OZ9910 データシートの表示（PDF） - O2Micro International

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OZ9910

Dual Forward PWM Controller

O2Micro International 

FUNCTIONAL BLOCK

DIAGRAM DESCRIPTION

Refer to the Functional Block Diagram in Figure 1,

page 2, and the Pin Description Table on page 3.

Voltage REF/Current Bias Block generates a bias

current reference for internal use and precision 5V

reference for both internal and external use. In

addition, it provides a feed-forward compensated

current to the Feedback Control Block.

LFOSC block supplies a low frequency ramp

signal to Feedback Control block. The ramp signal

is compared with the external ADJ signal to yield a

low-frequency, pulse-width-modulation (LPWM)

signal to regulate the power delivered to the load.

LFOSC also provides the striking time (turn-on) for

open-load protection.

The Feedback Control block consists of Current

Feedback Control, Voltage Feedback Control and

Control Logic. This block receives the command

signal from ADJ, feedback for output voltage

(VSEN) and load current (ISEN), Compensation

(CMP) and LPWM. When the voltage at ADJ is

greater than 1.5V, LPWM will not affect either the

current feedback or voltage feedback controls.

When the voltage at ADJ is less than 1.5V, the

LPWM signal is activated to modulate the current

feedback control loop. At this point, the analog

signal applied to the error amplifier is fixed at 1.5V.

The Control Logic selects either voltage feedback

or current feedback as the control command to the

output drives.

OZ9910

Depending on the system design, the Feedback

Control block selects either the voltage feedback

control or the current feedback control command

to provide suitable load regulation. In TWT

applications, the initial turn-on may rely on

regulating the current. In CCFL applications, the

initial turn-on is to regulate the ignition voltage.

The Feedback Control block provides a

high-degree of flexibility for various applications.

The error amplifiers for Current Feedback Control

and Voltage Feedback Control are configured as a

trans-impedance amplifier to work with either

voltage control or current control.

HFOSC block generates a high frequency ramp

signal. This signal is compared with the control

command from the Feedback Control block to

determine the appropriate drive outputs.

Protection block protects the IC and external

devices from over-voltage, open-load and over-

current conditions.

The High-side driver buffer provides a buffered

voltage of Vin minus 5V to the high-side switches

in the dual forward converter.

CONFIDENTIAL

OZ9910-DS-1.0

Page 6

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