AMS AS1324 Datasheet
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A S 1 3 2 4
1 . 5 M H z , 6 0 0 m A S y n c h r o n o u s D C / D C C o n v e r t e r
1 General Description
The AS1324 is a high-efficiency, constant-frequency synchronous buck converter available in adjustable- and fixed-voltage versions.
The wide input voltage range (2.7V to 5.5V), automatic powersave mode and minimal external component requirements make the
AS1324 perfect for any single Li-Ion battery-powered application.
Typical supply current with no load is 30µA and decreases to
≤
1µA in shutdown mode.
The AS1324 is available as the standard versions listed in
.
Table 1. Standard Versions
Model
AS1324-AD
AS1324-12
AS1324-15
AS1324-18
Output Voltage
Adjustable via External Resistors
Fixed: 1.2V
Fixed: 1.5V
Fixed: 1.8V
An internal synchronous switch increases efficiency and eliminates the need for an external Schottky diode. The internally fixed switching frequency (1.5MHz) allows for the use of small surface mount external components.
Very low output voltages can be delivered with the internal 0.6V feedback reference voltage.
The AS1324 is available in a 5-pin TSOT-23 package.
2 Key Features
High Efficiency: Up to 96%
Output Current: 600mA
Input Voltage Range: 2.7V to 5.5V
Constant Frequency Operation: 1.5MHz
Variable- and Fixed-Output Voltages
No Schottky Diode Required
Automatic Powersave Operation
Low Quiescent Current: 30µA
Internal Reference: 0.6V
Shutdown Mode Supply Current:
≤
1µA
Thermal Protection
5-pin TSOT-23 Package
3 Applications
The device is ideal for 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.
Figure 1. Typical Application Diagram – High Efficiency Step
Down Converter
V
IN
= 2.7V to 5.5V
C
IN
10µF
4
VIN
AS1324-18
3
SW
4.7µH
1
EN
5
VOUT
2
GND
V
OUT
= 1.8V, 600mA
C
OUT
10µF
EN
1
GND 2
AS1324-18
5 V OUT
SW 3 4 V IN www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
Datasheet - P i n A s s i g n m e n t s
4 Pin Assignments
Figure 2. Pin Assignments (Top View)
EN
1
GND 2
AS1324
5 V FB
SW
3 4 V IN
EN
1
GND 2
AS1324-12/
AS1324-15/
AS1324-18
5 V OUT
SW 3 4 V IN
4.1 Pin Descriptions
Table 2. Pin Descriptions
Pin Number Pin Name
1
2
3
4
5
EN
GND
SW
V
IN
V
FB
V
OUT
Description
Enable Input
. Driving this pin above 1.5V enables the device. Driving this pin below 0.3V puts the device in shutdown mode. In shutdown mode all functions are disabled while SW goes high impedance, drawing <1µA supply current.
Note:
This pin should not be left floating.
Ground.
Switch Node Connection to Inductor.
This pin connects to the drains of the internal main and synchronous power MOSFET switches.
Input Supply Voltage
. This pin must be closely decoupled to GND with a
≥
4.7µF ceramic capacitor.
Connect to any supply voltage between 2.7 to 5.5V.
Feedback Pin
. This pin receives the feedback voltage from the external resistor divider across the output. (Adjustable voltage variant only.)
Output Voltage Feedback Pin
. An internal resistor divider steps the output voltage down for comparison to the internal reference voltage. (Fixed voltage variants only.) www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
2 - 21
AS1324
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
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
VIN to GND
SW, EN, FB to GND
Min
-0.3
-0.3
Max
6
V
IN
+ 0.3
207.4
Units
V
V
Comments
Thermal Resistance
Θ
JA
ESD
Latch-Up
Operating Temperature Range
Storage Temperature Range
-100
-40
-65
2
+100
+85
+125
ºC/W kV mA
ºC
ºC on PCB
HBM MIL-Std. 883E 3015.7
methods
JEDEC 78
Package Body Temperature
Junction Temperature
Moisture Sensitive Level 1
+260
125
ºC
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).
Junction temperature (T
J
) is calculated from the ambient temperature (T
AMB
) and power dissipation
(PD) as:
T
J
= T
AMB
+ (PD)(207.4ºC/W) (EQ 1)
Represents an unlimited floor life time www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
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
V
IN
= EN = 3.6V, V
OUT
< V
IN
- 0.5V, T
AMB
= -40 to +85°C, typ. values @ T
AMB
= +25ºC
(unless otherwise specified)
.
Table 4. Electrical Characteristics
Symbol
V
IN
Parameter
Input Voltage Range
Conditions Min
2.7
Typ
I
I
Q
SHDN
Regulation
Quiescent Current
Shutdown Current
Powersave Mode; V
FB
= 0.62V or V
OUT
= 103%,
I
OUT
= 0mA,
T
AMB
= +25ºC
Shutdown Mode; V
EN
= 0V,
T
AMB
= +25ºC
30
0.1
∆
I
V
V
FB
FB
VFB
Regulated Feedback Voltage
1
Reference Voltage
Line Regulation
Feedback Current
AS1324, I
V
IN
OUT
= 100mA
= 2.7V to 5.5V
0.585
-30
0.6
0.1
V
OUT
Regulated Output Voltage
T
AMB
= +25ºC
AS1324-AD, I
OUT
= 100mA
2
AS1324-12, I
OUT
= 100mA
AS1324-15, I
OUT
= 100mA
AS1324-18, I
OUT
= 100mA
V
FB
1.164
1.455
1.746
1.20
1.50
1.80
V
∆
V
OUT
LOADREG
Output Voltage
Line Regulation
Output Voltage
Load Regulation
I
V
IN
OUT
= 2.7 to 5.5V
= 0 to 100mA
0.1
0.02
DC-DC Switches
R
R
PFET
NFET
I
LSW
Control Inputs
V
I
I
PK
EN
EN
Oscillator
Peak Inductor Current
P-Channel FET R
DS(ON)
N-Channel FET R
DS(ON)
SW Leakage
EN Threshold
EN Leakage Current
V
IN
= 3V, V
FB
= 0.5V or V
OUT
= 90%, T
AMB
=
25ºC
I
LSW
= 100mA
I
LSW
= -100mA
V
EN
= 0V, V
SW
= 0V or 5V
0.5
0.3
0.75
0.4
0.35
±0.01
1
±0.01 f
OSC
Oscillator Frequency
V
FB
= 0.6V or V
OUT
= 100%
V
FB
= 0V or V
OUT
= 0V, T
AMB
= 25ºC
1.2 1.5
115
1. The device is tested in a proprietary test mode where V
FB
is connected to the output of the error amplifier.
2. Please see
Feedback Resistor Selection on page 13 for resistor values.
0.615
1
30
1.236
1.545
1.854
1
1
±1
1.5
±1
1.8
Max
5.5
35
1
Units
V
µA
V
%/V
%/mA
V
µA
MHz kHz
A
Ω
Ω
µA
V
%/V nA
Note:
All limits are guaranteed. The parameters with min and max values are guaranteed with production tests or SQC (Statistical Quality
Control) methods.
www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
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
Parts used for measurement: 4.7µH (MOS6020-472) Inductor, 10µF (GRM188R60J106ME47) C
IN
and C
OUT
.
Figure 3. Efficiency vs. Input Voltage; V
OUT
= 1.8V
95
90
85
80
75
70
65
60
55
IOUT = 600mA
IOUT = 100mA
IOUT = 10mA
IOUT = 1mA
50
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Figure 5. Efficiency vs. Output Current; V
OUT
= 1.5V
100
95
90
85
80
75
70
65
60
55
50
1 10 100
Output Current (mA)
V IN = 2.5V
V IN = 2.7V
V IN = 3.7V
V IN = 4.2V
V IN = 5.5V
1000
Figure 7. Efficiency vs. Output Current; V
OUT
= 2.5V
100
95
90
85
80
75
70
65
60
55
50
1 10 100
Output Current (mA)
V IN = 3.7V
V IN = 4.2V
V IN = 5.5V
1000 www.ams.com/DC-DC_Step-Up/AS1324
Figure 4. Efficiency vs. Output Current; V
OUT
= 1.2V
100
95
90
85
80
75
70
65
60
55
50
1 10 100
Output Current (mA)
VIN = 2.5V
VIN = 2.7V
VIN = 3.7V
VIN = 4.2V
VIN = 5.5V
1000
Figure 6. Efficiency vs. Output Current; V
OUT
= 1.8V
100
95
90
85
80
75
70
65
60
55
50
1 10 100
Output Current (mA)
V IN = 2.5V
V IN = 2.7V
V IN = 3.7V
V IN = 4.2V
V IN = 5.5V
1000
Figure 8. Efficiency vs. Output Current; V
OUT
= 3.3V
100
95
90
85
80
75
70
65
60
55
50
1 10 100
Output Current (mA)
VIN = 4.2V
VIN = 5.5V
1000
Revision 1.06
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AS1324
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. Switching Frequency vs. Supply Voltage
1.6
1.55
Figure 10. Switching Frequency vs. Temperature
1.6
1.55
1.5
1.45
1.5
1.45
1.4
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
1.4
-45 -30 -15 0 15 30 45 60 75 90
Temperature (°C)
Figure 11. Feedback Voltage vs. Temperature
0.61
0.605
0.6
0.595
0.59
-45 -30 -15 0 15 30 45 60 75 90
Temperature (C°)
Figure 12. Output Voltage vs. Input Voltage
2
1.95
1.9
1.85
1.8
1.75
1.7
1.65
IOUT = 600mA
IOUT = 100mA
IOUT = 10mA
IOUT = 1mA
IOUT = 100µA
1.6
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Figure 13. V
OUT
vs. I
OUT
; V
OUTNOM
= 1.2V
1.3
Vin=2.5V
Vin=2.7V
Vin=5.5V
1.25
1.2
Figure 14. V
OUT
vs. I
OUT
; V
OUTNOM
= 1.5V
1.6
1.55
Vin=2.5V
Vin=2.7V
Vin=5.5V
1.5
1.15
1.45
1.1
0 100 200 300 400
Output Current (mA)
500 600 www.ams.com/DC-DC_Step-Up/AS1324
1.4
0
Revision 1.06
100 200 300 400
Output Current (mA)
500 600
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AS1324
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 15. Quiescent Current vs. Input Voltage
50
45
40
35
30
25
20
15
10
5
0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Figure 16. Quiescent Current vs. Temperature
50
45
40
35
30
25
20
15
10
5
0
-45 -30 -15 0 15 30 45 60 75 90
Temperature (°C)
Figure 17. Load Step 0mA to 600mA Figure 18. Load Step 10mA to 200mA
Figure 19. Startup
500µs/DIV
Figure 20. Powersave Mode
500µs/DIV
1ms/DIV www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
5µs/DIV
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AS1324
Datasheet - D e t a i l e d D e s c r i p t i o n
8 Detailed Description
The AS1324 is a high-efficiency buck converter that uses a constant-frequency current-mode architecture. The device contains two internal
MOSFET switches and is available in adjustable- and fixed-output voltage versions.
Figure 21. AS1324 - Block Diagram
5
V
OUT
/V
FB
1
EN
OSC
Ramp
Compensator
OSCN
Frequency
Shift
R
R
1
2
FB
0.6V
0.6V +
∆
V
OVL
+
Error
–
Amp
–
OVDET
+
–
+
0.6V
Reference
Shutdown
0.6V -
∆
V
OVL
–
ICOMP
+
AS1324
4
V
IN
C
IN
10µF
V
IN
Digital
Logic
Anti-
Shoot
Through
PMOS
NMOS
IRCMP
+
–
3
SW
4.7µH
2
GND
V
OUT
C
OUT
10µF
Not applicable to AS1324
AS1324-12: R
1
+ R
2
= 600k
Ω
AS1324-15: R
1
+ R
2
= 750k
Ω
AS1324-18: R
1
+ R
2
= 900k
Ω www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
Datasheet - D e t a i l e d D e s c r i p t i o n
8.1 Main Control Loop
During PWM operation the converters use a 1.5MHz fixed-frequency, current-mode control scheme. Basis of the current-mode PWM controller is an open-loop, multiple input comparator that compares the error-amp voltage feedback signal against the sum of the amplified current-sense signal and the slope-compensation ramp. At the beginning of each clock cycle, the internal high-side PMOS turns on until the PWM comparator trips. During this time the current in the inductor ramps up, sourcing current to the output and storing energy in the inductor’s magnetic field.
When the PMOS turns off, the internal low-side NMOS turns on. Now the inductor releases the stored energy while the current ramps down, still providing current to the output. The output capacitor stores charge when the inductor current exceeds the load and discharges when the inductor current is lower than the load. Under overload conditions, when the inductor current exceeds the current limit, the high-side PMOS is turned off and the low-side NMOS remains on until the next clock cycle.
When the PMOS is off, the NMOS is turned on until the inductor current starts to reverse (as indicated by the current reversal comparator
(IRCMP)), or the next clock cycle begins. The IRCMP detects the zero crossing.
The peak inductor current (I
PK
) is controlled by the error amplifier. When I
OUT
increases, V
FB
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.
The over-voltage detection comparator (OVDET) guards against transient overshoots by turning the main switch off and keeping it off until the transient is removed.
8.2 Powersave Operation
The AS1324 uses an automatic powersave mode where the peak inductor current (I
PK
) is set to approximately 200mA while independent of the output load. In powersave mode, load current is supplied solely from the output capacitor. As the output voltage drops, the error amplifier output rises above the powersave threshold signaling to switch into PWM fixed frequency mode and turn the PMOS on. This process repeats at a rate determined by the load demand.
Each burst event can last from a few cycles at light loads to almost continuous cycling (with short sleep intervals) at moderate loads. In between bursts, the power MOSFETs are turned off, as is any unneeded circuitry, reducing quiescent current to 30µA.
8.3 Short-Circuit Protection
In cases where the AS1324 output is shorted to ground, the oscillator frequency (f
OSC
) is reduced to 1/13 the nominal frequency (
≅
115kHz).
This frequency reduction ensures that the inductor current has more time to decay, thus preventing runaway conditions. f
OSC
will progressively increase to 1.5MHz when V
FB
/V
OUT
> 0V.
8.4 Shutdown
Connecting EN to GND or logic low places the AS1324 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 V
IN
or logic high.
Note:
Pin EN should not be left floating.
www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
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 AS1324 is perfect for mobile communications equipment like cell phones and smart phones, digital cameras and camcorders, portable MP3 and DVD players, PDA’s and palmtop computers and any other handheld instruments.
Figure 22. Single Li-Ion 1.2V/600mA Regulator for High-Efficiency
V
IN
2.7 to 4.2V
C
IN
2.2µF
4
V
IN
1
EN
AS1324
4.7µH
3
SW
22pF
5
V
FB
R
1
301k
Ω
301k
Ω
R
2
2
GND
C
OUT
10µF
V
OUT
1.2V
600mA
Figure 23. 5V Input to 3.3V/600mA Buck Regulator
V
IN
5V
C
IN
4.7µF
4
V
IN
1
EN
AS1324
4.7µH
3
SW
22pF
5
V
FB
R
1
301k
Ω
66.5k
Ω
R
2
2
GND
C
OUT
10µF
V
OUT
3.3V
600mA
Figure 24. Single Li-Ion 1.5V/600mA Regulator for High-Efficiency
V
IN
2.7 to 4.2V
C
IN
4.7µF
4
V
IN
AS1324-15
3
SW
4.7µH
1
EN
5
V
OUT
2
GND
C
OUT
10µF
V
OUT
1.5V
600mA www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
10 - 21
AS1324
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
Figure 25. Single Li-Ion 1.8V/600mA Regulator for Low Output Ripple
V
IN
2.7 to 4.2V
C
IN
10µF
4
V
IN
AS1324-18
3
SW
4.7µH
1
EN
5
V
OUT
2
GND
C
OUT
22µF
V
OUT
1.8V
600mA
9.1 External Component Selection
9.2 Inductor Selection
For most applications the value of the external inductor should be in the range of 2.2 to 6.8µH as the inductor value has a direct effect on the ripple current. The selected inductor must be rated for its DC resistance and saturation current. The inductor ripple current (
∆
I
L
) decreases with higher inductance and increases with higher V
IN
or V
OUT
.
In
the maximum inductor current in PWM mode under static load conditions is calculated. The saturation current of the inductor should be rated higher than the maxim um in
ductor current as calculated with Equation (EQ 3) . This is recommended because the inductor
current will rise above the calculated value during heavy load transients.
∆
I
L
=
V
OUT
×
1
–
V
--------------
V
------------------------
L
× f
(EQ 2)
I
LMAX
=
I
OUT MAX
+
∆
I
L
--------
2
Where:
f = Switching Frequency (1.5 MHz typical)
L = Inductor Value
I
Lmax
= Maximum Inductor current
∆
I
L =
Peak to Peak inductor ripple current
The recommended starting point for setting ripple current is
∆
I
L
= 240mA (40% of 600mA).
(EQ 3)
The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation.
Thus, a 720mA rated inductor should be sufficient for most applications (600mA + 120mA). A easy and fast approach is to select the inductor current rating fitting to the maximum switch current limit of the converter.
Note:
For highest efficiency, a low DC-resistance inductor is recommended.
Accepting larger values of ripple current allows the use of low inductance values, but results in higher output voltage ripple, greater core losses, and lower output current capability.
The total losses of the coil have a strong impact on the efficiency of the dc/dc conversion and consist of both the losses in the dc resistance and the following frequency-dependent components:
1. The losses in the core material (magnetic hysteresis loss, especially at high switching frequencies)
2. Additional losses in the conductor from the skin effect (current displacement at high frequencies)
3. Magnetic field losses of the neighboring windings (proximity effect)
4. Radiation losses www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
Table 5. Recommended Inductors
Part Number
LQH32CN2R2M33
LQH32CN4R7M33
LPS3008-222MLC
LPS3015-222MLC
MOS6020-222MLC
MOS6020-472MLC
CDRH3D16NP-2R2N
CDRH3D16ND-4R7N
L
2.2µH
4.7µH
2.2µH
2.2µH
2.2µH
4.7µH
2.2µH
4.7µH
DCR
97m
Ω
150m
Ω
175m
Ω
110m
Ω
35m
Ω
50m
Ω
72m
Ω
105m
Ω
Current Rating
790mA
650mA
1100mA
2000mA
3260mA
1820mA
1200mA
900mA
Figure 26. Efficiency Comparison of Different Inductors, V
IN
= 2.7V, V
OUT
= 1.8V and 1.2V
95
V
OUT
= 1.8V
95
V
OUT
= 1.2V
Dimensions (L/W/T)
3.2x2.5x2.0mm
3.2x2.5x2.0mm
3.1x3.1x0.8mm
3.1x3.1x1.5mm
6.0x6.8x2.4mm
6.0x6.8x2.4mm
4.0x4.0x1.8mm
4.0x4.0x1.8mm
Murata
Manufacturer
www.murata.com
Coilcraft www.coilcraft.com
Sumida www.sumida.com
90
90
85
80
85
80
75 75
70
1
LQH32CN2R2
LPS3015-222
LQH32CN4R7
LPS3008-222
M OS6020-222
M OS6020-472
10 100
Output Current (mA)
1000
70
1
LQH32CN2R2
LPS3015-222
LQH32CN4R7
LPS3008-222
M OS6020-222
M OS6020-472
10 100
Output Current (mA)
1000
9.3 Output Capacitor Selection
The advanced fast-response voltage mode control scheme of the AS1324 allows the use of tiny ceramic capacitors. Because of their lowest output voltage ripple low ESR ceramic capacitors are recommended. X7R or X5R dielectric output capacitor are recommended.
At high load currents, the device operates in PWM mode and the RMS ripple current is calculated as:
I
RMSC
OUT
= V
OUT
×
1 –
V
--------------
V
------------------------
L
× f
×
2
×
3
(EQ 4)
While operating in PWM mode the overall output voltage ripple is the sum of the voltage spike caused by the output capacitor ESR plus the voltage ripple caused by charging and discharging the output capacitor:
∆
V
OUT
=
V
OUT
×
1
–
V
--------------
V
------------------------
L
× f
×
8
×
C
1
OUT
× f
+
ESR
(EQ 5)
Higher value, low cost ceramic capacitors are available in very small case sizes, and their high ripple current, high voltage rating, and low ESR make them ideal for switching regulator applications. Because the AS1324 control loop is not dependant on the output capacitor ESR for stable operation, ceramic capacitors can be used to achieve very low output ripple and accommodate small circuit size.
At light loads, the converter operates in powersave mode and the output voltage ripple is in direct relation to the output capacitor and inductor value used. Larger output capacitor and inductor values minimize the voltage ripple in powersave mode and tighten DC output accuracy in powersave mode.
www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
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 Input Capacitor Selection
In continuous mode, the source current of the PMOS is a square wave of the duty cycle V
OUT
/V
IN
. To prevent large voltage transients while minimizing the interference with other circuits caused by high input voltage spikes, a low ESR input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitor current is given as:
I
RMS
=
I
MAX
×
V
OUT
× (
V
IN
– V
OUT
)
V
IN
(EQ 6)
where the maximum average output current I
MAX
equals the peak current minus half the peak-to-peak ripple current, I
MAX
= I
LIM
-
∆
I
L
/2
This formula has a maximum at V
IN
= 2V
OUT
where I
RMS
= I
OUT
/2. This simple worst-case condition is commonly used for design because even significant deviations only provide negligible affects.
The input capacitor can be increased without any limit for better input voltage filtering. Take care when using small ceramic input capacitors.
When a small ceramic capacitor is used at the input, and the power is being supplied through long wires, such as from a wall adapter, a load step at the output, or V
IN
step on the input, can induce ringing at the VIN pin. This ringing can then couple to the output and be mistaken as loop instability, or could even damage the part by exceeding the maximum ratings.
9.4.1 Ceramic Input and Output Capacitors
When choosing ceramic capacitors for C
IN
and C
OUT
, the X5R or X7R dielectric formulations are recommended. These dielectrics have the best temperature and voltage characteristics for a given value and size. Y5V and Z5U dielectric capacitors, aside from their wide variation in capacitance over temperature, become resistive at high frequencies and therefore should not be used.
Table 6. Recommended Input and Output Capacitor
Part Number
JMK212BJ226MG-T
GRM188R60J106ME47
GRM21BR71A475KA73
C
22µF
10µF
4.7µF
TC Code
X5R
X5R
X7R
Rated Voltage
6.3V
6.3V
10V
Dimensions (L/W/T)
0805
0603
0805
Manufacturer
Taiyo Yuden www.t-yuden.com
Murata www.murata.com
Because ceramic capacitors lose a lot of their initial capacitance at their maximum rated voltage, it is recommended that either a higher input capacity or a capacitance with a higher rated voltage is used.
9.5 Feedback Resistor Selection
In the AS1324-AD, the output voltage is set by an external resistor divider connected to V
FB
(see Figure 27) . This circuitry allows for remote
voltage sensing and adjustment.
Figure 27. Setting the AS1324 Output Voltage
AS1324
5
V
FB
2
GND
0.6V
≤
V
OUT
≤
5.5V
R
2
R
1
<<R
2
R
1
Resistor values for the circuit shown in
Figure 27 can be calculated as:
V
OUT
= 0,6
×
1 +
R
-------
R
1
(EQ 7)
The output voltage can be adjusted by selecting different values for R
1
and R
2
. For R
1
a value between 10k
Ω
and 500k
Ω is recommended. A higher resistance of R
1
and R
2
will result in a lower leakage current at the output. It is recommended to keep V
IN
500mV higher than V
OUT
.
www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
9.6 Efficiency
The efficiency of a switching regulator is equivalent to:
Efficiency = (P
OUT
/P
IN
)100% (EQ 8)
For optimum design, an analysis of the AS1324 is needed to determine efficiency limitations and to determine design changes for improved efficiency. Efficiency can be expressed as:
Efficiency = 100% – (L
1
+ L
2
+ L
3
+ ...) (EQ 9)
Where:
L
1
, L
2
, L
3
, etc. are the individual losses as a percentage of input power.
Although all dissipative elements in the circuit produce losses, those four main sources should be considered for efficiency calculation:
9.6.1 Input Voltage Quiescent Current Losses
The V
IN
current is the DC supply current given in the electrical characteristics which excludes MOSFET driver and control currents. V
IN
current results in a small (<0.1%) loss that increases with V
IN
, even at no load. The V
IN
quiescent current loss dominates the efficiency loss at very low load currents.
9.6.2 I²R Losses
Most of the efficiency loss at medium to high load currents are attributed to I²R loss, and are calculated from the resistances of the internal switches (R
SW)
and the external inductor (R
L
). In continuous mode, the average output current flowing through inductor L is split between the internal switches. Therefore, the series resistance looking into the SW pin is a function of both NMOS & PMOS R
DS(ON)
as well as the duty cycle (DC) and can be calculated as follows:
R
SW
= (R
DS(ON)PMOS
)(DC) + (R
DS(ON)NMOS
)(1 – DC) (EQ 10)
The R
DS(ON)
I²R losses = I
OUT
²(R
SW
+ R
L
) (EQ 11)
9.6.3 Switching Losses
The switching current is the sum of the control currents and the MOSFET driver. The MOSFET driver current results from switching the gate capacitance of the power MOSFETs. If a MOSFET gate is switched from low to high to low again, a packet of charge dQ moves from V
IN
to ground. The resulting dQ/dt is a current out of V
IN
that is typically much larger than the DC bias current. In continuous mode:
(EQ 12) I
GC
= f(Q
PMOS
+ Q
NMOS
)
Where:
Q
PMOS
and Q
NMOS
are the gate charges of the internal MOSFET switches.
The losses of the gate charges are proportional to V
IN
and thus their effects will be more visible at higher supply voltages.
9.6.4 Other Losses
Basic losses in the design of a system should also be considered. Internal battery resistances and copper trace can account for additional efficiency degradations in battery operated systems. By making sure that C
IN
has adequate charge storage and very low ESR at the given switching frequency, the internal battery and fuse resistance losses can be minimized. C
IN
and C
OUT
ESR dissipative losses and inductor core losses generally account for less than 2% total additional loss.
9.7 Thermal Shutdown
Due to its high-efficiency design, the AS1324 will not dissipate much heat in most applications. However, in applications where the AS1324 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 AS1324 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 +145°C again.
9.8 Checking Transient Response
The main loop response can be evaluated by examining the load transient response. Switching regulators normally take several cycles to respond to a step in load current. When a load step occurs, V
OUT
immediately shifts by an amount equivalent to:
V
DROP
=
∆
I
OUT
x ESR (EQ 13)
Where:
ESR is the effective series resistance of C
OUT
.
∆
I
OUT
also begins to charge or discharge C
OUT
, which generates a feedback error signal. The regulator loop then acts to return V
OUT
to its steady-state value. During this recovery time V
OUT
can be monitored for overshoot or ringing that would indicate a stability problem. www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
9.9 Design Example
shows the AS1324 used in a single lithium-ion (3.7V typ) battery-powered mobile phone application. The load current requirement is
600mA (max) but most of the time the device will require only 2mA (standby mode current).
Figure 28. Design Example
V
IN
3.7V
C
IN
4.7µF
CER
4
V
IN
1
EN
AS1324
3
SW
2.2µH
5
V
FB
R
1
22pF
1M
Ω
375k
Ω
R
2
2
GND
C
OUT
10µF
CER
V
OUT
2.2V
For the circuit shown in
external inductor, which is calculated as:
L =
V f
OUT
∆
I
L
×
1 –
V
--------------
V
IN
(EQ 14)
OUT
= 2.2V, V
IN
= 3.7V,
∆
I
L
= 240mA and f = 1.5MHz gives:
L
=
(
2,2V
----------------------------------------------------
1,5MHz 240mA
)
×
1
–
2,2V
------------
,
=
2,48
µ
H
(EQ 15)
Therefore, a standard 2.2µH inductor should be used for this design.
For best overall efficiency use an inductor with a rating of 720mA or greater and less than 0.2
Ω
series resistance. C
IN
will require an RMS current rating of at least 0.3A
≅
I
LOAD(MAX)
/2, whereas C
OUT
will require an ESR of less than 0.25
Ω
. In most cases, a ceramic capacitor will satisfy this requirement.
For the feedback resistors, select the value for R
1
= 375k
Ω
. R
2
can then be calculated from
to be:
R
2
= (V
OUT
/0.6 - 1)375k = 1000k
Ω www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
9.10 Layout Considerations
The AS1324 requires proper layout and design techniques for optimum performance.
The power traces (GND, SW, and V
IN
) should be kept as short, direct, and wide as is practical.
Pin V
FB
(AS1324 only) should be connected directly to the feedback resistors (R
1
and R
2
). A potentiometer as replacement for R
1
and R
2 should be avoided to minimize the output voltage ripple and to maintain the stability of the regulator.
The resistive divider (R
1
/R
2
) must be connected between the positive plate of C
OUT
and ground.
The positive plate of C
IN
should be connected as close to V
IN
as is practical since C
IN
provides the AC current to the internal power MOS-
FETs.
Switching node SW should be kept far away from the sensitive V
FB
node.
The negative plates of C
IN
and C
OUT
should be kept as close to each other as is practical. A starpoint to Ground is recommended.
Figure 29. AS1324 Basic PCB Layout
V
OUT
R
1
Via to V
IN
L
1
R
2
SW
1
2
3
C
OUT
AS1324
5
4
C
IN
GND
C
FWD
V
IN
Via to GND
Via to V
OUT
Figure 30. AS1324 Basic Diagram
V
OUT
1
EN
2
GND
C
OUT
L
1
3
SW
AS1324
5
V FB
C
IN
4
V IN
R
2
C
FWD
R
1
V
IN
High Current Path www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
Figure 31. AS1324-18 Basic PCB Layout
Via to V
IN
V
OUT
L
1
SW
C
1
2
AS1324-18
5
3 4
OUT
C
IN
GND
V
IN
Via to V
OUT
Figure 32. AS1324-18 Basic Diagram
V
OUT
1
EN
2
GND
AS1324-18
C
OUT
L
1
3
SW
C
IN
5
V OUT
4
V IN
V
IN
High Current Path www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
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 an 5-pin TSOT-23 package.
Figure 33. 5-pin TSOT-23 Package
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AS1324
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 34. 5-pin TSOT-23 Marking
Pin1
Bottom
Top
Pin1
ZZZZ XXXX
Package Code:
ZZZZ - Marking
XXXX - encoded Datecode www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
Datasheet
11 Ordering Information
The device is available as the following standard versions.
Table 7. Ordering Information
Ordering Code Marking Output
AS1324-BTTT-AD
AS1324-BTTT-12
AS1324-BTTT-15
AS1324-BTTT-18
ASKR
ASKT
ASKU
ASKS adjustable
1.2V
1.5V
1.8V
Description
1.5MHz, 600mA Synchronous DC/DC
Converter
1.5MHz, 600mA Synchronous DC/DC
Converter
1.5MHz, 600mA Synchronous DC/DC
Converter
1.5MHz, 600mA Synchronous DC/DC
Converter
Delivery Form
Tape and Reel
Tape and Reel
Tape and Reel
Tape and Reel
Package
5-pin TSOT-23
5-pin TSOT-23
5-pin TSOT-23
5-pin TSOT-23
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:[email protected]
or find your local distributor at http://www.ams.com/distributor ams www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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AS1324
Datasheet - O r d e r i n g I n f o r m a t i o n
Copyrights
Copyright © 1997-2010, 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 indirect, special, incidental or consequential damages, of any kind, in connection with or arising out of the furnishing, performance or use of the technical data herein. No obligation or liability to recipient or any third party shall arise or flow out of ams AG rendering of technical or other services.
Contact Information
Headquarters
ams AG
Tobelbaderstrasse 30
A-8141 Unterpremstaetten, Austria
Tel: +43 (0) 3136 500 0
Fax: +43 (0) 3136 525 01
For Sales Offices, Distributors and Representatives, please visit: http://www.ams.com/contact www.ams.com/DC-DC_Step-Up/AS1324 Revision 1.06
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