Semiconductor Components Industries, LLC, 2005

January, 2005 - Rev. 5

Publication Order Number:

NCP1511/D

NCP1511

Up to 500 mA, High

Efficiency Synchronous

Step-Down DC-DC Converter

in Chip Scale Package

The NCP1511 step-down PWM DC-DC converter is optimized

for portable applications powered from 1-cell Li-ion or 3-cell
Alkaline/NiCd/NiMH batteries. This DC-DC converter utilizes a
current-mode control architecture for easy compensation and better
line regulation. It also uses synchronous rectification to increase
efficiency and reduce external part count. The NCP1511 optimizes
efficiency in light load conditions when switched from a normal
PWM mode to a "pulsed switching" mode. The device also has a
built-in oscillator for the PWM circuitry, or it can be synchronized to
an external 500 kHz to 1000 kHz clock signal. Finally, it includes an
integrated soft-start, cycle-by-cycle current limiting, and thermal
shutdown protection. The NCP1511 is available in a chip scale
package.

Features

High Efficiency:

93% for 1.89 V Output at 3.6 V Input and 150 mA Load Current
92% for 1.89 V Output at 3.6 V Input and 300 mA Load Current

Digital Programmable Output Voltages: 1.0, 1.3, 1.5 or 1.89 V

Output Current up to 500 mA at V

= 3.6 V

Low Quiescent Current of 14

mA in Pulsed Switching Mode

Low 0.1

mA Shutdown Current

-30

C to 85

C Operation Temperature

Ceramic Input/Output Capacitor

9 Pin Chip Scale Package

Pb-Free Package is Available

Applications

Cellular Phones, Smart Phones and PDAs

Digital Still Cameras

MP3 Players and Portable Audio Systems

Wireless and DSL Modems

Portable Equipment

DAL

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Device

Package

Shipping

ORDERING INFORMATION

NCP1511FCT1

3000 Tape & Reel

9 PIN

MICRO BUMP

FC SUFFIX

CASE 499AC

MARKING
DIAGRAM

Micro Bump

XX = Device Code
A

= Assembly Location

= Year

WW = Work Week

Pin: A1. - GNDP

A2. - LX
A3. - VCC
B1. - SYNC
B2. - GNDA
B3. - FB
C1. - SHD
C2. - CB1
C3. - CB0

(Bottom View)

PIN CONNECTIONS

NCP1511FCT1G

3000 Tape & Reel

Micro Bump

(Pb-Free)

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.

Figure 1. Typical Application Circuit

VCC

SHD

SYNC

GNDA GNDP

CB0

CB1

2.5 V - 5.2 V

6.8

out

CB0 and CB1
Control Input

out

100

0.1

100

1000

PWM Mode

Pulsed Mode

EFFICIENCY

(

)

out

(mA)

Figure 2. Efficiency vs. Output Current

= 3.6 V

out

= 1.5 V

= 25

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Figure 3. Simplified Block Diagram

GNDA

CB0

CB1

SHD

ISENS

SENFET

ILIM

ZCL

MODE SELECTION

SYNC DETECT

AND

TIMING BLOCK

SYNC DETECT

AND

TIMING BLOCK

THERMAL

SHUTDOWN

ENABLE
DETECT

SELECT

LOGIC

BANDGAP

REFERENCE

AND SOFT

START

PWM

OVP

CMP

DVR

COMPENSATION

RAMP

CONTROL

BLOCK

(PWM,PM)

GNDP

SYNC

VCC

DAMPING

SWITCHING

CONTROL

DAMPING

SWITCHING

CONTROL

PIN FUNCTION DESCRIPTION

Pin No.

Symbol

Type

Description

GNDP

Power Ground

Ground Connection for the NFET Power Stage.

Analog Output

Connection from Power Pass Elements to the Inductor.

Analog Input

Power Supply Input for Power and Analog V

SYNC

Analog Input

Synchronization input for the PWM converter. If a clock signal is present, the converter
uses the rising edge for the turn on. If this pin is low, the converter is in the Pulsed mode.
If this pin is high, the converter uses the internal oscillator for the PWM mode. This pin
contains an internal pull down resistor.

GNDA

Analog Ground

Ground connection for the Analog Section of the IC. This is the GND for the FB, Ref,
Sync, CB, and SHD pins.

Analog Input

Feedback Voltage from the Output of the Power Supply.

SHD

Analog Input

Enable for Switching Regulator. This Pin is Active High to enable the NCP1511. The SHD
Pin has an internal pull down resistor to force the converter off if this pin is not connected
to the external circuit.

CB1

Analog Input

Selects V

out

. This pin contains an internal pull up resistor.

CB0

Analog Input

Selects V

out

. This pin contains an internal pull down resistor.

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MAXIMUM RATINGS

Rating

Symbol

Value

Unit

Maximum Voltage All Pins

max

5.5

Maximum Operating Voltage All Pins

max

5.2

Thermal Resistance, Junction-to-Air (Note 1)

159

C/W

Operating Ambient Temperature Range

-30 to 85

ESD Withstand Voltage

Human Body Model (Note 2)

Machine Model (Note 2)

ESD

> 2500

> 150

Moisture Sensitivity

MSL

Level 1

Storage Temperature Range

stg

-55 to 150

Junction Operating Temperature

-30 to 125

Maximum ratings are those values beyond which device damage can occur. Maximum ratings applied to the device are individual stress limit values
(not normal operating conditions) and are not valid simultaneously. If these limits are exceeded, device functional operation is not implied, damage
may occur and reliability may be affected.
1. For the 9-Pin Micro Bump package, the R

is highly dependent of the PCB heatsink area. R

= 159

C/W with 50 mm

PCB heatsink area.

2. This device series contains ESD protection and exceeds the following tests:

Human Body Model, 100 pF discharge through a 1.5 k

following specification JESD22/A114.

Machine Model, 200 pF discharged through all pins following specification JESD22/A115.
Latchup as per JESD78 Class II: > 100 mA.

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ELECTRICAL CHARACTERISTICS

= 3.6 V, Vo = 1.5 V, T

= 25

C, Fsyn = 600 kHz 50% Duty Cycle square wave for PWM

mode; T

= 30 to 85

C for Min/Max values, unless otherwise noted.

Characteristic

Symbol

Min

Typ

Max

Unit

VCC Pin

Quiescent Current of Sync Mode, I

out

= 0 mA

Iq PWM

175

Quiescent Current of PWM Mode, I

out

= 0 mA

Iq PWM

185

Quiescent Current of Pulsed Mode, I

out

= 0 mA

Iq Pulsed

Quiescent Current, SHD Low

Iq Off

0.1

0.5

Input Voltage Range (Note 3)

Vin

2.5

5.2

Sync Pin

Input Voltage

Vsync

-0.3

Vcc + 0.3

Frequency Operational Range

Fsync

500

600

1000

kHz

Minimum Synchronization Pulse Width

Dcsync Min

Maximum Synchronization Pulse Width

Dcsync Max

SYNC "H" Voltage Threshold

Vsynch

920

1200

SYNC "L" Voltage Threshold

Vsyncl

400

830

SYNC "H" Input Current, Vsync = 3.6 V

Isynch

2.2

SYNC "L" Input Current, Vsync = 0 V

Isyncl

-0.5

Output Level Selection Pins

Input Voltage

Vcb

-0.3

Vcc + 0.3

CB0, CB1 "H" Voltage Threshold

Vcb h

920

1200

CB0, CB1 "L" Voltage Threshold

Vcb l

400

830

CB0 "H" Input Current, CB = 3.6 V

Icb0 h

2.2

CB0 "L" Input Current, CB = 0 V

Icb0 l

-0.5

CB1 "H" Input Current, CB = 3.6 V

Icb1 h

0.3

1.0

CB1 "L" Input Current, CB = 0 V

Icb1 l

-2.2

Shutdown Pin

Input Voltage

Vshd

-0.3

Vcc + 0.3

SHD "H" Voltage Threshold

Vshd h

920

1200

SHD "L" Voltage Threshold

Vshd l

400

830

SHD "H" Input Current, SHD = 3.6 V

Ishd h

2.2

SHD "L" Input Current, SHD = 0 V

Ishd l

-0.5

Feedback Pin

Input Voltage

Vfb

-0.3

Vcc + 0.3

Input Current, Vfb = 1.5 V

Ifb

5.0

7.5

Sync PWM Mode Characteristics

Switching P-FET Current Limit

I lim

800

Minimum On Time

Ton min

nsec

Rdson Switching P-FET and N_FET

Rdson

0.23

Switching P-FET and N-FET Leakage Current

Ileak

1.0

Output Overvoltage Threshold

5.0

3. Recommended maximum input voltage is 5 V when the device frequency is synchronized with an external clock signal.

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ELECTRICAL CHARACTERISTICS (continued)

= 3.6 V, Vo = 1.5 V, T

= 25

C, Fsyn = 600 kHz 50% Duty Cycle square wave

for PWM mode; T

= 30 to 85

C for Min/Max values, unless otherwise noted.

Characteristic

Symbol

Min

Typ

Max

Unit

Sync PWM Mode Characteristics (continued)

Feedback Voltage Accuracy, V

out

Set = 1.0 V CB0 = L, CB1 = L

out

0.950

1.000

1.050

Feedback Voltage Accuracy, V

out

Set = 1.3 V CB0 = L, CB1 = H

out

1.261

1.300

1.339

Feedback Voltage Accuracy, V

out

Set = 1.5 V CB0 = H, CB1 = H

out

1.450

1.500

1.550

Feedback Voltage Accuracy, V

out

Set = 1.89 V CB0 = H CB1 = L

out

1.833

1.890

1.947

Load Transient Response

10 to 100 mA Load Step

out

Line Transient Response, I

out

= 100 mA

3.0 to 3.6 Vin Line Step

out

mVpp

PWM Mode with Internal Oscillator Characteristics

Switching P-FET Current Limit

I lim

800

Minimum On Time

Ton min

nsec

Internal Oscillator Frequency

Fosc

700

900

1200

kHz

Rdson Switching P-FET and N_FET

Rdson

0.23

Switching P-FET and N-FET Leakage Current

Ileak

1.0

Output Overvoltage Threshold

5.0

Feedback Voltage Accuracy, V

out

Set = 1.0 V CB0 = L, CB1 = L

out

0.950

1.000

1.050

Feedback Voltage Accuracy, V

out

Set = 1.3 V CB0 = L, CB1 = H

out

1.261

1.300

1.339

Feedback Voltage Accuracy, V

out

Set = 1.5 V CB0 = H, CB1 = H

out

1.450

1.500

1.550

Feedback Voltage Accuracy, V

out

Set = 1.89 V CB0 = H CB1 = L

out

1.833

1.890

1.947

Load Transient Response

10 to 100 mA Load Step

out

Line Transient Response, I

out

= 100 mA

3.0 to 3.6 Vin Line Step

out

mVpp

Pulsed Mode Characteristics

On Time

Ton

660

nsec

Output Ripple Voltage, I

out

= 100

out

Feedback Voltage Accuracy, V

out

Set = 1.0 V CB0 = L, CB1 = L

out

0.930

1.000

1.070

Feedback Voltage Accuracy, V

out

Set = 1.3 V CB0 = L, CB1 = H

out

1.241

1.300

1.359

Feedback Voltage Accuracy, V

out

Set = 1.5 V CB0 = H, CB1 = H

out

1.430

1.500

1.570

Feedback Voltage Accuracy, V

out

Set = 1.89 V CB0 = H CB1 = L

out

1.813

1.890

1.967

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Figure 4. Efficiency vs. Output Current in PWM

Mode

100

2.5

3.0

3.5

4.0

4.5

5.5

EFFICIENCY

(

)

INPUT VOLTAGE (V)

Figure 5. Efficiency vs. Input Voltage in PWM

Mode

out

= 150 mA

Freq = 1.0 MHz
T

= 25

Figure 6. Efficiency vs. Output Current at

Different Input Voltage

100

500 600

800

1000

1200

1400

1.0 V

out

1.3 V

out

1.5 V

out

1.89 V

out

FREQUENCY (kHz)

Figure 7. Efficiency vs. Frequency at

out

= 150 mA

= 3.6 V

out

= 150 mA

= 25

PWM

Figure 8. Efficiency vs. Frequency at

out

= 300 mA

EFFICIENCY

(

)

Figure 9. Efficiency vs. Output Current in

Pulsed Mode

100

200

300

400

500

EFFICIENCY

(

)

out

(mA)

100

1.0 V

out

1.3 V

out

1.5 V

out

1.89 V

out

100

200

300

400

500

5.2 V

3.6 V

2.7 V

EFFICIENCY

(

)

out

(mA)

out

= 1.5 V

PWM
T

= 25

100

700

900

1100

1300

1500

100

500 600

800

1000

1200

1400

1.0 V

out

1.3 V

out

1.5 V

out

1.89 V

out

FREQUENCY (kHz)

= 3.6 V

out

= 300 mA

= 25

PWM

EFFICIENCY

(

)

700

900

1100

1300

1500

100

0.01

100

1000

EFFICIENCY

(

)

out

(mA)

= 3.6 V

PM
T

= 25

1.0 V

out

1.3 V

out

1.5 V

out

1.89 V

out

0.1

5.0

1.0 V

out

1.3 V

out

1.5 V

out

1.89 V

out

= 3.6 V

PWM
T

= 25

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Figure 10. Input Current Comparison

0.6

0.8

1.2

1.4

1.6

1.8

100

200

300

400

500

= 3.6 V

= 25

PWM

out

(V)

Figure 11. Output Voltage vs. Output Current

1.0 V

out

1.3 V

out

1.5 V

out

1.89 V

out

(mA)

1000

100

out

(mA)

out

(mV)

-5

-10

= 3.6 V

= 25

Figure 12. Load Regulation in PWM Mode

100

-20

-40

TEMPERATURE (

out

(V)

1.8

1.2

= 3.6 V

out

= 150 mA

PWM

0.6

0.8

1.4

1.6

Figure 13. Output Voltage vs. Temperature

Figure 14. Oscillator Frequency vs. Temperature

Figure 15. Oscillator Frequency vs. Input

Voltage

(V)

FREQUENCY (kHz)

1.89 V

out

1.0 V

out

1.3 V

out

1.5 V

out

1.89 V

out

1.5 V

out

1.3 V

out

1.0 V

out

100

-20

-40

TEMPERATURE (

FREQUENCY (kHz)

910

890

850

870

950

= 3.6 V

out

= 1.5 V

out

= 150 mA

850

870

890

910

930

950

2.5

3.0

3.5

4.0

4.5

5.5

out

= 1.5 V

out

= 150 mA

= 25

PWM

out

(mA)

(
m

PWM Mode

Pulsed Mode

= 3.6 V

out

= 1.5 V

= 25

5.0

930

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(V)

Figure 16. Output Voltage vs. Shutdown Pin

Voltage

1.4

0.6

0.4

0.2

SHD

(V)

out

(V)

2.0

1.5

1.0

0.5

1.2

1.0

0.8

Figure 17. Transition Level of CB Pins

= 3.6 V

out

= 1.5 V

= 25

PWM Mode

1.4

0.6

0.4

0.2

out

(V)

2.0

1.5

1.0

0.5

1.2

1.0

0.8

= 3.6 V

out

= 1.5 V

= 25

PWM Mode

Figure 18. Light Load PWM Switching Waveform

= 3.6 V, V

out

= 1.5 V, I

out

= 30 mA)

Figure 19. Heavy Load PWM Switching Waveform

= 3.6 V, V

out

= 1.5 V, I

out

= 300 mA)

Figure 20. Pulsed Mode Switching Waveform

= 3.6 V, V

out

= 1.5 V, I

out

= 30 mA)

Figure 21. Soft-Start

= 3.6 V, V

out

= 1.5 V, I

out

= 150 mA)

s/div

out

AC Coupled
10 mV/div

1 V/div

s/div

out

AC Coupled
10 mV/div

1 V/div

500 ms/div

out

0.5 V/div

shdn

1 V/div

s/div

out

AC Coupled
10 mV/div

1 V/div

1.5 V

2 V

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DETAILED OPERATING DESCRIPTION

Overview

The NCP1511 is a monolithic micro-power high

frequency PWM step-down DC-DC converter specifically
optimized for applications requiring high efficiency and a
small PCB footprint such as portable battery powered
products. It integrates synchronous rectification to
improve efficiency as well as eliminate the external
Schottky diode. High switching frequency allows for a low
profile inductor and capacitors to be used. Four digital
selectable output voltages (1.0, 1.3, 1.5 and 1.89 V) can be
generated from the input supply that can range from
2.7-5.2 V. All loop compensation is integrated as well
further reducing the external component count as well.

The DC-DC converter has two operating modes (normal

PWM, pulsed switching), which are intended to allow for
optimum efficiency under either light (up to 30 mA) or
heavy loads. The user determines the operating mode by
controlling the SYNC input. In addition the SYNC input
can be used to synchronize the PWM to an external system
clock signal in the range of 500-1000 kHz.

PWM Operating Mode

The NCP1511 can be set to current mode PWM operation

by connecting SYNC pin to V

. In this mode, the output

voltage is regulated by modulating the on-time pulse width
of the main switch Q1 at a fixed frequency of 1.0 MHz. The
switching of the PMOS Q1 is controlled by a flip-flop
driven by the internal oscillator and a comparator that
compares the error signal from an error amplifier with the
sum of the sensed current signal and compensation ramp.
At the beginning of each cycle, the main switch Q1 is
turned ON by the rising edge of the internal oscillator
clock. The inductor current ramps up until the sum of the
current sense signal and compensation ramp becomes
higher than the error voltage amplifier. Once this has
occurred, the PWM comparator resets the flip-flop, Q1 is
turned OFF and the synchronous switch Q2 is turned ON.
Q2 replaces the external Schottky diode to reduce the
conduction loss and improve the efficiency. To avoid
overall power loss, a certain amount of dead time is
introduced to ensure Q1 is completely turned OFF before
Q2 is being turned ON.

In continuous conduction mode (CCM), Q1 is turned ON

after Q2 is completely turned OFF to start a new clock
cycle. In discontinuous conduction mode (DCM), the zero
crossing comparator (ZLC) will turn off Q2 when the
inductor current drops to zero.

Overvoltage Protection

The overvoltage protection circuit is present in PWM

mode to prevent the output voltage from going too high
under light load or fast load transient conditions. The
output overvoltage threshold is 5% above nominal set
value. If the output voltage rises above 5% of the nominal

value, the OVP comparator is activated and switch Q1 is
turned OFF. Switching will continue when the output
voltage falls below the threshold of OVP comparator.

Pulsed Mode (PM)

Under light load conditions (< 30 mA), the NCP1511 can

be configured to enter a low current pulsed mode operation
to reduce power consumption. This is accomplished by
applying a logic LOW to the SYNC pin. The output
regulation is implemented by pulse frequency modulation.
If the output voltage drops below the threshold of PM
comparator (typically Vnom-2%), a new cycle will be
initiated by the PM comparator to turn on the switch Q1. Q1
remains ON until the peak inductor current reaches 200 mA
(nom). Then ILIM comparator goes high to switch off Q1.
After a short dead time delay, switch rectifier Q2 is turn
ON. The zero crossing comparator will detect when the
inductor current drops to zero and send the signal to turn off
Q2. The output voltage continues to decrease through
discharging the output capacitor. When the output voltage
falls below the threshold of the PM comparator again, a
new cycle starts immediately.

Cycle-by-Cycle Current Limit

From the block diagram, an ILIM comparator is used to

realize cycle-by-cycle current limit protection. The
comparator compares the LX pin voltage with the
reference voltage from the SENFET, which is biased by a
constant current. If the inductor current reaches the limit,
the ILIM comparator detects the LX voltage falling below
the reference voltage from the SENFET and releases the
signal to turn off the switch Q1. The cycle-by-cycle
current limit is set at 800 mA (nom) in PWM and 200 mA
in PM.

Frequency Synchronization and Operating Mode
Selection

The SYNC pin can also be used for frequency

synchronization by connecting it with an external clock
signal. It operates in PWM mode when synchronized to an
external clock. The switching cycle initiates by the rising
edge of the clock. The 500 kHz to 1000 kHz
synchronization clock signal should be between 0.4 V and
1.2 V.

Gating on and off the clock, the SYNC pin can also be

used to select between PM and PWM modes. It allows
efficient dynamical power management by adjusting the
converter operation to the specific system requirement. Set
SYNC pin low to select PM mode at light load conditions
(up to 30 mA) and set SYNC pin high or connect with
external clock to select PWM mode at heavy load condition
to achieve optimum efficiency. Table 1 shows the mode
selection with three different SYNC pin states.

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Table 1. Operating Mode Selection

SYNC Pin State

Operating Mode

LOW

Pulsed Mode (PM)

HIGH

PWM, 1 MHz Switch Frequency

CLOCK

PWM, Frequency Synchronization

Output Voltage Selection

The output voltage is digitally programmed to one of

four voltage levels depending on the logic state of CB0 and
CB1. Therefore if the NCP1511's load, such as a digital
cellular phone's baseband processor, supports dynamic
power management, the device can lower or raise its core
voltage under software control. When combined with the
pulsed current mode function in low load situations, this
active voltage management further stretches the useful
operating life of the handset battery between charges.

The output voltage levels are listed in Table 2. The CB0

has a pull down resistor and the CB1 has a pullup resistor.
The default output voltage is 1.3 V when CB0 and CB1 are
floating.

Table 2. Truth Table for CB0 and CB1 with the
Corresponding Output Voltage

CB0

CB1

Vout(V)

1.0

1.3

1.5

1.89

Soft-Start

The NCP1511 uses soft-start to limit the inrush current

when the device is initially powered up or enabled.
Soft-start is implemented by gradually increasing the
reference voltage until it reaches the full reference voltage.
During startup, a pulsed current source charges the internal
soft-start capacitor to provide gradually increasing
reference voltage for the PWM loop. When the voltage
across the capacitor ramps up to the nominal reference
voltage, the pulsed current source will be switched off and
the reference voltage will switch to the regular reference
voltage.

Shutdown Mode

When the SHD pin has a voltage applied of less than

0.4 V, the NCP1511 will be disabled. In shutdown mode,
the internal reference, oscillator and most of the control
circuitries are turned off. Therefore, the typical current
consumption will be 0.1

mA (typical value).

Applying a voltage above 1.2 V to SHD pin will enable

the device for normal operation. The device will go through
soft-start to normal operation.

Thermal Shutdown

Internal Thermal Shutdown circuitry is provided to

protect the integrated circuit in the event that the maximum
junction temperature is exceeded. If the junction
temperature exceeds 160

C, the device shuts down. In this

mode switch Q1 and Q2 and the control circuits are all
turned off. The device restarts in soft-start after the
temperature drops below 135

_C. This feature is provided

to prevent catastrophic failures from accidental device
overheating and it is not intended as a substitute for proper
heatsinking.

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APPLICATIONS INFORMATION

Component Selection

Input Capacitor Selection

In PWM operating mode, the input current is pulsating

with large switching noise. Using an input bypass capacitor
reduces the peak current transients drawn from the input
supply source, thereby reducing switching noise
significantly. The capacitance needed for the input bypass
capacitor depends on the source impedance of the input
supply. The RMS capacitor current is calculated as:

IRMS

[

IO D

(eq. 1)

where:
D = duty cycle, which equals V

out

, and D' = 1 - D.

The maximum RMS current occurs at 50% duty cycle

with maximum output current, which is I

O,max

/2.

A low profile ceramic capacitor of 10

mF should be used

for most of the cases. For effective bypass results, the input
capacitor should be placed as close as possible to the V

pin.

Inductor Value Selection

Selecting the proper inductor value is based on the

desired ripple current. The relationship between the
inductance and the inductor ripple current is given by the
equation below.

Vout

Lfs

Vout

Vin

(eq. 2)

The DC current of the inductor should be at least equal

to the maximum load current plus half the ripple current to
prevent core saturation. For NCP1511, the compensation is
internally fixed and a fixed 6.8

mH inductor is needed for

most of the applications. For better efficiency, choose a low
DC resistance inductor.

Output Capacitor Selection

Selecting the proper output capacitor is based on the

desired output ripple voltage. Ceramic capacitors with low
ESR values will have the lowest output ripple voltage and
are strongly recommended. The output ripple voltage is
given by:

+ D

ESR

)

4fsCout

(eq. 3)

The RMS output capacitor current is given by:

IRMS(Cout)

2 3

(eq. 4)

Where f

is the switching frequency and ESR is the

effective series resistance of the output capacitor. A low
ESR, 22

mF ceramic capacitor is recommended for

NCP1511 in most of applications. For example, with TDK
C2012X5R0J226 output capacitor, the output ripple is less
than 10 mV at 300 mA.

Design Example

As a design example, assume that the NCP1511 is used

in a single lithium-ion battery application. The input
voltage, V

, is 3.0 V to 4.2 V. Output condition is V

out

1.5 V with a typical load current of 120 mA and a maximum
of 300 mA. For NCP1511, the inductor has a predetermined
value, 6.8

mH. The inductor ESR will factor into the overall

efficiency of the converter. The inductor needs to be
selected by the required peak current.

Equation 5 is the basic equation for an inductor and

describes the voltage across the inductor. The inductance
value determines the slope of the current of the inductor.

diL

(eq. 5)

Equation 5 is rearranged to solve for the change in

current for the on-time of the converter in Continuous
Conduction Mode.

(eq. 6)

iL, pk-pk

(Vin

Vout)

DTs

(Vin

Vout)

Vin

Vout

iL, max

IO, max

)

iL, pk-pk

Utilizing Equations 6, the peak-to-peak inductor current

is calculated using the following worst-case conditions.

Vin, max

4.2 V, Vout

1.5 V, fs

1 MHz-20%,

6.8

H-10%, iL, pk-pk

197 mA, iL, max

399 mA

Therefore, the inductor must have a maximum current

exceeding 405 mA.

Since the compensation is fixed internally in the IC, the

input and output capacitors as well as the inductor have a
predetermined value too: C

= 10

mF and C

out

= 22

mF. Low

ESR capacitors are needed for best performance.
Therefore, ceramic capacitors are recommended.

NCP1511

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PCB Layout Recommendations

Good PCB layout plays an important role in switching

mode power conversion. Careful PCB layout can help to
minimize ground bounce, EMI noise and unwanted feedback
that can affect the performance of the converter. Hints
suggested below can be used as a guideline in most situations.

1. Use star-ground connection to connect the IC ground

nodes and capacitor GND nodes together at one point.
Keep them as close as possible. And then connect this to the
ground plane through several vias. This will reduce noise
in the ground plane by preventing the switching currents
from flowing through the ground plane.

2. Place the power components (i.e., input capacitor,

inductor and output capacitor) as close together as possible

for best performance. All connecting traces must be short,
direct, and wide to reduce voltage errors caused by resistive
losses through the traces.

3. Separate the feedback path of the output voltage from

the power path. Keep this path close to the NCP1511
circuit. And also route it away from noisy components.
This will prevent noise from coupling into the voltage
feedback trace.

4. Place the DC-DC converter away from noise sensitive

circuitry, such as RF circuits.

The following shows the NCP1511 demo board layout

and bill of materials:

Figure 27. Top and Silkscreen Layer

Figure 28. Soldermask Top and Silkscreen Layer

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to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any
liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental
damages. "Typical" parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over
time. All operating parameters, including "Typicals" must be validated for each customer application by customer's technical experts. SCILLC does not convey any license under
its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body,
or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death
may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indemnify and hold SCILLC and its officers, employees,
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personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part.
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NCP1511/D

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