an30888b Panasonic Corporation of North America, an30888b Datasheet - Page 27

• Manufacturer Part Number: an30888b
• Description: High Brightness Led Driver Ic
• Manufacturer: Panasonic Corporation of North America

(10) Under Voltage Lock Out (UVLO)
Under Voltage lock out prevents IC from operation at supply voltage lower than 2.1 V.
This function prevent IC from abnormal operation when supply voltage V
voltage is lower than this lock out value of 2.1 V, external MOSFET will be switched off. When input voltage rises to 2.4 V or more,
device operation starts again. This means a hysteresis voltage of about 0.3 V.
(11) Power MOSFET consideration
When selecting the power MOSFET, it is important to consider parameters such as gate-source, drain-source breakdown voltage, total
gate capacitance, ON resistance and the drain current rating.
When power is turned on for IC operating in boost mode, output voltage needed to drive LED will be reflected to Drain-Source voltage
of the power MOSFET. Thus it is recommended to select a MOSFET that can handle this output voltage. Alternatively, output and
Drain-Source voltage can be protected and clamped by OVP circuit as mentioned in point (9).
Gate capacitance of the MOSFET chosen should ideally to be smaller than 3 nF.
(12) PWM operation
PWM signal can be generated externally and input into PWM pin of this IC. This PWM signal will turn on and off the output driver,
giving an average output LED current that is proportional to the duty cycle of the PWM signal.
A PWM frequency of 1 kHz or lower is recommended to minimize error due to rise and fall time of the converter output.
AN30888B
Technical Data (continued)
Functions and properties descriptions (continued)
I
I
I
Duty = The ratio of on pulse time compared to total period time of the PWM signal.
LED(avg.)
LED(avg.)
LED
= The nominal LED current set in part (7)
= The average output LED current after PWM is input
= I
LED
× Duty………………………………………
SDG00005AEB
IN
Eq[12]
drops below our recommended input range. When input
(Boost / Buck-Boost / Buck mode)
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