R1218N021A Datasheet, PDF (8/21 Pages) RICOH electronics devices division – Step-up DC/DC converter for White LED Backlight

R1218x
• Selection of Inductors
The peak current of the inductor at normal mode can be calculated as next formula:
ILXpeak=1.25 × ILED × VOUT / VIN + 0.5 × VIN × (VOUT − VIN) / (L × VOUT × fosc)
When the start-up or dimming control by CE pin, transient current flows, the peak current must be equal or
less than the current limit of the IC. The peak current should not beyond the rating current of the inductor. For
example, for 4 serial LED drive from VIN=3.6V, recommendation value of the inductor is 22µH or more.
• Selection of Capacitors
Set 1µF or more value bypass capacitor C1 between VIN pin and GND pin as close as posible.
Set 0.22µF or more capacitor C2 between VOUT and GND pin.
TEST CIRCUITS
A
VIN
LX
R1218x
Series
CE
VOUT
GND
VFB
VIN
LX
R1218x
Series
CE
VOUT
OSCILLOSCOPE
GND
VFB
Supply Current Test Circuit
UVLO Detector Threshold,
UVLO Released Voltage
VIN
LX
R1218x
Series
CE
VOUT
OSCILLOSCOPE
GND
VFB
VFB Voltage, Oscillator Frequency,
Maximum Duty Test Circuit
VIN
LX
R1218x
Series
CE
VOUT
OSCILLOSCOPE
GND
VFB
OVP Detector Threshold,
OVP Released Voltage Test Circuit
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