Analogic AAT2510 Dual 400ma, 1mhz step-down dc-dc converter Datasheet

AAT2510
Dual 400mA, 1MHz Step-Down DC-DC Converter
General Description
Features
The AAT2510 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 either fixed
or 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 96% Efficiency
25µA Quiescent Current Per Channel
VIN Range: 2.7V to 5.5V
Fixed VOUT Range: 0.6V to VIN
Adjustable VOUT Range: 0.6V to 2.5V
Output Current: 400mA
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
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 AAT2510 is available in a thermally-enhanced
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
VIN = 2.7 - 5.5V
AAT2510 Efficiency
U1
AAT2510
12
1
2.5V at 400mA
C8
0.1μF
L1
4.7μH
11
2
3
C1
4.7μF
10
VIN1
EN1
VIN2
EN2
LX1
LX2
FB1
FB2
SGND1 SGND2
GND1
GND2
100
95
9
4
8
5
1.8V at 400mA
L2
4.7μH
6
7
C2
4.7μF
Efficiency (%)
C3
10μF
90
85
2.5V
80
75
70
65
60
0.1
L1,L2 Sumida CDRH3D16-4R7 C1,C2 Murata GRM219R61A475KE19
C3 Murata GRM21BR60J106KE19
2510.2006.05.1.10
1.8V
VIN = 3.3V with unloaded output disabled
1
10
100
1000
Load Current (mA)
1
AAT2510
Dual 400mA, 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. For fixed output voltage versions, this pin is connected to the
converter output, forcing the converter to regulate to the specified voltage. For
adjustable versions, an external resistive divider ties to this point and programs the
output voltage to the desired value.
Signal ground. For external feedback, return the feedback resistive divider to this
ground. For internal fixed version, tie to the point of load return. 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
2510.2006.05.1.10
AAT2510
Dual 400mA, 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.
2510.2006.05.1.10
3
AAT2510
Dual 400mA, 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
V
V
mV
V
%
Step-Down Converter Channels
VIN
Input Voltage
VUVLO
UVLO Threshold
VOUT
Output Voltage Tolerance
VOUT
Output Voltage Range
IQ
ISHDN
ILIM
RDS(ON)H
RDS(ON)L
ILXLK
ΔVLinereg
VFB
IFB
RFB
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
FB Leakage Current
FB Impedance
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
Fixed Output Version
Adjustable Output Version2
No Load, 0.6V Adjustable Version,
Per Channel
EN = SGND = GND
100
1.8
-3.0
0.6
0.6
+3.0
4.0
2.5
25
50
µA
1.0
µA
mA
Ω
Ω
1
µA
%/V
mV
µA
kΩ
MHz
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
0.6V Output
>0.6V Output
TA = 25°C
V
597
600
0.2
615
0.2
250
0.7
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 AAT2510 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
2510.2006.05.1.10
AAT2510
Dual 400mA, 1MHz Step-Down DC-DC Converter
Typical Channel Characteristics
Efficiency vs. Load
Load Regulation
(VOUT = 2.5V; L = 4.7μ
μH)
(VOUT = 2.5V; L = 4.7μ
μH)
100
2.0
Efficiency (%)
VIN = 3.0V
Output Error (%)
VIN = 3.3V
90
VIN = 3.6V
80
70
60
0.1
1.0
10
100
1.0
VIN = 3.0V
0.0
VIN = 3.3V
-1.0
VIN = 3.6V
-2.0
1000
0.1
1.0
10
Output Current (mA)
DC Regulation
(VOUT = 1.8V; L = 4.7μ
μH)
(VOUT = 1.8V; L = 4.7μ
μH)
100
2.0
Output Error (%)
Efficiency (%)
VIN = 3.6V
VIN = 2.7V
90
80
VIN = 4.2V
70
60
0.1
1.0
10
100
1.0
VIN = 4.2V
0.0
VIN = 2.7V
-1.0
VIN = 3.6V
-2.0
1000
0.1
1.0
10
Output Current (mA)
100
1000
Output Current (mA)
Frequency vs. Input Voltage
Output Voltage Error vs. Temperature
(VOUT = 1.8V)
(VIN = 3.6V; VO = 1.5V)
2.0
1.0
0.5
Output Error (%)
Frequency Variation (%)
1000
Output Current (mA)
Efficiency vs. Load
50
100
0.0
-0.5
-1.0
-1.5
-2.0
1.0
0.0
-1.0
-2.0
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
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4.7
5.1
5.5
-40
-20
0
20
40
60
80
100
Temperature (°°C)
5
AAT2510
Dual 400mA, 1MHz Step-Down DC-DC Converter
Typical Channel Characteristics
Switching Frequency vs. Temperature
Quiescent Current vs. Input Voltage
(VIN = 3.6V; VO = 1.5V)
(VO = 1.8V)
35
Supply Current (μ
μA)
Variation (%)
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
100
2.5
3.0
3.5
4.0
Temperature (°°C)
Output Voltage
(top) (V)
RDS(ON) (mΩ
Ω)
550
85°C
25°C
400
350
300
2.5
3.0
3.5
4.0
4.5
5.0
5.5
2.0
1.4
1.9
1.2
1.0
1.8
1.7
300mA
1.6
0.8
0.6
30mA
1.5
0.4
1.4
0.2
1.3
0.0
-0.2
1.2
6.0
Load and Inductor Current
(200mA/div) (bottom)
100°C
600
450
6.0
Load Transient Response
700
500
5.5
(30mA - 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 10μ
μF)
750
120°C
5.0
Input Voltage (V)
P-Channel RDS(ON) vs. Input Voltage
650
4.5
Time (25μs/div)
Input Voltage (V)
Load Transient Response
700
RDS(ON) (mΩ
Ω)
650
120°C
600
100°C
550
500
85°C
450
400
25°C
350
300
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
0.1
(30mA - 300mA; VIN = 3.6V; VOUT = 1.8V;
μF; C4 = 100pF; see Figure 2)
C1 = 10μ
0.0
-0.1
-0.2
1.4
1.2
300mA
1.0
30mA
0.8
-0.3
0.6
-0.4
0.4
-0.5
0.2
-0.6
0.0
-0.7
-0.2
Load and Inductor Current
(200mA/div) (bottom)
750
Output Voltage (AC Coupled)
(top) (V)
N-Channel RDS(ON) vs. Input Voltage
Time (25μs/div)
Input Voltage (V)
6
2510.2006.05.1.10
AAT2510
Dual 400mA, 1MHz Step-Down DC-DC Converter
Typical Channel Characteristics
1.9
1.2
1.8
1.0
300mA
1.7
0.8
1.6
0.6
30mA
1.5
0.4
1.4
0.2
1.3
0.0
-0.2
1.2
1.90
7.0
1.85
6.5
1.80
6.0
1.75
5.5
1.70
5.0
1.65
4.5
1.60
4.0
1.55
3.5
1.50
Line Regulation
Soft Start
(VOUT = 1.8V)
(VIN = 3.6V; VOUT = 1.8V; 400mA)
-0.05
IOUT = 10mA
-0.1
-0.15
-0.2
IOUT = 400mA
-0.25
-0.3
-0.35
2.5
3.0
3.5
4.0
4.5
5.0
5.5
6.0
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)
Accuracy (%)
IOUT = 100mA
Enable and Output Voltage
(top) (V)
0.1
0
3.0
Time (25μ
μs/div)
Time (25μs/div)
0.05
Input Voltage
(bottom) (V)
1.4
Load and Inductor Current
(200mA/div) (bottom)
2.0
Output Voltage
(top) (V)
Line Transient
(VOUT = 1.8V @ 400mA)
Output Voltage
(top) (V)
Load Transient Response
(30mA - 300mA; VIN = 3.6V; VOUT = 1.8V; C1 = 4.7μ
μF)
250μ
μs/div
Input Voltage (V)
Output Ripple
40
0.9
20
0.8
0
0.7
-20
0.6
-40
0.5
-60
0.4
-80
0.3
-100
0.2
Inductor Current
(bottom) (A)
Output Voltage (AC Coupled)
(top) (mV)
(VIN = 3.6V; VOUT = 1.8V; 400mA)
0.1
-120
Time (250ns/div)
2510.2006.05.1.10
7
AAT2510
Dual 400mA, 1MHz Step-Down DC-DC Converter
Functional Block Diagram
FB1
VIN1
Err.
Amp.
DH
Comp.
LX1
Logic
Voltage
Reference
SGND1
DL
Control
Logic
EN1
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 AAT2510 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 for
the internally fixed version and up to 2.5V for the
externally adjustable version. 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 400mA load capability with up to 96% efficiency. Light load efficiency
exceeds 80% at a 500µA load.
2510.2006.05.1.10
AAT2510
Dual 400mA, 1MHz Step-Down DC-DC Converter
VIN = 2.7 - 5.5V
VIN
C3
10μF
12
1
2.5V at 400mA
L1
4.7μH
11
2
3
C1
4.7μF
10
VIN1
VIN2
EN1
EN2
LX1
LX2
FB1
FB2
SGND1 SGND2
GND1
GND2
C3
10μF
C8
0.1μF
U1
AAT2510
12
9
1.8V
4
8
5
1
1.8V at 400mA
L2
L1
4.7μH
C4
100pF
6
7
C2
4.7μF
C1
10μF
R1
118k
C8
0.1μF
U1
AAT2510
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
L1, L2 Sumida CDRH3D16-4R7 C1, C2 Murata GRM219R61A475KE19
C3 Murata GRM21BR60J106KE19
Figure 1: AAT2510 Fixed Output.
Soft Start
The AAT2510 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
2510.2006.05.1.10
Figure 2: AAT2510 Adjustable Output with
Enhanced Transient Response.
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
AAT2510
Dual 400mA, 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 AAT2510 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.
m=
0.75 ⋅ VO 0.75 ⋅ 1.5V
A
=
= 0.24
L
4.7μH
μsec
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
17mW which gives a 2.8% loss in efficiency for a
400mA 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
CIN =
μsec
=3
⋅ 2.5V = 7.5μH
A
In this case, a standard 10µH value is selected.
For high-voltage fixed versions (2.5V and above),
m = 0.48A/µsec. Table 1 displays inductor values
for the AAT2510 fixed and adjustable options.
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
0.6V to 2.0V
4.7µH
0.24A/µsec
2.5V to 3.3V
4.7µH
0.48A/µsec
Fixed Output
Table 1: Inductor Values.
10
2510.2006.05.1.10
AAT2510
Dual 400mA, 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.
CIN =
1
⎛ VPP
⎞
- ESR · 4 · FS
⎝ IO1 + IO2
⎠
Because the AAT2510 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
2510.2006.05.1.10
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
AAT2510. 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
AAT2510
Dual 400mA, 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 · ΔILOAD
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
· (VIN(MAX) - VOUT)
V
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 2 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 AAT2510 in combination with an external feedforward capacitor (C4 and
C5 of Figure 2) 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
2510.2006.05.1.10
AAT2510
Dual 400mA, 1MHz Step-Down DC-DC Converter
Thermal Calculations
There are three types of losses associated with the
AAT2510 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 AAT2510 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.
2510.2006.05.1.10
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 4. 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
AAT2510
Dual 400mA, 1MHz Step-Down DC-DC Converter
Design Example
Specifications
VO1 = 2.5V @ 400mA (adjustable using 0.6V version), pulsed load ΔILOAD = 300mA
VO2 = 1.8V @ 400mA (adjustable using 0.6V version), pulsed load ΔILOAD = 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.
ΔI1 =
⎛ 2.5V⎞
VO ⎛
V ⎞
2.5V
⋅ 1 - O1 =
⋅ ⎝1 = 100mA
VIN ⎠ 10μH ⋅ 1.0MHz
4.2V⎠
L1 ⋅ F ⎝
IPK1 = IO1 +
ΔI1
= 0.4A + 0.05A = 0.45A
2
PL1 = IO12 ⋅ DCR = 0.4A2 ⋅ 210mΩ = 34mW
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.
ΔI2 =
⎛ 1.8V ⎞
VO2 ⎛
V ⎞
1.8V
⋅ 1 - O2 =
⋅ 1= 218mA
VIN ⎠ 4.7μH ⋅ 1.0MHz ⎝ 4.2V⎠
L⋅F ⎝
IPK2 = IO2 +
ΔI2
= 0.4A + 0.11A = 0.51A
2
PL2 = IO22 ⋅ DCR = 0.4A2 ⋅ 105mΩ = 17mW
14
2510.2006.05.1.10
AAT2510
Dual 400mA, 1MHz Step-Down DC-DC Converter
2.5V Output Capacitor
COUT =
3 · ΔILOAD
3 · 0.3A
=
= 4.5μF
0.2V · 1MHz
VDROOP · FS
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 · ΔILOAD
3 · 0.3A
=
= 4.5μF
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
= 9.5μF
⎛ 25mV
⎞
- 5mΩ · 4 · 1MHz
⎝ 0.8A
⎠
IO1 + IO2
= 0.4Arms
2
P = esr · IRMS2 = 5mΩ · (0.4A)2 = 0.8mW
2510.2006.05.1.10
15
AAT2510
Dual 400mA, 1MHz Step-Down DC-DC Converter
AAT2510 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
=
0.42 · (0.725Ω · 2.5V + 0.7Ω · (2.7V - 2.5V)) + 0.42 · (0.725Ω · 1.8V + 0.7Ω · (2.7V - 1.8V))
2.7V
+ 5ns · 1MHz · 0.4A + 60μA) · 2.7V = 240mW
TJ(MAX) = TAMB + ΘJA · PLOSS = 85°C + (50°C/W) · 240mW = 97°C
Output 1 Enable
VIN
1 2 3
R1
see Table 3
C41
U1
AAT2510
1
2
C51
3
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
10μF
9
8
LX2
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 3: AAT2510 Evaluation Board Schematic.
1. For enhanced transient configuration C5, C4 = 100pF and C1, C2 = 10µF.
16
2510.2006.05.1.10
AAT2510
Dual 400mA, 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
Fixed Version
R2, R4 Not Used
VOUT (V)
Ω)
R1, R3 (kΩ
L1, L2 (µH)
0.6-3.3V
0
4.7
Table 3: Evaluation Board Component Values.
Figure 4: AAT2510 Evaluation Board Top Side.
Figure 5: AAT2510 Evaluation Board
Bottom Side.
1. For reduced quiescent current, R2 and R4 = 221kΩ.
2510.2006.05.1.10
17
AAT2510
Dual 400mA, 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
2510.2006.05.1.10
AAT2510
Dual 400mA, 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
OBXYY
AAT2510IWP-AA-T1
TDFN33-12
0.6V
3.3V
PNXYY
AAT2510IWP-AW-T1
TDFN33-12
1.8V
1.2V
PEXYY
AAT2510IWP-IE-T1
TDFN33-12
1.8V
1.5V
OTXYY
AAT2510IWP-IG-T1
TDFN33-12
1.8V
1.6V
QJXYY
AAT2510IWP-IH-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
Adjustable
(0.6V)
0.9
1.2
1.5
1.8
1.9
2.5
2.6
2.7
2.8
2.85
2.9
3.0
3.3
4.2
Code
A
B
E
G
I
Y
N
O
P
Q
R
S
T
W
C
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
2510.2006.05.1.10
19
AAT2510
Dual 400mA, 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°
Option A:
C0.30 (4x) max
Chamfered corner
Side View
Option B:
R0.30 (4x) max
Round corner
Detail "B"
Detail "A"
All dimensions in millimeters.
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20
2510.2006.05.1.10