Datasheet KB3426-ADJ, KB3426B-1.8, KB3426B-3.3 Datasheet (Kingbor) [ru]

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KB3426

FEATURES

■

High Efficiency: Up to 96%

■

Very Low Quiescent Current: Only 20µA
During Operation

■

800mA Output Current

■

2.5V to 6.5V Input Voltage Range

■

1.5MHz Constant Frequency Operation

■

No Schottky Diode Required

■

Low Dropout Operation: 100% Duty Cycle

■

0.6V Reference Allows Low Output Voltages

■

Shutdown Mode Draws )1µA Supply Current

■

Current Mode Operation for Excellent Line and
Load Transient Response

■

Overtemperature Protected

■

Low Profile (1mm) SOT23-5 Package

APPLICATIONS

■

Cellular Telephones

■

Personal Information Appliances

■

Wireless and DSL Modems

■

Digital Still Cameras

■

MP3 Players

■

Portable Instruments

1.5MHz,

800mA

Synchronous Step-Down

Regulator in

SOT23-5

DESCRIPTION

The KB3426 is a high efficiency monolithic synchro­nous buck regulator using a constant frequency, current
mode architecture. The device is available in an adjustable
version and fixed output voltages of 1.8V and 3.3V. Supply
current during operation is only 20µA and drops to ) 1µA
in shutdown. The 2.5V to 5.5V input voltage range makes
the KB3426 ideally suited for single Li-Ion battery-pow­ered applications. 100% duty cycle provides low dropout
operation, extending battery life in portable systems.
Automatic Burst Mode operation increases efficiency at
light loads, further extending battery life.

Switching frequency is internally set at 1.5MHz, allowing
the use of small surface mount inductors and capacitors.

The internal synchronous switch increases efficiency and
eliminates the need for an external Schottky diode. Low
output voltages are easily supported with the 0.6V feed­back reference voltage. The KB3426 is available in a low
profile (1mm) SOT23-5 package.

TYPICAL APPLICATION

V

3.6V

TO 6.5V

IN

+

C

IN

4.7µF
Tan

4

V

IN

KB3426-3.3

1

RUN

V

GND

2

Figure 1a. High Efficiency Step-Down Converter

SW

OUT

4.7µH

3

5

C

OUT

10µF
CER

V

OUT

3.3V
800mA

95

VIN = 3.6V

90

85

80

75

EFFICIENCY (%)

70

65

60

0.1 10 100 1000

VIN = 3.8V

VIN = 4.2V

1
OUTPUT CURRENT (mA)

V

OUT

Figure 1b. Efficiency vs Load Current

= 3.3V

1

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KB3426

ABSOLUTE MAXIMUM RATINGS

(Note 1)

Input Supply Voltage .................................. –0.3V to 6.5V

RUN, VFB Voltages ..................................... – 0.3V to V

IN

SW Voltage .................................. –0.3V to (VIN + 0.3V)

P-Channel Switch Source Current (DC) ............. 800mA

N-Channel Switch Sink Current (DC) ................. 800mA

PACkAGE/ORDER INFORMATION

ORDER PART

TOP VIEW

Marking

RUN 1

GND 2

SW 3

S5 PACKAGE

5-LEAD PLASTIC SOT-23

T

= 125°C, eJA = 250°C/ W, eJC = 90°C/ W

JMAX

5 V

4 V

FB

IN

NUMBER

KB3426-ADJ

Top Marking

A17x

A16x

x: date code

Peak SW Sink and Source Current ........................ 1.3A

Operating Temperature Range (Note 2) .. – 40°C to 85°C

Junction Temperature (Note 3)............................ 125°C

Storage Temperature Range ................ –65°C to 150°C

Lead Temperature (Soldering, 10 sec)................. 300°C

ORDER PART

TOP VIEW

Marking

RUN 1

GND 2

SW 3

S5 PACKAGE

5-LEAD PLASTIC SOT-23

T

= 125°C, eJA = 250°C/ W, eJC = 90°C/ W

JMAX

5 V

4 V

OUT

IN

NUMBER

KB3426B-3.3

Top Marking

A33x

KB3426B-1.8

Top Marking

A37x

x: date code

ELECTRICAL CHARACTERISTICS

The● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.
VIN = 3.6V unless otherwise specified.

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

I

VFB

V

FB

6V

FB

V

OUT

6V

OUT

I

PK

V

LOADREG

V

IN

I

S

f

OSC

R

PFET

R

NFET

I

LSW

Feedback Current ● ±30 nA

Regulated Feedback Voltage KB3426 (Note 4) TA = 25°C 0.5880 0.6 0.6120 V

KB3426 (Note 4) 0 °C T
KB3426 (Note 4) –40 °C ) T

Reference Voltage Line Regulation VIN = 2.5V to 5.5V (Note 4) ● 0.04 0.4 %/V

Regulated Output Voltage KB3426-1.8, I

KB3426-3.3, I

Output Voltage Line Regulation VIN = 2.5V to 5.5V ● 0.04 0.4 %/V

Peak Inductor Current VIN = 3V, VFB = 0.5V or V

Duty Cycle < 35%

Output Voltage Load Regulation 0.5 %

Input Voltage Range ● 2.5 6.5 V

Input DC Bias Current (Note 5)
Active Mode V
Sleep Mode V
Shutdown V

Oscillator Frequency VFB = 0.6V or V

R

of P-Channel FET ISW = 100mA 0.4 0.5 1

DS(ON)

R

of N-Channel FET ISW = –100mA 0.35 0.45 1

DS(ON)

SW Leakage V

= 0.5V or V

FB

= 0.62V or V

FB

= 0V, VIN = 4.2V 0.1 1 µA

RUN

= 0V or V

V

FB

= 0V, VSW = 0V or 5V, VIN = 5V ±0.01 ±1 µA

RUN

OUT
OUT

OUT

OUT

OUT

OUT

) 85°C 0.5865 0.6 0.6135 V

A

) 85°C ● 0.5850 0.6 0.6150 V

A

= 100mA ● 1.746 1.800 1.854 V
= 100mA ● 3.234 3.300 3.366 V

= 90%, 0.75 1 1.25 A

OUT

= 90%, I

= 103%, I

= 100% ● 1.2 1.5 1.8 MHz

= 0V 210 kHz

= 0A 300 400 µA

LOAD

= 0A 20 35 µA

LOAD

2

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KB3426

ELECTRICAL CHARACTERISTICS

The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.

= 3.6V unless otherwise specified.

V

IN

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

V

I

RUN

RUN

RUN Threshold

RUN Leakage Current ● ±0.01 ±1 µA

●

0.3 1 1.5 V

Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.

Note 2: The KB3426E is guaranteed to meet performance specifications
from 0°C to 70°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.

Note 3: T
dissipation P

Note 4: The KB3426 is tested in a proprietary test mode that connects
V

Note 5: Dynamic supply current is higher due to the gate charge being

is calculated from the ambient temperature TA and power

J

according to the following formula:

D

KB3426: T

to the output of the error amplifier.

FB

delivered at the switching frequency.

TYPICAL PERFORMANCE CHARACTERISTICS

(From Figure1a Except for the Resistive Divider Resistor Values)

Efficiency vs Input Voltage

100

I

95

90

85

80

75

70

EFFICIENCY (%)

65

60

55

50

= 100mA

OUT

I

= 1mA

OUT

I

= 650mA

OUT

I

= 0.1mA

OUT

V

= 1.8V

OUT

2

3

4

INPUT VOLTAGE (V)

I

OUT

= 10mA

5

6

Efficiency vs Output Current

95

V

= 1.2V

OUT

90

85

80

75

EFFICIENCY (%)

70

65

60

0.1 10 100 1000

VIN = 2.7V

VIN = 4.2V

VIN = 3.6V

1

OUTPUT CURRENT (mA)

= TA + (PD)(250°C/W)

J

Efficiency vs Output Current

95

V

90

85

80

75

EFFICIENCY (%)

70

65

60

0.1 10 100 1000

= 1.5V

OUT

VIN = 2.7V

VIN = 4.2V

VIN = 3.6V

1
OUTPUT CURRENT (mA)

Efficiency vs Output Current

100

V

= 2.5V

OUT

95

VIN = 2.7V

90

85

80

75

EFFICIENCY (%)

70

65

60

0.1 10 100 1000

VIN = 3.6V

VIN = 4.2V

1
OUTPUT CURRENT (mA)

Reference Voltage vs
Temperature

0.614
VIN = 3.6V

0.609

0.604

0.599

0.594

REFERENCE VOLTAGE (V)

0.589

0.584

–50

–25 0

TEMPERATURE (°C)

50 100 125

25 75

Oscillator Frequency vs
Temperature

1.70
VIN = 3.6V

1.65

1.60

1.55

1.50

1.45

FREQUENCY (MHz)

1.40

1.35

1.30

–50

–25 0

TEMPERATURE (°C)

50 100 125

25 75

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TYPICAL PERFORMANCE CHARACTERISTICS

(From Figure1a Except for the Resistive Divider Resistor Values)

KB3426

Oscillator Frequency vs
Supply Voltage

1.8

1.7

1.6

1.5

1.4

OSCILLATOR FREQUENCY (MHz)

1.3

1.2

0.7

0.6

0.5

0.4

(1)

0.3

DS(ON)

R

0.2

0.1

0

2

R

–50

34 56

SUPPLY VOLTAGE (V)

vs Temperature Supply Current vs Supply Voltage Supply Current vs Temperature

DS(ON)

VIN = 4.2V

MAIN SWITCH
SYNCHRONOUS SWITCH

–25 0

VIN = 3.6V

25 75

TEMPERATURE (°C)

VIN = 2.7V

50 100 125

Output Voltage vs Load Current

1.844
VIN = 3.6V

1.834

1.824

1.814

1.804

1.794

OUTPUT VOLTAGE (V)

1.784

1.774

100 900

0

200 300 400 500 600 700 800

LOAD CURRENT (mA)

50

V

= 1.8V

OUT

45

40

35

30

25

20

15

SUPPLY CURRENT (µA)

10

= 0A

I

LOAD

5

0

2

3

4

SUPPLY VOLTAGE (V)

R

) vs Input Voltage

DS(ON

0.7

0.6

0.5

0.4

(1)

0.3

DS(ON)

R

0.2

0.1

0

10

23

50

VIN = 3.6V

45

= 1.8V

V

OUT

= 0A

I

LOAD

40

35

30

25

20

15

SUPPLY CURRENT (µA)

10

5

0

5

6

–50

–25

0

MAIN
SWITCH

SYNCHRONOUS

SWITCH

46

INPUT VOLTAGE (V)

50

25

TEMPERATURE (°C)

57

100

125

75

Switch Leakage vs Temperature

300

VIN = 5.5V
RUN = 0V

250

200

150

100

SWITCH LEAKAGE (nA)

50

SYNCHRONOUS SWITCH

0

–50

–25 0

TEMPERATURE (°C)

MAIN SWITCH

50 100 125

25 75

4

Switch Leakage vs Input Voltage

120

RUN = 0V

100

80

60

40

SWITCH LEAKAGE (pA)

20

0

0

SYNCHRONOUS

234

1

INPUT VOLTAGE (V)

SWITCH

MAIN

SWITCH

56

SW

5V/DIV

V

OUT

100mV/DIV

AC COUPLED

200mA/DIV

Burst Mode Operation

I

L

V
I

LOAD

OUT

= 1.8V

= 50mA

4µs/DIVVIN = 3.6V

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TYPICAL PERFORMANCE CHARACTERISTICS

(From Figure 1a Except for the Resistive Divider Resistor Values)

KB3426

RUN

2V/DIV

V

OUT

2V/DIV

I

LOAD

500mA/DIV

Start-Up from Shutdown

IN

V

OUT

I

LOAD

= 3.6V

= 1.8V

= 800mA

40µs/DIVV

Load Step

V

OUT

100mV/DIV

AC COUPLED

I

L

500mA/DIV

I

LOAD

500mA/DIV

V

OUT

100mV/DIV

AC COUPLED

500mA/DIV

I

LOAD

500mA/DIV

Load Step

I

L

= 3.6V

IN

V

OUT

I

LOAD

= 1.8V

= 0mA TO 800mA

20µs/DIVV

V

OUT

100mV/DIV

AC COUPLED

500mA/DIV

I

LOAD

500mA/DIV

Load Step

I

L

V

OUT

100mV/DIV

AC COUPLED

500mA/DIV

I

LOAD

500mA/DIV

Load Step

I

L

= 3.6V

IN

= 1.8V

V

OUT

I

LOAD

20µs/DIVV

= 50mA TO 800mA

= 3.6V

IN

V

= 1.8V

OUT

= 100mA TO 800mA

I

LOAD

20µs/DIVV

PIN FUNCTIONS

RUN (Pin 1): Run Control Input. Forcing this pin above

1.5V enables the part. Forcing this pin below 0.3V shuts
down the device. In shutdown, all functions are disabled
drawing <1µA supply current. Do not leave RUN floating.

GND (Pin 2): Ground Pin.

SW (Pin 3): Switch Node Connection to Inductor. This pin

connects to the drains of the internal main and synchro­nous power MOSFET switches.

= 3.6V

IN

= 1.8V

V

OUT

= 200mA TO 800mA

I

LOAD

20µs/DIVV

VIN (Pin 4): Main Supply Pin. Must be closely decoupled
to GND, Pin 2, with a 2.2µF or greater ceramic capacitor.

VFB (Pin 5) (kB3426): Feedback Pin. Receives the feed­back voltage from an external resistive divider across the
output.

V

(Pin 5) (kB3426-1.8/kB3426-3.3): Output Volt-

OUT

age Feedback Pin. An internal resistive divider divides the
output voltage down for comparison to the internal refer­ence voltage.

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SIMPLIFIED BLOC DIAGRAM

SLOPE

COMP

OSC

–

+

EA

–

+

VFB/V

RUN

OSC

FREQ

OUT

5

V

IN

1

0.6V REF

SHIFT

R1

R2

0.6V

FB

0.4V

–

+

S

R

RS LATCH

BURST

Q

Q

SLEEP

SWITCHING

LOGIC

AND

BLANKING

CIRCUIT

0.65V

I

SHOOT-

–

COMP

ANTI-

THRU

KB3426

V

4

IN

+

51

SW

3

SHUTDOWN

OPERATION

(Refer to Functional Diagram)

Main Control Loop

The KB3426 uses a constant frequency, current mode
step-down architecture. Both the main (P-channel
MOSFET) and synchronous (N-channel MOSFET) switches
are internal. During normal operation, the internal top
power MOSFET is turned on each cycle when the oscillator
sets the RS latch, and turned off when the current com­parator, I
current at which I

, resets the RS latch. The peak inductor

COMP

resets the RS latch, is controlled by

COMP

the output of error amplifier EA. When the load current
increases, it causes a slight decrease in the feedback
voltage, FB, relative to the 0.6V reference, which in turn,
causes the EA amplifier’s output voltage to increase until
the average inductor current matches the new load cur­rent. While the top MOSFET is off, the bottom MOSFET is
turned on until either the inductor current starts to reverse,
as indicated by the current reversal comparator I

RCMP

, or

the beginning of the next clock cycle.

+

I

RCMP

–

GND

2

Burst Mode Operation

The KB3426 is capable of Burst Mode operation in which
the internal power MOSFETs operate intermittently based
on load demand.

In Burst Mode operation, the peak current of the inductor
is set to approximately 200mA regardless of the output
load. Each burst event can last from a few cycles at light
loads to almost continuously cycling with short sleep
intervals at moderate loads. In between these burst events,
the power MOSFETs and any unneeded circuitry are turned
off, reducing the quiescent current to 20µA. In this sleep
state, the load current is being supplied solely from the
output capacitor. As the output voltage droops, the EA
amplifier’s output rises above the sleep threshold signal­ing the BURST comparator to trip and turn the top MOSFET
on. This process repeats at a rate that is dependent on the
load demand.

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KB3426

OPERATION

(Refer to Functional Diagram)

Short-Circuit Protection

When the output is shorted to ground, the frequency of the
oscillator is reduced to about 210kHz, 1/7 the nominal
frequency. This frequency foldback ensures that the in­ductor current has more time to decay, thereby preventing
runaway. The oscillator’s frequency will progressively
increase to 1.5MHz when V

FB

or V

rises above 0V.

OUT

Dropout Operation

As the input supply voltage decreases to a value approach­ing the output voltage, the duty cycle increases toward the
maximum on-time. Further reduction of the supply voltage
forces the main switch to remain on for more than one cycle
until it reaches 100% duty cycle. The output voltage will then
be determined by the input voltage minus the voltage drop
across the P-channel MOSFET and the inductor.

An important detail to remember is that at low input supply
voltages, the R

of the P-channel switch increases

DS(ON)

(see Typical Performance Characteristics). Therefore, the
user should calculate the power dissipation when the
KB3426 is used at 100% duty cycle with low input voltage
(See Thermal Considerations in the Applications Informa­tion section).

in the maximum output current as a function of input
voltage for various output voltages.

Slope Compensation and Inductor Peak Current

Slope compensation provides stability in constant fre­quency architectures by preventing subharmonic oscilla­tions at high duty cycles. It is accomplished internally by
adding a compensating ramp to the inductor current
signal at duty cycles in excess of 40%. Normally, this
results in a reduction of maximum inductor peak current
for duty cycles >40%. However, the KB3426 uses a
patent-pending scheme that counteracts this compensat­ing ramp, which allows the maximum inductor peak
current to remain unaffected throughout all duty cycles.

1200

1000

V

= 1.8V

OUT

800

V

= 1.5V

OUT

600

400

200

MAXIMUM OUTPUT CURRENT (mA)

V

= 2.5V

OUT

Low Supply Operation

The KB3426 will operate with input supply voltages as
low as 2.5V, but the maximum allowable output current is
reduced at this low voltage. Figure 2 shows the reduction

0

2.5

Figure 2. Maximum Output Current vs Input Voltage

3.5 4.0 4.5

3.0
SUPPLY VOLTAGE (V)

5.0 5.5

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APPLICATIONS INFORMATION

KB3426

The basic KB3426 application circuit is shown in Figure 1.
External component selection is driven by the load require­ment and begins with the selection of L followed by C
C

.

OUT

IN

and

Inductor Selection

For most applications, the value of the inductor will fall in
the range of 1µH to 4.7µH. Its value is chosen based on the
desired ripple current. Large value inductors lower ripple
current and small value inductors result in higher ripple
currents. Higher VIN or V

also increases the ripple

OUT

current as shown in equation 1. A reasonable starting point
for setting ripple current is 6IL = 240mA (40% of 800mA).

6 =

I

1

L OUT

fL

()( )

£

1

V

<

²
¤

V

OUT

V

IN

¥
´

¦

(1)

The DC current rating of the inductor should be at least
equal to the maximum load current plus half the ripple
current to prevent core saturation. Thus, a 820mA rated
inductor should be enough for most applications (700mA
+ 120mA). For better efficiency, choose a low DC-resis­tance inductor.

The inductor value also has an effect on Burst Mode
operation. The transition to low current operation begins
when the inductor current peaks fall to approximately
200mA. Lower inductor values (higher 6IL) will cause this
to occur at lower load currents, which can cause a dip in
efficiency in the upper range of low current operation. In
Burst Mode operation, lower inductance values will cause
the burst frequency to increase.

Inductor Core Selection

Different core materials and shapes will change the size/
current and price/current relationship of an inductor.
Toroid or shielded pot cores in ferrite or permalloy mate­rials are small and don’t radiate much energy, but gener­ally cost more than powdered iron core inductors with
similar electrical characteristics. The choice of which style

inductor to use often depends more on the price vs size
requirements and any radiated field/EMI requirements
than on what the KB3426 requires to operate. Table 1
shows some typical surface mount inductors that work
well in KB3426 applications.

Table 1. Representative Surface Mount Inductors

PART VALUE DCR MAX DC SIZE
NUMBER (µH) (1 MAX) CURRENT (A) W × L × H (mm

Sumida 1.5 0.043 1.55 3.8 × 3.8 × 1.8
CDRH3D16 2.2 0.075 1.20

3.3 0.110 1.10

4.7 0.162 0.90

Sumida 2.2 0.116 0.950 3.5 × 4.3 × 0.8
CMD4D06 3.3 0.174 0.770

4.7 0.216 0.750

Panasonic 3.3 0.17 1.00 4.5 × 5.4 × 1.2
ELT5KT 4.7 0.20 0.95

Murata 1.0 0.060 1.00 2.5 × 3.2 × 2.0
LQH32CN 2.2 0.097 0.79

4.7 0.150 0.65

C

IN

and C

Selection

OUT

3

)

In continuous mode, the source current of the top MOSFET
is a square wave of duty cycle V

OUT/VIN

. To prevent large
voltage transients, a low ESR input capacitor sized for the
maximum RMS current must be used. The maximum
RMS capacitor current is given by:

OUT

12/

, where

VVV

[]

CI

required I

IN OMAX

RMS



OUT IN OUT

<

()

V

IN

This formula has a maximum at VIN = 2V
I

RMS

= I

/2. This simple worst-case condition is com-

OUT

monly used for design because even significant deviations
do not offer much relief. Note that the capacitor
manufacturer’s ripple current ratings are often based on
2000 hours of life. This makes it advisable to further derate
the capacitor, or choose a capacitor rated at a higher
temperature than required. Always consult the manufac­turer if there is any question.

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APPLICATIONS INFORMATION

KB3426

The selection of C

is driven by the required effective

OUT

series resistance (ESR).

Typically, once the ESR requirement for C

OUT

has been
met, the RMS current rating generally far exceeds the
I

RIPPLE(P-P)

requirement. The output ripple 6V

is deter-

OUT

mined by:

66 +

V I ESR

OUT L

£
²

¤

8

where f = operating frequency, C

fC

1

OUT

¥
´

¦

= output capacitance

OUT

and 6IL = ripple current in the inductor. For a fixed output
voltage, the output ripple is highest at maximum input
voltage since 6IL increases with input voltage.

Aluminum electrolytic and dry tantalum capacitors are
both available in surface mount configurations. In the case
of tantalum, it is critical that the capacitors are surge tested
for use in switching power supplies. An excellent choice is
the AVX TPS series of surface mount tantalum. These are
specially constructed and tested for low ESR so they give
the lowest ESR for a given volume. Other capacitor types
include Sanyo POSCAP, Kemet T510 and T495 series, and
Sprague 593D and 595D series. Consult the manufacturer
for other specific recommendations.

Using Ceramic Input and Output Capacitors

induce ringing at the input, V

. At best, this ringing can

IN

couple to the output and be mistaken as loop instability. At
worst, a sudden inrush of current through the long wires
can potentially cause a voltage spike at VIN, large enough
to damage the part.

When choosing the input and output ceramic capacitors,
choose the X5R or X7R dielectric formulations. These
dielectrics have the best temperature and voltage charac­teristics of all the ceramics for a given value and size.

Output Voltage Programming (kB3426 Only)

In the adjustable version, the output voltage is set by a
resistive divider according to the following formula:

R

2

VV

=+

OUT

£

06 1

.

²
¤

¥
´

¦

R

1

(2)

The external resistive divider is connected to the output,
allowing remote voltage sensing as shown in Figure 3.

KB3426

V

GND

0.6V ) V

FB

OUT

) 5.5V

R2

R1

Higher values, lower cost ceramic capacitors are now
becoming available in smaller case sizes. Their high ripple
current, high voltage rating and low ESR make them ideal
for switching regulator applications. Because the
KB3426’s control loop does not depend on the output
capacitor’s ESR for stable operation, ceramic capacitors
can be used freely to achieve very low output ripple and
small circuit size.

However, care must be taken when ceramic capacitors are
used at the input and the output. When a ceramic capacitor
is used at the input and the power is supplied by a wall
adapter through long wires, a load step at the output can

Figure 3. Setting the kB3426 Output Voltage

Efficiency Considerations

The efficiency of a switching regulator is equal to the
output power divided by the input power times 100%. It is
often useful to analyze individual losses to determine what
is limiting the efficiency and which change would produce
the most improvement. Efficiency can be expressed as:

Efficiency = 100% – (L1 + L2 + L3 + ...)

where L1, L2, etc. are the individual losses as a percentage
of input power.

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APPLICATIONS INFORMATION

Although all dissipative elements in the circuit produce
losses, two main sources usually account for most of the
losses in KB3426 circuits: V
losses. The VIN quiescent current loss dominates the
efficiency loss at very low load currents whereas the I2R
loss dominates the efficiency loss at medium to high load
currents. In a typical efficiency plot, the efficiency curve at
very low load currents can be misleading since the actual
power lost is of no consequence as illustrated in Figure 4.

quiescent current and I2R

IN

KB3426

2

2. I

R losses are calculated from the resistances of the
internal switches, R
continuous mode, the average output current flowing
through inductor L is “chopped” between the main
switch and the synchronous switch. Thus, the series
resistance looking into the SW pin is a function of both
top and bottom MOSFET R
(DC) as follows:

RSW= (R

DS(ON)TOP

, and external inductor RL. In

SW

and the duty cycle

DS(ON)

)(DC) + (R

DS(ON)BOT

)(1 – DC)

1

0.1

0.01

0.001

POWER LOSS (W)

0.0001

0.00001

V

= 1.2V

OUT

= 1.5V

V

OUT

= 1.8V

V

OUT

= 2.5V

V

OUT

0.1 1

Figure 4. Power Lost vs Load Current

10 100 1000

LOAD CURRENT (mA)

1. The VIN quiescent current is due to two components:
the DC bias current as given in the electrical character­istics and the internal main switch and synchronous
switch gate charge currents. The gate charge current
results from switching the gate capacitance of the
internal power MOSFET switches. Each time the gate is
switched from high to low to high again, a packet of
charge, dQ, moves from VIN to ground. The resulting
dQ/dt is the current out of VINthat is typically larger than
the DC bias current. In continuous mode, I

GATECHG

=
f(QT+ QB) where QT and QB are the gate charges of the
internal top and bottom switches. Both the DC bias and
gate charge losses are proportional to VIN and thus
their effects will be more pronounced at higher supply
voltages.

The R

for both the top and bottom MOSFETs can

DS(ON)

be obtained from the Typical Performance Charateristics
curves. Thus, to obtain I2R losses, simply add RSW to
RL and multiply the result by the square of the average
output current.

Other losses including CIN and C

ESR dissipative

OUT

losses and inductor core losses generally account for less
than 2% total additional loss.

Thermal Considerations

In most applications the KB3426 does not dissipate
much heat due to its high efficiency. But, in applications
where the KB3426 is running at high ambient tempera­ture with low supply voltage and high duty cycles, such
as in dropout, the heat dissipated may exceed the maxi­mum junction temperature of the part. If the junction
temperature reaches approximately 150°C, both power
switches will be turned off and the SW node will become
high impedance.

To avoid the KB3426 from exceeding the maximum
junction temperature, the user will need to do some
thermal analysis. The goal of the thermal analysis is to
determine whether the power dissipated exceeds the
maximum junction temperature of the part. The tempera­ture rise is given by:

TR= (PD)(eJA)

where PD is the power dissipated by the regulator and e

JA

is the thermal resistance from the junction of the die to the
ambient temperature.

10

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APPLICATIONS INFORMATION

KB3426

The junction temperature, TJ, is given by:

= TA+ T

T

J

R

where TA is the ambient temperature.

As an example, consider the KB3426 in dropout at an
input voltage of 2.7V, a load current of 800mA and an
ambient temperature of 70°C. From the typical perfor­mance graph of switch resistance, the R

DS(ON)

of the

P-channel switch at 70°C is approximately 0.521. There­fore, power dissipated by the part is:

LOAD

2

• R

DS(ON)

= 187.2mW

PD = I

For the SOT-23 package, the eJA is 250°C/W. Thus, the
junction temperature of the regulator is:

TJ= 70°C + (0.1872)(250) = 116.8°C

which is below the maximum junction temperature of
125°C.

Note that at higher supply voltages, the junction tempera­ture is lower due to reduced switch resistance (R

DS(ON)

).

A second, more severe transient is caused by switching in
loads with large (>1µF) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with C

, causing a rapid drop in V

OUT

. No regulator can

OUT

deliver enough current to prevent this problem if the load
switch resistance is low and it is driven quickly. The only
solution is to limit the rise time of the switch drive so that
the load rise time is limited to approximately (25 • C

LOAD

).
Thus, a 10µF capacitor charging to 3.3V would require a
250µs rise time, limiting the charging current to about
130mA.

PC Board Layout Checklist

When laying out the printed circuit board, the following
checklist should be used to ensure proper operation of the
KB3426. These items are also illustrated graphically in
Figures 5 and 6. Check the following in your layout:

1. The power traces, consisting of the GND trace, the SW

trace and the VIN trace should be kept short, direct and
wide.

Checking Transient Response

The regulator loop response can be checked by looking at
the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, V
equal to (6I
resistance of C
discharge C

• ESR), where ESR is the effective series

LOAD

OUT

, which generates a feedback error signal.

OUT

The regulator loop then acts to return V
state value. During this recovery time V

immediately shifts by an amount

OUT

. 6I

also begins to charge or

LOAD

to its steady-

OUT

can be moni-

OUT

tored for overshoot or ringing that would indicate a stability
problem. For a detailed explanation of switching control
loop theory, see Application Note 76.

2. Does the VFB pin connect directly to the feedback

resistors? The resistive divider R1/R2 must be con­nected between the (+) plate of C

3. Does the (+) plate of C

connect to VIN as closely as

IN

and ground.

OUT

possible? This capacitor provides the AC current to the
internal power MOSFETs.

4. Keep the switching node, SW, away from the sensitive

VFB node.

5. Keep the (–) plates of CIN and C

as close as possible.

OUT

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APPLICATIONS INFORMATION

KB3426

1

RUN

KB3426

2

–

V

C

OUT

OUT

+

L1

BOLD LINES INDICATE HIGH CURRENT PATHS

GND

3

SW

Figure 5a. kB3426 Layout Diagram

VIA TO V

PIN 1

V

OUT

SW

L1

KB3426

5

V

FB

R2

4

V

IN

C

IN

+

R1

C

FWD

–

V

OUT

+

V

IN

BOLD LINES INDICATE HIGH CURRENT PATHS

1

RUN

KB3426B-1.8

2

GND

C

OUT

3

L1

SW

5

V

OUT

4

V

IN

C

IN

+

V

IN

Figure 5b. kB3426B-1.8 Layout Diagram

VIA TO GND

R1

IN

R2

C

FWD

V

IN

VIA TO V

OUT

PIN 1

V

OUT

SW

L1

KB3426B-1.8

VIA TO V

VIA TO V

IN

OUT

V

IN

C

OUT

GND

C

IN

Figure 6a. kB3426 Suggested Layout

Design Example

As a design example, assume the KB3426 is used in a
single lithium-ion battery-powered cellular phone
application. The VIN will be operating from a maximum of

4.2V down to about 2.7V. The load current requirement
is a maximum of 0.6A but most of the time it will be in
standby mode, requiring only 2mA. Efficiency at both low
and high load currents is important. Output voltage is

2.5V. With this information we can calculate L using
equation (1),

L

1

=

fI

()6()

£

V

OUT

L

<

1

²
¤

V

OUT

V

IN

¥
´

¦

(3)

C

OUT

GND

C

IN

Figure 6b. kB3426-1.8 Suggested Layout

Substituting V

= 2.5V, VIN= 4.2V, 6IL= 240mA and

OUT

f = 1.5MHz in equation (3) gives:

V

25

L

1 5 240

.

MHz mA

.( )..

£

1

²
¤

25
42

V

¥

=µ

281

´
¦

V

H= <

.

A 2.2µH inductor works well for this application. For best
efficiency choose a 720mA or greater inductor with less
than 0.21 series resistance.

CINwill require an RMS current rating of at least 0.3A 
I

LOAD(MAX)

/2 at temperature and C

will require an ESR

OUT

of less than 0.251. In most cases, a ceramic capacitor will
satisfy this requirement.

12

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APPLICATIONS INFORMATION

KB3426

For the feedback resistors, choose R1 = 316k. R2 can
then be calculated from equation (2) to be:

R

2

V

2.7V

TO 6.5V

£

OUT

²
¤

06

IN

¥

Rk

1 1 1000= <

=

´
¦

.

4.7µH

4

V

C

IN

+

10µF
Tan

IN

KB3426

1

RUN

GND

** TAIYO YUDEN JMK316BJ106ML

3

SW

V

FB

2

22pF

5

1M

316k

C

OUT

10µF
CER

**

V

OUT

2.5V

V

Figure 7a

TYPICAL APPLICATION

Figure 7 shows the complete circuit along with its effi­ciency curve.

100

V

= 2.5V

OUT

95

VIN = 2.7V

90

85

80

75

EFFICIENCY (%)

70

65

60

0.1 10 100 1000

VIN = 3.6V

VIN = 4.2V

1
OUTPUT CURRENT (mA)

Figure 7b

95

V

= 1.5V

OUT

90

VIN = 2.7V

85

80

75

EFFICIENCY (%)

70

65

60

0.1 10 100 1000

VIN = 4.2V

VIN = 3.6V

1

OUTPUT CURRENT (mA)

Single Li-Ion 1.5V/800mA Regulator for

High Efficiency and Small Footprint

V

IN

2.7V

TO 6.5V

100mV/DIV

AC COUPLED

500mA/DIV

500mA/DIV

V

I

LOAD

+

OUT

C
10 µF
Tan

I

L

IN

V
I

LOAD

4

V

1

RUN

= 3.6V

IN

= 1.5V

OUT

= 0A TO 800mA

SW

IN

KB3426B-1.5

V

OUT

GND

2

20µs/DIVV

4.7µH

3

†

C

OUT1

10µF

5

†

TAIYO YUDEN JMK316BJ106ML

CER

100mV/DIV

AC COUPLED

500mA/DIV

500mA/DIV

V

1.5V

V

I

LOAD

OUT

OUT

I

L

= 3.6V

IN

= 1.5V

V

OUT

I

LOAD

20µs/DIVV

= 200mA TO 800mA

13

Kingbor Technology Co.,Ltd

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TYPICAL APPLICATION

Single Li-Ion 1.2V/800mA Regulator for High Efficiency and Small Footprint

KB3426

95

V

= 1.2V

OUT

90

85

80

75

EFFICIENCY (%)

70

65

60

0.1 10 100 1000

VIN = 2.7V

VIN = 4.2V

VIN = 3.6V

1
OUTPUT CURRENT (mA)

V

IN

2.7V

TO 6.5V

100mV/DIV

AC COUPLED

500mA/DIV

500mA/DIV

V

I

LOAD

OUT

C

+

10 µF
Tan

I

L

4

IN

1

= 1.2V

V

OUT

= 0mA TO 800mA

I

LOAD

V

IN

KB3426

RUN

GND

4.7µH

3

SW

V

FB

2

20µs/DIVVIN = 3.6V

22pF

5

300k

300k

** TAIYO YUDEN JMK316BJ106ML

V

1.2V

C

**

OUT

10µF
CER

V

OUT

100mV/DIV

AC COUPLED

500mA/DIV

I

LOAD

500mA/DIV

OUT

I

L

= 3.6V

IN

V

OUT

I

LOAD

= 1.2V

20µs/DIVV

= 200mA TO 800mA

V

IN

3.6V

to 6.5V

100

VIN = 5V

= 3.3V

V

OUT

95

90

85

80

75

EFFICIENCY (%)

70

65

60

0.1 10 100 1000

1
OUTPUT CURRENT (mA)

C

IN

+

4.7µF
Tan

Tiny 3.3V/800mA Buck Regulator

4.7µH

4

V

IN

KB3426B-3.3

1

RUN

GND

3

SW

NC

5

V

FB

2

0

NC

** TAIYO YUDEN JMK316BJ106ML

V

OUT

100mV/DIV

AC COUPLED

I

500mA/DIV

I

LOAD

500mA/DIV

C

**

OUT

10µF
CER

L

= 5V

IN

= 3.3V

V

OUT

= 200mA TO 800mA

I

LOAD

V

OUT

3.3V
800mA

20µs/DIVV

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PACAGE DESCRIPTION

KB3426

SOT23-5

2.9±0.2

1.9±0.2

(0.95) (0.95)

54

123



0.4±0.1

+0.2

1.6

–0.1

2.8±0.3

1.1

0.8

+0.2
–0.1

±0.1

0.15

0 to 0.1

0.2 MIN.

+0.1
–0.05

15

Kingbor Technology Co.,Ltd

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TYPICAL APPLICATION

Single Li-Ion 1.8V/800mA Regulator for Low Output Ripple and Small Footprint

KB3426

95

V

= 1.8V

OUT

90

85

80

75

EFFICIENCY (%)

70

65

60

VIN = 4.2V

0.1 10 100 1000

VIN = 2.7V

VIN = 3.6V

1

OUTPUT CURRENT (mA)

V

IN

2.7V

TO 6.5V

100mV/DIV

AC COUPLED

500mA/DIV

500mA/DIV

V

I

LOAD

OUT

C

+

10 µF
Tan

I

L

4

IN

1

= 3.6V

IN

= 1.8V

V

OUT

= 0mA TO 800mA

I

LOAD

V

IN

KB3426-1.8

RUN

GND

40µs/DIVV

4.7µH

3

SW

5

V

OUT

2

C

OUT1

47 µF

V

OUT

1.8V

V

OUT

100mV/DIV

AC COUPLED

500mA/DIV

I

LOAD

500mA/DIV

I

L

= 3.6V

IN

= 1.8V

V

OUT

I

LOAD

40µs/DIVV

= 200mA TO 800mA

16