ANALOGICTECH AAT2511IWP

AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
General Description
Features
The AAT2511 is a member of AnalogicTech's Total
Power Management IC™ (TPMIC™) product family. It is comprised of two 1MHz step-down converters designed to minimize external component
size and cost. The input voltage ranges from 2.7V
to 5.5V. The output voltage ranges from 0.6V to the
maximum applied input voltage and is externally
adjustable.
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Peak current mode control with internal compensation provides a stable converter with low ESR ceramic output capacitors for extremely low output ripple.
Each channel has a low 25µA quiescent operating
current, which is critical for maintaining high efficiency at light load.
For maximum battery life, each converter's highside P-channel MOSFET conducts continuously
when the input voltage approaches dropout (100%
duty cycle operation).
SystemPower™
Up to 97% Efficiency
25µA Quiescent Current Per Channel
VIN Range: 2.7V to 5.5V
VOUT Range: 0.6V to VIN
Output Current: 600mA
Low RDS(ON) 0.4Ω Integrated Power Switches
Low Drop Out 100% Duty Cycle
1.0MHz Switching Frequency
Shutdown Current <1µA
Current Mode Operation
Internal Reference Soft Start
Short-Circuit Protection
Fast Turn-On (100µs Typical)
Over-Temperature Protection
3mm x 3mm, < 1mm high
TDFN33-12 Package
-40°C to +85°C Temperature Range
Both regulators have independent input and
enable inputs.
Applications
The AAT2511 is available in a Pb-free, thermallyenhanced 12-pin TDFN33 package, and is rated
over the -40°C to +85°C temperature range.
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Cellular Phones
Digital Cameras
Handheld Instruments
Microprocessor/DSP Core/IO Power
PDAs and Handheld Computers
Portable Media Players
Typical Application
AAT2511 Efficiency
(VIN = 3.3V)
100
VIN
1.8V
1
L1
11
4.7µH
R1
118k
C1
10µF
C8
0.1µF
U1
AAT2511
12
2
3
R2
59.0k
10
VIN1
VIN2
EN1
EN2
LX1
LX2
FB1
FB2
SGND1
GND1
SGND2
GND2
95
9
Efficiency (%)
C3
10µF
2.5V
4
L2
8
5
10µH
6
7
R4
59.0k
R3
187k
C2
10µF
90
85
2.5V
80
75
1.8V
70
65
60
0.1
1
10
100
1000
Load Current (mA)
2511.2006.02.1.2
1
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Pin Descriptions
Pin #
Symbol
Function
1, 4
EN1, EN2
2, 5
FB1, FB2
3, 6
SGND1, SGND2
7, 10
GND2, GND1
8, 11
9, 12
EP
LX2, LX1
VIN2, VIN1
Converter enable input. A logic high enables the converter channel. A logic low
forces the channel into shutdown mode, reducing the channel supply current to less
than 1µA. This pin should not be left floating. When not actively controlled, this pin
can be tied directly to the source voltage (VIN1, VIN2).
Feedback input pin. An external resistive divider ties to this point and programs the
output voltage to the desired value.
Signal ground. Return the feedback resistive divider to this ground. See section on
PCB layout guidelines and evaluation board layout diagram.
Main power ground return. Connect to the input and output capacitor return. See section on PCB layout guidelines and evaluation board layout diagram.
Output switching node that connects to the respective output inductor.
Input supply voltage. Must be closely decoupled to the respective power gnd.
Exposed paddle (bottom). Use properly sized vias for thermal coupling to the ground
plane. See section on PCB layout guidelines.
Pin Configuration
TDFN33-12
(Top View)
EN1
FB1
SGND1
EN2
FB2
SGND2
2
1
12
2
11
3
10
4
9
5
8
6
7
VIN1
LX1
GND1
VIN2
LX2
GND2
2511.2006.02.1.2
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Absolute Maximum Ratings1
Symbol
VIN
VLX
VFB
VEN
TJ
TLEAD
Description
VIN1, VIN2 to SGND1, SGND2, GND1, and GND2
LX1, LX2 to GND1, GND2
FB1 and FB2 to SGND1, SGND2, GND1, and GND2
EN1 and EN2 to SGND1, SGND2, GND1, and GND2
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
6.0
-0.3 to VP + 0.3
-0.3 to VP + 0.3
-0.3 to 6.0
-40 to 150
300
V
V
V
V
°C
°C
Value
Units
2
50
W
°C/W
Thermal Information
Symbol
PD
θJA
Description
Maximum Power Dissipation
Thermal Resistance2
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 with exposed paddle connected to ground plane.
2511.2006.02.1.2
3
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Electrical Characteristics1
TA = -40°C to 85°C, unless otherwise noted. Typical values are TA = 25°C, VIN = 3.6V.
Symbol
Description
Conditions
Min
Typ
Max
Units
5.5
2.6
+3.0
4.0
V
V
mV
V
%
V
50
µA
1.0
µA
mA
Ω
Ω
1
µA
0.2
615
%/V
mV
µs
MHz
Step-Down Converter Channels
VIN
Input Voltage
VUVLO
UVLO Threshold
VOUT
VOUT
Output Voltage Tolerance
Output Voltage Range
IQ
ISHDN
ILIM
RDS(ON)H
RDS(ON)L
ILXLK
∆VLinereg
VFB
TS
FOSC
Quiescent Current
Shutdown Current
P-Channel Current Limit
High Side Switch On Resistance
Low Side Switch On Resistance
LX Leakage Current
THYS
Line Regulation
FB Threshold Voltage Accuracy
Start-Up Time
Oscillator Frequency
Over-Temperature Shutdown
Threshold
Over-Temperature Shutdown
Hysteresis
VEN(L)
VEN(H)
IEN
Enable Threshold Low
Enable Threshold High
Input Low Current
TSD
2.7
VIN Rising
Hysteresis
VIN Falling
IOUT = 0 to 400mA, VIN = 2.7 - 5.5V
100
1.8
-3.0
0.6
No Load, 0.6V Adjustable Version,
Per Channel
EN = SGND = GND
25
600
0.45
0.4
VIN = 5.5V, VLX = 0 to VIN,
EN = SGND = GND
VIN = 2.7V to 5.5V
0.6V Output, No Load, TA = 25°C
From Enable to Output Regulation
TA = 25°C
597
0.7
600
100
1.0
1.5
140
°C
15
°C
EN
0.6
VIN = VFB = 5.5V
1.4
-1.0
1.0
V
V
µA
1. The AAT2511 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.
2. For adjustable version with higher than 2.5V output, please consult your AnalogicTech representative.
4
2511.2006.02.1.2
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Typical Channel Characteristics
Efficiency vs. Load
DC Regulation
(VOUT = 3.3V; L = 10µ
µH)
(VOUT = 3.3V; L = 10µ
µH)
3.0
Output Error (%)
Efficiency (%)
100
VIN = 3.9V
90
VIN = 4.2V
80
70
60
0.1
1
10
100
2.0
0.0
-1.0
VIN = 3.9V
-2.0
-3.0
1000
VIN = 4.2V
1.0
0.1
1
10
Output Current (mA)
Output Error (%)
Efficiency (%)
VIN = 3.0V
VIN = 3.6V
80
70
1
10
100
1000
VIN = 3.3V
2.0
VIN = 3.6V
1.0
0.0
VIN = 3.0V
-1.0
-2.0
-3.0
1000
0.1
1
10
Output Current (mA)
Output Current (mA)
Efficiency vs. Load
DC Regulation
(VOUT = 1.5V; L = 4.7µ
µH)
(VOUT = 1.5V; L = 4.7µ
µH)
3.0
100
VIN = 2.7V
VIN = 3.6V
80
Output Error (%)
90
Efficiency (%)
100
3.0
90
VIN = 4.2V
70
60
50
1000
(VOUT = 2.5V; L = 10µ
µH)
VIN = 3.3V
0.1
100
DC Regulation
(VOUT = 2.5V; L = 10µ
µH)
60
1000
Output Current (mA)
Efficiency vs. Load
100
100
0.1
1
10
Output Current (mA)
2511.2006.02.1.2
100
1000
VIN = 4.2V
2.0
VIN = 3.6V
1.0
0.0
VIN = 2.7V
-1.0
-2.0
-3.0
0.1
1
10
Output Current (mA)
5
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Typical Channel Characteristics
Frequency vs. Input Voltage
Output Voltage Error vs. Temperature
(VOUT = 1.8V)
(VIN = 3.6V; VO = 2.5V)
2.0
1.5
0.5
Output Error (%)
Frequency Variation (%)
1.0
0.0
-0.5
-1.0
-1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
2.7
3.1
3.5
3.9
4.3
4.7
5.1
-2.0
-40
5.5
-20
0
80
Quiescent Current vs. Input Voltage
(VIN = 3.6V; VO = 1.5V)
(VO = 1.8V)
100
35
Supply Current (µ
µA)
Variation (%)
60
Switching Frequency vs. Temperature
0.20
0.10
0.00
-0.10
-0.20
-40
85°C
30
25°C
25
20
-40°C
15
-20
0
20
40
60
80
2.5
100
3.0
3.5
Temperature (°°C)
4.0
4.5
5.0
5.5
6.0
Input Voltage (V)
P-Channel RDS(ON) vs. Input Voltage
N-Channel RDS(ON) vs. Input Voltage
750
750
700
700
120°C
650
100°C
RDS(ON) (mΩ
Ω)
650
RDS(ON) (mΩ
Ω)
40
Temperature (°°C)
Input Voltage (V)
600
550
85°C
500
450
25°C
400
120°C
600
100°C
550
500
85°C
450
400
25°C
350
350
300
300
2.5
3.0
3.5
4.0
4.5
Input Voltage (V)
6
20
5.0
5.5
6.0
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Input Voltage (V)
2511.2006.02.1.2
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Typical Channel Characteristics
Load Transient Response
Load Transient Response
(30mA - 300mA; VIN = 3.6V; VOUT = 2.5V; C1 = 22µ
µF)
1.3
1.1
300mA
30mA
0.9
0.7
0.5
0.3
0.1
-0.1
2.65
1.5
2.55
Output Voltage
(top) (V)
1.5
1.3
0.9
30mA
2.35
0.7
0.5
2.25
0.3
2.15
0.1
2.05
-0.1
Time (25µs/div)
Time (25µs/div)
Line Transient
Line Regulation
(VOUT = 2.5V @ 500mA)
(VOUT = 1.5V)
7.0
2.55
6.5
2.50
6.0
2.45
5.5
2.40
5.0
2.35
4.5
2.30
2.25
4.0
2.20
3.5
2.15
3.0
2
1.5
Accuracy (%)
2.60
Input Voltage
(bottom) (V)
Output Voltage
(top) (V)
1.1
300mA
2.45
Load and Inductor Current
(200mA/div) (bottom)
1.65
1.60
1.55
1.50
1.45
1.40
1.35
1.30
1.25
1.20
1.15
1.10
1.05
1.00
Load and Inductor Current
(200mA/div) (bottom)
Output Voltage
(top) (V)
(30mA - 300mA; VIN = 3.6V; VOUT = 1.5V; C1 = 22µ
µF)
IOUT = 600mA
1
IOUT = 100mA
0.5
0
IOUT = 10mA
-0.5
-1
2.5
Time (25µ
µs/div)
3
3.5
4
4.5
5
5.5
6
Input Voltage (V)
Output Ripple
Soft Start
(VIN = 3.6V; VOUT = 1.5V; L = 4.7µ
µH)
0.8
0
0.7
-20
0.6
-40
0.5
-60
0.4
-80
0.3
-100
0.2
-120
0.1
Time (250ns/div)
2511.2006.02.1.2
Enable and Output Voltage
(top) (V)
0.9
20
4.0
3.5
3.0
3.0
2.0
2.5
1.0
2.0
0.0
1.5
-1.0
1.0
-2.0
0.5
-3.0
0.0
-4.0
-0.5
Inductor Current
(bottom) (A)
40
Inductor Current
(bottom) (A)
Output Voltage (AC Coupled)
(top) (mV)
(VIN = 3.6V; VOUT = 1.8V; 400mA)
Time (50µs/div)
7
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Functional Block Diagram
FB1
VIN1
Err.
Amp.
DH
Comp.
LX1
Logic
Voltage
Reference
DL
Control
Logic
EN1
SGND1
GND1
VIN2
See
Note
FB2
Err.
Amp.
DH
Comp.
LX2
Logic
Voltage
Reference
Control
Logic
EN2
DL
GND2
See
Note
SGND2
Note: Internal resistor divider included for ≥1.2V versions. For low voltage versions, the feedback pin is tied directly to the error amplifier input.
Operation
Device Summary
The AAT2511 is a constant frequency peak current
mode PWM converter with internal compensation.
Each channel has independent input, enable, feedback, and ground pins with non-synchronized
1MHz clocks.
8
Both converters are designed to operate with an
input voltage range of 2.7V to 5.5V. The output
voltage ranges from 0.6V to the input voltage. The
0.6V fixed model shown in Figure 1 is also the
adjustable version and is externally programmable
with a resistive divider as shown in Figure 2. The
converter MOSFET power stage is sized for
600mA load capability with up to 97% efficiency.
Light load efficiency exceeds 80% at a 500µA load.
2511.2006.02.1.2
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
VIN
C3
10µF
12
1.8V
1
L1
C4
100pF
C1
10µF
R1
118k
C8
0.1µF
U1
AAT2511
11
4.7µH
2
3
10
R2
59.0k
VIN1
VIN2
EN1
EN2
LX1
LX2
FB1
SGND1
GND1
FB2
SGND2
GND2
9
2.5V
4
L2
8
5
10µH
6
7
R4
59.0k
C5
100pF
R3
187k
C2
10µF
Figure 1: AAT2511 Adjustable Output with
Enhanced Transient Response.
Soft Start
The AAT2511 soft-start control prevents output voltage overshoot and limits inrush current when either
the input power or the enable input is applied.
When pulled low, the enable input forces the converter into a low-power, non-switching state with a
bias current of less than 1µA.
Low Dropout Operation
For conditions where the input voltage drops to the
output voltage level, the converter duty cycle
increases to 100%. As 100% duty cycle is
approached, the minimum off-time initially forces
the high side on-time to exceed the 1MHz clock
cycle and reduce the effective switching frequency.
Once the input drops below the level where the output can be regulated, the high side P-channel
2511.2006.02.1.2
MOSFET is turned on continuously for 100% duty
cycle. At 100% duty cycle, the output voltage tracks
the input voltage minus the I*R drop of the high
side P-channel MOSFET RDS(ON).
Low Supply
The under-voltage lockout (UVLO) feature guarantees sufficient VIN bias and proper operation of all
internal circuitry prior to activation.
Fault Protection
For overload conditions, the peak inductor current is
limited. Thermal protection disables switching when
the internal dissipation or ambient temperature
becomes excessive. The junction over-temperature
threshold is 140°C with 15°C of hysteresis.
9
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
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 AAT2511 is 0.24A/µsec. This
equates to a slope compensation that is 75% of the
inductor current down slope for a 1.5V output and
4.7µH inductor.
0.75 ⋅ VO 0.75 ⋅ 1.5V
A
=
= 0.24
L
4.7µH
µsec
m=
This is the internal slope compensation for the
adjustable (0.6V) version or low-voltage fixed version. When externally programming the 0.6V version to a 2.5V output, the calculated inductance
would be 7.5µH.
L=
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.
The 4.7µH CDRH3D16 series inductor selected
from Sumida has a 105mΩ DCR and a 900mA DC
current rating. At full load, the inductor DC loss is
38mW for a 600mA 1.5V output.
Input Capacitor
Select a 4.7µF to 10µF 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 C. The calculated
value varies with input voltage and is a maximum
when VIN is double the output voltage.
0.75V
0.75 ⋅ VO
µsec
≈ 3 A ⋅ VO
=
m
0.24A /µsec
=3
CIN =
µsec
⋅ 2.5V = 7.5µH
A
In this case, a standard 10µH value is selected.
V ⎞
VO ⎛
⋅ 1- O
VIN ⎝
VIN ⎠
⎛ VPP
⎞
- ESR ⋅ FS
⎝ IO
⎠
This equation provides an estimate for the input
capacitor required for a single channel.
Configuration
Output Voltage
Inductor
Slope Compensation
0.6V Adjustable With
External Resistive Divider
0.6V to 2.0V
4.7µH
0.24A/µsec
2.5V
10µH
0.24A/µsec
Table 1: Inductor Values.
10
2511.2006.02.1.2
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
The equation below solves for input capacitor size
for both channels. It makes the worst-case
assumptions that both converters are operating at
50% duty cycle and are synchronized.
1
CIN =
⎛ VPP
⎞
- ESR · 4 · FS
⎝ IO1 + IO2
⎠
Because the AAT2511 channels will generally operate at different duty cycles and are not synchronized, the actual ripple will vary and be less than
the ripple (VPP) used to solve for the input capacitor in the equation above.
Always examine the ceramic capacitor DC voltage
coefficient characteristics when selecting the proper value. For example, the capacitance of a 10µF
6.3V X5R ceramic capacitor with 5V DC applied is
actually about 6µF.
The maximum input capacitor RMS current is:
IRMS = IO1 · ⎛
⎝
VO1 ⎛
V ⎞
· 1 - O1 ⎞ + IO2 · ⎛
VIN ⎝
VIN ⎠ ⎠
⎝
VO2 ⎛
V ⎞
· 1 - O2 ⎞
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 of
both converters combined.
IRMS(MAX) =
IO1(MAX) + IO2(MAX)
2
This equation also makes the worst-case assumption that both converters are operating at 50% duty
cycle and are synchronized. Since the converters
are not synchronized and are not both operating at
50% duty cycle, the actual RMS current will always
be less than this. Losses associated with the input
ceramic capacitor are typically minimal.
VO
⎛
VO ⎞
The term VIN · ⎝1 - VIN ⎠ appears in both the input
voltage ripple and input capacitor RMS current
equations. It is a maximum when VO is twice VIN.
This is why the input voltage ripple and the input
2511.2006.02.1.2
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
AAT2511. Low ESR/ESL X7R and X5R ceramic
capacitors are ideal for this function. To minimize
the 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 (C3
and C8) can be seen in the evaluation board layout
in Figure 4. Since decoupling must be as close to
the input pins as possible, it is necessary to use
two decoupling capacitors. C3 provides the bulk
capacitance required for both converters, while C8
is a high frequency bypass capacitor for the second
channel (see C3 and C8 placement in Figure 4).
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 printed circuit board
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 converter performance, a high ESR tantalum or aluminum electrolytic capacitor should be
placed in parallel with the low ESR, ESL bypass
ceramic capacitor. This dampens the high Q network and stabilizes the system.
Output Capacitor
The output capacitor limits the output ripple and
provides holdup during large load transitions. A
4.7µF to 10µF X5R or X7R ceramic capacitor typically provides sufficient bulk capacitance to stabi-
11
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
lize 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. As the loop
responds, the inductor current increases to match
the load current demand. This typically takes two
to three switching cycles and can be estimated by:
COUT =
3 · ∆ILOAD
VDROOP · FS
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 4.7µF. 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.
The maximum output capacitor RMS ripple current
is given by:
1
V
· (VIN(MAX) - VOUT)
IRMS(MAX) =
· OUT
L · F · VIN(MAX)
2· 3
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
For applications requiring an adjustable output voltage, the 0.6V version can be programmed externally. Resistors R1 through R4 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, the minimum suggested
value for R2 and R4 is 59kΩ. Although a larger
value will reduce the quiescent current, it will also
increase the impedance of the feedback node,
making it more sensitive to external noise and
interference. Table 2 summarizes the resistor values for various output voltages with R2 and R4 set
to either 59kΩ for good noise immunity or 221kΩ
for reduced no load input current.
⎛ VOUT ⎞
⎛ 1.5V ⎞
R1 = V
-1 · R2 = 0.6V - 1 · 59kΩ = 88.5kΩ
⎝ REF ⎠
⎝
⎠
The adjustable version of the AAT2511 in combination with an external feedforward capacitor (C4 and
C5 of Figure 1) delivers enhanced transient
response for extreme pulsed load applications. The
addition of the feedforward capacitor typically
requires a larger output capacitor (C1 and C2) for
stability.
Ω
R2, R4 = 59kΩ
Ω
R2, R4 = 221kΩ
VOUT (V)
Ω)
R1, R3 (kΩ
Ω)
R1, R3 (kΩ
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
75
113
150
187
221
261
301
332
442
464
523
715
Table 2: Adjustable Resistor Values
For Use With 0.6V Version.
12
2511.2006.02.1.2
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Thermal Calculations
There are three types of losses associated with the
AAT2511 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 dual converter losses is given by:
Given the total losses, the maximum junction temperature can be derived from the θJA for the
TDFN33-12 package which is 50°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
PCB Layout
The following guidelines should be used to insure a
proper layout.
PTOTAL =
+
IO12 · (RDSON(HS) · VO1 + RDSON(LS) · [VIN -VO1])
VIN
IO22 · (RDSON(HS) · VO2 + RDSON(LS) · [VIN -VO2])
VIN
+ (tsw · F · [IO1 + IO2] + 2 · IQ) · VIN
IQ is the AAT2511 quiescent current for one channel and tsw is used to estimate the full load switching losses.
For the condition where channel one is in dropout
at 100% duty cycle, the total device dissipation
reduces to:
PTOTAL = IO12 · RDSON(HS)
+
IO22 · (RDSON(HS) · VO2 + RDSON(LS) · [VIN -VO2])
VIN
+ (tsw · F · IO2 + 2 · 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.
2511.2006.02.1.2
1. Due to the pin placement of VIN for both converters, proper decoupling is not possible with
just one input capacitor. The large input capacitor C3 should connect as closely as possible to
VP and GND, as shown in Figure 3. The additional input bypass capacitor C8 is necessary for
proper high frequency decoupling of the second
converter.
2. The output capacitor and inductor should be
connected as closely as possible. The connection of the inductor to the LX pin should also be
as short as possible.
3. The feedback trace 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. If
external feedback resistors are used, they
should be placed as closely as possible to the
FB pin. This prevents noise from being coupled
into the high impedance feedback node.
4. The resistance of the trace from the load return
to GND 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. For good thermal coupling, PCB vias are required
from the pad for the TDFN paddle to the ground
plane. The via diameter should be 0.3mm to
0.33mm and positioned on a 1.2 mm grid.
13
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Design Example
Specifications
VO1 = 2.5V @ 600mA (adjustable using 0.6V version), pulsed load ∆ILOAD = 300mA
VO2 = 1.8V @ 600mA (adjustable using 0.6V version), pulsed load ∆ILOAD = 300mA
VIN
= 2.7V to 4.2V (3.6V nominal)
FS
= 1.0 MHz
TAMB = 85°C
2.5V VO1 Output Inductor
L1 = 3
µsec
µsec
⋅ VO1 = 3
⋅ 2.5V = 7.5µH
A
A
(see Table 1)
For Sumida inductor CDRH3D16, 10µH, DCR = 210mΩ.
∆I1 =
⎛ 2.5V⎞
VO ⎛
V ⎞
2.5V
⋅ 1 - O1 =
⋅ ⎝1 = 100mA
L1 ⋅ F ⎝
VIN ⎠ 10µH ⋅ 1.0MHz
4.2V⎠
IPK1 = IO1 +
∆I1
= 0.6A + 0.05A = 0.65A
2
PL1 = IO12 ⋅ DCR = (0.4A)2 ⋅ 210mΩ = 76mW
1.8V VO2 Output Inductor
L2 = 3
µsec
µsec
⋅ VO2 = 3
⋅ 1.8V = 5.4µH (see Table 1)
A
A
For Sumida inductor CDRH3D16, 4.7µH, DCR = 105mΩ.
∆I2 =
⎛ 1.8V ⎞
VO2 ⎛
V ⎞
1.8V
⋅ 1 - O2 =
⋅ 1= 218mA
L⋅F ⎝
VIN ⎠ 4.7µH ⋅ 1.0MHz ⎝ 4.2V⎠
IPK2 = IO2 +
∆I2
= 0.6A + 0.11A = 0.71A
2
PL2 = IO22 ⋅ DCR = (0.6A)2 ⋅ 105mΩ = 38mW
14
2511.2006.02.1.2
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
2.5V Output Capacitor
COUT =
3 · ∆ILOAD
3 · 0.6A
=
= 9µF
VDROOP · FS
0.2V · 1MHz
IRMS(MAX) =
(VOUT) · (VIN(MAX) - VOUT)
1
2.5V · (4.2V - 2.5V)
·
= 29mArms
=
L · F · VIN(MAX)
2 · 3 10µH · 1MHz · 4.2V
2· 3
1
·
Pesr = esr · IRMS2 = 5mΩ · (29mA)2 = 4.2µW
1.8V Output Capacitor
COUT =
3 · ∆ILOAD
3 · 0.6A
=
= 9µF
0.2V · 1MHz
VDROOP · FS
IRMS(MAX) =
(VOUT) · (VIN(MAX) - VOUT)
1
1.8V · (4.2V - 1.8V)
·
= 63mArms
=
L · F · VIN(MAX)
2 · 3 4.7µH · 1.0MHz · 4.2V
2· 3
1
·
Pesr = esr · IRMS2 = 5mΩ · (63mA)2 = 20µW
Input Capacitor
Input Ripple VPP = 25mV.
CIN =
1
⎛ VPP
⎞
- ESR · 4 · FS
⎝ IO1 + IO2
⎠
IRMS(MAX) =
=
1
= 15.78µF
⎛ 25mV
⎞
- 5mΩ · 4 · 1MHz
⎝ 1.2A
⎠
IO1 + IO2
= 6Arms
2
P = esr · IRMS2 = 5mΩ · (0.6A)2 = 1.8mW
2511.2006.02.1.2
15
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
AAT2511 Losses
The maximum dissipation occurs at dropout where VIN = 2.7V. All values assume an ambient temperature of
85°C and a junction temperature of 120°C.
PTOTAL =
IO12 · (RDSON(HS) · VO1 + RDSON(LS) · (VIN -VO1)) + IO22 · (RDSON(HS) · VO2 + RDSON(LS) · (VIN -VO2))
VIN
+ (tsw · F · IO2 + 2 · IQ) · VIN
=
0.62 · (0.725Ω · 2.5V + 0.7Ω · (2.7V - 2.5V)) + 0.62 · (0.725Ω · 1.8V + 0.7Ω · (2.7V - 1.8V))
2.7V
+ 5ns · 1MHz · 0.6A + 60µA) · 2.7V = 527mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 527mW = 111°C
Output 1 Enable
VIN
1 2 3
R1
see Table 3
C41
U1
AAT2511
1
2
3
C51
R3
see Table 3
4
5
6
R4
59.0k
EN1
FB1
SGND1
VIN1
LX1
GND1
EN2
VIN2
FB2
LX2
SGND2
GND2
LX1
12
L1
see Table 3
11
VO1
C3
10
LX2
10µF
9
8
VO2
L2
see Table 3
C11
4.7µF
7
R2
59.0k
C8
C7
0.01µF
C6
0.01µF
C21
4.7µF
0.1µF
GND
GND
3 2 1
Output 2 Enable
Figure 2: AAT2511 Evaluation Board Schematic.
1. For enhanced transient configuration C5, C4 = 100pF and C1, C2 = 10µF.
16
2511.2006.02.1.2
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Adjustable Version
(0.6V device)
Ω
R2, R4 = 59kΩ
Ω1
R2, R4 = 221kΩ
VOUT (V)
Ω)
R1, R3 (kΩ
Ω)
R1, R3 (kΩ
L1, L2 (µH)
0.8
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
75.0
113
150
187
221
261
301
332
442
464
523
715
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7 or 6.8
10
Table 3: Evaluation Board Component Values.
Figure 3: AAT2511 Evaluation Board Top Side.
Figure 4: AAT2511 Evaluation Board
Bottom Side.
1. For reduced quiescent current, R2 and R4 = 221kΩ.
2511.2006.02.1.2
17
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Manufacturer
Sumida
Sumida
MuRata
MuRata
MuRata
Coilcraft
Coilcraft
Coiltronics
Coiltronics
Coiltronics
Coiltronics
Part Number
Inductance
(µH)
Max DC
Current (A)
DCR
Ω)
(Ω
Size (mm)
LxWxH
Type
CDRH3D16-4R7
CDRH3D16-100
LQH32CN4R7M23
LQH32CN4R7M33
LQH32CN4R7M53
LPO6610-472
LPO3310-472
SDRC10-4R7
SDR10-4R7
SD3118-4R7
SD18-4R7
4.7
10
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
4.7
0.90
0.55
0.45
0.65
0.65
1.10
0.80
1.53
1.30
0.98
1.77
0.11
0.21
0.20
0.15
0.15
0.20
0.27
0.117
0.122
0.122
0.082
3.8x3.8x1.8
3.8x3.8x1.8
2.5x3.2x2.0
2.5x3.2x2.0
2.5x3.2x1.55
5.5x6.6x1.0
3.3x3.3x1.0
4.5x3.6x1.0
5.7x4.4x1.0
3.1x3.1x1.85
5.2x5.2x1.8
Shielded
Shielded
Non-Shielded
Non-Shielded
Non-Shielded
1mm
1mm
1mm Shielded
1mm Shielded
Shielded
Shielded
Table 4: Typical Surface Mount Inductors.
Manufacturer
MuRata
MuRata
MuRata
Part Number
Value
Voltage
Temp. Co.
Case
GRM219R61A475KE19
GRM21BR60J106KE19
GRM21BR60J226ME39
4.7µF
10uF
22uF
10V
6.3V
6.3V
X5R
X5R
X5R
0805
0805
0805
Table 5: Surface Mount Capacitors.
18
2511.2006.02.1.2
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Ordering Information
Voltage
Package
Channel 1
Channel 2
Marking1
Part Number (Tape and Reel)2
TDFN33-12
0.6V
0.6V
QRXYY
AAT2511IWP-AA-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.
Legend
Voltage
Code
Adjustable
(0.6V)
A
1.2
E
1.5
G
1.6
H
1.8
I
1.9
Y
2.5
N
2.6
O
2.7
P
2.8
Q
2.85
R
2.9
S
3.0
T
3.3
W
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
2511.2006.02.1.2
19
AAT2511
Dual 600mA, 1MHz Step-Down DC/DC Converter
Package Information
TDFN33-12
2.40 ± 0.05
Detail "B"
3.00 ± 0.05
Index Area
(D/2 x E/2)
0.3 ± 0.10 0.16 0.375 ± 0.125
0.075 ± 0.075
3.00 ± 0.05
1.70 ± 0.05
Top View
Bottom View
Pin 1 Indicator
(optional)
0.23 ± 0.05
Detail "A"
0.45 ± 0.05
0.1 REF
0.05 ± 0.05
0.229 ± 0.051
+ 0.05
0.8 -0.20
7.5° ± 7.5°
Detail "B"
Option A:
C0.30 (4x) max
Chamfered corner
Side View
Option B:
R0.30 (4x) max
Round corner
Detail "A"
All dimensions in millimeters.
© Advanced Analogic Technologies, Inc.
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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.
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830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737-4600
Fax (408) 737-4611
20
2511.2006.02.1.2