Datasheet

A S1 3 4 1
6 50 m A , U lt r a lo w Ri p p le S te p Do w n D C/ DC Co n v e r te 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
An integrated current-limited 0.4Ω MOSFET delivers load currents
up to 600mA.
Output Current: Up to 600mA
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.
Input Voltage Range: 4.5V to 20V
1.25V Lowest Output Voltage
Efficiency: up to 96%
The AS1341 has a low quiescent current (12µA) to improve lightload efficiency and minimize battery use, and draws only 0.8µA in
shutdown mode.
Quiescent Supply Current: 12µA
High switching frequencies (up to 200kHz) allow the use of small
surface-mount inductors and output capacitors.
Internal 0.4Ω P-Channel MOSFET
Power-OK Output
Shutdown Current: 0.8µA
The device is available in a TDFN-8 3x3mm pin package.
100% Maximum Duty Cycle for Low Dropout
Current-Limited Architecture
Thermal Shutdown
TDFN-8 3x3mm 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. AS1341 - Typical Application
VIN
4.5V to 20V
CIN
5
4
IN
LX
L1
VOUT = 5V
D1
7
COUT
+
SHDNN
6
AS1341
ILIMIT
8
OUT
RPULL
3
POK
1
2
GND
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FB
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Indicates High-Power Trace
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AS1341
Datasheet - P i n A s s i g n m e n t s
4 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
4.1 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 this pin to GND. For adjustable output, connect to a
resistive divider between VOUT 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.
4.5V 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 11).
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. For the fixed 5V output connect this pin to
VOUT. For adjustable output connect this pin to GND.
Exposed Pad. This pad is not connected internally. Connect to GND or do not connect.
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AS1341
Datasheet - 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
ILIMIT, SHDNN, OUT, POK to GND
-0.3
VIN
+ 0.3
V
2
A
36.3
ºC/W
+150
ºC
+150
ºC
Comments
Electrical Parameters
Peak Input Current
Temperature Ranges and Storage Conditions
Thermal Resistance ΘJA
Storage Temperature Range
-55
Junction Temperature
Package Body Temperature
Humidity non-condensing
Moisture Sensitive Level
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5
+260
ºC
85
%
1
on PCB
The reflow peak soldering temperature (body
temperature) specified is in accordance with IPC/
JEDEC J-STD-020 “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).
Represents a max. floor life time of unlimited
Revision 1.09
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AS1341
Datasheet - 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
VIN = +12V, SHDNN = VIN, 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
Max
Units
TAMB
Operating Temperature Range
-45
85
°C
VIN
Input Voltage Range
4.5
20
V
Output Voltage (Preset Output)
VOUT
Conditions
FB = GND
Output Voltage (Adjustable)
VDROPOUT
Dropout Voltage
5.00
5.15
VIN
V
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)
IIN
Input Supply Current
IINDROP
Input Supply Current in Dropout
Input Shutdown Current
Input Undervoltage Lockout
Threshold
VIN rising
IFB
4.85
Typ
1.25
VFB
VUVLO
Min
1.212
1.25
1.288
V
12
18
µA
No load
45
60
µA
SHDNN = GND
0.8
3
µA
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
No load
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
VIN = 4.5V
0.5
Ω
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
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
0.8
SHDNN, ILIMIT = IN
2.4
Digital Input Leakage Current
VSHDNN, VILIMIT = 0 to 20V, VIN = 20V
-100
Power-OK Threshold
Falling edge, relative to VOUT
90
POK Output Voltage Low
V
+100
nA
95
%
IPOK = 1mA
0.4
V
VIN, VPOK = 16V, TAMB = 25°C
0.1
VIN, VPOK = 16V
1
Power-OK
POK Output Leakage Current
92.5
µA
Note: All limits are guaranteed. The parameters with min and max values are guaranteed with production tests or SQC (Statistical Quality
Control) methods.
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AS1341
Datasheet - 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
VOUT = 5V, TAMB = +25ºC (unless otherwise specified).
Figure 4. Efficiency vs. IOUT
Figure 3. Efficiency vs. IOUT
100
100
ILIMIT = high
95
85
VIN = 20V
80
VIN = 6V
VIN = 12V
90
VIN = 12V
Efficiency (%) .
Efficiency (%) .
90
ILIMIT = low
95
VIN = 6V
75
70
65
85
75
70
65
60
60
55
55
50
VIN = 20V
80
50
0.1
1
10
100
1000
0.1
1
Output Current (mA)
Figure 5. Efficiency vs. IOUT; VOUT = 3.3V
100
ILIMIT = high
95
95
90
90
VIN = 4.5V
85
80
VIN = 20V
75
VIN = 12V
70
65
ILIMIT = low
VIN = 4.5V
VIN = 12V
80
VIN = 20V
75
70
65
60
55
55
50
50
0.1
1
10
100
0.1
1000
1
10
100
1000
Output Current (mA)
Output Current (mA)
Figure 7. Efficiency vs. IOUT; VIN = 12V
Figure 8. Efficiency vs. IOUT; VIN = 12V
95
ILIMIT = high
90
ILIMIT = low
90
Efficiency (%) .
Efficiency (%) .
1000
85
60
95
100
Figure 6. Efficiency vs. IOUT; VOUT = 3.3V
Efficiency (%) .
Efficiency (%) .
100
10
Output Current (mA)
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
Datasheet - 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
Figure 10. Output Voltage vs. Input Voltage
100
5.15
IOUT = 1mA
IOUT = 100mA
95
IOUT = 300mA
5.1
IOUT = 500mA
Efficiency (%) .
IOUT = 600mA
90
VOUT (V) .
5.05
85
80
5
4.95
VOUT=3.3V, IOUT=500mA
75
4.9
VOUT=5V, IOUT=500mA
VOUT=3.3V, IOUT=250mA
VOUT=5V, IOUT=250mA
70
4.85
5
8
11
14
17
20
5
8
Input Voltage (V)
11
14
17
20
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 Frequency vs. Output Current;
VIN = 12V, VOUT = 5V, L = 10µH
14
17
20
Figure 14. Switching Frequency 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
Datasheet - 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
ILIMIT
= high
3.3
ILIMIT = low
ILIMIT = low
3.25
4.9
4.85
3.2
200
300
400
500
600
0
Output Current (mA)
300
500
600
10V/Div
50mV/Div
ILX
VLX
VOUT
100mV/Div
500mA
ILOAD
1A/Div
VOUT
15V
10V
200µs/Div
10mA
10µs/Div
10V/Div
50mV/Div
VSHDNN
5V/Div
VOUT
VLX
VOUT
ILX
Figure 20. Startup Waveform; RLOAD = 100Ω
1A/Div
Figure 19. LX Waveform; VIN = 20V, IOUT = 500mA
2µs/Div
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400
Figure 18. Load Transient Response
VIN
ILX
200
Output Current (mA)
Figure 17. Line Transient Response; IOUT = 500mA
IL
100
1A/Div
100
1A/Div
0
5V
0V
100µs/Div
Revision 1.09
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AS1341
Datasheet - 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. AS1341 - Block Diagram - 5V fixed Output Voltage
3
+
+
–
–
+
POK
–
RPULL
L1
5
4
IN
LX
8
CIN
AS1341
OUT
COUT
+
1
Q
7
R
FB
SHDNN
+
S
6
ILIMIT
D1
–
Current Limit
Control
Maximum OnTime Delay
Minimum Off-Time
Delay
–
100mV
+
VSET
1.25V
+
–
+
–
2
GND
8.1 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
Datasheet - D e t a i l e d D e s c r i p t i o n
8.2 Dropout Voltage
A buck converter’s minimum input-to-output voltage differential (dropout voltage) determines the lowest usable supply voltage. In batterypowered 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)
8.3 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.
8.4 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.
8.5 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
Datasheet - 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
9.1 Adjusting Output Voltage
The AS1341 feedback input features dual-mode operation. Connect FB to GND for the 5.0V preset output voltage (see Figure 21 on page 8).
Adjust the output voltage by connecting a voltage-divider from the output to GND (see Figure 22).
Figure 22. Adjustable Output Voltage Circuit
VIN
4.5V to 20V
5
4
IN
LX
1.25V to VIN
D1
7
CIN
L1
+
RPULL
SHDNN
AS1341
6
COUT
3
R1
POK
1
ILIMIT
FB
2
R2
8
GND
OUT
Indicates High-Power Trace
Select a value for R2 between 10k and 1MΩ.
Calculate R1 as:
VOUT
R 1 = R 2 ⋅  ------------- – 1
VFB
(EQ 2)
Where:
VFB = 1.25V.
VOUT may range from 1.25V to VIN.
9.2 Negative Output Voltage
VIN may range from 4.5V to (20V-VOUT). Therefore the maximum negative output voltage is -15V.
Figure 23. Adjustable Negative Output Voltage Circuit
VIN
4.5V to (20V-VOUT)
5
4
IN
LX
7
3
SHDNN
6
CIN
ILIMIT
2
GND
AS1341
POK
L1
D1
R1
1
+
FB
8
COUT
R2
OUT
VOUT = -1.25V to -15V
Indicates High-Power Trace
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AS1341
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
9.3 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) and does not
allow for reduced inductor package size.
9.4 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.
The trade-off for improved efficiency is a higher output ripple and slower transient response. On the other hand, low-value 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
MSS6132-103ML
10µH
85mΩ
1.4A
LPS4018-472ML
4.7µH
125mΩ
1.8A
MSS6132-393ML
39µH
345mΩ
0.8A
LPS4018-223ML
22µH
360mΩ
0.7A
CDRH6D28NP-150
15µH
62mΩ
1.4A
CDRH5D18NP-4R1
4.1µH
57mΩ
1.95A
CDRH6D28NP-470
47µH
176mΩ
0.8A
CDRH5D18NP-220
22µH
215mΩ
0.8A
LQH66SN-100M03
10µH
36mΩ
1.6A
LQH55DN-150M03
15µH
150mΩ
1.4A
LQH66SN-470M03
47µH
170mΩ
0.8A
LQH55DN-470M03
47µH
400mΩ
0.8A
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Revision 1.09
Manufacturer
Coilcraft
www.coilcraft.com
Sumida
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Murata
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AS1341
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
9.5 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
(EQ 6)
9.6 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 11). The worst-case ripple occurs at no-load.
Equations EQ 7, EQ 8, and EQ 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
T520V107M010ATE018
100µF
18mΩ
10V
A700V826M006ATE018
82µF
18mΩ
6.3V
T520B107M006ATE040
100µF
40mΩ
6V
T520A336M006ATE070
33µF
70mΩ
6.3V
A700V226M006ATE028
22µF
28mΩ
6.3V
510X107M020ATE040
10µF
40mΩ
20V
EEFUD0J101R
100µF
15mΩ
6.3V
EEFCD0K330R
33µF
18mΩ
8V
10TPB100ML
100µF
55mΩ
10V
6TPB47M
47µF
70mΩ
6.3V
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Manufacturer
Kemet
www.kemet.com
Panasonic
www.panasonic.com
Sanyo
www.edc.sanyo.com
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AS1341
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
9.7 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
TC Code
10µF
X7R
Rated Voltage
25V
Manufacturer
Murata www.murata.com
Taiyo Yuden www.t-yuden.com
Kemet www.kemet.com
Panasonic www.panasonic.com
Sanyo www.edc.sanyo.com
9.8 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 11),
and that its breakdown voltage exceeds VIN. Schottky diodes are recommended.
9.9 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.
9.10 Recommended Components
Table 8. Recommended Components
Input Voltage
Output Voltage
ILIMIT
Inductor
High
MSS6132-103ML
LQH66SN-100M03
LQH55DN-150M03
CDRH6D28NP-150
4.5V to 20V
1.25V to 5V
4.5v to 12V
CDRH5D18NP-4R1
LPS4018-472ML
4.5V to 20V
MSS6132-393ML
CDRH6D28NP-470
LQH66SN-470M03
LQH55DN-470M03
1.25V to 5V
Low
MSS6132-103ML
LPS4018-223ML
CDRH5D18NP-220
4.5V to 12V
6V to 20V
5V to VIN
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High or Low
See Inductors above
Revision 1.09
Output Capacitor
T520V107M010ATE018
A700V826M006ATE018
T520B107M006ATE040
EEFUD0J101R
10TPB100ML
EEFCD0K330R
6TPB47M
T520A336M006ATE070
A700V226M006ATE028
510X107M020ATE040
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AS1341
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
9.11 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.
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AS1341
Datasheet - 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 24. TDFN-8 3x3mm Marking
AS1341
XXXX
xxx - encoded Datecode
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Revision 1.09
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AS1341
Datasheet - 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
Figure 25. TDFN-8 3x3mm Package
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Revision 1.09
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AS1341
Datasheet - 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
Ordering Code
Marking
Description
Delivery Form
Package
AS1341-BTDT-1k
1341
20V, 600mA, 100% Duty Cycle, Step-Down Converter
Tape and Reel
1000 pcs
TDFN-8 3x3mm
AS1341-BTDT-6k
1341
20V, 600mA, 100% Duty Cycle, Step-Down Converter
Tape and Reel
6000 pcs
TDFN-8 3x3mm
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AS1341
Datasheet
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