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OB3362FHPA View Datasheet(PDF) - Unspecified

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OB3362FHPA Datasheet PDF : 13 Pages
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OB3362F
4 Channels High Performance LED Driver
Startup
When ENA is active high, the OB3362F checks
the topology connection first. The control signal at
FAULT pin turns on the external PMOS slowly, the
chip monitors the OVP pin to see if the Schottky
diode (boost diode) is connected or the boost
output is short to GND, if the voltage at OVP pin is
lower than 75mV, the output will be disabled and
the external PMOS is turned off. The OB3362F will
also check other faults (UVLO, OCP and OTP), if
there is no fault, then the boost converter will boost
up the output with the internal soft start.
T Figure3: Duty cycle of positive internal burst vs
IV DIM voltage
Dimming Control
Two commonly used PWM dimming modes,
internal burst mode dimming and external burst
LED String Open Protection
The open LED string protection is achieved by
o OVP. When one or more strings are open, the
t respective LEDX pins are discharged to ground.
(PWM) dimming, are supported without any
additional external components. Different dimming
modes are selected by BF/DMOD pin. The LED
l brightness is determined by the control signal at
a DIM pin.
External PWM burst dimming mode is selected by
i shorting BF/DMOD pin to ground. OB3362F
t accepts an external PWM signal to DIM pin with a
swing voltage of 0V to a level greater than 2.2V.
n The LED brightness is controlled by the duty cycle
e of the external PWM signal. The burst frequency is
equal to PWM frequency.
d Internal PWM burst mode dimming mode is
i obtained by connecting a capacitor from the
BF/DMOD pin to ground. A low frequency
f triangular waveform generator is formed by the
n capacitor and internal circuit of the IC. Duty cycle
so as to LED brightness is controlled by the analog
o signal at DIM pin. The burst mode dimming
C frequency Fburst is set by the following equation:
Fburst
=
3.5uF
C BF _ DMOD
(Hz)
t A DC voltage ranging from 0.2V to 2.2V at DIM pin
h corresponds to a LED brightness of approximately
g 0% to 100%, as shown in Figure 3.
i Duty = (VDIM 0.2) ×100%
r2
for
0.2V VDIM 2.2V
B Table 2. Dimming mode selection
n-Function
Pin Connection
BF/DMOD DIM
OInternal Burst
Capacitor 0.2V-2.2V
Polarity
Positive
Since the lowest LEDX is selected to be the input
of the error amplifier of the boost converter, as a
result, the output voltage will be charging until it
exceeds OVP threshold. If the voltage level at the
corresponding LEDX pin is less than 200mV while
OVP happens, then the LED string open is
recognized and the controller will mark off the
open string. Once the mark-off operation
completes, the remaining LED strings will force the
output voltage back into tight regulation. The
strings will keep the mark-off information until the
system shuts down. The IC shuts down the boost
converter if all strings in use are open.
LED String Short Protection
The OB3362F will determine if the short strings
happened by monitoring the voltage level at LEDX
pin. If one or more strings are shorted, the
respective LEDX pins will be pulled up to the boost
output and suffer high voltage stress. If the
voltage on the LEDX pin exceeds the preset
threshold level (5.5V), then the string shorting
condition is detected. Moreover, if this condition
continues for greater than 8192 clock cycles, the
respective string is marked off and its current
regulation is disabled. Once the string is marked
off, it is disconnected from the output voltage
regulation loop of the boost converter. The
marked-off strings will be shut down completely
until the system restarts.
External LPWM
<0.1V
PWM
Positive
©On-Bright Electronics
Confidential
-8-
Preliminary Datasheet
OB_DOC_DS_3362F00
 

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