AS1321
130mA Step-Up DC-DC Converter
www.austriamicrosystems.com/DC-DC_Step-Up/AS1321 Revision 1.03 1 - 13
Datasheet
1 General Description
The AS1321 is a high-efficiency step-up DC-DC converter designed
to generate a fixed output voltage of +5.0V.
The AS1321 achieves an efficiency of up to 96%. The minimum input
voltage is +1.5V, the output voltage is fixed at +5.0V, and output
current is up to 130mA @ 2V VBATT.
In order to save power the AS1321 features a shutdown mode,
where it draws less than 1µA. In shutdown mode the battery is
connected directly to the output enabling the supply of real-time-
clocks.
The AS1321 provides a power-on reset output that goes high-
impedance when the output reaches 90% of its regulation point.
The SHDNN trip threshold of the AS1321 can be used as an input
voltage detector that disables the device when the battery voltage
falls to a predetermined level.
An internal synchronous rectifier is included, which is parallel with
the external Schottky diode.
The AS1321 is available in a 6-pin SOT23 package.
Figure 1. AS1321 - Typical Application Diagram
2 Key Features
! Fixed Output Voltage: +5.0V
! Output Current: Up to 130mA @ 2V VBATT
! Internal Synchronous Rectifier
! Shutdown Mode Supply Current: Less Than 1µA
! Efficiency: Up to 96%
! Minimum Input Voltage: +1.5V
! Accurate Shutdown Low-Battery Cutoff Threshold
! Battery Input Connected to Pin OUT in Shutdown Mode for
Backup Power
! 6-pin SOT23 Package
3 Applications
The AS1321 is ideal for low-power applications where ultra-small
size is critical as in medical diagnostic equipment, hand-held
instruments, pagers, digital cameras, remote wireless transmitters,
cordless phones, and PC cards.
The device is also perfect as a local +5.0V supply or as a battery
backup.
AS1321
+1.5V to +5.0 V
Battery
+5.0V
Output
COUT
22µF
CIN
22µF
L1
10µH
RESETN Out-
put
R1
100kΩ
On
Off
4
LX
3
GND
2
BATT
6
RESETN
1
SHDNN
5
OUT
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AS1321
Datasheet - Pin Assignments
4 Pin Assignments
Figure 2. Pin Assignments (Top Vie w)
4.1 Pin Descriptions
Table 1. Pin Descriptions
Pin Number Pin Name Description
1 SHDNN Active-Low Logic Shutdown Input
0 = The AS1321 is off and the current into BATT is 1µA (typ).
1 = The AS1321 is on.
2BATT
Battery Voltage Input
3GND
Ground
4LX
External Inductor Connection
5OUT
Output Voltage
6 RESETN Active-Low reset output
AS1321
1
BATT 2
3
6
5
4
GND
SHDNN
OUT
LX
RESETN
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AS1321
Datashee t - A b s o l u t e M a x i mu 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 Section 6 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
All Pins to GND -0.3 7 V
LX Current 1 A
Latch-Up -100 100 mA JEDEC 78
Package Power Dissipation
(TAMB = +70ºC) 500 mW (ΘJA = 9.1mW/ºC above +70ºC)
Operating Temperature Range -40 +85 ºC
Electrostatic Discharge -500 +500 V HBM MIL-Std. 883E 3015.7 methods
Humidity (Non-Co nde nsi ng) 5 85 %
Storage Temperature Range -55 125 ºC
Junction Temperature 150 ºC
Package Body Temperature 260 ºC The reflow peak soldering temperature (body
temperature) specified is in compliance with IPC/JEDEC
J-STD-020 “Moisture/ Reflow Sensit ivity Classification for
Non-Hermetic Solid State Surface Mount Devices”.
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AS1321
Datasheet - Electrical Characteristics
6 Electrical Characteristics
TAMB = -40 to +85ºC, VBATT = +2 V, VOUT = +5.0, VSHDNN = +1.5V (unless otherwise specified). Typical values @ TAMB = +25ºC.
Table 3. Electrical Characteristics
Symbol Parameter Conditions Min Typ Max Unit
VBATT Battery Input Range 1.5 5.0 V
VSU Startup Battery Input Voltage 1
1. Guaranteed by design.
RLOAD = 100Ω, TAMB = +25ºC 1.22 1.5 V
RLOAD = 100Ω, TAMB = -40 to +85ºC 1.24
VOUT Output Voltage 2
2. Voltage which triggers next loading cycle. Ripple and rms value depend on external components.
TAMB = +25ºC 4.950 5.000 5.050 V
TAMB = -40 to +85ºC 4.875 5.125
RNCH N-Channel
On-Resistance ILX = 100mA, TAMB = +25ºC 0.3 1.2 Ω
ILX = 100mA, TAMB = -40 to +85ºC 1.5
RPCH P-Channel On-Resistance ILX = 100mA, TAMB = +25ºC 0.4 1.3 Ω
ILX = 100mA, TAMB = -40 to +85ºC 1.6
IMAX N-Channel Switch Current Limit 1TAMB = +25ºC 550 700 850 mA
TAMB = -40 to +85ºC 450 950
tON Switch Maximum
On-Time TAMB = +25ºC 5 7 9 µs
TAMB = -40 to +85º C 4 10
Synchronous Rectifier
Zero-Crossing Current TAMB = +25ºC 8 30 60 mA
TAMB = -40 to +85º C 0 65
Quiescent Current into OUT 3
3. The Quiescent current is measured while the DC-DC Converter is not switching.
Note: All limits are guaranteed. The parameters with min and max values are guaranteed with production tests or SQC (Statistical Quality
Control) methods.
VOUT = +5.5V, TAMB = +25ºC 35 55 µA
VOUT = +5.5V, TAMB = -40 to +85ºC 60
Shutdown Current into OUT VSHDNN = 0V, TAMB = +25ºC 0.01 1 µA
VSHDNN = 0V, TAMB = -40 to +85ºC 2
Quiescent Current into BATT3VOUT = +5.5V, TAMB = +25ºC 0.01 1 µA
VOUT = +5.5V, TAMB = -40 to +85ºC 2
Shutdown Current into BATT VSHDNN = 0V, TAMB = +25ºC 0.01 1 µA
VSHDNN = 0V, TAMB = -40 to +85ºC 2
SHDNN Logic Low 1VBATT = +1.5 to +5.0V 0.3 V
SHDNN Threshold Rising Edge, TAMB = +25ºC 1.185 1.228 1.271 V
Rising Edge, TAMB = -40 to +85ºC 1.170 1.286
SHDNN Threshold Hysteresis 0.02 V
RESETN Threshold Falling Edge, TAMB = +25ºC 4.288 4.500 4.712 V
Falling Edge, TAMB = -40 to +85ºC 4.242 4.758
RESETN Voltage Low
IRESETN = 1mA, VOUT = +2.5V,
TAMB = +25ºC 0.15 V
IRESETN = 1mA, VOUT = +2.5V,
TAMB = -40 to +85ºC 0.2
RESETN Leakage Current VRESETN = +5.5V, TAMB = +25ºC 0.1 100 nA
VRESETN = +5.5V, TAMB = +85ºC 1
LX Leakage Current TAMB = +25ºC 0.1 1000 nA
TAMB = +85ºC 10
ILOAD Maximum Load Current VBATT = +2V 130 mA
ηEfficiency VBATT = +3V, ILOAD = 100mA 91 %
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AS1321
Datasheet - Typical Operating Characteristics
7 Typical Operating Characteristics
VBATT = 2.0V, VOUT = 5.0V, TAMB = +25°C (unless otherwise spec ifi ed).
Figure 3. Efficiency vs. Load Current Figure 4. Efficiency vs. Input Voltage
75
80
85
90
95
100
1 10 100 1000
Load Current (mA)
Efficiency (%)
VBATT = 3V
VBATT = 2.5V
VBATT = 2V
VBATT = 1.5V
VBATT = 3.5V
VBATT = 4.5V
50
60
70
80
90
100
12345
B att er y Voltage ( V)
Efficiency (%)
Iou t = 1mA
Iou t = 10mA
Iou t = 100mA
Figure 5. VOUT vs. VBATT; On, 39
Ω
Figure 6. VOUT vs. VBATT; On, 470
Ω
0
1
2
3
4
5
6
012345
B att er y Voltage ( V)
Out put V oltage ( V )
0
1
2
3
4
5
6
012345
B att er y Voltage ( V)
Out put V oltage ( V )
Figure 7. VOUT vs. VBATT; Shutdown, 130mA Load Figure 8. VOUT vs. VBATT; Shutdown, no Load
0
1
2
3
4
5
6
1.5 2 2.5 3 3.5 4 4.5 5
B att er y Voltage ( V)
Out put V oltage ( V )
0
1
2
3
4
5
6
012345
B att er y Voltage ( V)
Out put V oltage ( V )
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AS1321
Datasheet - Typical Operating Characteristics
Figure 9. Maximum Output Current vs. VBATT Figure 10. Startup Voltage vs. Load Resistance
0
50
100
150
200
250
300
350
400
1.5 2 2.5 3 3.5 4 4.5 5
B att er y Voltage ( V)
Maximum Output Current (mA)
0
1
2
3
4
5
10 100 1000 10000
Load Resist ance (Ohm)
Supply Voltage (V
)
Figure 11. Input Current vs. Input Voltage Figure 12. Waveforms; RLOAD = 100
Ω
, VBATT = 3V
0
50
100
150
200
250
300
350
400
12345
Battery Voltage ( V)
I nput Current (µA)
Iou t = 4µA
Iou t = 34µA
10µs/Div
VOUT
VLX
50mV/Div
500mA/Div
IL
2V/Div
Figure 13. Line Transient Figure 14. Load Transient
100µs/Div
VIN
100mV/Div1V/Div
VOUT
500µs/Div
VOUT
IOUT
100mV/Div
130mA
2mA
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AS1321
Datasheet - Typical Operating Characteristics
Figure 15. On / Off Response; RLOAD = 100
Ω
Figure 16. Shutdown Response; RLOAD = 100
Ω
2ms/Div
VOUT
VIN
1V/Div1V/Div
500µs/Div
VOUT
VSHDNN
1V/Div2V/Div
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AS1321
Datasheet - Detailed Description
8 Detailed Description
The AS1321 is a high-efficiency, compact step-up converter with 35µA quiescent supply current which ensures the highest efficiency over a wide
load range. With a minimum of +1.5V input voltage, the device is well suited for applications with one- or two-cells, such as lithium ion (Li+),
nickel-metal-hydride (NiMH), or alkaline.
Figure 17. AS1321 - Bl ock Diagram
The input battery is connected to the device through an inductor and an internal P-FET when pin SHDNN is low. In this state, the step-up
converter is off and the voltage drop across the P-FET body diode is eliminated, and the input battery can be used as a battery-backup or real-
time-clock supply.
The built-in synchronous rectifier significantly improves efficiency.
8.1 Control Circuitry
The AS1321 integrated current-limited key circuitry provides low quiescent current and extremely-high efficiency over a wide VOUT range
without the need for an oscillator. Inductor current is limited by the 7µs switch maximum on-time or by the 0.7A N-channel current limit. At each
cycle, the inductor current must ramp down to zero after the on-time before the next cycle may start. When the error comparator senses that the
output has fallen below the regulation threshold, another cycle begins.
VREF
Zero
Crossing
Detector
AS1321
Driver
and
Control
Logic
Startup
Circuitry
10µH
+1.5 to +5.0V Bat-
tery
Current
Limiter
+1.228V
CIN
22µF
+
+
+1.1V
+5.0V
Output
COUT
22µF
4
LX
2
BATT 6
RESETN
1
SHDNN
5
OUT
GND 3
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AS1321
Datasheet - Detailed Description
8.2 Shutdown
When pin SHDNN is low the AS1321 is switched off and no current is drawn from battery; when pin SHDNN is high the device is switched on. If
SHDNN is driven from a logic-level output, the logic high-level (on) should be referenced to VOUT to avoid inte rmi t te nt ly sw it ch i ng t h e d evi c e o n .
Note: If pin SHDNN is not used, it should be connected directly to pin OUT.
In shutdown the battery input is connected to the output through the inductor and the internal synchronous rectifier P-FET. This allows the input
battery to provide backup power for devices such as an idle microcontroller, memory, or real-time-clock, without the usual diode forward drop. In
this way a separate backup battery is not needed.
In cases where there is residual voltage during shutdown, some small amount of energy will be transferred from pin OUT to pin BATT
immediately after shutdown, resulting in a momentary spike of the voltage at pin BATT. The ratio of CIN and COUT partly determine the size and
duration of this spike, as does the current-sink ability of the input device.
8.3 Low-Battery Cutoff
The AS1321 SHDNN trip threshold (1.228V) can be used as an input voltage detector that disables the device when the battery input voltage
falls to a pre-set level. An external resistor-divider network can be used to set the battery-detection voltage (see Figure 18).
Figure 18. Low-Battery Cutoff Application Diagram
For the resistor-divider network shown in Figure 18, calculate the value for R1 by:
R1 = R2 x ((VOFF/VSHDNN) - 1) (EQ 1)
Where:
VOFF is the battery voltage at which the AS1321 shuts down.
VSHDNN = 1.228V
The value of R2 should be between 100kΩ and 1MΩ to minimize battery drain.
Note: Input ripple can cause false shutdowns, therefore to minimize the effect of ripple, a low-value capacitor from SHDNN to GND should be
used to filter out input noise. The value of the capacitor should be such that the R/C time constant is > 2ms.
8.4 Power-On Reset
The AS1321 provides a power-on reset output (RESETN) that goes high-impedance when the output reaches 90% of its regulation point.
RESETN goes low when the output is below 90% of the regulation point. A 100kΩ to 1MΩ pullup resistor between pin RESETN and pin OUT
can provide a microprocessor logic control signal.
Note: Connect pin RESETN to GND when the power-on reset feature is not used.
+1.5 to +5.0 V
Battery +5.0V
Output
COUT
22µF
CIN
22µF
L1
10µH
Power-On
Reset
R3
100kΩ
10nF
R1
220kΩ
R2
1MΩ
AS1321
4
LX
3
GND
2
BATT
6
RESETN
1
SHDNN
5
OUT
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AS1321
Datasheet - Application Inform ation
9 Application Information
9.1 Inductor Selection
The control circuitry of the AS1321 permits a wide range of inductor values to be selected – from 4.7 to 47µH; 10µH is ideal for most
applications.
The intended application should dictate the value of L. The trade-off between required PCB surface area and desired output ripple are the
determining factors: smaller values for L require less PCB space, larger values of L reduce output ripple. If the value of L is large enough to
prevent IMAX from being reached before tON expires, the AS1321 output power will be reduced.
For maximum output current calculate the value for L as:
(VBATT(MAX) (1µs))/0.7A < L < (VBATT(MIN)(7µs))/0.7A (EQ 2)
IOUT(MAX) = (0.7A/2)(VBATT(MIN) - (0.7A/2)(RNCH + RIND))/VOUT (EQ 3)
Where:
RIND is the inductor series resistance.
RNCH is the RDS(ON) of the N-channel MOSFET (0.3Ω typ).
Note: Coils should be able to handle 500mARMS and have a ISAT 1A and should have a RIND 100mΩ.
9.2 Capacitor Selection
9.2.1 COUT Selection
Choose a COUT value to achieve the desired output ripple percentage. A 22µF ceramic capacitor is a good initial value. The value for COUT can
be determined by:
COUT > (L + 2.5µH) x VBATT(MAX)2/ (r% x 4) (EQ 4)
Where:
r is the desired output ripple in %.
9.2.2 CIN Selection
CIN reduces the peak current drawn from the battery and can be the same value as COUT. A larger value for CIN can be used to further reduce
ripple and improve AS1321 efficiency.
9.3 External Diode
An external Schottky diode must be connected, in parallel with the on-chip synchronous rectifier, from LX to OUT. Use diodes such as
MBR0520L, EP05Q03L, or the generic 1N5817. The diode should be rated for 500mA, since it carries current during startup and after the
synchronous rectifier turns off. The Schottky diode must be connected as close to the IC as possible. Ordinary rectifier diodes must not be used,
since the slow recovery rate will compromise efficiency.
9.4 PC Board Layout and Grounding
Well-designed printed circuit-board layout is important for minimizing ground bounce and noise.
! Place pin GND lead and the ground leads of CIN and COUT as close to the device as possible.
! Keep the lead to pin LX as short as possible.
! To maximize output power and efficiency and minimize output ripple voltage, use a ground plane and solder the GND pin directly to the
ground plane.
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AS1321
Datasheet - Package Drawings and Markings
10 Package Drawings and Markings
The AS1321 is available in a 6-pin SOT23 package.
Figure 19. 6-pi n SOT23 Package
Symbol Min Max
A 0.90 1.45
A1 0.00 0.15
A2 0.90 1.30
b 0.35 0.50
C 0.08 0.20
D 2.80 3.00
E 2.60 3.00
E1 1.50 1.75
L 0.35 0.55
e 0.95 REF
α 10º
Notes:
1. All dimensions are in millimeters.
2. Foot length is measured at the intercept point between datum A and lead
surface.
3. Package outline exclusive of mold flash and metal burr.
4. Pin 1 is the lower left pin when reading the top mark from left to right.
5. Pin 1 identifier dot is 0.3mm.φ min and is located above pin 1.
6. Meets JEDEC MO178.
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AS1321
Datasheet - Ordering Information
11 Ordering Information
The AS1321 is available as the standard products shown in Table 4.
Note: All products are RoHS compliant.
Buy our products or get free samples online at ICdirect: http://www.austriamicrosystems.com/ICdirect
Technical Support is found at http://www.austriamicrosystems.com/Technical-Support
For further information and requests, please contact us mailto:sales@austriamicrosystems.com
or find your local distributor at http://www.austriamicrosystems.com/distributor
Design the AS1321 online at http://www.austriamicrosystems.com/analogbench
analogbench is a powerful design and simulation support tool that operates in on-line and off-line mode to evaluate performance and
generate application-specific bill-of-materials for austriamicrosystems' power management devices.
Table 4. Ordering Information
Ordering Code Marking Description Delivery Form Package
AS1321-T ASKX 130mA Step-Up DC-DC Converter Tape and Reel 6-pin SOT23
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AS1321
Datasheet
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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.
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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 life-sustaining equipment are
specifically not recommended without additional processing by austriamicrosystems AG for each application. For shipments of less than 100
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