Analogic AAT1275 Boost converter with usb power switch Datasheet

PRODUCT DATASHEET
AAT1275
SwitchRegTM
Boost Converter with USB Power Switch
General Description
Features
The AAT1275 SwitchReg is a 2MHz, 500mA synchronous
boost converter with an integrated current-limiting 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 Lithium-Ion/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
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.
Applications
•
•
•
•
•
•
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, space-saving
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
AAT1275
Fault
RFB2
59k
FLT
Enable
EN
VBUS Output
OUT2
SET
RSET
1275.2008.04.1.7
COUT1
4.7µF
COUT2
1µF
GND
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1
PRODUCT DATASHEET
AAT1275
SwitchRegTM
Boost Converter with USB Power Switch
Pin Descriptions
Pin
TSOPJW-12
TDFN34-16
Symbol
1
2
3
4
5
6
1, 16
3, 15
13, 14
11, 12
10
9
LIN
IN
PGND
SW
OUT1
OUT2
7
8
SET
8
7
FLT
9
10
11
12
6
5
4
2
FB
GND
VCC
EN
EP
Function
Switched power input. Connect an inductor between this pin and the SW pin.
Supply input. Connect to VCC for proper operation.
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, open-drain output. A 10kΩ external pull-up resistor is recommended.
Boost converter voltage feedback pin.
Ground.
Bias supply for the internal circuitry. Connect to IN for proper operation.
Enable pin, active high.
Exposed paddle (bottom); connect to ground directly beneath the package.
Pin Configuration
TSOPJW-12
(Top View)
2
TDFN34-16
(Top View)
LIN
1
16
LIN
EN
2
15
IN
IN
3
14
PGND
VCC
4
13
PGND
GND
5
12
SW
FLT
FB
6
11
SW
SET
FLT
7
10
OUT1
SET
8
9
OUT2
LIN
1
12
EN
IN
2
11
VCC
PGND
3
10
GND
SW
4
9
FB
OUT1
5
8
OUT2
6
7
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1275.2008.04.1.7
PRODUCT DATASHEET
AAT1275
SwitchRegTM
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 VIN + 0.3
-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 an FR4 board.
1275.2008.04.1.7
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3
PRODUCT DATASHEET
AAT1275
SwitchRegTM
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
VIN, VCC
VOUTx
VUVLO
IQ
Description
Conditions
Operating Input Voltage Range
Maximum Output Voltage Range
Under-Voltage Lockout
FOSC
Typ
2.7
No Load, Switching
No Load, Not Switching, VFB = 1.5V
EN = GND
Quiescent Supply Current
ISHDN
Shutdown Current
Boost Converter
Continuous Output Current
IO
ILIMIT
Input Switch Current Limit
VFB
FB Pin Regulation
VOUT
Output Voltage Tolerance
∆VOUT
Load Regulation
(VOUT*∆VIN)
∆VOUT/VOUT Line Regulation
RDS(ON)H
High Side Switch On Resistance
RDS(ON)L
Low Side Switch On Resistance
RDS(ON)_IN
Input Disconnect Switch
TSS
Soft-Start Time
η
Min
100
45
3V < VIN < 5V, VO = 5V
No Load, TA = 25°C
ILOAD = 0 to 500mA, VIN = 2.7V to 5V
0.591
-3
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
Load Switch
RDS(ON)
Current Limit Switch On Resistance
Current Limit
ILIM
ILIM(MIN)
Minimum Current Limit
TRESP
Current Limit Response Time
TON
Turn-On Delay Time
TOFF
Turn-Off Delay Time
VFLT_LOW
FLT Logic Output Low
IFLT
FLT Logic Output High Leakage Current
Fault Blanking Time
TBLANK
Control
VTH-L
EN Threshold Low
VTH-H
EN Threshold High
IEN
EN Input Leakage
TJ-TH
TJ Thermal Shutdown Threshold
TJ-HYS
TJ Thermal Shutdown Hysteresis
Units
5.0
5.5
2.7
V
V
V
90
1.0
500
ILOAD = 0 to 500mA
Efficiency
Max
VOUT1 = 5V, TA = 25°C
RSET = 16.9kΩ
RSET = 40kΩ
VOUT1 = 5V
VOUT1 = 5V, RL = 10Ω
VOUT1 = 5V, RL = 10Ω
ISINK = 1mA
VFAULT = 5V
Rising and Falling Edge
2.5
0.6
0.609
3
µA
mA
A
V
%
0.005
%/mA
0.2
200
170
170
300
%/V
mΩ
mΩ
mΩ
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
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
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1275.2008.04.1.7
PRODUCT DATASHEET
AAT1275
SwitchRegTM
Boost Converter with USB Power Switch
Typical Characteristics
Efficiency vs. Load
DC Regulation
(VOUT = 5.0V)
1.5
80
60
VIN = 4.2V
VIN = 3.6V
VIN = 2.7V
Output Error (%)
Efficiency (%)
100
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
Line Regulation
100
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 (%)
10
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
4.5
4.8
5.0
120
100
80
60
40
20
0
0
50
100
150
Temperature (°°C)
Supply Voltage (V)
1275.2008.04.1.7
-50
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5
PRODUCT DATASHEET
AAT1275
SwitchRegTM
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
VIN
(500mV/div)
RDS(ON) (mΩ
Ω)
3.6V
5.064V
VOUT
(200mV/div)
150
100
-40°C
25°C
50
4.752V
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)
Time (100µs/div)
6
120°C
200
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1275.2008.04.1.7
PRODUCT DATASHEET
AAT1275
SwitchRegTM
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
2.5
4.5
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)
1275.2008.04.1.7
2.7
Time (50ms/div)
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7
PRODUCT DATASHEET
AAT1275
SwitchRegTM
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
10
100
4.0
2.0
0.0
-2.0
-4.0
-6.0
-50
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
4.0
4.2
Input Voltage (V)
8
0
-50
-25
0
25
50
75
100
Temperature (°C)
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1275.2008.04.1.7
PRODUCT DATASHEET
AAT1275
SwitchRegTM
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
Control Scheme
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.
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.
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 overcurrent and over-temperature conditions through an
open-drain fault reporting signal (FLT). The fault reporting signal has a 4ms turn-on delay.
1275.2008.04.1.7
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9
PRODUCT DATASHEET
AAT1275
SwitchRegTM
Boost Converter with USB Power Switch
Step-Up Converter
Application Information
Soft Start / Enable
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 cycle-by-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.
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 2.2µH (± 20%) inductor is
selected to maintain high frequency operation for the 5V
USB output voltage.
Input Current Limit and
Over-Temperature Protection
The switching of the N-channel MOSFET terminates
when input 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.
Shutdown and Output Disconnect
A typical synchronous step-up (boost) converter has a
conduction path from the input to the output via the
body diode of the P-channel MOSFET. The AAT1275
design disconnects this body diode from the output and
eliminates this conduction path. This enables the AAT1275
to provide true load disconnect during shutdown and
inrush current limit at turn-on.
Short-Circuit Protection
The P-channel synchronous MOSFET body diode disconnect feature also gives the AAT1275 the ability to provide output short-circuit current limit protection.
Under-Voltage Lockout
Output Voltage Programming
The output voltage is programmed through a resistor
divider network located from the OUT1 output capacitor
to the FB pin to ground.
10
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.
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.
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1275.2008.04.1.7
PRODUCT DATASHEET
AAT1275
SwitchRegTM
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 =
VO - VIN(MIN)
VO
VIN(MIN) · D
L · FS
IPP =
IP =
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, chiptype 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 minimizes 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.
IO
1-D
IPK = IP +
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.
IPP
2
Estimate the output capacitor required at the minimum
switching frequency (FS) of 800kHz (worst-case).
IV = IP - IPP
IRMS =
2
PK
I
COUT =
2
+ IPK · IV + IV
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.
1275.2008.04.1.7
IOUT · DMAX
FS · ∆VOUT
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.
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PRODUCT DATASHEET
AAT1275
SwitchRegTM
Boost Converter with USB Power Switch
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
⎝
⎠
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 pullup 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
432kΩ ⎞
⎛
= 0.6V · 1 + 59.0kΩ
⎝
⎠
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.
= 5.0V
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.
RSET (kΩ)
IOUT (mA)
11
12
14
16
18
20
30
40
740
690
590
550
450
420
160
100
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.
DMAX =
IPP =
VO - VIN(MIN)
VO
VIN(MIN) · DMAX
L · FS
IP =
IO
1-D
IPK = IP +
IV = IP - IPP
Table 1: Load Switch Current Limit vs. RSET.
Operation in Current Limit
IRMS(ON) =
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 overtemperature 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
IPP
2
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))
TJ(MAX) = PTOTAL · θJA + TAMB
12
www.analogictech.com
1275.2008.04.1.7
PRODUCT DATASHEET
AAT1275
SwitchRegTM
Boost Converter with USB Power Switch
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
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.
Figure 1: AAT1275 TSOPJW-12 Package
Evaluation Board Top Side Layout.
1275.2008.04.1.7
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.
Figure 2: AAT1275 TSOPJW-12 Package
Evaluation Board Bottom Side Layout.
www.analogictech.com
13
PRODUCT DATASHEET
AAT1275
SwitchRegTM
Boost Converter with USB Power Switch
VIN
L1 2.2µH
4
1
GND
R4
7
16.9kΩ
C6
120µF
CCase
SW
LIN
SET
FLT
8
OUT2
6
OUT1
5
10
GND
EN
12
11
VCC
FB
9
PGND
3
2
VIN
R1
10K
U1
AAT1275
VIN
FLT
VO2
VO1
J5
R2
432k
R3
59k
C3
4.7µF
10V
C2
4.7µF
10V
C1
4.7µF
GND
VIN
3
2
GND
1
Enable
Figure 3: AAT1275 TSOPJW-12 Package Evaluation Board Schematic.
Figure 4: AAT1275 TDFN34-16 Package
Evaluation Board Top Side Layout.
14
Figure 5: AAT1275 TDFN34-16 Package
Evaluation Board Bottom Side Layout.
www.analogictech.com
1275.2008.04.1.7
PRODUCT DATASHEET
AAT1275
SwitchRegTM
Boost Converter with USB Power Switch
AAT1275-TDFN34-16
L1
2.2µH
U1
1
3
VIN
4
C6
120µF
R1
10K
15
3
2
1
LIN
LIN
VIN
SW
VCC
SW
VIN
OUT2
2
EN
OUT1
7
FLT
16
12
11
Feedback Option
1 2 3
9
VOUT2
10
Enable
R5 1k
1
FB
6
PGND SET
GND
PGND GND
8
R2
432k
FLT
13
C3
4.7µF
10V
14
C4
100pF
VOUT1
C2
4.7µF
10V
C1
4.7µF
10V
5
R4
16.9k
R3
59k
Figure 6: AAT1275 TDFN34-16 Package Evaluation Board Schematic.
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 2: Typical Surface Mount Capacitors.
Manufacturer
Part Number
Inductance (µH)
Max DC
Current (A)
DCR (Ω)
Size (mm)
LxWxH
Type
Sumida
Sumida
Coiltronics
Coiltronics
CDRH2D14-2R2
CDRH4D11/HP-2R4
SD3112-2R2
SD3114-2R2
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 3: Typical Surface Mount Inductors.
1275.2008.04.1.7
www.analogictech.com
15
PRODUCT DATASHEET
AAT1275
SwitchRegTM
Boost Converter with USB Power Switch
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.
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
∆VOUT = 0.05V
COUT(MIN) =
16
IOUT · DMAX
0.3A · 0.46
=
= 3.0µF; use 4.7µF 10V MLC
FS · ∆VOUT
800kHz · 0.05V
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1275.2008.04.1.7
PRODUCT DATASHEET
AAT1275
SwitchRegTM
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 ·
1275.2008.04.1.7
110°C
+ 85°C = 109°C
W
www.analogictech.com
17
PRODUCT DATASHEET
AAT1275
SwitchRegTM
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
Package Information3
TSOPJW-12
2.85 ± 0.20
2.40 ± 0.10
0.20 + 0.10
- 0.05
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
www.analogictech.com
1275.2008.04.1.7
PRODUCT DATASHEET
AAT1275
SwitchRegTM
Boost Converter with USB Power Switch
TDFN34-16
3.000 ± 0.050
1.600 ± 0.050
Detail "A"
3.300 ± 0.050
4.000 ± 0.050
Index Area
0.350 ± 0.100
Top View
0.230 ± 0.050
Bottom View
C0.3
(4x)
0.050 ± 0.050
0.450 ± 0.050
0.850 MAX
Pin 1 Indicator
(optional)
0.229 ± 0.051
Side View
Detail "A"
All dimensions in millimeters.
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054
Phone (408) 737-4600
Fax (408) 737-4611
© 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. Except as provided in AnalogicTech’s terms and
conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty relating to the sale and/or use of AnalogicTech products including liability or warranties
relating to fitness for a particular purpose, merchantability, or infringement of any patent, copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate
design and operating safeguards must be provided by the customer to minimize inherent or procedural hazards. 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. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated. All other
brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
1275.2008.04.1.7
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19