NCP1402_06 ONSEMI [ON Semiconductor], NCP1402_06 Datasheet - Page 15

• Manufacturer Part Number: NCP1402_06
• Description: 200 mA, PFM Step−Up Micropower Switching Regulator
• Manufacturer: ONSEMI [ON Semiconductor]

Step−up Converter Design Equations
in continuous conduction mode can be defined by:
*NOTES:
EXTERNAL COMPONENT SELECTION
Inductor
inductor in most applications. 47 mH is a sufficiently low
value to allow the use of a small surface mount coil, but large
I
I
I
I
I
V
V
V
V
DQ
V
ESR − Equivalent series resistance of the output capacitor
M
PK
min
O
Omax
L
Calculation
NCP1402 step−up DC−DC converter designed to operate
The NCP1402 is designed to work well with a 47 mH
in
OUT
F
S
ripple
V
I
I
DQ
ripple
t
min
PK
off
L
− Peak inductor current
− Minimum inductor current
− Desired dc output current
− Desired maximum dc output current
− Average inductor current
− Nominal operating dc input voltage
− Desired dc output voltage
− Diode forward voltage
− Saturation voltage of the internal FET switch
− Charge stores in the C
− Output ripple voltage
− An empirical factor, when V
M = 8 x 10
−6
(t on ) t off )I O
, otherwise M = 5.3 x 10
[
(V in * V s) t on
C OUT
t off
v M
DQ
(V OUT ) V F * V in )
(I L * I O )t off
OUT
(V in * V s) t on
Equation
L
V OUT I Omax
) (I L * I O )ESR
during charging up
OUT
*
V
10 mF
in
V in 2
(V in * V S )t on
APPLICATIONS CIRCUIT INFORMATION
C1
≥ 3.0 V,
) I min
Figure 59. Typical Application Circuit
−6
2L
.
OUT
NC
CE
2
1
3
http://onsemi.com
NCP1402
NCP1402
47 mH
L1
15
enough to maintain low ripple. Low inductance values
supply higher output current, but also increase the ripple and
reduce efficiency. Note that values below 27 mH is not
recommended due to NCP1402 switch limitations. Higher
inductor values reduce ripple and improve efficiency, but
also limit output current.
W to minimize loss. It is necessary to choose an inductor with
saturation current greater than the peak current which the
inductor will encounter in the application.
Diode
The most importance parameters which affect their
efficiency are the forward voltage drop, V
recovery time, t
just by having a voltage across the device while a current
flowing through it. The reverse recovery time generates a
loss when the diode is reverse biased, and the current appears
to actually flow backwards through the diode due to the
minority carriers being swept from the P−N junction. A
Schottky diode with the following characteristics is
recommended:
Input Capacitor
minimize peak current ripple from the source. The value of
the capacitor depends on the impedance of the input source
used. Small Equivalent Series Resistance (ESR) Tantalum or
ceramic capacitor with value of 10 mF should be suitable.
GND
LX
5
4
The inductor should have small DCR, usually less than 1
The diode is the main source of loss in DC−DC converters.
Small forward voltage, V
Small reverse leakage current
Fast reverse recovery time/ switching speed
Rated current larger than peak inductor current,
I
Reverse voltage larger than output voltage,
V
The input capacitor can stabilize the input voltage and
rated
reverse
> I
D1
> V
PK
OUT
rr
. The forward voltage drop creates a loss
C2
68 mF
V
OUT
F
< 0.3 V
F
, and the reverse