AS1329

A S1 3 2 9
L o w Vo lt a g e, M i c ro p o w e r, D C- DC St ep - U p C o n v e r te r s
1 General Description
2 Key Features
The AS1329A, AS1329B and the AS1329C are synchronous, fixed
frequency, very high-efficiency DC-DC boost converters capable of
supplying 3.3V at 160mA from a single AA-supply. Compact size and
minimum external parts requirements make these devices perfect for
modern portable devices.
Low Start-Up Voltage: 0.85V
High-speed switching frequency (1.2MHz) and internally
compensated PWM current mode design provide highly-reliable DCDC conversion, especially when driving white LEDs. The converters
are available as the standard products listed in Table 1.
Operating with coils down to 2.2µH
Output Range: 2.5V to 5.0V
Single-Cell Operation
Delivers 160mA @ 3.3V (from Single AA Cell)
Delivers 220mA @ 5.0V (from Two AA Cells)
Table 1. Standard Products
Delivers 570mA @ 3.3V (from Two AA Cells)
Model
Light Load Switching
AS1329A
Medium Load
Automatic Powersave Operation
AS1329B
Light Load Automatic Powersave Operation
AS1329C
Continuous Switching
95% Efficiency
High-Speed Fixed-Frequency: 1.2MHz
Internal PMOS Synchronous Rectifier
Automatic Powersave Operation (AS1329A&B)
The devices contain two internal MOSFET switches: one NMOS
switch and one PMOS synchronous rectifier. Anti-ringing control
circuitry reduces EMI by damping the inductor in discontinuous
mode, and the devices exhibit extremely low quiescent current (<
1µA) in shutdown.
Continuous Switching at Light Loads (AS1329C)
Logic Controlled Shutdown (< 1µA)
6-pin TSOT-23 Package
In shutdown mode the battery is connected directly to the output
enabling the supply of real-time-clocks. The AS1329 is available in a
6-pin TSOT-23 package.
3 Applications
The AS1329 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,
MP3 players, LCD bias supplies, cordless phones, GPS receivers,
and PC cards.
Figure 1. Typical Application Diagram – Single Cell to 3.3V
Synchronous Boost Converter
L1
4.7µH
1
SW
6
AA Battery
5
VOUT
VIN
C1
10µF
On
Off
AS1329
4
C2
10µF
3
SHDNN
FB
2
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R1
1.02MΩ
1%
VOUT
3.3V
160mA
GND
Revision 1.12
R2
604kΩ
1%
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AS1329
Datasheet - P i n A s s i g n m e n t s
4 Pin Assignments
Figure 2. Pin Assignments (Top View)
SW 1
GND 2
6 VIN
AS1329
FB 3
5 VOUT
4 SHDNN
4.1 Pin Descriptions
Table 2. Pin Descriptions
Pin Number
Pin Name
1
SW
2
GND
3
FB
4
SHDNN
5
VOUT
6
VIN
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Description
Switch Pin. Connect an inductor between this pin and VIN. Keep the PCB trace lengths as
short and wide as is practical to reduce EMI and voltage overshoot. If the inductor current
falls to zero, or pin SHDNN is low, an internal 100Ω anti-ringing switch is connected from this
pin to VIN to minimize EMI.
Note: An optional Schottky diode can be connected between this pin and VOUT.
Signal and Power Ground. Provide a short, direct PCB path between this pin and the
negative side of the output capacitor(s).
Feedback Pin. Feedback input to the gm error amplifier. Connect a resistor divider tap to this
pin. The output voltage can be adjusted from 2.5 to 5V by: VOUT = 1.23V[1 + (R1/R2)]
Shutdown Pin. Logic controlled shutdown input.
1 = Normal operation, 1.2MHz typical operating frequency.
0 = Shutdown; quiescent current <1µA. If SHDNN is undefined, pin SW may ring.
Note: In a typical application, SHDNN should be connected to VIN through a 1MΩ pull-up
resistor.
Output Voltage Sense Input and Drain of the Internal PMOS Synchronous Rectifier.
Bias is derived from VOUT when VOUT exceeds VIN. PCB trace length from VOUT to the
output filter capacitor(s) should be as short and wide as is practical.
Input Voltage. The AS1329 gets its start-up bias from VIN unless VOUT exceeds VIN, in
which case the bias is derived from VOUT. Thus, once started, operation is completely
independent from VIN. Operation is only limited by the output power level and the internal
series resistance of the supply.
Revision 1.12
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AS1329
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 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 Section 6 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
VIN to GND
-0.3
7
V
SHDNN, SW to GND
-0.3
7
V
FB to GND
-0.3
5
V
VOUT
-0.3
7
V
Operating Temperature Range
-40
+85
ºC
Storage Temperature Range
-65
+125
ºC
Package Body Temperature
Moisture Sensitive Level
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+260
1
ºC
Notes
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 an unlimited floor life time
Revision 1.12
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AS1329
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
TAMB = -40°C to +85ºC, VIN = +1.2V, VOUT = +3.3V, VSHDNN = +1.2V (unless otherwise specified). Typ values @ TAMB = +25ºC.
Table 4. Electrical Characteristics
Symbol
VFB
Parameter
Conditions
Min
Minimum Start-Up Voltage
ILOAD = 1mA
Minimum Operating Voltage
SHDNN = VIN
Maximum Operating Voltage
SHDNN = VIN
Output Voltage Adjust Range
TAMB = 25ºC
2.5
Feedback Voltage
TAMB = TMIN to TMAX
1.192
1
Typ
Max
Units
0.85
1
V
0.65
0.85
V
5
V
5
V
1.268
V
1
2
1.23
IFB
Feedback Input Current
VFB = 1.25V
IQPWS
Quiescent Current
(Powersave Operation)
VFB = 1.4V , AS1329A only
30
50
µA
ISHDNN
Shutdown Current
VSHDNN = 0V
0.01
1
µA
IQ
Quiescent Current (Active)
VFB = 1.4V , AS1329B&C only
150
300
µA
INMOSSWL
NMOS Switch Leakage
VSW = 5V
0.1
5
µA
IPMOSSWL
PMOS Switch Leakage
VSW = 0V
0.1
5
µA
VOUT = 3.3V
0.35
0.8
RONNMOS
NMOS Switch On Resistance
4
0.20
0.7
VOUT = 3.3V
0.45
0.8
4
0.30
0.7
3
3
VOUT = 5V
RONPMOS
PMOS Switch On Resistance
VOUT = 5V
INMOS
IPS
NMOS Current Limit
1
VIN = 2.5V
nA
850
mA
3
mA
2
0.3
mA
%
AS1329A only
Max Duty Cycle
VFB = 1V, TAMB = TMIN to TMAX
80
87
TAMB = 25ºC
0.95
1.2
1.5
TAMB = TMIN to TMAX
0.85
1.2
1.5
fSW
Switching Frequency
VSHDNNH
SHDNN Input High
VSHDNNL
SHDNN Input Low
ISHDNN
SHDNN Input Current
Ω
2
Powersave Operation Current
Threshold
AS1329B only
Ω
1
VSHDNN = 5.0V
MHz
V
0.01
0.35
V
1
µA
1. Minimum VIN operation after start-up is only limited by the battery’s ability to provide the necessary power as it enters a deeply discharged state.
2. Specification is guaranteed by design and not 100% production tested.
3. IQPWS is measured at VOUT. Multiply this value by VOUT/VIN to get the equivalent input (battery) current.
4. Specification is guaranteed by design and not 100% production tested.
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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AS1329
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
All measurements are performed with AS1329A, VOUT = 3.3V, TAMB = +25ºC, unless otherwise specified.
Parts used for measurements: L= 10µH (MOS6020-103ML), CIN and COUT = 10µF (GRM31CR70J106KA01L)
Figure 4. VOUT vs. Temperature; IOUT = 10mA
3.5
3.36
3
3.34
Output Voltage (V) .
Output Voltage (V) .
Figure 3. VOUT vs. Battery Voltage; IOUT = 10mA
2.5
2
1.5
1
3.32
3.3
3.28
3.26
0.5
0
0
0.5
1
1.5
2
2.5
3
3.24
-50
3.5
-25
Battery Voltage (V)
Figure 5. Startup Voltage vs. Output Current
25
50
75
100
Figure 6. Powersave threshold vs. Input Voltage
1.8
120
AS1329A
1.7
Vout = 3.3V
AS1329B
Vout = 5.0V
1.6
Output Current (mA) .
Startup Voltage (V) .
0
Temperature (°C)
1.5
1.4
1.3
1.2
1.1
1
0.9
100
80
60
40
20
0.8
0.7
0
0.1
1
10
100
1
1.25
Output Current (mA)
1.5
1.75
2
2.25
2.5
Battery Voltage (V)
Figure 7. IOUT vs. VBATT; VOUT = 3.3V, 3% Tolerance
Figure 8. IOUT vs. VBATT; VOUT = 5.0V, 3% Tolerance
.
800
800
700
Output Current (mA)
900
.
900
Output Current (mA)
1000
700
600
500
400
300
200
600
500
400
300
200
100
100
0
0
0.5
1
1.5
2
2.5
3
0.5
Battery Voltage (V)
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1
1.5
2
2.5
3
3.5
4
Battery Voltage (V)
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AS1329
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. No Load Battery Current vs. Battery Voltage;
Figure 10. Efficiency vs. Battery Voltage; AS1329A
1000
100
80
Efficiency (%) .
Battery Current (µA) .
90
100
70
60
50
40
Il oad = 80µA
30
Il oad = 800µA
Il oad = 11mA
10
20
1.2 1.4 1.6 1.8
2
2.2 2.4 2.6 2.8
3
0.7
1.2
Battery Voltage (V)
2.2
2.7
3.2
Figure 12. Efficiency vs. Output Current of AS1329B
100
100
90
90
80
80
Efficiency (%) .
Efficiency (%) .
Figure 11. Efficiency vs. Output Current of AS1329A
70
60
50
40
70
60
50
40
Vi n = 1.0V
Vi n = 1.5V
30
Vi n = 1.0V
Vi n = 1.5V
30
Vi n = 2.2V
Vi n = 2.4V
20
Vi n = 2.2V
Vi n = 2.4V
20
0.1
1
10
100
1000
0.1
Output Current (mA)
1
10
100
1000
Output Current (mA)
Figure 13. Efficiency vs. Output Current of AS1329C
Figure 14. Efficiency vs. IOUT Comparison; VIN = 2.0V
100
100
90
90
80
80
Efficiency (%) .
Efficiency (%) .
1.7
Battery Voltage (V)
70
60
50
40
70
60
50
40
AS1329A
Vin = 1.0V
30
Vin = 1.5V
30
AS1329B
Vin = 2.2V
20
AS1329C
20
0.1
1
10
100
1000
1
Output Current (mA)
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10
100
Output Current (mA)
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AS1329
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 16. SW Pin Fixed Frequency Continuous Current; VIN =
1.3V, L=10µH, C=10µF, IOUT = 100mA
1V/Div
100ns/Div
100ns/Div
100mV/Div
60mA
VOUT(AC)
IOUT
1mA
100mV/Div
Figure 18. Fixed Frequency vs. Powersave Operation; VIN = 1.3V,
L = 10µH, C = 10µF
100mA
VIN = 1.3V,
40mA
IOUT
VOUT(AC)
Figure 17. VOUT Transient Response;
L = 10µH, C = 10µF
0V
VSW
0V
VSW
1V/Div
Figure 15. SW Pin Antiringing Operation; VIN = 1.3V, L = 10µH,
C = 10µF, IOUT = 5mA
100µs/Div
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10ms/Div
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AS1329
Datasheet - D e t a i l e d D e s c r i p t i o n
8 Detailed Description
The AS1329 can operate from a single-cell input voltage (VIN) below 1V, and features fixed frequency (1.2MHz) and current mode PWM control
for exceptional line- and load-regulation. With low RDS(ON) and gate charge internal NMOS and PMOS switches, the device maintains highefficiency from light to heavy loads.
Modern portable devices frequently spend extended time in low-power or standby modes, switching to high power-drain only when certain
functions are enabled. The AS1329A, AS1329B and AS1329C are ideal for portable devices since they maintain high-power conversion
efficiency over a wide output power range, thus increasing battery life in these types of devices.
In addition to high-efficiency at moderate and heavy loads, the AS1329A as well as the AS1329B includes an automatic powersave mode that
improves efficiency of the power converter at light loads. The powersave mode is initiated if the output load current falls below a factory
programmed threshold (see Figure 6 on page 5).
Note: The AS1329C does not support powersave mode and provides continuous operation at all loads, eliminating low-frequency VOUT ripple at the expense of light load efficiency.
Figure 19. AS1329 - Block Diagram
L1
4.7µH
1.5V
Single Cell
6
VIN
Start Up
OSC
CIN
1µF
1
SW
2.3V
–
A
B
VOUT
Good
A/B
MUX
PWM
Control
1.2MHz
Ramp
Generator
Slope
Compensator
+
VOUT
0.45Ω
0.35Ω
Sync Drive
Control
CFF*
Current
Sense
Σ
AS1329
+
PWM –
Comp
–
4
SHDNN
Shutdown
Control
Powersave
Shutdown
Powersave
Operation
Control
RC
80kΩ
CC
150pF
3.3V
Output
5
3
–
gm Error
Amp
+
R1
1.02MΩ
1%
COUT
4.7µF
FB
CP2
2.5pF
R2
640kΩ 1%
1.23V
Ref
2
GND
* Optional
8.1 Low-Voltage Start-Up
The AS1329 requires VIN of only 0.85V (typ) or higher to start up. The low-voltage start-up circuitry controls the internal NMOS switch up to a
maximum peak inductor current of 850mA (typ), with 1.5ms (approx.) off-time during start-up, allowing the devices to start up into an output load.
With a VOUT > 2.3V, the start-up circuitry is disabled and normal fixed-frequency PWM operation is initiated. In this mode, the AS1329 operates
independent of VIN, allowing extended operating time as the battery can drop to several tenths of a volt without affecting output regulation. The
limiting factor for the application is the ability of the battery to supply sufficient energy to the output.
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AS1329
Datasheet - D e t a i l e d D e s c r i p t i o n
8.2 Low-Noise Fixed-Frequency Operation
8.2.1
Oscillator
The AS1329 switching frequency is internally fixed at 1.2MHz allowing the use of very small external components.
8.2.2
Error Amplifier
The integrated error amplifier is an internally compensated trans-conductance (gm) type (current output). The internal 1.23V reference voltage is
compared to the voltage at pin FB to generate an error signal at the output of the error amplifier. A voltage divider from VOUT to GND programs
the output voltage from 2.5 to 5V via pin FB as:
VOUT = 1.23V(1 + (R1/R2))
8.2.3
(EQ 1)
Current Sensing
A signal representing the internal NMOS-switch current is summed with the slope compensator. The summed signal is compared to the error
amplifier output to provide a peak current control command for the PWM. Peak switch current is limited to approximately 850mA independent of
VIN or VOUT.
8.2.4
Zero Current Comparator
The zero current comparator monitors the inductor current to the output and shuts off the PMOS synchronous rectifier once this current drops to
20mA (approx.). This prevents the inductor current from reversing polarity and results in improved converter efficiency at light loads.
8.2.5
Anti-Ringing Control
Anti-ringing control circuitry prevents high-frequency ringing on pin SW as the inductor current approaches zero. This is accomplished by
damping the resonant circuit formed by the inductor and the capacitance on pin SW (CSW).
8.3 Powersave Operation (AS1329A, AS1329B)
In light load conditions, the integrated powersave feature removes power from all circuitry not required to monitor VOUT. When VOUT has
dropped approximately 1% from nominal, the AS1329A & B powers up and begins normal PWM operation.
COUT (see Figure 19 on page 8) recharges, causing the AS1329A and AS1329B to re-enter powersave mode as long as the output load
remains below the powersave threshold. The frequency of this intermittent PWM is proportional to load current; i.e., as the load current drops
further below the powersave threshold, the AS1329A and AS1329B turns on less frequently. When the load current increases above the
powersave threshold, the AS1329A and AS1329B will resume continuous, seamless PWM operation.
While the AS1329A switches to automatic powersave mode already at medium loads, the AS1329B will do so only at very light loads.
The AS1329C is a continuous switching device, hence the output voltage ripple is very low and no additional frequencies are produced which
may cause interference.
Notes:
1. An optional capacitor (CFF) between pins VOUT and FB in some applications can reduce VOUTp-p ripple and input quiescent current
during powersave mode. Typical values for CFF range from 15 to 220pF.
2. In powersave mode, the AS1329A and AS1329B draws only 30µA from the output capacitor(s), greatly improving converter efficiency.
8.4 Shutdown
When pin SHDNN is low the AS1329 is switched off and <1µA 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 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 CIN and COUT partly determine the size and
duration of this spike, as does the current-sink ability of the input device.
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AS1329
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
The AS1329 is perfectly suited for LED matrix displays, bar-graph displays, instrument-panel meters, dot matrix displays, set-top boxes, white
goods, professional audio equipment, medical equipment, industrial controllers to name a few applications.
Along with Figure 1 on page 1, Figures 20-23 depict a few of the many applications for which the AS1329 converters are perfectly suited.
Figure 20. Single AA Cell to 3.3V Synchronous Boost Converter with Load Disconnect in Shutdown
L1
4.7µH
D1
1
SW
5
6
AA
Battery
C1
4.7µF
On
Off
VOUT
3.3V, 160mA
VOUT
C2
4.7µF
VIN
AS1329
4
R3
510kΩ
R1
1.02MΩ
1%
3
SHDNN
FB
2
R2
604kΩ
1%
GND
Q1
R3
510kΩ
Figure 21. Single Lithium Cell to 5V, 250mA
2Ω
Optional
Snubber
100nF
L1
4.7µH
D1
1
SW
5
6
Lithium
Battery
VIN
C1
4.7µF
On
Off
AS1329
4
R1
1.02MΩ 1%
C3
100pF
3
SHDNN
FB
2
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VOUT
C2
4.7µF
GND
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R2
332kΩ 1%
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AS1329
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
Figure 22. Single AA Cell to ±3V Synchronous Boost Converter
C3
1µF
L1
4.7µH
1
SW
AA
Battery
C1
4.7µF
VOUT
C2
4.7µF
R1
1.02MΩ
1%
AS1329
On
Off
VOUT1
3V, 90mA
5
6
VIN
3
4
D1
FB
SHDNN
2
D2
C4
10µF
R2
750kΩ
1%
GND
VOUT2
-3V, 10mA
Figure 23. Single AA Cell to 2.5V Synchronous Boost Converter
L1
4.7µH
D1
1
SW
5
6
AA
Battery
C1
10µF
On
Off
R1
1.02MΩ
1%
AS1329
C2
10µF
3
4
SHDNN
FB
2
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VOUT
2.5V, 230mA
VOUT
VIN
GND
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1.02MΩ
1%
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AS1329
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
9.1 Output Voltage Ripple
The AS1329 is designed to work at high efficiency. In order to reduce the output ripple the following improvements are recommended:
Use a higher output capacitor, up to 44µF and a higher input capacitor (22µF).
Use smaller values for the resistor divider. R1 should be about 300kΩ. To avoid a high leakage current from pin VOUT through the resistor
divider to GND, R1 should not be less than 100kΩ..
To reduce the output ripple it’s also possible to speed up the feedback loop. To achieve this, place a 22pF (C4 in Figure 24) capacitor in
parallel to R1. Via C4 the fast transients are shorted to the FB pin and the feedback loop is even faster. A 1MΩ resistor for R1 slows down
the FB loop.
Due to noise and to their non linear behavior, the use of potentiometers is not recommended.
Figure 24. AS1329 - Typical Application for lower Output Voltage Ripple
L1
4.7µH
1
2xAA Battery
SW
C1
22µF
VOUT
C4
22pF
AS1329
On
Off
VOUT = 2.8V
5
6
VIN
R1
250kΩ
C2
22µF
C3
22µF
3
4
FB
SHDNN
2
GND
R2
196kΩ
Note: For correct measurements of the output ripple connect the oscilloscope probe as close as possible to the positive plate of the COUT
and connect the GND of the oscilloscope probe to the negative plate of the COUT. This will reduce the inductive coupling and will
deliver a more accurate measurement result.
The output ripple is getting higher as VIN is getting closer to VOUT. Figure 25 shows that the above mentioned improvements reduce the output
voltage ripple. If VIN is higher than VOUT the AS1329 stops switching and VIN is connected to VOUT via the inductor and the internal P-FET.
Figure 25. Output Voltage Ripple vs. Input Voltage; VOUT = 2.8V, IOUT = 0.8mA
Output Voltage Ripple (mVpp)
125
Cout = 44µF
Cout = 66µF
100
Cout = 44µF + C4 = 22pF
75
50
25
0
0.5
1
1.5
2
2.5
3
3.5
Input Voltage (V)
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AS1329
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
9.2 Smallest External Components
The AS1329 is also able to work with smallest Capacitors and Inductors (see Figure 26).
Figure 26. AS1329 - Typical Application for Smallest External Components
L1
2.2µH
1
2xAA Battery
SW
VOUT
VIN
C1
2.2µF
VOUT = 5V
5
6
AS1329
On
Off
C2
4.7µF
R1
kΩ
3
4
SHDNN
FB
2
R2
kΩ
GND
Table 5. Recommended Smallest Components
Part Number
Value
Code
Rating
Size
C1
GRM188R61A225KE34
2.2µF
X5R
10V
0603
C2
GRM188R60J475KE19
4.7µF
X5R
6.3V
0603
L1
LQM31PN2R2M00
2.2µH
238mΩ
0.9A
1206
Manufacturer
Murata
www.murata.com
Figure 27. Efficiency vs. Output Current with Smallest External Components
100
90
Efficiency (%) .
80
70
60
50
40
Vi n = 3.3V
30
Vi n = 3.5V
Vi n = 3.8V
20
1
10
100
1000
Output Current (mA)
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Revision 1.12
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AS1329
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 External Component Selection
9.3.1
Inductor Selection
The fast switching frequency (1.2MHz) of the AS1329 allows for the use of small surface mount or chip inductor for the external inductor (see
Figure 19 on page 8).
The required minimum values for the external inductor are:
3.3µH for applications ≤ 3.6V
4.7µH for applications > 3.6V
Larger inductor values allow greater output current capability by reducing the inductor ripple current. Increasing the inductance above 10µH will
increase size while providing negligible improvement in output current capability.
The approximate output current capability of the AS1329 versus inductor value is given in:
V IN ⋅ D
I OUT ( MAX ) = η ⋅  I P – ------------------ ⋅ ( 1 – D )

f ⋅ L ⋅ 2
(EQ 2)
Where:
η is the estimated efficiency;
IP is the peak current limit value (0.6A);
VIN is the input voltage;
D is the steady-state duty ratio = (VOUT - VIN)/VOUT;
f is the switching frequency (1.2MHz typ);
L is the inductor value.
The inductor current ripple is typically set for 20 to 40% of the maximum inductor current (IP). High-frequency ferrite core inductor materials
reduce frequency dependent power losses compared to less expensive powdered iron types, which result in improved converter efficiency.
The inductor should have low ESR to reduce the I²R power losses, and must be able to handle the peak inductor current without saturating.
Molded chokes and some chip inductors normally do not have enough core to support the peak inductor currents of the AS1329 (850mA typ). To
minimize radiated noise, use a toroid, pot core, or shielded bobbin inductor.
Table 6. Recommended Inductors
Part Number
L
DCR
Current Rating
Dimensions (L/W/T)
MOS6020-103ML
10µH
93mΩ
1A
6.8x6.0x2.4mm
MOS6020-472ML
4.7µH
50mΩ
1.5A
6.8x6.0x2.4mm
MOS6020-332ML
3.3µH
46mΩ
1.8A
6.8x6.0x2.4mm
CDRH4D18-100
10µH
200mΩ
0.61A
6.9x5.0x2.0mm
CDRH4D18-6R8
6.8µH
200mΩ
0.76A
6.9x5.0x2.0mm
CR43-6R8
6.8µH
131.2mΩ
0.95A
4.8x4.3x3.5mm
CDRH4D18-4R7
4.7µH
162mΩ
0.84A
6.9x5.0x2.0mm
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Revision 1.12
Manufacturer
Coilcraft
www.coilcraft.com
Sumida
www.sumida.com
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AS1329
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
Figure 28. Efficiency Comparison of Different Inductors, VIN = 1.5V, VOUT = 3.3V
90
92
85
90
80
88
Efficiency (%)
Efficiency (%)
75
70
65
60
10uH - Coi l cr af t (M OS6020-103M L)
55
86
84
82
10uH - Sumi da(CDRH4D18-100)
10uH - Coi l c r af t (M OS6020-103M L)
80
6. 8uH - Sumi da(CDRH4D18-6R8)
50
10uH - Sumi da(CDRH4D18-100)
6. 8uH - Sumi da(CR43-6R8)
6. 8uH - Sumi da(CDRH4D18-6R8)
6. 8uH - Sumi da(CR43-6R8)
4. 7uH - Coi l cr af t(M OS6020-472M L)
45
78
4. 7 uH - Sumi da(CDRH4D18-4R7)
4. 7uH - Coi l c r af t (M OS6020-472M L)
4. 7 uH - Sumi da(CDRH4D18-4R7)
3. 3 uH - Coi l c r af t (M OS6020-332M L)
3. 3 uH - Coi l cr af t (M OS6020-332M L)
40
76
0.1
1
10
10
Output Current (mA)
9.3.2
Output Current (mA)
100
Output Capacitor Selection
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. A 2.2 to 10µF output 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.
An additional phase lead capacitor may be required with output capacitors larger than 10µF to maintain acceptable phase margin. X5R and X7R
dielectric materials are recommended due to their ability to maintain capacitance over wide voltage and temperature ranges.
Table 7. Recommended Output Capacitor
Part Number
C
TC Code
Rated Voltage
Dimensions (L/W/T)
JMK212BJ226MG-T
22µF ±20%
X5R
6.3V
2x1.3x1.3mm
Manufacturer
Taiyo Yuden
www.t-yuden.com
Input Capacitor Selection. Low ESR input capacitors reduce input switching noise and reduce the peak current drawn from the battery.
Ceramic capacitors are recommended for input decoupling and should be located as close to the device as is practical. A 4.7µF input capacitor
is sufficient for most applications. Larger values may be used without limitations.
Table 8. Recommended Input Capacitor
Part Number
C
TC Code
Rated Voltage
Dimensions (L/W/T)
GRM31CR70J106KA01L
10µF ±10%
X7R
6.3V
3.2x1.6x1.6mm
Manufacturer
Murata
www.murata.com
Diode Selection. A Schottky diode should be used to carry the output current for the time it takes the PMOS synchronous rectifier to switch
on. For VOUT < 4.5V a Schottky diode is optional, although using one will increase device efficiency by 2% to 3%.
Note: Do not use ordinary rectifier diodes, since the slow recovery times will compromise efficiency.
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Revision 1.12
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AS1329
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
9.4 PCB Layout Guidelines
The high-speed operation of the AS1329 requires proper layout for optimum performance. Figure 29 shows the recommended component
layout.
A large ground pin copper area will help to lower the device temperature.
A multi-layer board with a separate ground plane is recommended.
Traces carrying large currents should be direct.
Trace area at pin FB should be as small as is practical.
The lead-length to the battery should be as short as is practical.
Figure 29. Recommended Single-Layer Component Placement
Optional
VIN 6
1 SW
AS1329
VIN
R2
2 GND
VOUT
5
CIN
SHDNN
3
FB
R1
SHDNN 4
COUT
VOUT
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Revision 1.12
16 - 20
AS1329
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
The device is available in a 6-pin TSOT-23 package.
Figure 30. 6-pin TSOT-23 Package
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Revision 1.12
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AS1329
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 31. 6-pin TSOT-23 Marking
Pin1
Top
ZZZZ
Bottom
XXXX
Pin1
Package Code:
ZZZZ - Marketingcode
XXXX - encoded Datecode
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Revision 1.12
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AS1329
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 listed in Table 9.
Table 9. Ordering Information
Ordering Code
Marking
Description
Delivery Form
Package
AS1329A-BTTT
ASPA
Low Voltage, Micropower, DC-DC Step-Up Converter with
Automatic Powersave Operation beginning at Medium
Loads
Tape and Reel
6-pin TSOT-23
AS1329B-BTTT
ASPB
Low Voltage, Micropower, DC-DC Step-Up Converter with
Automatic Powersave Operation beginning at Light Loads
Tape and Reel
6-pin TSOT-23
AS1329C-BTTT
ASPC
Low Voltage, Micropower, DC-DC Step-Up Converter with
Continuous Switching
Tape and Reel
6-pin TSOT-23
Note: All products are RoHS compliant.
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Technical Support is found at http://www.ams.com/Technical-Support
For further information and requests, please contact us mailto:[email protected]
or find your local distributor at http://www.ams.com/distributor
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AS1329
Datasheet - O r d e r i n g I n f o r m a t i o n
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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
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