EOREX EP4001

eorex
EP4001
High Efficiency, Step-Up Converter with EXT
Features
Description
• Low Start-up Voltage: 1.0V
• 35μA Quiescent Supply Current in Switch-off
mode
• <1μA Shutdown Current
• 90% Efficiency
• Excellent Load and Line Regulation
Characteristics
• 350mΩ Internal MOSFET
• 450KHz Fixed Switching Frequency
• Small 6-Lead SOT-23 Package
The EP4001 is a micropower, high efficiency, and
low voltage step-up DC/DC converter intended
for use in battery powered wireless applications.
With the low start-up input voltage below 1V, the
device is suitable for applications with 1 or 2 AA
cells, providing up to 300mA output current at
3.3V output. The 35µA low quiescent current,
zero shutdown current and high efficiency
maintains long battery lifetime. A switching
frequency of 450KHz minimizes solution footprint
by allowing the use of small inductors and
ceramic capacitors. The device is offered in a low
profile (1mm) small 6-lead SOT-23 package.
The current mode PWM design is optimized for
stable and high efficiency operations over a wide
range of load currents. With low resistance
internal MOSFET switches, the EP4001
maintains high efficiency over a wide range of
load current. In addition to its high efficiency at
moderate and heavy loads, the EP4001 includes
automatic PFM operation that improves efficiency
of the power converter at light loads.
Applications
• PDA
• DSC
• LCD Panel
• RF-Tags
• MP3
• Portable Equipment
• Wireless key board and mouse
Typical Application
⎛
⎝
VOUT= FB × ⎜1 +
R1 ⎞
⎟
R2 ⎠
Where FB=1.22V
Figure 1-Basic application circuit with EP4001
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Pin Assignment
Ordering Information
Pin Description
Pin
Name
Function
1
EN
Chip enable EP4001 gets into shutdown mode when EN pin set to low
2
3
EXT
Output pin for driving external NMOS.
GND
Ground.
4
SW
Pin for switching.
5
VIN
Supply Input Pin. Must be closely decoupled to GND, Pin 2, with a 2.2µF or
greater ceramic capacitor.
6
FB
Feedback input pin Internal reference voltage for the error amplifier is
1.25V
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Thermal Resistance (Note 1)
Package
θJA
θJC
TSOT23-6
220°C/W
110°C/W
Absolute Maximum Rating (Note 2)
Symbol
Item
Rating
Units
VIN
Input Supply Voltage
-0.3 ~ +6
V
VSW
SW Pin Switch Voltage
-0.3 ~ +6
V
-0.3 ~ VIN+0.3
V
Other I/O Pin Voltage
ISW
SW Pin Switch Current
2.5
A
IEXT
EXT Pin Driver Current
150
mA
TJ
Junction Temperature
+125
°C
-65 ~ +150
°C
TSTG
(Note 3)
Storage Temperature Range
Note 1:Thermal Resistance is specified with approximately 1 square of 1 oz cooper.
Note 2:Absolute Maximum ratings are threshold limit values that must not be exceeded even for an
instant under any conditions. Moreover, such values for any two items must not be reached
simultaneously. Operation above these absolute maximum ratings may cause degradation
or permanent damage to the device. These are stress ratings only and do not necessarily
imply functional operation below these limits.
Note 3:TJ is calculated from the ambient temperature TA and power dissipation PD according to the
following formula: TJ = TA + (PD) × (220°C/W)
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EP4001
Electrical Characteristics
(VIN = 1.5V, VOUT=3.3V, IL = 0mA, TA=25°C, Test Circuit Figure 2, unless otherwise specified)
Symbol
VS
IQ
Parameter
Quiescent Current (No Load
Current)
ILIMIT
Feedback Reference Voltage
V
V
0.01
1
µA
VIN=6V
35
50
µA
VIN=EN=3.3V,
VFB=GND
0.4
0.6
mA
Output Voltage
VOUT
Output Voltage
∆VLINE
Line Regulation
∆VLOAD
Load Regulation
∆VLOAD
Load Regulation
Min.
2
110
µA
TA =+25°C
1.195
1.220
1.245
V
0°C≤TA ≤ 85°C
1.190
1.220
1.250
V
-40°C≤TA ≤ 85°C
1.183
1.220
1.257
V
380
85
450
90
0.03
2
16
18
520
KHz
%
Ω
A
Ω
Ω
3.200
3.300
3.400
V
3.200
3.300
3.400
V
Switching Frequency
Maximum Duty
SW ON Resistance
Current Limit Setting
EXT ON Resistance to VIN
EXT ON Resistance to GND
VOUT
TS
Units
1.05
4.2
EN pin = 0V, VIN=4.5V
IQ
FS
DMAX
Max.
Quiescent Current (Shutdown
Current)
IQ
VFB
Typ.
0.85
IL=1mA
VIN pin voltage
Quiescent Current (Switch-off
Current)
Quiescent Current (Continuous
Switching Current)
IQ
Conditions
Start-up Voltage
Operating VOUT Range
VIN=1.5V, IL=100mA
-40°C≤TA ≤ 85°C
VIN=3.0V, IL=300mA
-40°C≤TA ≤ 85°C
VIN=1V to 3V, IL=1mA
VIN=1.5V, IL=1mA to
100mA
VIN=3.0V, IL=1mA to
300mA
EN Pin Trip Level
Temperature Stability for VOUT
Thermal Shutdown
Thermal Shutdown Hysteresis
0.4
Aug. 2006
1.1
0.3
mV/V
0.4
mV/mA
0.4
mV/mA
0.8
110
165
10
1.2
V
ppm/°C
°C
°C
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Typical Performance Characteristics
Efficiency (%)
Start Up Voltage (V)
Supply Current (uA)
Output Voltage (V)
Switching Frequency (KHz)
Efficiency (%)
(Test Figure 2 above unless otherwise specified)
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Functional Block Diagram
Figure 3-EP4001 Functional Block Diagram
Operation
The EP4001 is a current mode PWM boost converter with a fixed switching frequency at 450KHz. It is
able to operate from an input voltage below 1V. With its low RDS(ON) internal MOSFET switch, this device
maintains the high efficiency over a wide range of load current.
Low Voltage Start-Up
The EP4001 will start up with a typical VIN voltage at 1V. The low voltage start-up circuitry controls the
internal NMOS switch allowing the devices to start up into an output load. Once VOUT exceeds 1.8V, the
start-up circuitry is disabled and normal fixed frequency PWM operation is initiated. In this mode, the
EP4001 operates independent of VIN. The limiting factor for the application becomes the ability of the
battery to supply sufficient energy to the output. Low Noise Fixed Frequency Operation Oscillator: The
frequency of operation is internally set to 450KHz.
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EP4001
Low Noise Fixed Frequency Operation Oscillator
The frequency of operation is internally set to 450KHz.
Error Amp: The internal 1.22V reference voltage is compared to the voltage at the FB pin to generate an
error signal at the output of the error amplifier. A voltage divider from VOUT to ground programs the output
according to the equation:
⎛ R1 ⎞
VOUT= FB × ⎜1 +
⎟
⎝ R2 ⎠
Where FB=1.22V
Due to device performance limitation, the EP4001 is limited to applications with output voltage less than
4.2V, until the problem is corrected at later date.
PWM Mode
Refer to Figure 3, functional block diagram. The main gain block is a comparator that sums four signals:
feedback voltage, reference, current-sensing and slope compensation ramp. This direct-summing
method approaches the ideal of cycle-by-cycle control of output voltage. Under heavy loads, the
controller operates in full PWM mode. Every pulse from the oscillator sets the output latch and turns on
the NMOS switch for a period determined by the duty factor and current limit.
PFM Mode Operation
Portable devices frequently spend extended time in low power or standby mode, only switching to high
power mode when specific functions are enabled. Maintain high efficiency over a wide range of load
current is critical for prolong battery life. In addition to its high efficiency at moderate and heavy loads,
the EP4001 includes automatic PFM operation that improves efficiency of the converter at light load.
PFM operation is initiated if the output load current falls below an internally programmed threshold. Once
initiated, the PFM operation circuitry shuts down most of the device, only keeping alive the circuitry
required to monitor the output voltage.
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EP4001
Applications Information
Figure 4-EP4001 for Higher Current Applications
Figure 5-EP4001 for Multi-Output Applications
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EP4001
Inductor Selection
The EP4001 can utilize small surface mount and chip inductors operating at 450KHz switching frequency.
The inductor current ripple is typically set for 20% to 40% of the maximum inductor current. The inductor
should have low ESR (series resistance of the windings) to reduce the I2R power losses, and must be
able to handle the peak inductor current without saturating.
Output and Input Capacitor Selection
Low ESR (equivalent series resistance) capacitors should be used to minimize the output voltage ripple.
Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the
battery. The input decoupling capacitor should be located as close as possible to the device.
Output Voltage Setting
The output voltage of the switching regulator (VOUT) is determined by (Eq.1)
Feedback Loop Design
The value selection for R1 and R2 is based on the trade-off between quiescent current consumption and
interference immunity. Higher values for R1 and R2 will reduce the quiescent current, while Lower values
for R1 and R2 has the advantage of a better noise immunity, and is less sensitive to other interferences.
However, a resistor having a value higher than 5mΩ is not recommended. The noise immunity of the
feedback loops can be improved by using a proper value of feed forward capacitor in parallel with R1.
The value for this capacitor is between 0 to 33pF for feedback resistors of mΩ, and 10nF to 0.1μF for
feedback resistors of tens to hundreds kΩ. Be aware that such kind of “high impedance feedback Loops”
is sensitive to any interference, which require careful layout and avoid any interference.
Layout Guide
1. The power traces, which are consisted of GND trace, the SW trace and the VIN trace should be kept
short, direct and wide.
2. Keep the switching node, SW, away from the sensitive FB node.
3. Keep the distance between pin SW and L1 as close as possible, and no more than 3-4mm.
4. Keep the distance between capacitor C3 and L1 as close as possible, no more than 3-4mm.
5. Connect the (+) plate of CIN to VIN as closely as possible. This capacitor provides the AC current to the
internal power MOSFETs.
6. Connect pin FB directly to the feedback resistors. The resistive divider R1/ R2 must be connected
between the (+) plate of COUT and ground.
7. Keep the (-) plates of CIN and COUT as close as possible.
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EP4001
Package Description
6pin TSOT-23
DIM
MILLIMETERS
INCHES
MIN.
NOM.
MAX.
MIN.
NOM.
MAX.
A
0.90
−
1.10
0.035
−
0.043
A1
0.01
−
0.13
0.0004
−
0.005
B
0.30
−
0.50
0.012
−
0.020
C
0.09
−
0.20
0.004
−
0.008
D
2.80
−
3.00
0.110
−
0.118
H
2.50
−
3.10
0.098
−
0.122
E
1.50
−
1.70
0.059
−
0.067
e
0.95 REF.
0.037 REF.
e1
1.90 REF.
0.075 REF.
L1
0.20
−
0.55
0.008
−
0.022
L
0.35
−
0.80
0.014
−
0.031
Q
0°
−
10°
0°
−
10°
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