ETC KB3406-V1.2

Kingbor Technology Co.,Ltd
KB3406
TEL:(86)0755-83095458 FAX:(86)0755-88364052
1.5MHz, 600mA
Synchronous Step-Down
Regulator in SOT23-5
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FEATURES
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DESCRIPTIO
High Efficiency: Up to 96%
Very Low Quiescent Current: Only 20µA
During Operation
600mA Output Current
2.5V to 5.5V 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) SOT23-6 Package
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Cellular Telephones
Personal Information Appliances
Wireless and DSL Modems
Digital Still Cameras
MP3 Players
Portable Instruments
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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 KB3406 is available in a low
profile (1mm) SOT23-5 package.
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APPLICATIO S
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The KB3406 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 1.5V and 1.8V. Supply
current during operation is only 20µA and drops to )1µA
in shutdown. The 2.5V to 5.5V input voltage range makes
the KB3406 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.
TYPICAL APPLICATIO
95
90
4
CIN**
4.7µF
CER
VIN
SW
3
2.2µH*
COUT†
10µF
CER
KB3406-1.8
1
RUN
VOUT
5
GND
2
*MURATA LQH32CN2R2M33
**TAIYO YUDEN JMK212BJ475MG
†
TAIYO YUDEN JMK316BJ106ML
Figure 1a. High Efficiency Step-Down Converter
VOUT
1.8V
600mA
85
EFFICIENCY (%)
VIN
2.7V
TO 5.5V
VIN = 2.7V
VIN = 3.6V
80
VIN = 4.2V
75
70
65
60
0.1
VOUT = 1.8V
1
10
100
OUTPUT CURRENT (mA)
1000
Figure 1b. Efficiency vs Load Current
1
Kingbor Technology Co.,Ltd
KB3406
TEL:(86)0755-83095458 FAX:(86)0755-88364052
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ABSOLUTE
RATI GS
(Note 1)
Input Supply Voltage .................................. – 0.3V to 6V
RUN, VFB Voltages ..................................... – 0.3V to VIN
SW Voltage .................................. – 0.3V to (VIN + 0.3V)
P-Channel Switch Source Current (DC) ............. 800mA
N-Channel Switch Sink Current (DC) ................. 800mA
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
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PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
TOP VIEW
RUN 1
5 VFB
GND 2
SW 3
KB3406-ADJ
4 VIN
ORDER PART
NUMBER
TOP VIEW
RUN 1
5 VOUT
KB3406B-1.5
KB3406B-1.8
GND 2
SW 3
4 VIN
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
S5 PACKAGE
5-LEAD PLASTIC TSOT-23
TJMAX = 125°C, eJA = 250°C/ W, eJC = 90°C/ W
TJMAX = 125°C, eJA = 250°C/ W, eJC = 90°C/ W
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
IVFB
Feedback Current
VFB
Regulated Feedback Voltage
CONDITIONS
MIN
TYP
MAX
UNITS
±30
nA
0.6
0.6
0.6
0.6120
0.6135
0.6150
V
V
V
0.04
0.4
1.500
1.800
1.545
1.854
0.04
0.4
%/V
1
1.25
A
●
KB3406 (Note 4) T A = 25°C
KB3406 (Note 4) 0 °C TA ) 85°C
KB3406 (Note 4) –40 °C ) TA ) 85°C
●
0.5880
0.5865
0.5850
6VFB
Reference Voltage Line Regulation
VIN = 2.5V to 5.5V (Note 4)
●
VOUT
Regulated Output Voltage
KB3406-1.5, I OUT = 100mA
KB3406-1.8, I OUT = 100mA
●
●
6VOUT
Output Voltage Line Regulation
VIN = 2.5V to 5.5V
●
IPK
Peak Inductor Current
VIN = 3V, VFB = 0.5V or VOUT = 90%,
Duty Cycle < 35%
VLOADREG
Output Voltage Load Regulation
VIN
Input Voltage Range
IS
Input DC Bias Current
Active Mode
Sleep Mode
Shutdown
(Note 5)
VFB = 0.5V or VOUT = 90%, ILOAD = 0A
VFB = 0.62V or VOUT = 103%, ILOAD = 0A
VRUN = 0V, VIN = 4.2V
fOSC
Oscillator Frequency
VFB = 0.6V or VOUT = 100%
VFB = 0V or VOUT = 0V
RPFET
RDS(ON) of P-Channel FET
ISW = 100mA
RNFET
RDS(ON) of N-Channel FET
ISW = –100mA
ILSW
SW Leakage
VRUN = 0V, VSW = 0V or 5V, VIN = 5V
±0.01
2
1.455
1.746
0.75
0.5
●
●
2.5
1.2
%/V
V
V
%
5.5
V
300
20
0.1
400
35
1
µA
µA
µA
1.5
210
1.8
MHz
kHz
0.4
0.5
1
0.35
0.45
1
±1
µA
Kingbor Technology Co.,Ltd
KB3406
TEL:(86)0755-83095458 FAX:(86)0755-88364052
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
VRUN
RUN Threshold
CONDITIONS
●
IRUN
RUN Leakage Current
●
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The KB3406E 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.
MIN
TYP
MAX
UNITS
0.3
1
1.5
V
±0.01
±1
µA
Note 3: TJ is calculated from the ambient temperature TA and power
dissipation PD according to the following formula:
KB3406: T J = TA + (PD)(250°C/W)
Note 4: The KB3406 is tested in a proprietary test mode that connects
VFB to the output of the error amplifier.
Note 5: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency.
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TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure1a Except for the Resistive Divider Resistor Values)
Efficiency vs Input Voltage
95
IOUT = 100mA
95
Efficiency vs Output Current
Efficiency vs Output Current
100
IOUT = 10mA
95
VOUT = 1.2V
VIN = 2.7V
90
90
85
IOUT = 600mA
80
75
70
IOUT = 0.1mA
65
VIN = 2.7V
85
EFFICIENCY (%)
EFFICIENCY (%)
EFFICIENCY (%)
90
85 IOUT = 1mA
VOUT = 1.5V
VIN = 4.2V
80
VIN = 3.6V
75
VIN = 4.2V
80
VIN = 3.6V
75
70
70
65
65
60
55
3
2
4
5
INPUT VOLTAGE (V)
60
0.1
6
EFFICIENCY (%)
VIN = 3.6V
85
80
VIN = 4.2V
75
70
1.60
0.604
0.599
0.594
1
10
100
OUTPUT CURRENT (mA)
1000
1.55
1.50
1.45
1.40
0.589
65
60
0.1
VIN = 3.6V
1.65
0.609
VIN = 2.7V
1000
1.70
VIN = 3.6V
90
1
10
100
OUTPUT CURRENT (mA)
Oscillator Frequency vs
Temperature
0.614
VOUT = 2.5V
REFERENCE VOLTAGE (V)
95
60
0.1
1000
Reference Voltage vs
Temperature
Efficiency vs Output Current
100
1
10
100
OUTPUT CURRENT (mA)
FREQUENCY (MHz)
50
VOUT = 1.8V
0.584
–50 –25
1.35
50
25
75
0
TEMPERATURE (°C)
100
125
1.30
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
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Kingbor Technology Co.,Ltd
KB3406
TEL:(86)0755-83095458 FAX:(86)0755-88364052
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TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure1a Except for the Resistive Divider Resistor Values)
Oscillator Frequency vs
Supply Voltage
1.6
1.5
1.4
1.3
VIN = 3.6V
1.834
0.6
1.824
0.5
1.814
1.804
3
4
5
SUPPLY VOLTAGE (V)
1.784
0.1
0
6
RDS(ON) vs Temperature
VIN = 2.7V
VIN = 3.6V
0.3
0.2
35
30
25
20
15
100
Switch Leakage vs Temperature
SWITCH LEAKAGE (pA)
SWITCH LEAKAGE (nA)
200
150
100
MAIN SWITCH
6
4
3
5
SUPPLY VOLTAGE (V)
RUN = 0V
SW
5V/DIV
SYNCHRONOUS
SWITCH
80
60
VOUT
100mV/DIV
AC COUPLED
MAIN
SWITCH
IL
200mA/DIV
40
20
4
0
125
50
25
0
75
TEMPERATURE (°C)
Burst Mode Operation
VIN = 3.6V
VOUT = 1.8V
ILOAD = 50mA
SYNCHRONOUS SWITCH
100
15
5
100
250
50
25
75
0
TEMPERATURE (°C)
20
Switch Leakage vs Input Voltage
VIN = 5.5V
RUN = 0V
0
–50 –25
25
0
–50 –25
120
50
30
5
2
300
0
7
35
0
125
6
10
10
0.1
5
4
2
3
INPUT VOLTAGE (V)
VIN = 3.6V
45 VOUT = 1.8V
= 0A
I
40 LOAD
VOUT = 1.8V
ILOAD = 0A
SUPPLY CURRENT (µA)
0.4
1
Supply Current vs Temperature
40
0.5
MAIN SWITCH
SYNCHRONOUS SWITCH
0
50
–50 –25
25
75
0
TEMPERATURE (°C)
0
50
45
SUPPLY CURRENT (µA)
VIN = 4.2V
SYNCHRONOUS
SWITCH
0
100 200 300 400 500 600 700 800 900
LOAD CURRENT (mA)
Supply Current vs Supply Voltage
50
0.6
0.3
0.2
1.774
2
MAIN
SWITCH
0.4
1.794
0.7
RDS(ON) (1)
0.7
RDS(ON) (1)
OUTPUT VOLTAGE (V)
OSCILLATOR FREQUENCY (MHz)
1.7
1.2
RDS(ON) vs Input Voltage
Output Voltage vs Load Current
1.844
1.8
1
2
3
4
INPUT VOLTAGE (V)
5
6
4µs/DIV
100
125
Kingbor Technology Co.,Ltd
KB3406
TEL:(86)0755-83095458 FAX:(86)0755-88364052
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TYPICAL PERFOR A CE CHARACTERISTICS
(From Figure 1a Except for the Resistive Divider Resistor Values)
Start-Up from Shutdown
RUN
2V/DIV
VOUT
2V/DIV
Load Step
Load Step
VOUT
100mV/DIV
AC COUPLED
VOUT
100mV/DIV
AC COUPLED
ILOAD
500mA/DIV
VIN = 3.6V
VOUT = 1.8V
ILOAD = 600mA
40µs/DIV
IL
500mA/DIV
IL
500mA/DIV
ILOAD
500mA/DIV
ILOAD
500mA/DIV
VIN = 3.6V
20µs/DIV
VOUT = 1.8V
ILOAD = 50mA TO 600mA
VIN = 3.6V
20µs/DIV
VOUT = 1.8V
ILOAD = 0mA TO 600mA
Load Step
Load Step
VOUT
100mV/DIV
AC COUPLED
VOUT
100mV/DIV
AC COUPLED
IL
500mA/DIV
IL
500mA/DIV
ILOAD
500mA/DIV
ILOAD
500mA/DIV
VIN = 3.6V
20µs/DIV
VOUT = 1.8V
ILOAD = 100mA TO 600mA
VIN = 3.6V
20µs/DIV
VOUT = 1.8V
ILOAD = 200mA TO 600mA
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PI FU CTIO S
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.
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) (kB3406): Feedback Pin. Receives the feedback voltage from an external resistive divider across the
output.
VOUT (Pin 5) (kB3406-1.5/kB3406-1.8): Output Voltage Feedback Pin. An internal resistive divider divides the
output voltage down for comparison to the internal reference voltage.
5
Kingbor Technology Co.,Ltd
KB3406
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SLOPE
COMP
0.65V
OSC
OSC
4 VIN
FREQ
SHIFT
–
VFB /VOUT
+
5
0.6V
R1
FB
–
+
– EA
0.4V
R2
SLEEP
–
+
BURST
S
Q
R
Q
RS LATCH
VIN
RUN
SWITCHING
LOGIC
AND
BLANKING
CIRCUIT
ANTISHOOTTHRU
3 SW
0.6V REF
+
1
51
+
ICOMP
SHUTDOWN
IRCMP
2 GND
–
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OPERATIO (Refer to Functional Diagram)
Main Control Loop
Burst Mode Operation
The KB3406 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, ICOMP, resets the RS latch. The peak inductor
current at which ICOMP resets the RS latch, is controlled by
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 IRCMP, or
the beginning of the next clock cycle.
The KB3406 is capable of Burst Mode operation in which
the internal power MOSFETs operate intermittently based
on load demand.
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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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KB3406
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OPERATIO (Refer to Functional Diagram)
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 VFB or VOUT rises above 0V.
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 RDS(ON) of the P-channel switch increases
(see Typical Performance Characteristics). Therefore, the
user should calculate the power dissipation when the
KB3406 is used at 100% duty cycle with low input voltage
(See Thermal Considerations in the Applications Information section).
Low Supply Operation
The KB3406 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
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 KB3406 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
MAXIMUM OUTPUT CURRENT (mA)
Short-Circuit Protection
1000
800
600
VOUT = 1.8V
VOUT = 2.5V
VOUT = 1.5V
400
200
0
2.5
3.0
3.5
4.0
4.5
SUPPLY VOLTAGE (V)
5.0
5.5
Figure 2. Maximum Output Current vs Input Voltage
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KB3406
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APPLICATIO S I FOR ATIO
The basic KB3406 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 CIN and
COUT.
inductor to use often depends more on the price vs size
requirements and any radiated field/EMI requirements
than on what the KB3406 requires to operate. Table 1
shows some typical surface mount inductors that work
well in KB3406 applications.
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 VOUT also increases the ripple
current as shown in equation 1. A reasonable starting point
for setting ripple current is 6IL = 240mA (40% of 600mA).
6IL =
£ V ¥
1
VOUT ² 1 < OUT ´
( f)(L) ¤ VIN ¦
(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 720mA rated
inductor should be enough for most applications (600mA
+ 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
8
Table 1. Representative Surface Mount Inductors
PART
NUMBER
VALUE
(µH)
DCR
(1 MAX)
MAX DC
SIZE
CURRENT (A) W × L × H (mm3)
Sumida
CDRH3D16
1.5
2.2
3.3
4.7
0.043
0.075
0.110
0.162
1.55
1.20
1.10
0.90
3.8 × 3.8 × 1.8
Sumida
CMD4D06
2.2
3.3
4.7
0.116
0.174
0.216
0.950
0.770
0.750
3.5 × 4.3 × 0.8
Panasonic
ELT5KT
3.3
4.7
0.17
0.20
1.00
0.95
4.5 × 5.4 × 1.2
Murata
LQH32CN
1.0
2.2
4.7
0.060
0.097
0.150
1.00
0.79
0.65
2.5 × 3.2 × 2.0
CIN and COUT Selection
In continuous mode, the source current of the top MOSFET
is a square wave of duty cycle VOUT/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:
1/ 2
VOUT (VIN < VOUT )]
[
CIN required IRMS  IOMAX
VIN
This formula has a maximum at VIN = 2VOUT, where
IRMS = IOUT/2. This simple worst-case condition is commonly 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.
Kingbor Technology Co.,Ltd
KB3406
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APPLICATIO S I FOR ATIO
The selection of COUT is driven by the required effective
series resistance (ESR).
Typically, once the ESR requirement for COUT has been
met, the RMS current rating generally far exceeds the
IRIPPLE(P-P) requirement. The output ripple 6VOUT is determined by:
£
1 ¥
6VOUT  6IL ² ESR +
´
¤
8fC OUT ¦
where f = operating frequency, COUT = output capacitance
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.
induce ringing at the input, VIN. At best, this ringing can
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 (kB3406 Only)
In the adjustable version, the output voltage is set by a
resistive divider according to the following formula:
£ R2 ¥
VOUT = 0.6 V ² 1 + ´
¤ R1¦
(2)
The external resistive divider is connected to the output,
allowing remote voltage sensing as shown in Figure 3.
0.6V ) VOUT ) 5.5V
R2
VFB
KB3406
R1
GND
Using Ceramic Input and Output Capacitors
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
KB3406’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
3406 F03
Figure 3. Setting the kB3406 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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APPLICATIO S I FOR ATIO
Although all dissipative elements in the circuit produce
losses, two main sources usually account for most of the
losses in KB3406 circuits: V IN quiescent current and I2R
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.
1
POWER LOSS (W)
0.1
Other losses including CIN and COUT ESR dissipative
losses and inductor core losses generally account for less
than 2% total additional loss.
0.001
0.0001
Thermal Considerations
1
10
100
LOAD CURRENT (mA)
1000
3406 F04
Figure 4. Power Lost vs Load Current
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 VIN that is typically larger than
the DC bias current. In continuous mode, IGATECHG =
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.
10
RSW = (RDS(ON)TOP)(DC) + (RDS(ON)BOT)(1 – DC)
The RDS(ON) for both the top and bottom MOSFETs can
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.
VOUT = 1.2V
VOUT = 1.5V
VOUT = 1.8V
VOUT = 2.5V
0.01
0.00001
0.1
2. I2R losses are calculated from the resistances of the
internal switches, RSW, and external inductor RL. In
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 RDS(ON) and the duty cycle
(DC) as follows:
In most applications the KB3406 does not dissipate
much heat due to its high efficiency. But, in applications
where the KB3406 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 KB3406 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 eJA
is the thermal resistance from the junction of the die to the
ambient temperature.
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The junction temperature, TJ, is given by:
T J = TA + TR
where TA is the ambient temperature.
As an example, consider the KB3406 in dropout at an
input voltage of 2.7V, a load current of 600mA and an
ambient temperature of 70°C. From the typical performance graph of switch resistance, the RDS(ON) of the
P-channel switch at 70°C is approximately 0.521. Therefore, power dissipated by the part is:
PD = ILOAD2 • RDS(ON) = 187.2mW
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 (RDS(ON)).
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, VOUT immediately shifts by an amount
equal to (6ILOAD • ESR), where ESR is the effective series
resistance of COUT. 6ILOAD also begins to charge or
discharge COUT, which generates a feedback error signal.
The regulator loop then acts to return VOUT to its steadystate value. During this recovery time VOUT can be monitored for overshoot or ringing that would indicate a stability
problem. For a detailed explanation of switching control
loop theory, see Application Note 76.
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 COUT, causing a rapid drop in VOUT. No regulator can
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 • CLOAD).
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
KB3406. 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.
2. Does the VFB pin connect directly to the feedback
resistors? The resistive divider R1/R2 must be connected between the (+) plate of COUT and ground.
3. Does the (+) plate of CIN connect to VIN as closely as
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 COUT as close as possible.
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1
RUN
VFB
5
KB3406
2
–
R2
GND
3
+
L1
SW
RUN
KB3406-1.8
COUT
VOUT
1
R1
VIN
2
CFWD
4
GND VOUT
–
COUT
VOUT
CIN
5
3
+
L1
VIN
SW
VIN
4
CIN
VIN
BOLD LINES INDICATE HIGH CURRENT PATHS
BOLD LINES INDICATE HIGH CURRENT PATHS
Figure 5a. kB3406 Layout Diagram
Figure 5b. kB3406-1.8 Layout Diagram
VIA TO GND
R1
L1
PIN 1
CFWD
KB3406
L1
Figure 6b. kB3406-1.8 Suggested Layout
Design Example
As a design example, assume the KB3406 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),
12
CIN
GND
Figure 6a. kB3406 Suggested Layout
£ V ¥
1
VOUT ² 1 < OUT ´
( f)(6IL ) ¤ VIN ¦
SW
COUT
CIN
GND
L=
KB3406-1.8
VOUT
SW
COUT
VIN
VIA TO VOUT
R2
PIN 1
VOUT
VIA TO VOUT
VIA TO VIN
VIN
VIA TO VIN
(3)
Substituting VOUT = 2.5V, VIN = 4.2V, 6IL = 240mA and
f = 1.5MHz in equation (3) gives:
L=
2.5V
£ 2.5V ¥
²1 <
´ = 2.81µH
1.5MHz(240mA) ¤ 4.2V ¦
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.
CIN will require an RMS current rating of at least 0.3A 
ILOAD(MAX)/2 at temperature and COUT will require an ESR
of less than 0.251. In most cases, a ceramic capacitor will
satisfy this requirement.
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For the feedback resistors, choose R1 = 316k. R2 can
then be calculated from equation (2) to be:
Figure 7 shows the complete circuit along with its efficiency curve.
£V
¥
R2 = ² OUT < 1´ R1 = 1000k
¤ 0.6
¦
100
95
VOUT = 2.5V
VIN = 2.7V
VIN
2.7V
TO 4.2V
4
CIN†
2.2µF
CER
SW
VIN
2.2µH*
3
VOUT
2.5V
22pF
COUT**
10µF
CER
KB3406
1
VFB
RUN
GND
2
EFFICIENCY (%)
90
5
VIN = 3.6V
85
80
VIN = 4.2V
75
70
1M
65
316k
60
0.1
1
10
100
OUTPUT CURRENT (mA)
*MURATA LQH32CN2R2M33
** TAIYO YUDEN JMK316BJ106ML
†
TAIYO YUDEN LMK212BJ225MG
1000
Figure 7b
Figure 7a
U
TYPICAL APPLICATIO S
Single Li-Ion 1.5V/600mA Regulator for
High Efficiency and Small Footprint
VIN
2.7V
TO 4.2V
4
CIN**
4.7µF
CER
SW
VIN
3
COUT1†
KB3406-1.5
1
RUN
VOUT
2.2µH*
5
VOUT
1.5V
10µF
CER
GND
2
*MURATA LQH32CN2R2M33
**TAIYO YUDEN JMK212BJ475MG
†
TAIYO YUDEN JMK316BJ106ML
95
VOUT = 1.5V
90
VOUT
100mV/DIV
AC COUPLED
VOUT
100mV/DIV
AC COUPLED
VIN = 2.7V
EFFICIENCY (%)
85
VIN = 4.2V
80
IL
500mA/DIV
IL
500mA/DIV
ILOAD
500mA/DIV
ILOAD
500mA/DIV
VIN = 3.6V
75
70
VIN = 3.6V
20µs/DIV
VOUT = 1.5V
ILOAD = 0A TO 600mA
65
60
0.1
1
10
100
OUTPUT CURRENT (mA)
VIN = 3.6V
20µs/DIV
VOUT = 1.5V
ILOAD = 200mA TO 600mA
1000
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TYPICAL APPLICATIO S
Single Li-Ion 1.2V/600mA Regulator for High Efficiency and Small Footprint
VIN
2.7V
TO 4.2V
4
†
CIN
2.2µF
CER
3
SW
VIN
301k
301k
2
VOUT = 1.2V
COUT**
10µF
CER
5
VFB
RUN
GND
90
VOUT
1.2V
22pF
KB3406
1
95
2.2µH*
*MURATA LQH32CN2R2M33
** TAIYO YUDEN JMK316BJ106ML
†
TAIYO YUDEN LMK212BJ225MG
VOUT
100mV/DIV
AC COUPLED
VOUT
100mV/DIV
AC COUPLED
VIN = 2.7V
EFFICIENCY (%)
85
VIN = 4.2V
80
IL
500mA/DIV
IL
500mA/DIV
ILOAD
500mA/DIV
ILOAD
500mA/DIV
VIN = 3.6V
75
70
VIN = 3.6V
20µs/DIV
VOUT = 1.2V
ILOAD = 0mA TO 600mA
65
60
0.1
1
10
100
OUTPUT CURRENT (mA)
VIN = 3.6V
20µs/DIV
VOUT = 1.2V
ILOAD = 200mA TO 600mA
1000
Tiny 3.3V/600mA Buck Regulator
VIN
5V
4
†
CIN
4.7µF
CER
SW
VIN
3
2.2µH*
VOUT
3.3V
600mA
22pF
COUT**
10µF
CER
KB3406
1
VFB
RUN
GND
2
5
301k
66.5k
*MURATA LQH32CN2R2M33
** TAIYO YUDEN JMK316BJ106ML
†
TAIYO YUDEN JMK212BJ475MG
100
VIN = 5V
95 VOUT = 3.3V
VOUT
100mV/DIV
AC COUPLED
EFFICIENCY (%)
90
IL
500mA/DIV
85
80
ILOAD
500mA/DIV
75
70
VIN = 5V
20µs/DIV
VOUT = 3.3V
ILOAD = 200mA TO 600mA
65
60
0.1
14
1
10
100
OUTPUT CURRENT (mA)
1000
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PACKAGE DESCRIPTIO
S5 Package
5-Lead Plastic TSOT-23
0.62
MAX
0.95
REF
2.90 BSC
(NOTE 4)
1.22 REF
1.4 MIN
3.85 MAX 2.62 REF
2.80 BSC
1.50 – 1.75
(NOTE 4)
PIN ONE
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
0.30 – 0.45 TYP
5 PLCS (NOTE 3)
0.95 BSC
0.80 – 0.90
0.20 BSC
0.01 – 0.10
1.00 MAX
DATUM ‘A’
0.30 – 0.50 REF
0.09 – 0.20
(NOTE 3)
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
1.90 BSC
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TYPICAL APPLICATIO
Single Li-Ion 1.8V/600mA Regulator for Low Output Ripple and Small Footprint
VIN
2.7V
TO 4.2V
4
CIN**
4.7µF
CER
3
SW
VIN
VOUT
1.8V
+
KB3406-1.8
1
4.7µH*
RUN
5
VOUT
COUT1†
100µF
GND
2
*MURATA LQH32CN4R7M34
**TAIYO YUDEN CERAMIC JMK212BJ475MG
†
SANYO POSCAP 4TPB100M
95
VOUT = 1.8V
90
EFFICIENCY (%)
85
VOUT
100mV/DIV
AC COUPLED
VOUT
100mV/DIV
AC COUPLED
VIN = 2.7V
VIN = 3.6V
80
VIN = 4.2V
IL
500mA/DIV
IL
500mA/DIV
ILOAD
500mA/DIV
ILOAD
500mA/DIV
75
70
VIN = 3.6V
40µs/DIV
VOUT = 1.8V
ILOAD = 0mA TO 600mA
65
60
0.1
16
1
10
100
OUTPUT CURRENT (mA)
1000
VIN = 3.6V
40µs/DIV
VOUT = 1.8V
ILOAD = 200mA TO 600mA