internal LS-FET current

exceeds

the

current

limit

threshold,

the

MOSFET turns off until the next clock cycle

begins.

Over-Current Protection (OCP)

The FT_OCP flag is set when over-current

protection

(OCP)

occurs.

To

prevent

the

transient over-current from setting the FT_OCP

bit, the MP3313 designs an OCP counter. If the

inductor current always reaches the threshold in

a 128µs period, the counter increases by 1.

Every eight 128µs periods, if the OCP counter is

higher than 2, the FT_OCP bit is set to 1.

If OCP_SD = 0, the IC latches off when OCP is

triggered. If OCP_SD = 1, the IC is recoverable

when OCP is triggered.

Over-Voltage Protection and Open-String

Protection

protection (OVP) threshold, OVP is triggered,

the IC stops switching, and the FT_OVP bit is

set. When the output voltage drops low,

switching recovers.

The OVP threshold is set by the internal register

OVP1:0. Four different thresholds can be

selected.

 OVP1:0 = 00: 17V

 OVP1:0 = 01: 23V

 OVP1:0 = 10: 30V

 OVP1:0 = 11: 38V (default)

If the LED string is open, the feedback voltage is

up and continues charging the output capacitor

and OVP is triggered. The IC also monitors the

LEDx voltage. When the LEDx voltage is lower

than 40mV, open LED protection is triggered.

Three

different

actions

can

be

set

by

triggered.

 OVP_MD1:0 = 00: FT_OVP is set, and

FT_OLP is set.

 OVP_MD1:0 = 01: FT_OVP is set, FT_OLP

is set, and the string is marked off with LEDx

< 40mV.

 OVP_MD1:0 = 10: FT_OVP is set, and the

IC latches off when the OVP fault is

detected.

Short LED Protection

The MP3313 monitors the LEDx voltage to

determine if a short string has occurred. If a

short occurs, the respective LEDx pin is pulled

up and can tolerate high voltage stress. If the

LEDx voltage is higher than the short-protection

threshold and lasts for 2ms, a short string fault is

detected. The threshold is set by S_TH1:0.

Short

LED

protection

is

programmed

by

SLP_MD1:0.