ANALOGICTECH AAT1161

PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
General Description
Features
The AAT1161 is an 800kHz high efficiency step down
DC-DC converter with wide input voltage range. With
4.0V to 13.2V input rating, the AAT1161 is the perfect
choice for 2-cell Li+ battery powered devices and mid
power range regulated 12V powered applications. The
internal power switch is capable of delivering up to 3A
load current.
• Input Voltage Range : 4.0V to 13.2V
• Up to 3A Load Current
• Fixed or Adjustable Output:
▪ Output Voltage: 0.6V to VIN
• Less than 1μA Shutdown Current
• Up to 95% Efficiency
• Integrated High-Side Power Switch
• External Schottky Rectifier
• 800kHz Switching Frequency
• Soft Start Function
• Short-Circuit and Over-Temperature Protection
• Minimum External Components
• Tiny 14-pin 3x3mm TDFN Package
• Temperature Range: -40°C to +85°C
The AAT1161 is a highly integrated device in order to
simplify system level design for the users. It is a nonsynchronous converter that is used with an external
Schottky diode rectifier for low-cost applications.
Minimum external components are required for the converter. All the control circuits are integrated in the IC.
The AAT1161 optimizes efficiency throughout the entire
load range. It operates in a combination PWM/Light Load
mode for improved light-load efficiency. It can also operate in a forced Pulse Width Modulation (PWM) mode for
easy control of the switching noise as well as faster transient response. The high switching frequency allows the
use of small external components. The low current shutdown feature disconnects the load from VIN and drops
shutdown current to less than 1μA.
Applications
•
•
•
•
•
Digital Camcorders
Industrial Applications
Portable DVD Players
Rack Mounted Systems
Set Top Boxes
The AAT1161 is available in a Pb-free, space-saving,
thermally-enhanced 14-pin TDFN33 package and is rated
over an operating temperature range of -40°C to +85°C.
Typical Application
L1
3.8µH
VIN 4.5V- 13.2V
6
C6
10µF
R4
10Ω
C8
1µF
EN
LX
8
IN
LX
9
10
C2
0.1µF
11
IN
AAT1161
C1
D1 100pF
1
R3
432 kΩ
C3, 4, 5
66µF
13
AIN
4, 5
7
PGND
12
DGND
COMP
2
AGND
3
N/C
PGND
EP1
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FB
VOUT
5V, 3A
LDO
R6
59kΩ
R5
51kΩ
14
C9
1µF
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C7
150pF
1
PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
Pin Descriptions
Pin #
Symbol
1
FB
2
COMP
3
AGND
4, 5
DGND
6
EN
7
N/C
8, 9
LX
10, 11
IN
12, EP
PGND
13
AIN
14
LDO
Function
Output voltage feedback input. FB senses the output voltage for regulation control. For fixed output versions, connect FB to the output voltage. For adjustable versions, drive FB from the output voltage through
a resistive voltage divider. The FB regulation threshold is 0.6V.
Control compensation node. In most configurations external compensation is not required. If external
compensation is required, connect a series RC network from COMP to AGND. See Compensation section.
Analog signal ground. Used for the Compensation, LDO bypass and feedback divider ground. Connect
AGND to DGND/PGND at a single point as close to the IC as possible or directly under the package exposed thermal pad (EP).
Digital/Power Ground. Used for the input and enable ground. Connect DGND to AGND/PGND at a single
point as close to the IC as possible or directly under the package exposed thermal pad (EP).
Active high enable input. Drive EN high to turn on the AAT1161; drive it low to turn it off. For automatic
startup, connect EN to IN through a 4.7kΩ resistor. EN must be biased high, biased low, or driven to a
logic level by an external source. Do not let the EN pin float when the device is powered.
No Connect. Leave floating; do not connect anything to this pin.
Power switching node. LX is the drain of the internal P-channel switch. Connect the external rectifier
from LX to PGND and the external LC output filter from LX to the load.
Power source input. Connect IN to the input power source. Bypass IN to DGND with a 10μF or greater
capacitor. Connect both IN pins together as close to the IC as possible. An additional 100nF ceramic
capacitor should also be connected between the two IN pins and DGND.
Power Ground. The exposed thermal pad (EP) should be connected to board ground plane and pins 3, 4,
5 and 12 directly under the package. The ground plane should include a large exposed copper pad under
the package for thermal dissipation (see package outline).
Internal analog bias input. AIN supplies internal power to the AAT1161. Connect AIN to the input source
voltage and bypass to AGND with a 0.1μF or greater capacitor. For additional noise rejection, connect to
the input power source through a 10Ω or lower value resistor.
Internal LDO bypass node. The output voltage of the internal LDO is bypassed at LDO. The internal circuitry of the AAT1161 is powered from LDO. Do not draw external power from LDO. Bypass LDO to AGND
with a 1μF or greater capacitor.
Pin Configuration
TDFN33-14
(Top View)
FB
COMP
AGND
DGND
DGND
EN
N/C
2
1
14
2
13
3
12
4
11
5
10
6
9
7
8
LDO
AIN
PGND
IN
IN
LX
LX
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1161.2008.03.1.0
PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
Absolute Maximum Ratings1
Symbol
VIN, VAIN
VLX
VFB
VEN
TJ
Description
Input Voltage
LX to GND Voltage
FB to GND Voltage
EN to GND Voltage
Operating Junction Temperature Range
Value
Units
-0.3 to 14
-0.3 to VIN + 0.3
-0.3 to VIN + 0.3
-0.3 to VIN + 0.3
-40 to 150
V
V
V
V
°C
Value
Units
2.0
50
W
°C/W
Thermal Information2
Symbol
PD
θJA
Description
Maximum Power Dissipation3
Thermal Resistance
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions
specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Mounted on an FR4 board.
3. Derate 20mW/°C above 25°C.
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3
PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
Electrical Characteristics
4.0V < VIN < 13.2V. CIN= 22µF, COUT= 66µF; L= 2.2µH or 3.8µH, TA= -40 to +85°C unless otherwise noted. Typical values are at TA= 25°C.
Symbol
VIN
Description
Input Under-Voltage Lockout
IQ
ISHDN
Supply Current
Shutdown Current
VOUT
Output Voltage Range
VFB
IFBLEAK
FOSC
TS
DC
TON
TSS
RDS(ON)H
η
ILIM
ILXLEAK
TSD
THYS
VILEN
VIHEN
IEN
Min
Input Voltage Range
VUVLO
VOUT
∆VLINEREG/
∆VIN
∆VLOADREG
Conditions
Typ
4.0
Rising
Hysteresis
No Load
VEN = GND
0.3
150
0.6
Output Voltage Accuracy
IOUT = 0A to 3A
Line Regulation
VIN = 4.5V to 13.2V
Load Regulation
Feedback Reference Voltage (adjustable
version)
VIN = 12V, VOUT = 5V, IOUT = 0A to 3A
FB Leakage Current
No Load, TA = 25°C
VOUT = 1.2V
Oscillator Frequency
Start-Up Time
Foldback Frequency
Maximum Duty Cycle
Minimum Turn-On Time
Soft-Start Time
-2.5
0.59
Adjustable Version
Fixed Version
Max
Units
13.2
4.0
V
300
1
0.94
VIN
2.5
0.6
Efficiency
PMOS Current Limit
LX Leakage Current
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
EN Logic Low Input Threshold
EN Logic High Input Threshold
EN Input Current
VIN = 12V
VIN = 6V
VIN = 12V, VOUT = 5V, IOUT = 3A
4.0
%
0.60
0.61
2
0.8
2
200
1
100
2
0.12
0.15
90
6.0
V
µA
MHz
ms
kHz
%
ns
ms
Ω
1
140
25
0.4
VEN = 0V, VEN = 13.2V
%
0.4
VIN = 13.2V, VLX = 0 to VIN
1.4
-1.0
V
%/V
94
P-Channel On Resistance
µA
µA
0.023
0.2
IOUT = 3A, VOUT = 5V
V
1.0
%
A
µA
°C
°C
V
V
µA
1. The AAT1161 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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1161.2008.03.1.0
PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
Efficiency vs. Load Current
Efficiency vs. Load Current
(VOUT = 5V)
(VOUT = 3.3V)
100
100
90
90
80
80
Efficiency (%)
Efficiency (%)
Typical Characteristics
70
60
50
VIN = 6V
VIN = 7V
VIN = 10V
VIN = 12V
VIN = 13.2V
40
30
20
10
0
0.0001
0.001
0.01
0.1
1
70
60
50
VIN = 5V
VIN = 7V
VIN = 10V
VIN = 12V
VIN = 13.2V
40
30
20
10
0
0.0001
10
0.001
0.01
Load Current (A)
Load Current (A)
Load Regulation
Load Regulation
0.75
0.5
0.25
0
VIN = 13.2V
VIN = 12V
VIN = 10V
VIN = 7V
VIN = 6V
-0.25
-0.5
-0.75
0.001
0.01
0.1
1
10
1
0.75
0.4
0.2
0
0
-0.25
-0.5
0.0001
0.001
0.01
Line Regulation
(VOUT = 3.3V)
-0.4
-0.6
-0.8
6
7
8
9
10
11
12
1
0.8
0.6
0.4
0.2
0
-0.2
3A
1.5A
1A
100mA
10mA
-0.4
-0.6
-0.8
-1
Input Voltage (V)
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0.1
Line Regulation
-0.2
-1
10
0.5
0.25
Load Current (A)
3A
1.5A
1A
100mA
10mA
0.6
1
VIN = 13.2V
VIN = 12V
VIN = 10V
VIN = 7V
VIN = 6V
1.25
Load Current (A)
Output Voltage Difference (%)
Output Voltage Difference (%)
1
10
1.5
(VOUT = 5V)
0.8
1
(VOUT = 3.3V)
1
Output Voltage Difference (%)
Output Voltage Difference (%)
(VOUT = 5V)
-1
0.0001
0.1
5
6
7
8
9
10
11
12
Input Voltage (V)
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PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
Typical Characteristics
P-Channel RDS(ON) vs. Temperature
(VIN = 6V)
180
200
85°C
25°C
-40°C
170
160
180
Resistance (mΩ
Ω)
Non Switching Supply Current (µA)
Non Switching Supply Current vs. Input Voltage
150
140
130
120
160
6V
140
120
12V
100
80
60
40
110
20
0
-40
100
5
6
7
8
9
10
11
12
-15
VOUT Tolerance vs. Temperature
(VOUT = 3.3V; ILOAD = 3A)
Output Voltage Difference (%)
Switching Frequency (kHz)
60
(VIN = 6V)
810
805
800
795
790
785
780
VIN = 12V
VIN = 6V
775
770
-40
-15
10
35
60
85
85
1
0.8
0.6
0.4
0.2
0
-0.2
-0.4
-0.6
-0.8
-40
-15
10
35
60
85
Temperature (°C)
Load Transient
(VOUT = 5.0V; CFF = 100pF; IOUT = 1A to 3A; COUT = 66µF)
20
5.1
18
16
5.0
14
4.9
12
4.8
10
4.7
8
5.6
8
5.4
7
5.2
6
5.0
5
4.8
4
4.6
3
4.4
2
4.6
6
4.2
1
4.5
4
4.0
0
Load Current
(bottom) (A)
5.2
Output Voltage
(top) (V)
Line Transient
(VOUT = 5.0V; CFF = 100pF; VIN = 6V to 11V;
IOUT = 3A; CIN = 10µF; COUT = 66µF; L = 3.8µH)
Input Voltage
(bottom) (V)
Output Voltage
(top) (V)
35
Switching Frequency vs. Temperature
Temperature (°C)
Time (200ms/div)
Time (200ms/div)
6
10
Temperature (°C)
Input Voltage (V)
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PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
Typical Characteristics
Load Transient
Start-Up Time
5.4
7
5.2
6
5.0
5
4.8
4
4.6
3
4.4
2
4.2
1
4.0
0
Enable and Input Voltage
(top) (V)
8
Time (200ms/div)
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(VOUT = 5.0V; CFF = 100pF; RLOAD = 1.67Ω
Ω;
CIN = 10µF; COUT = 22µF; L = 3.8µH)
7
7
6
5
5
3
4
1
3
2
-1
VENABLE
VOUT
ILOAD
-3
-5
-7
1
Load Current
(bottom) (A)
5.6
Load Current
(bottom) (A)
Output Voltage
(top) (V)
(VOUT = 5.0V; CFF = 100pF; IOUT = 50mA to 3A; COUT = 66µF)
0
-1
Time (1ms/div)
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PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
Functional Block Diagram
LDO
Internal
Power
*
FB
AIN
IN
LDO
Current
Sense Amp
Err
Amp
DH
Comp
Voltage
Reference
Control
Logic
LX
PGND
EN
Input
DGND
AGND
COMP
* For fixed output voltage versions, FB is connected to the error amplifier through the resistive voltage divider shown.
Functional Description
Control Loop
The AAT1161 is a current-mode step-down DC/DC converter that operates over a wide 4V to 13.2V input voltage
range and is capable of supplying up to 3A to the load
with the output voltage regulated as low as 0.6V. The
P-channel power switch is internal, reducing the number
of external components required. An external Schottky
diode is used for the low side rectifier. The output voltage
is adjusted by an external resistor divider; fixed output
voltage versions are available upon request. The regulation system is externally compensated, allowing the circuit to be optimized for each application. The AAT1161
includes cycle-by-cycle current limiting, frequency foldback for improved short-circuit performance, and thermal
overload protection to prevent damage in the event of an
external fault condition.
The AAT1161 regulates the output voltage using constant frequency current mode control. The AAT1161
monitors current through the high-side P-channel
MOSFET and uses that signal to regulate the output voltage. This provides improved transient response and
eases compensation. Internal slope compensation is
included to ensure the current “inside loop” stability.
High efficiency is maintained under light load conditions
by automatically switching to variable frequency Light
Load control. In this condition, transition losses are
reduced by operating at a lower frequency at light loads.
The AAT1161 uses an external Schottky rectifier diode to
minimize cost.
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1161.2008.03.1.0
PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
Low Dropout Operation
Applications Information
The AAT1161 operates with duty cycle up to 100% to
minimize the dropout voltage, increasing the available
input voltage range for a given output voltage. As the
input voltage decreases toward the output voltage, the
duty cycle increases until it reaches the maximum ontime. Further reduction of the supply voltage forces the
PMOS on 100%; the output voltage is determined by the
p-channel MOSFET switch and inductor voltage drops.
Setting the Output Voltage
Figure 1 shows the basic application circuit for the AAT1161
and output setting resistors. Resistors R3 and R6 program
the output to regulate at a voltage higher than 0.6V. To
limit the bias current required for the external feedback
resistor string while maintaining good noise immunity, the
minimum suggested value for R6 is 5.9kΩ. Although a
larger value will further reduce quiescent current, it will
also increase the impedance of the feedback node, making
it more sensitive to external noise and interference. Table
1 summarizes the resistor values for various output voltages with R6 set to either 5.9kΩ for good noise immunity
or 59kΩ for reduced no load input current. The external
resistors set the output voltage according to the following equation:
Short-Circuit Protection
The AAT1161 uses a cycle-by-cycle current limit to protect itself and the load from an external fault condition.
When the inductor current reaches the internally set
6.0A current limit, the P-channel MOSFET switch turns
off, limiting the inductor and the load current. During an
overload condition, when the output voltage drops below
25% of the regulation voltage (0.15V at FB), the
AAT1161 switching frequency drops by a factor of 4. This
gives the inductor current ample time to reset during the
off time to prevent the inductor current from rising
uncontrolled in a short-circuit condition.
⎛
R3 ⎞
VOUT = 0.6V 1 +
⎝
R6 ⎠
or
⎛ VOUT ⎞
R3 = V
-1 · R6
⎝ REF ⎠
Thermal Protection
The adjustable feedback resistors, combined with an
external feed forward capacitor (C1 in Figure 1), deliver
enhanced transient response for extreme pulsed load
applications. The addition of the feed forward capacitor
typically requires a larger output capacitor C3/C4/C5 for
stability. Larger C3/C4/C5 values reduce overshoot and
undershoot during startup and load changes. However,
do not exceed 470pF to maintain stable operation.
The AAT1161 includes thermal protection that disables
the regulator when the die temperature reaches 140ºC.
It automatically restarts when the temperature decreases by 25ºC or more.
L1
3.8µH
VIN 4.5V- 13.2V
6
C6
10µF
R4
10Ω
C8
1µ F
EN
LX
IN
LX
10
C2
0.1µ F
11
IN
AAT1161
FB
VOUT
5V, 3A
8
C1
D1 100pF
9
1
R3
432 kΩ
C3, 4, 5
66µF
13
AIN
4, 5
7
PGND
12
DGND
COMP
2
AGND
3
N/C
PGND
EP1
LDO
R6
59kΩ
R5
51kΩ
14
C9
1µ F
C7
150pF
Figure 1: Typical Application Circuit.
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PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
Table 1 shows the resistor selection for different output
voltage settings.
VOUT (V)
R6 = 5.9kΩ
R3 (kΩ)
R6 = 59kΩ
R3 (kΩ)
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
3.3
5.0
1.96
2.94
3.92
4.99
5.90
6.81
7.87
8.87
11.8
12.4
13.7
18.7
26.7
43.2
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
432
Table 1: Resistor Selection for Different Output
Voltage Settings. Standard 1% Resistors are
Substituted for Calculated Values.
Inductor Selection
For most designs, the AAT1161 operates with inductors
of 2µH to 4.7µH. Low inductance values are physically
smaller, but require faster switching, which results in
some efficiency loss. The inductor value can be derived
from the following equation:
L1 =
VOUT · (VIN - VOUT)
VIN · ∆IL · FOSC
Where ∆IL is inductor ripple current. Large value inductors lower ripple current and small value inductors result
in high ripple currents. Choose inductor ripple current
approximately 32% of the maximum load current 3A, or
∆IL = 959mA. For output voltages above 3.3V, the mini-
Manufacturer
Part Number
mum recommended inductor is 3.8µH. For 3.3V and
below, use a 2 to 2.2µH inductor. For optimum voltagepositioning load transients, choose an inductor with DC
series resistance in the 15mΩ to 20mΩ range. For
higher efficiency at heavy loads (above 1A), or minimal
load regulation (but some transient overshoot), the
resistance should be kept below 18mΩ. 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 (3A + 526mA). Table 2 lists
some typical surface mount inductors that meet target
applications for the AAT1161.
Manufacturer’s specifications list both the inductor DC
current rating, which is a thermal limitation, and the
peak current rating, which is determined by the saturation characteristics. The inductor should not show any
appreciable saturation under normal load conditions.
Some inductors may meet the peak and average current
ratings yet result in excessive losses due to a high DCR.
Always consider the losses associated with the DCR and
its effect on the total converter efficiency when selecting
an inductor. For example, the 3.7μH CDR7D43 series
inductor selected from Sumida has an 18.9mΩ DCR and
a 4.3ADC current rating. At full load, the inductor DC
loss is 170mW which gives only a 1.13% loss in efficiency for a 3A, 5V output.
Input Capacitor Selection
The input capacitor reduces the surge current drawn
from the input and switching noise from the device. The
input capacitor impedance at the switching frequency
shall be less than the input source impedance to prevent
high frequency switching current passing to the input. A
low ESR input capacitor sized for maximum RMS current
must be used. Ceramic capacitors with X5R or X7R
dielectrics are highly recommended because of their low
ESR and small temperature coefficients. A 22µF ceramic
capacitor is sufficient for most applications.
L (µH)
Max DCR
(mΩ)
Rated DC
Current (A)
Size WxLxH
(mm)
Sumida
CDRH103RNP-2R2N
2.2
16.9
5.10
10.3x10.5x3.1
Sumida
Coilcraft
CDR7D43MNNP-3R7NC
MSS1038-382NL
3.7
3.8
18.9
13
4.3
4.25
7.6x7.6x4.5
10.2x7.7x3.8
Table 2: Typical Surface Mount Inductors.
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1161.2008.03.1.0
PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
To estimate the required input capacitor size, determine
the acceptable input ripple level (VPP) and solve for C.
The calculated value varies with input voltage and is a
maximum when VIN is double the output voltage.
CIN =
V ⎞
VO ⎛
· 1- O
VIN ⎝
VIN ⎠
⎛ VPP
⎞
- ESR · FOSC
⎝ IO
⎠
VO ⎛
V ⎞
1
· 1 - O = for VIN = 2 · VO
VIN ⎝
VIN ⎠
4
CIN(MIN) =
1
⎛ VPP
⎞
- ESR · 4 · FOSC
⎝ IO
⎠
Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value.
For example, the capacitance of a 10μF, 16V, X5R ceramic capacitor with 12V DC applied is actually about
8.5μF.
The maximum input capacitor RMS current is:
IRMS = IO ·
VO ⎛
V ⎞
· 1- O
VIN ⎝
VIN ⎠
D · (1 - D) =
0.52 =
1
2
for VIN = 2 · VO
IO
2
The term
appears in both the input voltage ripple and input capacitor RMS current equations and is at
maximum when VO is twice VIN. This is why the input
voltage ripple and the input capacitor RMS current ripple
are a maximum at 50% duty cycle. The input capacitor
provides a low impedance loop for the edges of pulsed
current drawn by the AAT1161. Low ESR/ESL X7R and
X5R ceramic capacitors are ideal for this function. To
minimize stray inductance, the capacitor should be
placed as closely as possible to the IC. This keeps the
high frequency content of the input current localized,
1161.2008.03.1.0
The output capacitor is required to keep the output voltage ripple small and to ensure regulation loop stability.
The output capacitor must have low impedance at the
switching frequency. Ceramic capacitors with X5R or
X7R dielectrics are recommended due to their low ESR
and high ripple current. The output ripple VOUT is determined by:
∆VOUT ≤
IRMS(MAX) =
VO ⎛
V ⎞
· 1- O
VIN ⎝
VIN ⎠
A laboratory test set-up typically consists of two long
wires running from the bench power supply to the evaluation board input voltage pins. The inductance of these
wires, along with the low-ESR ceramic input capacitor,
can create a high Q network that may affect converter
performance. This problem often becomes apparent in
the form of excessive ringing in the output voltage during load transients. Errors in the loop phase and gain
measurements can also result. Since the inductance of a
short PCB trace feeding the input voltage is significantly
lower than the power leads from the bench power supply, most applications do not exhibit this problem. In
applications where the input power source lead inductance cannot be reduced to a level that does not affect
the converter performance, a high ESR tantalum or aluminum electrolytic should be placed in parallel with the
low ESR, ESL bypass ceramic. This dampens the high Q
network and stabilizes the system.
Output Capacitor Selection
The input capacitor RMS ripple current varies with the
input and output voltage and will always be less than or
equal to half of the total DC load current:
VO ⎛
V
· 1 - O⎞ =
VIN ⎝ VIN⎠
minimizing EMI and input voltage ripple. The proper
placement of the input capacitor (C6) can be seen in the
evaluation board layout in Figure 3. Additional noise filtering for proper operation is accomplished by adding a
small 0.1µF capacitor on the IN pins (C2).
⎞
VOUT · (VIN - VOUT) ⎛
1
· ESR +
⎝
VIN · FOSC · L
8 · FOSC · COUT⎠
The output capacitor limits the output ripple and provides holdup during large load transitions. A 10μF to
47μF X5R or X7R ceramic capacitor typically provides
sufficient bulk capacitance to stabilize the output during
large load transitions and has the ESR and ESL characteristics necessary for low output ripple. The output voltage droop due to a load transient is dominated by the
capacitance of the ceramic output capacitor. During a
step increase in load current, the ceramic output capacitor alone supplies the load current until the loop
responds. Within two or three switching cycles, the loop
responds and the inductor current increases to match
the load current demand. The relationship of the output
www.analogictech.com
11
PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
voltage droop during the three switching cycles to the
output capacitance can be estimated by:
COUT =
FOSC is the switching frequency and COUT is based on the
output capacitor calculation. The CCOMP value can be
determined from the following equation:
3 · ∆ILOAD
VDROOP · FOSC
CCOMP (C) =
4
2πRCOMP (R5) ·
Once the average inductor current increases to the DC
load level, the output voltage recovers. The above equation establishes a limit on the minimum value for the
output capacitor with respect to load transients. The
internal voltage loop compensation also limits the minimum output capacitor value to 22μF. This is due to its
effect on the loop crossover frequency (bandwidth),
phase margin, and gain margin. Increased output capacitance will reduce the crossover frequency with greater
phase margin.
The maximum output capacitor RMS ripple current is
given by:
IRMS(MAX) =
1
VOUT · (VIN(MAX) - VOUT)
L · FOSC · VIN(MAX)
2· 3
·
Schottky Diode Selection
Power dissipation is the limiting factor when choosing a
diode. The worst-case average power can be calculated
as follows:
⎛ V ⎞
PDIODE = 1 - OUT ⋅ IOUT ⋅ VF
VIN ⎠
⎝
where VF is the voltage drop across the diode at the
given output current IOUTMAX. The total power dissipation
of the diode is the combined totaI of forward power dissipation, reverse power dissipation and switching loss.
Ensure that the selected diode will be able to dissipate
the power based on the equation:
Dissipation due to the RMS current in the ceramic output
capacitor ESR is typically minimal, resulting in less than
a few degrees rise in hot-spot temperature.
TJ(MAX) = TAMB + ΘJA · PDIODE
Where:
Compensation
The AAT1161 step-down converter uses peak current
mode control with slope compensation scheme to maintain stability with lower value inductors for duty cycles
greater than 50%. The regulation feedback loop in the
IC is stabilized by the components connected to the
COMP pin, as shown in Figure 1.
To optimize the compensation components, the following
equations can be used. The compensation resistor RCOMP
(R5) is calculated using the following equation:
RCOMP (R5)=
FOSC
10
θJA = Package Thermal Resistance (°C/W)
TJ(MAX) = Maximum Device Junction Temperature (°C)
TA = Ambient Temperature (°C)
For reliable operation over the input voltage range,
ensure that the reverse-repetitive maximum voltage is
greater than the maximum input voltage (VRRM>VINMAX).
The diode’s forward-current specification must meet or
exceed the maximum output current (IF(AV)>=IOUTMAX).
See Table 3 for recommended diodes for different IOUT
conditions.
2πVOUT · COUT · FOSC
10GEA · GCOMP · VFB
Where VFB = 0.6V, GCOMP = 40.1734 and GEA = 9.091 ·
10-5.
12
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1161.2008.03.1.0
PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
Part Number
VF
IF(AV)
VRRM
θJA
TJ(MAX)
Manufacturer
Dimensions (mm)
M1FM3
D1FH3
SK32
SS5820
30BQ040/LSM345
B220/A
SDM100K30L
B0520WS
0.46V
0.36V
0.5V
0.475A
0.43
0.5V
0.485V
0.43V
3A
3A
3A
3A
3A
2A
1A
0.5A
30V
30V
20V
20V
40V
20V
30V
20V
80°C/W
65°C/W
60°C/W
55°C/W
46°C/W
25°C/W
426°C/W
426°C/W
150°C
125°C
150°C
125°C
150°C
150°C
125°C
125°C
Shindengen
Shindengen
MCC
Jinan Jingheng
IR/Microsemi
Diodes Inc.
Diodes Inc.
Diodes Inc.
2.8x1.8
4.4x2.5
7x6
4.3x3.6
7x6
4.3x3.6
1.7x1.3
1.7x1.3
Table 3: Recommended Schottky Diodes for Different Output Current Requirements.
Layout Guidance
4.
Figure 2 is the schematic for the evaluation board. When
laying out the PC board, the following layout guideline
should be followed to ensure proper operation of the
AAT1161:
5.
1.
2.
3.
Exposed pad EP1 must be reliably soldered to PGND/
DGND/AGND. The exposed thermal pad should be
connected to board ground plane and pins 6, 11, 13,
and 16. The ground plane should include a large
exposed copper pad under the package for thermal
dissipation.
The power traces, including GND traces, the LX
traces and the VIN trace should be kept short, direct
and wide to allow large current flow. The L1 connection to the LX pins should be as short as possible.
Use several via pads when routing between layers.
Exposed pad pin EP2 must be reliably soldered to the
LX pins 1 and 2. The exposed thermal pad should be
connected to the board LX connection and the inductor L1 and also pins 1 and 2. The LX plane should
include a large exposed copper pad under the package for thermal dissipation.
1161.2008.03.1.0
6.
7.
8.
The input capacitors (C2 and C6) should be connected as close as possible to IN (Pins 4 and 5) and
DGND (Pin 6) to get good power filtering.
Keep the switching node LX away from the sensitive
FB node.
The feedback trace for the FB pin should be separate
from any power trace and connected as closely as
possible to the load point. Sensing along a highcurrent load trace will degrade DC load regulation.
The feedback resistors should be placed as close as
possible to the FB pin (Pin 9) to minimize the length
of the high impedance feedback trace.
The output capacitors C3, 4, and 5 and L1 should be
connected as close as possible and there should not
be any signal lines under the inductor.
The resistance of the trace from the load return to
the PGND (Pin 16) should be kept to a minimum.
This will help to minimize any error in DC regulation
due to differences in the potential of the internal
signal ground and the power ground.
www.analogictech.com
13
PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
JP1
EN
R1
R2
4.75K
NP
D1
Schottky
TP1
LX
DGND
U1
TP3
VIN
VIN
R3
10
TB2
VIN
TB3
C1
0.1µF
6
10
11
13
4
12
C7
22µF
5
AAT1161
EN
IN
IN
LX
LX
FB
COMP
AIN
AGND
DGND
PGND
DGND
C8
0.1µF
N/C
EP
LDO
VOUT
C2
100pF
3
7
14
TP4
C6
150pF
NP
R4
43.2K
R5
51.0K
LDO
C9
150pF
TB1
C3
22µF
R6
5.90K
C4
22µF
C5
22µF
VOUT
TB4
GND
TP5
GND
TP2
3.3µH
C10
0.1µF
GND
VOUT
L1
9
8
1
2
TP7
DGND PGND
PGND
GND
AGND
Note: Connect GND, DGND, PGND, and AGND at IC
C2 - Increase C2 to reduce overshoot
Figure 2: AAT1161 Evaluation Board Schematic.
Figure 3: AAT1161 Evaluation Board
Top Side Layout.
14
Figure 4: AAT1161 Evaluation Board
Bottom Side Layout.
www.analogictech.com
1161.2008.03.1.0
PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
Design Example
Specifications
VOUT
VIN
FOSC
TAMB
5V @ 3A, Pulsed Load ∆ILOAD = 3A
12V nominal
800kHz
85°C in TDFN34-16 Package
Output Inductor
L1 =
VOUT · (VIN - VOUT)
= 3.8µH; see Table 2.
VIN · ∆IL · FOSC
∆IL = 0.32 · ILOAD
For Coilcraft inductor MSS1038 3.8µH DCR = 13mΩ max.
∆I1 =
⎛
VOUT
5V
5V ⎞
⎛ V ⎞
⋅ 1 - O1 =
⋅ 1= 959mA
L1 ⋅ FOSC ⎝ VIN ⎠ 3.8µH ⋅ 800kHz ⎝ 12V⎠
IPK1 = ILOAD +
∆I1
= 3A + 0.479A = 3.48A
2
PL1 = ILOAD2 ⋅ DCR = 3A2 ⋅ 13mΩ = 117mW
Output Capacitor
VDROOP = 0.2V
COUT =
3 · ∆ILOAD
3 · 3A
=
= 56µF; use three 22µF
VDROOP · FOSC
0.2V · 800kHz
IRMS(MAX) =
(VOUT) · (VIN(MAX) - VOUT)
1
5V · (12V - 5V)
·
= 277mArms
=
L · FOSC · VIN(MAX)
2 · 3 3.8µH · 800kHz · 12V
2· 3
1
·
Pesr = esr · IRMS2 = 5mΩ · (277mA)2 = 384µW
1161.2008.03.1.0
www.analogictech.com
15
PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
Input Capacitor
Input Ripple VPP = 50mV
CIN =
⎛ VPP
⎝ ILOAD
IRMS(MAX) =
1
1
=
= 26µF; use 22µF
⎞
⎛ 50mV
⎞
- 5mΩ · 4 · 800kHz
- ESR · 4 · FOSC
⎠
⎝ 3A
⎠
ILOAD
= 1.5Arms
2
P = esr · IRMS2 = 5mΩ · (1.5A)2 = 11.25mW
AAT1161 Losses
Total losses can be estimated by calculating at the nominal input voltage (12V). All values assume an 85°C ambient
temperature and a 140°C junction temperature with the TDFN 50°C/W package.
RDS(ON) = 0.18Ω
tSW = 5ms
IQ = 300µA
PLOSS =
ILOAD2 · (RDS(ON) · VOUT)
VIN
+ [(tsw · FOSC · ILOAD + IQ) · VIN]
PLOSS = 823mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 0.823W = 126°C
16
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1161.2008.03.1.0
PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TDFN33-14
1HXYY
AAT1161IWO-0.6-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/about/quality.aspx.
Package Information
TDFN33-14
Detail "A"
3.000 ± 0.050
2.500 ± 0.050
Index Area
3.000 ± 0.050
1.650 ± 0.050
Top View
Bottom View
+ 0.100
- 0.000
Pin 1 Indicator
(Optional)
0.180 ± 0.050
Side View
0.400 BSC
0.000
0.203 REF
0.750 ± 0.050
0.425 ± 0.050
Detail "A"
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.
1161.2008.03.1.0
www.analogictech.com
17
PRODUCT DATASHEET
AAT1161
SwitchRegTM
13.2V Input, 3A Step-Down Converter
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.
18
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1161.2008.03.1.0