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PDF NCP1597A Data sheet ( Hoja de datos )
| Número de pieza | NCP1597A | |
| Descripción | 2.0 A Synchronous Buck Regulator | |
| Fabricantes | ON Semiconductor | |
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NCP1597A
www.DataSheet4U.com
1 MHz, 2.0 A Synchronous
Buck Regulator
The NCP1597A family are fixed 1 MHz, high−output−current,
synchronous PWM converters that integrate a low−resistance,
high−side P−channel MOSFET and a low−side N−channel MOSFET.
The NCP1597A utilizes current mode control to provide fast transient
response and excellent loop stability. It regulates input voltages from
4.0 V to 5.5 V down to an output voltage as low as 0.8 V and is able to
supply up to 2.0 A.
The NCP1597A includes an internally fixed switching frequency
(FSW), and an internal soft−start to limit inrush currents. Using the EN
pin, shutdown supply current is reduced to 3 mA maximum.
Other features include cycle−by−cycle current limiting,
short−circuit protection, power saving mode and thermal shutdown.
Features
• Input Voltage Range: from 4.0 V to 5.5 V
• Internal 140 mW High−Side Switching P−Channel MOSFET and
90 mW Low−Side N−Channel MOSFET
• Fixed 1 MHz Switching Frequency
• Cycle−by−Cycle Current Limiting
• Overtemperature Protection
• Internal Soft−Start
• Start−up with Pre−Biased Output Load
• Adjustable Output Voltage Down to 0.8 V
• Power Saving Mode During Light Load
• These are Pb−Free Devices
Applications
• DSP Power
• Hard Disk Drivers
• Computer Peripherals
• Home Audio
• Set−Top Boxes
• Networking Equipment
• LCD TV
• Wireless and DSL/Cable Modem
• USB Power Devices
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1
DFN6
CASE 506AH
MARKING
DIAGRAM
1 1597A
AYWWG
G
A = Assembly Location
Y = Year
WW = Work Week
G = Pb−Free Package
(Note: Microdot may be in either location)
PIN CONNECTIONS
FB 1
GND 2
LX 3
6 EN
5 VCC
4 VCCP
ORDERING INFORMATION
Device
Package
Shipping†
NCP1597AMNTWG DFN6
3000 / Tape &
(Pb−Free)
Reel
†For information on tape and reel specifications,
including part orientation and tape sizes, please
refer to our Tape and Reel Packaging Specifications
Brochure, BRD8011/D.
© Semiconductor Components Industries, LLC, 2010
June, 2010 − Rev. 0
1
Publication Order Number:
NCP1597/D
1 page  
NCP1597A
TYPICAL OPERATING CHARACTERISTICS
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3.7
3.6
3.5
3.4
3.3
3.2
3.1−40
1.3
1.2
1.1
1.0
0.9
0.8
0.7
−40
2.0
UVLO Rising Threshold
UVLO Falling Threshold
−15 10 35 60
TA, AMBIENT TEMPERATURE (°C)
Figure 3. Undervoltage Lockout vs.
Temperature
−15 10 35 60
TA, AMBIENT TEMPERATURE (°C)
Figure 5. Switching Frequency vs.
Temperature
85
85
1.8
1.6
1.4
1.2
1.0
−40
−15 10 35 60
TA, AMBIENT TEMPERATURE (°C)
Figure 7. Quiescent Current Into VCC vs.
Temperature
85
815
810
805
800
795
790
785−40
−15 10 35 60
TA, AMBIENT TEMPERATURE (°C)
Figure 4. Feedback Input Threshold vs.
Temperature
6.0
85
5.5 ILIM (Soft−Start)
5.0
4.5
4.0 ILIM (Regulation)
3.5
−40
−15 10 35 60
TA, AMBIENT TEMPERATURE (°C)
Figure 6. Current Limit vs. Temperature
85
2.0
1.8
1.6
1.4
1.2
1.0
−40
−15 10 35 60
TA, AMBIENT TEMPERATURE (°C)
Figure 8. Quiescent Current Into VCC vs.
Temperature
85
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5
5 Page 
NCP1597A
APPLICATION INFORMATION
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Programming the Output Voltage
The output voltage is set using a resistive voltage divider
from the output voltage to FB pin (see Figure 25). So the
output voltage is calculated according to Eq.1.
Vout
+
VFB
@
R1 ) R2
R2
(eq. 1)
Vout
COUT(min)
+
8
@
Iripple
f @ Vripple
(eq. 3)
Where Vripple is the allowed output voltage ripple.
The required ESR for this amount of ripple can be
calculated by equation 5.
ESR
+
Vripple
Iripple
(eq. 4)
R1
FB
R2
Based on Equation 2 to choose capacitor and check its
ESR according to Equation 3. If ESR exceeds the value from
Eq.4, multiple capacitors should be used in parallel.
Ceramic capacitor can be used in most of the applications.
In addition, both surface mount tantalum and through−hole
aluminum electrolytic capacitors can be used as well.
Figure 25. Output divider
Maximum Output Capacitor
NCP1597A family has internal 1 ms fixed soft−start and
overcurrent limit. It limits the maximum allowed output
capacitor to startup successfully. The maximum allowed
output capacitor can be determined by the equation:
Inductor Selection
The inductor is the key component in the switching
regulator. The selection of inductor involves trade−offs
among size, cost and efficiency. The inductor value is
selected according to the equation 2.
ǒ ǓL
+
f
Vout
@ Iripple
@
1
*
Vout
Vin(max)
(eq. 2)
Where Vout − the output voltage;
f − switching frequency, 1.0 MHz;
Iripple − Ripple current, usually it’s 20% − 30% of output
current;
Vin(max) − maximum input voltage.
Choose a standard value close to the calculated value to
maintain a maximum ripple current within 30% of the
maximum load current. If the ripple current exceeds this
30% limit, the next larger value should be selected.
The inductor’s RMS current rating must be greater than
the maximum load current and its saturation current should
be about 30% higher. For robust operation in fault conditions
(start−up or short circuit), the saturation current should be
high enough. To keep the efficiency high, the series
resistance (DCR) should be less than 0.1 W, and the core
material should be intended for high frequency applications.
Output Capacitor Selection
The output capacitor acts to smooth the dc output voltage
and also provides energy storage. So the major parameter
necessary to define the output capacitor is the maximum
allowed output voltage ripple of the converter. This ripple is
related to capacitance and the ESR. The minimum
capacitance required for a certain output ripple can be
calculated by Equation 4.
Cout(max)
+
Ilim(min) * Iload(max) *
VoutńTSS(min)
Dip−p
2
(eq. 5)
Where TSS(min) is the minimum soft−start period (1ms);
DiPP is the current ripple.
This is assuming that a constant load is connected. For
example, with 3.3 V/2.0 A output and 20% ripple, the max
allowed output capacitors is 546 mF.
Input Capacitor Selection
The input capacitor can be calculated by Equation 6.
Cin(min)
+
Iout(max)
@
Dmax
@
f
@
1
Vin(ripple)
(eq. 6)
Where Vin(ripple) is the required input ripple voltage.
Dmax
+
Vout
Vin(min)
is
the
maximum
duty
cycle.
(eq. 7)
Power Dissipation
The NCP1597A is available in a thermally enhanced
6−pin, DFN package. When the die temperature reaches
+185°C, the NCP1597A shuts down (see the
Thermal−Overload Protection section). The power
dissipated in the device is the sum of the power dissipated
from supply current (PQ), power dissipated due to switching
the internal power MOSFET (PSW), and the power
dissipated due to the RMS current through the internal
power MOSFET (PON). The total power dissipated in the
package must be limited so the junction temperature does
not exceed its absolute maximum rating of +150°C at
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| Páginas | Total 13 Páginas | |
| PDF Descargar | [ Datasheet NCP1597A.PDF ] | |
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