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NCP1450ASN19T1G

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NCP1450A
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16
14
0.1
32
I
IN
, NO LOAD INPUT CURRENT (mA)
0.01
V
IN
, INPUT VOLTAGE (V)
Figure 69. NCP1450ASNXXT1 No Load Input
Current vs. Input Voltage (Using MOSFET)
Figure 70. NCP1450ASNXXT1 No Load Input
Current vs. Input Voltage (Using BJT)
I
IN
, NO LOAD INPUT CURRENT (mA)
10
V
IN
, INPUT VOLTAGE (V)
1
51 43250
0.1
0.01
100
1
10
A. V
OUT
= 1.9 V, R
b
= 1 k
B. V
OUT
= 3.0 V, R
b
= 1 k
C. V
OUT
= 5.0 V, R
b
= 1 k
D. V
OUT
= 1.9 V, R
b
= 560
E. V
OUT
= 3.0 V, R
b
= 560
F. V
OUT
= 5.0 V, R
b
= 560
NCP1450ASNXXT1
L = 10 H
Q = MMJT9410
C
OUT
= 220 F
T
A
= 25°C
A
D
B
E
C
F
NCP1450ASNXXT1
L = 10 H
Q = NTGS3446T1
C
OUT
= 220 F
T
A
= 25°C
V
OUT
= 5.0 V
V
OUT
= 3.0 V
V
OUT
= 1.9 V
Components Supplier
Parts Supplier Part Number Description Phone
Inductor: L1, L2 Sumida Electric Co. Ltd. CD54−100MC
Inductor 10 H/1.44 A
(852) 2880−6688
Schottky Diode: D1, D2 ON Semiconductor MBRM110L Schottky Power Rectifier (852) 2689−0088
MOSFET: Q1 ON Semiconductor NTGS3446T1 Power MOSFET N−Channel (852) 2689−0088
BJT: Q2 ON Semiconductor MMJT9410 Bipolar Power Transistor (852) 2689−0088
Output Capacitor: C1, C3 KEMET Electronics Corp. T494D227K006AS Low ESR Tantalum Capacitor
220 F/6.0 V
(852) 2305−1168
Input Capacitor: C2, C4 KEMET Electronics Corp. T491C106K016AS Low Profile Tantalum Capacitor
10 F/16 V
(852) 2305−1168
NCP1450A
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17
DETAILED OPERATING DESCRIPTION
Operation
The NCP1450A series are monolithic power switching
controllers optimized for battery powered portable products
where large output current is required.
The NCP1450A series are low noise fixed frequency
voltage−mode PWM DC−DC controllers, and consist of
startup circuit, feedback resistor divider, reference voltage,
oscillator, loop compensation network, PWM control
circuit, and low ON resistance driver. Due to the on−chip
feedback resistor and loop compensation network, the
system designer can get the regulated output voltage from
1.8 V to 5.0 V with 0.1 V stepwise with a small number of
external components. The quiescent current is typically
93 A (V
OUT
= 2.7 V, f
OSC
= 180 kHz), and can be further
reduced to about 1.5 A when the chip is disabled (V
CE
t
0.3 V).
The NCP1450A operation can be best understood by
referring to the block diagram in Figure 2. The error
amplifier monitors the output voltage via the feedback
resistor divider by comparing the feedback voltage with the
reference voltage. When the feedback voltage is lower than
the reference voltage, the error amplifier output will
decrease. The error amplifier output is then compared with
the oscillator ramp voltage at the PWM controller. When the
ramp voltage is higher than the error amplifier output, the
high−side driver is turned on and the low−side driver is
turned off which will then switch on the external transistor;
and vice versa. As the error amplifier output decreases, the
high−side driver turn−on time increases and duty cycle
increases. When the feedback voltage is higher than the
reference voltage, the error amplifier output increases and
the duty cycle decreases. When the external power switch is
on, the current ramps up in the inductor, storing energy in the
magnetic field. When the external power switch is off, the
energy stored in the magnetic field is transferred to the
output filter capacitor and the load. The output filter
capacitor stores the charge while the inductor current is
higher than the output current, then sustains the output
voltage until the next switching cycle.
As the load current is decreased, the switch transistor turns
on for a shorter duty cycle. Under the light load condition,
the controller will skip switching cycles to reduce power
consumption, so that high efficiency is maintained at light
loads.
Soft Start
There is a soft start circuit in NCP1450A. When power is
applied to the device, the soft start circuit first pumps up the
output voltage to approximately 1.5 V at a fixed duty cycle.
This is the voltage level at which the controller can operate
normally. In addition to that, the startup capability with
heavy loads is also improved.
Oscillator
The oscillator frequency is internally set to 180 kHz at an
accuracy of "20% and with low temperature coefficient of
0.11%/°C.
Regulated Converter Voltage (V
OUT
)
The V
OUT
is set by an integrated feedback resistor
network. This is trimmed to a selected voltage from 1.8 V to
5.0 V range in 100 mV steps with an accuracy of "2.5%.
Compensation
The device is designed to operate in continuous
conduction mode. An internal compensation circuit was
designed to guarantee stability over the full input/output
voltage and full output load range.
Enable/Disable Operation
The NCP1450A series offer IC shutdown mode by chip
enable pin (CE pin) to reduce current consumption. When
voltage at pin CE is equal or greater than 0.9 V, the chip will
be enabled, which means the controller is in normal
operation. When voltage at pin CE is less than 0.3 V, the chip
is disabled, which means IC is shutdown.
Important: DO NOT apply a voltage between 0.3 V to 0.9 V
to pin CE as this is the CE pin’s hysteresis voltage range.
Clearly defined output states can only be obtained by
applying voltage out of this range.
NCP1450A
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18
APPLICATION CIRCUIT INFORMATION
Step−up Converter Design Equations
The NCP1450A PWM step−up DC−DC controller is
designed to operate in continuous conduction mode and can
be defined by the following equations. External components
values can be calculated from these equations, however, the
optimized value should obtained through experimental
results.
Calculation Equation
D
v
V
OUT
) V
D
* V
IN
V
OUT
) V
D
* V
S
I
L
I
O
(1 * D)
L
(V
OUT
) V
D
* V
IN
)(1 * D)
2
f I
O
DIR
I
PK
I
L
(1 )
DIR
2
)
Q
(I
L
* I
O
)(1 * D)
f
V
PP
[
Q
C
OUT
) (I
L
* I
O
) ESR
NOTES:
D − On−time duty cycle
I
L
− Average inductor current
I
PK
− Peak inductor current
DIR − Delta inductor current to average inductor current ratio
I
O
− Desired dc output current
V
IN
− Nominal operating dc input voltage
V
OUT
− Desired dc output voltage
V
D
− Diode forward voltage
V
S
− Saturation voltage of the external transistor switch
Q
− Charge stores in the C
OUT
during charging up
ESR
− Equivalent series resistance of the output capacitor
Design Example
It is supposed that a step−up DC−DC controller with 3.3 V
output delivering a maximum 1000 mA output current with
100 mV output ripple voltage powering from a 2.4 V input
is to be designed.
Design parameters:
V
IN
= 2.4 V
V
OUT
= 3.3 V
I
O
= 1.0 A
V
pp
= 100 mV
f = 180 kHZ
DIR = 0.2 (typical for small output ripple voltage)
Assume the diode forward voltage and the transistor
saturation voltage are both 0.3 V. Determine the maximum
steady state duty cycle at V
IN
= 2.4 V:
D +
3.3V ) 0.3V * 2.4V
3.3V ) 0.3V * 0.3V
+ 0.364
Calculate the maximum inductance value which can
generate the desired current output and the preferred delta
inductor current to average inductor current ratio:
L v
(3.3V ) 0.3V * 2.4V)(1 * 0.364)
2
180000Hz 1A 0.2
+ 13.5H
Determine the average inductor current and peak inductor
current:
I
L
+
1
1 * 0.364
+ 1.57A
I
PK
+ 1.57A (1 )
0.2
2
) + 1.73A
Therefore, a 12 H inductor with saturation current larger
than 1.73 A can be selected as the initial trial.
Calculate the delta charge stored in the output capacitor
during the charging up period in each switching cycle:
Q +
(1.57A * 1A)(1 * 0.364)
18000Hz
+ 2.01C
Determine the output capacitance value for the desired
output ripple voltage:
Assume the ESR of the output capacitor is 0.15 ,
C
OUT
u
2.01C
100mV * (1.57A * 1A) 0.15
+ 138.6F
Therefore, a Tantalum capacitor with value of 150 F to
220 F and ESR of 0.15 can be used as the output
capacitor. However, according to experimental result,
220F output capacitor gives better overall operational
stability and smaller ripple voltage.
External Component Selection
Inductor Selection
The NCP1450A is designed to work well with a 6.8 to
12 H inductors in most applications 10 H is a sufficiently
low value to allow the use of a small surface mount coil, but
large enough to maintain low ripple. Lower inductance
values supply higher output current, but also increase the
ripple and reduce efficiency.
Higher inductor values reduce ripple and improve
efficiency, but also limit output current.
The inductor should have small DCR, usually less than
1, to minimize loss. It is necessary to choose an inductor
with a saturation current greater than the peak current which
the inductor will encounter in the application.
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NCP1450ASN19T1G

Mfr. #:
Buy NCP1450ASN19T1G
Manufacturer:
ON Semiconductor
Description:
Switching Voltage Regulators 1.9V 1A Boost DC-DC PWM
Lifecycle:
New from this manufacturer.
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