BD93941EFV Datasheet, PDF (10/30 Pages) Rohm – LED pin rating 60V

BD93941EFV BD93941FP
Datasheet
○ISET (14pin)
The ISET pin is an output current setting resistor. Output current ILED varies in inverse proportion to resistance.
The relation between output current ILED and the resistance of ISET pin connection resistor RISET is given by the following
equation:
I _LED [mA] 
R
3000
ISET ^[kΩ]

V
ADIM
[V
]
(ADIM=0.2V to2.7V)
I _LED [mA]

7500
R_ISET [kΩ]
(ADIM>4V to 35V)
Output current setting should be made in the range of 30 to 200mA.
It prepares automatically to suitable LED feedback voltage that can output LED current set by ISET pin.
In short LED feedback voltage is dropped when the LED current is small and the IC heating is held automatically.
In case of a large current is needed, raise the LED pin feedback voltage. And it adjusts automatically to LED pin voltage
that can be flow large LED current.
The calculation is as below.
VLED  3.7  I _LED [ A] [V ] 　
The LED feedback voltage (VLED) is clamped to 0.3V (typ.) when the LED current (ILED) is less than 81.1mA.
ADIM input range is from 0V to 35V. And the range which the LED currents change with linearity is from 0.2V to 2.7V.
When it reaches under VISET×0.90V(typ.), the LED current is off to prevent from passing a large current to the LED pin
when the RISET is shorted and the ISET pin is shorted to the GND. And as the ISET pin returns to a normal state, the LED
current returns.
○GND (15pin)
The GND pin is an internal analog circuit ground of the IC.
○SS (16pin)
The SS pin is used to make setting of soft start time and duty for soft start. It performs constant current charge of 2.0 uA to
the external capacitor connected with SS terminal, which enables soft-start of DC/DC converter.
Since the LED protection function (OPEN/SHORT detection) works when the SS terminal voltage reaches 3.7 V (typ.) or
higher, it must be set to bring stability to conditions such as DC/DC output voltage and LED constant current drive operation,
etc. before the voltage of 3.7 V is detected.
○FB (17pin)
The FB pin is an output pin used for DC/DC current mode control error amplifier. In other words, the FB pin detects the
voltages of LED pins (1 to 4) and controls inductor current so that the pin voltage of the LED located in the row with the
highest Vf will come to 0.37V (ADIM=2.5V, ILED=100mA). As a result, the pin voltages of other LEDs become higher by Vf
variation. After completion of soft start, the FB pin is put into the high-impedance state with the PWM signal being in the low
state, thus maintaining the FB voltage.
○RT (18pin)
The RT pin is used to connect a DC/DC frequency setting resistor. DC/DC drive frequency is determined by connecting the
RT resistor.
Drive frequency vs. RT resistance (Ideal)
R _RT

15000
f _SW [kHz ]
[k]
When RT is 100kΩ, Fsw is 150kHz(typ.). However, drive frequency setting should be made in the range of 100 kHz to 800
kHz.
○ADIM (19pin)
ADIM pin is for analog dimming. Output current is proportionality with input voltage. Basically, ADIM pin assumes the
voltage inputted externally using high accuracy of resistive divider and etc., IC internally is in OPEN (High impedance)
condition. Cannot use in an OPEN condition.
If you don't use analog dimming, please connect pull-up resistor to over 5V (for example REG58).
○VCC (20pin)
The VCC pin is used to supply power for the IC in the range of 9 to 35V.
If the VCC pin voltage reaches 7.5V (Typ.) or more, the IC will initiate operation. If it reaches 7.2V (Typ.) or less, the IC will
be shut down.
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TSZ22111・15・001
10/27
TSZ02201-0F1F0C100270-1-2
10.Oct.2013 Rev.001