Analogic AAT1275 Boost converter with usb power switch Datasheet

AAT1275
Boost Converter with USB Power Switch
General Description
Features
The AAT1275 SwitchReg is a 2MHz, 500mA synchronous boost converter with an integrated currentlimiting load switch controlled output. The AAT1275
operates from a single-cell Lithium-ion/ polymer battery source and provides a regulated 5V, current
limit controlled output to support USB port VBUS
applications in portable consumer electronic products. The AAT1275 can support both USB 2.0 host
port and USB on-the-go operation, as well as general purpose applications where a 5V supply with a
user programmable current limit is needed.
•
High Frequency Boost With 5V / 500mA
Output Capability From a Single-Cell LithiumIon/Polymer Battery
Input Voltage Range: 2.7V to 5V
VOUT1 Adjustable or Fixed (5V)
>90% Efficiency
Up to 2MHz Switching Frequency
True Load Disconnect
Load Switch With Programmable Current Limit
Over-Temperature, Over-Current Protection
Inrush Current Limit
Fault Report
Low Shutdown Current < 1µA Typical
-40°C to +85°C Temperature Range
TSOPJW-12 and TDFN34-16 Packages
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The high efficiency boost converter section of the
AAT1275 is typically set for a 5V output and can
deliver up to 500mA load current to support USB
VBUS operation from an input supply as low as
2.7V. The high boost converter switching frequency (up to 2.0MHz) provides fast load transient and
allows the use of small external components. Fully
integrated control circuitry simplifies system design
and reduces total solution size.
SwitchReg™
Applications
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The integrated, programmable current limiting load
switch provides USB port protection for portable
devices allowing the AAT1275 to supply a 5V USB
VBUS up to 500mA. The load switch provides an
active low fault flag to alert the system in the event
of an over-current condition applied to the
AAT1275 output.
USB On-the-Go
Cell Phones
Digital Still Cameras
PDAs and Portable Media Players
Smart Phones
Other Hand-Held Devices
The AAT1275 is available in the Pb-free, spacesaving 12-pin TSOPJW and 16-pin TDFN34 packages and is rated over the -40°C to +85°C operating temperature range.
Typical Application
L1 2.2µH
LIN
VIN
SW
OUT1
IN
CIN
4.7µF
RFB1
432k
VCC
FB
10k
Fault
AAT1275
RFB2
59k
FLT
Enable
EN
VBUS Output
OUT2
SET
RSET
1275.2007.01.1.3
COUT1
4.7µF
GND
COUT2
1µF
1
AAT1275
Boost Converter with USB Power Switch
Pin Descriptions
Pin #
TSOPJW-12
TDFN34-16
Symbol
1
2
3
4
5
6
7
1, 16
3, 15
13, 14
11, 12
10
9
8
LIN
IN
PGND
SW
OUT1
OUT2
SET
8
7
FLT
9
10
11
12
6
5
4
2
EP
FB
GND
VCC
EN
Function
Switched power input. Connect an inductor between this pin and the SW pin.
Supply input.
Power ground.
Switch pin. Boost inductor is connected between SW and LIN.
Boost converter output.
Load switch output.
Load switch current limit programming pin. Connect a set resistor between
this pin and ground.
Load switch over-current or over-temperature fault flag. Active low, opendrain output. A 10kΩ external pull-up resistor is recommended.
Boost converter voltage feedback pin.
Ground.
Bias supply for the internal circuitry.
Enable pin, active high.
Exposed paddle (bottom); connect to ground directly beneath the package.
Pin Configuration
TSOPJW-12
(Top View)
LIN
IN
PGND
SW
OUT1
OUT2
2
1
12
2
11
3
10
4
9
5
8
6
7
TDFN34-16
(Top View)
EN
VCC
GND
FB
FLT
SET
LIN
EN
IN
VCC
GND
FB
FLT
SET
1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
LIN
IN
PGND
PGND
SW
SW
OUT1
OUT2
1275.2007.01.1.3
AAT1275
Boost Converter with USB Power Switch
Absolute Maximum Ratings
Symbol
VCC, IN, OUT
SW
LIN, FB
EN, SET, FLT
TJ
TLEAD
Description
IN, OUTx to GND
SW to GND
LIN, FB to GND
EN, SET, FLT to GND
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
6.0
-0.3 to VOUT + 0.3
-0.3 to VIN + 0.3
-0.3 to 6.0
-40 to 150
300
V
V
V
V
°C
°C
Value
Units
Thermal Characteristics1
Symbol
Description
θJA
Maximum Thermal Resistance
PD
Maximum Power Dissipation @ TA = 25°C
TSOPJW-12
TDFN34-16
TSOPJW-12
TDFN34-16
110
50
909
2.0
°C/W
mW
W
1. Mounted on a FR4 board.
1275.2007.01.1.3
3
AAT1275
Boost Converter with USB Power Switch
Electrical Characteristics1
VCC = VIN = 3.6V, VOUT1 = 5V, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = 25°C.
Symbol
Description
VIN, VCC
VOUTx
VUVLO
Operating Input Voltage Range
Maximum Output Voltage Range
Under-Voltage Lockout
IQ
Quiescent Supply Current
ISHDN
Shutdown Current
Boost Converter
IO
Continuous Output Current
ILIMIT
Input Switch Current Limit
VFB
FB Pin Regulation
VOUT
ΔVOUT
(VOUT*ΔVIN)
ΔVOUT/VOUT
RDS(ON)H
RDS(ON)L
RDS(ON)_IN
TSS
η
FOSC
Load Switch
RDS(ON)
ILIM
ILIM(MIN)
TRESP
TON
TOFF
VFLT_LOW
IFLT
TBLANK
Control
VTH-L
VTH-H
IEN
TJ-TH
TJ-HYS
Output Voltage Tolerance
Conditions
No Load, TA = 25°C
ILOAD = 0 to 500mA,
VIN = 2.7V to 5V
Line Regulation
High Side Switch On Resistance
Low Side Switch On Resistance
Input Disconnect Switch
VIN = 2.7V to 5V
VOUT1 = 5V, IOUT1 = 500mA
VOUT1 = 5V, IOUT1 = 500mA
VOUT1 = 5V, IOUT1 = 500mA
From Enable to Output
Regulation
IOUT1 = 250mA, L = 2.2µH,
VIN = 3.6V, VOUT1 = 5V
TA = 25°C, IOUT1 = 500mA,
VIN = 3.6V, VOUT1 = 5V
Switching Frequency
Current Limit Switch On Resistance
Current Limit
Minimum Current Limit
Current Limit Response Time
Turn-On Delay Time
Turn-Off Delay Time
FLT Logic Output Low
FLT Logic Output High Leakage Current
Fault Blanking Time
EN Threshold Low
EN Threshold High
EN Input Leakage
TJ Thermal Shutdown Threshold
TJ Thermal Shutdown Hysteresis
2.7
5.0
5.5
2.7
100
45
3V < VIN < 5V, VO = 5V
ILOAD = 0 to 500mA
Efficiency
Typ Max Units
No Load, Switching
No Load, Not Switching, VFB = 1.5V
EN = GND
Load Regulation
Soft-Start Time
Min
90
1.0
500
0.591
2.5
0.6
-3
µA
0.609
mA
A
V
3
%
%/mA
0.2
200
170
170
%/V
mΩ
mΩ
mΩ
300
µs
90
%
2.0
MHz
500
100
0.4
4
10
0.5
4
0.2
625
0.4
1
0.4
VEN = 5V, VIN = 5V
µA
0.005
VOUT1 = 5V, TA = 25°C
VOUT1 = 5V
VOUT1 = 5V, RL = 10Ω
VOUT1 = 5V, RL = 10Ω
ISINK = 1mA
VFAULT = 5V
Rising and Falling Edge
V
V
V
1.4
-1
1
140
15
Ω
mA
mA
µs
ms
µs
V
µA
ms
V
V
µA
°C
°C
1. The AAT1275 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
4
1275.2007.01.1.3
AAT1275
Boost Converter with USB Power Switch
Typical Characteristics
Efficiency vs. Load
DC Regulation
(VOUT = 5.0V)
1.5
80
60
VIN = 3.6V
VIN = 2.7V
Output Error (%)
Efficiency (%)
100
VIN = 4.2V
40
20
0
0.1
1
10
100
VIN = 4.2V
1.0
0.5
0.0
-1.0
-1.5
0.1
1000
1
10
Line Regulation
1000
Output Voltage vs. Temperature
(VIN = 3.6V; 50Ω
Ω Load)
(IOUT = 300mA)
4.960
0.1
4.958
Output Voltage (V)
Output Voltage Accuracy (%)
100
Output Current (mA)
Output Current (mA)
4.956
4.954
4.952
4.950
4.948
4.946
4.944
0.0
-0.1
-0.2
-0.3
-0.4
-0.5
-0.6
4.942
4.940
VIN = 3.6V
VIN = 2.7V
-0.5
3.6
3.7
3.8
3.9
4.0
4.1
-0.7
4.2
-50
-25
0
Input Voltage (V)
25
50
75
100
Temperature (°C)
No Load Current vs. Supply Voltage
No Load Current vs. Temperature
(VIN = 3.6V; VOUT = 5.0V)
140
120
No Load Current (µA)
No Load Current (µA)
140
85°C
100
80
-40°C
60
25°C
40
20
0
2.7
2.9
3.2
3.4
3.6
3.9
4.1
4.3
Supply Voltage (V)
1275.2007.01.1.3
4.5
4.8
5.0
120
100
80
60
40
20
0
-50
0
50
100
150
Temperature (°°C)
5
AAT1275
Boost Converter with USB Power Switch
Typical Characteristics
Light Load Switching Waveform
Heavy Load Switching Waveform
(VIN = 3.6V; VOUT = 5.0V; 10mA Load)
(VIN = 3.6V; VOUT = 5.0V; 500mA Load)
VLX
(2V/div)
VLX
(2V/div)
VOUT1
(25mV/div)
VOUT1
(100mV/div)
VOUT2
(100mV/div)
ILX
(500mA/div)
VOUT2
(25mV/div)
ILX
(500mA/div)
Time (5µs/div)
Time (500ns/div)
Load Transient Response
Load Transient Response
(VIN = 3.6V; VOUT = 5.0V)
(VIN = 3.6V; VOUT = 5.0V)
5.062V
5.0V
VOUT
(100mV/div)
VOUT
(50mV/div)
4.87V
500mA
4.92V
500mA
IOUT
(400mA/div)
IOUT
(200mA/div)
1mA
250mA
Time (100µs/div)
Time (100µs/div)
Load Switch RDS(ON) vs. Input Voltage
Line Transient Response
(16Ω
Ω Load)
250
85°C
4.2V
RDS(ON) (mΩ
Ω)
3.6V
5.064V
VOUT
(200mV/div)
150
100
-40°C
25°C
50
4.752V
Time (100µs/div)
6
120°C
200
VIN
(500mV/div)
0
2.5
2.7
2.9
3.1
3.3
3.5
3.7
3.9
4.1
4.3
4.5
Supply Voltage (V)
1275.2007.01.1.3
AAT1275
Boost Converter with USB Power Switch
Typical Characteristics
P-Channel RDS(ON) vs. Supply Voltage
N-Channel RDS(ON) vs. Supply Voltage
350
320
100°C
260
85°C
240
220
25°C
200
100°C
300
125°C
280
RDS(ON) (mΩ
Ω)
RDS(ON) (mΩ
Ω)
300
125°C
250
85°C
200
25°C
150
180
100
160
2.5
2.7
2.9
3.1
3.3
3.5
3.7
3.9
4.1
4.3
4.5
2.5
Supply Voltage (V)
2.9
3.1
3.3
3.5
3.7
3.9
4.1
4.3
4.5
Supply Voltage (V)
Enable Soft Start
Enable Soft Start
(VIN = 3.6V; 500mA Load)
(VIN = 4.2V; 500mA Load)
EN
(2V/div)
EN
(2V/div)
VOUT2
(2V/div)
VOUT2
(2V/div)
VOUT1
(2V/div)
VOUT1
(2V/div)
IIN
(500mA/div)
IIN
(500mA/div)
Time (1ms/div)
Time (1ms/div)
Enable Soft Start
Shutdown
(VIN = 3.6V; CVOUT2 = 120µF; 16Ω
Ω Load)
(VIN = 3.6V; CVOUT2 = 120µF; 16Ω
Ω Load)
EN
(2V/div)
EN
(2V/div)
VOUT1
(1V/div)
VOUT1
(2V/div)
VOUT2
(2V/div)
VOUT2
(2V/div)
Time (100µs/div)
1275.2007.01.1.3
2.7
Time (50ms/div)
7
AAT1275
Boost Converter with USB Power Switch
Typical Characteristics
Current Limit vs. RSET
Current Limit vs. Temperature
(RSET = 20.3kΩ
Ω)
6.0
RSET (kΩ
Ω)
Current Limit (%)
100
100
2.0
0.0
-2.0
-4.0
-6.0
-50
10
10
4.0
1000
-25
Switching Frequency vs. Input Voltage
50
75
100
Switching Frequency vs. Temperature
(VIN = 3.6V; 16.5Ω
Ω Load; L = 2.2µH)
(24W Load; L = 2.2µH)
1000
940
800
920
FS (kHz)
FS (kHz)
25
Temperature (°C)
Current Limit (mA)
600
400
200
900
880
860
840
820
0
3.0
3.2
3.4
3.6
3.8
Input Voltage (V)
8
0
4.0
4.2
-50
-25
0
25
50
75
100
Temperature (°C)
1275.2007.01.1.3
AAT1275
Boost Converter with USB Power Switch
Functional Block Diagram
LIN
SW
OUT1
IN
VCC
Boost Regulator Control
FB
EN
OUT2
SET
Load Switch Control
FLT
GND
Functional Description
through an open-drain fault reporting signal (FLT).
The fault reporting signal has a 4ms turn-on delay.
The AAT1275 is a 500mA synchronous boost converter with a current-limited load switch targeted for
single-cell Lithium-ion/polymer devices acting as a
portable host for USB power.
Control Scheme
The AAT1275 has integrated control and synchronous MOSFETs, minimizing the cost and the number of external components. Additional features
include a soft-start function which allows the load
voltage to ramp up in a controlled manner, eliminating output voltage overshoot and minimizing
inrush current. Typical soft-start time for the boost
converter is approximately 300µs.
The AAT1275 also has a load switch with user-programmable current limiting. The load switch reports
over-current and over-temperature conditions
1275.2007.01.1.3
The control circuit uses hysteretic current mode
control with internal inductor current sensing for
very high efficiency over a wide output current
range. For heavy load, the boost converter operates in continuous conduction mode (CCM). This
minimizes the RMS current and optimizes the efficiency at load conditions where the losses are
dominated by the power MOSFET RDS(ON). This
also keeps the ripple current to a minimum and
minimizes the output voltage ripple and the output
capacitor size. A zero current comparator senses
the inductor current and prevents reverse current
flow for optimum light load efficiency.
9
AAT1275
Boost Converter with USB Power Switch
Step-Up Converter Application
Information
2.2µH (± 20%) inductor is selected to maintain high
frequency operation for the 5V USB output voltage.
The AAT1275 step-up converter provides the benefits of current mode control with a simple hysteretic feedback loop. The device maintains exceptional DC regulation, transient response, and cycleby-cycle current limit without additional compensation components. The AAT1275 modulates the
power MOSFET switching current in response to
changes in output voltage. The voltage loop programs the required inductor current in response to
changes in the output load and input voltage.
Output Voltage Programming
The switching cycle initiates when the N-channel
MOSFET is turned ON and the inductor current
ramps up. The ON interval is terminated when the
inductor current reaches the programmed peak
current level. During the OFF interval, the input current decays until the lower threshold, or zero inductor current is reached. The lower current is equal to
the peak current minus a preset hysteresis threshold, which determines the inductor ripple current.
The peak current is adjusted by the controller until
the output current requirement is met.
The magnitude of the feedback error signal determines the average input current. Therefore, the
AAT1275 boost controller implements a programmed current source connected to the output
capacitor and load resistor. There is no right-half
plane zero, and loop stability is achieved with no
additional external compensation components.
At light load, the inductor OFF interval current goes
to zero and the boost converter enters discontinuous mode operation. Further reduction in the load
results in a corresponding reduction in the switching frequency, which reduces switching losses and
maintains high efficiency at light loads.
The operating frequency varies with changes in the
input voltage, output voltage, and inductor size.
Once the boost converter has reached continuous
mode, increasing the output load will not significantly change the operating frequency. A small
10
The output voltage is programmed through a resistor divider network located from the OUT1 output
capacitor to the FB pin to ground.
Soft Start / Enable
The input disconnect switch is activated when a
valid input voltage is present and the EN pin is
pulled high. The slew rate control on the P-channel
MOSFET ensures minimal inrush current as the
output voltage is charged to the input voltage prior
to switching of the N-channel power MOSFET. The
soft-start circuitry guarantees monotonic turn-on
and eliminates output voltage overshoot across the
full input voltage range for all load conditions.
Current Limit and Over-Temperature
Protection
The switching of the N-channel MOSFET terminates when current limit of 2.5A (typical) is exceeded. This minimizes the power dissipation and component stresses under overload and short-circuit
conditions. Switching resumes when the current
decays below the limit.
Thermal protection disables the AAT1275 boost
converter when the internal power dissipation
becomes excessive. The junction over-temperature threshold is 140°C with 15°C of temperature
hysteresis. The output voltage automatically recovers when the over-temperature or over-current fault
condition is removed.
Under-Voltage Lockout
Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal
circuitry prior to soft start. Internal bias of all circuits
is controlled via the VCC input, which is connected
to VIN.
1275.2007.01.1.3
AAT1275
Boost Converter with USB Power Switch
Selecting the Boost Inductor
The AAT1275 boost controller utilizes hysteretic
control and the switching frequency varies with output load and input voltage. The value of the inductor determines the maximum switching frequency
of the boost converter. Increasing output inductance decreases the switching frequency, resulting
in higher peak currents and increased output voltage ripple. To maintain the 2MHz switching frequency and stable operation, an output inductor
sized from 1.5µH to 2.7µH is recommended.
Manufacturer's specifications list both the inductor
DC current rating, which is a thermal limitation, and
peak inductor current rating, which is a function of
the saturation characteristics.
Measure the inductor current at full load and high
ambient temperature to ensure that the inductor
does not saturate or exhibit excessive temperature
rise. Select the output inductor (L) to avoid saturation at the minimum input voltage and maximum
load. The RMS current flowing through the boost
inductor is equal to the DC plus AC ripple components. The maximum inductor RMS current occurs
at the minimum input voltage and the maximum
load. Use the following equations to calculate the
maximum peak and RMS current:
DMAX =
IPP =
VO - VIN(MIN)
VO
VIN(MIN) · D
L · FS
IP =
IO
1-D
IPK = IP +
IPP
2
IV = IP - IPP
1275.2007.01.1.3
IRMS =
IPK2 + IPK · IV + IV2
3
PLOSS(INDUCTOR) = I2RMS · DCR
At light load and low output voltage, the controller
reduces the operating frequency to maintain maximum efficiency. As a result, further reduction in output load does not reduce the peak current. The
minimum peak current ranges from 0.5A to 0.75A.
Compare the RMS current values with the manufacturer's temperature rise, or thermal derating
guidelines. For a given inductor type, smaller
inductor size leads to an increase in DCR winding
resistance and, in most cases, increased thermal
impedance. Winding resistance degrades boost
converter efficiency and increases the inductor's
operating temperature.
Shielded inductors provide decreased EMI and
may be required in noise sensitive applications.
Unshielded chip inductors provide significant space
savings at a reduced cost compared to shielded
inductors. In general, chip-type inductors have
increased winding resistance (DCR) when compared to shielded, wound varieties.
Selecting the Step-Up Converter
Capacitors
The high output ripple inherent in the boost converter necessitates low impedance output filtering.
Multi-layer ceramic (MLC) capacitors provide small
size, adequate capacitance, with low parasitic
equivalent series resistance (ESR) and equivalent
series inductance (ESL). This makes them well
suited for use with the AAT1275. MLC capacitors of
type X7R or X5R ensure good capacitance stability over the full operating range. MLC capacitors
exhibit significant capacitance reduction with an
applied DC voltage. Output ripple measurements
can confirm that the capacitance used meets the
specific ripple requirements. Voltage derating mini-
11
AAT1275
Boost Converter with USB Power Switch
mizes this factor, but results may vary with package
size and among specific manufacturers.
Use a 4.7µF 10V ceramic output capacitor to minimize output ripple for the 5V output. Small 0805
sized ceramic capacitors are available which meet
these requirements.
Estimate the output capacitor required at the minimum switching frequency (FS) of 800kHz (worstcase).
COUT =
IOUT · DMAX
FS · ΔVOUT
The boost converter input current flows during both
ON and OFF switching intervals. The input ripple
current is less than the output ripple and, as a
result, less input capacitance is required. A ceramic output capacitor from 1µF to 4.7µF is recommended. Minimum 6.3V rated capacitors are
required at the input. Ceramic capacitors sized as
small as 0603 are available which meet these
requirements.
Setting the Output Voltage
Program the output voltage through a resistive
divider located from the output to the FB pin to
ground. The internal error amplifier reference voltage is 0.6V. A 59.0kΩ programming resistor value
from VFB to GND with a 432kΩ resistor from FB to
the output will set the output voltage to 5V.
R2⎞
⎛
VOUT = VREF · 1 + R3
⎝
⎠
432kΩ ⎞
⎛
= 0.6V · 1 + 59.0kΩ
⎝
⎠
= 5.0V
12
USB Load Switch Application
Information
Setting the Load Switch Current Limit
In most applications, the variation in ILIM must be
taken into account when determining RSET. The ILIM
variation is due to processing variations from part
to part, as well as variations in the voltages at
OUT1 and OUT2, plus the operating temperature.
The typical RSET value for a 300mA load is in the
range of 20 to 22kΩ.
Operation in Current Limit
When a heavy load is applied to OUT2 of the
AAT1275, the load current is limited to the value of
ILIM (determined by RSET) causing a drop in the
output voltage. This increases the AAT1275 power
dissipation and die temperature. When the die temperature exceeds the over-temperature limit, the
AAT1275 shuts down until it has cooled sufficiently,
at which point it will start up again. The AAT1275
will continue to cycle on and off until the load is
removed, power is removed, or until a logic low
level is applied to the EN pin.
A fault flag indicates when the OUT2 pin load current has exceeded the current limit level set by
RSET. The fault flag is an active low, open-drain pin
that requires 10kΩ pull-up to VIN. The fault signal
has a 4ms blanking time to prevent false over current indicator during the charging of the USB bus
capacitor.
Steady-State Maximum Power
Dissipation
The maximum power dissipation for the AAT1275
occurs at the minimum input voltage, where it operates in continuous conduction mode (CCM). The
total power dissipation at full load is dominated by
the RDS(ON) losses of the power MOSFET. The dissipation includes the losses in the input and output
switch, as well as both synchronous switches.
1275.2007.01.1.3
AAT1275
Boost Converter with USB Power Switch
Due to the magnitude of the inductor ripple current,
it cannot be neglected when analyzing the RDS(ON)
power dissipation. Once the ripple current has
been determined, the RMS current during the on
and the off period can be calculated.
RDS(ON)IN is the input disconnect switch, RDS(ON)N is
the high-side synchronous switch, RDS(ON)P is the
low-side synchronous switch, and RDS(ON) is the
current limit load switch.
PCB Layout Guidelines
DMAX =
IPP =
VO - VIN(MIN)
VO
VIN(MIN) · DMAX
L · FS
IP =
IO
1-D
IPK = IP +
IPP
2
IV = IP - IPP
IRMS(ON) =
IRMS(OFF) =
(IP2 + IPK · IV + IV2) · DMAX
3
(IP2 + IPK · IV + IV2) · (1 - DMAX)
3
PTOTAL = IRMS(ON)2 · (RDS(ON)IN + RDS(ON)N)
+ IRMS(OFF)2 · (RDS(ON)IN + RDS(ON)P + RDS(ON))
The step-up converter performance can be
adversely affected by poor layout. Possible impact
includes high input and output voltage ripple, poor
EMI performance, and reduced operating efficiency.
Every attempt should be made to optimize the layout in order to minimize parasitic PCB effects (stray
resistance, capacitance, inductance) and EMI coupling from the high frequency SW node.
A suggested PCB layout for the AAT1275 is shown
in Figures 1 and 2. The following PCB layout guidelines should be considered:
1. Minimize the distance from capacitors C2 and
C3 to the IC. This is especially true for the output capacitor C2, which conducts high ripple current associated with the step-up converter output capacitor.
2. Place the feedback resistor close to the output
terminals. Route the output pin directly to resistor R2 to maintain good output regulation. R3
should be routed close to the output GND pin
and should not share a significant return path
with output capacitor C2.
3. Minimize the distance between L1 and the
switching pin SW; minimize the size of the PCB
area connected to the SW pin.
4. Maintain a ground plane and connect to the IC
RTN pin(s), as well as the GND terminals of C1
and C2.
TJ(MAX) = PTOTAL · θJA + TAMB
1275.2007.01.1.3
13
AAT1275
Boost Converter with USB Power Switch
Figure 1: AAT1275 Evaluation Board
Top Side Layout.
Figure 2: AAT1275 Evaluation Board
Bottom Side Layout.
Manufacturer
Part Number
Value
Voltage
Temp. Co.
Case
MuRata
MuRata
MuRata
MuRata
GRM21BR61A475KA73L
GRM18BR60J475KE19D
GRM21BR60J106KE19
GRM21BR60J226ME39
4.7µF
4.7µF
10µF
22µF
10V
6.3V
6.3V
6.3V
X5R
X5R
X5R
X5R
0805
0603
0805
0805
Table 1: Typical Surface Mount Capacitors.
Manufacturer
Part Number
Sumida
Sumida
Coiltronics
Coiltronics
CDRH2D14-2R2
CDRH4D11/HP-2R4
SD3112-2R2
SD3114-2R2
Inductance
(µH)
Max DC
Current (A)
DCR
Ω)
(Ω
Size (mm)
LxWxH
Type
2.2
2.4
2.2
2.2
1.6
1.7
1.12
1.48
0.094
0.105
0.140
0.086
3.2x3.2x1.55
4.8x4.8x1.2
3.1x3.1x1.2
3.1x3.1x1.4
Shielded
Shielded
Shielded
Shielded
Table 2: Typical Surface Mount Inductors.
14
1275.2007.01.1.3
AAT1275
Boost Converter with USB Power Switch
VIN
L1 2.2µH
R4
GND
VIN
4
SW
FLT
8
1
LIN
OUT2
6
SET
OUT1
5
10
GND
EN
12
11
VCC
FB
9
PGND
3
7
16.9kΩ
2
C6
120µF
CCase
R1
10K
U1
AAT1275
C3
4.7µF
10V
VIN
FLT
VO1
R2
432k
R3
59k
VO2
J5
C2
4.7µF
10V
C1
4.7µF
GND
VIN
3
2
GND
1
Enable
Figure 3: AAT1275 Evaluation Board Schematic
Step-Up Converter Design Example
Specifications
VOUT = 5V
IOUT = 300mA
VIN = 2.7V to 4.2V (3.6V nominal)
TAMB = 50°C
Output Inductor
DMAX =
VOUT - VIN(MIN)
5V - 2.7V
=
= 0.46
VOUT
5V
From the characterization curves, the switching frequency at room temperature with a 300mA load and 2.2µH
inductor is about 800kHz.
1275.2007.01.1.3
15
AAT1275
Boost Converter with USB Power Switch
IPP =
IP =
VIN(MIN) · DMAX
L · FS
IO
1-D
IPK = IP +
IPP
2
IV = IP - IPP
IV = IP - IPP = 0.9A - 0.7A = 0.20A
IRMS =
IPK2 + IPK · IV + IV2
=
3
0.9A2 + 0.9A · 0.2A + 0.2A2
= 0.59A
3
For the Sumida CDRH2D14-2R2 inductor, ISAT = 1.0A, IDC(MAX) = 1.6A and DCR = 94mΩ.
PLOSS(INDUCTOR) = I2RMS · DCR = (590mA)2 · 94mΩ = 32mW
5V Output Capacitor
ΔVOUT = 0.05V
COUT(MIN) =
16
IOUT · DMAX
0.3A · 0.46
=
= 3.0µF; use 4.7µF 10V MLC
FS · ΔVOUT
800kHz · 0.05V
1275.2007.01.1.3
AAT1275
Boost Converter with USB Power Switch
AAT1275 Losses
IRMS(ON) =
IRMS(OFF) =
(IPK2 + IPK · IV + IV2) · DMAX
=
3
(0.9A2 + 0.9A · 0.2A + 0.2A2) · 0.46
= 0.4A
3
(IPK2 + IPK · IV + IV2) · (1 - DMAX)
=
3
(0.9A2 + 0.9A · 0.2A + 0.2A2) · (1 - 0.46)
= 0.43A
3
PTOTAL = IRMS(ON)2 · (RDS(ON)IN + RDS(ON)N) + IRMS(OFF)2 · (RDS(ON)IN + RDS(ON)P + RDS(ON))
= 0.4A2 · (0.25Ω + 0.3Ω) + 0.422 · (0.25Ω + 0.3Ω + 0.2Ω) = 0.22W
TJ(MAX) = PTOTAL · θJA + TAMB = 0.22W ·
1275.2007.01.1.3
110°C
+ 85°C = 109°C
W
17
AAT1275
Boost Converter with USB Power Switch
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TSOPJW-12
TDFN34-16
USXYY
USXYY
AAT1275ITP-5.0-T1
AAT1275IRN-5.0-T1
All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means
semiconductor products that are in compliance with current RoHS standards, including
the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more
information, please visit our website at http://www.analogictech.com/pbfree.
Package Information3
TSOPJW-12
2.85 ± 0.20
+ 0.10
- 0.05
2.40 ± 0.10
0.20
0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC
7° NOM
0.04 REF
0.055 ± 0.045
0.15 ± 0.05
+ 0.10
1.00 - 0.065
0.9625 ± 0.0375
3.00 ± 0.10
4° ± 4°
0.45 ± 0.15
0.010
2.75 ± 0.25
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the
lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required
to ensure a proper bottom solder connection.
18
1275.2007.01.1.3
AAT1275
Boost Converter with USB Power Switch
TDFN34-16
3.00 ± 0.05
Detail "A"
4.00 ± 0.05
Index Area
0.35 ± 0.10
Top View
0.23 ± 0.05
Bottom View
(4x)
0.45 ± 0.05
0.85 MAX
Pin 1 Indicator
(optional)
0.05 ± 0.05
0.229 ± 0.051
Side View
Detail "A"
All dimensions in millimeters.
© Advanced Analogic Technologies, Inc.
AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work rights,
or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service without notice.
Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech
warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech’s standard warranty. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty. Specific testing of all parameters of each device is not necessarily performed.
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830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737- 4600
Fax (408) 737- 4611
1275.2007.01.1.3
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