AS1335_05 [AMSCO]
1.5A, 1.5MHz, Synchronous DC/DC Step-Down Converter; 1.5A ， 1.5MHz的同步DC / DC降压转换器
| 型号： | AS1335_05 |
| 厂家： | 
AMS(艾迈斯) |
| 描述： | 1.5A, 1.5MHz, Synchronous DC/DC Step-Down Converter |
| 文件： | 总19页 (文件大小：2337K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
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ams AG
The technical content of this austriamicrosystems datasheet is still valid.
Contact information:
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ams AG
Tobelbaderstrasse 30
8141 Unterpremstaetten, Austria
Tel: +43 (0) 3136 500 0
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Datasheet
AS1335
1.5A, 1.5MHz, Synchronous DC/DC Step-Down Converter
1 General Description
2 Key Features
ꢀ High Efficiency: Up to 96%
The AS1335 is a high-efficiency, constant-frequency
synchronous buck converter available in a fixed or an
adjustable output voltage version. The wide input volt-
age range (2.6V to 5.25V), the high output current (up to
1.5A) and minimal external component requirements
make the AS1335 perfect for any single Li-Ion battery-
powered application.
ꢀ Output Current: 1.5A
ꢀ Input Voltage Range: 2.6V to 5.25V
ꢀ Output Voltage Range: 0.6V to VIN
ꢀ Constant Frequency Operation: 1.5MHz
ꢀ No Schottky Diode Required
Typical supply current with no load is 400µA and
decreases to ≤1µA in shutdown mode. The highly effi-
cient duty cycle (100%) provides low dropout operation,
prolonging battery life in portable systems.
ꢀ Power OK with 215ms delay
ꢀ Low Dropout Operation: 100% DutCycle
ꢀ Low Quiescent Supply Currnt: 400µA
ꢀ Shutdwn Mode Suppy Current: ≤1µA
The device also offers a power-ok signal with a 215ms
delay, which can be reseted or delayed further via the
RSI pin.
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.
Current Mode Operation for Excellent Line/Load
Transient Respose
ꢀ Thermal Protecon
The AS1335 is available in a 10-pin TDFN 3x3mm pack-
age.
ꢀ 10-pin FN x3mm 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 applica-
tion with low power-consumption requirements.
Figure 1. AS1335 - Typical Applicaion Diagram
2.2µH
VOUT
V
1.0V, 1.5A
2.6to 5.25V
COUT
SW
VIN
CIN
22µF
NC
22µF
PGND
AS1335
GND
FB
EN
POK
GND
RSI
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AS1335
Datasheet - Pinout
4 Pinout
Pin Assignments
Figure 2. Pin Assignments (Top View)
VIN
NC
1
2
3
4
5
10 SW
9
8
7
6
PGND
AS1335
EN
GND
FB
POK
GND
11
RSI
Pin Descriptions
Table 1. Pin Descriptions
Pin
Pin Name
Number
Descrption
Positive Supply Voltage. This must be closely decoupled to PGND with a ≥ 22µF
ceramic capacitor.
1
2
VIN
NC
Not Connected.
Enable Input. Driving this pin above 1.4V enables he device. Driving this pin below 0.3V
puts the device in shutdown mode. In shutdomode all functions are disabled, drawing
≤1µA supply current.
3
EN
Note: This pin shold not be left floating.
Power-OK Output. Open-drain output wth 215ms delay. Connect a 100kΩ pull-up resistor
to VOUT r pVIN for logic levels. Lave this pin unconnected if the Power-OK feature is
not used.
LOW Signal: Out of regulatio
HIGH signal: Within Reulation (after 215ms delay)
4
5
POK
GND
Analog Ground.
Reset Input for PK. This input resets the 215ms timer of the POK signal.
As long as RSI low the POK signal will work as described above.
A high input to I will reset the 215ms POK timer and delay the signal as long as RSI
stays hih. A RSI low-to-high transition restarts the 215ms counter as long as the output
voltage s wihin regulation.
6
RSI
FB
Nte: Do not leave this pin floating.
Feedback Pin. Feedback input to the gm error amplifier. Connect a resistor divider tap to
tis pin. The output can be adjusted from 0.6V to 5.25V by VOUT = 0.6V[1+(R1/R2)].
7
If the fixed output voltage version is used, connect this pin to VOUT.
Analog Ground. GND and PGND should only have one point connection.
Power-Ground. Connect all power grounds to this pin.
8
9
GND
PGND
Switch Node Connection to Inductor. This pin connects to the drains of the internal main
and synchronous power MOSFET switches.
10
11
SW
Exposed Pad. The exposed pad must be connected to PGND. Ensure a good connection
to the PCB to achieve optimal thermal performance.
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AS1335
Datasheet - Absolute Maximum Ratings
5 Absolute Maximum Ratings
Stresses beyond those listed in Table 2 may cause permanent damage to the device. These are stress ratings only,
and functional operation of the device at these or any other conditions beyond those indicated in Electrical Character-
istics on page 4 is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Table 2. Absolute Maximum Ratings
Parameter
VIN to GND
Min
-0.3
-0.3
-0.3
Max
6
Units
V
Comments
SW to GND
VIN + 0.3
VIN
V
EN, FB to GND
V
P-Channel Switch Source Current (DC)
N-Channel Switch Source Current (DC)
Peak SW Sink and Source Current
Thermal Resistance ΘJA
Latch-Up
1.5
A
1.5
A
3
A
36.7
100
ºC/W
mA
k
C
ºC
ºC
oPCB
-100
@85°C, JEEC 78
Electrostatic Discharge
Operating Temperature Range
Storage Temperature Range
Junction Temperature
2
HBM MIL-Std. 88E 3015.7 methods
-40
-65
+8
+150
125
e reflow peak soldering temperature (body
emperature) specified is in accordance with
IPC/JEDEC J-STD-020D “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
+260
C
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AS1335
Datasheet - Electrical Characteristics
6 Electrical Characteristics
VIN = EN = 3.6V, VOUT = VIN-0.5V, TAMB = -40°C to +85°C, typ. values @ TAMB = +25ºC (unless otherwise specified).
Table 3. Electrical Characteristics
Symbol
Parameter
Conditions
Min
Typ
Max
Units
VIN
Input Voltage Range
2.6
5.25
V
Normal Operation; VFB = 0.5V or VOUT =
90% of regulated output voltage,
ILOAD = 0 A
Quiescent Supply
Current1
IQ
300
400
µA
IOUT
ISHDN
Output Current RMS
Shutdown Current
1.5
0.1
A
Shutdown Mode; VEN = 0V,
VIN = 4.2V
1
µA
Regulation
fixed VOUT
0.975
0.6
1.0
1025
V
V
VOUT
Regulated Output
Voltage
VIN -
0.5V
adjustable VOUT
TAMB = +25C
0.5880
0.5850
0.
.6
0.6120
0.6150
Regulated Feedback
Voltage2,3
VFB
IFB
V
TAMB = -40°C to +5°C
Feedback Current3
-30
+30
nA
mV
Reference Voltage
Line Regulation
ΔVLNR
VN = 2.6V to 5.25V
ILOAD = 0A to 15A
100
100
Output Voltage
Load Regulation
ΔVLOADREG
mA
DC-DC Switches
VIN = 3V, VFB = 0.5V r VOUT = 90% of
regulated put oltage,
Duty < 35%
IPK
Peak Inductor Current
2.4
A
RPFET
RNFET
P-Channel FET RDS(ON)
N-Channel FET RDS(ON)
ILSW = 100mA
W = -100mA
0.4
Ω
Ω
0.35
VEN = 0V, VSW = 0V or 5V,
VIN = 5V
ILSW
SW Leakage
-1
0.01
0.01
+1
µA
Enable
VIH
Input High
Input Low
1.4
-1
Logic Input Thresho
EN Leakae Current
V
VIL
0.4
+1
IEN
VIN = 3.6V, VEN = 0V to 3.6V
µA
Power-OK Output
Rising
Falling
Rising
Falling
89.5
85
92
88
94.5
91
Power Good Low
%
Voltage Threshold
VOUT
VPOK
108.2
104
110.7
107
215
113.2
110
Power Good High
Voltage Threshold
%
VOUT
tDAY
POK Delay Time
150
275
ms
V
POK Output Voltage
Low
VOL
ISINK = 1mA, VFB = 0.7V
0.3
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AS1335
Datasheet - Electrical Characteristics
Table 3. Electrical Characteristics
Symbol
IPOK
Parameter
Conditions
Min
Typ
Max
Units
POK Output Leakage
Current
VPOK = VIN = 3.6V
0.01
1
µA
Oscillator
fOSC
VFB = 0.6V or VOUT = 100% of regulated
output voltage
Oscillator Frequency
1.2
1.5
1.8
MHz
Thermal Shutdown
Thermal Shutdown
150
25
°C
C
Thermal Shutdown
Hysteresis
1. The dynamic supply current is higher due to the gate charge delivered at the switching frequency. The Quies-
cent Current is measured while the DC-DC Converter is not switching.
2. The device is tested in a proprietary test mode where VFB is connected to the output of the DC/C cnverter.
3. Only valid for the adjustable version;
Note: All limits are guaranteed. The parameters with min and max vaes are guaranteed witproduction tests or
SQC (Statistical Quality Control) methods.
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AS1335
Datasheet - Typical Operating Characteristics
7 Typical Operating Characteristics
VOUT = 1.0V, IOUT = 100mA, TAMB = +25°C (unless otherwise specified).
Figure 3. Efficiency vs. Output Current, VOUT = 1.0V
Figure 4. Efficiency vs. Output Current, VOUT = 1.5V
100
100
90
80
70
60
50
40
30
20
10
0
90
80
70
60
50
40
Vin = 5.5V
Vi n =5.5V
n =5.0V
Vi n .0V
Vi n =3.6V
Vi n =2.6V
30
Vin =4.0V
Vin = 3.5V
20
Vin =3.0V
10
Vin = 2.5V
0
10
100
1000
10000
10
100
1000
10000
Output Current (mA)
Output Current (mA)
Figure 5. Efficiency vs. Output Current, VOUT = 2.5V
ure 6. Efficiency vs. Output Current, VOUT = 3.0V
100
100
90
80
70
60
50
40
90
80
70
60
0
40
30
30
Vi n =5.5V
Vi n =5.0V
Vin=5.5V
20
20
Vi n =4.0V
Vin=5.0V
=3.6V
Vin=4.0V
10
10
Vin=3.6V
0
0
10
100
1000
10000
10
100
1000
10000
Output Curret (mA)
Output Current (mA)
Figure 7. Efficiency vs. Output urrent, VOUT = 3.5V
Figure 8. Efficiency vs. Input Voltage, VOUT = 1.0V
100
100
90
80
70
60
50
40
90
80
70
60
Iout = 100mA
30
Iout =300mA
Vi n =5.5V
20
Iout = 700mA
Vi n =5.0V
50
Vi n =4.5V
Iout = 1000mA
10
Vi n =4.0V
Iout = 1500mA
0
40
10
100
1000
10000
2.5
3.5
4.5
5.5
Output Current (mA)
Input Voltage (V)
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AS1335
Datasheet - Typical Operating Characteristics
Figure 9. Efficiency vs. Input Voltage, VOUT = 3.5V
Figure 10. Load Regulation, VOUT = 1.0V
100
1.05
90
80
1.03
1.01
0.99
70
Vin = 5.5V
Vin = 5.0V
Iout =400mA
Iout =600mA
60
0.97
Vin = 4.5V
Iout =800mA
Iout =950mA
Vin = 3.5V
Vin = 2.5V
50
0.95
2.6
3
3.4
3.8
4.2
4.6
5
10
100
100
10000
Input Voltage (V)
Output Current (mA
Figure 11. Load Regulation, VOUT = 1.5V
Figur12. Le Regulation, VOUT vs. VIN;
1.7
1.02
1.65
1.6
1
0.98
0.9
1.55
1.5
1.45
Iout = 100mA
Iout =300mA
0.94
0.92
0.9
1.4
Iout = 700mA
Iout = 1000mA
Iout = 1500mA
Vin=5.5V
Vin=5.0V
1.35
Vin=3.6V
1.3
10
100
1000
10000
2.5
3
3.5
4
4.5
5
5.5
Output Current (mA)
Input Voltage (V)
Figure 13. Load Step 40mA to 50mA; VIN = 4V
Figure 14. Load Step 40mA to 1A; VIN = 4V
100µs/Div
100µs/Div
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AS1335
Datasheet - Typical Operating Characteristics
Figure 15. Shutdown Response; VIN = 3.4V
Figure 16. Startup Response; VIN = 3.4V
200µs/Div
20µs/Div
Figure 17. Line Transient Response;
VIN = 3.5V to 4.5V, IOUT = 500mA
100µs/Div
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AS1335
Datasheet - Detailed Description
8 Detailed Description
The AS1335 is a high-efficiency buck converter that uses a constant-frequency current-mode architecture. The device
contains two internal MOSFET switches and is available with a user-adjustable output voltage.
Figure 18. AS1335 - Block Diagram
Ramp
Compensator
–
ICOMP
OSC
VIN
+
OSCN
Frequency
Shift
AS1335
FB
+
Error
0.6V
Amp
–
Main
–
OVDET
+
Digita
Logic
Anti-
Shoot
Through
0.6V +
ΔVOVL
–
+
SW
0.6V
Reference
0.6V -
ΔVOVL
EN
CMP
–
PoweOK
Cmare
Logic
Shutdown
GND
POK
RSI
Main Control Loop
During normal operation, the internal top power MSFEis turned on each cycle when the oscillator sets the RS latch.
This switch is turned off when the current omparator (ICOMP) resets the RS latch. The peak inductor current (IPK) at
which ICOMP resets the RS latch, is controlld by the error amplifier. When ILOAD increases, VFB decreases slightly
relative to the internal 0.6V reference, caung te error amplifier’s output voltage to increase until the average inductor
current matches the new load current.
When the top MOSFET is off, the ottom MOSFET 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 over-voltage detection comparator
(OVDET) guards against transiet overshoots >7.8% by turning the main switch off and keeping it off until the transient
is removed.
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AS1335
Datasheet - Detailed Description
Short-Circuit Protection
This frequency reduction ensures that the inductor current has more time to decay, thus preventing runaway condi-
tions. fOSC will progressively increase to 1.5MHz when VOUT > 0V or VFB > 0V.
Dropout Operation
The AS1335 is working with a low input-to-output voltage difference by operating at 100% duty cycle. In this state, the
PMOS is always on. This is particularly useful in battery-powered applications with a 3.3V output.
The AS1335 allows the output to follow the input battery voltage as it drops below the regulation voltage. The quies-
cent current in this state rises minimally to only 400µA (max), which aids in extending battery life. This dropout (100%
duty-cycle) operation achieves long battery life by taking full advantage of the entire battery range.
The input voltage requires maintaining regulation and is a function of the output voltage and the load. The difference
between the minimum input voltage and the output voltage is called the dropout voltage. The dropout voltage is the
fore a function of the on-resistance of the internal PMOS (RDS(ON)PMOS) and the inductor resistance (DCR) and his is
proportional to the load current.
Note: At low VIN values, the RDS(ON) of the P-channel switch increases (see Electrical Charactestics on page 4).
Therefore, power dissipation should be taken in consideration.
Shutdown
Connecting EN to GND or logic low places the AS1335 in shutdon moe and reduces e supply current to 0.1µA. In
shutdown the control circuitry and the internal NMOS and MOS turn off and SW becomes high impedance discon-
necting the input from the output. The output capacitance acurrent detere the voltage decay rate. For nor-
mal operation connect EN to VIN or logic high.
Note: Pin EN should not be left floating.
Power-OK Functionality
The AS1335’s power-ok circuitry offers a 215s delayed power-ok gnal. As long as the output voltage is outside of
the power-ok regulation window the POK in drives an open-drailow signal. As soon as the output voltage is within
the regulation window, the internal opedrain MOSFET is turnd off and the POK pin can be externally pulled to high.
The output of the power-ok signal is dyed by 215ms.
RSI Signal
With the RSI signal the internal power-ok timer can e eseted or delayed. As long as the input to RSI is high the POK
signal remains low, regardless of the output oltage condition.
Thermal Shutdown
Due to its high-efficiency design, te AS1335 will not dissipate much heat in most applications. However, in applica-
tions where the AS1335 is running at hgh ambient temperature, uses a low supply voltage, and runs with high duty
cycles (such as in dropout) the eat dissipated may exceed the maximum junction temperature of the device.
As soon as the junction tempeature reaches approximately 150ºC the AS1335 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 +125°C agi.
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AS1335
Datasheet - Application Information
9 Application Information
The AS1335 is perfect for mobile communications equipment, 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.
Adjustable Output Voltage
For the fixed output voltage (VOUT=1.0V) connect pin FB to VOUT (see Figure 19). For the adjustable output voltage
version connect a voltage divider to pin FB (see Figure 20).
The voltage divider from VOUT to GND programs the output voltage from 0.6V to 5.25V via pin FB as:
VOUT = 0.6V(1 + (R1/R2))
(EQ
Figure 19. AS1335 - Step-Down Converter, Single Li-Ion to 1.0V / 1.5A fixed Output
VOUT
1V, 1.5A
VIN
2.7V to 4.2V
2.2µH
VIN
NC
COU
100µF
W
CIN
22µF
PGND
GND
AS1335-100
EN
100kΩ
FB
POK
GND
RSI
Figure 20. AS1335 - Step-Down Converter, SinglLi-Ioto 3.3V adjustable Output
VOUT
3.3V
VIN
2.2µH
3.35V to 5.25V
V
NC
COUT
100µF
SW
CIN
22µF
PGND
GND
680kΩ
AS1335-AD
EN
10kΩ
FB
POK
GND
150kΩ
RSI
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AS1335
Datasheet - Application Information
External Component Selection
Inductor Selection
For most applications the value of the external inductor should be in the range of 2.2µH to 4.7µH 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
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 = 600mA (40of 1.5A).
The DC current rating of the inductor should e at east equal to thmaximum load current plus half the ripple current
to prevent core saturation. Thus, a 1.8A rted iductor should be sufficnt for most applications (1.5A + 300mA).
Note: For highest efficiency, a low DCesistance inductor is ecommended.
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 curret caability.
The total losses of the coil have a strong imact on the efficiency of the DC/DC conversion and consist of both the
losses in the DC resistance and the following fequency-dependent components:
1. The losses in the core material (magnhysteresis loss, especially at high switching frequencies).
2. Additional losses in the conducor from the skin effect (current displacement at high frequencies).
3. Magnetic field losses of the neihboing windings (proximity effect).
4. Radiation losses.
Output Capacitor Selection
The advanced fast-esponse voltage mode control scheme of the AS1335 allows the use of tiny ceramic capacitors.
Because of thir lowet output voltage ripple low ESR ceramic capacitors are recommended. X7R or X5R dielectric
output capacir arrecommended.
At high 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:
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AS1335
Datasheet - Application Information
VOUT
-------------
VIN
1 –
(EQ 5)
1
⎛
⎝
⎞
----------------------
------------------------------
ΔVOUT = VOUT
×
×
+ ESR
⎠
L × f
8 × COUT × f
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 AS1335 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 outpu
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 the PMOS is a square wave of the duty cycle VOUT/VIN. To revent large
voltage transients while minimizing the interference with other circuits caused by high input voltage pike, a low ESR
input capacitor sized for the maximum RMS current must be used. The maximum RMS capacitocurrnt is given as:
(EQ 6)
VUT × (– VOUT
-----------------------------------------------
×
)
IRMS = IMAX
VN
where the maximum average output current IMAX equals the eak current minuhalf e peak-to-peak ripple current,
IMAX = ILIM - ΔIL/2
This formula has a maximum at VIN = 2VOUT where IRM= IOUT/2. This le worst-case condition is commonly used
for design because even significant deviations oly provide negligble acts
The input capacitor can be increased without ny limit for better inpuvoltage filtering. Take care when using small
ceramic input capacitors. When a small ceamic capacitor is used t the input, and the power is being supplied through
long wires, such as from a wall adaperload step at the outp, or VIN step on the input, can induce ringing at the VIN
pin. This ringing can then couple to thutput and be mien as loop instability, or could even damage the part by
exceeding the maximum ratings.
Ceramic Input and Output Capacitos
When choosing ceramic capacitors for CIN nd COUT, the X5R or X7R dielectric formulations are recommended.
These dielectrics have the best temperature ad voltage characteristics for a given value and size. Y5V and Z5U
dielectric capacitors, aside from their wde iation in capacitance over temperature, become resistive at high frequen-
cies and therefore should not be used.
Table 4. Recommended Exteral Components
Name
Pat Number
Value
Rating
Type
Size
Manufacturer
Kemet
B
COUT
T520107M006ATE040
100µF
6.3V
Tantal
(3.5x2.8x1.9mm) www.kemet.com
Murata
0805
CIN, COUT
L
GRM21BR60J226ME39
22µF
6.3V
X5R
www.murata.com
Coilcraft
MOS6020-222ML
MOS6020-472ML
2.2µH
4.7µH
3.26A
1.82A
35mΩ
50mΩ
6.8x6.0x2.4mm
6.8x6.0x2.4mm
www.coilcraft.com
Becae 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.
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AS1335
Datasheet - Application Information
Efficiency
The efficiency of a switching regulator is equivalent to:
Efficiency = (POUT/PIN)x100%
(EQ 7)
For optimum design, an analysis of the AS1335 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 8)
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 feffi-
ciency calculation:
Input Voltage Quiescent Current Losses
The VIN current is the DC supply current given in the electrical characteristics which excludeMOSET driver and con-
trol currents. VIN current results in a small (<0.1%) loss that increses wth VIN, even at no loadThe 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 attributed to I²R lossand are calculated from the resis-
tances of the internal switches (RSW) and the external inductr (RL). In continos mode, the average output current
flowing through inductor L is split between the internal switches. Therefore, te series resistance looking into the SW
pin is a function of both NMOS & PMOS RDS(ON) s weas the the duty cle (C) and can be calculated as follows:
RSW = (RDON)POS)(DC) + (RDS(ON)NMS)(1 – DC)
(EQ 9)
The RDS(ON) for both MOSFETs can bbtained from the ectrial Characteristics on page 4. Thus, to obtain I²R
losses calculate as follows:
I²R losses = IOUT²(RSW + RL)
(EQ 10)
Switching Losses
The switching current is the sum of the controcurrents and the MOSFET driver. The MOSFET driver current results
from switching the gate capacitance of he ower MOSFETs. If a MOSFET gate is switched from low to high to low
again, a packet of charge dQ moves from N to ground. The resulting dQ/dt is a current out of VIN that is typically
much larger than the DC bias curnt. In continuous mode:
IGC = f(QPMOS + QNMOS)
(EQ 11)
Where: QPMOS and QNMOare the gate charges of the internal MOSFET switches.
The losses of the gte carges are proportional to VIN and thus their effects will be more visible at higher supply volt-
ages.
Other Lses
Bsic loses n the design of a system should also be considered. Internal battery resistances and copper trace can
accunt 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.
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AS1335
Datasheet - Application Information
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 = ΔILOAD x ESR
(EQ 12)
Where:
ESR is the effective series resistance of COUT.
ΔILOAD 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 tha
would indicate a stability problem.
Layout Considerations
The AS1335 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 FB should be connected directly to the Output Voltage.
The positive plate of CIN should be connected as close to VIN as is practical since CIN pides he AC current to
the internal power MOSFETs.
ꢀ
ꢀ
Switching node SW should be kept far away from the sensitivFB ode.
The negative plates of CIN and COUT should be kept ae to each other ais practical. A starpoint to Ground is
recommended.
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AS1335
Datasheet - Package Drawings and Markings
10 Package Drawings and Markings
The device is available in an 10-pin TDFN 3x3mm package.
Figure 21. 10-pin TDFN 3x3mm Package
D2
D
SEE
DETAIL B
D2/2
B
L
PIN 1 INDEX AREA
(D/2 xE/2)
N N-1
b
PIN 1 INDEX AREA
(D/2 xE/2)
aaa
C
2x
e
bbb
C
C A
TOP VIEW
(ND-1) X e
BTM VIEW
ddd
e
Terminal Tip
DETAIL B
ccc
C
C
SEATING
PLANE
0.0
SIDE VIE
DatumA or B
ODD TERMINAL SIDE
Symbol
A
Min
0.70
0.00
Typ
0.75
ax
0
0.05
Notes
1, 2
1, 2
12
12
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
Symbol
Min
Typ
3.00
3.00
Max
Notes
1, 2
D BSC
A1
0.02
E BSC
1, 2
A3
0.20 REF
D2
E2
L
2.20
1.40
0.30
0º
2.70
1.75
0.50
14º
1, 2
L1
0.03
0.15
0.13
1, 2
L2
0.40
1, 2
aaa
bbb
ccc
ddd
eee
ggg
0.15
0.10
0.10
0.05
0.08
0.1
θ
K
1, 2
0.20
0.18
1, 2
b
0.25
0.50
10
0.30
1, 2, 5
e
N
1, 2
ND
5
1, 2, 5
Notes:
1. Figure 21 ishown for illustration only.
2. All dimensins re in millimeters; angles in degrees.
3. Dimeoning and tolerancing conform to ASME Y14.5 M-1994.
. N is the total number of terminals.
5. Thterminal #1 identifier and terminal numbering convention shall conform to JEDEC 95-1, SPP-012. Details of ter-
minal #1 identifier are optional, but must be located within the zone indicated. The terminal #1 identifier may be either
a mold or marked feature.
6. Dimension b applies to metallized terminal and is measured between 0.15mm and 0.30mm from the terminal tip.
7. ND refers to the maximum number of terminals on side D.
8. Unilateral coplanarity zone applies to the exposed heat sink slug as well as the terminals.
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AS1335
Datasheet - Ordering Information
11 Ordering Information
The device is available as the following standard versions.
Table 5. Ordering Information
Ordering Code
Marking
Description
Delivery Form
Package
1.5A, 1.5MHz, Synchronous DC/DC Step-Down
Converter, fixed VOUT = 1.0V
10-pin TDFN
3x3mm
ASSI
Tape and Reel
AS1335-BTDT-100
1.5A, 1.5MHz, Synchronous DC/DC Step-Down
Converter, user-adjustable Output Voltage
10-pin TDFN
3x3mm
ASSC
Tape and Reel
AS1335-BTDT-AD
Note: All products are RoHS compliant and Pb-free.
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AS1335
Datasheet
Copyrights
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Therefore, prior to designing this product into a system, it is necessary to check with austriamicrosystems AG f
current information. This product is intended for use in normal commercial applications. Applications requiring
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