AS1321
130mA Step-Up DC-DC Converter
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D a ta S h e e t
1 General Description
The AS1321 is a high-efficiency step-up DC-DC con-
verter 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 V
BATT
).
In order to save power the AS1321 features a shutdown
mode, where it draws less than 1A. 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 reg-
ulation 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. Application Diagram
2 Key Features
!
Fixed Output Voltage: +5.0V
!
Output Current: Up to 130mA (@ 2V V
BATT
)
!
Internal Synchronous Rectifier
!
Shutdown Mode Supply Current: Less Than 1A
!
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 equip-
ment, 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
+1.5 to +5.0V
Battery
+5.0V
Output
C
OUT
22F
C
IN
22F
L1
10H
RESETN
Output
R
1
100k
On
Off
4
LX
3
GND
2
BATT
6
RESETN
1
SHDNN
5
OUT
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Data Sheet
4 Absolute Maximum Ratings
Stresses beyond those listed in
Table 1
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 5 Electrical
Characteristics on page 3
is not implied. Exposure to absolute maximum rating conditions for extended periods may
affect device reliability.
Table 1. 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
(T
AMB
= +70C)
500
mW
(
JA
= 9.1mW/C above +70C)
Operating Temperature Range
-40
+85
C
Electrostatic Discharge
-500
+500
V
HBM MIL-Std. 883E 3015.7 methods
Humidity (Non-Condensing)
5
85
%
Storage Temperature Range
-55
125
C
Junction Temperature
150
C
Package Body Temperature
260
C
The reflow peak soldering temperature (body
temperature) specified is in compliance with
IPC/JEDEC J-STD-020C "Moisture/ Reflow
Sensitivity Classification for Non-Hermetic
Solid State Surface Mount Devices".
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Data Sheet
5 Electrical Characteristics
T
AMB
= -40 to +85C, V
BATT
= +2V, V
OUT
= +5.0, V
SHDNN
= +1.5V (unless otherwise specified). Typ values @ T
AMB
= +25C.
Table 2. Electrical Characteristics
Parameter
Symbol
Conditions
Min
Typ
Max
Unit
Battery Input Range
V
BATT
1.5
5.0
V
Startup Battery Input Voltage
1
1. Guaranteed by design.
V
SU
R
LOAD
= 100
, T
AMB
= +25C
1.22
1.5
V
R
LOAD
= 100
, T
AMB
= -40 to +85C
1.24
Output Voltage
2
2. Voltage which triggers next loading cycle. Ripple and rms value depend on external components.
V
OUT
T
AMB
= +25C
4.950 5.000
5.050
V
T
AMB
= -40 to +85C
4.875
5.125
N-Channel
On-Resistance
R
NCH
I
LX
= 100mA, T
AMB
= +25C
0.3
1.2
I
LX
= 100mA, T
AMB
= -40 to +85C
1.5
P-Channel On-Resistance
R
PCH
I
LX
= 100mA, T
AMB
= +25C
0.4
1.3
I
LX
= 100mA, T
AMB
= -40 to +85C
1.6
N-Channel Switch Current Limit
1
I
MAX
T
AMB
= +25C
550
700
850
mA
T
AMB
= -40 to +85C
450
950
Switch Maximum
On-Time
t
ON
T
AMB
= +25C
5
7
9
s
T
AMB
= -40 to +85C
4
10
Synchronous Rectifier
Zero-Crossing Current
T
AMB
= +25C
8
30
60
mA
T
AMB
= -40 to +85C
0
65
Quiescent Current into OUT
V
OUT
= +5.5V, T
AMB
= +25C
35
55
A
V
OUT
= +5.5V, T
AMB
= -40 to +85C
60
Shutdown Current into OUT
V
SHDNN
= 0V, T
AMB
= +25C
0.01
1
A
V
SHDNN
= 0V, T
AMB
= -40 to +85C
2
Quiescent Current into BATT
V
OUT
= +5.5V, T
AMB
= +25C
0.01
1
A
V
OUT
= +5.5V, T
AMB
= -40 to +85C
2
Shutdown Current into BATT
V
SHDNN
= 0V, T
AMB
= +25C
0.01
1
A
V
SHDNN
= 0V, T
AMB
= -40 to +85C
2
SHDNN Logic Low
1
V
BATT
= +1.5 to +5.0V
0.3
V
SHDNN Threshold
Rising Edge, T
AMB
= +25C
1.185 1.228
1.271
V
Rising Edge, T
AMB
= -40 to +85C
1.170
1.286
SHDNN Threshold Hysteresis
0.02
V
RESETN Threshold
Falling Edge, T
AMB
= +25C
4.288 4.500
4.712
V
Falling Edge, T
AMB
= -40 to +85C
4.242
4.758
RESETN Voltage Low
I
RESETN
= 1mA, V
OUT
= +2.5V,
T
AMB
= +25C
0.15
V
I
RESETN
= 1mA, V
OUT
= +2.5V,
T
AMB
= -40 to +85C
0.2
RESETN Leakage Current
V
RESETN
= +5.5V, T
AMB
= +25C
0.1
100
nA
V
RESETN
= +5.5V, T
AMB
= +85C
1
LX Leakage Current
T
AMB
= +25C
0.1
1000
nA
T
AMB
= +85C
10
Maximum Load Current
I
LOAD
V
BATT
= +2V
130
mA
Efficiency
V
BATT
= +3V, I
LOAD
= 100mA
91
%
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Data Sheet
6 Typical Operating Characteristics
V
OUT
= 5.0V, V
BATT
= +2V, T
AMB
= +25C.
Figure 2. V
OUT
vs. V
BATT
; On, 39
Figure 3. V
OUT
vs. V
BATT
; On, 470
Figure 4. V
OUT
vs. V
BATT
; Shutdown, 130mA Load
Figure 5. V
OUT
vs. V
BATT
; Shutdown, No Load
Figure 6. Maximum Output Current vs. V
BATT
Figure 7. Startup Voltage vs. Load Resistance
0
1
2
3
4
5
6
0
1
2
3
4
5
Battery Voltage (V)
O
u
t
put
V
o
l
t
ag
e
(
V
)
.
0
1
2
3
4
5
6
0
1
2
3
4
5
Battery Voltage (V)
O
u
t
put
V
o
l
t
ag
e
(
V
)
.
0
1
2
3
4
5
6
0
1
2
3
4
5
6
Battery Voltage (V)
O
u
t
put
V
o
l
t
ag
e
(
V
)
.
0
1
2
3
4
5
6
0
1
2
3
4
5
6
Battery Voltage (V)
O
u
t
put
V
o
l
t
ag
e
(
V
)
.
0
50
100
150
200
250
300
350
1.5
2
2.5
3
3.5
4
4.5
5
Battery Voltage (V)
M
a
x
i
m
u
m
O
u
t
put
Cur
r
ent
(
m
A
)
.
0
1
2
3
4
5
10
100
1000
10000
Load Resistance (Ohm)
S
uppl
y
V
o
l
t
age
(
V
)
.
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Data Sheet
Figure 8. Line Transient
Figure 9. Load Transient
Figure 10. On/Off Response; R
LOAD
= 100
Figure 11. Shutdown Response; R
LOAD
= 100
Figure 12. Waveforms; R
LOAD
= 100
, V
BATT
= 3V
Figure 13. Efficiency vs. Load Current
130mA
2mA
500s/Div
V
IN
100s/Div
1V
/D
iv
100mV
/
Div
V
OUT
(A
C Cou
p
led)
I
OUT
100mV
/
Div
V
OUT
(A
C Cou
p
led
)
V
OUT
V
SDHNN
500s/Div
2ms/Div
V
OU
T
V
IN
1V/Div
1V
/D
iv
2V
/Div
1V
/Div
75
80
85
90
95
100
1
10
100
1000
Load Current (mA)
E
f
f
i
ci
e
n
c
y (
%
)
.
10s/Div
V
BATT
= 3V
V
BATT
= 2.5V
V
BATT
= 2V
V
BATT
= 1.5V
V
OU
T
(AC Coupl
ed)
V
LX
I
L
2V/Div
5
0
mV/Div
500
mA
V
BATT
= 3.5V
V
BATT
= 4.5V
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Data Sheet
Control Circuitry
7 Detailed Description
The AS1321 is a high-efficiency, compact step-up converter with 35A 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 applica-
tions with one- or two-cells, such as lithium ion (Li+), nickel-metal-hydride (NiMH), or alkaline.
Figure 14. Block 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 bat-
tery can be used as a battery-backup or real-time-clock supply.
The built-in synchronous rectifier significantly improves efficiency.
Control Circuitry
The AS1321 integrated current-limited key circuitry provides low quiescent current and extremely-high efficiency over
a wide V
OUT
range without the need for an oscillator. Inductor current is limited by the 7s 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.
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
V
OUT
to avoid intermittently switching the device on.
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
C
IN
and C
OUT
partly determine the size and duration of this spike, as does the current-sink ability of the input device.
V
REF
Zero
Crossing
Detector
AS1321
Driver
and
Control
Logic
Startup
Circuitry
10H
+1.5 to +5.0V
Battery
Current
Limiter
+1.228V
C
IN
22F
+
+
+1.1V
+5.0V
Output
C
OUT
22F
4
LX
2
BATT
6
RESETN
1
SHDNN
5
OUT
GND 3
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Data Sheet
Low-Battery Cutoff
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 15)
.
Figure 15. Low-Battery Cutoff Application Diagram
For the resistor-divider network shown in
Figure 15
, calculate the value for R
1
by:
R
1
= R
2
x ((V
OFF
/V
SHDNN
) - 1)
(EQ 1)
Where:
V
OFF
is the battery voltage at which the AS1321 shuts down.
V
SHDNN
= 1.228V
The value of R
2
should be between 100k
and 1M
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.
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 100k
to 1M
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 +5.0V
Battery
+5.0V
Output
C
OUT
22F
C
IN
22F
L1
10H
Power-On
Reset
R
3
100k
10nF
R
1
220k
R
2
1M
AS1321
4
LX
3
GND
2
BATT
6
RESETN
1
SHDNN
5
OUT
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Data Sheet
Inductor Selection
8 Application Information
Inductor Selection
The control circuitry of the AS1321 permits a wide range of inductor values to be selected from 4.7 to 47H; 10H 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 I
MAX
from being reached before t
ON
expires, the AS1321 output
power will be reduced.
For maximum output current calculate the value for L as:
(V
BATT(MAX)
(1s))/0.7A < L < (V
BATT(MIN)
(7s))/0.7A
(EQ 2)
I
OUT(MAX)
= (0.7A/2)(V
BATT(MIN)
- (0.7A/2)(R
NCH
+ R
IND
))/V
OUT
(EQ 3)
Where:
R
IND
is the inductor series resistance.
R
NCH
is the R
DS(ON)
of the N-channel MOSFET (0.3
typ).
Note: Coils should be able to handle 500mA
RMS
and have a I
SAT
1A and should have a R
IND
100m
.
Capacitor Selection
C
OUT
Selection
Choose a C
OUT
value to achieve the desired output ripple percentage. A 22F ceramic capacitor is a good initial value.
The value for C
OUT
can be determined by:
C
OUT
> (L + 2.5H) x V
BATT(MAX)
2
/ (r% x 4)
(EQ 4)
Where:
r is the desired output ripple in %.
C
IN
Selection
C
IN
reduces the peak current drawn from the battery and can be the same value as C
OUT
. A larger value for C
IN
can be
used to further reduce ripple and improve AS1321 efficiency.
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.
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 C
IN
and C
OUT
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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Data Sheet
Pin Assignments
9 Pinout and Packaging
Pin Assignments
Figure 16. Pin Assignments (Top View)
Pin Descriptions
Table 3. Pin Descriptions
Name
Pin Number
Description
SHDNN
1
Active-Low Logic Shutdown Input
0 = The AS1321 is off and the current into BATT is
1A (typ).
1 = The AS1321 is on.
BATT
2
Battery Voltage Input
GND
3
Ground
LX
4
External Inductor Connection
OUT
5
Output Voltage
RESETN
6
Active-Low reset output
AS1321
1
BATT 2
3
6
5
4
GND
SHDNN
OUT
LX
RESETN
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Data Sheet
Package Drawings and Markings
Package Drawings and Markings
The AS1321 is available in a 6-pin SOT23 package.
Figure 17. 6-pin 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
0
10
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.
min and is located above pin 1.
6. Meets JEDEC MO178.
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Data Sheet
10 Ordering Information
The AS1321 is available as the standard products shown in
Table 4
.
Table 4. Ordering Information
Part
Marking
Description
Delivery Form
Package
AS1321-T
ASKX
130mA Step-Up DC-DC Converter
Tape and Reel
6-pin SOT23
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Data Sheet
Copyrights
Copyright 1997-2006, austriamicrosystems AG, Schloss Premstaetten, 8141 Unterpremstaetten, Austria-Europe.
Trademarks Registered . All rights reserved. The material herein may not be reproduced, adapted, merged, trans-
lated, 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. austriami-
crosystems 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 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 tech-
nical 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:
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