NCP5030
http://onsemi.com
11
Current Selection
Figure 22 shows an application schematic to drive two
selected currents I1 and I2.
ILED +I1)I2(eq. 2)
200 mV
R1
M1
NTHS5404
R2
LED
FB
PGND
NCP5030
Figure 22. Two Current Selections
RSENSE
VOUT
VS
FLASH/TORCH
I1
I2
An active low logic level of M1 enables the low current
mode, So I2 = 0 and I1 = ILED = 200 mV / R1. For example,
should one need 200 mA for low current mode and 800 mA
for high current mode, R1 should be selected according to
the following below:
R1+FBV
I1
+200 mV
200 mA +1.0 W(eq. 3)
So an active high logic level M1 on gate enables the high
current mode then IFLASH = I1 + I2 and according Equation
2 and 3, R2 should be selected regarding the following
equation:
R2+FBV
IFLASH *I1
*RDSON_M1
(eq. 4)
R2+200 mV
800 mA *200 mA *33 mW
R2+300 mW
Some recommended resistors include, but are not limited
to:
PANASONIC ERJ3BQF1R0V (1.0 W 1% 0603)
PANASONIC ERJ3BQFR30V (300 mW 1% 0603)
PANASONIC ERJ3BQJ1R0V (1.0 W 5% 0603)
PANASONIC ERJ3BQJR30V (300 mW 5% 0603)
Analogue Dimming
In white LED applications, it is desirable to operate the
LEDs at a specific operating current, as the color shift as the
bias current. As a consequence, it is recommended to dim
the LED current by Pulse Width Modulation techniques. A
low frequency PWM signal can be applied to the CTRL
input. LED brightness can be changed by varying the duty
cycle. To avoid any optical flicker the frequency must be
higher than 100 Hz and preferably less than 300 Hz.
Because of the soft−start function set at 1000 ms (nominal),
higher frequency would cause the device to remain active
with lower than expected brightness. Nevertheless, in this
case a dimming control using a filtered PWM signal can be
used. In addition, for DC voltage control the same
technique is suitable and the filter is taken away. Please
refer to “NPC5030 Dimming Control Application Note”.
Inductor Selection
Three main electrical parameters need to be considered
when choosing an inductor: the value of the inductor, the
saturation current and the DCR. Firstly, we need to check
if the inductor is able to handle the peak current without
saturating. Therefore, we have to consider that the
maximum peak inductor current is in Buck−Boost mode
when VOUT is closed TBOOST threshold for the lower
operating VIN. Obviously, the peak current inductor is
higher when this device supplies the maximum required
current. In this case, the DC−DC converter is supposed to
operate in Continuous Conduction Mode (CCM) so the
dotted curve in Figure 23 gives the inductor peak current
as a function of load current:
Figure 23. Inductor Peak Currents Vs. IOUT (mA)
Iout (mA)
900700 800600400200
0
0.5
1
1.5
2
2.5
Ipeak (A)
Switch Current Limit
Setup by RPCA
500300100
Operating Inductor Peak Current
Finally, an acceptable DCR must be selected regarding
losses in the coil and must be lower than 100 mW to limit
excessive voltage drop. In addition, as DCR is reduced,
overall efficiency will improve. Some recommended
inductors are included but are not limited to:
TDK VLF5014AT−4R71R1
TDK RLF7030T−4R7M3R4
COPPER BUSSMANN FP3−4R7
MURATA LQH43CN4R7M03L
NIC: NIP16W4R7MTRF
Switch Current Limit
This safety feature is clamping the maximum allowed
current in the inductor according to external RPCA resistor,
which is connected between PCA input and the ground.
This allows the user to reduce the peak current being drawn