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AAT1121
1.5MHz, 250mA Step-Down Converter General Description
The AAT1121 SwitchReg is a 1.5MHz step-down converter with an input voltage range of 2.7V to 5.5V and output as low as 0.6V. Its low supply current, small size, and high switching frequency make the AAT1121 the ideal choice for portable applications. The AAT1121 delivers 250mA of load current, while maintaining a low 30A no load quiescent current. The 1.5MHz switching frequency minimizes the size of external components, while keeping switching losses low. The AAT1121 feedback and control delivers excellent load regulation and transient response with a small output inductor and capacitor. The AAT1121 is available in a Pb-free, 8-pin, 2x2mm TDFN or STDFN package and is rated over the -40C to +85C temperature range.
Features
* * * * * * * * * * * * *
SwitchRegTM
VIN Range: 2.7V to 5.5V VOUT Range: 0.6V to VIN 250mA Max Output Current Up to 96% Efficiency 30A Typical Quiescent Current 1.5MHz Switching Frequency Soft-Start Control Over-Temperature and Current Limit Protection 100% Duty Cycle Low-Dropout Operation <1A Shutdown Current Small External Components Ultra-Small TDFN22-8 or STDFN22-8 Package Temperature Range: -40C to +85C
Applications
* * * * * * BluetoothTM Headsets Cellular Phones Digital Cameras Handheld Instruments Portable Music Players USB Devices
Typical Application
VIN AAT1121 VP VIN C1 4.7F EN FB LX L1 3.0H R1 118k R2 59k C2 4.7F
VO = 1.8V
250mA
GND
PGND
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AAT1121
1.5MHz, 250mA Step-Down Converter Pin Descriptions
Pin #
1 2 3 4 5 6 7 8 EP
Symbol
VP VIN GND FB N/C EN LX PGND
Function
Input power pin; connected to the source of the P-channel MOSFET. Connect to the input capacitor. Input bias voltage for the converter. Non-power signal ground pin. Feedback input pin. Connect this pin to an external resistive divider for adjustable output. No connect. Enable pin. A logic high enables normal operation. A logic low shuts down the converter. Switching node. Connect the inductor to this pin. It is connected internally to the drain of both high- and low-side MOSFETs. Input power return pin; connected to the source of the N-channel MOSFET. Connect to the output and input capacitor return. Exposed paddle (bottom): connect to ground directly beneath the package.
Pin Configuration
TDFN22-8/STDFN22-8 (Top View)
VP VIN GND FB
1 2 3 4
8 7 6 5
PGND LX EN N/C
2
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AAT1121
1.5MHz, 250mA Step-Down Converter Absolute Maximum Ratings1
Symbol
VIN VLX VOUT VEN TJ TLEAD
Description
Input Voltage and Bias Power to GND LX to GND FB to GND EN to GND Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
6.0 -0.3 to VIN + 0.3 -0.3 to VIN + 0.3 -0.3 to 6.0 -40 to 150 300
Units
V V V V C C
Thermal Information
Symbol
PD JA
Description
Maximum Power Dissipation Thermal Resistance2
Value
2 50
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. Mounted on an FR4 board. 1121.2007.03.1.2
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AAT1121
1.5MHz, 250mA Step-Down Converter Electrical Characteristics1
VIN = 3.6V, TA = -40C to +85C, unless otherwise noted; typical values are TA = 25C. Symbol
VIN VUVLO VOUT VOUT IQ ISHDN ILIM RDS(ON)H RDS(ON)L ILXLEAK VLinereg/VIN VFB IFB FOSC TS TSD THYS VEN(L) VEN(H) IEN
Description
Input Voltage UVLO Threshold
Conditions
VIN Rising Hysteresis VIN Falling IOUT = 0 to 250mA, VIN = 2.7V to 5.5V No Load EN = GND
Min
2.7
Typ
Max
5.5 2.6
Units
V V mV V % V A A mA A %/V V A MHz s C C V V A
250 2.0 -3.0 0.6 30 1.0 600 0.59 0.42 3.0 VIN
Output Voltage Tolerance2 Output Voltage Range Quiescent Current Shutdown Current P-Channel Current Limit High-Side Switch On Resistance Low-Side Switch On Resistance LX Leakage Current Line Regulation Feedback Threshold Voltage Accuracy FB Leakage Current Oscillator Frequency Startup Time Over-Temperature Shutdown Threshold Over-Temperature Shutdown Hysteresis Enable Threshold Low Enable Threshold High Input Low Current
VIN = 5.5V, VLX = 0 to VIN VIN = 2.7V to 5.5V VIN = 3.6V VOUT = 1.0V From Enable to Output Regulation
1.0 0.591 0.2 0.600 1.5 100 140 15 0.6 1.4 -1.0 0.609 0.2
VIN = VEN = 5.5V
1.0
1. The AAT1121 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. 2. Output voltage tolerance is independent of feedback resistor network accuracy.
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AAT1121
1.5MHz, 250mA Step-Down Converter Typical Characteristics
Efficiency vs. Load
(VOUT = 1.2V; L = 1.5H)
100 90 1.0
DC Load Regulation
(VOUT = 1.2V; L = 1.5H)
VIN = 2.7V
Output Error (%)
Efficiency (%)
80 70 60 50 40 30 0.1
VIN = 3.6V VIN = 4.2V VIN = 5.0V
0.5
VIN = 3.6V
0.0
-0.5
VIN = 2.7V
VIN = 4.2V
1
10
100
1000
-1.0 0.1 1 10 100 1000
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 1.8V; L = 3.3H)
100 90 1.0
DC Load Regulation
(VOUT = 1.8V; L = 3.3H)
VIN = 2.7V
Output Error (%)
Efficiency (%)
VIN = 3.6V
0.5
80 70 60 50 40 0.1 1 10 100 1000
VIN = 3.6V
0.0
VIN = 4.2V
VIN = 2.7V
-0.5
VIN = 4.2V
1 10 100 1000
-1.0 0.1
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
(VOUT = 3.0V; L = 4.7H)
100 90
1.0
DC Load Regulation
(VOUT = 3.0V; L = 4.7H)
VIN = 3.6V
Output Error (%)
0.5
Efficiency (%)
80 70 60 50 40
VIN = 4.2V VIN = 5.0V
VIN = 4.2V
0.0
VIN = 3.6V VIN = 5.0V
-0.5
-1.0
0.1
1
10
100
1000
0.1
1
10
100
1000
Output Current (mA)
Output Current (mA)
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AAT1121
1.5MHz, 250mA Step-Down Converter Typical Characteristics
Soft Start
(VIN = 3.6V; VOUT = 1.8V; IOUT = 250mA; CFF = 100pF)
Line Regulation
(VOUT = 1.8V)
0.6 0.5 0.4
Enable and Output Voltage (top) (V)
5.0 4.0 3.0 2.0 1.0 0.0
VEN
Accuracy (%)
IOUT = 0mA IOUT = 50mA IOUT = 150mA
Inductor Current (bottom) (A)
0.3 0.2 0.1 0.0 -0.1 -0.2 -0.3 2.5 3.0 3.5
0.8 0.6
VO IL Time (100s/div)
0.4 0.2 0.0
IOUT = 10mA IOUT = 250mA
4.0 4.5 5.0 5.5 6.0
Input Voltage (V)
Output Voltage Error vs. Temperature
(VIN = 3.6V; VOUT = 1.8V; IOUT = 250mA)
3.0 10.0 2.0 1.0 0.0 -1.0 -2.0 -3.0 -40 8.0
Switching Frequency Variation vs. Temperature
(VIN = 3.6V; VOUT = 1.8V)
Output Error (%)
Variation (%)
-20 0 20 40 60 80 100
6.0 4.0 2.0 0.0 -2.0 -4.0 -6.0 -8.0 -10.0 -40 -20 0 20 40 60 80 100
Temperature (C)
Temperature (C)
Frequency Variation vs. Input Voltage
2.0
No Load Quiescent Current vs. Input Voltage
50
Frequency Variation (%)
Supply Current (A)
1.0 0.0 -1.0 -2.0 -3.0 -4.0
VOUT = 1.8V
45 40 35 30 25 20 15 10 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
85C 25C -40C
VOUT = 3.0V
2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
Input Voltage (V)
Input Voltage (V)
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AAT1121
1.5MHz, 250mA Step-Down Converter Typical Characteristics
P-Channel RDS(ON) vs. Input Voltage
1000 900 750
N-Channel RDS(ON) vs. Input Voltage
120C
100C
700
RDS(ON)H (m)
RDS(ON)L (m)
800 700 600 500 400 300 2.5 3.0 3.5 4.0
85C
650 600 550 500 450 400 350
120C
100C 85C
25C
25C
2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
4.5
5.0
5.5
6.0
300
Input Voltage (V)
Input Voltage (V)
Load Transient Response
(10mA to 250mA; VIN = 3.6V; VOUT = 1.8V; COUT = 4.7F; CFF = 100pF)
2.0 1.9 2.0 1.9
Load Transient Response
(10mA to 250mA; VIN = 3.6V; VOUT = 1.8V; COUT = 4.7F)
Load and Inductor Current (bottom) (200mA/div)
Load and Inductor Current (bottom) (200mA/div)
Output Voltage (top) (V)
1.7 1.6
Output Voltage (top) (V)
1.8
VO IO ILX
10mA 0.2 0.0 -0.2
1.8 1.7 1.6
VO
250mA 10mA
250mA
IO ILX
0.2 0.0 -0.2
Time (25s/div)
Time (25s/div)
Line Response
(VOUT = 1.8V @ 250mA; CFF = 100pF)
1.90 1.85
Output Voltage (top) (V)
1.80 1.75 1.70
VO
Input Voltage (bottom) (V)
5.0 4.5
VIN
4.0 3.5 3.0
Time (25s/div)
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AAT1121
1.5MHz, 250mA Step-Down Converter Typical Characteristics
Output Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 1mA)
40 40
Output Ripple
(VIN = 3.6V; VOUT = 1.8V; IOUT = 250mA)
Output Voltage (AC Coupled) (top) (mV)
20 0 -20
Output Voltage (AC Coupled) (top) (mV)
VO
0.04 0.03 0.02
20 0 -20
VO
Inductor Current (bottom) (A)
Inductor Current (bottom) (A)
0.3
IL
0.01 0.00 -0.01
IL
0.2 0.1 0.0
Time (2s/div)
Time (200ns/div)
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AAT1121
1.5MHz, 250mA Step-Down Converter Functional Block Diagram
FB VIN VP
Err Amp
DH Voltage Reference Logic
LX
EN
INPUT
DL
PGND GND
Functional Description
The AAT1121 is a high performance 250mA, 1.5MHz monolithic step-down converter designed to operate with an input voltage range of 2.7V to 5.5V. The converter operates at 1.5MHz, which minimizes the size of external components. Typical values are 3.3H for the output inductor and 4.7F for the ceramic output capacitor. The device is designed to operate with an output voltage as low as 0.6V. Power devices are sized for 250mA current capability while maintaining over
90% efficiency at full load. Light load efficiency is maintained at greater than 80% down to 1mA of load current. At dropout, the converter duty cycle increases to 100% and the output voltage tracks the input voltage minus the RDS(ON) drop of the P-channel highside MOSFET. A high-DC gain error amplifier with internal compensation controls the output. It provides excellent transient response and load/line regulation. Soft start eliminates any output voltage overshoot when the enable or the input voltage is applied.
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AAT1121
1.5MHz, 250mA Step-Down Converter
Control Loop
The AAT1121 is a 250mA current mode step-down converter. The current through the P-channel MOSFET (high side) is sensed for current loop control, as well as short-circuit and overload protection. A fixed slope compensation signal is added to the sensed current to maintain stability for duty cycles greater than 50%. The peak current mode loop appears as a voltage-programmed current source in parallel with the output capacitor. The output of the voltage error amplifier programs the current mode loop for the necessary peak switch current to force a constant output voltage for all load and line conditions. Internal loop compensation terminates the transconductance voltage error amplifier output. The error amplifier reference is fixed at 0.6V.
Applications Information
Inductor Selection
The step-down converter uses peak current mode control with slope compensation to maintain stability for duty cycles greater than 50%. The output inductor value must be selected so the inductor current down slope meets the internal slope compensation requirements. The internal slope compensation for the adjustable and low-voltage fixed versions of the AAT1121 is 0.45A/sec. This equates to a slope compensation that is 75% of the inductor current down slope for a 1.8V output and 3.0H inductor.
m=
0.75 VO 0.75 1.8V A = = 0.45 L 3.0H sec
Soft Start / Enable
Soft start increases the inductor current limit point in discrete steps when the input voltage or enable input is applied. It limits the current surge seen at the input and eliminates output voltage overshoot. When pulled low, the enable input forces the AAT1121 into a low-power, non-switching state. The total input current during shutdown is less than 1A.
This is the internal slope compensation for the AAT1121. When externally programming to 3.0V, the calculated inductance is 5.0H.
L=
0.75 VO = m
0.75 VO sec 1.67 A VO A 0.45A sec
= 1.67
sec 3.0V = 5.0H A
Current Limit and Over-Temperature Protection
For overload conditions, the peak input current is limited. As load impedance decreases and the output voltage falls closer to zero, more power is dissipated internally, raising the device temperature. Thermal protection completely disables switching when internal dissipation becomes excessive, protecting the device from damage. The junction over-temperature threshold is 140C with 15C of hysteresis.
In this case, a standard 4.7H value is selected. For most designs, the AAT1121 operates with an inductor value of 1H to 4.7H. Table 1 displays inductor values for the AAT1121 with different output voltage options. 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.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VIN power. Under-voltage lockout (UVLO) guarantees sufficient VIN bias and proper operation of all internal circuits prior to activation.
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AAT1121
1.5MHz, 250mA Step-Down Converter
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.
Output Voltage (V)
1.0 1.2 1.5 1.8 2.5 3.0 3.3
L1 (H)
1.5 2.2 2.7 3.0 3.9 4.7 5.6
VO V * 1- O = VIN VIN
for VIN = 2 x VO
D * (1 - D) =
0.52 =
1 2
Table 1: Inductor Values. The 3.0H CDRH2D09 series inductor selected from Sumida has a 150m DCR and a 470mA DC current rating. At full load, the inductor DC loss is 9.375mW which gives a 2.08% loss in efficiency for a 250mA, 1.8V output.
IRMS(MAX) =
IO 2
Input Capacitor
Select a 4.7F to 10F X7R or X5R ceramic capacitor for the input. To estimate the required input capacitor size, determine the acceptable input ripple level (VPP) and solve for CIN. The calculated value varies with input voltage and is a maximum when VIN is double the output voltage.
The term VIN VIN appears in both the input voltage ripple and input capacitor RMS current equations and is a 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 AAT1121. 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 (C1) can be seen in the evaluation board layout in Figure 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.
VO
V * 1- O
CIN =
VO V * 1- O VIN VIN
VPP - ESR * FS IO
VO V 1 * 1 - O = for VIN = 2 x VO VIN VIN 4
CIN(MIN) =
1
VPP - ESR * 4 * FS IO
Always examine the ceramic capacitor DC voltage coefficient characteristics when selecting the proper value. For example, the capacitance of a 10F, 6.3V, X5R ceramic capacitor with 5.0V DC applied is actually about 6F. The maximum input capacitor RMS current is:
IRMS = IO *
VO V * 1- O VIN VIN
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AAT1121
1.5MHz, 250mA Step-Down Converter
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. The maximum output capacitor RMS ripple current is given by:
IRMS(MAX) = VOUT * (VIN(MAX) - VOUT) L * F * VIN(MAX) 2* 3 * 1
Output Capacitor
The output capacitor limits the output ripple and provides holdup during large load transitions. A 4.7F to 10F 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. For enhanced transient response and low temperature operation application, a 10F (X5R, X7R) ceramic capacitor is recommended to stabilize extreme pulsed load conditions. 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:
3 * ILOAD VDROOP * FS
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.
Adjustable Output Resistor Selection
Resistors R1 and R2 of Figure 1 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 suggested value for R2 is 59k. Decreased resistor values are necessary to maintain noise immunity on the FB pin, resulting in increased quiescent current. Table 2 summarizes the resistor values for various output voltages.
VOUT 3.3V R1 = V -1 * R2 = 0.6V - 1 * 59k = 267k REF
With enhanced transient response for extreme pulsed load application, an external feed-forward capacitor, (C3 in Figure 1), can be added. R2 = 59k 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
COUT =
R2 = 221k R1 (k)
75 113 150 187 221 261 301 332 442 464 523 715 1000
R1 (k)
19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267
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 4.7F. 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.
Table 2: Adjustable Resistor Values For Step-Down Converter. 12
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AAT1121
1.5MHz, 250mA Step-Down Converter
Thermal Calculations
There are three types of losses associated with the AAT1121 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 losses is given by:
I
2 O
For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to:
PTOTAL = IO2 * RDSON(H) + IQ * 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 JA for the TDFN22-8 package which is 50C/W.
TJ(MAX) = PTOTAL * JA + TAMB
PTOTAL =
* (RDSON(H) * VO + RDSON(L) * [VIN - VO]) VIN
+ (tsw * F * IO + IQ) * VIN
IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load stepdown converter switching losses.
U1 VIN
1 2 3 4
VP VIN GND FB
PGND LX EN N/C
8 7 6 5
LX
L1 +VOUT C3 (optional) 100pF
C1 4.7F
AAT1121
C2 4.7F
R1 Adj.
R2 59k GND GND
Figure 1: AAT1121 Schematic.
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AAT1121
1.5MHz, 250mA Step-Down Converter
Layout
The suggested PCB layout for the AAT1121 is shown in Figures 2, 3, and 4. The following guidelines should be used to help ensure a proper layout. 1. The input capacitor (C1) should connect as closely as possible to VP (Pin 1), PGND (Pin 8), and GND (Pin 3) 2. C2 and L1 should be connected as closely as possible. The connection of L1 to the LX pin should be as short as possible. Do not make the node small by using narrow trace. The trace should be kept wide, direct and short. 3. The feedback pin (Pin 4) should be separate from any power trace and connect as closely as possible to the load point. Sensing along a high-current load trace will degrade DC load regulation. Feedback resistors should be placed as closely as possible to the FB pin (Pin 4) to minimize the length of the high impedance feedback trace. If possible, they should also be placed away from the LX (switching node) and inductor to improve noise immunity. 4. The resistance of the trace from the load return to PGND (Pin 8) and GND (Pin 3) 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. A high density, small footprint layout can be achieved using an inexpensive, miniature, nonshielded, high DCR inductor.
Figure 2: AAT1121 Evaluation Board Top Side Layout.
Figure 3: Exploded View of AAT1121 Evaluation Board Top Side Layout.
Figure 4: AAT1121 Evaluation Board Bottom Side Layout.
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AAT1121
1.5MHz, 250mA Step-Down Converter Step-Down Converter Design Example
Specifications
VO VIN FS TAMB = 1.8V @ 250mA, Pulsed Load ILOAD = 200mA = 2.7V to 4.2V (3.6V nominal) = 1.5MHz = 85C
1.8V Output Inductor
L1 = 1.67 sec sec VO2 = 1.67 1.8V = 3H A A
(use 3.0H; see Table 1)
For Sumida inductor CDRH2D09-3R0, 3.0H, DCR = 150m.
VO V 1.8V 1.8V 1- O = 1= 228mA L1 F VIN 3.0H 1.5MHz 4.2V
IL1 =
IPKL1 = IO +
IL1 = 250mA + 114mA = 364mA 2
PL1 = IO2 DCR = 250mA2 150m = 9.375mW
1.8V Output Capacitor
VDROOP = 0.1V
3 * ILOAD 3 * 0.2A = = 4F (use 4.7F) 0.1V * 1.5MHz VDROOP * FS (VO) * (VIN(MAX) - VO) 1 1.8V * (4.2V - 1.8V) * = 66mArms = 3.0H * 1.5MHz * 4.2V L1 * FS * VIN(MAX) 2* 3 2* 3 1 *
COUT = IRMS =
Pesr = esr * IRMS2 = 5m * (66mA)2 = 21.8W
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AAT1121
1.5MHz, 250mA Step-Down Converter
Input Capacitor
Input Ripple VPP = 25mV
CIN =
1
VPP - ESR * 4 * FS IO
=
1 = 1.38F (use 4.7F) 25mV - 5m * 4 * 1.5MHz 0.2A
IRMS =
IO = 0.1Arms 2
P = esr * IRMS2 = 5m * (0.1A)2 = 0.05mW
AAT1121 Losses
PTOTAL = IO2 * (RDSON(HS) * VO + RDSON(LS) * [VIN -VO]) VIN
+ (tsw * F * IO + IQ) * VIN
=
0.22 * (0.59 * 1.8V + 0.42 * [4.2V - 1.8V])
4.2V
+ (5ns * 1.5MHz * 0.2A + 30A) * 4.2V = 26.14mW
TJ(MAX) = TAMB + JA * PLOSS = 85C + (50C/W) * 26.14mW = 86.3C
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AAT1121
1.5MHz, 250mA Step-Down Converter
Output Voltage VOUT (V)
0.6 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
2
R2 = 59k R1 (k)
-- 19.6 29.4 39.2 49.9 59.0 68.1 78.7 88.7 118 124 137 187 267
R2 = 221k1 R1 (k)
-- 75 113 150 187 221 261 301 332 442 464 523 715 1000
L1 (H)
1.5 1.5 1.5 1.5 1.5 1.5 1.5 2.2 2.7 3.0/3.3 3.0/3.3 3.0/3.3 3.9/4.2 5.6
Table 3: Evaluation Board Component Values.
Manufacturer
Sumida Sumida Sumida Sumida Sumida Sumida Sumida Sumida Sumida Sumida Sumida Taiyo Yuden Taiyo Yuden Taiyo Yuden Taiyo Yuden FDK FDK FDK FDK
Part Number
CDRH2D09-1R5 CDRH2D09-2R2 CDRH2D09-2R5 CDRH2D09-3R0 CDRH2D09-3R9 CDRH2D09-4R7 CDRH2D09-5R6 CDRH2D11-1R5 CDRH2D11-2R2 CDRH2D11-3R3 CDRH2D11-4R7 NR3010 NR3010 NR3010 NR3010 MIPWT3226D-1R5 MIPWT3226D-2R2 MIPWT3226D-3R0 MIPWT3226D-4R2
Inductance (H)
1.5 2.2 2.5 3 3.9 4.7 5.6 1.5 2.2 3.3 4.7 1.5 2.2 3.3 4.7 1.5 2.2 3 4.2
Max DC Current (mA)
730 600 530 470 450 410 370 900 780 600 500 1200 1100 870 750 1200 1100 1000 900
DCR (m)
88 115 135 150 180 230 260 54 78 98 135 80 95 140 190 90 100 120 140
Size (mm) LxWxH
3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.2x3.2x1.2 3.2x3.2x1.2 3.2x3.2x1.2 3.2x3.2x1.2 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.0x3.0x1.0 3.2x2.6x0.8 3.2x2.6x0.8 3.2x2.6x0.8 3.2x2.6x0.8
Type
Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Shielded Chip shielded Chip shielded Chip shielded Chip shielded
Table 4: Suggested Inductors and Suppliers.
1. For reduced quiescent current, R2 = 221k. 2. R2 is opened, R1 is shorted. 1121.2007.03.1.2
17
AAT1121
1.5MHz, 250mA Step-Down Converter
Manufacturer
Murata Murata
Part Number
GRM118R60J475KE19B GRM188R60J106ME47D
Value (F)
4.7 10
Voltage Rating
6.3 6.3
Temp. Co.
X5R X5R
Case Size
0603 0603
Table 5: Surface Mount Capacitors.
18
1121.2007.03.1.2
AAT1121
1.5MHz, 250mA Step-Down Converter Ordering Information
Output Voltage
0.6V 0.6V
Package
TDFN22-8 STDFN22-8
Marking1
RWXYY RWXYY
Part Number (Tape and Reel)2
AAT1121IPS-0.6-T1 AAT1121IES-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/pbfree.
Package Information3
TDFN22-8
0.600 0.050 0.350 0.100
Index Area
Detail "A"
2.000 0.050
1.270 0.050
0.1 REF (optional)
C0.3
0.450 0.050
2.000 0.050
Bottom View
Pin 1 Indicator (optional)
Top View
0.230 0.050 0.229 0.051
4x
0.850 MAX
Detail "A"
0.050 0.050
Side View
All dimensions in millimeters.
1. XYY = assembly and date code. 2. Sample stock is generally held on all part numbers listed in BOLD. 3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection. 1121.2007.03.1.2
19
AAT1121
1.5MHz, 250mA Step-Down Converter
STDFN22-8
Index Area (D/2 x E/2)
2.00 0.05
0.80 0.05
Detail "A"
2.00 0.05
Top View
Bottom View
0.35 0.05
0.55 0.05
0.15 0.025
1.45 0.05
0.05 0.05
Side View
Pin 1 Indicator (optional)
0.23 0.05
Detail "A"
All dimensions in millimeters.
(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.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737- 4600 Fax (408) 737- 4611 20
1121.2007.03.1.2
0.45 0.05

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