MP4655–PURE, SINGLE-STAGE, LLC, LED CURRENT AND SYSTEM VOLTAGE CONTROLLER

MP4655 Rev 1.0

www.MonolithicPower.com

15

2/2/2016

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© 2016 MPS. All Rights Reserved.

PIN FUNCTIONS

Pin #

Name

Description

1

VDR_DN

Drive voltage for the extra MOSFET.

VDR_DN is formed by the charge pump and is

referred to SOURCE.

2

GATEN

Gate of the extra N-channel MOSFET.

3

SOURCE

Source of the extra N-channel MOSFET.

4

FTH_CMODE

FTH_CMODE sets the threshold frequency to shut down the LLC when capacitive

mode is detected.

Its typical voltage is 1.2V. The sourcing current through

FTH_CMODE determines the threshold frequency. When capacitive mode is detected,

the IC discharges SS and increases the operating frequency. If the operating frequency

is higher than this threshold frequency when capacitive mode is detected, the IC latches

up LLC and the IOCP/FAULT signal output is high.

5

CMODE

Detection of capacitive mode.

The secondary side winding voltage is fed back on

CMODE for capacitive mode detection.

6

SS

Soft start.

SS functions as a soft start and also sets the operating frequency together

with FSET. Connect a capacitor from SS to GND to set the soft-start time. An internal

10µA sourcing current charges this capacitor to 2.4V at soft start. Connect a resistor

between SS and FSET to set the operating frequency together with the resistor from

FSET to GND.

7

VOCP

Over-current protection of the system bus voltage stage.

VOCP senses the

secondary current of the system bus voltage stage. When VOCP is lower than -203mV,

the IC triggers a bus stage protection. VOCP is also used for the inner current control

loop for the bus voltage compensation to control the extra MOSFET duty cycle.

8

FSET

Frequency set.

Connect a resistor from FSET to GND, and another resistor between

FSET and SS. The operating frequency is determined by the sourcing current through

FSET. The voltage of FSET and the operating frequency are programmed by the

current control loop and the voltage control loop.

9

VCOMP

Feedback compensation node of the voltage control loop.

Connect a compensation

capacitor or an R-C network from VCOMP to GND. The VCOMP voltage is internally

clamped between 1.02V and 2.28V, which limits the operating frequency range.

10

VFB

Bus voltage feedback.

VFB feeds back the bus voltage for regulation. Its inner

reference voltage is 1.2V. VFB is also used for over-voltage protection of the bus

voltage stage. When VFB exceeds 1.5V, the over-voltage protection of the bus voltage

stage is triggered. VFB also functions as the open feedback loop protection. If VFB is

lower than 50% of its reference voltage and VCOMP or DCOMP is saturated for 512

cycles, the IC triggers the bus voltage stage protection.

11

DCOMP

Feedback compensation node of the voltage control loop

. DCOMP is used to

program the duty cycle of the extra N-channel MOSFET. Connect a compensation

capacitor or an R-C network from DCOMP to GND.

12

IFB

LED current feedback input.

IFB feeds back the LED current through a sensing

resistor. The internal error amplifier sinks a current from ICOMP proportional to the

absolute value of the voltage at IFB. The average voltage at IFB is regulated to the

reference voltage (controlled by the ADIM voltage, 199mV when ADIM is high). The

voltage on IFB is also used for LED over-current detection. When the voltage on IFB

rises higher than 415mV for 340μs or when the voltage rises higher than 555mV, the IC

triggers the LED stage protection. IFB also functions as the LED current open feedback

loop protection. If the IFB voltage is lower than 50% of its reference voltage and the

ICOMP is saturated for 1024 cycles, the IC triggers the LED stage protection.