MP3360 – HIGHLY INTEGRATED PHOTO FLASH CHARGER AND IGBT DRIVER

MP3360 Rev. 0.9

www.MonolithicPower.com

7

1/29/2010

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OPERATION

The

MP3360

controlled

flyback

charger

operates in critical conduction mode with peak

current set by the CHG pin. The output voltage

is divided down through internal 300: 1 resistive

divider from the positive terminal of the

transformer secondary (FB pin) and compares it

with the internal 1.2V reference. The low to

high transition of the CHG pin will enable the

flyback converter to switch.

output voltage is below 20V to avoid inrush

current.

The boundary mode operation will

follow to minimize charge time when the output

serves as blanking for turn off transition. The

circuit will stop switching and RDYB will be

pulled low once the flash capacitor is charged

to 300V, a value set by the internal 300:1 R

divider and 1.2V reference. VIGBT will be

regulated to 2.7V.

When the charge is full,

then part will shut down its internal circuitry with

CHG pin will restart charge cycle. Bringing the

CHG pin low terminates the power delivery and

prevents pulling current from a depleted battery.

detection.

CURRENT LIMIT PROGRAMMING

The current limit can be programmed using the

CHG pin. After asserting the CHG, it should be

held high for at least 30us. After that, it takes

two pulses to enter the programming mode. In

the programming mode, each pulse advances

the internal counter to the next higher current

limit by 50mA until 750mA is reached and by

100mA increments beyond 750mA. The first

pulse is for 400mA current limit. The next pulse

will set the current limit to 450mA, etc. This

programming should be done within 60us.

Otherwise, the programming pulses will be

ignored after the programming window expires.

When you have advanced to the desired

current limit setting, the high state should be

held to make the part switch with the set current

limit. To set the current limit to 1.5A (highest

possible), the previous procedure is not

necessary. Asserting and holding high the CHG

pin will make the part switches with a 1.5A

current limit. See the following timing diagram

for detailed timing information.

CHG

ON

(Internal)

ENPRG

(Internal)

First Two required to initiate

programming

Falling edge of the following

pulses advance the internal

counter

During this time, the low state of CHG can not

shut-down the part.

Switching starts.

ILIM Programming Timing Diagram

(600mA Current Limit)

400mA

600mA