ETC AT1308

AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
Feature
Description
•Operating Voltage:2.5V~6.0V
The AT1308 step-up converter is designed for
small or medium size LCD panel of high bias
voltage with a constant current to provide PDAs,
and other hand-held devices. It features a fast 1.0
MHz current-mode PWM control with a built-in
0.3Ω N-MOS that allows for smaller capacitor and
inductor. Fault condition protection uses cycle-bycycle current limiting to sense maximum inductor
current and thermal protection. Also included
soft-start circuitry eliminates inrush current during
start-up. The AT1308 is available in 5-pin SOT-25
packages.
•High Operating Frequency: 1MHz
•Built-in N-MOS, Rds(on)≒ 0.3Ω (TYP)
•High Output Voltage: Up to 28V
•Shutdown Current <1µA
•Built-in Cycle-by-Cycle Current-limited.
•Built-in Soft-Start Function.
•1.5% 1.23V Reference.
•Tiny SOT-25 Package
Application
• STN/OLED Bias
• Personal Digital Assistants (PDAs)
• DSC
Block Diagram
VIN
LX
ON/OFF
Control
Logic
EN
VBG
1.23V
Soft-Start
Thermal
Protection
VBG
N
+
Control Logic
FB
-
Current Limit
400mA
+
-
GND
Aimtron reserves the right without notice to change this circuitry and specifications.
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
1
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
Pin Configuration
SOT-25
(TOP VIEW)
LX
1
GND
2
FB
3
5
VIN
4
EN
Ordering Information
Part number
AT1308X
AT1308X_GRE
Package
SOT-25
SOT-25,Green
Marking
Date Code
,Date Code with one bottom line
Pin Description
Pin N0. Symbol
1
LX
2
GND
I/O
I
P
3
FB
I
4
EN
I
5
VIN
P
Description
Step-up Regulator N-MOS Drain. Place output diode and inductor.
Ground
Step-Up Regulator Feedback Input. Connect a resistive divider from
output to FB to analog ground.
Enable Control Input. Pull EN low to force the controller into shutdown.
If unused , connect EN to Vin for normal operation.
Power supply.
Absolute Maximum Ratings[note1]
Parameter
VIN voltage
LX voltage
EN , FB to GND
Switch Current (ILX)
Continuous power dissipation (SOT-25 Ta=+25OC)
Operating Junction Temperature Range
Lead Temperature (Soldering 5 sec)
Storage Temperature
Package Thermal Resistance (ΘJA)
ESD Susceptibility (HBM)
ESD Susceptibility (MM)
Rated Value
-0.3 to +6.5
-0.3 to +30
-0.3 to +6.5
0.8
0.25
-30 to 85
260
-65 to 125
250
2
200
Unit
V
V
V
A
W
℃
℃
℃
℃/W
KV
V
Note1:Permanent device damage may occur if Absolute Maximum Ratings are exceeded. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
2
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
Recommended Operation Conditions
Parameter
Power supply voltage
Operating temperature
Values
Typ.
―
+25
Symbol
VIN
Top
Min.
2.5
-20
Unit
Max.
6.0
+85
V
℃
Electrical Characteristics
(VIN=2.5V, Ta=+25℃, unless otherwise noted)
Parameter
Operating V IN Range
Symbol
Test Condition
VIN input Voltage
VIN
Min.
Under Voltage Thershold
Switch- Off Input Current
Shutdown Current
Feedback Reference
FB Input Bais Current
UVLO
IIN1
IIN3
VFB
IFB
2.2
100 120
1
1.212 1.23 1.248
1
Output Voltage Line Regulation
Switching Frequency
Maximum Duty
Soft-Start charging time
Switching Current Limit
LX ON Resistance
LX Leakage Current
EN Input Current
EN Input Level
Thermal Shutdown
fOSC
DMAX
tSS
ILX
RLX
ILeakage
IEN
VIH
VIL
VIN falling, 100mV hysteresis
No Switching
EN=0V
VFB =1.23V
2.5V< VIN <6.0V
VIN=3.0V,duty cycle=80%
ILX =350mA
VLX =29V, EN=0V
EN=5V
0.1V hysteresis
2.5
Typ. Max. Units
-
6.0
V
V
uA
uA
V
uA
-
0.1
-
%
-
1
90
0.5
400
0.3
120
-
MHz
%
ms
mA
Ω
uA
uA
V
V
℃
2.0
-
1
8
0.8
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
3
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
Application Circuit
10uH
VIN
2.5V to 4.2V
MBR140WS
1uF
3.3V/
50mA
L1
4u7F/
6V3
VIN
LX
10uH
L2
10pF
500K
AT1308
EN
10uF/
6V3
R1
FB
R2
297K
※L1, L2 : SR0302 (0.25Ohm/0.8A)
GND
※VOUT=VREFX (1+R1/R2)
Fig1. 1-Cell Li-Ion to 3.3V SEPIC Converter
10uH
VIN
3.0V to 6.0V
MBR140WS
1uF
5V/
40mA
L1
4u7F/
6V3
VIN
LX
10uH
10pF
L2
10uF/
6V3
AT1308
R1
500K
FB
EN
R2
GND
163K
※L1, L2 :SR0302 (0.25Ohm/0.8A)
※VOUT=VREFX (1+R1/R2)
Fig2. 4-Cell to 5V SEPIC Converter
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
4
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
0.1uF
10uH
VIN
2.5V to 5.0V
4.7uF/
16V
BAT54S
-15V/
4mA
0.1uF
15V/
4mA
L1
4u7F/
6V3
VIN
BAT54S
LX
10pF
AT1308
4.7uF/
16V
500K
FB
EN
44K
GND
※L1 :SR0302 (0.25Ohm/0.8A)
Fig3. ±15V Dual Output Converter with Output Disconnect
10uH
VIN
2.5V to 5.0V
15V/
20mA
L1
4.7uF/
6V3
VIN
MBR140WS
LX
10uF/
16V
10pF
AT1308
500K
R1
FB
EN
44K
R2
GND
※L1 :SR0302 (0.25Ohm/0.8A)
※VOUT=VREFX (1+R1/R2)
Fig4. 15V Boost Converter
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
5
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
VOUT3
-13V_TFT
510
VOUT2
17V_TFT
10K
BAT54S
1uF/25V
0.1uF
BAT54S
0.1uF
1uF/25V
Zener
13V
10uF/25V
Zener
17V
open
open
1uF
0.1uF
BAT54S
0.1uF
1uF
BAT54S
4.7uH
VOUT1
7.5V_TFT
VIN
5V
MBR140S
10uF/10V
VIN
LX
10pF
SW
1uF
AT1308
500K
FB
EN
98K
GND
Fig5. TFT_ Power solution
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
6
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
Efficiency-%
Typical Characteristics
90
85
80
75
70
65
60
55
50
45
40
EFFICIENCY vs OUTPUT CURRENT
Vo=15V
L=10uH
2.5V
3.6V
5.0V
Efficiency-%
1
90
85
80
3
5
8 10 13 15 18 20
Io-Output Current-mA
EFFICIENCY vs LOAD CURRENT
Vo=15V
Vin=3.3V
75
70
65
60
55
50
6.8uH
10uH
22uH
1
3
5
7
10 13 15 18 20
Io-Load Current-mA
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
7
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
90
EFFICIENCY vs INPUT VOLTAGE
Vo=15V
L=10uH
Efficiency-%
85
80
75
5mA
10mA
20mA
70
2.5
3
3.3 3.6 3.9 4.2 4.5
5
5.5
Vin-Input Voltage-V
CURRENT LIM IT vs SUPPLY VO LTAG E
700
CURRENT LIMIT (mA)
650
Vo=15V
600
550
500
450
400
L=10uH
350
L=22uH
300
2.5
3
3.5
4
4.5
5
5.5
6
VIN-SUPPLY VO LTAG E (V)
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
8
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
Q U IESC EN T C U R R EN T vs IN PU T V O LTA G E
QUIESCENT CURRENT (uA)
500
450
400
Vo=15V
L=10uH
350
300
TA=25OC
250
200
150
100
50
0
2.5 2.8
3
3.3 3.6
4
4.2 4.5
5
5.5
6
V IN -IN PU T V O LTA G E (V )
SWITCHING FREQUENCY (KHz)
SW ITC H IN G FR EQ U EN C Y v s TEM PER A TU R E
975
970
VIN=2.5V
Vo=15V
L=10uH
965
960
955
950
945
940
-20
-1 0
0
10
25
40
55
85
TE M PER A TU R E ( o C )
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
9
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
Load Transient Response
VIN=2.5V, Vout=15V, L=10uH, Iout=5mA to 25mA
Ch1:Vout (AC mode), Ch4:Iout, Time:0.5ms/div
Line Transient Response
VIN=2.5V to 6.0V, Vout=15V, L=10uH, Iout=20mA
Ch1:VIN, Ch2:Vout (AC mode), Ch4:IIN, Time:0.5s/div
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
10
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
Start up Waveform with Load
VIN=2.5V, Vout=15V, L=10uH, Iout=20mA
Ch1:Vout, Ch2:EN, Ch4:IIN, Time:1.0ms/div
LX Switching Waveform
VIN=3.3V, Vout=20V, L=10uH
Ch1:LX, Ch4:ILX, Time:0.5us/div
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
11
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
Function Description
The AT1308 is designed primarily for use in STN/OLED bias applications. The output voltage of the
step-up converter can be set from Vin to 26V with external resistive voltage divider. The boost
converter operates in current-mode PWM and a constant frequency of 1.0 MHz. Depending on duty
cycle of each switching cycle can regulate output voltage. On the rising edge of the internal clock, the
control and driver logic block sets internal flip-flop when the output voltage is too low, which turns on
the N-MOS . The external inductor current ramps up linearly, storing energy in a magnetic filed. Once
peak current of inductor over trans-conductance output level , the N-MOS turns off, the flip-flop resets,
and external schottky diode turns on . This forces the current through the inductor to ramp back down,
transferring the energy stored in the magnetic field to the output capacitor and load. To reduce external
component amount, the device will be built-in internal loop compensation.
Enable Control
Digital logic of EN provides an electrical ON/OFF control of the power supply. Connecting this pin to
ground or to any voltage less than 0.7V will completely turn off the regulator. In this state, current
drain from the input supply is less than 1uA , the internal reference, error amplifier, comparators, and
biasing circuitry turn off .
EN works as a simple on/off control. Drive EN high to enable the device, or drive EN low for
shutdown.
Soft-Start
Soft-start allows a gradual increase of the internal current-limit level for the step-up converter during
power-up to reduce input surge currents. As the internal current source charges the internal soft-start
capacitor, the peak N-MOS current is limited by the voltage on the capacitor.
Cycle-by-Cycle Over-Current Protection
The AT1308 provides cycle-by-cycle over-current protection. Current limit is accomplished using a separate
dedicated comparator. The cycle-by-cycle current limit abbreviates the on-time of the N-MOS in event that
the current of flowing N-MOS is greater than the current limit value. The current-limit feature protection
against a hard short or over-current fault at the output.
Thermal-Overload Protection
Thermal-overload protection limits total power dissipation in the AT1308. When the junction
temperature exceeds Tj=130 ℃, a thermal sensor activates the thermal protection, which shuts down
the IC, allowing the IC to cool. Once the device cools down by 10 ℃, IC will automatically recover
normal operation. For continuous operation , do not exceed the absolute maximum
junction-temperature rating of Tj=120 ℃.
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
12
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
Power dissipation consideration
The AT1308 maximum power dissipation depends on the thermal resistance of the IC package and
circuit board, the temperature difference between the die junction and ambient air, and the rate of any
airflow. The power dissipation in the device depends on the operating conditions of the regulator.
The step-up converter dissipates power across the internal N-MOS as the controller ramps up the
inductor current. In continuous condition, the power dissipated internally can be approximated by :
Pboost = [(
I O × VO 2 1 Vin × D 2
) ] × RDS ( ON ) × D
) + (
Vin
12 f OSC × L
where
IO : It is the load current.
fOSC : It is a switching frequency.
Applications Information
External components of boost converter can be designed by performing simple calculations. It need to
follow regulation by the output voltage and the maximum load current, as well as maximum and
minimum input voltages. Begin by selecting an inductor value. Once L is know, choose the diode and
capacitors.
Boost inductor
Inductor selection depends on input voltage, output voltage, maximum current , switching frequency
and availability of inductor values. The following boost circuit equations are useful in choosing the
inductor values based on the application. They allow the trading of peak current and inductor value
while allowing for consideration of component availability and cost.
The peak inductor current is given by:
I Lpeak = I LAVG +
I LAVG =
∆I L
2
IO
1− D
where:
△IL is the inductor peak-to-peak current ripple and is decided by:
∆I L =
Vin
D
×
L
f OSC
D is the MOSFET turn on ratio and is decided by:
D=
VO −V in
VO
fOSC is the switching frequency.
The inductor should be chosen to be able to handle this current and inductor saturation current rating
should be greater than IPEAK.
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: serv[email protected]
13
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
Diode selection
The output diode has average current of IO, and peak current the same as the inductor’s peak current
and a voltage rating at least 1.5 times the output voltage. Schottky diode is recommended and it should
be able to handle those current.
Output Capacitor
The AT1308 is specially compensated to be stable with capacitors, which have a worst- case minimum
value of 1uF at the particular VOUT being set. Output ripple voltage requirements also determine the
minimum value and type of capacitors. Output ripple voltage consists of two components the voltage
drop caused by the switching current through the ESR of the output capacitor and the charging and
discharging of the output capacitor:
V RIPPLE = I LPEAK × ESR +
VO − Vin
IO
×
VO
C OUT × f OSC
For low ESR ceramic capacitors, the output ripple is dominated by the charging or discharging of the
output capacitor.
Impacting frequency stability of the overall control loop, Ceramic capacitors are preferred on the
output capacitance, but tantalum capacitor may also suffice., If it use tantalum capacitor on the output
terminal, that in addition the capacitance parallel with feedback resistor network is necessary. These
frequency response effects together with the internal frequency compensation circuitry of AT308
modify the gain and phase shift of the closed loop system.
PCB layout guidelines
Careful printed circuit layout is extremely important to avoid causing parasitical capacitance and line
inductance. The following layout guidelines are recommended to achieve optimum performance.
• Please the boost converter diode and inductor close to the LX pin and no via. Keep traces short,
direct, and wide.
• Please ceramic bypass capacitors near the input/output pin.
• Locate all feedback sense resistor as close to the feedback pins as possible.
• The ground connections of VIN and VOUT should be as close together as possible.
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
14
Rev A ; 01/18/05
AT1308
Preliminary Product Information
Micro-Power Step up DC-DC Converter
Small Outline SOT-25
2F, No.10, Prosperity RD. II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C.
Tel: 886-3-563-0878
WWW: http://www.aimtron.com.tw
Fax: 886-3-563-0879
Email: [email protected]
15
Rev A ; 01/18/05