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AT1361
1MHz,1A Synchronous Buck Converter
Features * High efficiency (95%) possible * No Schottky Diode Required * 1A Output Current at 5V input 3.3V output * Oscillation frequency 1.0MHz * Built-in ON/OFF Function * Built-in Short Circuit Protection * Low Dropout Operation: 100% Duty Cycle * Stand-by current max. 1A * Input voltage: 2.5V ~5.5V Applications * Power Supply for portable devices General Description The AT1361 provides complete control for a DC/DC converter optimized for high-performance microprocessor applications. It is operated on current mode architecture for excellent line and load transient response. 1MHz operation frequency is allowing the use of small surface mount inductor and capacitor. The internal synchronous switch increases efficiency and eliminates the need for an external Schottky diode. The AT1361 is a family of low-noise synchronous step-down DC/DC converters that is ideally suited for systems powered from a 1-cell Li-ion battery or from a 3-cell to 4-cell NiCd, NiMH, or alkaline battery. It can also be used to USB-Based power system.
Block Diagram
Aimtron reserves the right without notice to change this circuitry and specifications.
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 1/11/2008 REV:1.0 Email:service@aimtron.com.tw 1
AT1361
1MHz,1A Synchronous Buck Converter Pin Configuration
Ordering Information
Part number AT1361X_GRE Package SOT-25, Green Marking : Date Code with one bottom line
*For more marking information, contact our sales representative directly
Pin Description
Symbol Pin No. Descript
RUN GND SW VIN FB
1 2 3 4 5
ON/OFF Control Power ground Switch Node Connection to Inductor Power Supply Output Feedback
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AT1361
1MHz,1A Synchronous Buck Converter
Absolute Maximum Ratings:(TA=25C)
Parameter Power Supply Voltage Input Pin Voltage P-Channel Switch Source Current (DC) N-Channel Switch Sink Current (DC) Peak SW Sink and Source Current Thermal Resistance from Junction to Ambient JA Operating temperature TA Storage temperature ESD Susceptibility *2 Condition -- RUN,FB SW -- -- -- SOT-25 -- -- HBM MM Rated Value Min. Max. -0.3 +6.0 -0.3 VIN -0.3 VIN+0.3 1200 -35 -55 2 200 1200 1.5 200 +85 +150 Unit V V V mA mA A C /W C C KV V
1. Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 2. Device are ESD sensitive. Handling precaution recommended. The Human Body model is a 100pF capacitor discharged through a 1.5K resistor into each pin.
Recommended Operating Conditions
(TA=+25C)
Parameter Power supply voltage Operating temperature* Operating junction temperature
*Using X5R or X7R input capacitors.
Symbol VIN TA TJ Min. 2.5 -20 -
Values Typ. -+25 Max. 5.5 +85 +150
Unit
C C
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AT1361
1MHz,1A Synchronous Buck Converter Electrical Characteristics
(VIN =5V, TA=+25C , unless otherwise noted. )
Parameter
Symbol
Condition Min.
Values Typ. -2.3 0.1 70 0.5 0.600 0.1 0.5 -1.8 -1.0 200 0.4 0.35 0.1 --0.1 Max. 5.5 --100 1 0.612 0.5 1.0 200 --1.2 -0.5 0.45 1 -0.3 1
Unit
Input Supply Range Input Under-Voltage Lock Out threshold UVLO hysteresis Quiescent Current* Current in standby mode Feedback Voltage Feedback Voltage line-regulation Feedback Variation with Temperature Feedback current Peak Inductor Current* Maximum Output Current* Oscillator Frequency RDS(ON) of P-Channel MOSFET RDS(ON) of N-Channel MOSFET SW Leakage Current
VIN VUVLO IN Rising
2.5 ---
V V V A A V %/V % nA A A MHz KHz A V V A
IS IST VFB VFB-Line
FB=0.6V,ILOAD=0A Active Mode RUN=0V, VIN=5.5V
--0.588
VIN =2.5V to 5.5V TA=-20C to +85C
----
IFB IPK IO fosc1 fosc2 RPFET RNFET ILSW
H
VIN=5V,VOUT=3.3V VIN=5V5%, VOUT=3.3V, L=4.7H, TA=25C FB=0.6V FB=0V ISW=600mA ISW=-600mA RUN=0V,SW=0V or 5V,VIN=5V VIN =2.5V to 5.5V VIN =2.5V to 5.5V
1.2 1 0.8 ----1.5 ---
RUN High-Level Input VRUN Voltage RUN Low-Level Input VRUN Voltage RUN leakage Current IRUN
L
* I PK = I O +
(V - VOUT ) x t ON I = I O + IN 2 2x L
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 1/11/2008 REV:1.0 Email:service@aimtron.com.tw 4
AT1361
1MHz,1A Synchronous Buck Converter Typical Application Circuit
L1:Sumida
CDRH4D28-4R7
Figure 1 .Adjustable Voltage Regulator
Efficiency VS. Load Current 90
80
70 Efficiency(%
60
50
40
30 10 Load Current(mA) 100
L1:Sumida
CDRH4D28-4R7
Figure 2 .Buck-Boost Regulator
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 1/11/2008 REV:1.0 Email:service@aimtron.com.tw 5
AT1361
1MHz,1A Synchronous Buck Converter Typical characteristics :
Quiescent Current vs. Input Voltage
Reference Voltage vs. Input Voltage
Quisecent Current(uA)
Reference Voltage(V)
Input Voltage(V)
Input Voltage(V)
Oscillator Frequency vs. Temperature
1.3
Oscillator Frequency vs. Input Voltage
1.25 1.2
Oscillator Frequency (MHz
1.15 1.1 1.05 1 0.95 0.9 0.85 0.8 0.75 0.7 -30 -20 -10 0 10
Oscillator Frequency(MHz)
Load=1A
Load=0.8A
20
30
40
50
60
70
80
90
Input Voltage(V)
Temperature ( )
Vout Voltage vs. Temperature
Vout Voltage vs. Temperature
Vout Voltage(V)
Vout Voltage(V)
Temperature ( )
Temperature ( )
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 1/11/2008 REV:1.0 Email:service@aimtron.com.tw 6
AT1361
1MHz,1A Synchronous Buck Converter Typical characteristics :
Vout Voltage vs. Temperature
Vout Voltage vs. Temperature
Vout Voltage(V)
Temperature ( )
Vout Voltage(V)
Temperature ( )
Efficiency VS. Load Current
100 100
Efficiency VS. Load Current
90
90
80
80
70
70
Efficiency(%)
Efficiency(%
60
60
50
50
40
40
30
30
20
20
10 10
10
Load Current(mA)
100
1000
10
100 Load C urre nt(mA)
1000
Efficiency VS. Load Current
100
90
80
70
Efficiency(%
60
50
40
30
20
10 10
Load Current(mA)
100
1000
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AT1361
1MHz,1A Synchronous Buck Converter Typical characteristics : Power ON/OFF
CH1: VOUT CH2: VIN CH3:SW CH4:IIN VIN=5V,VOUT=3.3V,Load=1A,Power OFF VIN=5V,VOUT=3.3V,Load=1A, Power ON
EN pin ON/OFF
CH1: VOUT CH2:EN CH3:SW CH4:IIN VIN=5V,VOUT=3.3V,Load=1A,EN Turn-OFF VIN=5V,VOUT=3.3V,Load=1A,EN Turn-ON
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AT1361
1MHz,1A Synchronous Buck Converter Transient response
CH2:VOUT CH4:IOUT VIN=5V,VOUT=3.3V,C2=100pF
IOUT=0mA to1A
IOUT=50mA to 1A
IOUT=100mA to 1A
IOUT=200mA to1A
Ripple noise
VIN=5V,VOUT=3.3V,Load=0A VIN=5V,VOUT=3.3V,Load=1A
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AT1361
1MHz,1A Synchronous Buck Converter Application Information Short Circuit Protection Function The AT1361 has short circuit protection(see the Electrical Characteristics frequency item). When the output is shorted to ground, the frequency of the oscillator is reduced to about 200KHz. This frequency foldback ensures that the inductor current has more time to decay. It will prevent the inductor current and internal P-MOSFET current runaway to damage the device. The frequency will return to the normal values when the short circuit condition is removed and the feedback voltage reaches 0.6V. Capacitor Selection In continuous mode, the source current of the top MOSFET is square wave of duty cycle. The Primary function of the input capacitor is to provide a low impedance loop for the edges of pulsed current drawn by the AT1361. A load step at the output can induce ringing at the input VIN. This ringing can couple to the output and be mistaken as loop instability. The oscillation can be improved by add the capacitance of the input capacitor. A typical value is 4.7~22F ceramic (X5R or X7R), POSCAP or Aluminum Polymer. These capacitors will provide good high frequency bypassing and their low ESR will reduce resistive losses for higher efficiency. 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:
VO V (1 - O ) VIN VIN
I RMS = I OMAX
The output capacitor depends on the suitable ripple voltage. Low ripple voltage corresponds to lower effective series resistance (ESR). The output ripple voltage is determined by:
VOUT I L ( ESR +
1 ) 8 fC OUT
The output capacitor RMS ripple current is given by:
I RMS = 1 VOUT x (VIN - VOUT ) L x f x VIN 23
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AT1361
1MHz,1A Synchronous Buck Converter
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.
Inductor Selection The inductor is chosen based on the desired ripple current. Large value inductors lower ripple current and small value inductors result in higher ripple current. Always consider the losses associated with the DCR and its effect on the total converter efficiency when selecting an inductor. The 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. The formula of inductance value is as below:
I L = 0.2 ~ 0.4 x I OUT ( MAX )
L= VOUT f x I L VOUT 1 - VIN
Adjustable Output Voltage The AT1361 appears a 0.6V reference voltage at FB pin. The output voltage is set by a resistive divider which is according to the following formula:
0.6V=VOUT=5.5V
R2 FB
VOUT
R2 = 0.6V x (1 + ) R1
GND
R1
*R1=150K for stability consideration.
7F, No.9, PARK AVENUE II, Science-Based Industrial Park, Hsinchu 300,Taiwan, R.O.C. Tel: 886-3-563-0878 Fax: 886-3-563-0879 WWW: http://www.aimtron.com.tw 1/11/2008 REV:1.0 Email:service@aimtron.com.tw 11
AT1361
1MHz,1A Synchronous Buck Converter The Dissipation The power loss is given by:
2 2 PLOSS = I O x RDS (ON ) - P x D + I O x R DS ( ON ) - N x (1 - D) +
1 x VIN x I O x (t r + t f ) x f s 2
1 + x VD x I O x (t r + t f ) x f s + VIN x I Q 2
TJ ( MAX ) = T A + JA x PLOSS
Inductance(H) 4.7 4.7
Inductors Surface Mount Manufacturer/Part No. Sumida CDRH4D28-4R7 ABC SH40284R7YSB Capacitors Surface Mount Manufacturer/Part No. TDK C3216X5R0J226M TDK C3225X5R0J46M GRM42-6X5R 106K6.3 TAIYO JMK212BJ475MG
Manufacturer Website www.sumida.com www.atec-group.com
Capacitance(F) 22 47 10 4.7
Manufacturer Website www.tdk.com www.tdk.com www.murata.com www.t-yuden.com
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AT1361
1MHz,1A Synchronous Buck Converter PC Board Layout
1. The most critical aspect of the layout is the placement of the input capacitor C1. It must be placed as close as possible to the AT1361 to reduce the input ripple voltage. 2. Power loops on the input and output of the converter should be laid out with the shortest and widest traces possible. The longer and narrower the trace, the higher resistance and inductance it will have. The length of traces in series with the capacitors increases its ESR and ESL and reduces their effectiveness at high frequency. 3. The FB pin should connect to feedback resistors directly. And the route should be away from the noise source, such as inductor of SW line. 4. Grounding all components at the same point may effectively reduce the occurrence of loop.
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AT1361
1MHz,1A Synchronous Buck Converter Package Outline :SOT-25
SYMBOL A A1 A2 b C D E E1 L e e1 r
INCHES MIN 0.035 0.000 0.035 0.010 0.003 0.110 0.102 0.059 0.014 0.037ref 0.075ref 00 100 MAX 0.057 0.006 0.051 0.020 0.008 0.122 0.118 0.069 0.022
MILLIMETERS MIN MAX 0.90 1.45 0.00 0.15 0.90 1.30 0.25 0.50 0.08 0.20 2.80 3.10 2.60 3.00 1.50 1.75 0.35 0.55 0.95ref 1.90ref 00 100
NOTES -
-
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AT1361
1MHz,1A Synchronous Buck Converter Reflow Profiles
Profile Feature
Sn-Pb Eutectic Assembly Large Body Small Body Pkg. thickness Pkg. thickness <2.5mm or Pkg. 2.5mm or Pkg. 3 volume 350mm3 volume <350mm 3C/second max.
Average ramp-up rate (TL to TP) Preheat -Temperature Min(Tsmin) -Temperature Max (Tsmax) -Time (min to max)(ts) Tsmax to TL -Ramp-up Rate Time maintained above: -Temperature (TL) -Time (tL) Peak Temperature(TP) Time within 5C of actual Peak Temperature (tP) Ramp-down Rate Time 25C to Peak Temperature
Pb-Free Assembly Large Body Small Body Pkg. thickness Pkg. thickness 2.5mm or Pkg. 2.5mm or Pkg. volume 350mm3 volume 350mm3 3C/second max.
100C 150C 60-120 seconds
150C 200C 60-180 seconds 3C/second max.
183C 60-150 seconds 225+0/-5C 10-30 seconds 240+0/-5C 10-30 seconds
217C 60-150 seconds 245+0/-5C 10-30 seconds 250+0/-5C 20-40 seconds
6C/second max. 6 minutes max.
3C/second max. 8 minutes max.
*All temperatures refer to topside of the package, measured on the package body surface.
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