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PRODUCT DATASHEET
AAT1162
SwitchRegTM
General Description
The AAT1162 is an 800kHz high efficiency step-down DC/DC converter. With a wide input voltage range of 4.0V to 13.2V, the AAT1162 is an ideal choice for dualcell Lithium-ion battery-powered devices and mid-power-range regulated 12V-powered industrial applications. The internal power switches are capable of delivering up to 1.5A to the load. The AAT1162 is a highly integrated device, simplifying system-level design. Minimum external components are required for the converter. The AAT1162 optimizes efficiency throughout the entire load range. It operates in a combination PWM/Light Load mode for improved light-load efficiency. 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 1A. The AAT1162 is available in a Pb-free, space-saving, thermally-enhanced 16-pin TDFN34 packageand is rated over an operating temperature range of -40C to +85C.
12V, 1.5A Step-Down DC/DC Converter
Features
* Input Voltage Range: 4.0V to 13.2V * Up to 1.5A Load Current * Fixed or Adjustable Output: Output Voltage: 0.6V to VIN * Low 115A No-Load Operating Current * Less than 1A Shutdown Current * Up to 96% Efficiency * Integrated Power Switches * 800kHz Switching Frequency * Soft Start Function * Short-Circuit and Over-Temperature Protection * Minimum External Components * TDFN34-16 Package * Temperature Range: -40C to +85C
Applications
* * * * * * * Distributed Power Systems Industrial Applications Laptop Computers Portable DVD Players Portable Media Players Set-Top Boxes TFT LCD Monitors and HDTVs
Typical Application
Input: 4.0V ~ 13.2V IN C6 10F R4 10 C2 0.1F EN DGND AIN C8 1F COMP R5 24k C7 330pF C9 1F LDO PGND AGND LX 2.2 to 4.7H L1 Output: 0.6V min, 1.5A max
AAT1162
FB C3 22F
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PRODUCT DATASHEET
AAT1162
SwitchRegTM
Pin Descriptions
Pin #
1, 2, EP2 3, 12 4, 5 6, 13, 14, EP1 7
12V, 1.5A Step-Down DC/DC Converter
Symbol
LX N/C IN
Function
Power switching node. LX is the drain of the internal P-channel switch and N-channel synchronous rectifier. Connect the output inductor to the two LX pins and to EP2. A large exposed copper pad under the package should be used for EP2. Not connected. Power source input. Connect IN to the input power source. Bypass IN to DGND with a 22F 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, pin 6 Exposed Pad 1 Digital Ground, DGND. The exposed thermal pad (EP1) should be connected to board ground plane and pins 6, 13, and 14. 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 AAT1162. Connect AIN to the input source voltage and bypass to AGND with a 0.1F or greater capacitor. For additional noise rejection, connect to the input power source through a 10 or lower value resistor. Internal LDO bypass node. The output voltage of the internal LDO is bypassed at LDO. The internal circuitry of the AAT1162 is powered from LDO. Do not draw external power from LDO. Bypass LDO to AGND with a 1F or greater capacitor. 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. Connect a series RC network from COMP to AGND, R = 51k and C = 150pF. Analog signal ground. Connect AGND to PGND at a single point as close to the IC as possible. Active high enable input. Drive EN high to turn on the AAT1162; drive it low to turn it off. For automatic startup, connect EN to IN through a 4.7k 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. Power ground. Connect AGND to PGND at a single point as close to the IC as possible.
DGND
AIN
8
LDO
9 10 11 15 16
FB COMP AGND EN PGND
Pin Configuration
TDFN34-16 (Top View)
LX LX N/C IN IN DGND AIN LDO
1 2 3 4 5 6 7 8
16
EP2
PGND EN DGND DGND N/C AGND COMP FB
15 14 13 12
EP1
11 10 9
2
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PRODUCT DATASHEET
AAT1162
SwitchRegTM
Absolute Maximum Ratings1
Symbol
VIN, VAIN VLX VFB VEN TJ
12V, 1.5A Step-Down DC/DC Converter
Description
Input Voltage LX to GND Voltage FB to GND Voltage EN to GND Voltage Operating Junction Temperature Range
Value
-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
Units
V V V V C
Thermal Information3
Symbol
PD JA
Description
Maximum Power Dissipation4 Thermal Resistance
Value
2.7 37
Units
W C/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. Based on long-term current density limitation. 3. Mounted on an FR4 board. 4. Derate 2.7mW/C above 25C.
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PRODUCT DATASHEET
AAT1162
SwitchRegTM
Electrical Characteristics1
4.0V < VIN < 13.2V. CIN = COUT = 22F; L = 2.2 or 3.8H, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = 25C. Symbol
VIN VUVLO IQ ISHDN VOUT VOUT VOUT/ VOUT/VIN VOUT/ IOUT VFB IFBLEAK FOSC DC TON TS RDS(ON)H RDS(ON)L ILIM ILXLEAK TSD THYS VIL VIH IEN
12V, 1.5A Step-Down DC/DC Converter
Description
Input Voltage Range Input Under-Voltage Lockout Supply Current Shutdown Current Output Voltage Range Output Voltage Accuracy Line Regulation Load Regulation Feedback Reference Voltage (adjustable version) FB Leakage Current PWM Oscillator Frequency Foldback Frequency Maximum Duty Cycle Minimum Turn-On Time Soft-Start Time P-Channel On Resistance N-Channel On Resistance 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
Conditions
Rising Hysteresis No Load VEN = GND
Min
4.0
Typ
Max
13.2 4.0
Units
V V A A V % %/V %
0.3 150 0.6
IOUT = 0A to 1.5A VIN = 4.5V to 13.2V VIN = 12V, VOUT = 5V, IOUT = 0A to 1.5A No Load, TA = 25C Adjustable Version VOUT = 1.2V Fixed Version
-2.5 0.023 0.4 0.59 0.60 2 0.8 200 100 200 0.12 0.15 0.06 0.08 90 6.0
300 1 0.94 VIN 2.5 0.100
0.61 0.2 1 94
V A MHz kHz % ns ms % A A C C V V A
0.6
VIN VIN VIN VIN VIN
= = = = =
12V 6V 12V 6V 12V, VOUT = 5V, IOUT = 1.5A 4.0
VIN = 13.2V, VLX = 0 to VIN 140 25
1
0.4 VEN = 0V, VEN = 13.2V 1.4 -1.0 1.0
1. The AAT1162 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
AAT1162
SwitchRegTM
Typical Characteristics
Test circuit of Figure 2, unless otherwise specified.
12V, 1.5A Step-Down DC/DC Converter
Efficiency vs. Output Current
(VOUT = 5V)
100 90 80
Load Regulation
(VOUT = 5V) Output Voltage Difference (%)
0.5 0.4 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 -0.5 0.0001 0.001 0.01 0.1 1 10
Efficiency (%)
70 60 50 40 30 20 10 0 0.0001 0.001 0.01 0.1
VIN = 6V VIN = 8.4V VIN = 10V VIN = 12V VIN = 13.2V
VIN = 6V VIN = 8.4V VIN = 10V VIN = 12V VIN = 13.2V
1 10
Output Current (A)
Output Current (A)
Efficiency vs. Output Current
(VOUT = 3.3V)
90
Load Regulation
(VOUT = 3.3V)
0.6
Output Voltage Error (%)
100 80 70 60 50 40 30 20 10 0 0.0001 0.001 0.01 0.1
0.4 0.2 0.0 -0.2 -0.4 -0.6 1 10 100 1000
Efficiency (%)
VIN = 5V VIN = 8.4V VIN = 10V VIN = 12V VIN = 13.2V
VIN = 5V VIN = 8.4V VIN = 10V VIN = 12V VIN = 13.2V
1 10
10000
Output Current (A)
Output Current (A)
Line Regulation
(VOUT = 5V) Output Voltage Difference (%)
0.4 0.3 0.2 0.1 0 -0.1 -0.2 -0.3 -0.4 6 7 8 9 10 11
Line Regulation
(VOUT = 3.3V) Output Voltage Difference (%)
0.05 0.04 0.03 0.02 0.01 0 -0.01 -0.02 -0.03 -0.04 5 6 7 8 9 10 11 12
1.5A 1mA 10mA 100mA
1.5A 1mA 10mA 100mA
12
Input Voltage (V)
Input Voltage (V)
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PRODUCT DATASHEET
AAT1162
SwitchRegTM
Typical Characteristics
Test circuit of Figure 2, unless otherwise specified.
12V, 1.5A Step-Down DC/DC Converter
Supply Current vs. Input Voltage
(VOUT = 5V)
170 170 160
Switching Current vs. Temperature
(VOUT = 5V)
Quiescent Current (A)
160
On Time (ns)
150 140 130 120 110
150 140 130 120 110 -40 -15 10 35 60 85
85C 25C -40C
6 7 8 9 10 11 12
VIN = 12V VIN = 6V
Input Voltage (V)
Temperature (C)
N-Channel RDS(ON) vs. Temperature
120 100 80 60 40 20 0 -40 -15 10 35 60 85
P-Channel RDS(ON) vs. Temperature
(VIN = 6V)
200 180
Resistance (m)
Resistance (m)
160 140 120 100 80 60 40 20 0 -40 -15 10 35 60 85
VIN = 12V VIN = 6V
VIN = 6V VIN = 12V
Temperature (C)
Temperature (C)
Switching Frequency vs. Temperature
Switching Frequency (Hz)
810 805 800 795 790 785 780 775 770 -40 -15 10 35 60 6 5 4 3 2 1 0 85
Start-up Time
(VOUT = 5.0V; CFF = 100pF; RLOAD = 1.5A; CIN = 10F; COUT = 22F; L = 3.8H) Input Current (bottom) (A) Enable Voltage (top) (V)
6 5 4
VEN VOUT
3 2
VIN = 6V VIN = 12V
I LOAD
1 0
Temperature (C)
Time (500s/div)
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1162.2008.01.1.3
PRODUCT DATASHEET
AAT1162
SwitchRegTM
Typical Characteristics
Test circuit of Figure 2, unless otherwise specified.
12V, 1.5A Step-Down DC/DC Converter
Line Transient
(VOUT = 5.0V; CFF = 100pF; VIN = 7.6V to 11V; IOUT = 1.5A; CIN = 10F; COUT = 22F; L = 3.8H)
12 5.30 5.25 5.20 5.15 5.10 5.05 5.00 4.95 4.90 3.6
Load Transient
(VOUT = 3.3V; CFF = 100pF; COUT = 66F) Output Voltage (bottom) (V) Load and Inductor Current (bottom) (1A/div) Output Voltage (top) (V)
3.4 3.2 3 2.8 2.6 2.4 2.2 2 10mA 1.5A
Input Voltage (top) (V)
11 10 9 8 7 6 5 4
Time (100s/div)
Time (50s/div)
Load Transient
(VOUT = 3.3V; COUT = 66F; No CFF)
3.6 5.4
Load Transient
(VOUT = 5V; CFF = 100pF; COUT = 66F) Load and Inductor Current (bottom) (1A/div) Load and Inductor Current (bottom) (1A/div) Output Voltage (top) (V)
5.1 4.8 4.5 4.2 3.9 3.6 3.3 3 10mA 1.5A
Output Voltage (top) (V)
3.4 3.2 3 2.8 2.6 2.4 2.2 2 10mA 1.5A
Time (50s/div)
Time (50s/div)
Load Transient
(VOUT = 5V; COUT = 66F; No CFF)
5.4
VOUT vs. Temperature
(VOUT = 3.3V; ILOAD = 1.5A) Output Voltage Difference (%)
1 0.8 0.6 0.4 0.2 0 -0.2 -0.4 -0.6 -0.8 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90
Load and Inductor Current (bottom) (1A/div)
Output Voltage (top) (V)
5.1 4.8 4.5 4.2 3.9 3.6 3.3 3 10mA 1.5A
Time (50s/div)
Temperature (C)
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PRODUCT DATASHEET
AAT1162
SwitchRegTM
Typical Characteristics
Test circuit of Figure 2, unless otherwise specified.
12V, 1.5A Step-Down DC/DC Converter
Load Transient
(VOUT = 3.3V; CFF = 100pF; COUT = 22F)
3.9 3.7
Load Transient
(VOUT = 3.3V; COUT = 22F; No CFF) Load and Inductor Current (bottom) (1A/div) Load and Inductor Current (bottom) (1A/div) Output Voltage (top) (V)
3.3 2.9 2.5 2.1 1.7 1.3 0.9 0.5 10mA 1.5A
Output Voltage (top) (V)
3.6 3.3 3 2.7 2.4 2.1 1.8 1.5 10mA 1.5A
Time (50s/div)
Time (50s/div)
Load Transient
(VOUT = 5V; CFF = 100pF; COUT = 22F)
5.4 5.4
Load Transient
(VOUT = 5V; COUT = 22F; No CFF) Load and Inductor Current (bottom) (1A/div) Load and Inductor Current (bottom) (1A/div) Output Voltage (top) (V)
5.1 4.8 4.5 4.2 3.9 3.6 3.3 3 10mA 1.5A
Output Voltage (top) (V)
5.1 4.8 4.5 4.2 3.9 3.6 3.3 3 10mA 1.5A
Time (50s/div)
Time (50s/div)
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PRODUCT DATASHEET
AAT1162
SwitchRegTM
Functional Block Diagram
LDO Note 1 FB LDO Current Sense Amp + + + Error Amp Current Mode Comparator Control Logic LX AIN IN
12V, 1.5A Step-Down DC/DC Converter
Reference
PGND AGND
EN DGND
COMP . Note 1: For fixed output voltage versions, FB is connected to the error amplifier through the resistive voltage divider shown.
Functional Description
The AAT1162 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 1.5A to the load with the output voltage regulated as low as 0.6V. Both the P-channel power switch and N-channel synchronous rectifier are internal, reducing the number of external components required. 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 AAT1162 includes cycle-by-cycle current limiting, frequency fold-
back for improved short-circuit performance, and thermal overload protection to prevent damage in the event of an external fault condition.
Control Loop
The AAT1162 regulates the output voltage using constant frequency current mode control. The AAT1162 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.
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PRODUCT DATASHEET
AAT1162
SwitchRegTM
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.
12V, 1.5A Step-Down DC/DC Converter
Applications Information
Setting the Output Voltage
Figure 1 shows the basic application circuit for the AAT1162 and output setting resistors. Resistors R1 and R2 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 R2 is 5.9k. 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 R2 set to either 5.9k for good noise immunity or 59k for reduced no load input current.
EP2 VIN 4.5V- 13.2V R4 10 3 EN 4 IN 5 IN 7 AIN 6 DGND 13 DGND 16 PGND LX LX LX 1 2 9 L1 3.8H C1 100pF VOUT 5V, 1.5A R3 432k R6 59k
Short-Circuit Protection
The AAT1162 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 3.0A current limit, the P-channel MOSFET switch turns off and the N-channel synchronous rectifier is turned on, limiting the inductor and the load current. During an overload condition, when the output voltage drops below 50% of the regulation voltage (0.3V at FB), the AAT1162 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.
Thermal Protection
The AAT1162 includes thermal protection that disables the regulator when the die temperature reaches 140C. It automatically restarts when the temperature decreases by 25C or more.
C6 10F
C2 0.1 F
AAT1162
FB
C3 22F
C8 1 F
COMP 10 AGND 11 DGND DGND EP1 LDO 14 8
R5 24k
C9 1 F
C7 330pF
Figure 1: Typical Application Circuit. 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 for stability. Larger C1 values reduce overshoot and undershoot during startup and load changes. However, do not exceed 470pF to maintain stable operation.
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PRODUCT DATASHEET
AAT1162
SwitchRegTM
The external resistors set the output voltage according to the following equation:
12V, 1.5A Step-Down DC/DC Converter
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 1.5A, or IL = 480mA. For output voltages above 3.3V, the minimum recommended inductor is 3.8H. For 3.3V and below, use a 2 to 3.8H inductor. For optimum voltagepositioning load transients, choose an inductor with DC series resistance in the 15m to 20m range. For higher efficiency at heavy loads (above 1A), or minimal load regulation (but some transient overshoot), the resistance should be kept below 18m. 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 (1.5A + 280mA). Table 2 lists some typical surface mount inductors that meet target applications for the AAT1162. 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 4.7H WE-TPC series inductor selected from Wurth has an 38m DCR and a 2.4ADC current rating. At full load, the inductor DC loss is 85mW which gives only a 1.1% loss in efficiency for a 1.5A, 5V output.
R1 VOUT = 0.6V 1 + R2
or
VOUT R1 = V -1 * R2 REF
Table 1 shows the resistor selection for different output voltage settings. R2 = 5.9(k) R1 (k)
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
VOUT (V)
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
R2 = 59(k) R1 (k)
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.
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 10F ceramic capacitor is sufficient for most applications.
Inductor Selection
For most designs, the AAT1162 operates with inductors of 2H to 4.7H. 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 * 3.8H 3.3
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PRODUCT DATASHEET
AAT1162
SwitchRegTM
Manufacturer
Sumida Sumida Coilcraft Cooper Bussman Wurth
12V, 1.5A Step-Down DC/DC Converter
Part Number
CDRH103RNP-2R2N CDR7D43MNNP-3R7NC MSS1038-382NL DR73-4R7-R 7440530047
L (H)
2.2 3.7 3.8 4.7 4.7
Max DCR (m)
16.9 18.9 13 29.7 38
Rated DC Current (A)
5.10 4.3 4.25 3.09 2.40
Size WxLxH (mm)
10.3x10.5x3.1 7.6x7.6x4.5 10.2x7.7x3.8 6.0x7.6x3.55 5.8x5.8x2.8
Table 2: Typical Surface Mount Inductors. 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.
IRMS(MAX) =
VO
IN
IO 2
CIN =
V VO * 1- O VIN VIN
VPP - ESR * FOSC IO
VO V 1 * 1 - O = for VIN = 2 * VO VIN VIN 4 1
VPP - ESR * 4 * FOSC IO
CIN(MIN) =
Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value. For example, the capacitance of a 10F, 16V, X5R ceramic capacitor with 12V DC applied is actually about 8.5F. The maximum input capacitor RMS current is:
The term V V 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 AAT1162. 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, 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 0.1F capacitor on the IN pins (C2).
IN
V * 1- O
IRMS = IO *
VO V * 1- O VIN VIN
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
for VIN = 2 * VO
D * (1 - D) =
0.52 =
1 2
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.
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PRODUCT DATASHEET
AAT1162
SwitchRegTM
Output Capacitor Selection
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:
12V, 1.5A Step-Down DC/DC Converter
The maximum output capacitor RMS ripple current is given by:
IRMS(MAX) =
VOUT * (VIN(MAX) - VOUT) L * FOSC * VIN(MAX) 2* 3 *
1
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.
VOUT
VOUT * (VIN - VOUT) 1 * ESR + VIN * FOSC * L 8 * FOSC * COUT
Compensation
The AAT1162 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:
The output capacitor limits the output ripple and provides holdup during large load transitions. A 10F to 47F 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 voltage droop during the three switching cycles to the output capacitance can be estimated by:
RCOMP (R5)=
2VOUT * COUT * FOSC 10GEA * GCOMP * VFB
Where VFB = 0.6V, GCOMP = 40.1734 and GEA = 9.091 * 10-5. FOSC is the switching frequency and COUT is based on the output capacitor calculation. The CCOMP value can be determined from the following equation:
COUT =
3 * ILOAD VDROOP * FOSC
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 22F. 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.
CCOMP (C7) =
4
2RCOMP (R5) * FOSC 10
The feed forward capacitor CFF (C1) provides faster transient response for pulsed load applications. The addition of the feed forward capacitor typically requires a larger output capacitor C1 for stability. Larger C1 values reduce overshoot and undershoot during startup and line/load changes. The CFF value can be from 100pF to 470pF, but do not exceed 470pF to maintain stable operation.
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PRODUCT DATASHEET
AAT1162
SwitchRegTM
Layout Guidance
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 AAT1162: 1. 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, 14 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. 4.
12V, 1.5A Step-Down DC/DC Converter
The input capacitors (C9 and C1) 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.
5. 6.
2.
7.
8.
3.
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1162.2008.01.1.3
PRODUCT DATASHEET
AAT1162
SwitchRegTM
JP1 Enable TP1 GND
12V, 1.5A Step-Down DC/DC Converter
TP14 GND
R1 4.75K
R2 4.75K TP3 LX 1 2 9 10 11 12 14 8 C9 1F C7 330pF TP11 GND GND DGND *Note: Connect GND, DGND, and AGND at IC EP1 L1 3.8H C1 100pF R5 24K R3 432K C3 22F C4 NP C5 NP VOUT TP4 VOUT TP6 VOUT TB2 VOUT TP8 GND TP12 LX EP2 Enable U1 15 4 5 3 7 TP2
TP5 VIN TP7 VIN TB1 VIN TP9 GND TP13 GND
VIN R4 10 C6 10F C8 1F C2 0.1F
EN LX IN AAT1162 LX IN FB N/C COMP AGND N/C DGND LDO GND EP1 *
AIN 6 DGND 13 DGND 16 PGND
R6 59K
Figure 2: AAT1162 Evaluation Board Schematic.
Figure 3: AAT1162 Evaluation Board Component Side Layout.
Figure 4: AAT1162 Evaluation Board Solder Side Layout.
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15
PRODUCT DATASHEET
AAT1162
SwitchRegTM
Design Example
Specifications
VOUT VIN FOSC TAMB 5V @ 1.5A, Pulsed Load ILOAD = 1.5A 12V nominal 800kHz 85C in TDFN34-16 Package
12V, 1.5A Step-Down DC/DC Converter
Output Inductor
L= VOUT * 3.8H = 5.75H; use 4.7H (see Table 2) 3.3
IL = 0.32 * ILOAD = 480mA
For Cooper Bussman inductor DR73-4R7-R 4.7H DCR = 29.7mW max.
I1 =
VOUT 5V 5V V 1 - O1 = 1= 480mA L1 FOSC VIN 4.7H 800kHz 12V
IPK1 = ILOAD +
I1 = 1.5A + 0.480A = 1.98A 2
PL1 = ILOAD2 DCR = 3A2 13m = 117mW
Output Capacitor
VDROOP = 0.2V
COUT =
3 * ILOAD 3 * 1.5A = = 28F; use 22F 0.2V * 800kHz VDROOP * FOSC (VOUT) * (VIN(MAX) - VOUT) 1 5V * (12V - 5V) * = 139mArms = L * FOSC * VIN(MAX) 2 * 3 4.7H * 800kHz * 12V 2* 3 1 *
IRMS(MAX) =
Pesr = esr * IRMS2 = 5m * (277mA)2 = 384W
Input Capacitor
Input Ripple VPP = 50mV
CIN =
1 1 = = 11F; use 10F VPP 50mV - 5m * 4 * 800kHz - ESR * 4 * FOSC ILOAD 1.5A
ILOAD = 0.75Arms 2
IRMS(MAX) =
P = esr * IRMS2 = 5m * (0.75A)2 = 2.81mW
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PRODUCT DATASHEET
AAT1162
SwitchRegTM
AAT1162 Losses
Total losses can be estimated by calculating the dropout (VIN = VO) losses where the power MOSFET RDS(ON) will be at the maximum value. All values assume an 85C ambient temperature and a 140C junction temperature with the TDFN 37C/W package.
12V, 1.5A Step-Down DC/DC Converter
PLOSS = ILOAD2 * RDS(ON)H = 1.5A2 * 0.158 = 0.355W TJ(MAX) = TAMB + JA * PLOSS = 85C + (37C/W) * 355mW = 96.6C
The total losses are also investigated at the nominal input voltage (12V). The simplified version of the RDS(ON) losses assumes that the N-channel and P-channel RDS(ON) are equal.
PTOTAL = ILOAD2 * RDS(ON) + [(tsw * FOSC * ILOAD + IQ) * VIN]
= 1.5A2 * 100m + [(5ns * 800kHz * 1.5A + 150A) * 12V] = 299mW
TJ(MAX) = TAMB + JA * PLOSS = 85C + (37C/W) * 299mW = 96C
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PRODUCT DATASHEET
AAT1162
SwitchRegTM
Ordering Information
Package
TDFN34-16
12V, 1.5A Step-Down DC/DC Converter
Marking1
YYXYY
Part Number (Tape and Reel)2
AAT1162IRN-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
TDFN34-16
3.000 0.050 0.070 0.050 1.600 0.050
Index Area
4.000 0.050
2.350 0.050
0.230 0.050
0.25 REF 1.600 0.050
0.430 0.050
Top View
Bottom View
0.750 0.050
0.050 0.050
0.230 0.050
Side View
All dimensions in millimeters.
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD.
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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0.450 0.050
0.35 REF
1162.2008.01.1.3

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