TS3406
600mA / 1.5MHz Synchronous Buck Converter
SOT-25
Pin Definition:
1. EN
2. Ground
3. Switching Output
4. Input
5. Feedback
General Description
The TS3406 is a high efficiency monolithic synchronous buck regulator using a 1.5MHz constant frequency,
current mode architecture. The device is available in an adjustable version. Supply current with no load is 300µA
and drops to <1µA in shutdown. The 2.5V to 5.5V input voltage range makes the TS3406 ideally suited for single
Li-Ion battery-powered applications. 100% duty cycle provides low dropout operation, 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 TS3406 can supply 600mA of load
current at VCC=3V.
Features
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High Efficiency: Up to 96%
2.5V to 5.5V Input Voltage Range
Short Circuit Protection (SCP)
1.5MHz Constant Frequency Operation
Low Dropout Operation: 100% Duty Cycle
0.6V Reference Allows Low Output Voltages
600mA Output Current at Vcc=3V
Low Quiescent Current: 300uA
No Schottky Diode Required in Application
≤1uA
Shutdown Current
Current Mode Operation for Excellent Line and
Load Transient Response
Application
●
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●
Cellular Phones
Digital Still Cameras
Portable Electronics
USB Devices
Pin Description
Name
EN
GND
SW
VCC
FB
Description
Power-off pin
H：normal operation
L：Step-down operation stopped
(All circuits deactivated)
Ground pin
Switch output pin. Connect external
inductor here. Minimize trace area at this
pin to reduce EMI.
IC power supply pin
Output Feedback pin
Ordering Information
Part No.
TS3406CX5 RF
Package
SOT-25
Packing
3Kpcs/ 7” Reel
Application Circuit
1/7
Version: C12
TS3406
600mA / 1.5MHz Synchronous Buck Converter
Absolute Maximum Rating
Characteristics
V
IN
Pin Voltage
Feedback Pin Voltage
RUN Pin Voltage
Switch Pin Voltage
Peak SW Sink & Source Current
Operating Supply Voltage
Power Dissipation
Storage Temperature Range
Operating Temperature Range
Junction Temperature
Thermal Resistance from Junction to case
Thermal Resistance from Junction to ambient
Symbol
V
IN
V
FB
V
RUN
V
SW
I
PSW
V
OP
P
D
T
ST
T
OP
T
J
θ
JC
θ
JA
2
Rating
Gnd - 0.3 to Gnd + 6
Gnd - 0.3 to V
IN
+ 0.3
Gnd - 0.3 to V
IN
+ 0.3
Gnd - 0.3 to V
IN
+ 0.3
1.5
+2.5 to +5.5
(T
J
-T
A
) /
θ
JA
-40 to +150
-40 to +85
+125
110
250
Unit
V
V
V
V
A
V
mW
o
o
o
o
o
C
C
C
C/W
C/W
Note1:
θ
JA
is measured with the PCB copper area of approximately 1 in (Multi-layer). that need connect to Gnd pin
of the TS3406.
Electrical Specifications
(Ta = 25
o
C, V
IN
=V
RUN
=3.6V unless otherwise noted)
Characteristics
Feedback Voltage
Quiescent Current
Feedback Bias Current
Shutdown Supply Current
Maximum Output Current
Current Limit
Line Regulation
Load Regulation
Oscillation Frequency
Frequency of SCP
R
DS(ON)
of P-CH MOSFET
R
DS(ON)
of N-CH MOSFET
Efficiency
RUN Threshold
RUN Pin Input Current
Symbol
V
FB
I
CCQ
I
FB
I
SD
I
OUT(MAX)
I
LIMIT
△V
OUT
/V
OUT
△V
OUT
/V
OUT
F
OSC
F
OSC1
R
DSON
R
DSON
E
FFI
V
RUN
I
RUN
Conditions
T
A
=25℃,I
OUT
=50mA
V
FB
=0.5V
V
FB
=0.65V
V
RUN
=0V
V
CC
=3V
V
CC
=3V
V
CC
= 2.5V~5.5V
I
OUT
= 0.01 to 0.6A
SW pin
SW pin
I
SW
= 300mA
I
SW
= -300mA
V
OUT
=1.8V,I
OUT
= 0.5A
Min
0.588
--
--
--
0.6
0.85
--
--
1.2
--
--
--
--
0.3
--
Typ
0.6
270
--
0.08
--
1.2
0.5
0.4
1.5
300
0.30
0.20
89
0.45
±0.1
Max
0.612
400
±30
1
--
--
1
0.6
1.8
--
0.50
0.45
--
1.3
±1
Units
V
uA
nA
uA
A
A
%
%
MHz
KHz
Ω
Ω
%
V
uA
Note2: 100% production test at +25° Specification s over the temperature range are guaranteed by design and
C.
characterization.
2/7
Version: C12
TS3406
600mA / 1.5MHz Synchronous Buck Converter
Block Diagram
Function Description
Operation
TS3406 is a monolithic switching mode Step-Down DC-DC converter. It utilizes internal MOSFETs to achieve high
efficiency and can generate very low output voltage by using internal reference at 0.6V. It operates at a fixed
switching frequency, and uses the slope compensated current mode architecture. This Step-Down DC-DC
Converter supplies 600mA output current at VCC = 3V with input voltage range from 2.5V to 5.5V.
Current Mode PWM Control
Slope compensated current mode PWM control provides stable switching and cycle-by-cycle current limit for
excellent load and line responses and protection of the internal main switch (P-CH MOSFET) and synchronous
rectifier (N-CH MOSFET). During normal operation, the internal P-CH MOSFET is turned on for a certain time to
ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor
current is above the error voltage. The current comparator, ICOMP, limits the peak inductor current. When the main
switch is off, the synchronous rectifier will be turned on immediately and stay on until either the inductor current
starts to reverse, as indicated by the current reversal comparator, IZERO, or the beginning of the next clock cycle.
The OVDET comparator controls output transient overshoots by turning the main switch off and keeping it off until
the fault is no longer present.
Idle Mode Operation
At very light loads, the TS3406 automatically enters Idle Mode. In the Idle Mode, the inductor current may reach
zero or reverse on each pulse. The PWM control loop will automatically skip pulses to maintain output regulation.
The bottom MOSFET is turned off by the current reversal comparator, IZERO and the switch voltage will ring. This
is discontinuous mode operation, and is normal behavior for the switching regulator. When the input voltage
decreases toward the value of the output voltage, the TS3406 allows the main switch to remain on for more than
one switching cycle and increases the duty cycle until it reaches 100%. The output voltage then is the input voltage
minus the voltage drop across the main switch and the inductor. At low input supply voltage, the RDS(ON) of the P-
CH MOSFET increases, and the efficiency of the converter decreases. Caution must be exercised to ensure the
heat dissipated not to exceed the maximum junction temperature of the IC.
3/7
Version: C12
TS3406
600mA / 1.5MHz Synchronous Buck Converter
Function Description (Continue)
Maximum Load Current
The TS3406 will operate with input supply voltage as low as 2.5V, however, the maximum load current decreases
at lower input due to large IR drop on the main switch and synchronous rectifier. The slope compensation signal
reduces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations at duty cycles
greater than 50%. Conversely the current limit increases as the duty cycle decreases.
Application Information
Setting the Output Voltage
Application circuit item shows the basic application circuit with TS3406 adjustable output version. The external
resistor sets the output voltage according to the following equation:
Table 1: Resistor Select for Output Voltage Setting
VOUT
R2
R1
1.2V
300K
300K
1.5V
300K
450K
1.8V
300K
600K
2.5V
300K
950K
Inductor Selection
For most designs, the TS3406 operates with inductors of 1µH to 4.7µH. Low inductance values are physically
smaller but require faster switching, which results in some efficiency loss. The inductor value can be derived from
the following equation:
Table 2: Inductor Select for Output Voltage Setting (Vcc-3.6V)
VOUT
1.2V
1.5V
1.8V
2.5V
Inductor
2.2uH
2.2uH
2.2uH
2.2uH
Part Number
7440430027
7440430027
WE-TPC
Note: Part Type MH or M (www.we-online.com)
7440430027
7440430022
Where is inductor Ripple Current. Large value inductors lower ripple current and small value inductors result in high
ripple currents. Choose inductor ripple current approximately 35% of the maximum load current 600mA,
∆IL=210mA.
For output voltages above 2.0V, when light-load efficiency is important, the minimum recommended inductor is
2.2µH. For optimum voltage-positioning load transients, choose an inductor with DC series resistance in the 50mΩ
to 150mΩ range. For higher efficiency at heavy loads (above 200mA), or minimal load regulation (but some
transient overshoot), the resistance should be kept below 100mΩ. 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 (600mA+105mA).
Input Capacitor Selection
The input capacitor reduces the surge current drawn from the input and switching noise from the device. The input
capacitor impedance at the switching frequency shall be less than input source impedance to prevent high
frequency switching current passing to the input. A low ESR input capacitor sized for maximum RMS current must
be used. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and
small temperature coefficients. A 4.7µF ceramic capacitor for most applications is sufficient.
4/7
Version: C12
TS3406
600mA / 1.5MHz Synchronous Buck Converter
Application Information (Continue)
Output Capacitor Selection
The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability. The
output capacitor must have low impedance at the switching frequency. Ceramic capacitors with X5R or X7R
dielectrics are recommended due to their low ESR and high ripple current.
Compensation Capacitor Selection
The compensation capacitors for increasing phase margin provide additional stability. It is required and more than
22p, Refer to Demo Board Schematic, The optimum values for C4 is 47pF.
5/7
Version: C12
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