L5107_15 Datasheet, PDF (7/8 Pages) Unisonic Technologies – CONSTANT CUTTENT BOOST CONTROLLER FOR DRIVING HIGH POWER LEDS

L5107
Preliminary
LINEAR INTEGRATED CIRCUIT
 POWER TOPOLOGY(Cont.)
Output Over Voltage Protection (OVP)
The UTC L5107 provides an OVP circuitry with a reference value of 1.25V in order to protect the system from an
over voltage fault condition. This OVP point can be programmed through the use of external resistors (R1 and R2 in
Figure 2). This OVP voltage can be calculated using Equation 3:
Eq. (3)
V_OVP

1.25  (R₁
R₂
 R₂ )
Current Limit
The UTC L5107 features a current limit protection feature to prevent any current runaway conditions. The current
limit circuitry monitors current on a pulse by pulse basis. It limits the current through the inductor by sensing the
voltage across R_CS. When 0.45V is present at the IS pin, the pulse is truncated. The next pulse continues as
normally until the IS pin reaches 0.45V and it is truncated once again. This will continue until the output load is
decreased.
Select R_CS using Equation 4:
Eq. (4)
  ^{RCS }
0.45
V - V OUTMAX
INMIN
L  FSW
D
 ILPK_LIMIT
Slope Compensation
The UTC L5107 requires slope compensation for the peak current mode controller. The UTC L5107 uses an
external resistor, R_SLC for slope compensation. The ability to set the proper slope compensation through the use of a
single external component results in design flexibility. Select R_SLC using Equation 5:
Eq. (5)
  _{RSLC }
V  V OUTMAX
INMIN
 RCS
L  250μΑ  FSW
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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QW-R125-026.b