MP3360 – HIGHLY INTEGRATED PHOTO FLASH CHARGER AND IGBT DRIVER
MP3360 Rev. 0.9 www.MonolithicPower.com 7
1/29/2010 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.
© 2010 MPS. All Rights Reserved.
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.
A constant T
OFF
of 20µs is used when the
output voltage is below 20V to avoid inrush
current. The boundary mode operation will
follow to minimize charge time when the output
voltage is above 20V. A minimum T
OFF
of 200ns
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
less than 1uA drawn from V
IN
. Toggling the
CHG pin will restart charge cycle. Bringing the
CHG pin low terminates the power delivery and
put the part in shutdown. A maximum T
ON
timer
prevents pulling current from a depleted battery.
If the ON time exceeds maximum T
ON
, the
switch is forced OFF regardless of the I
PEAK
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
t
HI
t
EN-delay
t
LO
t
PW
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
