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

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OZ9910

Dual Forward PWM Controller

O2Micro International 

3. Soft Start

To avoid component stresses and in-rush current

to the load during turn-on, a soft-function is

implemented to provide reliable load operation.

The soft-start function is initiated when the voltage

at ENA (pin 8) is greater than 2V. The soft-start

time is determined by capacitor C22 connected to

CMP_SST (pin 10). The Feedback Control

circuitry provides a current to charge capacitor

C22.

4. Ignition

During striking (turn-on), OZ9910 generates a

higher frequency for CCFL ignition. This

frequency is approximately 30% higher than the

normal operating frequency. The ignition (turn-on)

time is determined by capacitor C9 connected to

LCT (pin 6) and is approximated by the following

equation:

T[second] = CLCT[nF]*0.33

The striking frequency is approximated by the

following equation:

3770/ RCT [kΩ] + 15

fstriking[kHz] =

4*CCT[pF]

5. Normal Operation

x 1000

Once the IC is enabled, the voltage at CMP_SST

(pin 10) controls the rate of power delivered to the

load. The voltage increases to a level such that

the CCFLs are ignited. The voltage feedback loop

takes control to regulate lamp voltage during the

striking period. Once the current is sense at a

threshold of ~0.6V, when ADJ≤1.5V or 0.4*DIM,

when ADJ>1.5V, the IC will switch to normal

operating frequency. The operating frequency is

determined by resistor R4 and capacitor C2

connected to CT (pin 5). The operating

frequency is approximated by the following

equation:

fop[kHz] =

9.35×105

CCT[pF]×RCT[kΩ]

6. Protection

The IC provides time-out protection, open-load

protection and over-voltage protection features.

Time-out protection for striking (turn-on): An

internal counter is started when the IC is enabled.

If the lamp fails to ignite after approximately 1.5

seconds, the IC will shut down

OZ9910

Open-load protection: If the lamp is removed

during normal operation, the voltage of CMP_SST

will increase rapidly. Once the voltage at

CMP_SST (pin 10) reaches a threshold of

approximately 2.5V, the IC will shut down.

Over-voltage protection: During normal operation,

if the voltage at VSEN (pin 9) reaches a threshold

of approximately 3.0V, the output of the error

amplifier will maintain a constant voltage level.

Meanwhile, an internal clock triggers a timer.

When the timer expires (approximately 10ms), the

IC shuts down.

7. Error Amplifier

OZ9910 implements two error amplifiers, one for

current feedback and the other for voltage

feedback. For a CCFL working in the ignition

period, the voltage feedback loop controls the

ignition voltage. The non-inverting input is fixed

at 3V. Once the lamp is ignited, the current

feedback loop controls the amount of power

delivered to the lamp. The non-inverting input is

either ADJ when ADJ pin is greater than 1.5V or

fixed at 1.5V when ADJ pin is less than 1.5V.

8. Combined Analog and Digital

Dimming Control

A built-in function combines the low-frequency

PWM (LPWM) and analog adjustment dimming

functions to perform wide dimming control for the

CCFL. The LPWM frequency is determined by

capacitor C9 and resistor R1 connected to LCT

(pin 6). The frequency is approximated by the

following equation:

2.9×106

fLF[Hz] =

CLCT [pF] ×RLCT [MegΩ]

When the ADJ pin input voltage is less than 1.5V,

the ADJ pin is compared with the triangle LCT

waveform and yields a proper low frequency pulse

width to modulate the CCFL brightness. The peak

and valley of the LCT signal are 1.5V and 0V

respectively. When the ADJ pin input voltage is

increased above 1.5V, the low frequency pulse

width achieves 100% duty cycle and ADJ pin input

voltage serves as the command signal to regulate

the CCFL current.

CONFIDENTIAL

OZ9910-DS-1.0

Page 8

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