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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 -40C to 85C.
High Voltage Step-Down Regulator
Features
* * * * * * * * * * * * * 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 <35A 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 -40C to 85C Temperature Range
Applications
* * * * DSL and Cable Modems Notebook Computers Satellite Set Top Box Wireless LAN Systems
Typical Application
VIN 6V - 24V TSOPJW -12 IN BST C2 0.1F LX D1 BAS16 + C1 25F 25V C12 1F 25V EN RS D2 B340A R1 2.32K C4 68nF C7 330pF R4 44.2k R7 499 C8 22F L1 4.7H VOUT 5V/1.2A
AAT1184
VL OS FB C3 2.2F R2 24.3K COMP GND
C5 220pF C6 56pF
R5 6.04k
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Pin Descriptions
Pin #
1 2 3 4, 5 6, 7 8 9 10 11 12
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
1 2 3 4 5 6
12 11 10 9 8 7
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
V V V V V A C C
Thermal Information
Symbol
JA PD
Description
Thermal Resistance Maximum Power Dissipation2
Value
140 0.7
Units
C/W W
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 25C ambient temperature.
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Electrical Characteristics1
VIN = 12V; TA = -40C to 85C, unless noted otherwise. Typical values are at TA = 25C. Symbol
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
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 = 25C VIN = 24.0V, VEN = Low VIN = 6.0 to 24.0V VL = 4.5V
Min
6.0
Typ
Max
24.0 5.0
Units
V V mV V V % V %/V %/A
300 3.0 1.5 -2.5 0.591 5.5 2.5 0.609
0.600 0.02 0.2 0.4 2.5 0.6 100 85 100 70 490 100 2.5 135 15
80 -1.0
35.0 120 1.0
350 Current Limit Triggered From Enable to Output Regulation
650
0.6 2.5 -1.0 1.0
mA A mV A % ns m kHz kHz ms C C V V A
1. The AAT1184 is guaranteed to meet performance specifications over the -40C to +85C 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
(VOUT = 3.3V; L = 4.7H)
100 90 80 100 90 80
High Voltage Step-Down Regulator
Step-Down Converter Efficiency vs. Load
(VOUT = 5V; L = 4.7H)
Efficiency (%)
70 60 50 40 30 20 10 0 0.1 1 10 100
Efficiency (%)
70 60 50 40 30 20 10 0 0.1 1 10 100
VIN = 6V VIN = 8V VIN = 12V VIN = 18V VIN = 24V
1000 10000
VIN = 6V VIN = 8V VIN = 12V VIN = 18V VIN = 24V
1000 10000
Output Current (mA)
Output Current (mA)
Step-Down Converter DC Regulation
(VOUT = 3.3V; L = 4.7H)
2.0 1.5 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
Step-Down Converter DC Regulation
(VOUT = 5V; L = 4.7H)
Output Error (%)
1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 0.1
Output Error (%)
VIN = 6V VIN = 8V VIN = 12V VIN = 18V VIN = 24V
1 10 100 1000 10000
VIN = 6V VIN = 8V VIN = 12V VIN = 18V VIN = 24V
0.1 1 10 100 1000 10000
Output Current (mA)
Output Current (mA)
Step-Down Converter Line Regulation
(VOUT = 3.3V; L = 4.7H)
1.5 1.0 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
Step-Down Converter Line Regulation
(VOUT = 5V; L = 4.7H)
Accuracy (%)
0.5 0.0 -0.5 -1.0 -1.5 6 8 10 12 14 16 18 20 22 24
Accuracy (%)
IOUT = 0.1mA IOUT = 10mA IOUT = 100mA IOUT = 600mA IOUT = 1200mA
IOUT = 0.1mA IOUT = 10mA IOUT = 100mA IOUT = 600mA IOUT = 1200mA
6 8 10 12 14 16 18 20 22 24
Input Voltage (V)
Input Voltage (V)
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Typical Characteristics
Step-Down Converter Output Ripple
(VIN = 12V; VOUT = 3.3V; IOUT = 1mA) Output Voltage (AC Coupled) (bottom) (V) Output Voltage (AC Coupled) (bottom) (V) LX Voltage (top) (V) Inductor Current (middle) (A)
12V
High Voltage Step-Down Regulator
Step-Down Converter Output Ripple
(VIN = 12V; VOUT = 5V; IOUT = 1mA) LX Voltage (top) (V) Inductor Current (middle) (A)
12V
0V 0.2 0.1 0.0
3.31 3.30 3.29
0V 0.2 0.1 0.0 5.02 5.00 4.98
Time (2s/div)
Time (2s/div)
Step-Down Converter Output Ripple
(VIN = 12V; VOUT = 3.3V; IOUT = 1.2A) Output Voltage (AC Coupled) (bottom) (V) Output Voltage (AC Coupled) (bottom) (V) LX Voltage (top) (V) Inductor Current (middle) (A)
12V
Step-Down Converter Output Ripple
(VIN = 12V; VOUT = 5V; IOUT = 1.2mA) LX Voltage (top) (V) Inductor Current (middle) (A)
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 (1s/div)
Time (1s/div)
Step-Down Converter Load Transient Response
(IOUT = 0.12A to 1.2A; VIN = 12V; VOUT = 3.3V; COUT = 2x22F) Output Voltage (AC Coupled) (bottom) (V)
1.5
Step-Down Converter Load Transient Response
(IOUT = 0.12A to 1.2A; VIN = 12V; VOUT = 5V; COUT = 2x22F)
1.5
Output Voltage (AC Coupled) (bottom) (V)
Output Current (top) (A)
Output Current (top) (A)
1.2A 0.12A
1.0 0.5 0.0
1.2A 0.12A
1.0 0.5 0.0
3.7 3.5 3.3 3.1 2.9
5.2 5.0 4.8 4.6
Time (100s/div)
Time (100s/div)
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1184.2008.07.1.0
PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Typical Characteristics
Step-Down Converter Load Transient Response
(IOUT = 0.6A to 1.2A; VIN = 12V; VOUT = 3.3V; COUT = 2x22F) Output Voltage (AC Coupled) (bottom) (V)
1.5
High Voltage Step-Down Regulator
Step-Down Converter Load Transient Response
(IOUT = 0.6A to 1.2A; VIN = 12V; VOUT = 5V; COUT = 2x22F) Output Voltage (AC Coupled) (bottom) (V)
1.5
Output Current (top) (A)
Output Current (top) (A)
1.2A 0.6A
1.0 0.5 0.0
1.2A 0.6A
1.0 0.5 0.0
3.5 3.4 3.3 3.2 3.1
5.1 5.0 4.9
Time (100s/div)
Time (100s/div)
Step-Down Converter Load Transient Response
(IOUT = 0.6A to 1.2A; VIN = 12V; VOUT = 3.3V; COUT = 2x22F) Output Voltage (AC Coupled) (bottom) (V)
1.5
Step-Down Converter Load Transient Response
(IOUT = 0.9A to 1.2A; VIN = 12V; VOUT = 5V; COUT = 2x22F) Output Voltage (AC Coupled) (bottom) (V)
1.5
Output Current (top) (A)
Output Current (top) (A)
1.2A 0.9A
1.0 0.5 0.0
1.2A 0.9A
1.0 0.5 0.0 -0.5
3.5 3.4 3.3 3.2 3.1
5.1 5.0 4.9
Time (100s/div)
Time (100s/div)
Step-Down Converter Line Transient Response
(VIN = 6V to 10V; VOUT = 3.3V; IOUT = 1.2A) Output Voltage (AC Coupled) (bottom) (V) Input Voltage (top) (V)
15 10 5 0 3.35 3.30 3.25
Step-Down Converter Line Transient Response
(VIN = 6V to 10V; VOUT = 5V; IOUT = 1.2A) Output Voltage (AC Coupled) (bottom) (V) Input Voltage (top) (V)
15 10 5 0 5.2 5.0 4.8 4.6
Time (100ms/div)
Time (100ms/div)
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Typical Characteristics
Step-Down Converter Soft Start
(VIN = 12V; VEN = 10V; VOUT = 3.3V; IOUT = 1.2A) Enable Voltage (top) (V) Output Voltage (middle) (V) Enable Voltage (top) (V) Output Voltage (middle) (V)
15 10 15 10
High Voltage Step-Down Regulator
Step-Down Converter Soft Start
(VIN = 12V; VEN = 10V; VOUT = 5V; IOUT = 1.2A)
Inductor Current (bottom) (A)
Inductor Current (bottom) (A)
5 0
5 0
2 1 0
2 1 0
Time (500s/div)
Time (500s/div)
Step-Down Converter Switching Frequency vs. Input Voltage
(VIN = 6V to 24V; VOUT = 3.3V; IOUT = 1.2A) Frequency Variation (%) Output Voltage Error (%)
2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 6 8 10 12 14 16 18 20 22 24 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -50
Step-Down Converter Output Voltage Error vs. Temperature
(VIN = 12V; VOUT = 3.3V)
IOUT = 0.1mA IOUT = 10mA IOUT = 100mA IOUT = 600mA IOUT = 1200mA
-25
0
25
50
75
100
Input Voltage (V)
Temperature (C)
Step-Down Converter Output Voltage Error vs. Temperature
(VIN = 12V; VOUT = 5V) Output Voltage Error (%)
1.0 0.8 0.6 0.4 0.2 0.0 -0.2 -0.4 -0.6 -0.8 -1.0 -50 -25 0 25 50 75 100
No Load Step-Down Converter Input Current vs. Input Voltage
(VEN = VIN)
650
Input Current (A)
IOUT = 0.1mA IOUT = 10mA IOUT = 100mA IOUT = 600mA IOUT = 1200mA
600 550 500 450 400 350 300 6 9 12 15 18 21 24
85C 25C -40C
Temperature (C)
Input Voltage (V)
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Typical Characteristics
VIH and VIL vs. Input Voltage
1.35 1.30
High Voltage Step-Down Regulator
VIH
VIH and VIL (%)
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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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Functional Block Diagram
High Voltage Step-Down Regulator
VINT
VL
Reg.
IN
OT
OSC
FB
Error Amp
Comp. Comp.
BST
COMP
Logic
Control Logic Voltage Ref
EN
LX
20
Comp
RS OS 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 -40C to 85C.
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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
The step-down converter utilizes constant frequency (PWM-mode) voltage mode control. A 4.7H 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:
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)
1.5 1.8 1.85 2.0 2.5 3.0 3.3 5.0
R5 = 6.04k R4 (k)
9.09 12.1 12.4 14.0 19.1 24.3 27.4 44.2
PD = IOUT * VD * 1 -
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:
R4 =
(VOUT - 0.6) * R5 0.6
R4 is rounded to the nearest 1% resistor value.
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 =
Buck Regulator Output Capacitor Selection
A 22F 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
1 2 * * L * COUT
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
Eq. 2: FESR =
High Voltage Step-Down Regulator
1 2 * * ESR * COUT
Eq. 4: FZ2 =
1 2 * * (R7 + R4) * C7
1
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 =
Eq. 5: FP1 =
2 * * R2 *
Eq. 6: FP2 =
C5 * C6 C5 + C6
1 2 * * R7 * C7
1 2 * * R2 * C5
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
R2
C7
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
Components
R4 R5 C7 R7 C5 C6 R2 C4 R1 R3 R6 R8
VOUT = 3.3V
27.4k 6.02k 330pF 499 470pF 56pF 24.3k 68nF 2.32k 0k Open Open
VOUT = 5.0V
44.2k 6.02k 330pF 499 220pF 56pF 24.3k 68nF 2.32k 0k Open Open
Current Limit
Table 2: AAT1184 Feedback and Compensation Network Components for VOUT = 3.3V and VOUT = 5.0V.
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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 135C. 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 135C 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:
PTOTAL = IOUT2 * RDS(ON)H * D + (tSW * FS * IOUT + IQ) * VIN
where D = VOUT is the duty cycle. VIN
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 140C/W.
TJ(MAX) = PTOTAL * JA + TAMB
PTOTAL =
IOUT2 * (RDS(ON)H * VOUT + RDS(ON)L * [VIN - VOUT]) VIN
+ (tSW * FS * IOUT + IQ) * VIN
VOUT 5V/1.2A LX L1 4.7H R1 2.32k RS R3 OS R6
OS LX L1 4.7H R1 2.32k RS R8 C4 68nF
V OUT 5.0V/1.2A
C4 68nF
R3
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.
3.
4.
5. 6.
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.
7.
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
U1
4
High Voltage Step-Down Regulator
L1 LX
5
VOUT 5V/1.2A
LX
C2 0.1F
3
4.7H D2 B340A C4 68nF R8 open R3 0
BST RS
1
R1 2.32k
C7 330pF R7 499 R4 44.2k
D1 BAS16
8
VL
OS
12
C8 22F
C9 open
C10 open
VIN 6V - 24V
C3 2.2F
6
AAT 1184
IN FB
10
R6 open
7
+ C1 22F 25V C11 open C12 1F 25V
IN
COMP
11
R5 6.04k R2 24.3K C5 220pF
EN
2
EN
GND
9
TSOPJW-12
C6 56pF
U1 C1 C2 C3 C4,C5,C6,C7 C8 C12 D1 D2 L1 R1-R6
AAT1189 Analogic Technologies, Hi-Voltage Buck, TSOPJW-12 Cap, MLC, 100F/25V, Electrolytic cap Cap, MLC, 0.1F/6.3V, 0603 Cap, MLC, 2.2F/6.3V, 0602 Cap, MLC, misc, 0603 Cap, MLC, 22F/6.3V, 1206 Cap, MLC, 1F/25V, 1206 BAS16, Generic, Rectifier, 0.2A/85V, Ultrafast, SOT-23 B340A, Generic, Schottky Rectifier, 3A/40V, SMA SLF7045T-4R7M2R0-PF, TDK, 4.7H, ISAT = 2A, DCR = 30m 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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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
AAT1184 Design Example
Specifications
VOUT = 5.0V @ 1.2A, Pulsed Load ILOAD = 1.2A VIN = 12V FS = 490kHz TAMB = 85C in TSOPJW-12 Package
High Voltage Step-Down Regulator
Output Inductor
For TDK inductor SLF7045T-4R7M2R0-PF, 4.7H, DCR = 30m max.
I =
VOUT VOUT 5V 5V * 1= * 1= 1.2A L1 * FS VIN 4.7H * 490kHz 12V I = 1.2A + 0.6A = 1.8A 2
IPK = IOUT +
PL1 = IOUT2 * DCR = 1.8A2 * 11.7m = 37.9mW
Output Capacitor
VDROOP = 0.33V (10% Output Voltage)
COUT =
3 * ILOAD 3 * 1.2A = = 22.3F; use 22F 0.33V * 490kHz VDROOP * FS 1 2* 3
IRMS(MAX) =
*
VOUT * (VIN(MAX) - VOUT1) 1 5.0V * (24V - 5.0V) * = 496mARMS = 4.7H * 490kHz * 24V L * FS * VIN1(MAX) 2* 3
PRMS = ESR * IRMS2 = 5m * (496mA)2 = 1.2mW
Input Capacitor
Input Ripple VPP = 25mV
CIN =
1 VPP - ESR * 4 * FS IOUT
=
1 25mV - 5mW * 4 * 490kHz 1.2A
= 32F
For low cost applications, a 100F/25V electrolytic capacitor in parallel with a 1F/25V ceramic capacitor is used to reduce the ESR.
IRMS =
IOUT = 0.6A 2
P = ESR * (IRMS)2 = 5m * (0.6A)2 = 1.8mW
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Current Limit
Over-Current Offset Voltage: VOCP = 100mV Total trace parasitic resistor and inductor DCR is 30m ILIMIT = 3A
High Voltage Step-Down Regulator
IPRESET =
VOCP 100mV = = 3.3A DCR 30m
AAT1184 Losses
All values assume an 85C ambient temperature and thermal resistance of 50C/W in the TSOPJW-12 package.
PTOTAL = IOUT2 * RDS(ON)H * D + (tSW * FS * IOUT + IQ) * VIN
2 PTOTAL = 1.2A * 70m * 5V + (5ns * 490kHz * 1.2A + 70A) * 12V 12V
PTOTAL = 78mW TJ(MAX) = TAMB + JA * PLOSS = 85C + (140C/W) * 78mW = 96C
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM
Ordering Information
Package
TSOPJW-12
High Voltage Step-Down Regulator
Voltage
0.6
Marking1
3QXYY
Part Number (Tape and Reel)2
AAT1184ITP-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
TSOPJW-12
0.20 + 0.10 - 0.05
2.40 0.10
0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC
2.85 0.20
7 NOM 3.00 0.10
0.9625 0.0375 + 0.10 1.00 - 0.065
0.04 REF
0.15 0.05
0.055 0.045
4 4
0.010
0.45 0.15 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.
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PRODUCT DATASHEET
AAT1 184
SwitchRegTM High Voltage Step-Down Regulator
Advanced Analogic Technologies, Inc. 3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737-4600 Fax (408) 737-4611
(c) 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.
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