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AS1346-49
Dual Step-Down Converter with Battery Monitoring
1 General Description
The AS1346, AS1347, AS1348, AS1349 family is a high-efficiency,
constant-frequency dual buck converter available with fixed voltage
versions. The device provides two independent DC/DC Converters
with output currents between 0.5A and 1.2A. The wide input voltage
range (2.7V to 5.5V), automatic powersave mode and minimal
external component requirements make the AS134x family perfect
for SSD and many other battery-powered applications.
In shutdown mode the typical supply current decreases to ≤1μA.
The highly efficient duty cycle (100%) provides low dropout
operation, prolonging battery life in portable systems.
An internal synchronous switching scheme increases efficiency and
eliminates the need for an external Schottky diode. The fixed
switching frequency (2.0MHz) allows the use of small surface mount
inductors.
The integrated monitoring function can be configured that either the
output voltage (Power Okay function ) or the input voltage (Battery
Monitoring Function) can be supervised.
The AS1346-49 is available in a 12-Pin TDFN 3x3mm package.
2 Key Features
High Efficiency: Up to 95%
Output Current: see Table 1
Input Voltage Range: 2.7V to 5.5V
Output Voltage Range: 1.2V to 3.6V (available in 100mV steps)
Constant Frequency Operation: 2.0MHz
180º Out of Phase Operation
Low Battery Detection
Low Dropout Operation: 100% Duty Cycle
Shutdown Mode Supply Current: 1μA
No Schottky Diode Required
Output Disconnect in Shutdown
Non standard variants available within two weeks
12-Pin TDFN 3x3mm Package
3 Applications
The device is ideal for SSD applications, mobile communication
devices, laptops and PDAs, ultra-low-power systems, threshold
detectors/discriminators, telemetry and remote systems, medical
instruments, or any other space-limited application with low power-
consumption requirements.
Table 1. Available Products
Devices IOUT1 IOUT2
AS1346 1.2A 0.5A
AS1347 0.5A 0.5A
AS1348 0.5A 0.95A
AS1349 1.2A 1.2A
AS1346
COUT1
CIN
VIN
2.7V to 5.5V
VOUT1
3.3V 1200mA
Figure 1. AS1346 - Typical Application Diagram with POK Function
SW1
COUT2
VOUT2
1.8V 500mA
FB1
FB2
SW2
AGND
EN2
PVIN
VDD
EN1
LBO
LBI
L1 = 3.3μH
POK Function
L2 = 3.3μH
PVIN
PGND
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AS1346-49
Datasheet - Pin Assignments
4 Pin Assignments
Figure 2. Pin Assignments (Top View)
4.1 Pin Descriptions
Table 2. Pin Descriptions
Pin Number Pin Name Description
1 SW1 Switch Node1 Connection to Inductor. This pin connects to the drains of the internal main and
synchronous power MOSFET switches.
2, 11 PVIN Power Supply Connector. This pin must be closely decoupled to PGND with a 4.7μF ceramic
capacitor.
3 EN1
Enable1 Input. Driving this pin above 1.2V enables VOUT1. Driving this pin below 0.5V puts the device in
shutdown mode. In shutdown mode all functions are disabled, drawing 1μA supply current.
This pin should not be left floating.
4FB1 Feedback Pin 1. Feedback input to the error amplifier, connect this pin to VOUT1. The output can be
factory set from 1.2V to 3.6V. For further information see Ordering Information on page 15.
5 EN2
Enable2 Input. Driving this pin above 1.2V enables VOUT2. Driving this pin below 0.5V puts the device in
shutdown mode. In shutdown mode all functions are disabled, drawing 1μA supply current.
This pin should not be left floating.
6LBO
Low Battery Comperator Output. This open-drain output is low when:
- the voltage on LBI is higher than 1.2V or
- LBI is connected to GND and VOUT1 is below 92.5% of its nominal value.
7 LBI Low Battery Comperator Input. 1.2V Threshold. May not be left floating. If connected to GND, LBO is
working as Output Power Okay for VOUT1.
8AGND Analog Ground.
9FB2 Feedback 2 Pin. Feedback input to the error amplifier, connect this pin to VOUT2. The output can be
factory set from 1.2V to 3.6V. For further information see Ordering Information on page 15.
10 VDD Supply Connector. Connect this pin to PVIN
12 SW2 Switch Node2 Connection to Inductor. This pin connects to the drains of the internal main and
synchronous power MOSFET switches.
13 PGND Exposed Pad. The exposed pad must be connected to AGND. Ensure a good electrical connection to the
PCB to achieve optimal thermal performance.
AS1346
PVIN 2
FB1 4
SW1 1
EN1 3
FB2
9
VDD
10
PVIN
11
SW2
12
13
EN2 5AGND
8
LBO 6LBI
7
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AS1346-49
Datasheet - Absolute Maximum Ratings
5 Absolute Maximum Ratings
Stresses beyond those listed in Table 3 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 3. Absolute Maximum Ratings
Parameter Min Max Units Notes
Electrical Parameters
VDD, PVIN to AGND -0.3 +7.0 V
PGND to AGND -0.3 +0.3 V
EN, FB AGND - 0.3 VDD + 0.3 V 7.0V max
SW PGND - 0.3 PVIN + 0.3 V
PVIN to VDD -0.3 +0.3 V
Electrostatic Discharge
Human Body Model 1 kV Norm: MIL 883 E method 3015
Temperature Ranges and Storage Conditions
Junction Temperature (TJ-MAX)+150 ºC
Storage Temperature Range -55 +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
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AS1346-49
Datasheet - Electrical Characteristics
6 Electrical Characteristics
PVIN = VDD = EN = 5V, unless otherwise noted
.
Typical values are at TA=25°C. All limits are guaranteed. The parameters with min and max
values are guaranteed with production tests or SQC (Statistical Quality Control) methods.
Table 4. Electrical Characteristics
Symbol Parameter Conditions Min Typ Max Units
TAOperating Temperature Range -40 +85 °C
TJOperating Junction Temperature Range -40 +125 °C
VIN Input Voltage Range VIN VOUT 2.7 5.5 V
VOUT Output Voltage Range (see Table 8 on page 15) 1.2 3.6 V
IQ Quiescent Supply Current12 2.8 mA
IOUT1 Output current 1
AS1346, VOUT1 = 3.3V 1200 mA
AS1347 500 mA
AS1348 500 mA
AS1349 1200 mA
IOUT2 Output current 2
AS1346, VOUT2 = 1.8V 500 mA
AS1347 500 mA
AS1348 950 mA
AS1349 1200 mA
ISHDN Shutdown Current 0.1 1 μA
Regulation
VOUT1
Output Voltage 1 AS1346, IOUT1 = 100mA 3.234 3.3 3.366 V
Accuracy +2 %
VOUT2
Output Voltage 2 AS1346, IOUT2 = 100mA 1.764 1.8 1.836 V
Accuracy +2 %
Line Transient Response VIN = 4.5V to 5.5V, IOUT1 = 500mA,
VOUT1 = 3.3V, EN2 = 0V 50 mVpk
Load Transient Response VIN = 5V, IOUT1 = 0 to 500mA, VOUT1
= 3.3V, EN2 = 0V 50 mVpk
fOSC Oscillator frequency 1.8 2 2.2 MHz
tON Turn on time 350 μs
DC-DC Switches
ISW1 SW1 Current Limit AS1346 1.55 A
ISW2 SW2 Current Limit AS1346 800 mA
RDSON1(P) Pin-Pin Resistance for PMOS1 VDD = 5.0V, ISW = 200mA 150 m
RDSON1(N) Pin-Pin Resistance for NMOS1 VDD = 5.0V, ISW = 200mA 250 m
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AS1346-49
Datasheet - Electrical Characteristics
RDSON2(P) Pin-Pin Resistance for PMOS2 VDD = 5.0V, ISW = 200mA 150 m
RDSON2(N) Pin-Pin Resistance for NMOS2 VDD = 5.0V, ISW = 200mA 250 m
Enable
VIH,EN Logic high input threshold 1.2 V
VIH,EN Logic low input threshold 0.5V V
Low Battery & Power-OK
VLBI LBI Threshold Falling Edge 1.16 1.2 1.24 V
LBI Hysteresis 10 mV
LBI Leakage Current LBI = 5V, TA = 25°C 1 nA
LBO Voltage Low2ILBO = 0.1mA 0.05 V
LBO Leakage Current LBO = 5V, TA = 25°C 1 nA
Power-OK Threshold LBI = 0V, Falling Edge 85 88 90 %
1. The dynamic supply current is higher due to the gate charge delivered at the switching frequency. The Quiescent Current is measured
while the DC-DC Converter is not switching.
2. LBO goes low in startup mode as well as during normal operation if,
1) The voltage at the LBI pin is higher than LBI threshold.
2) The voltage at the LBI pin is below 0.1V (connected to GND) and VOUT1 is below 92.5% of its nominal value.
Table 4. Electrical Characteristics
Symbol Parameter Conditions Min Typ Max Units
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AS1346-49
Datasheet - Typical Operating Characteristics
7 Typical Operating Characteristics
Figure 3. AS1346 Efficiency vs. IOUT, VOUT1 = 3.3V Figure 4. AS1346 Efficiency vs. IOUT, VOUT2 = 1.8V
Figure 5. AS1346 Efficiency vs. VIN, VOUT1 = 3.3V Figure 6. AS1346 Efficiency vs. VIN, VOUT2 = 1.8V
Figure 7. Efficiency vs. IOUT, VOUT1 = 2.5V Figure 8. Efficiency vs. IOUT, VOUT2 = 1.2V
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AS1346-49
Datasheet - Typical Operating Characteristics
Figure 9. AS1346 Load Regulation; VIN = 4.0V, VOUT1 = 3.3V Figure 10. AS1346 Load Regulation; VIN = 4.0V, VOUT2 =1.8V
Figure 11. AS1346 Line Regulation, VOUT1 = 3.3V Figure 12. AS1346 Line Regulation, VOUT2 = 1.8V
LDO mode
Figure 13. AS1346 VOUT vs. Temp.; VIN = 5.5V, IOUT = 1A Figure 14. AS1346 VOUT vs. Temp.; VIN = 5.5V, IOUT = 500mA
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AS1346-49
Datasheet - Detailed Description
8 Detailed Description
The AS1346, AS1347, AS1348, AS1349 family is a high-efficiency buck converter that uses a constant-frequency current-mode architecture.
The device contains two internal MOSFET switches and is available with a fixed output voltage (see Ordering Information on page 15).
Figure 17. AS1346 - Block Diagram
Mosfet
Control
Logic
Shutdown
Control
Main Control
Soft Start
Current
Sense
PVIN
PWM
COMP
VDD
Error
Amplifier
FB1
EN1
SW1
AGND
AS1346
Mosfet
Control
Logic
Soft Start
Oscillator
Current
Sense
PWM
COMP
Error
Amplifier
FB2
EN2 PVIN
VDD
SW2
LBO
LBI
Power-OK
Compare
Logic
PGND
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AS1346-49
Datasheet - Detailed Description
8.1 Main Control Loop
During normal operation, the internal top power MOSFET is turned on each cycle when the oscillator sets the RS latch. This switch is turned off
when the current comparator resets the RS latch. The peak inductor current (IPK) at which ICOMP resets the RS latch, is controlled by the error
amplifier. When ILOAD increases, VFB decreases slightly relative to the internal 0.6V reference, causing the error amplifier’s output voltage to
increase until the average inductor current matches the new load current.
When the top MOSFET is off, the bottom MOSFET is turned on until the inductor current starts to reverse as indicated by the current reversal
comparator, or the next clock cycle begins. The over-voltage detection comparator guards against transient overshoots >7.8% by turning the
main switch off and keeping it off until the transient is removed.
8.2 Short-Circuit Protection
The short-circuit protection turns off the power switches as long as the short is applied. When the short is removed the device is continuing
normal operation.
8.3 Dropout Operation
The AS1346, AS1347, AS1348, AS1349 is working with a low input-to-output voltage difference by operating at 100% duty cycle. In this state,
the PMOS is always on. This is particularly useful in battery-powered applications with a 3.3V output.
The AS1346, AS1347, AS1348, AS1349 allows the output to follow the input battery voltage as it drops below the regulation voltage. The
quiescent current in this state is reduced to a minimal value, which aids in extending battery life. This dropout (100% duty-cycle) operation
achieves long battery life by taking full advantage of the entire battery range.
The input voltage requires maintaining regulation and is a function of the output voltage and the load. The difference between the minimum input
voltage and the output voltage is called the dropout voltage. The dropout voltage is therefore a function of the on-resistance of the internal PMOS
(RDS(ON)PMOS) and the inductor resistance (DCR) and this is proportional to the load current.
Note: At low VIN values, the RDS(ON) of the P-channel switch increases (see Electrical Characteristics on page 4). Therefore, power dissipa-
tion should be taken in consideration.
8.4 Shutdown
Connecting EN to GND or logic low places the AS1346, AS1347, AS1348, AS1349 in shutdown mode and reduces the supply current to 0.1μA.
In shutdown the control circuitry and the internal NMOS and PMOS turn off and SW becomes high impedance disconnecting the input from the
output. The output capacitance and load current determine the voltage decay rate. For normal operation connect EN to VIN or logic high.
Note: Pin EN should not be left floating.
8.4.1 Power-OK and Low-Battery-Detect Functionality
LBO goes low in startup mode as well as during normal operation if,
- The voltage at the LBI pin is above LBI threshold (1.2V). This can be used to monitor the battery voltage.
- LBI pin is connected to GND and VOUT1 is below 92.5% of its nominal value. LBO works as a power-OK signal in this case.
The LBI pin can be connected to a resistive-divider to monitor a particular definable voltage and compare it with a 1.2V internal reference. If LBI
is connected to GND (see Figure 1 on page 1) an internal resistive-divider is activated and connected to the output. Therefore, the Power-OK
functionality can be realized with no additional external components.
The Power-OK feature is not active during shutdown. To obtain a logic-level output, connect a pull-up resistor from pin LBO to pin VOUT or VDD.
Larger values for this resistor will help to minimize current consumption; a 100k resistor is perfect for most applications (see Figure 18 on page
11).
For the circuit shown in the left of Figure 18 on page 11, the input bias current into LBI is very low, permitting large-value resistor-divider networks
while maintaining accuracy. Place the resistor-divider network as close to the device as possible. Use a defined resistor for R2 and then calculate
R1 as:
Where:
VLBI (the internal sense reference voltage) is 1.2V.
In case of the LBI pin is connected to GND, an internal resistor-divider network is activated and compares the output voltage with a 92.5%
voltage threshold (see AS1346 - Typical Application Diagram with POK Function on page 1). For this particular Power-OK application, no
external resistive components (R1 and R2) are necessary.
(EQ 1)
R1R2
VIN
VLBI
------------ 1–
=
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AS1346-49
Datasheet - Detailed Description
Figure 18. Typical Application Diagram with Adjustable Battery Monitoring
8.5 Thermal Shutdown
Due to its high-efficiency design, the AS1346 will not dissipate much heat in most applications. However, in applications where the AS1346 is
running at high ambient temperature, uses a low supply voltage, and runs with high duty cycles (such as in dropout) the heat dissipated may
exceed the maximum junction temperature of the device.
As soon as the junction temperature reaches approximately 150ºC the AS1346 goes in thermal shutdown. In this mode the internal PMOS &
NMOS switch are turned off. The device will power up again, as soon as the temperature falls below +140ºC again.
R3
R1
R2
AS1346
COUT1
CIN
VIN
4.5V to 5.5V
VOUT1
3.3V 1200mA
SW1
COUT2
VOUT2
1.8V 500mA
FB1
FB2
SW2
AGND
EN2
PVIN
VDD
EN1
LBI
LBO
L1 = 3.3μH
L2 = 3.3μH
PVIN
PGND
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AS1346-49
Datasheet - Application Information
9 Application Information
9.1 Component Selection
Only three power components are required to complete the design of the buck converter. For the adjustable LBI two external resistors are
needed.
9.2 Inductor Selection
For the external inductor, a 3.3μH inductor is recommended. Minimum inductor size is dependant on the desired efficiency and output current.
Inductors with low core losses and small DCR at 2MHz are recommended.
Calculation of IMAX:
9.3 Capacitor Selection
A 10μF capacitor is recommended for CIN as well as a 10μF for COUT. Small-sized X5R or X7R ceramic capacitors are recommended as they
retain capacitance over wide ranges of voltages and temperatures.
9.3.1 Input and Output Capacitor Selection
Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery. Also low ESR capacitors should be
used to minimize VOUT ripple. Multi-layer ceramic capacitors are recommended since they have extremely low ESR and are available in small
footprints.
For input decoupling the ceramic capacitor should be located as close to the device as practical. A 22μF input capacitor is sufficient for most
applications. Larger values may be used without limitations.
A 2.2μF to 10μF output ceramic capacitor is sufficient for most applications. Larger values up to 22μF may be used to obtain extremely low
output voltage ripple and improve transient response.
Table 5. Recommended Inductor
L DCR Current Rating
3.3μHmIMAX
Table 6. Recommended Input and Output Capacitor
C TC Code Rated Voltage
CIN 10 - 47μF X5R 6.3V
COUT1, COUT2 2.2 - 10μF X7R 25V
(EQ 2)
IMAX
IOUT 1VOUT 1
IOUT 2VOUT 2
+
07VIN
--------------------------------------------------------------------------------------=
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AS1346-49
Datasheet - Package Drawings and Markings
10 Package Drawings and Markings
Figure 19. 12-Pin TDFN 3x3mm Marking
Table 7. Packaging Code YYWWQZZ
XXXX YY WW Q ZZ
marketing code year manufacturing week plant identifier free choice / traceability code
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AS1346-49
Datasheet - Ordering Information
11 Ordering Information
The device is available as the standard products listed below.
Receive samples within 2 weeks for any non standard output voltage variant!
Note: All products are RoHS compliant.
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 8. Ordering Information
Ordering Code Marking Channel Vout Iout Description Delivery Form Package
AS1346-BTDT-3318 ASSL
OUT1 3.3V 1.2A Dual Step-Down
Converter with Battery
Monitoring
Tape and Reel 12-Pin TDFN
3x3mm
OUT2 1.8V 0.5A
AS1347-BTDT-1812 ASU6
OUT1 1.8V 0.5A Dual Step-Down
Converter with Battery
Monitoring
Tape and Reel 12-Pin TDFN
3x3mm
OUT2 1.2V 0.5A
AS1347-BTDT-3310 ASU7
OUT1 3.3V 0.5A Dual Step-Down
Converter with Battery
Monitoring
Tape and Reel 12-Pin TDFN
3x3mm
OUT2 1.0V 0.5A
AS1348-BTDT-3312 ASTZ
OUT1 3.3V 0.5A Dual Step-Down
Converter with Battery
Monitoring
Tape and Reel 12-Pin TDFN
3x3mm
OUT2 1.2V 0.95A
AS1346-BTDT-xxyy1
1. Non-standard devices from 1.2V to 3.6V are available in 100mV steps.
For more information and inquiries contact http://www.ams.com/contact
tbd
OUT1 xx 1.2A Dual Step-Down
Converter with Battery
Monitoring
Tape and Reel 12-Pin TDFN
3x3mm
OUT2 yy 0.5A
AS1347-BTDTxxyy1tbd
OUT1 xx 0.5A Dual Step-Down
Converter with Battery
Monitoring
Tape and Reel 12-Pin TDFN
3x3mm
OUT2 yy 0.5A
AS1348-BTDTxxyy1tbd
OUT1 xx 0.5A Dual Step-Down
Converter with Battery
Monitoring
Tape and Reel 12-Pin TDFN
3x3mm
OUT2 yy 0.95A
AS1349-BTDTxxyy1tbd
OUT1 xx 1.2A Dual Step-Down
Converter with Battery
Monitoring
Tape and Reel 12-Pin TDFN
3x3mm
OUT2 yy 1.2A
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AS1346-49
Datasheet
Copyrights
Copyright © 1997-2011, ams AG, Tobelbaderstrasse 30, 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 ams AG are covered by the warranty and patent indemnification provisions appearing in its Term of Sale. ams 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. ams 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 ams 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 life-sustaining equipment are specifically not recommended without additional processing
by ams 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 ams AG is believed to be correct and accurate. However, ams 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
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services.
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