AS1324-18 [AMSCO]
1.5MHz, 600mA, DC/DC Step-Down Regulator; 1.5MHz的, 600毫安, DC / DC降压型稳压器型号: | AS1324-18 |
厂家: | AMS(艾迈斯) |
描述: | 1.5MHz, 600mA, DC/DC Step-Down Regulator |
文件: | 总20页 (文件大小:910K) |
中文: | 中文翻译 | 下载: | 下载PDF数据表文档文件 |
Data Sheet
AS1324
1.5MHz, 600mA, DC/DC Step-Down Regulator
1 General Description
2 Key Features
ꢀ High Efficiency: Up to 96%
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.
ꢀ 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
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.
Table 1. Standard Versions
Model
Output Voltage
Adjustable via External Resistors
Fixed: 1.2V
AS1324-AD
AS1324-12
AS1324-15
AS1324-18
ꢀ Shutdown Mode Supply Current: ≤1µA
ꢀ Thermal Protection
Fixed: 1.5V
Fixed: 1.8V
ꢀ 5-pin TSOT-23 Package
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.
3 Applications
Very low output voltages can be delivered with the inter-
nal 0.6V feedback reference voltage.
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 applica-
tion with low power-consumption requirements.
The AS1324 is available in a 5-pin TSOT-23 package.
Figure 1. Typical Application Diagram – High Efficiency Step Down Converter
4.7µH
VOUT = 1.8V, 600mA
VIN = 2.7V to 5.5V
4
3
EN
1
5 VOUT
VIN
SW
CIN
10µF
COUT
10µF
AS1324-
18
AS1324-
18
GND 2
SW 3
5
1
VOUT
EN
4 VIN
GND
2
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AS1324
Data Sheet - Pinout and Packaging
4 Pinout and Packaging
Pin Assignments
Figure 2. Pin Assignments (Top View)
EN
EN
1
2
3
5
VFB
1
2
3
5
VOUT
AS1324-12/
AS1324-15/
AS1324-18
AS1324
GND
SW
GND
SW
4
VIN
4 VIN
Pin Descriptions
Table 2. Pin Descriptions
Pin
Pin Name
Number
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.
1
EN
Note: This pin should not be left floating.
Ground.
2
3
GND
SW
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.
4
5
VIN
VFB
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.)
VOUT
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AS1324
Data Sheet - Absolute Maximum Ratings
5 Absolute Maximum Ratings
Stresses beyond those listed in Table 3 may cause permanent damage to the device. These are stress ratings only,
and functional operation of the device at these or any other conditions beyond those indicated in 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
Comments
VIN to GND
-0.3
7
V
VIN
+ 0.3
SW, EN, FB to GND
-0.3
V
Thermal Resistance ΘJA
ESD
207.4
ºC/W
kV
on PCB
HBM MIL-Std. 883E 3015.7 methods
JEDEC 78
2
Latch-Up
-100
-40
+100
+85
mA
ºC
Operating Temperature Range
Storage Temperature Range
-65
+125
ºC
The reflow peak soldering temperature (body
temperature) specified is in accordance with
IPC/JEDEC J-STD-020C “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).
Package Body Temperature
Junction Temperature
+260
125
ºC
ºC
Junction temperature (TJ) is calculated from
the ambient temperature (TAMB) and power
dissipation (PD) as:
TJ = TAMB + (PD)(207.4ºC/W)
(EQ 1)
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AS1324
Data Sheet - Electrical Characteristics
6 Electrical Characteristics
VIN = EN = 3.6V, VOUT < VIN - 0.5V, TAMB = -40 to +85°C, typ. values @ TAMB = +25ºC (unless otherwise specified).
Table 4. Electrical Characteristics
Symbol
Parameter
Conditions
Min
Typ
Max
Units
VIN
Input Voltage Range
2.7
5.5
V
Powersave Mode; VFB = 0.62V or VOUT =
IQ
Quiescent Current
Shutdown Current
30
35
1
103%, IOUT = 0mA,
T
AMB = +25ºC
µA
ISHDN
Shutdown Mode; VEN = 0V,
TAMB = +25ºC
0.1
Regulation
Regulated Feedback
Voltage 1
VFB
AS1324, IOUT = 100mA
VIN = 2.7V to 5.5V
0.585
0.6
0.1
0.615
V
Reference Voltage
Line Regulation
ΔVFB
1
%/V
nA
IVFB
Feedback Current
TAMB = +25ºC
-30
30
AS1324-AD, IOUT = 100mA2
AS1324-12, IOUT = 100mA
AS1324-15, IOUT = 100mA
AS1324-18, IOUT = 100mA
VFB
1.164
1.455
1.746
1.20
1.50
1.80
1.236
1.545
1.854
Regulated Output
Voltage
VOUT
V
Output Voltage
Line Regulation
ΔVOUT
VIN = 2.7 to 5.5V
0.1
1
%/V
Output Voltage
Load Regulation
VLOADREG
IOUT = 0 to 100mA
0.02
%/mA
DC-DC Switches
VIN = 3V, VFB = 0.5V or VOUT = 90%,
TAMB = 25ºC
IPK
Peak Inductor Current
0.5
0.75
1
A
RPFET
RNFET
ILSW
P-Channel FET RDS(ON)
N-Channel FET RDS(ON)
SW Leakage
ILSW = 100mA
ILSW = -100mA
0.4
0.35
±0.01
Ω
Ω
VEN = 0V, VSW = 0V or 5V
±1
µA
Control Inputs
VEN
EN Threshold
0.3
1.2
1
1.5
±1
V
IEN
EN Leakage Current
±0.01
µA
Oscillator
VFB = 0.6V or VOUT = 100%
1.5
1.8
MHz
kHz
fOSC
Oscillator Frequency
VFB = 0V or VOUT = 0V, TAMB = 25ºC
115
1. The device is tested in a proprietary test mode where VFB is connected to the output of the error amplifier.
2. Please see Feedback Resistor Selection on page 13 for resistor values.
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AS1324
Data Sheet - Typical Operating Characteristics
7 Typical Operating Characteristics
Parts used for measurement: 4.7µH (MOS6020-472) Inductor, 10µF (GRM188R60J106ME47) CIN and COUT.
Figure 3. Efficiency vs. Input Voltage; VOUT = 1.8V
Figure 4. Efficiency vs. Output Current; VOUT = 1.2V
95
100
95
90
85
80
75
70
90
85
80
75
70
65
65
IOUT = 600mA
VIN =2.5V
VIN =2.7V
60
60
IOUT = 100mA
VIN =3.7V
VIN =4.2V
VIN = 5.5V
IOUT = 10mA
55
55
IOUT = 1mA
50
50
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
1
10
100
1000
Input Voltage (V)
Output Current (mA)
Figure 5. Efficiency vs. Output Current; VOUT = 1.5V
Figure 6. Efficiency vs. Output Current; VOUT = 1.8V
100
100
95
90
85
80
75
70
95
90
85
80
75
70
65
65
VIN =2.5V
VIN =2.7V
VIN =3.7V
VIN =2.5V
VIN =2.7V
60
60
VIN =3.7V
VIN =4.2V
VIN = 5.5V
55
VIN =4.2V
VIN = 5.5V
55
50
50
1
10
100
1000
1
10
100
1000
Output Current (mA)
Output Current (mA)
Figure 7. Efficiency vs. Output Current; VOUT = 2.5V
Figure 8. Efficiency vs. Output Current; VOUT = 3.3V
100
100
95
90
85
80
75
70
65
95
90
85
80
75
70
65
60
VIN =3.7V
60
VIN =4.2V
VIN =4.2V
55
55
VIN = 5.5V
VIN = 5.5V
50
50
1
10
100
1000
1
10
100
1000
Output Current (mA)
Output Current (mA)
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AS1324
Data Sheet - Typical Operating Characteristics
Figure 9. Switching Frequency vs. Supply Voltage
Figure 10. Switching Frequency vs. Temperature
1.6
1.6
1.55
1.5
1.55
1.5
1.45
1.4
1.45
1.4
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
-45 -30 -15
0
15 30 45 60 75 90
Input Voltage (V)
Temperature (°C)
Figure 11. Feedback Voltage vs. Temperature
Figure 12. Output Voltage vs. Input Voltage
0.61
2
1.95
1.9
0.605
0.6
1.85
1.8
1.75
1.7
0.595
0.59
IOUT = 600mA
IOUT = 100mA
IOUT = 10mA
IOUT = 1mA
1.65
1.6
IOUT = 100µA
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
-45 -30 -15
0
15 30 45 60 75 90
Temperature (C°)
Input Voltage (V)
Figure 13. VOUT vs. IOUT; VOUTNOM = 1.2V
Figure 14. VOUT vs. IOUT; VOUTNOM = 1.5V
1.6
1.3
Vin=2.5V
Vin=2.7V
Vin=5.5V
Vin=2.5V
Vin=2.7V
Vin=5.5V
1.55
1.5
1.25
1.2
1.45
1.4
1.15
1.1
0
100
200
300
400
500
600
0
100
200
300
400
500
600
Output Current (mA)
Output Current (mA)
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AS1324
Data Sheet - Typical Operating Characteristics
Figure 15. Quiescent Current vs. Input Voltage
Figure 16. Quiescent Current vs. Temperature
50
50
45
40
35
30
25
20
15
10
5
45
40
35
30
25
20
15
10
5
0
0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
-45 -30 -15
0
15 30 45 60 75 90
Input Voltage (V)
Temperature (°C)
Figure 17. Load Step 0mA to 600mA
Figure 18. Load Step 10mA to 200mA
500µs/DIV
500µs/DIV
Figure 19. Startup
Figure 20. Powersave Mode
1ms/DIV
5µs/DIV
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AS1324
Data Sheet - Detailed Description
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. Block Diagram
Ramp
Compensator
–
VIN
4
ICOMP
+
OSC
VIN
CIN
10µF
OSCN
Frequency
Shift
5
AS1324
VOUT/VFB
0.6V
+
Error
R1
Amp
–
FB
R2
–
PMOS
NMOS
OVDET
+
Digital
Logic
Anti-
Shoot
Through
0.6V +
ΔVOVL
4.7µH
VOUT
3
–
+
SW
COUT
10µF
1
0.6V
Reference
0.6V -
ΔVOVL
EN
+
IRCMP
Shutdown
2
–
GND
Not applicable to AS1324
AS1324-12: R1 + R2 = 600kΩ
AS1324-15: R1 + R2 = 750kΩ
AS1324-18: R1 + R2 = 900kΩ
Main Control Loop
During PWM operation the converters use a 1.5MHz fixed-frequency, current-mode control scheme. Basis of the cur-
rent-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 (IPK) is controlled by the error amplifier. When IOUT increases, VFB decreases slightly relative
to the internal 0.6V reference, causing the error amplifier’s output voltage to increase until the average inductor current
matches the new load current.
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.
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AS1324
Data Sheet - Detailed Description
Powersave Operation
The AS1324 uses an automatic powersave mode where the peak inductor current (IPK) 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 quies-
cent current to 30µA.
Short-Circuit Protection
In cases where the AS1324 output is shorted to ground, the oscillator frequency (fOSC) is reduced to 1/13 the nominal
frequency (≅ 115kHz). This frequency reduction ensures that the inductor current has more time to decay, thus pre-
venting runaway conditions. fOSC will progressively increase to 1.5MHz when VFB/VOUT > 0V.
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 discon-
necting the input from the output. The output capacitance and load current determine the voltage decay rate. For nor-
mal operation connect EN to VIN or logic high.
Note: Pin EN should not be left floating.
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AS1324
Data Sheet - Application Information
9 Application Information
The AS1324 is perfect for mobile communications equipment like cell phones and smart phones, digital cameras and
camcorders, portabel 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
4.7µH
VOUT
1.2V
600mA
4
3
VIN
2.7 to 4.2V
VIN
SW
CIN
2.2µF
COUT
10µF
22pF
AS1324
301kΩ
5
1
R2
EN
VFB
301kΩ
R1
GND
2
Figure 23. 5V Input to 3.3V/600mA Buck Regulator
4.7µH
VOUT
3.3V
600mA
4
3
VIN
5V
CIN
4.7µF
COUT
10µF
VIN
SW
22pF
AS1324
301kΩ
5
1
R2
EN
VFB
R1
66.5kΩ
GND
2
Figure 24. Single Li-Ion 1.5V/600mA Regulator for High-Efficiency
4.7µH
VOUT
1.5V
600mA
4
3
VIN
2.7 to 4.2V
VIN
SW
COUT
10µF
CIN
4.7µF
AS1324-
15
5
1
EN
VOUT
GND
2
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AS1324
Data Sheet - Application Information
Figure 25. Single Li-Ion 1.8V/600mA Regulator for Low Output Ripple
4.7µH
VOUT
1.8V
600mA
4
3
VIN
2.7 to 4.2V
VIN
SW
CIN
10µF
COUT
22µF
AS1324-
18
5
1
EN
VOUT
GND
2
External Component Selection
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 cur-
rent. The inductor ripple current (ΔIL) decreases with higher inductance and increases with higher VIN or VOUT.
In Equation (EQ 2) the maximum inductor current in PWM mode under static load conditions is calculated. The satura-
tion current of the inductor should be rated higher than the maximum inductor current as calculated with Equation (EQ
3). This is recommended because the inductor current will rise above the calculated value during heavy load tran-
sients.
VOUT
--------------
1 –
(EQ 2)
(EQ 3)
VIN
-----------------------
×
ΔIL = VOUT
L × f
ΔIL
-------
+
ILMAX = IOUTMAX
2
Where:
f = Switching Frequency (1.5 MHz typical)
L = Inductor Value
ILmax = Maximum Inductor current
ΔIL = Peak to Peak inductor ripple current
The recommended starting point for setting ripple current is ΔIL = 240mA (40% of 600mA).
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 con-
verter.
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.
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AS1324
Data Sheet - Application Information
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
Table 5. Recommended Inductors
Part Number
L
DCR
97mΩ
150mΩ
175mΩ
110mΩ
35mΩ
50mΩ
72mΩ
105mΩ
Current Rating Dimensions (L/W/T)
Manufacturer
Murata
www.murata.com
LQH32CN2R2M33
LQH32CN4R7M33
LPS3008-222MLC
LPS3015-222MLC
MOS6020-222MLC
MOS6020-472MLC
CDRH3D16NP-2R2N
CDRH3D16ND-4R7N
2.2µH
4.7µH
2.2µH
2.2µH
2.2µH
4.7µH
2.2µH
4.7µH
790mA
650mA
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
Coilcraft
www.coilcraft.com
1100mA
2000mA
3260mA
1820mA
1200mA
900mA
Sumida
www.sumida.com
Figure 26. Efficiency Comparison of Different Inductors, VIN = 2.7V, VOUT = 1.8V and 1.2V
95
90
85
80
75
70
95
90
85
80
75
70
VOUT = 1.8V
VOUT = 1.2V
LQH32CN2R2
LPS3015-222
LQH32CN4R7
LPS3008-222
M OS6020-222
M OS6020-472
LQH32CN2R2
LPS3015-222
LQH32CN4R7
LPS3008-222
M OS6020-222
M OS6020-472
1
10
100
1000
1
10
100
1000
Output Current (mA)
Output Current (mA)
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:
VOUT
--------------
1 –
(EQ 4)
VIN
----------------------- ----------------
1
IRMSC
= VOUT
×
×
OUT
L × f
2 ×
3
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:
VOUT
--------------
1 –
(EQ 5)
VIN
-----------------------
1
⎛
⎝
⎞
--------------------------------
ΔVOUT = VOUT
×
×
+ ESR
⎠
L × f
8 × COUT × f
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AS1324
Data Sheet - Application Information
Higher value, low cost ceramic capacitors are available in very small case sizes, and their high ripple current, high volt-
age 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 out-
put 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 power-
save mode and tighten DC output accuracy in powersave mode.
Input Capacitor Selection
In continuous mode, the source current of thePMOS is a square wave of the duty cycle VOUT/VIN. To prevent large volt-
age 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:
(EQ 6)
VOUT × (VIN – VOUT
-----------------------------------------------------------
×
)
IRMS = IMAX
VIN
where the maximum average output current IMAX equals the peak current minus half the peak-to-peak ripple current,
IMAX = ILIM - ΔIL/2
This formula has a maximum at VIN = 2VOUT where IRMS = IOUT/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 VIN 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.
Ceramic Input and Output Capacitors
When choosing ceramic capacitors for CIN and COUT, 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 frequen-
cies and therefore should not be used.
Table 6. Recommended Input and Output Capacitor
Part Number
C
TC Code Rated Voltage Dimensions (L/W/T)
Manufacturer
Taiyo Yuden
www.t-yuden.com
JMK212BJ226MG-T
22µF
X5R
6.3V
0805
0603
0805
Murata
www.murata.com
GRM188R60J106ME47
GRM21BR71A475KA73
10µF
X5R
X7R
6.3V
10V
4.7µF
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.
Feedback Resistor Selection
In the AS1324-AD, the output voltage is set by an external resistor divider connected to VFB (see Figure 27). This cir-
cuitry allows for remote voltage sensing and adjustment.
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AS1324
Data Sheet - Application Information
Figure 27. Setting the AS1324 Output Voltage
0.6V ≤ VOUT ≤ 5.5V
R2
5
R1<<R2
VFB
R1
AS1324
2
GND
Resistor values for the circuit shown in Figure 27 can be calculated as:
R2
------
(EQ 7)
VOUT = 0,6 × 1 +
R1
The output voltage can be adjusted by selecting different values for R1 and R2. For R1 a value between 10kΩ and
500kΩ is recommended. A higher resistance of R1 and R2 will result in a lower leakage current at the output. It is rec-
ommended to keep VIN 500mV higher than VOUT.
Efficiency
The efficiency of a switching regulator is equivalent to:
Efficiency = (POUT/PIN)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% – (L1 + L2 + L3 + ...)
(EQ 9)
Where:
L1, L2, L3, etc. are the individual losses as a percentage of input power.
Althought all dissipative elements in the circuit produce losses, those four main sources should be considered for effi-
ciency calculation:
Input Voltage Quiescent Current Losses
The VIN current is the DC supply current given in the electrical characteristics which excludes MOSFET driver and con-
trol currents. VIN current results in a small (<0.1%) loss that increases with VIN, even at no load. The VIN quiescent cur-
rent loss dominates the efficiency loss at very low load currents.
I²R Losses
Most of the efficiency loss at medium to high load currents are attributed to I²R loss, and are calculated from the resis-
tances of the internal switches (RSW) and the external inductor (RL). 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 RDS(ON) as well as the the duty cycle (DC) and can be calculated as follows:
RSW = (RDS(ON)PMOS)(DC) + (RDS(ON)NMOS)(1 – DC)
(EQ 10)
The RDS(ON) for both MOSFETs can be obtained from the Electrical Characteristics on page 4. Thus, to obtain I²R
losses calculate as follows:
I²R losses = IOUT²(RSW + RL)
(EQ 11)
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 VIN to ground. The resulting dQ/dt is a current out of VIN that is typically
much larger than the DC bias current. In continuous mode:
IGC = f(QPMOS + QNMOS)
(EQ 12)
Where: QPMOS and QNMOS are the gate charges of the internal MOSFET switches.
The losses of the gate charges are proportional to VIN and thus their effects will be more visible at higher supply volt-
ages.
Other Losses
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AS1324
Data Sheet - Application Information
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 CIN has adequate
charge storage and very low ESR at the given switching frequency, the internal battery and fuse resistance losses can
be minimized. CIN and COUT ESR dissipative losses and inductor core losses generally account for less than 2% total
additional loss.
Thermal Shutdown
Due to its high-efficiency design, the AS1324 will not dissipate much heat in most applications. However, in applica-
tions 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.
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, VOUT immediately shifts by an
amount equivalent to:
VDROP = ΔIOUT x ESR
(EQ 13)
Where:
ESR is the effective series resistance of COUT.
ΔIOUT also begins to charge or discharge COUT, which generates a feedback error signal. The regulator loop then acts
to return VOUT to its steady-state value. During this recovery time VOUT can be monitored for overshoot or ringing that
would indicate a stability problem.
Design Example
Figure 28 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
2.2µH
4
3
VOUT
2.2V
VIN
3.7V
VIN
SW
CIN
4.7µF
CER
COUT
10µF
CER
22pF
AS1324
1MΩ
5
1
R2
EN
VFB
R1
375kΩ
GND
2
For the circuit shown in Figure 28, efficiency at low- and high-load currents is an important consideration when select-
ing the value for the external inductor, which is calculated as:
VOUT
--------------
fΔIL
VOUT
--------------
VIN
⎛
⎞
⎠
(EQ 14)
L =
× 1 –
⎝
From (EQ 14), substituting VOUT = 2.2V, VIN = 3.7V, ΔIL = 240mA and f = 1.5MHz gives:
2,2V
2,2V
⎞
⎛
(EQ 15)
----------------------------------------------------
------------
= 2,48μH
L =
× 1 –
⎝
⎠
3,7V
(1,5MHz × 240mA)
Therefore, a standard 2.2µH inductor should be used for this design.
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AS1324
Data Sheet - Application Information
For best overall efficiency use an inductor with a rating of 720mA or greater and less than 0.2Ω series resistance. CIN
will require an RMS current rating of at least 0.3A ≅ ILOAD(MAX)/2, whereas COUT will require an ESR of less than
0.25Ω. In most cases, a ceramic capacitor will satisfy this requirement.
For the feedback resistors, select the value for R1 = 375kΩ. R2 can then be calculated from (EQ 7) to be:
R2 = (VOUT/0.6 - 1)375k = 1000kΩ
Layout Considerations
The AS1324 requires proper layout and design techniques for optimum performance.
ꢀ
ꢀ
The power traces (GND, SW, and VIN) should be kept as short, direct, and wide as is practical.
Pin VFB (AS1324 only) should be connected directly to the feedback resistors (R1 and R2). A potentiometer as
replacement for R1 and R2 should be avoided to minimize the output voltage ripple and to maintain the stability of
the regulator.
ꢀ
ꢀ
The resistive divider (R1/R2) must be connected between the positive plate of COUT and ground.
The positive plate of CIN should be connected as close to VIN as is practical since CIN provides the AC current to
the internal power MOSFETs.
ꢀ
ꢀ
Switching node SW should be kept far away from the sensitive VFB node.
The negative plates of CIN and COUT should be kept as close to each other as is practical. A starpoint to Ground is
recommended.
Figure 29. AS1324 Basic PCB Layout
R1
VIN
Via to VIN
R2
Via to GND
Via to VOUT
1
5
AS1324
4
2
3
VOUT
L1
CFWD
SW
COUT
CIN
GND
Figure 30. AS1324 Basic Diagram
High Current Path
1
5
EN
VFB
AS1324
2
R2
R1
GND
COUT
CFWD
VOUT
3
4
L1
VIN
SW
CIN
VIN
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AS1324
Data Sheet - Application Information
Figure 31. AS1324-18 Basic PCB Layout
Via to VIN
1
VIN
Via to VOUT
5
AS1324-
18
2
3
VOUT
L1
SW
4
COUT
CIN
GND
Figure 32. AS1324-18 Basic Diagram
High Current Path
1
5
EN
VOUT
AS1324-18
2
GND
COUT
VOUT
3
4
VIN
SW
L1
CIN
VIN
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AS1324
Data Sheet - Package Drawings and Markings
10 Package Drawings and Markings
The device is available in an 5-pin TSOT-23 package.
Figure 33. 5-pin TSOT-23 Package
Symbol
Min
Typ
Max
1.00
0.10
0.90
0.45
0.39
0.20
Notes
Symbol
Min
Typ
0.40
Max
Notes
A
A1
A2
b
L
L1
L2
N
0.30
0.50
0.01
0.84
0.30
0.31
0.12
0.05
0.87
0.60REF
0.25BSC
5
b1
c
0.35
0.15
R
0.10
0.10
R1
0.25
8º
c1
0.08
0.13
0.16
0º
4º
4º
θ
θ1
D
E
2.90BSC
2.80BSC
1.60BSC
0.95BSC
1.90BSC
3,4
3,4
3,4
10º
12º
Tolerances of Form and Position
E1
e
aaa
bbb
ccc
ddd
0.15
0.25
0.10
0.20
e1
Notes:
1. Dimensioning and tolerancing conform to ASME Y14.5M - 1994.
2. Dimensions are in millimeters.
3. Dimension D does not include mold flash, protrusions, or gate burrs. Mold flash, protrusions, and gate burrs shall
not exceed 0.15mm per end. Dimension E1 does not include interlead flash or protrusion. Interlead flash or pro-
trusion shall not exceed 0.15mm per side. Dimensions D and E1 are determined at datum H.
4. The package top can be smaller than the package bottom. Dimensions D and E1 are determined at the outer-
most extremes of the plastic body exclusive of mold flash, tie bar burrs, gate burrs, and interlead flash, but
include any mistmatches between the top of the package body and the bottom. D and E1 are determined at
datum H.
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AS1324
Data Sheet - Ordering Information
11 Ordering Information
The device is available as the following standard versions.
Table 7. Ordering Information
Model
Marking
Description
Delivery Form
Package
Output
1.5MHz, 600mA Synchronous
DC/DC Converter
5-pin TSOT-23
AS1324-BTTT-AD
ASKR
adjustable
Tape and Reel
1.5MHz, 600mA Synchronous
DC/DC Converter
5-pin TSOT-23
5-pin TSOT-23
5-pin TSOT-23
AS1324-BTTT-12
AS1324-BTTT-15
AS1324-BTTT-18
ASKT
ASKU
ASKS
1.2V
1.5V
1.8V
Tape and Reel
Tape and Reel
Tape and Reel
1.5MHz, 600mA Synchronous
DC/DC Converter
1.5MHz, 600mA Synchronous
DC/DC Converter
All devices are RoHS compliant and free of halogene substances.
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AS1324
Data Sheet
Copyrights
Copyright © 1997-2009, 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. austria-
microsystems 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 informa-
tion. 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:
http://www.austriamicrosystems.com/contact-us
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