202000A.pdf

DATA SHEET
AAT1184
High Voltage Step-Down Regulator
General Description
Features
The AAT1184 is a single output step-down (Buck) DC
output regulator with an integrated high side MOSFET.
The input range is 6V to 24V making it the ideal power IC
solution for consumer communications equipment operating from a low cost AC/DC adapter with 12V output.
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The step-down regulator provides up to 1.2A output current in a small package. 490kHz fixed switching frequency allows small L/C filtering components.
Voltage mode control allows for optimum performance
across the entire output voltage and load range.
The controller includes programmable over-current, integrated soft-start and over-temperature protection.
The AAT1184 is available in the Pb-free, low profile
12-pin TSOPJW package. The rated operating temperature range is -40C to 85C.
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VIN = 6.0 to 24.0V
VOUT Adjustable from 1.5V to 5.5V
IOUT up to 1.2A
Small Solution Size
Low-Cost Non-Synchronous Solution
Shutdown Current <35μA
High Switching Frequency
Voltage Mode Control
PWM Fixed Frequency for Lowest Noise
▪ Programmable Over-Current Protection
Over-Temperature Protection
Internal Soft Start
Low Profile 3x3mm TSOPJW-12 Package
-40°C to 85°C Temperature Range
Applications
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DSL and Cable Modems
Notebook Computers
Satellite Set Top Box
Wireless LAN Systems
Typical Application
VIN
6V - 24V
TSOPJW -12
IN
BST
C2
0.1µF
L1
4.7µH
VOUT
5V/1.2A
LX
D1
BAS16
+
C1
25µF
25V
D2
B340A
EN
C12
1µF
25V
RS
AAT1184
R4
44.2k
R7
499
C4
68nF
OS
VL
C7
330pF
R1
2.32K
C8
22µF
FB
C3
2.2µF
R2
24.3K
C5
220pF
COMP
GND
C6
56pF
R5
6.04k
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1
DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Pin Descriptions
Pin #
Symbol
1
RS
2
EN
3
BST
4, 5
LX
6, 7
IN
8
VL
9
GND
10
FB
11
COMP
12
OS
Function
Output current sense pin. Connect a small signal resistor from this pin to switching node (LX) to enable over-current sense for step-down converter.
Enable input pin. Active high.
Boost drive input pin. Connect the cathode of fast rectifier from this pin and connect a 100nF capacitor from this pin to the switching node (LX) for internal hi-side MOSFET gate drive.
Step-down converter switching pin. Connect output inductor to this pin. Connect LX pins together.
Input supply voltage pin for step-down regulator. Connect both IN pins together. Connect the input
capacitor close to this pin for best noise performance.
Internal linear regulator. Connect a 2.2μF/6.3V capacitor from this pin to GND pin.
Ground pin for step-down converter. Connect input and output capacitors return terminals close to
this pin for best noise performance.
Feedback input pin for step-down converter. Connect an external resistor divider to this pin to program the output voltage to the desired value.
Compensation pin for step-down regulator. Connect a series resistor, capacitor network to compensate the voltage mode control loop.
Output voltage sense pin. Connect to the output capacitor to enable over-current sense for stepdown converter.
Pin Configuration
TSOPJW-12
(Top View)
RS
EN
BST
LX
LX
IN
2
1
12
2
11
3
10
4
9
5
8
6
7
OS
COMP
FB
GND
VL
IN
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DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Absolute Maximum Ratings1
Symbol
VIN(HI)
VIN(LO)
VBST1-LX
VCONTROL
VEN
IIN(PULSED)
TJ
TLEAD
Description
IN, LX to GND
VL to GND
BST to LX
FB, COMP, OS, RS to GND
EN to GND
IN to LX
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
-0.3 to 30.0
-0.3 to 6.0
-0.3 to 6.0
-0.3 to VIN(LO) + 0.3
-0.3 to 6.0
12.0
-40 to 150
300
V
V
V
V
V
A
C
C
Value
Units
140
0.7
C/W
W
Thermal Information
Symbol
JA
PD
Description
Thermal Resistance
Maximum Power Dissipation2
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. Derate 7mW/°C above 25°C ambient temperature.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Electrical Characteristics1
VIN = 12V; TA = -40°C to 85°C, unless noted otherwise. Typical values are at TA = 25°C.
Symbol
Description
VIN
Input Voltage
VUVLO
VOUT
VFB
ΔVLINEREG/
ΔVIN
ΔVLOADREG/
ΔIIN
IQ
ISHDN
VOCP
ILX
DMAX
TON(MIN)
RDSON(H)
FOSC
FFOLDBACK
TSS
TSD
VEN(L)
VEN(H)
IEN
UVLO Threshold
Output Voltage Range
Output Voltage Accuracy
Feedback Pin Voltage
Line Regulation
Load Regulation
Quiescent Current
Shutdown Current
Over-Current Offset Voltage
LX Pin Leakage Current
Maximum Duty Cycle
Minimum On-Time
Hi Side On-Resistance
Oscillator Frequency
Short Circuit Foldback Frequency
Soft-Start Time
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
Enable Threshold Low
Enable Threshold High
Input Low Current
Conditions
Min
Typ
6.0
VIN Rising
VIN Hysteresis
VIN Falling
IOUT = 0A to 1.2A
VIN = 6V to 24V, VOUT = 3.3V, IOUT = 1.2A
VIN = 6V to 24V, VOUT = 5.0V, IOUT = 1.2A
VIN = 12V, VOUT = 3.3V, IOUT = 0A to 1.2A
VIN = 12V, VOUT = 5V, IOUT = 0A to 1.2A
VEN = High, No load
VEN = Low, VL = 0V
VEN = High, VIN = 6.0V to 24.0V, TA = 25°C
VIN = 24.0V, VEN = Low
Max
Units
24.0
5.0
V
V
mV
V
V
%
V
300
3.0
1.5
-2.5
0.591
80
-1.0
VIN = 6.0 to 24.0V
VL = 4.5V
350
Current Limit Triggered
From Enable to Output Regulation
0.600
0.02
0.2
0.4
2.5
0.6
100
85
100
70
490
100
2.5
135
15
5.5
2.5
0.609
%/V
%/A
35.0
120
1.0
650
0.6
2.5
-1.0
1.0
mA
μA
mV
μA
%
ns
mΩ
kHz
kHz
ms
°C
°C
V
V
μA
1. The AAT1184 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
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Step-Down Converter Efficiency vs. Load
Step-Down Converter Efficiency vs. Load
(VOUT = 3.3V; L = 4.7µH)
(VOUT = 5V; L = 4.7µH)
100
100
90
90
80
80
Efficiency (%)
Efficiency (%)
Typical Characteristics
70
60
50
40
VIN = 6V
VIN = 8V
VIN = 12V
VIN = 18V
VIN = 24V
30
20
10
0
0.1
1
10
100
1000
70
60
50
VIN = 6V
VIN = 8V
VIN = 12V
VIN = 18V
VIN = 24V
40
30
20
10
0
0.1
10000
1
10
Output Current (mA)
Step-Down Converter DC Regulation
Output Error (%)
Output Error (%)
1.5
1.0
0.5
0.0
VIN = 6V
VIN = 8V
VIN = 12V
VIN = 18V
VIN = 24V
-0.5
-1.0
-1.5
10
100
1000
10000
3.0
2.5
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
VIN = 6V
VIN = 8V
VIN = 12V
VIN = 18V
VIN = 24V
0.1
1
10
Output Current (mA)
100
1000
10000
Output Current (mA)
Step-Down Converter Line Regulation
Step-Down Converter Line Regulation
(VOUT = 3.3V; L = 4.7µH)
(VOUT = 5V; L = 4.7µH)
1.5
Accuracy (%)
1.0
Accuracy (%)
10000
(VOUT = 5V; L = 4.7µH)
2.0
1
1000
Step-Down Converter DC Regulation
(VOUT = 3.3V; L = 4.7µH)
-2.0
0.1
100
Output Current (mA)
0.5
0.0
IOUT = 0.1mA
IOUT = 10mA
IOUT = 100mA
IOUT = 600mA
IOUT = 1200mA
-0.5
-1.0
-1.5
6
8
10
12
14
16
18
Input Voltage (V)
20
22
24
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
-3.0
-3.5
-4.0
IOUT = 0.1mA
IOUT = 10mA
IOUT = 100mA
IOUT = 600mA
IOUT = 1200mA
6
8
10
12
14
16
18
20
22
24
Input Voltage (V)
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DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Step-Down Converter Output Ripple
(VIN = 12V; VOUT = 3.3V; IOUT = 1mA)
(VIN = 12V; VOUT = 5V; IOUT = 1mA)
0V
0.2
0.1
0.0
3.31
3.30
3.29
12V
0V
0.2
0.1
0.0
5.02
5.00
4.98
Time (2µs/div)
Step-Down Converter Output Ripple
(VIN = 12V; VOUT = 3.3V; IOUT = 1.2A)
(VIN = 12V; VOUT = 5V; IOUT = 1.2mA)
0V
2
1
0
3.31
3.30
3.29
5.0
12V
4.0
0V
3.0
2.0
1.0
0.0
5.02
5.00
4.98
Time (1µs/div)
LX Voltage (top) (V)
Inductor Current (middle) (A)
12V
Output Voltage (AC Coupled)
(bottom) (V)
Step-Down Converter Output Ripple
LX Voltage (top) (V)
Inductor Current (middle) (A)
Output Voltage (AC Coupled)
(bottom) (V)
Time (2µs/div)
LX Voltage (top) (V)
Inductor Current (middle) (A)
12V
Output Voltage (AC Coupled)
(bottom) (V)
Step-Down Converter Output Ripple
LX Voltage (top) (V)
Inductor Current (middle) (A)
Output Voltage (AC Coupled)
(bottom) (V)
Typical Characteristics
Time (1µs/div)
Step-Down Converter Load Transient Response
(IOUT = 0.12A to 1.2A; VIN = 12V; VOUT = 5V; COUT = 2x22µF)
0.5
0.12A
0.0
3.7
3.5
3.3
3.1
2.9
Output Voltage
(AC Coupled) (bottom) (V)
1.0
1.2A
1.0
0.5
0.12A
0.0
5.2
5.0
4.8
4.6
Time (100µs/div)
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Output Current (top) (A)
1.2A
Time (100µs/div)
6
1.5
1.5
Output Current (top) (A)
Output Voltage
(AC Coupled) (bottom) (V)
Step-Down Converter Load Transient Response
(IOUT = 0.12A to 1.2A; VIN = 12V; VOUT = 3.3V; COUT = 2x22µF)
DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Typical Characteristics
(IOUT = 0.6A to 1.2A; VIN = 12V; VOUT = 5V; COUT = 2x22µF)
1.5
1.0
0.5
0.0
3.5
3.4
3.3
3.2
3.1
1.5
1.2A
1.0
0.6A
0.5
0.0
5.1
5.0
4.9
Time (100µs/div)
Output Current (top) (A)
0.6A
Output Current (top) (A)
1.2A
Output Voltage
(AC Coupled) (bottom) (V)
Step-Down Converter Load Transient Response
(IOUT = 0.6A to 1.2A; VIN = 12V; VOUT = 3.3V; COUT = 2x22µF)
Output Voltage
(AC Coupled) (bottom) (V)
Step-Down Converter Load Transient Response
Time (100µs/div)
(IOUT = 0.9A to 1.2A; VIN = 12V; VOUT = 5V; COUT = 2x22µF)
1.5
0.5
0.0
3.5
3.4
3.3
3.2
3.1
1.5
1.2A
0.9A
1.0
0.5
0.0
-0.5
5.1
5.0
4.9
Output Current (top) (A)
0.9A
1.0
Output Current (top) (A)
1.2A
Output Voltage
(AC Coupled) (bottom) (V)
Step-Down Converter Load Transient Response
(IOUT = 0.6A to 1.2A; VIN = 12V; VOUT = 3.3V; COUT = 2x22µF)
Output Voltage
(AC Coupled) (bottom) (V)
Step-Down Converter Load Transient Response
Step-Down Converter Line Transient Response
Step-Down Converter Line Transient Response
(VIN = 6V to 10V; VOUT = 3.3V; IOUT = 1.2A)
(VIN = 6V to 10V; VOUT = 5V; IOUT = 1.2A)
5
0
3.35
3.30
3.25
Time (100ms/div)
15
10
5
0
5.2
5.0
4.8
4.6
Output Voltage
(AC Coupled) (bottom) (V)
10
Output Voltage
(AC Coupled) (bottom) (V)
15
Input Voltage (top) (V)
Time (100µs/div)
Input Voltage (top) (V)
Time (100µs/div)
Time (100ms/div)
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DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Step-Down Converter Soft Start
(VIN = 12V; VEN = 10V; VOUT = 5V; IOUT = 1.2A)
15
10
0
2
1
0
15
10
5
0
2
1
0
Time (500µs/div)
Time (500µs/div)
Step-Down Converter Switching Frequency
vs. Input Voltage
Step-Down Converter Output
Voltage Error vs. Temperature
(VIN = 12V; VOUT = 3.3V)
Output Voltage Error (%)
Frequency Variation (%)
(VIN = 6V to 24V; VOUT = 3.3V; IOUT = 1.2A)
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
8
10
12
14
16
18
20
22
1.5
IOUT = 0.1mA
IOUT = 10mA
IOUT = 100mA
IOUT = 600mA
IOUT = 1200mA
1.0
0.5
0.0
-0.5
-1.0
-1.5
-50
-2.0
6
24
-25
Input Voltage (V)
0
0.0
-0.2
-0.4
-0.6
600
550
500
450
400
85°C
25°C
-40°C
350
-0.8
300
-1.0
-50
-25
0
25
50
Temperature (°C)
8
100
(VEN = VIN)
IOUT = 0.1mA
IOUT = 10mA
IOUT = 100mA
IOUT = 600mA
IOUT = 1200mA
0.2
75
650
Input Current (µA)
Output Voltage Error (%)
(VIN = 12V; VOUT = 5V)
0.4
50
No Load Step-Down Converter
Input Current vs. Input Voltage
1.0
0.6
25
Temperature (°C)
Step-Down Converter Output
Voltage Error vs. Temperature
0.8
Inductor Current
(bottom) (A)
5
Enable Voltage (top) (V)
Output Voltage (middle) (V)
Step-Down Converter Soft Start
(VIN = 12V; VEN = 10V; VOUT = 3.3V; IOUT = 1.2A)
Inductor Current
(bottom) (A)
Enable Voltage (top) (V)
Output Voltage (middle) (V)
Typical Characteristics
75
100
6
9
12
15
18
Input Voltage (V)
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24
DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Typical Characteristics
VIH and VIL vs. Input Voltage
1.35
VIH and VIL (%)
1.30
VIH
1.25
1.20
1.15
1.10
VIL
1.05
1.00
5
10
15
20
25
Input Voltage (V)
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DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Functional Block Diagram
VINT
Reg.
VL
IN
OT
FB
Error
Amp
OSC
Comp.
Comp.
BST
COMP
Logic
LX
Control
Logic
EN
20Ω
Voltage
Ref
RS
OS
Comp
VOCP
= 0.1V
GND
Functional Description
The AAT1184 is a high voltage step-down (Buck) regulator with input voltage range from 6.0V to 24.0V, providing high output current in a small package. The output
voltage is user-programmable from 1.5V to 5.5V. The
device is optimized for low-cost 12V adapter inputs.
The device utilizes voltage mode control configured for
optimum performance across the entire output voltage
and load range.
The controller includes integrated over-current, softstart and over-temperature protection. Over-current is
sensed through the output inductor DC winding resistance (DCR). An external resistor and capacitor network
adjusts the current limit according to the DCR of the
inductor and the desired output current limit. Frequency
reduction limits the over-current stress during overload
and short-circuit events. The operating frequency returns
to the nominal setting when over-current conditions are
removed.
The AAT1184 is available in the Pb-free 12-pin TSOPJW
package with rated operating temperature range of
-40°C to 85°C.
10
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DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Applications Information
The high voltage DC/DC step-down converter provides
an output voltage from 1.5V to 5.5V. The integrated
high-side n-channel MOSFET device provides up to 1.2A
output current1. Input voltage range is 6.0V to 24.0V.
The step-down converter utilizes constant frequency
(PWM-mode) voltage mode control to achieve high operating efficiency while maintaining extremely low output
noise across the operating range. High 490kHz (nominal)
switching frequency allows small external filtering components, achieving minimum cost and solution size.
External compensation allows the designer to optimize
the transient response while achieving stability across
the operating range.
Output Voltage and Current
The output voltage is set using an external resistor
divider as shown in Table 1. Minimum output voltage is
1.5V and maximum output voltage is 5.5V. Typical maximum duty cycle is 85%.
VOUT(V)
R5 = 6.04k
R4(k)
1.5
1.8
1.85
2.0
2.5
3.0
3.3
5.0
9.09
12.1
12.4
14.0
19.1
24.3
27.4
44.2
Table 1: Feedback Resistor Values.
Alternatively, the feedback resistor may be calculated
using the following equation:
R4 =
(VOUT - 0.6) · R5
0.6
R4 is rounded to the nearest 1% resistor value.
Buck Regulator Output
Capacitor Selection
A 22μF ceramic output capacitor is required to filter the
inductor current ripple and supply the load transient current for IOUT = 1.2A. The 1206 package with 10V minimum voltage rating is recommended for the output
capacitors to maintain a minimum capacitance drop with
DC bias.
Output Inductor Selection
The step-down converter utilizes constant frequency
(PWM-mode) voltage mode control. A 4.7μH inductor
value is selected to maintain the desired output current
ripple and minimize the converter’s response time to
load transients. The peak switch current should not
exceed the inductor saturation current, the MOSFET or
the external Schottky rectifier peak current ratings.
Rectifier Selection
When the high-side switch is on, the input voltage will be
applied to the cathode of the Schottky diode. The rectifier's rated reverse breakdown voltage must be chosen
at least equal to the maximum input voltage of the stepdown regulator.
When the high-side switch is off, the current will flow
from the power ground to the output through the
Schottky diode and the inductor. The power dissipation
of the Schottky diode during the time-off can be determined by the following equation:
PD = IOUT · VD · 1 -
VOUT
VIN
Where VD is the voltage drop across the Schottky diode.
Input Capacitor Selection
For low cost applications, a 100μF/25V electrolytic
capacitor is selected to control the voltage overshoot
across the high side MOSFET. A small ceramic capacitor
with voltage rating at least 1.05 times greater than the
maximum input voltage is connected as close as possible
to the input pin (Pin 14) for high frequency decoupling.
Feedback and Compensation Networks
The transfer function of the Error Amplifier is dominated
by the DC Gain and the L COUT output filter of the regulator. This output filter and its equivalent series resistor
(ESR) create a double pole at FLC and a zero at FESR in the
following equations:
Eq. 1: FLC =
1
2 · π · L · COUT
1. Output current capability may vary and is dependent on package selection, maximum ambient temperature, airflow and PCB heatsinking.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Eq. 2: FESR =
1
2 · π · ESR · COUT
The feedback and compensation networks provide a
closed loop transfer function with the highest 0dB crossing frequency and adequate phase margin for system
stability. Equations 3, 4, 5 and 6 relate the compensation network’s poles and zeros to the components R2,
R3, R4, C5, C6, and C7:
Eq. 3: FZ1 =
1
2 · π · R2 · C5
Eq. 4: FZ2 =
1
2 · π · ( R 7 + R 4) · C7
Eq. 5: FP1 =
1
2 · π · R2 ·
Eq. 6: FP2 =
C5 · C6
C5 + C6
1
2 · π · R7 · C7
Components of the feedback, feed forward, compensation, and current limit networks need to be adjusted to
maintain system stability for different input and output
voltage applications as shown in Table 2.
C6
C5
C7
R2
R7
VOUT
COMP
R4
FB
R5
REF
Figure 1: AAT1184 Feedback and Compensation Networks for Type III Voltage-Mode Control Loop.
Network
Feedback
Feed-forward
Compensation
Current Limit
Components
VOUT = 3.3V
VOUT = 5.0V
R4
R5
C7
R7
C5
C6
R2
C4
R1
R3
R6
R8
27.4k
6.02k
330pF
499
470pF
56pF
24.3k
68nF
2.32k
0k
Open
Open
44.2k
6.02k
330pF
499
220pF
56pF
24.3k
68nF
2.32k
0k
Open
Open
Table 2: AAT1184 Feedback and Compensation Network Components for VOUT = 3.3V and VOUT = 5.0V.
12
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DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Thermal Protection
The AAT1184 has an internal thermal protection circuit
which will turn on when the device die temperature
exceeds 135°C. The internal thermal protection circuit
will actively turn off the high side regulator output device
to prevent the possibility of over temperature damage.
The Buck regulator output will remain in a shutdown
state until the internal die temperature falls back below
the 135°C trip point. The combination and interaction
between the short circuit and thermal protection systems allows the Buck regulator to withstand indefinite
short-circuit conditions without sustaining permanent
damage.
Thermal Calculations
There are two types of losses associated with the
AAT1184 step-down converter: switching losses, conduction losses, and quiescent current losses. Conduction
losses are associated with the RDS(ON) characteristics of
the power output switching devices. Switching losses are
dominated by the gate charge of the power output
switching devices. At full load, assuming continuous conduction mode (CCM), a simplified form of the synchronous step-down converter losses is given by:
PTOTAL =
IQ is the step-down converter current. The term tSW is
used to estimate the full load step-down converter
switching losses.
For asynchronous Step-Down converter, the power dissipation is only in the internal high side MOSFET during
the on time. When the switch is off, the power dissipates
on the external Schottky diode. Total package losses for
AAT1184 reduce to the following equation:
PTOTAL = IOUT2 · RDS(ON)H · D + (tSW · FS · IOUT + IQ) · VIN
where D =
VOUT
is the duty cycle.
VIN
Since RDS(ON), quiescent current, and switching losses all
vary with input voltage, the total losses should be investigated over the complete input voltage range.
Given the total losses, the maximum junction temperature can be derived from the θJA for the TSOPJW-12
package, which is 140°C/W.
TJ(MAX) = PTOTAL · θJA + TAMB
IOUT2 · (RDS(ON)H · VOUT + RDS(ON)L · [VIN - VOUT])
VIN
+ (tSW · FS · IOUT + IQ) · VIN
VOUT
5V/1.2A
LX
LX
L1
4.7µH
R1
2.32k
V OUT
5.0V/1.2A
C4
68nF
L1
4.7µH
R1
2.32k
RS
C4
68nF
RS
R8
R3
OS
R3
OS
R6
Figure 2: Resistor Network to Adjust the
Current Limit Less than the Pre-Set
Over-Current Threshold (Add R6, R7).
Figure 3: Resistor Network to Adjust the
Current Limit Greater than the Pre-Set
Over-Current Level (Add R6, R8).
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13
DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Over-Current Protection
2.
The controller provides true-load DC output current
sensing which protects the load and limits component
stresses. The output current is sensed through the DC
resistance in the output inductor (DCR). The controller
reduces the operating frequency when an over-current
condition is detected; limiting stresses and preventing
inductor saturation. This allows the smallest possible
inductor for a given output load. A small resistor divider
may be necessary to adjust the over-current threshold
and compensate for variation in inductor DCR.
3.
The preset current limit threshold is triggered when the
differential voltage from RS to OS exceeds 100mV
(nominal).
Layout Considerations
The suggested PCB layout for the AAT1184 is shown in
Figures 5 and 6. The following guidelines should be used
to help ensure a proper layout.
1.
14
The power input capacitors (C1 and C12) should be
connected as close as possible to high voltage input
pin (IN) and power ground.
4.
5.
6.
7.
C2, L1, D2, and C8 should be placed as close as possible to minimize any parasitic inductance in the
switched current path which generates a large voltage spike during the switching interval. The connection of inductor to switching node should be as short
as possible.
The feedback trace or FB pin should be separated
from any power trace and connected as close as
possible to the load point. Sensing along a highcurrent load trace will degrade DC load regulation.
The resistance of the trace from the load returns to
PGND 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.
Connect unused signal pins to ground to avoid
unwanted noise coupling.
The critical small signal components include feedback components, and compensation components
should be placed close to the FB and COMP pins. The
feedback resistors should be located as close as possible to the FB pin with its ground tied directly to the
signal ground plane which is separated from power
ground plane.
C4 should be connected close to the RS and OS pins,
while R1 should be connected directly to the output
pin of the inductor. For the best current limit performance, C4 and R1 should be placed on the bottom
layer to avoid noise coupling from the inductor.
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DATA SHEET
AAT1184
High Voltage Step-Down Regulator
U1
4
LX
LX
4.7µH
C2
0.1µF
D2
B340A
3
RS
8
C3
2.2µF
VIN
6V - 24V
7
+
C11
open
C12
1µF
25V
2
EN
VL
OS
1
IN
FB
IN
COMP
EN
GND
12
C7
330pF
R3
0
R7
499
R4
44.2k
C8
22µF
C9
open
C10
open
R6
open
10
R5
6.04k
11
R2
24.3K
C5
220pF
9
TSOPJW-12
U1
C1
C2
C3
C4,C5,C6,C7
C8
C12
D1
D2
L1
R1-R6
C4
68nF
R8
open
AAT 1184
6
C1
22µF
25V
R1
2.32k
BST
D1
BAS16
VOUT
5V/1.2A
L1
5
C6
56pF
AAT1189 Skyworks, Hi-Voltage Buck, TSOPJW-12
Cap, MLC, 100µF/25V, Electrolytic cap
Cap, MLC, 0.1µF/6.3V, 0603
Cap, MLC, 2.2µF/6.3V, 0602
Cap, MLC, misc, 0603
Cap, MLC, 22µF/6.3V, 1206
Cap, MLC, 1µF/25V, 1206
BAS16, Generic, Rectifier, 0.2A/85V, Ultrafast, SOT-23
B340A, Generic, Schottky Rectifier, 3A/40V, SMA
SLF7045T-4R7M2R0-PF, TDK, 4.7µH, ISAT = 2A, DCR = 30mΩ
Carbon film resistor, 0402
Figure 4: AAT1184ITP Evaluation Board Schematic.
Figure 5: AAT1184ITP Evaluation Board
Top Layer.
Figure 6: AAT1184ITP Evaluation Board
Bottom Layer.
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15
DATA SHEET
AAT1184
High Voltage Step-Down Regulator
AAT1184 Design Example
Specifications
VOUT = 5.0V @ 1.2A, Pulsed Load ILOAD = 1.2A
VIN = 12V
FS = 490kHz
TAMB = 85°C in TSOPJW-12 Package
Output Inductor
For TDK inductor SLF7045T-4R7M2R0-PF, 4.7μH, DCR = 30m max.
ΔI =
VOUT
VOUT
5V
5V
· 1=
· 1= 1.2A
L1 · FS
VIN
4.7µH · 490kHz
12V
IPK = IOUT +
ΔI
= 1.2A + 0.6A = 1.8A
2
PL1 = IOUT2 · DCR = 1.8A2 · 11.7mΩ = 37.9mW
Output Capacitor
VDROOP = 0.33V (10% Output Voltage)
COUT =
3 · ΔILOAD
3 · 1.2A
=
= 22.3µF; use 22µF
0.33V · 490kHz
VDROOP · FS
IRMS(MAX) =
1
2· 3
·
VOUT · (VIN(MAX) - VOUT1)
1
5.0V · (24V - 5.0V)
·
= 496mARMS
=
4.7µH
· 490kHz · 24V
L · FS · VIN1(MAX)
2· 3
PRMS = ESR · IRMS2 = 5mΩ · (496mA)2 = 1.2mW
Input Capacitor
Input Ripple VPP = 25mV
CIN =
1
VPP
- ESR · 4 · FS
IOUT
=
1
25mV
- 5mW · 4 · 490kHz
1.2A
= 32µF
For low cost applications, a 100μF/25V electrolytic capacitor in parallel with a 1μF/25V ceramic capacitor is used to
reduce the ESR.
IRMS =
IOUT
= 0.6A
2
P = ESR · (IRMS)2 = 5mΩ · (0.6A)2 = 1.8mW
16
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DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Current Limit
Over-Current Offset Voltage: VOCP = 100mV
Total trace parasitic resistor and inductor DCR is 30m
ILIMIT = 3A
IPRESET =
VOCP
100mV
=
= 3.3A
DCR
30mΩ
AAT1184 Losses
All values assume an 85°C ambient temperature and thermal resistance of 50°C/W in the TSOPJW-12 package.
PTOTAL = IOUT2 · RDS(ON)H · D + (tSW · FS · IOUT + IQ) · VIN
2
PTOTAL = 1.2A · 70mΩ · 5V + (5ns · 490kHz · 1.2A + 70µA) · 12V
12V
PTOTAL = 78mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (140°C/W) · 78mW = 96°C
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17
DATA SHEET
AAT1184
High Voltage Step-Down Regulator
Ordering Information
Package
Voltage
Marking1
Part Number (Tape and Reel)2
TSOPJW-12
0.6
3QXYY
AAT1184ITP-0.6-T1
Skyworks Green™ products are compliant with
all applicable legislation and are halogen-free.
For additional information, refer to Skyworks
Definition of Green™, document number
SQ04-0074.
Package Information
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.
Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
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Customers are responsible for their products and applications using Skyworks products, which may deviate from published specifications as a result of design defects, errors, or operation of products outside of published parameters or design specifications. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for applications assistance, customer product
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Skyworks, the Skyworks symbol, and “Breakthrough Simplicity” are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and names are for
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