ANALOGICTECH AAT2500BIZL-BAA-T1

PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
General Description
Features
The AAT2500B is a three-channel regulator consisting of
a step-down converter with an input voltage range of 2.7V
to 5.5V plus two low dropout (LDO) linear regulators.
• VIN Range: 2.7V to 5.5V
• 800mA Buck Converter
• Linear Regulators
▪ LDOA: 500mA
▪ LDOB: 150mA
• Adjustable Output Voltage
• Low Dropout Voltage
• High Output Accuracy: ±1.5%
• High Efficiency Step-Down Converter
• 85μA (Typical) of Total IQ
• Independent Enable Pins
• Integrated Power MOSFETs
• 2MHz Switching Frequency
• Over-Temperature and Current Limit Protection
• QFN34-20 Package
• -40°C to +85°C Temperature Range
The step-down converter delivers up to 800mA of output
current, while consuming 30μA of typical no load quiescent current. The switching frequency is 2MHz, minimizing the size of external components.
The two LDOs (LDOA/LDOB) have independent inputs
and are capable of delivering up to 500mA and 150mA
respectively. A Power-OK (POK) function provides an
open drain output signal when LDOA is within regulation.
Both LDOs feature low quiescent current and a low dropout voltage. The output voltages for both LDOs are
adjustable to as low as 0.6V. The linear regulators have
independent Enable pins.
The AAT2500B is available in a Pb-free 3x4mm QFN34-20
package and is rated over the -40°C to +85°C temperature range.
Applications
•
•
•
•
•
Cellular Phones
Digital Cameras
Handheld Instruments
Microprocessor/DSP Core/IO Power
PDAs and Handheld Computers
Typical Application
L
LX
VOUT (Buck)
AAT2500B
FB
VIN
VIN
R1
OUTA
R1A
100kΩ
VLDOA
VLDOB
VP
SYNC
POK
EN
2500B.2008.03.1.0
C OUT
POK
FBA
OUTB
OUTB
R1B
FBB
ENA
ENB
OUTA
R2B
R2A
2.2μF
R2
2.2μF
PGND
AGND
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1
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Pin Descriptions
Pin #
Symbol
1
FBB
2
ENA
3
ENB
4
SYNC
5
FB
6
7
AGND
PGND
8, 9
LX
10
VP
11, 12
13
N/C
VIN
14
EN
15
POK
16
FBA
17
18
19
20
EP
OUTA
VLDOA
VLDOB
OUTB
Function
Feedback input pin for LDOB. This pin is connected to OUTB. It is used to see the output of LDOB to regulate
to the desired value via an external resistor divider. For fixed versions, short FBB to OUTB.
Enable pin for LDOA. When connected low, LDOA is disabled and consumes less than 1μA of current. When
connected high, normal operation.
Enable pin for LDOB. When connected low, LDOB is disabled and consumes less than 1μA of current. When
connected high, normal operation.
Oscillator synchronization pin for the step-down converter. The internal oscillator is disabled and the stepdown converter can be synchronized to an external clock applied to this pin.
Feedback input pin for the step-down converter. This pin is connected to the converter output. It is used to
see the output of the converter to regulate to the desired value via an external resistor divider.
Ground connection pin.
Main power ground return pin for the step-down converter. Connect to the output and input capacitor return.
Connect inductor to this pin. Switching node internally connected to the drain of both high- and low-side
MOSFETs.
Bias supply. Supply power for the internal circuitry. Connect to input power via low pass filter with decoupling to AGND.
Not connected.
Input supply voltage for the converter. Must be closely decoupled.
Enable for the step-down converter. A logic low disables the converter and it consumes less than 1μA of current. A logic high enables normal operation.
Power-OK pin with open drain output. It is pulled low when the OUTA pin is outside the regulation window of
±10%. Place a pull-up resistor between POK and OUTA.
Feedback input pin for LDOA. This pin is connected to OUTA. It is used to see the output of LDOA to regulate
to the desired value via an external resistor divider. For fixed versions, short FBA to OUTA.
LDOA output pin; should be closely decoupled with a low-ESR ceramic capacitor.
Input voltage pin for linear regulator A; should be closely decoupled.
Input voltage pin for linear regulator B; should be closely decoupled.
LDOB output pin; should be closely decoupled with a low-ESR ceramic capacitor.
Exposed paddle; connect to ground directly beneath the package.
Pin Configuration
QFN34-20
(Top View)
OUTA
VLDOA
VLDOB
OUTB
17
18
19
20
FBB
ENA
ENB
SYNC
FB
AGND
1
16
2
15
3
14
4
13
5
12
6
11
FBA
POK
EN
VIN
N/C
N/C
9
10
8
7
VP
LX
LX
PGND
2
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2500B.2008.03.1.0
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Absolute Maximum Ratings1
Symbol
VP, VIN, VLDO
VLX
VFB
VEN
TJ
TLEAD
Description
Input Voltage and Bias Power to GND
LX to GND
FB to GND
EN and EN_LDO to GND
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
2.0
50
W
°C/W
Thermal Information
Symbol
PD
θJA
Description
Maximum Power Dissipation (TA = 25°C)
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.
2500B.2008.03.1.0
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3
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Electrical Characteristics1
VIN = 3.6V; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C.
Symbol
Description
Conditions
Bias Power Supply
IQ
Quiescent Current
ISHDN
Shutdown Current
UVLO
Min
ENA = ENB = EN = VIN; ILOAD = 0
ENA = ENB = EN = GND
VIN Rising
Hysteresis
VIN Falling
Under-Voltage Lockout Voltage
LDOA, LDOB
Input Voltage
VLDO
VOUT
VFB
VDOA
VDOB
ΔVOUT/
VOUT*ΔVIN
VEN(L)
VEN(H)
ISHT
TSD
THYS
LDOA
VPOK
Output Voltage Tolerance
IOUT = 1mA to IOUT(MAX)
Feedback Voltage
Dropout Voltage2, 3
Dropout Voltage2, 3
IOUT = 500mA
IOUT = 150mA
Line Regulation4
VIN = VOUT + 1 to 5.0V
Enable Threshold Low
Enable Threshold High
Shutdown Current
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
VIN = 5V
Power-OK Trip Threshold
VOUT Rising, TA = 25°C
VPOKHYS
Power-OK Hysteresis
VPOK(LO)
IPOK
Power-OK Output Voltage Low
Power-OK Output Leakage Current
TA = 25°C
TA = -40°C to +85°C
Typ
Max
Units
80
145
1.0
2.6
μA
μA
V
mV
V
5.5
1.5
2.5
0.607
500
150
V
%
V
mV
mV
0.09
%/V
0.6
V
V
μA
°C
°C
250
2.0
1.8
-1.5
-2.5
0.593
0.6
1.5
1.0
140
15
82
94
98
1.0
ISINK = 1mA
VPOK <5.5V, VOUT in Regulation
0.4
1.0
% of
VOUT
% of
VOUT
V
μA
1. The AAT2500B 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. VDO is defined as VIN - VOUT when VOUT is 98% of nominal.
3. For VOUT < 2.1V, VDO = 1.8 - VOUT.
4. CIN = 10μF.
4
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2500B.2008.03.1.0
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Electrical Characteristics (continued)1
VIN = 3.6V; TA = -40°C to +85°C, unless otherwise noted. Typical values are TA = 25°C.
Symbol
Step-Down
VIN
VOUT
VOUT
VFB
ISHDN
ILX_LEAK
IFB
ILIM
RDS(ON)H
RDS(ON)L
ΔVOUT/VOUT
ΔVOUT/
VOUT*ΔVIN
FOSC
TSD
THYS
VEN(L)
VEN(H)
IEN
Description
Conditions
Converter; IOUT = 800mA
Input Voltage
Output Voltage Tolerance
VOUT Programmable Range
Feedback Threshold Voltage
Shutdown Current
LX Leakage Current
Feedback Leakage
Current Limit
High Side Switch On Resistance
Low Side Switch On Resistance
Load Regulation
IOUT = 0 to 800mA; VIN = 2.7V to 5.5V
Min
2.7
-3.0
0.9
0.891
Typ
Max
Units
5.5
3.0
VIN
0.909
1.0
1.0
0.2
1.2
280
160
0.5
V
%
V
V
μA
μA
μA
A
mΩ
mΩ
%
0.2
%/V
0.9
EN = GND
VIN = 5.5, VLX = 0 - VIN
VFB = 1.0V
ILOAD = 0 to 800mA
Line Regulation
Oscillator Frequency
Over-Temperature Shutdown Threshold
Over-Temperature Shutdown Hysteresis
Enable Threshold Low
Enable Threshold High
EN Input Leakage
1.6
2.0
140
15
2.4
0.6
VEN = 5V, VIN = 5V
1.4
-1.0
1.0
MHz
°C
°C
V
V
μA
1. The AAT2500B 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.
2500B.2008.03.1.0
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PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Typical Characteristics–Step-Down Converter
Step-Down Converter Efficiency vs. Output Current
Output Voltage Error vs. Temperature
(VOUT = 1.8V)
(VIN = 3.6V; VOUT = 2.5V)
0.4
90
0.3
Efficiency (%)
80
70
60
VIN = 5.5V
VIN = 4.2V
50
40
VIN = 3.6V
30
20
PWM/Light Load Mode
VIN = 2.7V
10
Output Error (%)
100
Forced PWM Mode
1
10
0.2
0.1
0.0
-0.1
800mA 100mA
-0.2
-0.3
-0.4
0
0.1
100
-0.5
-40
1000
-15
Output Current (mA)
60
85
(VOUT = 2.5V; Forced PWM)
0.2
0.4
VIN = 3V
0.1
Output Voltage Error (%)
Output Voltage Error (%)
35
Step-Down Converter Line Regulation
(VOUT = 2.5V; Forced PWM)
VIN = 3.6V
0.0
-0.1
VIN = 4.2V
-0.2
VIN = 5.5V
-0.3
0.3
50mA
1mA
0.2
100mA
0.1
0.0
600mA
-0.1
800mA
-0.2
0.1
1
10
100
1000
2.8
3.1
Output Current (mA)
3.7
4.0
4.3
4.6
4.9
5.2
Step-Down Converter Output Ripple
Step-Down Converter Load Transient
(VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA)
(VIN = 3.6V; IOUT = 300mA to 650mA)
1.79
1.0
0.8
0.6
0.4
0.2
2.2
Output Voltage (top) (V)
1.80
IINDUCTOR
5.5
2.0
VOUT
1.8
1.6
Time (200ns/div)
I OUT
0.9
IL
0.6
0.3
0.0
Load and Inductor Current
(bottom) (A)
VOUT
Inductor Current (bottom) (A)
1.81
3.4
Input Voltage (V)
1.82
Output Voltage (top) (V)
10
Temperature (°C)
Step-Down Converter Load Regulation
6
400mA
600mA
Time (20µs/div)
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2500B.2008.03.1.0
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Typical Characteristics–Step-Down Converter (continued)
Step-Down Converter Line Transient
No Load Quiescent Current vs. Input Voltage
(VOUT = 1.8V; IOUT = 800mA; VIN = 3.6V-4.2V)
(Step-Down Converter Enabled; Both LDOs Enabled)
4.0
3.5
0.02
0.00
-0.02
160
Quiescent Current (µA)
Input Voltage (top) (V)
4.5
Output Voltage (AC Coupled)
(bottom) (V)
5.0
140
120
85°C
100
25°C
80
60
-40°C
40
20
0
2.7
3.1
3.5
3.9
Time (20µs/div)
Switching Frequency (MHz)
Quiescent Current (µA)
110
100
90
85°C
70
25°C
50
40
-40°C
30
20
2.7
3.1
3.5
3.9
4.3
4.7
5.1
(VIN = 3.6V; VOUT = 1.2V)
600mA
2.00
800mA
400mA
1.95
1.90
1.85
1.80
1.75
5.5
-40
-15
10
35
60
Step-Down Converter Turn-Off
(VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA)
(VIN = 3.6V; VOUT = 1.8V; IOUT = 800mA)
0
VOUT
0V
1.5
1.0
0.5
IL
0.0
4
Enable (top) (V)
VOUT (middle) (V)
1.8V
6
Time (50µs/div)
2500B.2008.03.1.0
EN
2
0
VOUT
1.8V
IL
1.0
0V
0.5
0.0
Inductor Current (bottom) (A)
EN
Inductor Current (bottom) (A)
6
2
85
Temperature (ºC)
Step-Down Converter Soft Start
4
5.5
2.05
Input Voltage (V)
Enable (top) (V)
VOUT (middle) (V)
5.1
Step-Down Converter Switching Frequency
vs. Temperature
(Step-Down Converter Enabled; Both LDOs Disabled)
60
4.7
Input Voltage (V)
No Load Quiescent Current vs. Input Voltage
80
4.3
Time (100µs/div)
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PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Typical Characteristics–Step-Down Converter (continued)
High Side Switch On Resistance vs. Input Voltage
Low Side Switch On Resistance vs. Input Voltage
400
350
120°C
380
100°C
RDS(ON)L (mΩ
Ω)
RDS(ON)H (mΩ
Ω)
300
85°C
360
340
320
300
280
260
25°C
250
200
150
25°C
100
240
220
50
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
8
120°C
100°C 85°C
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
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2500B.2008.03.1.0
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Typical Characteristics–LDO Regulator
LDO Load Regulation
LDO Load Regulation
(VOUT = 1.8V)
(VOUT = 1.2V)
1.2
Output Voltage Error (%)
Output Voltage Error (%)
2.0
1.6
1.2
VIN = 3.3V
0.8
VIN = 2.7V
0.4
0.0
-0.4
-0.8
VIN = 3.6V
-1.2
VIN = 4.2V
VIN = 5.5V
-1.6
VIN = 4.2V
0.9
VIN = 3.6V
0.6
0.3
0.0
-0.3
VIN = 2.7V
-0.6
1
10
100
0.1
1000
1
Output Current (mA)
100
LDO Line Regulation
(VOUT = 2.7V)
(VOUT = 2.7V)
2.0
VIN = 5.5V
0.9
1.6
VIN = 4.2V
VIN = 3.6V
0.6
0.3
0.0
-0.3
1000
Output Current (mA)
VIN = 3.0V
-0.6
VIN = 3.3V
-0.9
Output Voltage (V)
Output Voltage Error (%)
10
LDO Load Regulation
1.2
400mA
1.2
500mA
0.8
0.4
0.0
200mA
100mA
-0.4
300mA
-0.8
-1.2
-1.6
-2.0
3.0
-1.2
0.1
1
10
100
1000
3.5
Output Current (mA)
4.0
4.5
5.0
5.5
Input Voltage (V)
Output Voltage vs. Input Voltage
LDO Output Voltage Variation vs. Temperature
(VOUT = 2.7V)
(VOUT = 2.7V)
0.1
Output Voltage Error (%)
3.0
2.9
Output Voltage (V)
VIN = 3.3V
-0.9
-1.2
-2.0
0.1
2.8
VIN = 5.0V
100mA
2.7
500mA
400mA
300mA
200mA
2.6
2.5
2.4
2.3
2.2
2.7
2.9
3.1
3.3
3.5
3.7
0.0
-0.2
-0.3
150mA
-0.4
-0.5
-0.6
-0.7
-0.8
-40
Input Voltage (V)
2500B.2008.03.1.0
500mA
-0.1
-15
10
35
60
85
Temperature (°C)
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PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Typical Characteristics–LDO Regulator (continued)
Dropout Voltage vs. Temperature
LDO Load Transient
(VOUT = 2.7V)
(VOUT = 1.8V; IOUT = 500mA)
Output Voltage
(AC coupled) (top) (mV)
Dropout Voltage (mV)
350
300
250
500mA
200
150
300mA
100
50
150mA
0
-40
50
0
-50
0.6
0.4
0.2
0.0
-15
10
35
60
85
Temperature (°C)
Time (50µs/div)
LDO Load Transient
LDO Line Transient
(VOUT = 1.8V; IOUT = 150mA)
(VOUT = 1.8V; IOUT = 500mA)
-20
0.3
0.2
0.1
0.0
Output Voltage
(AC coupled) (top) (mV)
0
100
Time (50µs/div)
50
0
-50
4.5
4.0
3.5
3.0
Input Voltage (bottom) (V)
20
Output Current (bottom) (A)
40
Output Voltage
(AC coupled) (top) (mV)
Output Current (bottom) (A)
100
400
Time (50µs/div)
LDO Line Transient
(VOUT = 1.8V; IOUT = 150mA)
Output Voltage
(AC coupled) (top) (mV)
50
0
-50
4.5
4.0
3.5
3.0
Input Voltage (bottom) (V)
100
Time (50µs/div)
10
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2500B.2008.03.1.0
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Functional Block Diagram
FB
VP
VIN
See Note
Voltage
Reference
DH
Err.
Amp.
SYNC
LX
Logic
Control
Logic
EN
DL
PGND
OUTA
VLDOA
Over-Current
Protection
ENB
ENA
FBA
Err.
Amp.
VLDOB
Err.
Amp.
Over-Current
Protection
Voltage
Reference
91%
VREF
See Note
POK
OUTB
See Note
FBB
AGND
Note: For adjustable version, the internal feedback divider is omitted and
the FB pin is tied directly to the internal error amplifier.
Functional Description
Switch-Mode Step-Down Converter
The AAT2500B is a high performance power management IC comprised of a step-down converter and two
linear regulators. The step-down converter operates in
both fixed and variable frequency modes for high efficiency performance. The switching frequency is 2MHz,
minimizing the size of the inductor. The converter
requires only three external components (CIN, COUT, and
L). LDOA can deliver 500mA. LDOA can deliver 150mA.
Each regulator has independent input voltage and enable
pins and operates wth ceramic capacitors.
The switching regulator is a monolithic step-down converter operating with input voltage range of 2.7V to
5.5V. Power devices are sized for 800mA current capability while maintaining over 90% efficiency at full load. It
consumes 30μA of typical no load quiescent current,
making it also ideal for light load applications. The oscillator operates at 2MHz, minimizing the cost and size of
external components.
2500B.2008.03.1.0
A logic low on the EN pin shuts the converter down and
makes it consume less than 1μA of current.
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11
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
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.
For overload conditions, the peak input current is limited. As load impedance decreases and the output voltage
falls closer to zero, more power is internally dissipated,
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 140°C with
15°C of hysteresis.
Linear Regulators
The two linear regulators are high performance LDOs
where LDOA sources 500mA and LDOB sources 150mA
of current. For added flexibility, both regulators have
independent input voltages operating from 1.8V to 5.5V.
An external feedback pin for each LDO allows programming the output voltage from 3.6V to 0.6V. The regulators have short-circuit and thermal protection in case of
adverse operating conditions.
LDOA features an integrated Power-OK comparator
which indicates when the output is out of regulation. The
POK is an open drain output and it is held low when the
AAT2500B is in shutdown mode.
Under-Voltage Lockout
Internal bias of all circuits is controlled via the VIN pin.
Under-voltage lockout guarantees sufficient VIN bias and
proper operation of all internal circuits prior to activation.
Over-Temperature Protection
Thermal protection completely disables switching when
internal dissipation becomes excessive. The junction
over-temperature threshold is 140°C with 15°C of hysteresis. Once an over-temperature or over-current fault
conditions is removed, the output voltage automatically
recovers.
Applications Information
Step-Down Converter 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 AAT2500B stepdown converter is 0.51A/μsec. This equates to a slope
compensation that is 75% of the inductor current down
slope for a 1.5V output and 2.2μH inductor.
m=
0.75 ⋅ VO 0.75 ⋅ 1.5V
A
=
= 0.51
L
2.2μH
μsec
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 2.2μH CDRH2D14 series Sumida inductor has a
94mΩ DCR and a 1.5A DC current rating. At full 800mA
load, the inductor DC loss is 60mW which gives a 4.16%
loss in efficiency for a 800mA, 1.8V output.
Input Capacitor
Select a 4.7μF to 10μF X7R or X5R ceramic capacitor for
the input of the step-down converter. 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.
CIN =
V ⎞
VO ⎛
· 1- O
VIN ⎝
VIN ⎠
⎛ VPP
⎞
- ESR · FS
⎝ IO
⎠
VO ⎛
V ⎞
1
· 1 - O = for VIN = 2 · VO
VIN ⎝
VIN ⎠
4
CIN(MIN) =
12
www.analogictech.com
1
⎛ VPP
⎞
- ESR · 4 · FS
⎝ IO
⎠
2500B.2008.03.1.0
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
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 5.0V DC applied is actually about 6μF.
The maximum input capacitor RMS current is:
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 ⎠
D · (1 - D) =
0.52 =
1
2
for VIN = 2 · VO:
IRMS(MAX) =
VO
IO
2
⎛
V ⎞
· 1- O
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 AAT2500B. 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.
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.
2500B.2008.03.1.0
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.
Configuration
Output Voltage
Inductor
0.9V Adjustable With
External Feedback
1V, 1.2V
1.5V, 1.8V
2.5V, 3.3V
1.5μH
2.2μH
3.3μH
Table 1: Inductor Values.
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 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:
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.
www.analogictech.com
13
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Adjustable Output Resistor Selection
The output voltage on the step-down converter is programmed with external resistors R2 and R6. To limit the
bias current required for the external feedback resistor
string while maintaining good noise immunity, the minimum suggested value for R6 is 59kΩ. 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
2 summarizes the resistor values for various output voltages with R6 set to either 59kΩ for good noise immunity or 221kΩ for reduced no load input current.
With enhanced transient response for extreme pulsed
load application, an external feed-forward capacitor (C1
in Fig.3) can be added.
VOUT (V)
R6 = 59kΩ
R2 (kΩ)
R6 = 221kΩ
R2 (kΩ)
0.9*
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
2.8
3.0
3.3
0
6.65
13.3
19.6
26.1
32.4
39.2
59.0
61.9
71.5
105
124
137
158
0
24.3
48.7
73.2
97.6
124
147
221
232
274
392
464
511
590
Table 2: Step-Down Converter Resistor Values for
Various Output Voltages.
Thermal Calculations
There are three types of losses associated with the
AAT2500B 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 LDO losses
is given by:
PTOTAL =
IO2 · (RDSON(HS) · VO + RDSON(LS) · [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 step-down converter switching losses.
For the condition where the step-down converter is in
dropout at 100% duty cycle, the total device dissipation
reduces to:
PTOTAL = IO2 · RDSON(HS) + 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 θJA for the QFN34-20 package which is 50°C/W.
TJ(MAX) = PTOTAL · ΘJA + TAMB
LDO Linear Regulator Input Capacitor
A 1μF or larger capacitor is typically recommended for
CIN in most applications. A CIN capacitor is not required
for basic LDO regulator operation; however, if the
AAT2500B is physically located more than three centimeters from an input power source, a CIN capacitor will
be needed for stable operation. CIN should be located as
closely to the device VLDO pins as practically possible.
CIN values greater than 1μF will offer superior input line
transient response and will assist in maximizing the
highest possible power supply ripple rejection.
Ceramic, tantalum, or aluminum electrolytic capacitors
may be selected for CIN. There is no specific capacitor
ESR requirement for CIN; however, ceramic capacitors
are recommended for CIN due to their inherent capability
over tantalum capacitors to withstand input current
surges from low impedance sources such as batteries in
portable devices.
* For the 0.9V output, R6 is open.
14
www.analogictech.com
2500B.2008.03.1.0
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Output Capacitor
For proper load voltage regulation and operational stability, a capacitor is required between pins OUTA, OUTB,
and GND. The COUT capacitor connection to the LDO
regulator ground pin should be made as direct as practically possible for maximum device performance. The
AAT2500B has been specifically designed to function
with very low ESR ceramic capacitors. For best performance, ceramic capacitors are recommended.
Typical output capacitor values for maximum output current conditions range from 1μF to 10μF.
Applications utilizing the exceptionally low output noise
and optimum power supply ripple rejection characteristics of the AAT2500B should use 2.2μF or greater for
COUT. If desired, COUT may be increased without limit. In
low output current applications where output load is less
than 10mA, the minimum value for COUT can be as low as
0.47μF.
generally have tight tolerance and are very stable over
temperature. Larger capacitor values are usually composed of X7R, X5R, Z5U, or Y5V dielectric materials.
NPO and C0G material types are not recommended for
use with LDO regulators since the capacitor tolerance
can vary more than ±50% over the operating temperature range of the device. A 2.2μF Y5V capacitor could be
reduced to 1μF over temperature; this could cause problems for circuit operation. X7R and X5R dielectrics are
much more desirable. The temperature tolerance of X7R
dielectric is better than ±15%. Capacitor area is another contributor to ESR. Capacitors which are physically
large in size will have a lower ESR when compared to a
smaller sized capacitor of an equivalent material and
capacitance value. These larger devices can improve
circuit transient response when compared to an equal
value capacitor in a smaller package size. Consult
capacitor vendor datasheets carefully when selecting
capacitors for LDO regulators.
Adjustable Output Resistor Selection
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the
AAT2500B. Ceramic capacitors offer many advantages
over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very low ESR, is
lower cost, has a smaller PCB footprint, and is nonpolarized. Line and load transient response of the LDO
regulator is improved by using low ESR ceramic capacitors. Since ceramic capacitors are non-polarized, they
are not prone to incorrect connection damage.
Equivalent Series Resistance
ESR is a very important characteristic to consider when
selecting a capacitor. ESR is the internal series resistance associated with a capacitor that includes lead
resistance, internal connections, size and area, material
composition, and ambient temperature. Typically, capacitor ESR is measured in milliohms for ceramic capacitors
and can range to more than several ohms for tantalum
or aluminum electrolytic capacitors.
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1μF are typically made
from NPO or C0G materials. NPO and C0G materials
The output voltage on the linear regulator is programmed
with external resistors: R4 and R7 for LDOA and R5 and
R8 for LDOB. Table 3 summarizes the resistor values for
various output voltages with R4 and R5 set to either
59kΩ for good noise immunity or 221kΩ for reduced no
load input current.
LDO
VOUT (V)
R7, R8 = 59kΩ
R4, R5 (kΩ)
R7, R8 = 221kΩ
R4, R5 (kΩ)
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
0
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
0
75
113
150
187
221
261
301
332
442
464
523
715
1000
Table 3: LDO Linear Regulators Resistor Values
for Various Output Voltages.
* For the 0.6V output, R7 and R8 are open.
2500B.2008.03.1.0
www.analogictech.com
15
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
POK Output
LDOA of the AAT2500B features an integrated Power OK
comparator which can be used as an error flag. The POK
open drain output goes low when output voltage is 10%
(typ) below its nominal regulation voltage. Additionally,
any time LDOA is in shutdown, the POK output is pulled
low. Connect a pull-up resistor from POK to OUTA.
to COUT will effect a slower CIN decay rate during shutdown, thus preventing VOUT from exceeding VIN. In applications where there is a greater danger of VOUT exceeding
VIN for extended periods of time, it is recommended to
place a Schottky diode across VIN to VOUT (connecting the
cathode to VIN and anode to VOUT). The Schottky diode
forward voltage should be less than 0.45V.
Thermal Considerations and
High Output Current Applications
Enable Function
The AAT2500B features an LDO regulator enable/disable
function. Each LDO has its own dedicated enable pin.
These pins (ENA, ENB) are active high and are compatible
with CMOS logic. To assure the LDO regulators will switch
on, ENA/B must be greater than 1.4V. The LDO regulators
will shut down when the voltage on the ENA/B pins falls
below 0.6V. In shutdown, the LDO regulators will consume less than 1.0μA of current. If the enable function is
not needed in a specific application, it may be tied to VIN
to keep the LDO regulator in a continuously on state.
Thermal Protection
Each of the two LDOs of the AAT2500B has an internal
thermal protection circuit which will turn on when the
device die temperature exceeds 140°C. The LDO regulator
outputs will remain in a shutdown state until the internal
die temperature falls back below the 125°C trip point.
The LDOs of the AAT2500B are designed to deliver continuous output load currents of 300mA each under normal operation. This is desirable for circuit applications
where there might be a brief high in-rush current during
a power-on event.
The limiting characteristic for the maximum output load
current safe operating area is essentially package power
dissipation and the internal preset thermal limit of the
device. In order to obtain high operating currents, careful device layout and circuit operating conditions need to
be taken into account.
The following discussions will assume the LDO regulator is
mounted on a printed circuit board utilizing the minimum
recommended footprint as stated in the layout considerations section of this document. At any given ambient
temperature (TA), the maximum package power dissipation can be determined by the following equation:
No-Load Stability
The LDOs in the AAT2500B are designed to maintain output voltage regulation and stability under operational
no-load conditions. This is an important characteristic for
applications where the output current may drop to zero.
Reverse Output-to-Input
Voltage Conditions and Protection
Under normal operating conditions, a parasitic diode
exists between the output and input of the LDO regulator. The input voltage should always remain greater than
the output load voltage maintaining a reverse bias on
the internal parasitic diode. Conditions where VOUT might
exceed VIN should be avoided since this would forward
bias the internal parasitic diode and allow excessive current flow into the VOUT pin, possibly damaging the LDO
regulator. In applications where there is a possibility of
VOUT exceeding VIN for brief amounts of time during normal operation, the use of a larger value CIN capacitor is
highly recommended. A larger value of CIN with respect
16
PD(MAX) =
TJ(MAX) - TA
θJA
Constants for the AAT2500B are TJ(MAX) (the maximum
junction temperature for the device, which is 125°C) and
θJA = 50°C/W (the package thermal resistance). Typically,
maximum conditions are calculated at the maximum
operating temperature of TA = 85°C and under normal
ambient conditions where TA = 25°C. Given TA = 85°C,
the maximum package power dissipation is 800mW. At TA
= 25°C, the maximum package power dissipation is 2W.
The maximum continuous output current for the AAT2500B
is a function of the package power dissipation and the
input-to-output voltage drop across the LDO regulator.
To determine the maximum output current for a given
output voltage, refer to the following equation. This calculation accounts for the total power dissipation of the
LDO regulator, including that caused by ground current.
PD(MAX) = [(VIN - VOUTA)IOUTA + (VIN · IGND)] + [(VIN - VOUTB)IOUTB + (VIN · IGND)]
www.analogictech.com
2500B.2008.03.1.0
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Layout
3.
The suggested PCB layout for the AAT2500B is shown in
Figures 1 and 2. The following guidelines should be used
to help ensure a proper layout.
1.
2.
The input capacitors (C4, C7, C8, and C9) should connect as closely as possible to VIN, VLDOA, VLDOB, VP,
and PGND.
The output capacitor (C5, and C6) of the LDOs connect as closely as possible to OUT. 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 a narrow trace.
The trace should be kept wide, direct, and short.
Figure 1: AAT2500B Evaluation Board
Top Side Layout.
2500B.2008.03.1.0
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. Feedback resistors
should be placed as closely as possible to VOUT 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
the PGND should be kept to a minimum. This will
help to minimize any error in DC regulation due to
differences in the potential of the internal signal
ground and the power ground.
5. Ensure all ground pins are tied to the ground plane.
No pins should be left floating. For maximum power
dissipation, it is recommended that the exposed pad
(EP) must be soldered to a good conductive PCB
ground plane layer to further increase local heat
dissipation.
Figure 2: AAT2500B Evaluation Board
Bottom Side Layout.
www.analogictech.com
17
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
SYNC
U1
R10
100k
VIN
FB
5
MODE/SYNC
4
R1
AAT2500B
FB
LX
9
LX
LX
VOUT_BUCK
L1
VIN 13
MODE/SYNC LX
VIN
OUTA
Buckout
8
CDRH2D14
17
OUTA
C2
10μF
100
3
2
1
C4
0.1μF
VLDOA 18
VLDOA
POK
R3
15
100k
C8
1μF
VINA
3
2
1
VINB
VLDOB 19
C9
1μF
VLDOB
FBA
16
FBA
20
OUTB
1
FBB
C3
R2
C1
100pF
.01μF
R4
OUTA
VP 10
VP
OUTB
EN
FBB
OUTB
EN
EN 14
1
2
3
ENB
ENB 3
1
2
3
ENA 2
ENA
R12
(open)
ENB
PGND
ENA
AGND
R5
7
R7
59.0k
R8
59.0k
C6
2.2μF
R6
59.0k
C5
2.2μF
6
GND
C7
10μF
EP
1
2
3
GND
GND
POK
POK
GND
VOUT_BUCK (V)
0.9
1.0
1.1
1.2
1.3
1.4
1.5
1.8
1.85
2.0
2.5
2.8
3.0
3.3
R2 (kΩ)
0
6.65
13.3
19.6
26.1
32.4
39.2
59
61.9
71.5
105
124
137
158
L1 (μH)
1.5
1.5
1.5
1.5
1.5
1.5
2.2
2.2
2.2
2.2
3.3
3.3
3.3
3.3
VOUT_LDO (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
R4, R5 (kΩ)
19.6
29.4
39.2
49.9
59.0
68.1
78.7
88.7
118
124
137
187
267
U1 AAT2500B QFN34-20
L1 Sumida CDRH2D14 or Coltronics SD3812
C2, C7 10μF, 6.3V, X5R, 0805 GRM219R60J106KE19
C5, C6 2.2μF, 10V, X5R, 0603 GRM188R61A225KE34
C8, C9 1μF, 6.3V, X5R, 0603 GRM185R60J105KE26
Figure 3: AAT2500B Evaluation Board Schematic.
18
www.analogictech.com
2500B.2008.03.1.0
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Manufacturer
Part Number
Value (μF)
Voltage Rating
Temp. Co.
Case Size
Murata
Murata
Murata
Murata
Murata
GRM219R60J106KE19
GRM188R60J475KE19
GRM188R61A225KE34
GRM188R61A105KA61
GRM185R60J105KE26
10
4.7
2.2
1.0
1.0
6.3
6.3
10
10
6.3
X5R
X5R
X5R
X5R
X5R
0805
0603
0603
0603
0603
Table 4: Surface Mount Capacitors.
Manufacturer
Part Number
Inductance (μH)
Saturated Rated
Current (mA)
DCR (mΩ)
Size (mm)
LxWxH
Type
Sumida
Sumida
Sumida
Coiltronics
Coiltronics
Coiltronics
Taiyo Yuden
Taiyo Yuden
Taiyo Yuden
CDRH2D14-1R5
CDRH2D14-2R2
CDRH2D14-3R3
SD3812-1R5
SD3812-2R2
SD3812-3R3
NR3010-1R5
NR3010-2R2
NR3010-3R3
1.5
2.2
3.3
1.5
2.2
3.3
1.5
2.2
3.3
1800
1500
1200
1580
1320
1100
1200
1100
870
63
94
125
78
111
159
80
95
140
3.2x3.2x1.55
3.2x3.2x1.55
3.2x3.2x1.55
4.0x4.0x1.2
4.0x4.0x1.2
4.0x4.0x1.2
3.0x3.0x1.0
3.0x3.0x1.0
3.0x3.0x1.0
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Shielded
Table 5: Suggested Inductors and Suppliers.
2500B.2008.03.1.0
www.analogictech.com
19
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Ordering Information
Voltage
Package
Channel 1
Channel 2
Channel 3
Marking1
Part Number (Tape and Reel)2
QFN34-20
Adj. (0.9V)
Adj. (0.6V)
Adj. (0.6V)
YUXYY
AAT2500BIZL-BAA-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.
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.
20
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2500B.2008.03.1.0
PRODUCT DATASHEET
AAT2500B
SystemPowerTM
Adjustable 3-Channel Regulator
Package Information1
QFN34-20
Index Area
(D/2 x E/2)
Detail "A"
Detail "B"
4.00 ± 0.05
0.925 ± 0.125
7.5° ± 7.5°
0.025 ± 0.025
0.214 ± 0.036
Side View
3.00 ± 0.05
Top View
Bottom View
0.40 ± 0.10
0.075 ± 0.075
Option B:
R0.30 (4x) max
Round corner
0.50 ± 0.05
Option A:
C0.30 (4x) max
Chamfered corner
0.24 ± 0.06
Pin 1 indicator
(optional)
Detail "A"
Detail "B"
All dimensions in millimeters.
1. 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.
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054
Phone (408) 737-4600
Fax (408) 737-4611
© 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.
2500B.2008.03.1.0
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21