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

MP4655 Rev 1.0

www.MonolithicPower.com

18

2/2/2016

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© 2016 MPS. All Rights Reserved.

OPERATION

The MP4655 is a pure, single-stage, LLC, LED

current and system voltage controller for LED

backlighting located on the secondary side. The

MP4655 uses the LLC power stage and an extra

N-channel MOSFET to regulate both the LED

current and the system supply voltage. The

MP4655 is powered by 9V to 35V input supplies

that output two 180 degree phase shifted driving

signals for the external LLC power stages. Its

enhanced 12V gate driver provides adequate

driving capability and can directly drive the

external LLC MOSFETs through an external gate

driving transformer. The MP4655 also provides a

direct driving signal to control the extra N-

channel MOSFET and regulates the system

supply voltage.

The MP4655 uses frequency control on the LLC

power stage to regulate the LED current at the

PWM dimming on interval and the system bus

voltage at the PWM dimming off interval. The

duty cycle of the extra N-channel MOSFET

regulates the system bus voltage at the PWM on

interval. Both the LED current and the system

bus voltage are regulated accurately.

Internal Regulator

The MP4655 includes an internal linear regulator

(VCC). VCC is the supply voltage for the LLC

gate driver, the charge pump, and the internal

circuit. The MP4655 features under-voltage

lockout for both the VCC regulator and the inner

circuit. Until VIN exceeds its UVLO threshold, the

VCC regulator does not work. The chip is

disabled until VCC exceeds its UVLO threshold.

The internal VCC regulator is also controlled by

the IC enable signal (PS_ON).

Charge Pump and Extra N-Channel MOSFET

Driver

The MP4655 integrates a charge pump that

drives the extra N-channel MOSFET directly (see

Figure 2). The charge pump is powered by VCC

and outputs a high-frequency square wave signal.

Together with an external C-diode network, the

charge pump forms a floating driver supply

voltage on VDR_DN referred to the SOURCE

voltage with an amplitude close to VCC. This

floating driver supply voltage can directly drive

the extra N-channel MOSFET.

Figure 2: Charge Pump for Extra N-Channel

MOSFET Driver

Operation Modes and System Start-Up

The MP4655 is controlled by its enable signal

(PS_ON) and uses the following operating

modes:

1. PS_ON > 2V: the IC is enabled in normal

operation mode.

2. 0.8V < PS_ON ≤ 2V for 1ms: the IC is

disabled and no circuits work.

3. PS_ON ≤ 0.8V: the IC is enabled in standby

mode.

It is very easy to set up the system connection,

whether the MP4655 is required to do so in

standby or not.

When the MP4655 is enabled and the VIN supply

is higher than its UVLO threshold, VCC is

charged up. When VCC passes its UVLO

threshold, the IC starts up. The voltage resets the

control loop for LLC frequency control, voltage

control loop for the extra N-channel MOSFET

duty cycle control, and the soft-start capacitor.

EN_LED and PWMIN control the start-up of the

LED driver stage. If either EN_LED or PWMIN

are low, the LED driver stage is disabled and

DIMO is pulled low. The system operates in

through the LLC frequency control. The extra N-

channel MOSFET is on in this condition. If either

EN_LED or PWMIN are high, the LED driver