www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 1 - 18
AS1341
650mA, Ultra low Ri pple S tep Do w n DC/DC Converter
1 General Description
The AS1341 is a high-efficiency step-down converter with adjustable
output voltages from 1.25V to V
IN
using supply voltages of up to
20V.
An integrated current-limited 0.4Ω MOSFET delivers load currents
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.
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.
Figure 1. AS1341 - Typical Application
2 Key Features
Output Voltages: Fixed 5V or Adjustable
Input Voltage Range: 4.5V to 20V
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
3 Applications
The device is ideal for notebook computers, distributed power
systems, keep-alive supplies, and any other battery-operated,
portable device.
V
IN
4.5V to 20V 5
IN
1
FB
CIN
V
OUT
= 5V
AS1341
2
GND
8
OUT
D1
COUT +
Indicates High-Power Trace
3
POK
R
PULL
7
SHDNN
6
ILIMIT
4
LX
L1
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 2 - 18
AS1341
Datasheet - Pin A s s ig n m e n t s
4 Pin Assignments
Figure 2. Pin Assignments (Top View)
4.1 Pin Descriptions
Table 1. Pin Descriptions
Pin Number Pin Name Description
1 FB Feedback Input. For the fixed 5V output connect this pin to GND. For adjustable output, connect to a
resistive divider between V
OUT
and GND to set the output voltage between 1.25V and V
IN
.
2 GND Ground
3 POK Power OK. Active-low open-drain reset output.
Note: Connect pin POK to GND when the Power-Ok feature is not used.
4 LX Inductor Connection. Connect this pin to an external inductor.
5 IN 4.5V to 20V Input Supply Voltage
6 ILIMIT Peak Current Control Input. Connect this pin to IN or GND to set peak current limit (see Setting
Current Limit on page 11).
7 SHDNN 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.
8 OUT Regulated Output Voltage High-Impedance Sense Input. For the fixed 5V output connect this pin to
V
OUT
. For adjustable output connect this pin to GND.
9 NC Exposed Pad. This pad is not connected internally. Connect to GND or do not connect.
5IN
3POK
2GND
1FB 8 OUT
AS1341
4
LX
7 SHDNN
6 ILIMIT
9
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 3 - 18
AS1341
Datasheet - Abs o l u t e M a x i m u m R at 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 Comments
Electrical Parameters
IN to GND -0.3 +23 V
LX to GND -2 V
IN
+ 0.3 V
FB to GND -0.3 +5 V
ILIMIT, SHDNN, OUT, POK to GND -0.3 V
IN
+ 0.3 V
Peak Input Current 2 A
Temperature Ranges and Storage Conditions
Thermal Resistance Θ
JA
36.3 ºC/W on PCB
Storage Temperature Range -55 +150 ºC
Junction Temperature +150 ºC
Package Body Temperature +260 ºC
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).
Humidity non-condensing 5 85 %
Moisture Sensitive Level 1 Represents a max. floor life time of unlimited
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 4 - 18
AS1341
Datasheet - Ele c t r i ca l C h a ra c t e ris t i c s
6 Electrical Characteristics
V
IN
= +12V, SHDNN = V
IN
, Typical values are at T
AMB
= +25ºC (unless otherwise specified). Specifications based on circuit shown in Figure 1
on page 1.
Note: All limits are guaranteed. The parameters with min and max values are guaranteed with production tests or SQC (Statistical Quality
Control) methods.
Table 3. Electrical Characteristics
Symbol Parameter Conditions Min Typ Max Units
T
AMB
Operating Temperature Range -45 85 °C
V
IN
Input Voltage Range 4.5 20 V
V
OUT
Output Voltage (Preset Output) FB = GND 4.85 5.00 5.15 V
Output Voltage (Adjustable) 1.25 V
IN
V
DROPOUT
Dropout Voltage I
OUT
= 600mA, ILIMIT = V
IN
250 mV
Line Regulation V
IN
= 6V to 20V, 200Ω load 0.1 %/V
Load Regulation ILIMIT = V
IN
, I
OUT
= 0 to 500mA 1 %
V
FB
Feedback Set Voltage (Adjustable
Output) 1.212 1.25 1.288 V
I
IN
Input Supply Current No load 12 18 µA
I
INDROP
Input Supply Current in Dropout No load 45 60 µA
Input Shutdown Current SHDNN = GND 0.8 3 µA
V
UVLO
Input Undervoltage Lockout
Threshold
V
IN
rising 3.6 4.0 4.4 V
V
IN
falling 3.5 3.9 4.3
OUT Bias Current V
OUT
= 5.5V 2 3.5 5 µA
I
FB
FB Bias Current V
FB
= 1.3V -25 +25 nA
FB Threshold Low 50 100 150 mV
Thermal Shutdown 10ºC hysteresis 145 ºC
DC-DC Switches
t
OFFMIN
LX Switch Minimum Off-Time 0.2 0.4 0.6 µs
t
ONMAX
LX Switch Maximum On-Time V
FB
= 1.3V 8 10 12 µs
R
LX
LX Switch On-Resistance V
IN
= 6V 0.4 Ω
V
IN
= 4.5V 0.5
I
LXPEAK
LX Current Limit ILIMIT = GND, L = 39µH 500 700 900 mA
ILIMIT = IN, L = 10µH 1000 1400 1800
LX Zero-Crossing Threshold -75 +75 mV
Zero-Crossing Timeout LX does not rise above the threshold 30 µs
LX Switch Leakage Current V
IN
= 20V, LX = GND, T
AMB
= +25ºC 0.1 µA
V
IN
= 20V, LX = GND 1
Control Inputs
Digital Input Level SHDNN, ILIMIT = GND 0.8 V
SHDNN, ILIMIT = IN 2.4
Digital Input Leakage Current V
SHDNN
, V
ILIMIT
= 0 to 20V, V
IN
= 20V -100 +100 nA
Power-OK
Power-OK Threshold Falling edge, relative to V
OUT
90 92.5 95 %
POK Output Voltage Low I
POK
= 1mA 0.4 V
POK Output Leakage Current V
IN
, V
POK
= 16V, T
AMB
= 25°C 0.1 µA
V
IN
, V
POK
= 16V 1
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 5 - 18
AS1341
Datasheet - Ty p ica l O per a t i n g C h a r a c t e r isti c s
7 Typical Operating Characteristics
V
OUT
= 5V, T
AMB
= +25ºC (unless otherwise specified).
Figure 3. Efficiency vs. I
OUT
Figure 4. Efficiency vs. I
OUT
50
55
60
65
70
75
80
85
90
95
100
0.1 1 10 100 1000
Output Current (mA)
Efficiency (%) .
V
IN
= 20V
V
IN
= 12V
V
IN
= 6V
ILIMIT = high
50
55
60
65
70
75
80
85
90
95
100
0.1 1 10 100 1000
Output Current (mA)
Efficiency (%) .
V
IN
= 20V
V
IN
= 12V
V
IN
= 6V
ILIMIT = low
Figure 5. Efficiency vs. I
OUT
; V
OUT
= 3.3V Figure 6. Efficiency vs. I
OUT
; V
OUT
= 3.3V
50
55
60
65
70
75
80
85
90
95
100
0.1 1 10 100 1000
Output Current (mA)
Efficiency (%) .
V
IN
= 20V
V
IN
= 12V
V
IN
= 4.5V
ILIMIT = high
50
55
60
65
70
75
80
85
90
95
100
0.1 1 10 100 1000
Output Current (mA)
Efficiency (%) .
V
IN
= 20V
V
IN
= 12V
V
IN
= 4.5V
ILIMIT = low
Figure 7. Efficiency vs. I
OUT
; V
IN
= 12V Figure 8. Efficiency vs. I
OUT
; V
IN
= 12V
65
70
75
80
85
90
95
0.1 1 10 100 1000
Output Current (mA)
Efficiency (%) .
22uH
10uH
4.1uH
ILIMIT = high
65
70
75
80
85
90
95
0.1 1 10 100 1000
Output Current (mA)
Efficiency (%) .
10uH
39uH
22uH
ILIMIT = low
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 6 - 18
AS1341
Datasheet - Ty p i ca l O p e r a t in g Ch ar a c t e r is t i c s
Figure 9. Efficiency vs. Input Voltage Figure 10. Output Voltage vs. Input Voltage
70
75
80
85
90
95
100
5 8 11 14 17 20
Input Voltage (V)
Efficiency (%) .
VOUT=3.3V, IOUT=500mA
VOUT=5V, IOUT=500mA
VOUT=3.3V, IOUT=250mA
VOUT=5V, IOUT=250mA
4.85
4.9
4.95
5
5.05
5.1
5.15
5 8 11 14 17 20
Input Voltage (V)
V
OUT
(V) .
IOUT = 1mA
IOUT = 100mA
IOUT = 300mA
IOUT = 500mA
IOUT = 600mA
Figure 11. Output Voltage vs. Input Voltage;
V
OUT
= 3.3V
Figure 12. Peak Switch Current vs. Input Voltage;
V
OUT
= 3.3V
3.2
3.25
3.3
3.35
3.4
4 6 8 10 12 14 16 18 20
Input Voltage (V)
V
OUT
(V) .
IOUT = 1mA
IOUT = 100mA
IOUT = 300mA
IOUT = 500mA
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
5 8 11 14 17 20
Input Voltage (V)
Peak Switch Current (A) .
ILIMIT = high
L=10µH
ILIMIT = high
L=39µH
ILIMIT = low
L=10µH
ILIMIT = low
L=39µH
Figure 13. Switching Frequency vs. Output Current;
V
IN
= 12V, V
OUT
= 5V, L = 10µH
Figure 14. Switching Frequency vs. Output Current;
V
IN
= 12V, V
OUT
= 3.3V, L = 10µH
0
50
100
150
200
250
0 100 200 300 400 500 600
Output Current (mA)
Switching Frequency (kHz) .
ILIMIT = high
ILIMIT = low
0
50
100
150
200
250
0 100 200 300 400 500 600
Output Current (mA)
Switching Frequency (kHz) .
ILIMIT = high
ILIMIT = low
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 7 - 18
AS1341
Datasheet - Ty p i ca l O p e r a t in g Ch ar a c t e r is t i c s
Figure 15. Load Regulation, V
OUT
vs. I
OUT
;
V
IN
= 12V, V
OUT
= 5V
Figure 16. Load Regulation, V
OUT
vs. I
OUT
;
V
IN
= 12V, V
OUT
= 3.3V
4.85
4.9
4.95
5
5.05
5.1
5.15
0 100 200 300 400 500 600
Output Current (mA)
Output Voltage (V) .
ILIMIT = high
ILIMIT = low
ILIMIT = high
ILIMIT = low
3.2
3.25
3.3
3.35
3.4
0 100 200 300 400 500 600
Output Current (mA)
Output Voltage (V) .
ILIMIT = high
ILIMIT = low
Figure 17. Line Transient Response; I
OUT
= 500mA Figure 18. Load Transient Response
200µs/Div
VIN VOUT ILX
10V
15V
1A/Div
100mV/Div
10µs/Div
VLX ILX
VOUTILOAD
50mV/Div
10mA
500mA
1A/Div10V/Div
Figure 19. LX Waveform; V
IN
= 20V, I
OUT
= 500mA Figure 20. Startup Waveform; R
LOAD
= 100Ω
2µs/Div
50mV/Div
VLX IL
VOUT
10V/Div 1A/Div
100µs/Div
1A/Div
ILX
VSHDNN VOUT
5V/Div
0V
5V
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 8 - 18
AS1341
Datasheet - D e t a il e d D e s cr i p t io 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
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.
AS1341
4
LX
8
OUT
5
IN
1
FB
6
ILIMIT
Current Limit
Control
2
GND
+–
Maximum On-
Time Delay
Q R
S
Minimum Off-Time
Delay
+
–
+
–
100mV
VSET
1.25V
+
–
+
–
+
–
+
–L1
CIN
COUT +
D1
R
PULL
3
POK
7
SHDNN
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 9 - 18
AS1341
Datasheet - D e t a il e d D e s cr i p t io n
8.2 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 (R
DSON
) and inductor series
resistance (R
INDUCTOR
), and thus it is proportional to the load current:
V
DROPOUT
= I
OUT
x (R
DSON
+ R
INDUCTOR
) (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 T
J
= +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.
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 10 - 18
AS1341
Datasheet - A p p lic a t i o n I n for m a ti on
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
Select a value for R
2
between 10k and 1MΩ.
Calculate R
1
as:
(EQ 2)
Where:
V
FB
= 1.25V.
V
OUT
may range from 1.25V to V
IN
.
9.2 Negative Output Voltage
V
IN
may range from 4.5V to (20V-V
OUT
). Therefore the maximum negative output voltage is -15V.
Figure 23. Adjustable Negative Output Voltage Circuit
V
IN
4.5V to 20V 5
IN
7
SHDNN
8
OUT
CIN
1.25V to VIN
2
GND
6
ILIMIT 1
FB
D1
COUT
+
R2
R1
Indicates High-Power Trace
AS1341
3
POK
R
PULL
4
LX
L1
R
1
R
2
V
OUT
V
FB
------------- 1–
⋅=
V
IN
4.5V to (20V-V
OUT)
5
IN
7
SHDNN
4
LX
8
OUT
CIN
V
OUT
= -1.25V to -15V
2
GND
6
ILIMIT
1
FB
D1
L1
R2
R1
Indicates High-Power Trace
AS1341
3
POK
COUT
+
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 11 - 18
AS1341
Datasheet - A p p lic a t i o n I n for m a ti on
9.3 Setting Current Limit
The AS1341 adjustable peak current limit is set by connecting ILIMIT as shown in Table 4.
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:
L
MIN
= ((V
INMAX
- V
OUTPUT
) x t
ONMIN
/I
LXPEAK
(EQ 3)
Where:
t
ONMIN
= 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:
I
PEAK
= (I
LXPEAK
+ (V
IN
- V
OUTPUT
) 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 4. Setting Peak Current Limit
Current Limit ILIMIT Connected To
700mA GND
1400mA IN
Table 5. Recommended Inductors
Part Number L DCR Current Rating Manufacturer
MSS6132-103ML 10µH 85mΩ1.4A Coilcraft
www.coilcraft.com
LPS4018-472ML 4.7µH 125mΩ1.8A
MSS6132-393ML 39µH 345mΩ0.8A
LPS4018-223ML 22µH 360mΩ0.7A
CDRH6D28NP-150 15µH 62mΩ1.4A Sumida
www.sumida.com
CDRH5D18NP-4R1 4.1µH 57mΩ1.95A
CDRH6D28NP-470 47µH 176mΩ0.8A
CDRH5D18NP-220 22µH 215mΩ0.8A
LQH66SN-100M03 10µH 36mΩ1.6A Murata
www.murata.com
LQH55DN-150M03 15µH 150mΩ1.4A
LQH66SN-470M03 47µH 170mΩ0.8A
LQH55DN-470M03 47µH 400mΩ0.8A
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 12 - 18
AS1341
Datasheet - A p p lic a t i o n I n for m a ti on
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:
I
LOADMAX
= 1/2 x I
LXPEAKMIN
(EQ 5)
For low-input voltages, the maximum on-time may be reached and the load current is limited by:
I
LOAD
= (1/2 x (V
IN
- V
OUT
) 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:
V
RIPPLE
≅ V
RIPPLEESR
+ V
RIPPLEC
(EQ 7)
The output voltage ripple as a consequence of the ESR and output capacitance is:
V
RIPPLEESR
= ESR x I
PEAK
(EQ 8)
V
RIPPLEC
= (L x (I
PEAK
- I
OUTPUT
)2)/(2 x (C
OUT
x V
OUTPUT
)) x V
IN
/(V
IN
- V
OUTPUT
) (EQ 9)
Where:
I
PEAK
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 Manufacturer
T520V107M010ATE018 100µF 18mΩ10V Kemet
www.kemet.com
A700V826M006ATE018 82µF 18mΩ6.3V
T520B107M006ATE040 100µF 40mΩ6V
T520A336M006ATE070 33µF 70mΩ6.3V
A700V226M006ATE028 22µF 28mΩ6.3V
510X107M020ATE040 10µF 40mΩ20V
EEFUD0J101R 100µF 15mΩ6.3V Panasonic
www.panasonic.com
EEFCD0K330R 33µF 18mΩ8V
10TPB100ML 100µF 55mΩ10V Sanyo
www.edc.sanyo.com
6TPB47M 47µF 70mΩ6.3V
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 13 - 18
AS1341
Datasheet - A p p lic a t i o n I n for m a ti on
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 (I
RMS
) imposed by the switching current defined as:
I
RMS
= (I
LOAD
x V
OUTPUT
)/V
IN
x
√
((4/3) x (V
IN
- V
OUTPUT
) - 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.
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 V
IN
. 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 7. Recommended Input Capacitor
C TC Code Rated Voltage Manufacturer
10µF X7R 25V
Murata www.murata.com
Taiyo Yuden www.t-yuden.com
Kemet www.kemet.com
Panasonic www.panasonic.com
Sanyo www.edc.sanyo.com
Table 8. Recommended Components
Input Voltage Output Voltage ILIMIT Inductor Output Capacitor
4.5V to 20V
1.25V to 5V High
MSS6132-103ML
LQH66SN-100M03
LQH55DN-150M03
CDRH6D28NP-150
T520V107M010ATE018
A700V826M006ATE018
T520B107M006ATE040
EEFUD0J101R
10TPB100ML
4.5v to 12V CDRH5D18NP-4R1
LPS4018-472ML
4.5V to 20V
1.25V to 5V Low
MSS6132-393ML
CDRH6D28NP-470
LQH66SN-470M03
LQH55DN-470M03
EEFCD0K330R
6TPB47M
T520A336M006ATE070
A700V226M006ATE028
4.5V to 12V
MSS6132-103ML
LPS4018-223ML
CDRH5D18NP-220
6V to 20V 5V to V
IN
High or Low See Inductors above 510X107M020ATE040
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 14 - 18
AS1341
Datasheet - A p p lic a t i o n I n for m a ti on
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 (C
IN
, C
OUT
, 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.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 17 - 18
AS1341
Datasheet - O r d er ing I n fo rma t i o n
11 Ordering Information
The device is available as the standard products shown in Table 9.
Note: All products are RoHS compliant and ams green.
Buy our products or get free samples online at ICdirect: http://www.ams.com/ICdirect
Technical Support is found at http://www.ams.com/Technical-Support
For further information and requests, please contact us mailto:sales@ams.com
or find your local distributor at http://www.ams.com/distributor
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
www.ams.com/DC-DC_Step-Up/AS1341 Revision 1.09 18 - 18
AS1341
Datasheet
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