T8302 데이터 시트보기 (PDF) - Taiwan Memory Technology
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T8302 Datasheet PDF : 12 Pages
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tm TE
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T8302
Applications Information
Setting nominal average output current with external resistor RS
The nominal average output current in the LED(s) is determined by the value of the external current
sense resistor (RS) connected between VIN and ISENSE and is given by:
IOUTnom = 0.1/RS [for RS ≥ 0.1 ohm]
The table below gives values of nominal average output current for several preferred values of
current setting resistor (RS) in the typical application circuit :
RS (ohm)
0.1
0.142
0.285
Nominal average output current (mA) 1000
700
350
The above values assume that the ADJ pin is floating and at a nominal voltage of VREF (=1.25V).
Note that RS = 0.1ohm is the minimum allowed value of sense resistor under these conditions to
maintain switch current below the specified maximum value.
It is possible to use different values of RS if the ADJ pin is driven from an external voltage. (See
next section)
Output current adjustment by external DC control voltage
The ADJ pin can be driven by an external dc voltage (VADJ), as shown, to adjust the output current
to a value above or below the nominal average value defined by RS.
The nominal average output current in this case is given by:
IOUTdc = (VADJ /1.25) x (0.1V / RS), [for 0.1 < VADJ <2.5V]
Note that 100% brightness setting corresponds to VADJ = VREF. When driving the ADJ pin above
1.25V, RS must be increased in proportion to prevent IOUTdc exceeding 1A maximum.
The input impedance of the ADJ pin is 64kohm ±25%.
Output current adjustment by PWM control
Directly driving ADJ input
A Pulse Width Modulated (PWM) signal with duty cycle DPWM can be applied to the ADJ pin, as
shown below, to adjust the output current to a value above or below the nominal average value set
by resistor RS:
TM Technology, Inc. reserves the right
P. 6
to change products or specifications without notice.
Publication Date:April 2014
Revision: E
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