ncp1400a ON Semiconductor, ncp1400a Datasheet - Page 13

• Manufacturer Part Number: ncp1400a
• Description: 100ma, Fixed Frequency Pwm Step-up Micropower Switching Regulator
• Manufacturer: ON Semiconductor

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Step−up Converter Design Equations
discontinuous conduction mode can be defined by:
External Component Selection
Inductor
suitable values for NCP1400A. In general, smaller
inductance values can provide larger peak inductor current
and output current capability, and lower conversion
efficiency, and vice versa. Select an inductor with smallest
possible DCR, usually less than 1.0 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. The inductor selected should be
able to handle the worst case peak inductor current without
saturation.
D
I
I
V
V
V
Assume saturation voltage of the internal FET switch is negligible.
PK
O
General step−up DC−DC converter designed to operate in
Inductance values between 18 mH and 27 mH are the best
IN
OUT
F
Calculation
− Duty cycle
− Peak inductor current
− Desired dc output current
− Nominal operating dc input voltage
− Desired dc output voltage
− Diode forward voltage
I
I
D
PK
O
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2L(V
Equation
Figure 41. Typical Step−Up Converter Application
(V
out
V
V
t
in
in
T
on
L
C1
10 mF
) V
t
IN
)
APPLICATION CIRCUIT INFORMATION
on
2
(t
on
F
)
* V
2
f
in
)
OUT
NC
CE
http://onsemi.com
1
2
3
NCP1400A
22 mH
L1
13
Diode
converters. The most importance parameters which affect
their efficiency are the forward voltage drop, V
reverse recovery time, trr. The forward voltage drop creates
a loss 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.
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.
Output Capacitor
voltage when the internal MOSFET is switched on and
smoothing the ripple voltage. Low ESR capacitor should be
used to reduce output ripple voltage. In general, a 47 mF to
68 mF low ESR (0.15 W to 0.30 W) Tantalum capacitor
should be appropriate.
LX
GND
5
4
The diode is the largest source of loss in DC−DC
The input capacitor can stabilize the input voltage and
The output capacitor is used for sustaining the output
Small forward voltage, V
Small reverse leakage current
Fast reverse recovery time/switching speed
Rated current larger than peak inductor current,
Reverse voltage larger than output voltage,
I
V
rated
reverse
D1
u I
A
u V
PK
C2
68 mF
Schottky
V
OUT
OUT
diode
F
t 0.3 V
with
the
F
following
, and the