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EUP3408 1.5MHz, 800mA Synchronous Step-Down Converter with Soft Start
DESCRIPTION
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.
FEATURES
High Efficiency up to 96% 1.5MHz Constant Switching Frequency 800mA Available Load Current 270A 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 O 1A 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
Cellular and Smart Phones Portable Media Players/ MP3 Players Digital Still and Video Cameras Portable Instruments WLAN PC Cards
Typical Application Circuit
Figure 1. Adjustable Output
DS3408 Ver1.2 Nov. 2007
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EUP3408
Typical Application Circuit (continued)
Figure 2. Fixed 1.2V/1.8V/3.3V Output
Pin Configurations
Package Type Pin Configurations Package Type Pin Configurations
SOT23-5 TSOT23-5
ADJ Voltage
SOT23-5 TSOT23-5
Fixed Voltage
Pin Description
PIN EN GND SW VIN VFB VOUT Pin 1 2 3 4 5 5 DESCRIPTION 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. Feedback Pin (EUP3408). Output Voltage Feedback Pin (EUP3408-1.2/1.8/3.3)
DS3408 Ver1.2
Nov. 2007
2
EUP3408
Block Diagram
Ordering Information
Order Number EUP3408VIR1 EUP3408-1.2VIR1 EUP3408-1.8VIR1 EUP3408-3.3VIR1 EUP3408OIR1 EUP3408-1.2OIR1 EUP3408-1.8OIR1 EUP3408-3.3OIR1 Package Type SOT23-5 SOT23-5 SOT23-5 SOT23-5 TSOT23-5 TSOT23-5 TSOT23-5 TSOT23-5 Marking Operating Temperature range 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 1/4 -40 C to 85C -40 C to 85C -40 C to 85C -40 C to 85C -40 C to 85C -40 C to 85C -40 C to 85C -40 C to 85C
a A 1/4
1/4
a T 1/4 a D 1/4 a H 1/4 a A 1/4 a T 1/4 a D 1/4 a H 1/4
EUP3408 1/4
1/4
1/4
1/4
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
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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 ----------------------------------------------- -40C to 85C Junction Temperature ------------------------------------------------------------------- 125C Storage Temperature ------------------------------------------------------- -65C to 150C Lead Temp (Soldering, 10sec) ------------------------------------------------------260C
Electrical Characteristics
Unless otherwise specified, TA=25C, VIN=3.6V.
Symbol
VIN IVFB IQ ISHDN IPK VFB VOUT VOUT VFB VLOADREG fOSC RPFET RNFET ILSW VEN IEN
Parameter
Input Voltage Range Feedback Current Quiescent Current Shutdown Current Peak Inductor Current Regulated Output Voltage Output Voltage Line Regulation Reference Voltage Line Regulation Output Voltage Load Regulation Oscillator Frequency RDS(ON) of P-Channel FET RDS(ON) of N-Channel FET SW Leakage Current EN Threshold EN Leakage Current
Conditions
Min
2.5
EUP3408 Typ Max.
5.5 30 270 370 1
Unit
V nA A A A V % %/V %/V %
VFB=0.5V or VOUT=90%, SW Open VEN=0V, VIN= 4.2V VIN=3V, VFB=0.5V or VOUT=90% ILOAD =0 VIN=2.5V to 5.5V, ILOAD=0 VIN=2.5V to 5.5V ILOAD= 0mA to 800mA VFB=0.6V or VOUT=100% VFB=0V or VOUT=0V ISW=200mA ISW=-200mA VEN=0V, VSW=0V or 5V, VIN=5V 0.3 1.2 1.05 0.588 -3
1.25 0.6 0.25 0.25 0.5 1.5 700 0.28 0.30 1.0 0.4 0.4 1 1.5 1 1.8 0.612 3 0.4 0.4
Regulated Feedback Voltage (Note 1)
MHz kHz A V A
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
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EUP3408
Typical Operating Characteristics
DS3408 Ver1.2
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EUP3408
DS3408 Ver1.2
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EUP3408
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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 RMS =I O x
V V O x 1 - O V V IN IN

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:
VOUT = 0.6V 1 +
I
L
=
V 1 - OUT V (f)(L) OUT V IN
1

R2 R1
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. 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 4.7F. 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:
DS3408 Ver1.2 Nov. 2007
For adjustable voltage package, the external resistive divider is connected to the output, allowing remote voltage sensing as shown in below figure.
8
EUP3408
Thermal Considerations 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: TR=(PD)(JA) Where PD=ILOAD2 N RDS(ON) is the power dissipated by the regulator ; JA 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 125C. PC Board Layout Checklist 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.
DS3408 Ver1.2
Nov. 2007
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EUP3408
Packaging Information
SOT23-5
SYMBOLS A A1 D E1 E L b e
MILLIMETERS MIN. 0.00 2.90 1.60 2.60 0.30 0.30 0.95 3.00 0.60 0.50 0.102 0.012 0.012 MAX. 1.30 0.15 MIN. 0.000
INCHES MAX. 0.052 0.006 0.114 0.063 0.118 0.024 0.020 0.037
DS3408 Ver1.2
Nov. 2007
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EUP3408
Packaging Information (continued)
TSOT23-5
SYMBOLS A A1 D E1 E L b e
MILLIMETERS MIN. 0.00 2.90 1.60 2.60 0.30 0.30 0.95 3.00 0.60 0.50 0.102 0.012 0.012 MAX. 1.00 0.15 MIN. 0.000
INCHES MAX. 0.039 0.006 0.114 0.063 0.118 0.024 0.020 0.037
DS3408 Ver1.2
Nov. 2007
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