AS1335 Datasheet

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Datasheet
AS1335
1 . 5 A , 1 . 5 M H z , S y n c h r o n o u s D C / D C St e p - D o w n C o n v e r t e r
2 Key Features
Typical supply current with no load is 400µA and
decreases to ≤1µA in shutdown mode. The highly efficient duty cycle (100%) provides low dropout operation,
prolonging battery life in portable systems.
High Efficiency: Up to 96%
!
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
!
Power OK with 215ms delay
!
Low Dropout Operation: 100% Duty Cycle
!
Low Quiescent Supply Current: 400µA
!
Shutdown Mode Supply Current: ≤1µA
!
Current Mode Operation for Excellent Line/Load
Transient Response
!
Thermal Protection
!
10-pin TDFN 3x3mm Package
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The device also offers a power-ok signal with a 215ms
delay, which can be reseted or delayed further via the
RSI pin.
!
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The AS1335 is a high-efficiency, constant-frequency
synchronous buck converter available in a fixed or an
adjustable output voltage version. The wide input voltage 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 batterypowered application.
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1 General Description
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.
The AS1335 is available in a 10-pin TDFN 3x3mm package.
3 Applications
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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.
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Figure 1. AS1335 - Typical Application Diagram
2.2µH
VIN
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2.6V to 5.25V
CIN
22µF
VIN
SW
NC
1.0V, 1.5A
PGND
AS1335
EN
GND
POK
FB
GND
RSI
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VOUT
COUT
22µF
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AS1335
Datasheet - P i n o u t
4 Pinout
Pin Assignments
VIN 1
10 SW
NC 2
9 PGND
EN 3
AS1335
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Figure 2. Pin Assignments (Top View)
8 GND
POK 4
7 FB
11
6 RSI
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GND 5
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Pin Descriptions
Table 1. Pin Descriptions
Pin
Number
Pin Name
1
VIN
2
NC
Positive Supply Voltage. This pin must be closely decoupled to PGND with a ≥ 22µF
ceramic capacitor.
Not Connected.
Enable Input. Driving this pin above 1.4V enables the device. Driving this pin below 0.3V
puts the device in shutdown mode. In shutdown mode all functions are disabled, drawing
≤1µA supply current.
Note: This pin should not be left floating.
EN
4
POK
5
GND
6
RSI
Power-OK Output. Open-drain output with 215ms delay. Connect a 100kΩ pull-up resistor
to VOUT or pin VIN for logic levels. Leave this pin unconnected if the Power-OK feature is
not used.
LOW Signal: Out of regulation
HIGH signal: Within Regulation (after 215ms delay)
Analog Ground.
Reset Input for POK. This input resets the 215ms timer of the POK signal.
As long as RSI is low the POK signal will work as described above.
A high input to RSI will reset the 215ms POK timer and delay the signal as long as RSI
stays high. A RSI low-to-high transition restarts the 215ms counter as long as the output
voltage is within regulation.
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3
Description
FB
Feedback Pin. Feedback input to the gm error amplifier. Connect a resistor divider tap to
this pin. The output can be adjusted from 0.6V to 5.25V by VOUT = 0.6V[1+(R1/R2)].
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Note: Do not leave this pin floating.
If the fixed output voltage version is used, connect this pin to VOUT.
GND
9
PGND
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8
10
11
SW
Analog Ground. GND and PGND should only have one point connection.
Power-Ground. Connect all power grounds to this pin.
Switch Node Connection to Inductor. This pin connects to the drains of the internal main
and synchronous power MOSFET switches.
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 - A b s o l u t e M a x i m u m R a t i n g s
5 Absolute Maximum Ratings
Stresses beyond those listed in Table 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 Characteristics on page 4 is not implied. Exposure to absolute maximum rating conditions for extended periods may affect
device reliability.
Max
Units
VIN to GND
-0.3
6
V
SW to GND
-0.3
VIN + 0.3
V
EN, FB to GND
-0.3
VIN
V
P-Channel Switch Source Current (DC)
1.5
A
N-Channel Switch Source Current (DC)
1.5
A
Peak SW Sink and Source Current
3
A
Comments
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Table 2. Absolute Maximum Ratings
Thermal Resistance ΘJA
Latch-Up
-100
Electrostatic Discharge
36.7
ºC/W
on PCB
100
mA
@85°C, JEDEC 78
kV
HBM MIL-Std. 883E 3015.7 methods
2
Operating Temperature Range
-40
+85
ºC
Storage Temperature Range
-65
+150
ºC
125
ºC
Junction Temperature
+260
ºC
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Package Body Temperature
The reflow peak soldering temperature (body
temperature) 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).
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AS1335
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
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
VIN
Input Voltage Range
IQ
Quiescent Supply
1
Current
IOUT
Output Current RMS
ISHDN
Conditions
Shutdown Current
Min
2.6
Normal Operation; VFB = 0.5V or VOUT =
90% of regulated output voltage,
ILOAD = 0 A
300
1.5
Shutdown Mode; VEN = 0V,
VIN = 4.2V
0.1
Regulation
VOUT
Regulated Feedback
2,3
Voltage
IFB
Feedback Current
5.25
V
400
1
adjustable VOUT
0.6
TAMB = +25°C
0.5880
0.6
0.6120
TAMB = -40°C to +85°C
0.5850
0.6
0.6150
3
1.0
-30
Line Regulation
Output Voltage
Load Regulation
µA
A
0.975
Reference Voltage
DC-DC Switches
Units
µA
1.025
V
VIN 0.5V
V
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VFB
ΔVLOADREG
Max
fixed VOUT
Regulated Output
Voltage
ΔVLNR
Typ
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Parameter
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Symbol
+30
V
nA
VIN = 2.6V to 5.25V
100
mV
ILOAD = 0A to 1.5A
100
mA
Peak Inductor Current
VIN = 3V, VFB = 0.5V or VOUT = 90% of
regulated output voltage,
Duty Cycle < 35%
2.4
A
RPFET
P-Channel FET RDS(ON)
ILSW = 100mA
0.4
Ω
RNFET
N-Channel FET RDS(ON)
ILSW = -100mA
0.35
Ω
ILSW
SW Leakage
VEN = 0V, VSW = 0V or 5V,
VIN = 5V
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IPK
Enable
VIL
IEN
Input High
Logic Input Threshold
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VIH
EN Leakage Current
-1
0.01
+1
1.4
Input Low
0.4
µA
V
VIN = 3.6V, VEN = 0V to 3.6V
-1
0.01
+1
µA
Rising
89.5
92
94.5
Falling
85
88
91
%
VOUT
Rising
108.2
110.7
113.2
Falling
104
107
110
%
VOUT
150
215
275
ms
0.3
V
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Power-OK Output
Power Good Low
Voltage Threshold
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VPOK
Power Good High
Voltage Threshold
tDELAY
POK Delay Time
VOL
POK Output Voltage
Low
ISINK = 1mA, VFB = 0.7V
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AS1335
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
Table 3. Electrical Characteristics
Symbol
Parameter
Conditions
IPOK
POK Output Leakage
Current
VPOK = VIN = 3.6V
Oscillator Frequency
VFB = 0.6V or VOUT = 100% of regulated
output voltage
Min
Typ
Max
Units
0.01
1
µA
1.5
1.8
MHz
fOSC
1.2
Thermal Shutdown
150
Thermal Shutdown
Hysteresis
25
°C
°C
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Thermal Shutdown
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Oscillator
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1. The dynamic supply current is higher due to the gate charge delivered at the switching frequency. The Quiescent 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/DC converter.
3. Only valid for the adjustable version;
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Note: All limits are guaranteed. The parameters with min and max values are guaranteed with production tests or
SQC (Statistical Quality Control) methods.
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AS1335
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
VOUT = 1.0V, IOUT = 100mA, TAMB = +25°C (unless otherwise specified).
100
90
90
80
80
70
70
50
40
Vin = 5.5V
30
20
60
50
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Figure 4. Efficiency vs. Output Current, VOUT = 1.5V
100
Efficiency (%)
Efficiency (%)
Figure 3. Efficiency vs. Output Current, VOUT = 1.0V
40
Vin = 4.0V
30
Vin = 3.5V
20
Vi n = 5.5V
Vi n = 5.0V
Vi n = 4.0V
Vin = 3.0V
Vi n = 3.6V
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10
10
Vin = 2.5V
0
Vi n = 2.6V
0
10
100
1000
10000
10
Output Current (mA)
Figure 5. Efficiency vs. Output Current, VOUT = 2.5V
100
1000
10000
Figure 6. Efficiency vs. Output Current, VOUT = 3.0V
100
90
90
80
80
70
Efficiency (%)
Efficiency (%)
100
Output Current (mA)
60
50
40
30
Vi n = 5.0V
50
40
20
Vi n = 4.0V
Vi n = 5.5V
Vi n = 5.0V
Vi n = 3.6V
10
60
30
Vi n = 5.5V
20
70
10
Vi n = 4.0V
Vi n = 3.6V
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0
10
100
1000
0
10000
10
Output Current (mA)
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Figure 7. Efficiency vs. Output Current, VOUT = 3.5V
100
90
Efficiency (%)
60
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Efficiency (%)
70
50
40
30
80
70
60
Iout = 100mA
Iout = 300mA
Vi n = 5.5V
Vi n = 5.0V
Iout = 700mA
50
Iout = 1000mA
Vi n = 4.5V
10
10000
Figure 8. Efficiency vs. Input Voltage, VOUT = 1.0V
80
20
1000
100
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90
100
Output Current (mA)
Vi n = 4.0V
0
Iout = 1500mA
40
10
100
1000
10000
2.5
Output Current (mA)
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3.5
4.5
5.5
Input Voltage (V)
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AS1335
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 10. Load Regulation, VOUT = 1.0V
100
1.05
90
1.03
80
70
Iout = 400mA
0.99
Vin = 5.5V
Vin = 5.0V
Vin = 4.5V
0.97
Iout = 600mA
Iout = 800mA
Vin = 3.5V
Vin = 2.5V
Iout = 950mA
50
0.95
2.6
3
3.4
3.8
4.2
4.6
5
10
100
1000
10000
Output Current (mA)
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Input Voltage (V)
Figure 11. Load Regulation, VOUT = 1.5V
Figure 12. Line Regulation, VOUT vs. VIN;
1.02
1.7
1.65
1
1.6
Output Voltage (V)
Output Voltage (V)
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1.01
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Output Voltage (V)
Efficiency (%)
Figure 9. Efficiency vs. Input Voltage, VOUT = 3.5V
1.55
1.5
1.45
1.4
Vi n = 5.5V
1.35
0.98
0.96
0.94
Iout
Iout
Iout
Iout
Iout
0.92
Vi n = 5.0V
= 100mA
= 300mA
= 700mA
= 1000mA
= 1500mA
Vi n = 3.6V
0.9
100
1000
2.5
10000
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3.5
4
4.5
5
5.5
200mA/Div
IOUT
VOUT
Figure 14. Load Step 40mA to 1A; VIN = 4V
100mV/Div
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VOUT
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IOUT
Figure 13. Load Step 40mA to 500mA; VIN = 4V
100µs/Div
100µs/Div
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Input Voltage (V)
Output Current (mA)
500mA/Div
10
50mV/Div
1.3
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AS1335
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
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500mA/Div
EN
IIN
1V/Div
20µs/Div
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200µs/Div
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1V/Div
VOUT
20mA/Div
EN
IIN
VOUT
2V/Div
Figure 16. Startup Response; VIN = 3.4V
2V/Div
Figure 15. Shutdown Response; VIN = 3.4V
VOUT
100mV/Div
VIN
500mV/Div
Figure 17. Line Transient Response;
VIN = 3.5V to 4.5V, IOUT = 500mA
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100µs/Div
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AS1335
Datasheet - D e t a i l e d D e s c r i p t i o n
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.
–
OSCN
+
ICOMP
OSC
VIN
Frequency
Shift
FB
+
Error
Amp
–
AS1335
Main
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0.6V
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Ramp
Compensator
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Figure 18. AS1335 - Block Diagram
–
OVDET
0.6V +
ΔVOVL
+
Digital
Logic
AntiShoot
Through
–
0.6V
Reference
EN
0.6V ΔVOVL
Shutdown
RSI
SW
+
+
IRCMP
Power-OK
Compare
Logic
–
GND
POK
Main Control Loop
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During normal operation, the internal top power MOSFET is turned on each cycle when the oscillator sets the RS latch.
This switch is turned off when the current comparator (ICOMP) resets the RS latch. The peak inductor current (IPK) at
which ICOMP resets the RS latch, is controlled by the error amplifier. When ILOAD 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.
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When the top MOSFET is off, the bottom 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 transient overshoots >7.8% by turning the main switch off and keeping it off until the transient
is removed.
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AS1335
Datasheet - D e t a i l e d D e s c r i p t i o n
Short-Circuit Protection
This frequency reduction ensures that the inductor current has more time to decay, thus preventing runaway conditions. fOSC will progressively increase to 1.5MHz when VOUT > 0V or VFB > 0V.
Dropout Operation
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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 quiescent 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.
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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 therefore a function of the on-resistance of the internal PMOS (RDS(ON)PMOS) and the inductor resistance (DCR) and this is
proportional to the load current.
Shutdown
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Note: At low VIN values, the RDS(ON) of the P-channel switch increases (see Electrical Characteristics on page 4).
Therefore, power dissipation should be taken in consideration.
Connecting EN to GND or logic low places the AS1335 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 VIN or logic high.
Note: Pin EN should not be left floating.
Power-OK Functionality
The AS1335’s power-ok circuitry offers a 215ms delayed power-ok signal. As long as the output voltage is outside of
the power-ok regulation window the POK pin drives an open-drain low signal. As soon as the output voltage is within
the regulation window, the internal open-drain MOSFET is turned off and the POK pin can be externally pulled to high.
The output of the power-ok signal is delayed by 215ms.
RSI Signal
With the RSI signal the internal power-ok timer can be reseted or delayed. As long as the input to RSI is high the POK
signal remains low, regardless of the output voltage condition.
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Thermal Shutdown
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Due to its high-efficiency design, the AS1335 will not dissipate much heat in most applications. However, in applications where the AS1335 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.
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As soon as the junction temperature 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 again.
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AS1335
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 AS1335 is perfect for mobile communications equipment, LED matrix displays, bar-graph displays, instrumentpanel meters, dot matrix displays, set-top boxes, white goods, professional audio equipment, medical equipment,
industrial controllers to name a few applications.
Adjustable Output Voltage
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))
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VIN
2.7V to 4.2V
CIN
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(EQ 1)
Figure 19. AS1335 - Step-Down Converter, Single Li-Ion to 1.0V / 1.5A fixed Output
22µF
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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).
VOUT
2.2µH
VIN
1.0V, 1.5A
COUT
SW
100µF
NC
PGND
AS1335-100
EN
100kΩ
GND
POK
FB
GND
RSI
Figure 20. AS1335 - Step-Down Converter, Single Li-Ion to 3.3V adjustable Output
VIN
3.35V to 5.25V
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CIN
VIN
SW
NC
PGND
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AS1335-AD
680kΩ
GND
POK
FB
GND
RSI
150kΩ
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EN
3.3V
COUT
100µF
22µF
100kΩ
VOUT
2.2µH
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AS1335
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
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 current. The inductor ripple current (ΔIL) decreases with higher inductance and increases with higher VIN or VOUT.
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ΔI L
I LMAX = I OUTMAX + -------2
(EQ 2)
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V OUT
1 – ------------V IN
ΔI L = V OUT × ----------------------L×f
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In Equation (EQ 2) 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 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 transients.
(EQ 3)
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 (40% of 1.5A).
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 1.8A rated inductor should be sufficient for most applications (1.5A + 300mA).
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:
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4. Radiation losses.
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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).
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Output Capacitor Selection
The advanced fast-response voltage mode control scheme of the AS1335 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.
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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 IN
1
= V OUT × ----------------------- × ---------------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:
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AS1335
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
ΔV OUT
V OUT
1 – ------------V IN
1
= V OUT × ----------------------- × ⎛⎝ ------------------------------- + ESR⎞⎠
L×f
8 × C OUT × f
(EQ 5)
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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 AS1335 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.
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Input Capacitor Selection
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In continuous mode, the source current of the PMOS is a square wave of the duty cycle VOUT/VIN. 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:
V OUT × ( V IN – V OUT )
I RMS = I MAX × ---------------------------------------------------------V IN
(EQ 6)
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
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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 frequencies and therefore should not be used.
Name
Part Number
Value
Rating
Type
T520B107M006ATE040
100µF
6.3V
Tantal
GRM21BR60J226ME39
22µF
6.3V
X5R
MOS6020-222ML
2.2µH
3.26A
35mΩ
MOS6020-472ML
4.7µH
1.82A
50mΩ
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COUT
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Table 4. Recommended External Components
CIN, COUT
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L
Size
Manufacturer
Kemet
B
(3.5x2.8x1.9mm) www.kemet.com
Murata
0805
www.murata.com
Coilcraft
6.8x6.0x2.4mm
www.coilcraft.com
6.8x6.0x2.4mm
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.
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AS1335
Datasheet - A p p l i c a t i o n I n f o r m a t i o n
Efficiency
The efficiency of a switching regulator is equivalent to:
Efficiency = (POUT/PIN)x100%
(EQ 7)
Efficiency = 100% – (L1 + L2 + L3 + ...)
Where:
L1, L2, L3, etc. are the individual losses as a percentage of input power.
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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:
(EQ 8)
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Althought all dissipative elements in the circuit produce losses, those four main sources should be considered for efficiency calculation:
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Input Voltage Quiescent Current Losses
The VIN current is the DC supply current given in the electrical characteristics which excludes MOSFET driver and control currents. VIN current results in a small (<0.1%) loss that increases with VIN, even at no load. The VIN quiescent current 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 resistances 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 9)
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)
Switching Losses
(EQ 10)
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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:
(EQ 11)
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IGC = f(QPMOS + QNMOS)
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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 voltages.
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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 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 - A p p l i c a t i o n I n f o r m a t i o n
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)
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Where:
ESR is the effective series resistance of COUT.
Layout Considerations
The AS1335 requires proper layout and design techniques for optimum performance.
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!
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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 provides the AC current to
the internal power MOSFETs.
Switching node SW should be kept far away from the sensitive FB 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.
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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 that
would indicate a stability problem.
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AS1335
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 10-pin TDFN 3x3mm package.
Figure 21. 10-pin TDFN 3x3mm Package
D2
SEE
DETAIL B
A
D
D2/2
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B
PIN 1 INDEX AREA
(D/2 xE/2)
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aaa C 2x
E
E2
E2/2
L
K
PIN 1 INDEX AREA
(D/2 xE/2)
N N-1
aaa C 2x
e
TOP VIEW
(ND-1) X e
bbb
C
C A B
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DETAIL B
b
ddd
BTM VIEW
Terminal Tip
A3
ccc C
A
C
0.08 C
SIDE VIEW
A1
SEATING
PLANE
Datum A or B
ODD TERMINAL SIDE
Min
0.70
0.00
Max
0.80
0.05
0.15
0.13
0.15
0.10
0.10
0.05
0.08
0.10
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0.03
Typ
0.75
0.02
0.20 REF
Notes
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
Symbol
D BSC
E BSC
D2
E2
L
θ
K
b
e
N
ND
Min
2.20
1.40
0.30
0º
0.20
0.18
Typ
3.00
3.00
0.40
0.25
0.50
10
5
Max
2.70
1.75
0.50
14º
0.30
Notes
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2
1, 2, 5
1, 2
1, 2, 5
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Symbol
A
A1
A3
L1
L2
aaa
bbb
ccc
ddd
eee
ggg
Notes:
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1. Figure 21 is shown for illustration only.
2. All dimensions are in millimeters; angles in degrees.
3. Dimensioning and tolerancing conform to ASME Y14.5 M-1994.
4. N is the total number of terminals.
5. The terminal #1 identifier and terminal numbering convention shall conform to JEDEC 95-1, SPP-012. Details of terminal #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 - O r d e r i n g I n f o r m a t i o n
11 Ordering Information
The device is available as the following standard versions.
Table 5. Ordering Information
Marking
Description
Delivery Form
AS1335-BTDT-100
ASSI
1.5A, 1.5MHz, Synchronous DC/DC Step-Down Tape and Reel
Converter, fixed VOUT = 1.0V
AS1335-BTDT-AD
ASSC
1.5A, 1.5MHz, Synchronous DC/DC Step-Down Tape and Reel
Converter, user-adjustable Output Voltage
Package
10-pin TDFN
3x3mm
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Ordering Code
10-pin TDFN
3x3mm
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Note: All products are RoHS compliant and Pb-free.
Buy our products or get free samples online at ICdirect: http://www.austriamicrosystems.com/ICdirect
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For further information and requests, please contact us mailto:[email protected]
or find your local distributor at http://www.austriamicrosystems.com/distributor
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AS1335
Datasheet
Copyrights
Copyright © 1997-2009, austriamicrosystems 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.
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Disclaimer
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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.
austriamicrosystems AG reserves the right to change specifications and prices at any time and without notice.
Therefore, prior to designing this product into a system, it is necessary to check with austriamicrosystems AG for
current information. This product is intended for use in normal commercial applications. Applications requiring
extended temperature range, unusual environmental requirements, or high reliability applications, such as military,
medical life-support or life-sustaining equipment are specifically not recommended without additional processing by
austriamicrosystems AG for each application. For shipments of less than 100 parts the manufacturing flow might show
deviations from the standard production flow, such as test flow or test location.
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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
technical 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.
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Contact Information
Headquarters
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austriamicrosystems 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.austriamicrosystems.com/contact
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