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AAT1 184

SwitchRegTM

PRODUCT DATASHEET
AAT1 184
SwitchRegTM
General Description
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. 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.
High Voltage Step-Down Regulator
Features
Applications
· · · · 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 LX D1 BAS16 + C1 25µF 25V C12 1µF 25V EN RS D2 B340A R1 2.32K C4 68nF C7 330pF R4 44.2k R7 499 C8 22µF L1 4.7µH VOUT 5V / 1.2A
AAT1184
VL OS FB C3 2.2µF R2 24.3K COMP GND
C5 220pF C6 56pF
R5 6.04k
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Pin Descriptions
High Voltage Step-Down Regulator
Symbol
RS EN BST LX IN VL GND FB COMP 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 2.2F / 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
OS COMP FB GND VL IN
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Absolute Maximum Ratings1
Symbol
VIN(HI) VIN(LO) VBST1-LX VCONTROL VEN IIN(PULSED) TJ TLEAD
High Voltage Step-Down Regulator
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
-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
Units
Thermal Information
Symbol
Description
Thermal Resistance Maximum Power Dissipation2
Value
Units
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.
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Electrical Characteristics1
VIN VUVLO VOUT VFB VLINEREG / VIN VLOADREG / IIN IQ ISHDN VOCP ILX DMAX TON(MIN) RDSON(H) FOSC FFOLDBACK TSS TSD VEN(L) VEN(H) IEN
High Voltage Step-Down Regulator
Description
Input Voltage 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
Units
350 Current Limit Triggered From Enable to Output Regulation
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.
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Typical Characteristics
Step-Down Converter Efficiency vs. Load
High Voltage Step-Down Regulator
Step-Down Converter Efficiency vs. Load
Output Current (mA)
Step-Down Converter DC Regulation
Output Current (mA)
Step-Down Converter Line Regulation
Input Voltage (V)
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Typical Characteristics
Step-Down Converter Output Ripple
High Voltage Step-Down Regulator
Step-Down Converter Output Ripple
0V 0.2 0.1 0.0
0V 0.2 0.1 0.0 5.02 5.00 4.98
Time (2µs / div)
Step-Down Converter Output Ripple
12V 0V 3.0 2.0 1.0 0.0 5.02 5.00 4.98 5.0 4.0
0V 2 1 0 3.31 3.30 3.29
Time (1µs / div)
Step-Down Converter Load Transient Response
Output Voltage (AC Coupled) (bottom) (V)
Output Current (top) (A)
1.2A 0.12A
Time (100µs / div)
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Typical Characteristics
Step-Down Converter Load Transient Response
High Voltage Step-Down Regulator
Step-Down Converter Load Transient Response
Output Current (top) (A)
1.2A 0.6A
Time (100µs / div)
Step-Down Converter Load Transient Response
Output Current (top) (A)
1.2A 0.9A
Time (100µs / div)
Step-Down Converter Line Transient Response
Time (100ms / div)
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Typical Characteristics
Step-Down Converter Soft Start
High Voltage Step-Down Regulator
Step-Down Converter Soft Start
Inductor Current (bottom) (A)
Time (500µs / div)
Step-Down Converter Switching Frequency vs. Input Voltage
Step-Down Converter Output Voltage Error vs. Temperature
Input Voltage (V)
Temperature (°C)
Step-Down Converter Output Voltage Error vs. Temperature
No Load Step-Down Converter Input Current vs. Input Voltage
Input Current (µA)
85°C 25°C -40°C
Temperature (°C)
Input Voltage (V)
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Typical Characteristics
VIH and VIL vs. Input Voltage
High Voltage Step-Down Regulator
Input Voltage (V)
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Functional Block Diagram
High Voltage Step-Down Regulator
Error Amp
Comp. Comp.
Logic
Control Logic Voltage Ref
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.
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
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.
High Voltage Step-Down Regulator
capacitors to maintain a minimum capacitance drop with DC bias.
Output Inductor Selection
Rectifier Selection
Output Voltage and Current
VOUT VIN
Where VD is the voltage drop across the Schottky diode.
Input Capacitor Selection
For low cost applications, a 100F / 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.
Table 1: Feedback Resistor Values. Alternatively, the feedback resistor may be calculated using the following equation:
(VOUT - 0.6) · R5 0.6
Feedback and Compensation Networks
Buck Regulator Output Capacitor Selection
1. Output current capability may vary and is dependent on package selection, maximum ambient temperature, airflow and PCB heatsinking.
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
High Voltage Step-Down Regulator
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.
COMP R4
FB R5 REF
Figure 1: AAT1184 Feedback and Compensation Networks for Type III Voltage-Mode Control Loop.
Network
Feedback Feed-forward Compensation
Components
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
Current Limit
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
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.
High Voltage Step-Down Regulator
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:
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:
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 JA for the TSOPJW-12 package, which is 140°C / W.
IOUT2 · (RDS(ON)H · VOUT + RDS(ON)L · VIN - VOUT) VIN
+ (tSW · FS · IOUT + IQ) · VIN
VOUT 5V / 1.2A LX L1 4.7µH R1 2.32k RS R3 OS R6
OS LX L1 4.7µH R1 2.32k RS R8 C4 68nF
V OUT 5.0V / 1.2A
C4 68nF
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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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Over-Current Protection
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. The preset current limit threshold is triggered when the differential voltage from RS to OS exceeds 100mV (nominal). 2.
High Voltage Step-Down Regulator
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.
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. The power input capacitors (C1 and C12) should be connected as close as possible to high voltage input pin (IN) and power ground.
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
High Voltage Step-Down Regulator
VOUT 5V / 1.2A
C2 0.1µF
4.7µH D2 B340A C4 68nF R8 open R3 0
BST RS
R1 2.32k
C7 330pF R7 499 R4 44.2k
D1 BAS16
C8 22µF
C9 open
C10 open
VIN 6V - 24V
C3 2.2µF
AAT 1184
R6 open
+ C1 22µF 25V C11 open C12 1µF 25V
R5 6.04k R2 24.3K C5 220pF
TSOPJW-12
C6 56pF
U1 C1 C2 C3 C4, C5, C6, C7 C8 C12 D1 D2 L1 R1-R6
Figure 4: AAT1184ITP Evaluation Board Schematic.
Figure 5: AAT1184ITP Evaluation Board Top Layer.
Figure 6: AAT1184ITP Evaluation Board Bottom Layer.
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
AAT1184 Design Example
Specifications
High Voltage Step-Down Regulator
Output Inductor
Output Capacitor
Input Capacitor
1 25mV - 5mW · 4 · 490kHz 1.2A
For low cost applications, a 100F / 25V electrolytic capacitor in parallel with a 1F / 25V ceramic capacitor is used to reduce the ESR.
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Current Limit
High Voltage Step-Down Regulator
AAT1184 Losses
All values assume an 85°C ambient temperature and thermal resistance of 50°C / W in the TSOPJW-12 package.
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Ordering Information
Package
TSOPJW-12
High Voltage Step-Down Regulator
Voltage
Marking1
3QXYY
Part Number (Tape and Reel)2
AAT1184ITP-0.6-T1
Package Information
TSOPJW-12
0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC
0.04 REF
All dimensions in millimeters.
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PRODUCT DATASHEET
AAT1 184
SwitchReg High Voltage Step-Down Regulator
Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611
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