AMSCO AS1341

AS1341
D a ta S he e t
2 0 V, 6 0 0 m A , 1 0 0 % D u t y C y c le , St e p - D o w n C o n v e r t e r
1 General Description
2 Key Features
The AS1341 is a high-efficiency step-down converter
with adjustable output voltages from 1.25V to VIN using
supply voltages of up to 20V.
!
Output Voltages: Fixed 5V or Adjustable
!
Input Voltage Range: 4.5 to 20V
An integrated current-limited 0.4Ω MOSFET delivers
load currents up to 600mA.
!
Output Current: Up to 600mA
!
1.25V Lowest Output Voltage
!
Efficiency: up to 96%
!
Quiescent Supply Current: 12µA
!
Power-OK Output
!
Internal 0.4Ω P-Channel MOSFET
!
Shutdown Current: 0.8µA
!
100% Maximum Duty Cycle for Low Dropout
!
Current-Limited Architecture
!
Thermal Shutdown
!
TDFN-8 3x3mm Package
The AS1341 also includes a 100% duty cycle LDO
mode with a low dropout of only 250mV for high efficiency if input voltages is in the range of the output voltage.
The AS1341 has a low quiescent current (12µA) to
improve light-load efficiency and minimize battery use,
and draws only 0.8µA in shutdown mode.
High switching frequencies (up to 200kHz) allow the use
of small surface-mount inductors and output capacitors.
The device is available in a TDFN-8 3x3mm pin package.
3 Applications
The device is ideal for notebook computers, distributed
power systems, keep-alive supplies, and any other battery-operated, portable device.
Figure 1. Typical Application
4.5 to 20V
5
IN
CIN
L1
4
5V
FB 1
D1
7
+
GND 2
COUT
AS1341
ILIMIT
7 SHDNN
AS1341
SHDNN
6
8 OUT
LX
POK 3
8
OUT
RPULL
LX 4
6 ILIMIT
9
5 IN
3
2
GND
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POK
1
Indicates High-Power Trace
FB
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AS1341
Data Sheet - P i n o u t
4 Pinout
Pin Assignments
Figure 2. Pin Assignments (Top View)
FB 1
8 OUT
GND 2
7 SHDNN
AS1341
POK 3
LX 4
6 ILIMIT
9
5 IN
Pin Descriptions
Table 1. Pin Descriptions
Pin Number
Pin Name
1
FB
2
GND
3
POK
4
5
LX
IN
6
ILIMIT
7
SHDNN
8
OUT
9
NC
Description
Feedback Input. For the fixed 5V output connect to GND. For adjustable output,
connect to a resistive divider between pins OUT and GND to set the output voltage
between 1.25V and VIN.
Ground
Power OK. Active-low open-drain reset output.
Note: Connect pin POK to GND when the Power-Ok feature is not used.
Inductor Connection. Connect this pin to an external inductor.
4.5 to 20V Input Supply Voltage
Peak Current Control Input. Connect this pin to IN or GND to set peak current limit
(see Setting Current Limit on page 10).
Shutdown Input. A low on this pin puts the AS1341 into shutdown mode. Supply
current is reduced to 0.8µA and LX goes high-impedance.
Regulated Output Voltage High-Impedance Sense Input. This pin is connected to
the internal resistor-divider network. Connect this pin to GND when not used.
Exposed Pad. This pad is not connected internally. Connect to GND or do not
connect.
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AS1341
Data Sheet - A b s o l u t e M a x i m u m R a t i n g s
5 Absolute Maximum Ratings
Stresses beyond those listed in Table 2 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 Electrical Characteristics on page 4 is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Table 2. Absolute Maximum Ratings
Parameter
Min
Max
Units
IN to GND
-0.3
+23
V
LX to GND
-2
VIN
+ 0.3
V
FB to GND
-0.3
+5
V
-0.3
VIN
+ 0.3
V
Peak Input Current
2
A
Thermal Resistance ΘJA
36.3
ºC/W
ILIMIT, SHDNN, OUT, POK to GND
Operating Temperature Range
-40
+85
ºC
Storage Temperature Range
-65
+150
ºC
+150
ºC
Junction Temperature
Package Body Temperature
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+260
ºC
Revision 1.00
Comments
on PCB
The reflow peak soldering temperature (body
temperature) specified is in accordance with
IPC/JEDEC J-STD-020C “Moisture/Reflow
Sensitivity Classification for Non-Hermetic
Solid State Surface Mount Devices”.
The lead finish for Pb-free leaded packages is
matte tin (100% Sn).
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AS1341
Data Sheet - E l e c t r i c a l C h a r a c t e r i s t i c s
6 Electrical Characteristics
DC Electrical Characteristics
VIN = +12V, SHDNN = VIN, TAMB = -40 to +85ºC. Typical values are at TAMB = +25ºC (unless otherwise specified).
Specifications based on circuit shown in Figure 1 on page 1.
Table 3. Electrical Characteristics
Symbol
Parameter
VIN
VOUT
Conditions
Min
FB = GND
4.85
Input Voltage Range
Output Voltage (Preset Output)
Units
20
V
5.00
5.15
1.25
VIN
V
Dropout Voltage
IOUT = 600mA, ILIMIT = VIN
250
mV
Line Regulation
VIN = 6V to 20V, 200Ω load
0.1
%/V
Load Regulation
ILIMIT = VIN, IOUT = 0 to 500mA
1
%
Feedback Set Voltage
(Adjustable Output)
VFB
Max
4.5
Output Voltage (Adjustable)
VDROPOUT
Typ
1.212
1.25
1.288
V
IIN
Input Supply Current
No load
12
18
µA
IINDROP
Input Supply Current in
Dropout
No load
45
60
µA
Input Shutdown Current
SHDNN = GND
0.8
3
µA
Input Undervoltage Lockout
Threshold
VIN rising
3.6
4.0
4.4
VIN falling
3.5
3.9
4.3
OUT Bias Current
VOUT = 5.5V
2
3.5
5
µA
FB Bias Current
VFB = 1.3V
-25
+25
nA
150
mV
VUVLO
IFB
FB Threshold Low
Thermal Shutdown
50
10ºC hysteresis
100
145
V
ºC
DC-DC Switches
tOFFMIN
LX Switch Minimum Off-Time
tONMAX
LX Switch Maximum On-Time
RLX
LX Switch On-Resistance
ILXPEAK
LX Current Limit
VFB = 1.3V
LX Switch Leakage Current
0.4
0.6
µs
8
10
12
µs
VIN = 6V
0.4
0.8
VIN = 4.5V
0.5
0.95
ILIMIT = GND, L = 39µH
500
700
900
ILIMIT = IN, L = 10µH
1000
1400
1800
LX Zero-Crossing Threshold
Zero-Crossing Timeout
0.2
-75
LX does not rise above the threshold
+75
30
Ω
mA
mV
µs
VIN = 20V, LX = GND, TAMB = +25ºC
0.1
VIN = 20V, LX = GND
1
µA
Control Inputs
Digital Input Level
SHDNN, ILIMIT = GND
SHDNN, ILIMIT = IN
Digital Input Leakage Current VSHDNN, VILIMIT = 0 to 20V, VIN = 20V
0.8
2.4
-100
V
+100
nA
95
%
V
Power-OK
Power-OK Threshold
POK Output Voltage Low
POK Output Leakage Current
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Falling edge, relative to VOUT
90
92.5
IPOK = 1mA
0.4
VIN, VPOK = 16V, TAMB = 25°C
0.1
VIN, VPOK = 16V
1
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µA
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AS1341
Data Sheet - Ty p i c a l O p e r a t i n g C h a r a c t e r i s t i c s
7 Typical Operating Characteristics
Figure 3. Efficiency vs. IOUT; VOUT = 5V, Circuit 1
100
100
ILIMIT = high
95
Efficiency (%) .
85
VIN = 20V
75
70
65
VIN = 12V
85
75
70
65
60
55
55
50
VIN = 20V
80
60
50
0.1
1
10
100
1000
0.1
1
Output Current (mA)
100
ILIMIT = high
95
95
90
90
VIN = 4.5V
85
80
VIN = 20V
75
VIN = 12V
70
65
VIN = 12V
VIN = 20V
70
65
55
50
50
100
VIN = 4.5V
75
55
10
ILIMIT = low
80
60
1
0.1
1000
1
10
100
1000
Output Current (mA)
Output Current (mA)
Figure 7. Efficiency vs. IOUT; VOUT = 5V, VIN = 12V
Figure 8. Efficiency vs. IOUT; VOUT = 5V, VIN = 12V
95
ILIMIT = high
90
ILIMIT = low
90
Efficiency (%) .
Efficiency (%) .
1000
85
60
0.1
100
Figure 6. Efficiency vs. IOUT; VOUT = 3.3V, Circuit 3
Efficiency (%) .
Efficiency (%) .
100
10
Output Current (mA)
Figure 5. Efficiency vs. IOUT; VOUT = 3.3V, Circuit 1
95
VIN = 6V
90
VIN = 12V
80
ILIMIT = low
95
VIN = 6V
90
Efficiency (%) .
Figure 4. Efficiency vs. IOUT; VOUT = 5V, Circuit 3
85
80
75
70
22uH
85
80
75
70
10uH
10uH
39uH
4.1uH
65
22uH
65
0.1
1
10
100
1000
0.1
Output Current (mA)
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1
10
100
1000
Output Current (mA)
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AS1341
Data Sheet - Ty p i c a l O p e r a t i n g C h a r a c t e r i s t i c s
Figure 9. Efficiency vs. Input Voltage;
Circuit 1 or Circuit 3
Figure 10. Output Voltage vs. Input Voltage;
VOUT = 5V
100
5.15
95
5.1
90
5.05
IOUT = 1mA
IOUT = 100mA
IOUT = 300mA
IOUT = 500mA
VOUT (V) .
Efficiency (%) .
IOUT = 600mA
85
5
4.95
80
Ci r cui t 1: VOUT=3.3V, IOUT=500mA
75
4.9
Ci r cui t 1: VOUT=5V, IOUT=500mA
Ci r cui t 3: VOUT=3.3V, IOUT=250mA
Ci r cui t 3: VOUT=5V, IOUT=250mA
4.85
70
5
8
11
14
17
5
20
8
11
14
17
20
Input Voltage (V)
Input Voltage (V)
Figure 11. Output Voltage vs. Input Voltage;
VOUT = 3.3V
Figure 12. Peak Switch Current vs. Input Voltage;
VOUT = 3.3V
1.8
3.4
IOUT = 100mA
.
IOUT = 1mA
1.6
ILIMIT = high
L=10µH
1.4
ILIMIT = high
L=39µH
IOUT = 500mA
VOUT (V) .
3.35
3.3
3.25
Peak Switch Current (A)
IOUT = 300mA
1.2
1
ILIMIT = low
L=10µH
0.8
ILIMIT = low
L=39µH
0.6
0.4
0.2
0
3.2
4
6
8
10
12
14
16
18
5
20
8
Figure 13. Switching Freqency vs. Output Current;
VIN = 12V, VOUT = 5V, L = 10µH
14
17
20
Figure 14. Switching Freqency vs. Output Current;
VIN = 12V, VOUT = 3.3V, L = 10µH
250
250
.
.
ILIMIT = low
200
Switching Frequency (kHz)
Switching Frequency (kHz)
11
Input Voltage (V)
Input Voltage (V)
150
100
ILIMIT = high
50
0
200
ILIMIT = low
150
100
ILIMIT = high
50
0
0
100
200
300
400
500
600
0
Output Current (mA)
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100
200
300
400
500
600
Output Current (mA)
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AS1341
Data Sheet - Ty p i c a l O p e r a t i n g C h a r a c t e r i s t i c s
Figure 15. Load Regulation, VOUT vs. IOUT;
VIN = 12V, VOUT = 5V
Figure 16. Load Regulation, VOUT vs. IOUT;
VIN = 12V, VOUT = 3.3V
5.15
3.4
5.05
Output Voltage (V) .
Output Voltage (V) .
5.1
ILIMIT = high
5
ILIMIT = low
4.95
3.35
ILIMIT = high
3.3
ILIMIT = low
3.25
4.9
4.85
3.2
200
300
400
500
600
0
Output Current (mA)
300
ILX
VLX
VOUT
200µs/Div
600
10mA
10µs/Div
ILX
5V/Div
VOUT
10V/Div
50mV/Div
VSHDNN
VLX
VOUT
1A/Div
Figure 20. Startup Waveform;
RLOAD = 100Ω
1A/DIV
Figure 19. LX Waveform;
VIN = 20V, IOUT = 500mA
IL
500
500mA
ILOAD
VIN
15V
10V
2µs/Div
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400
Figure 18. Load Transient Response;
100mV/Div 1A/DIV
ILX
200
Output Current (mA)
Figure 17. Line Transient Response;
IOUT = 500mA
VOUT
100
1A/DIV
100
50mV/DIV 10V/DIV
0
5V
0V
100µs/Div
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AS1341
Data Sheet - D e t a i l e d D e s c r i p t i o n
8 Detailed Description
The AS1341 step-down converter was specifically designed for battery-powered portable devices, including laptop
computers, PDAs, and MP3/DVD/CD players. The advanced current-limited control scheme provides high-efficiency
over a wide range of output loads. The highly-efficient operation (up to 100% duty cycle) allows extremely low dropout
voltage, increasing the usable supply voltage range. In no-load conditions the AS1341 draws only 12µA; in shutdown
mode it draws only 0.8µA to further reduce power consumption and extend battery life.
The AS1341 features an integrated 20V switching MOSFET, internal current sensing, and a high switching frequency,
for minimal PCB space and external component requirements.
Figure 21. Block Diagram
3
+
–
–
+
+ –
POK
RPULL
L1
4
5
LX
8
IN
CIN
AS1341
OUT
+
COUT
1
Q
7
R
FB
SHDNN
+
S
6
ILIMIT
D1
–
Current Limit
Control
Maximum OnTime Delay
–
100mV
+
Minimum OffTime Delay
VSET
1.25V
+
–
+
–
2
GND
Current-Limit Control
The AS1341 uses a proprietary current-limiting control scheme with operation up to 100% duty cycle. The DC-DC converter pulses as needed to maintain regulation, resulting in a variable switching frequency that increases with the load.
This eliminates the high-supply currents associated with conventional constant-frequency pulse-width-modulation
(PWM) controllers that unnecessarily switch the MOSFET.
When the output voltage is too low, the error comparator sets a flip-flop, which turns on the internal P-channel MOSFET and begins a switching cycle. The inductor current ramps up linearly, storing energy in a magnetic field while
charging the output capacitor and servicing the load (see Figure 19 on page 7).
The MOSFET turns off when the peak current limit is reached, or when the maximum on-time of 10µs is exceeded and
the output voltage is in regulation. If the output is out of regulation and the peak current is never reached, the MOSFET
remains on, allowing a duty cycle up to 100%. This feature ensures the lowest possible dropout voltage.
Once the MOSFET turns off, the flip-flop resets, the inductor current is pulled through D1 (see Figure 21), and the current through the inductor ramps back down, transferring the stored energy to the output capacitor and load. The MOSFET remains off until the 0.4µs minimum off-time expires, and the output voltage goes out of regulation.
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AS1341
Data Sheet - D e t a i l e d D e s c r i p t i o n
Dropout Voltage
A buck converter’s minimum input-to-output voltage differential (dropout voltage) determines the lowest usable supply
voltage. In battery-powered systems, this limits the useful end-of-life battery voltage. To maximize battery life, the
AS1341 operates with duty cycles up to 100%, which minimizes the dropout voltage and eliminates switching losses
while in dropout. When the supply voltage approaches the output voltage, the P-channel MOSFET remains on continuously to supply the load.
Note: Dropout voltage is defined as the difference between the input and output voltages when the input is low
enough for the output to drop out of regulation.
For a step-down converter with 100% duty cycle, dropout is related to the MOSFET drain-to-source on-resistance
(RDSON) and inductor series resistance (RINDUCTOR), and thus it is proportional to the load current:
VDROPOUT = IOUT x (RDSON + RINDUCTOR)
(EQ 1)
Shutdown
A logic low on pin SHDNN shuts down the AS1341; a logic high on SHDNN powers on the device.
In shutdown mode the supply current drops to 0.8µA to maximize battery life, and the internal P-channel MOSFET
turns off to isolate the output from the input. The output capacitance and load current determine the output voltage
decay rate.
Note: Pin SHDNN should not be left floating. If the shutdown feature is not used, connect SHDNN to IN.
Power-OK Output
The AS1341 provides a Power OK output (POK) that goes high-impedance when the output reaches 92.5% of its regulation point. POK goes low when the output is below 92.5% of the regulation point and the AS1341 is turned on
(IN ≥ 4.5V and SHDNN ≥ 2.4V). A 12kΩ to 1MΩ pullup resistor between pin POK and pin IN or pin OUT or another voltage (≤ IN) can provide a microprocessor logic control signal.
Note: Connect pin POK to GND when the Power-Ok feature is not used.
Thermal-Overload Protection
Integrated thermal-overload protection limits total power dissipation in the AS1341. During continuous thermal-overload conditions, when the AS1341 junction temperature exceeds TJ = +145ºC, the internal thermal sensor turns off the
pass transistor, allowing the AS1341 to cool down. When the AS1341 junction temperature cools by 10ºC, the thermal
sensor turns the pass transistor on again resulting in a pulsed output.
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AS1341
Data Sheet - A p p l i c a t i o n I n f o r m a t i o n
9 Application Information
Adjusting Output Voltage
The AS1341 feedback input features dual-mode operation. Connect FB to GND for the 5.0V preset output voltage.
Adjust the output voltage by connecting a voltage-divider from the output to GND (Figure 4).
Figure 22. Adjustable Output Voltage Circuit
5
4.5 to
20V
IN
D1
+
COUT
RPULL
SHDNN
6
1.25V
to VIN
LX
7
CIN
L1
4
AS1341
3
POK
1
ILIMIT
R1
FB
2
8
GND
R2
OUT
Indicates High-Power Trace
Select a value for R2 between 10k and 1MΩ.
Calculate R1 as:
V OUT
R 1 = R 2 ⋅ ⎛ -------------- – 1⎞
⎝ V FB
⎠
(EQ 2)
Where:
VFB = 1.25V.
VOUTPUT may range from 1.25V to VIN.
Setting Current Limit
The AS1341 adjustable peak current limit is set by connecting ILIMIT as shown in Table 4.
Table 4. Setting Peak Current Limit
Current Limit
ILIMIT Connected To
700mA
GND
1400mA
IN
The current limit chosen should reflect the maximum load current. The maximum output current is half of the peak current limit. Choosing a lower current limit allows using an inductor with a lower current rating, however, it requires a
higher inductance (see Inductor Selection on page 10) and does not allow for reduced inductor package size.
Inductor Selection
The AS1341 operates with a wide range of inductance values. For most applications, values between 10µH and 47µH
work best with the controller’s high switching frequency. Larger inductor values will reduce the switching frequency and
thereby improve efficiency and EMI.
Note: The four key factors in inductor selection are inductance value, saturation rating, series resistance, and size.
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AS1341
Data Sheet - A p p l i c a t i o n I n f o r m a t i o n
The trade-off for improved efficiency is a higher output ripple and slower transient response. On the other hand, lowvalue inductors respond faster to transients, improve output ripple, offer smaller physical size, and minimize cost. If the
inductor value is too small, the peak inductor current exceeds the current limit due to current-sense comparator propagation delay, potentially exceeding the inductor’s current rating. Calculate the minimum inductance value as follows:
LMIN = ((VINMAX - VOUTPUT) x tONMIN/ILXPEAK
(EQ 3)
Where:
tONMIN = 1µs
The inductor saturation current rating must be greater than the peak switch current limit, plus the overshoot due to the
250ns current-sense comparator propagation delay. Saturation occurs when the magnetic flux density of the inductor
reaches the maximum level the core can support and the inductance starts to fall. Choose an inductor with a saturation
rating greater than IPEAK in the following equation:
IPEAK = (ILXPEAK + (VIN - VOUTPUT) x 250ns)/L
(EQ 4)
Inductor series resistance affects both efficiency and dropout voltage (see Dropout Voltage on page 9). High series
resistance limits the maximum current available at lower input voltages, and increases the dropout voltage. For optimum performance, select an inductor with the lowest possible DC resistance that fits in the allotted dimensions.
Table 5. Recommended Inductors
Part Number
L
DCR
Current Rating
Circuit
MSS6132-103ML
10µH
85mΩ
1.4A
1, 4, 5
LPS4018-472ML
4.7µH
125mΩ
1.8A
2, 5
MSS6132-393ML
39µH
345mΩ
0.8A
3, 5
LPS4018-223ML
22µH
360mΩ
0.7A
4, 5
CDRH6D28NP-150
15µH
62mΩ
1.4A
1, 5
CDRH5D18NP-4R1
4.1µH
57mΩ
1.95A
2, 5
CDRH6D28NP-470
47µH
176mΩ
0.8A
3, 5
CDRH5D18NP-220
22µH
215mΩ
0.8A
4, 5
LQH66SN-100M03
10µH
36mΩ
1.6A
1, 5
LQH55DN-150M03
15µH
150mΩ
1.4A
1, 5
LQH66SN-470M03
47µH
170mΩ
0.8A
3, 5
LQH55DN-470M03
47µH
400mΩ
0.8A
3, 5
Manufacturer
Coilcraft
www.coilcraft.com
Sumida
www.sumida.com
Murata
www.murata.com
Maximum Output Current
The AS1341 output current determines the regulator’s switching frequency. When the converter approaches continuous mode, the output voltage falls out of regulation. For the typical application, the maximum output current is approximately:
ILOADMAX = 1/2 x ILXPEAKMIN
(EQ 5)
For low-input voltages, the maximum on-time may be reached and the load current is limited by:
ILOAD = (1/2 x (VIN - VOUT) x 10µs)/L
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(EQ 6)
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AS1341
Data Sheet - A p p l i c a t i o n I n f o r m a t i o n
Output Capacitor
Choose the output capacitor to service the maximum load current with acceptable voltage ripple. The output ripple has
two components: variations in the charge stored in the output capacitor with each LX pulse, and the voltage drop
across the capacitor’s equivalent series resistance (ESR) caused by the current into and out of the capacitor:
VRIPPLE ≅ VRIPPLEESR + VRIPPLEC
(EQ 7)
The output voltage ripple as a consequence of the ESR and output capacitance is:
VRIPPLEESR = ESR x IPEAK
(EQ 8)
VRIPPLEC = (L x (IPEAK - IOUTPUT)2)/(2 x (COUT x VOUTPUT)) x VIN/(VIN - VOUTPUT)
(EQ 9)
Where:
IPEAK is the peak inductor current (see Inductor Selection on page 10). The worst-case ripple occurs at no-load.
Equations 7, 8, and 9 are suitable for initial capacitor selection, but actual values should be set by testing a prototype
or evaluation circuit. As a general rule, a smaller amount of charge delivered in each pulse results in less output ripple.
Since the amount of charge delivered in each oscillator pulse is determined by the inductor value and input voltage, the
voltage ripple increases with larger inductance, and as the input voltage decreases.
Table 6. Recommended Output Capacitor
Part Number
C
ESR
Rated Voltage
Circuit
T520V107M010ATE018
100µF
18mΩ
10V
1, 2
A700V826M006ATE018
82µF
18mΩ
6.3V
1, 2
T520B107M006ATE040
100µF
40mΩ
6V
1, 2
T520A336M006ATE070
33µF
70mΩ
6.3V
3, 4
A700V226M006ATE028
22µF
28mΩ
6.3V
3, 4
510X107M020ATE040
10µF
40mΩ
20V
5
EEFUD0J101R
100µF
15mΩ
6.3V
1, 2
EEFCD0K330R
33µF
18mΩ
8V
3, 4
10TPB100ML
100µF
55mΩ
10V
1, 2
6TPB47M
47µF
70mΩ
6.3V
3, 4
Manufacturer
Kemet
www.kemet.com
Panasonic
www.panasonic.com
Sanyo
www.edc.sanyo.com
Input Capacitor
The input filter capacitor reduces peak currents drawn from the power source and reduces noise and voltage ripple on
the input caused by the circuit’s switching. The input capacitor must meet the ripple-current requirement (IRMS)
imposed by the switching current defined as:
IRMS = (ILOAD x VOUTPUT)/VIN x
√((4/3) x (VIN - VOUTPUT) - 1)
(EQ 10)
For most applications, non-tantalum type (ceramic, aluminum, polymer, or OS-CON) are preferred due to their robustness to high in-rush currents typical of systems with low-impedance battery inputs. Alternatively, connect two (or more)
smaller value low-ESR capacitors in parallel to reduce cost. Choose an input capacitor that exhibits less than +10ºC
temperature rise at the RMS input current for optimal circuit life.
Table 7. Recommended Input Capacitor
C
10µF
TC Code Rated Voltage
X7R
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25V
Circuit
1-5
Manufacturer
Murata www.murata.com
Taiyo Yuden www.t-yuden.com
Kemet www.kemet.com
Panasonic www.panasonic.com
Sanyo www.edc.sanyo.com
Revision 1.00
12 - 16
AS1341
Data Sheet - A p p l i c a t i o n I n f o r m a t i o n
Diode Selection
The current in the D1 (see Figure 22 on page 10) changes abruptly from zero to its peak value each time the LX switch
turns off. To avoid excessive losses, the diode must have a fast turn-on time and a low forward voltage.
Note: Ensure that the diode peak current rating exceeds the peak current limit set by the current limit (see Setting
Current Limit on page 10), and that its breakdown voltage exceeds VIN. Schottky diodes are recommended.
Stable Operation
A well-designed system and selection of high-quality external components can eliminate excessive noise on pins OUT,
FB, or GND, which can lead to unstable device operation. Instability typically manifests itself as grouped switching
pulses with large gaps and excessive low-frequency output ripple (motorboating) during no-load or light-load conditions.
Recommended Components
Table 8. Recommended Components
Circuit
1
Input
Voltage (V)
Output
Voltage (V)
3
Inductor
High
MSS6132-103ML
LQH66SN-100M03
LQH55DN-150M03
CDRH6D28NP-150
4.5 to 20
1.25 to 5
2
ILIMIT
4.5 to 12
CDRH5D18NP-4R1
LPS4018-472ML
4.5 to 20
MSS6132-393ML
CDRH6D28NP-470
LQH66SN-470M03
LQH55DN-470M03
1.25 to 5
4
4.5 to 12
5
6 to 20
Low
MSS6132-103ML
LPS4018-223ML
CDRH5D18NP-220
5 to VIN
High or Low
See Circuit 1-4
Output Capacitor
T520V107M010ATE018
A700V826M006ATE018
T520B107M006ATE040
EEFUD0J101R
10TPB100ML
EEFCD0K330R
6TPB47M
T520A336M006ATE070
A700V226M006ATE028
510X107M020ATE040
PC Board Layout and Grounding
High switching frequencies and large peak currents make PC board layout an important part of AS1341-based
designs. Good PCB layout can avoid switching noise being introduced into the feedback path, resulting in jitter, instability, or degraded performance.
- High-power traces (see Figure 22 on page 10) should be as short and wide as possible.
- The current loops formed by the external components (CIN, COUT, L1, and D1 see Figure 22 on page 10) should
be as short as possible to avoid radiated noise. Connect the ground pins of these power components at a common node in a star-ground configuration.
- Separate noisy traces, such as the LX node, from the feedback network with grounded copper.
- Keep the extra copper on the PCB and integrate it into a pseudo-ground plane.
- When using external feedback, place the resistors as close to pin FB as possible to minimize noise coupling.
www.austriamicrosystems.com
Revision 1.00
13 - 16
AS1341
Data Sheet - P a c k a g e D r a w i n g s a n d M a r k i n g s
10 Package Drawings and Markings
Figure 23. TDFN-8 3x3mm Package
D2
A
D
D2/2
DETAIL B
B
aaa C 2x
E
E2
E2/2
NX L
P IN 1 INDEX AREA
(D/2 xE /2)
4
NX K
P IN 1 IN DEX AREA
(D /2 xE /2)
aaa
4
C
7
2x
TOP VIEW
e
N N-1
NX b
e
(ND-1) X e
6
5
C A B
bbb
C
ddd
BTM VIEW
Terminal Tip
A3
5
C
A
ccc C
S EATIN G
P LA NE
7
NX
0.08 C
A1
SIDE VIEW
Datum A or B
ODD TERMINAL SIDE
Symbol
A
A1
A3
L1
L2
aaa
bbb
ccc
ddd
eee
ggg
Min
0.70
0.00
Typ
0.75
0.02
0.20 REF
0.03
Max
0.80
0.05
0.15
0.13
0.15
0.10
0.10
0.05
0.08
0.10
Notes
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
Symbol
D BSC
E BSC
D2
E2
L
θ
K
b
e
N
ND
Min
1.60
1.35
0.30
0º
0.20
0.18
Typ
3.00
3.00
0.40
0.25
0.50
8
4
Max
2.50
1.75
0.50
14º
0.30
Notes
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2, 5
1, 2
1, 2, 5
Notes:
1. Dimensioning and tolerancing conform to ASME Y14.5 M-1994.
2. All dimensions are in millimeters; angles in degrees.
3. N is the total number of terminals.
4. The terminal #1 identifier and terminal numbering convention shall conform to JEDEC 95-1, SPP-012. Details of terminal #1 identifier are optional, but must be located within the zone indicated. The terminal #1 identifier may be either
a mold or marked feature.
5. Dimension b applies to metallized terminal and is measured between 0.15mm and 0.30mm from the terminal tip.
6. ND refers to the maximum number of terminals on side D.
7. Figure 23 is shown for illustration only.
8. Unilateral coplanarity zone applies to the exposed heat sink slug as well as the terminals
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Revision 1.00
14 - 16
AS1341
Data Sheet - O r d e r i n g I n f o r m a t i o n
11 Ordering Information
The device is available as the standard products shown in Table 9.
Table 9. Ordering Information
Model
Description
Delivery Form
Package
AS1341-BTDT
20V, 600mA, 100% Duty Cycle, Step-Down Converter
Tape and Reel
TDFN-8 3x3mm
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Revision 1.00
15 - 16
AS1341
Data Sheet
Copyrights
Copyright © 1997-2007, austriamicrosystems AG, Schloss Premstaetten, 8141 Unterpremstaetten, Austria-Europe.
Trademarks Registered ®. All rights reserved. The material herein may not be reproduced, adapted, merged, translated, stored, or used without the prior written consent of the copyright owner.
All products and companies mentioned are trademarks or registered trademarks of their respective companies.
Disclaimer
Devices sold by austriamicrosystems AG are covered by the warranty and patent indemnification provisions appearing
in its Term of Sale. austriamicrosystems AG makes no warranty, express, statutory, implied, or by description regarding
the information set forth herein or regarding the freedom of the described devices from patent infringement. austriamicrosystems AG reserves the right to change specifications and prices at any time and without notice. Therefore, prior
to designing this product into a system, it is necessary to check with austriamicrosystems AG for current information.
This product is intended for use in normal commercial applications. Applications requiring extended temperature
range, unusual environmental requirements, or high reliability applications, such as military, medical life-support or lifesustaining equipment are specifically not recommended without additional processing by austriamicrosystems AG for
each application. For shipments of less than 100 parts the manufacturing flow might show deviations from the standard
production flow, such as test flow or test location.
The information furnished here by austriamicrosystems AG is believed to be correct and accurate. However,
austriamicrosystems AG shall not be liable to recipient or any third party for any damages, including but not limited to
personal injury, property damage, loss of profits, loss of use, interruption of business or indirect, special, incidental or
consequential damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical data herein. No obligation or liability to recipient or any third party shall arise or flow out of
austriamicrosystems AG rendering of technical or other services.
Contact Information
Headquarters
austriamicrosystems AG
A-8141 Schloss Premstaetten, Austria
Tel: +43 (0) 3136 500 0
Fax: +43 (0) 3136 525 01
For Sales Offices, Distributors and Representatives, please visit:
http://www.austriamicrosystems.com/contact
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Revision 1.00
16 - 16