EUTECH EUP3408

EUP3408
1.5MHz, 800mA Synchronous
Step-Down Converter with Soft Start
DESCRIPTION
FEATURES
The EUP3408 is a constant frequency, current mode,
PWM step-down converter. The device integrates a
main switch and a synchronous rectifier for high
efficiency. The 2.5V to 5.5V input voltage range makes
the EUP3408 ideal for powering portable equipment
that runs from a single cell Lithium-Ion (Li+) battery or
3-cell NiMH/ NiCd batteries. The output voltage can be
regulated as low as 0.6V. The EUP3408 supports up to
800mA load current and can also run at 100% duty
cycle for low dropout applications, extending battery
life in portable systems.
Switching frequency is internally set at 1.5MHz,
allowing the use of small surface mount inductors and
capacitors. The internal synchronous switch increases
efficiency while eliminates the need for an external
Schottky diode. The EUP3408 is available in an
adjustable version and fixed output voltage of
1.2V ,1.8V and 3.3V.
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High Efficiency up to 96%
1.5MHz Constant Switching Frequency
800mA Available Load Current
270µA Typical Quiescent Current
2.5V to 5.5V Input Voltage Range
Adjustable Output Voltage as Low as 0.6V
100% Duty Cycle Low Dropout Operation
No Schottky Diode Required
Short Circuit and Thermal Protection
Excellent Line and Load Transient Response
<1µA Shutdown Current
Soft Start Function
Over Voltage Protection
Available in 1.2V,1.8V,3.3V and adjustable
voltages
Available in SOT23-5, TSOT23-5 Package
RoHS Compliant and 100% Lead(Pb)-Free
APPLICATIONS
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Typical Application Circuit
Cellular and Smart Phones
Portable Media Players/ MP3 Players
Digital Still and Video Cameras
Portable Instruments
WLAN PC Cards
Figure 1. Adjustable Output
DS3408 Ver1.2
Nov. 2007
1
EUP3408
Typical Application Circuit (continued)
Figure 2. Fixed 1.2V/1.8V/3.3V Output
Pin Configurations
Package
Type
Package
Type
Pin Configurations
SOT23-5
SOT23-5
TSOT23-5
TSOT23-5
ADJ Voltage
Fixed Voltage
Pin Configurations
Pin Description
PIN
Pin
EN
1
GND
2
SW
3
VIN
4
Chip Enable Pin. Forcing this pin above 1.5V enables the part. Forcing this pin below
0.3V shuts down the device. Do not leave EN floating.
Common Ground.
Switch Node Connection to Inductor. This pin connects to the drains of the internal main
and synchronous power MOSFET switches.
Supply Voltage Pin.
VFB
5
Feedback Pin (EUP3408).
VOUT
5
Output Voltage Feedback Pin (EUP3408-1.2/1.8/3.3)
DS3408 Ver1.2
Nov. 2007
DESCRIPTION
2
EUP3408
Block Diagram
Ordering Information
Order Number
Package Type
Marking
Operating Temperature range
EUP3408VIR1
SOT23-5
aA □ □ □
-40 °C to 85°C
EUP3408-1.2VIR1
SOT23-5
aT □ □ □
-40 °C to 85°C
EUP3408-1.8VIR1
SOT23-5
aD □ □ □
-40 °C to 85°C
EUP3408-3.3VIR1
SOT23-5
aH □ □ □
-40 °C to 85°C
EUP3408OIR1
TSOT23-5
aA □ □ □
-40 °C to 85°C
EUP3408-1.2OIR1
TSOT23-5
aT □ □ □
-40 °C to 85°C
EUP3408-1.8OIR1
TSOT23-5
aD □ □ □
-40 °C to 85°C
EUP3408-3.3OIR1
TSOT23-5
aH □ □ □
-40 °C to 85°C
EUP3408 □ □ □ □
Lead Free Code
1: Lead Free 0: Lead
Packing
R: Tape & Reel
Operating temperature range
I: Industry Standard
Package Type
V: SOT23
O: TSOT
DS3408 Ver1.2
Nov. 2007
3
EUP3408
Absolute Maximum Ratings
„
„
„
„
„
„
„
„
„
Input Supply Voltage ----------------------------------------------------------- -0.3V to 6V
EN, VFB Voltages -------------------------------------------------------------- -0.3V to VIN
P-Channel Switch Source Current (DC) ----------------------------------------------- 1A
N-Channel Switch Sink Current (DC) --------------------------------------------------- 1A
Peak SW Sink and Source Current -------------------------------------------------1.6A
Operating Temperature Range ----------------------------------------------- -40°C to 85°C
Junction Temperature ------------------------------------------------------------------- 125°C
Storage Temperature ------------------------------------------------------- -65°C to 150°C
Lead Temp (Soldering, 10sec) ------------------------------------------------------260°C
Electrical Characteristics
Unless otherwise specified, TA=25°C, VIN=3.6V.
Symbol
Parameter
Conditions
VIN
Input Voltage Range
IVFB
Feedback Current
IQ
Quiescent Current
VFB=0.5V or VOUT=90%, SW Open
ISHDN
Shutdown Current
VEN=0V, VIN= 4.2V
IPK
Peak Inductor Current
VIN=3V, VFB=0.5V or VOUT=90%
VFB
Regulated Feedback Voltage (Note 1)
VOUT
Regulated Output Voltage
Output Voltage Line
Regulation
Reference Voltage Line
Regulation
Output Voltage Load
Regulation
∆VOUT
∆VFB
VLOADREG
fOSC
Oscillator Frequency
RPFET
Min
EUP3408
Typ
Max.
2.5
5.5
±30
ILOAD =0
270
1.05
1.25
0.588
0.6
-3
Unit
V
nA
370
µA
1
µA
A
0.612
V
3
%
VIN=2.5V to 5.5V, ILOAD=0
0.25
0.4
%/V
VIN=2.5V to 5.5V
0.25
0.4
%/V
ILOAD= 0mA to 800mA
0.5
VFB=0.6V or VOUT=100%
1.2
1.5
%
1.8
MHz
VFB=0V or VOUT=0V
700
RDS(ON) of P-Channel FET
ISW=200mA
0.28
0.4
Ω
RNFET
RDS(ON) of N-Channel FET
ISW=-200mA
0.30
0.4
Ω
ILSW
SW Leakage Current
VEN=0V, VSW=0V or 5V, VIN=5V
±1
µA
VEN
EN Threshold
1.5
V
IEN
EN Leakage Current
1
µA
0.3
1.0
kHz
Note 1: The EUP3408 is tested in a proprietary test mode that connects VFB to the output of the error amplifier.
DS3408 Ver1.2
Nov. 2007
4
EUP3408
Typical Operating Characteristics
DS3408 Ver1.2
Nov. 2007
5
EUP3408
DS3408 Ver1.2
Nov. 2007
6
EUP3408
DS3408 Ver1.2
Nov. 2007
7
EUP3408
Application Information
Main Control Loop
The EUP3408 uses a slope-compensated constant
frequency, current mode architecture. Both the main
(P-Channel MOSFET) and synchronous (N-channel
MOSFET) switches are internal. During normal
operation, the EUP3408 regulates output voltage by
switching at a constant frequency and then modulating
the power transferred to the load each cycle using PWM
comparator. The duty cycle is controlled by three
weighted differential signals: the output of error
amplifier, the main switch sense voltage and the
slope-compensation ramp. It modulates output power by
adjusting the inductor-peak current during the first half
of each cycle. An N-channel, synchronous switch turns
on during the second half of each cycle (off time). When
the inductor current starts to reverse or when the PWM
reaches the end of the oscillator period, the synchronous
switch turns off. This keeps excess current from flowing
backward through the inductor, from the output
capacitor to GND, or through the main and synchronous
switch to GND.
Inductor Selection
The output inductor is selected to limit the ripple current
to some predetermined value, typically 20%~40% of the
full load current at the maximum input voltage. Large
value inductors lower ripple currents. Higher VIN or
VOUT also increases the ripple current as shown in
equation. A reasonable starting point for setting ripple
current is ∆IL=320mA (40% of 800mA).
∆I
L
=
 V
1 − OUT
V
(f)(L) OUT 
V

IN
1




O
×

V
V
O × 1 − O
 V
V
IN 
IN
8




The output capacitor COUT has a strong effect on loop
stability.
The selection of COUT is driven by the required effective
series resistance (ESR).
ESR is a direct function of the volume of the capacitor;
that is, physically larger capacitors have lower ESR.
Once the ESR requirement for COUT has been met, the
RMS current rating generally far exceeds the IRIPPLE(P-P)
requirement. The output ripple ∆VOUT is determined by:

∆V
≅ ∆I  ESR +
L
OUT
8fC




OUT 
1
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
The output voltage is set by a resistive divider according
to the following formula:


CIN and COUT Selection
In continuous mode, the source current of the top
MOSFET is a square wave of duty cycle VOUT/VIN. The
primary function of the input capacitor is to provide a
low impedance loop for the edges of pulsed current
drawn by the EUP3408. A low ESR input capacitor sized
for the maximum RMS current must be used. The size
required will vary depending on the load, output voltage
and input voltage source impedance characteristics. A
typical value is around 4.7µF.
The input capacitor RMS current varies with the input
voltage and the output voltage. The equation for the
maximum RMS current in the input capacitor is:
Nov. 2007
RMS
=I
VOUT = 0.6V 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 960mA rated
inductor should be enough for most applications
(800mA+160mA). For better efficiency, choose a low
DC-resistance inductor.
DS3408 Ver1.2
I
R2 

R1 
For adjustable voltage package, the external resistive
divider is connected to the output, allowing remote
voltage sensing as shown in below figure.
EUP3408
Thermal Considerations
PC Board Layout Checklist
To avoid the EUP3408 from exceeding the maximum
junction temperature, the user will need to do a thermal
analysis. The goal of the thermal analysis is to determine
whether the operating conditions exceed the maximum
junction temperature of the part. The temperature rise is
given by:
When laying out the printed circuit board, the following
guidelines should be used to ensure proper operation of
the EUP3408.
1. The input capacitor CIN should connect to VIN as
closely as possible. This capacitor provides the AC
current to the internal power MOSFETs.
2. The power traces, consisting of the GND trace, the
SW trace and the VIN trace should be kept short,
direct and wide.
3. The VFB pin should connect directly to the feedback
resistors. The resistive divider R1/R2 must be
connected between the COUT and ground.
4. Keep the switching node, SW, away from the
sensitive VFB node.
TR=(PD)(θJA)
Where PD=ILOAD2 × RDS(ON) is the power dissipated by
the regulator ; θJA is the thermal resistance from the
junction of the die to the ambient temperature.
The junction temperature, TJ, is given by:
TJ=TA+TR
Where TA is the ambient temperature.
TJ should be below the maximum junction temperature
of 125°C.
DS3408 Ver1.2
Nov. 2007
9
EUP3408
Packaging Information
SOT23-5
SYMBOLS
INCHES
MIN.
MAX.
MIN.
MAX.
A
-
1.30
-
0.052
A1
0.00
0.15
0.000
0.006
D
2.90
0.114
E1
1.60
0.063
E
2.60
3.00
0.102
0.118
L
0.30
0.60
0.012
0.024
b
0.30
0.50
0.012
0.020
e
DS3408 Ver1.2
MILLIMETERS
Nov. 2007
0.95
0.037
10
EUP3408
Packaging Information (continued)
TSOT23-5
SYMBOLS
INCHES
MIN.
MAX.
MIN.
MAX.
A
-
1.00
-
0.039
A1
0.00
0.15
0.000
0.006
D
2.90
0.114
E1
1.60
0.063
E
2.60
3.00
0.102
0.118
L
0.30
0.60
0.012
0.024
b
0.30
0.50
0.012
0.020
e
DS3408 Ver1.2
MILLIMETERS
Nov. 2007
0.95
0.037
11