AAT AAT3236 300ma cmos high performance ldo Datasheet

AAT3236
300mA CMOS High Performance LDO
General Description
Features
The AAT3236 is a MicroPower low dropout (LDO)
linear regulator designed to deliver a continuous
300mA output load current and is capable of handling short duration current peaks up to 500mA.
With a very small footprint SOT23-5 package, it is
ideally suited for portable applications where low
noise, high power supply ripple rejection (PSRR),
extended battery life, and small size are critical.
The AAT3236 features fast transient response and
low output self noise for powering sensitive RF circuitry. Other features include low quiescent current, typically 100µA, and low dropout voltage, typically 300mV at full output load current. The device
has internal output short-circuit protection and thermal shutdown to prevent damage under extreme
conditions.
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The AAT3236 also features a low-power shutdown
mode for longer battery life. A bypass pin is provided to improve PSRR performance by connecting an external capacitor from the device reference
output to ground.
The AAT3236 is available in a Pb-free, space-saving SOT23-5 or SC70JW-8 package in nine factory-programmed voltages: 2.5V, 2.7V, 2.8V, 2.85V,
3.0V, 3.1V, 3.3V, 3.5V, or 3.6V.
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PowerLinear™
500mA Peak Output Current
Low Dropout - Typically 300mV at 300mA
Guaranteed 300mA Output
High Accuracy: ±1.5%
100µA Quiescent Current
High Power Supply Ripple Rejection
— 70dB at 1kHz
— 50dB at 10kHz
Very Low Self Noise: 45µVrms
Noise Reduction Bypass Capacitor
Short-Circuit Protection
Over-Temperature Protection
Shutdown Mode for Longer Battery Life
Low Temperature Coefficient
Nine Factory-Programmed Output Voltages
SOT23 5-Pin or SC70JW 8-Pin Package
Applications
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Cellular Phones
Notebook Computers
Personal Portable Electronics
Portable Communication Devices
Typical Application
VIN
VOUT
IN
ON/OFF
AAT3236
EN
OUT
BYP
GND
1μF
GND
3236.2007.03.1.4
10nF
2.2μF
GND
1
AAT3236
300mA CMOS High Performance LDO
Pin Descriptions
Pin #
Symbol
Function
SOT23-5
SC70JW-8
1
5, 6
IN
2
8
GND
3
7
EN
Enable pin. When pulled low, the PMOS pass transistor turns
off and all internal circuitry enters low-power mode, consuming
less than 1µA. This pin should not be left floating.
4
1
BYP
Bypass capacitor connection; to improve AC ripple rejection,
connect a 10nF capacitor to GND. This will also provide a softstart function.
5
2, 3, 4
OUT
Output pin; should be decoupled with 2.2µF capacitor.
Input voltage pin; should be decoupled with 1µF or greater
capacitor.
Ground connection pin.
Pin Configuration
SOT23-5
(Top View)
IN
2
1
GND
2
EN
3
SC70JW-8
(Top View)
5
4
OUT
BYP
BYP
OUT
OUT
OUT
1
8
2
7
3
6
4
5
GND
EN
IN
IN
3236.2007.03.1.4
AAT3236
300mA CMOS High Performance LDO
Absolute Maximum Ratings1
TA = 25°C, unless otherwise noted.
Symbol
Description
VIN
VENIN(MAX)
IOUT
TJ
Input Voltage
Maximum EN to Input Voltage
DC Output Current
Operating Junction Temperature Range
Value
Units
6
0.3
PD/(VIN - VO)
-40 to 150
V
V
mA
°C
Value
Units
190
526
°C/W
mW
Rating
Units
(VOUT + 0.3) to 5.5
-40 to +85
V
°C
Thermal Information2
Symbol
ΘJA
PD
Description
Maximum Thermal Resistance (SOT23-5, SC70JW-8)
Maximum Power Dissipation (SOT23-5, SC70JW-8)
Recommended Operating Conditions
Symbol
VIN
T
Description
Input Voltage
Ambient Temperature Range
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 a demo board.
3236.2007.03.1.4
3
AAT3236
300mA CMOS High Performance LDO
Electrical Characteristics
VIN = VOUT(NOM) + 1V, IOUT = 1mA, COUT = 2.2µF, CIN = 1µF, CBYP = 10nF, TA = -40°C to +85°C, unless otherwise noted. For typical values, TA = 25°C.
Symbol
VOUT
IOUT
VDO
ISC
IQ
ISD
ΔVOUT/
VOUT*ΔVIN
Description
Conditions
Output Voltage Tolerance
IOUT = 1mA to 300mA
Output Current
Dropout Voltage1
Short-Circuit Current
Ground Current
Shutdown Current
VOUT > 1.2V
IOUT = 300mA
VOUT < 0.4V
VIN = 5V, No Load, EN = VIN
VIN = 5V, EN = 0V
Line Regulation
VIN = VOUT + 1 to 5.5V
ΔVOUT(line) Dynamic Line Regulation
ΔVOUT(load)
VEN(L)
VEN(H)
IEN
PSRR
TSD
THYS
eN
TC
Dynamic Load Regulation
Enable Threshold Low
Enable Threshold High
Leakage Current Enable Pin
Power Supply Rejection Ratio
Min
Typ
TA = 25°C
-1.5
TA = -40 to 85°C -2.5
300
300
600
100
VIN = VOUT + 1V to VOUT + 2V,
IOUT = 150mA, TR/TF = 2µs
IOUT = 1mA to 150mA, TR <5µs
Max
Units
1.5
2.5
%
150
1
mA
mV
mA
µA
µA
0.07
%/V
500
1
mV
30
0.6
1.5
VEN = 5V
1kHz
IOUT = 10mA, CBYP = 10nF 10kHz
1MHz
Over-Temperature Shutdown
Threshold
Over-Temperature Shutdown
Hysteresis
Output Noise
Output Voltage Temperature
Coefficient
1
mV
V
V
µA
70
50
47
dB
150
°C
10
°C
45
µVRMS
22
ppm/°C
1. VDO is defined as VIN - VOUT when VOUT is 98% of nominal.
4
3236.2007.03.1.4
AAT3236
300mA CMOS High Performance LDO
Typical Characteristics
Dropout Characteristics
Dropout Voltage vs. Temperature
3.1
Output Voltage (V)
Dropout Voltage (mV)
400
350
IL = 300mA
300
250
200
150
IL = 150mA
100
IL = 100mA
50
IOUT = 10mA
IOUT = 0mA
3.0
IOUT = 50mA
2.9
IOUT = 100mA
IOUT = 150mA
2.8
IOUT = 300mA
IL = 50mA
0
2.7
-40
-20
0
20
40
60
80
100
120
2.9
3.0
3.3
Ground Current vs. Input Voltage
Ground Current vs. Temperature
105
Ground Current (μA)
120
100
95
90
85
VOUT = 3.0V
100
IOUT = 0
80
IOUT = 150mA
IOUT = 300mA
IOUT = 50mA
60
40
20
0
80
-50
0
50
100
2
150
3
4
5
Input Voltage (V)
Temperature (°C)
Dropout Voltage vs. Output Current
Output Voltage vs. Temperature
350
3.014
300
Output Voltage (V)
Dropout Voltage (mV)
3.2
Input Voltage (V)
Temperature (°C)
Ground Current (μA)
3.1
85 C
250
25 C
200
-40 C
150
100
50
3.013
3.012
3.011
3.01
3.009
3.008
3.007
0
0
50
100
150
200
Output Current (mA)
3236.2007.03.1.4
250
300
-50
0
50
100
150
Temperature (°C)
5
AAT3236
300mA CMOS High Performance LDO
Typical Characteristics
On/Off Transient Response
On/Off Transient Response
(No CBYP Capacitor)
(CBYP = 10nF)
EN (2V/div)
EN (2V/div)
150mA
VOUT (1V/div)
10mA
300mA
Time (100µs/div)
Time (5ms/div)
Line Transient Response
Load Transient Response
3.15
5
3.10
4
3.05
3
3.00
2
2.95
2.90
3.10
1200
3.05
1000
3.00
800
2.95
600
2.90
400
1
2.85
200
0
2.80
Output Voltage (V)
6
0
Time (5µs/div)
Time (100µs/div)
Power Supply Rejection Ratio
vs. Frequency
1.2
90
1
80
PSRR (dB)
Short-Circuit Current (A)
Short-Circuit Current
0.8
0.6
0.4
Output Current (mA)
3.20
Input Voltage (V)
Output Voltage (V)
150mA
300mA
70
4.7μF
60
2.2μF
10μF
50
40
0.2
1.0μF
30
0
10
Time (10ms/div)
6
VOUT (1V/div)
10mA
100
1k
10k
100k
1m
10m
Frequency (Hz)
3236.2007.03.1.4
AAT3236
300mA CMOS High Performance LDO
Typical Characteristics
Noise Amplitude in nVrms/√Hz
(50nVrms/√Hz per div)
Output Self Noise
VEN(H) and VEN(L) vs. VIN
500
1.25
1.2
VEN(H)
1.15
1.1
1.05
VEN(L)
0
10
100
1k
10k
100k
Frequency (Hz)
3236.2007.03.1.4
1m
10m
1
2.5
3
3.5
4
4.5
5
5.5
VIN (V)
7
AAT3236
300mA CMOS High Performance LDO
Functional Block Diagram
IN
OUT
Over-Current
Protection
Over-Temperature
Protection
EN
BYP
Voltage
Reference
GND
Functional Description
The AAT3236 is intended for LDO regulator applications where output current load requirements
range from no load to 300mA. The AAT3236 is
capable of handling peak output currents up to
500mA. Refer to the Thermal Considerations section of this datasheet for details on device operation
at 500mA peak loads.
The advanced circuit design of the AAT3236 provides excellent input-to-output isolation, which
allows for good power supply ripple rejection characteristics. To optimize for very low output self
noise performance, a bypass capacitor pin has
been provided to decrease noise generated by the
internal voltage reference.
8
The LDO regulator output has been specifically
optimized to function with low-cost, low-equivalent
series resistance (ESR) ceramic capacitors.
However, the design will allow for operation over a
wide range of capacitor types.
The device enable circuit is provided to shut down
the LDO regulator for power conservation in portable
products. The enable circuit has an additional output capacitor discharge circuit to assure sharp application circuit turn-off upon device shutdown.
This LDO regulator has complete short-circuit and
thermal protection. The integral combination of
these two internal protection circuits gives the
AAT3236 a comprehensive safety system during
extreme adverse operating conditions.
3236.2007.03.1.4
AAT3236
300mA CMOS High Performance LDO
Applications Information
Input Capacitor
Typically, a 1µF or larger capacitor is recommended for CIN in most applications. A CIN capacitor is
not required for basic LDO regulator operation.
However, if the AAT3236 is physically located more
than six centimeters from an input power source, a
CIN capacitor will be needed for stable operation.
CIN should be located as closely to the device VIN
pin 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, for
300mA LDO regulator output operation, 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.
Output Capacitor
For proper load voltage regulation and operational
stability, a capacitor is required between pins VOUT
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 AAT3236 has been specifically designed to
function with very low ESR ceramic capacitors.
Although the device is intended to operate with
these low ESR capacitors, it is stable over a very
wide range of capacitor ESR, thus it will also work
with higher ESR tantalum or aluminum electrolytic
capacitors.
However, 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 AAT3236 should use 2.2µF or
greater for COUT. If desired, COUT may be
increased without limit.
3236.2007.03.1.4
In low output current applications where output
load is less than 10mA, the minimum value for
COUT can be as low as 0.47µF.
Bypass Capacitor and Low Noise
Applications
A bypass capacitor pin is provided to enhance the
very low noise characteristics of the AAT3236 LDO
regulator. The bypass capacitor is not necessary
for operation of the AAT3236. However, for best
device performance, a small ceramic capacitor
should be placed between the bypass pin (BYP)
and the device ground pin (GND). The value of
CBYP may range from 470pF to 10nF. For lowest
noise and best possible power supply ripple rejection performance a 10nF capacitor should be used.
To practically realize the highest power supply ripple rejection and lowest output noise performance,
it is critical that the capacitor connection between
the BYP pin and GND pin be direct and PCB traces
should be as short as possible. Refer to the PCB
Layout Recommendations section of this datasheet
for examples.
There is a relationship between the bypass capacitor value and the LDO regulator turn-on time. In
applications where fast device turn-on time is
desired, the value of CBYP should be reduced.
In applications where low noise performance
and/or ripple rejection are less of a concern, the
bypass capacitor may be omitted. The fastest
device turn-on time will be realized when no
bypass capacitor is used.
DC leakage on this pin can affect the LDO regulator output noise and voltage regulation performance. For this reason, the use of a low leakage,
high quality ceramic (NPO or C0G type) or film
capacitor is highly recommended.
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use
with the AAT3236. 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
9
AAT3236
300mA CMOS High Performance LDO
footprint, and is non-polarized. 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 generally have tight tolerance and are very stable over
temperature. Larger capacitor values are usually
composed of X7R, X5R, Z5U, or Y5V dielectric
materials. These two 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 that are physically large in size will have
a lower ESR when compared to a smaller sized
capacitor of 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.
Enable Function
The AAT3236 features an LDO regulator enable /
disable function. This pin (EN) is active high and is
compatible with CMOS logic. To assure the LDO
10
regulator will switch on, the EN turn-on control level
must be greater than 2.0V. The LDO regulator will
go into the disable shutdown mode when the voltage on the EN pin falls below 0.6V. 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.
When the LDO regulator is in the shutdown mode,
an internal 1.5kΩ resistor is connected between
VOUT and GND. This is intended to discharge COUT
when the LDO regulator is disabled. The internal
1.5kΩ has no adverse effect on device turn-on time.
Short-Circuit Protection
The AAT3236 contains an internal short-circuit protection circuit that will trigger when the output load
current exceeds 750mA. Under short-circuit conditions, the output will be limited to 750mA until the
LDO regulator package power dissipation exceeds
the device thermal limit or the until the short-circuit
condition is removed.
Thermal Protection
The AAT3236 has an internal thermal protection circuit which will turn on when the device die temperature exceeds 150°C. The internal thermal protection circuit will actively turn off the LDO regulator
output pass device to prevent the possibility of overtemperature damage. The LDO regulator output
will remain in a shutdown state until the internal die
temperature falls back below the 150°C trip point.
The combination and interaction between the shortcircuit and thermal protection systems allows the
LDO regulator to withstand indefinite short-circuit
conditions without sustaining permanent damage.
No-Load Stability
The AAT3236 is designed to maintain output voltage regulation and stability under operational noload conditions. This is an important characteristic
for applications where the output current may drop
to zero.
3236.2007.03.1.4
AAT3236
300mA CMOS High Performance LDO
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 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
The AAT3236 is designed to deliver a continuous
output load current of 300mA under normal operations and can supply up to 500mA during circuit
start-up conditions. This is desirable for circuit
applications where there might be a brief high inrush 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 datasheet.
At any given ambient temperature (TA), the maximum package power dissipation can be determined by the following equation:
3236.2007.03.1.4
PD(MAX) =
TJ(MAX) - TA
θJA
Constants for the AAT3236 are TJ(MAX), the maximum junction temperature for the device which is
125°C, and ΘJA = 190°C/W, the package thermal
resistance. Typically, maximum conditions are calculated at the maximum operating temperature
where TA = 85°C, under normal ambient conditions
TA = 25°C. Given TA = 85°C, the maximum package power dissipation is 211mW. At TA = 25°C, the
maximum package power dissipation is 526mW.
The maximum continuous output current for the
AAT3236 is a function of the package power dissipation and the input-to-output voltage drop across
the LDO regulator. Refer to the following simple
equation:
IOUT(MAX) <
PD(MAX)
VIN - VOUT
For example, if VIN = 4.2V, VOUT = 3.3V, and TA =
25°C, IOUT(MAX) < 584mA. If the output load current
were to exceed 584mA or if the ambient temperature were to increase, the internal die temperature
would increase. If the condition remained constant, the LDO regulator thermal protection circuit
would activate.
To determine the maximum input voltage for a
given load current, 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 - VOUT)IOUT + (VIN x IGND)
This formula can be solved for VIN to determine the
maximum input voltage.
VIN(MAX) =
PD(MAX) + (VOUT × IOUT)
IOUT + IGND
The following is an example for an AAT3236 set for
a 3.0V output:
11
AAT3236
300mA CMOS High Performance LDO
VOUT
= 3.0V
IOUT
= 500mA
IGND
= 150μA
VIN(MAX)
526mW + (3.0V × 500mA)
=
500mA + 150μA
For a 500mA output current and a 1.2 volt drop
across the AAT3236 at an ambient temperature of
25°C, the maximum on-time duty cycle for the
device would be 87.57%.
The following family of curves show the safe operating area for duty-cycled operation from ambient
room temperature to the maximum operating level.
VIN(MAX) = 4.05V
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 25°C)
Higher input-to-output voltage differentials can be
obtained with the AAT3236, while maintaining device
functions within the thermal safe operating area. To
accomplish this, the device thermal resistance must
be reduced by increasing the heat sink area or by
operating the LDO regulator in a duty-cycled mode.
For example, an application requires VIN = 4.2V
while VOUT = 3.0V at a 500mA load and TA = 25°C.
VIN is greater than 4.05V, which is the maximum
safe continuous input level for VOUT = 3.0V at
500mA for TA = 25°C. To maintain this high input
voltage and output current level, the LDO regulator
must be operated in a duty-cycled mode. Refer to
the following calculation for duty-cycle operation:
Voltage Drop (V)
Thus, the AAT3236 can sustain a constant 3V output
at a 500mA load current as long as VIN is ≤ 4.05V at
an ambient temperature of 25°C.
3.5
200 mA
3
500 mA
2.5
2
400 mA
1.5
300 mA
1
0.5
0
0
10
20
30
40
50
60
70
80
90
100
Duty Cycle (%)
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 50°C)
3.5
Voltage Drop (V)
From the discussion above, PD(MAX) was determined to equal 526mW at TA = 25°C.
200 mA
3
100 mA
500 mA
2.5
2
400 mA
1.5
1
300 mA
0.5
0
0
IGND = 150μA
IOUT
= 500mA
VIN
= 4.2V
30
40
50
60
70
80
90
100
Device Duty Cycle vs. VDROP
(VOUT = 2.5V @ 85°C)
PD(MAX)
(VIN - VOUT)IOUT + (VIN × IGND)
%DC = 87.57%
PD(MAX) is assumed to be 526mW.
Voltage Drop (V)
3.5
526mW
%DC = 100
(4.2V - 3.0V)500mA + (4.2V × 150μA)
12
20
Duty Cycle (%)
VOUT = 3.0V
%DC = 100
10
3
100 mA
2.5
200 mA
2
1.5
500 mA
1
400 mA
0.5
300 mA
0
0
10
20
30
40
50
60
70
80
90
100
Duty Cycle (%)
3236.2007.03.1.4
AAT3236
300mA CMOS High Performance LDO
High Peak Output Current Applications
Some applications require the LDO regulator to
operate at a continuous nominal level with short
duration, high-current peaks. The duty cycles for
both output current levels must be taken into
account. To do so, first calculate the power dissipation at a nominal continuous level and then factor
in the additional power dissipation due to the short
duration, high-current peaks.
For example, a 3.3V system using an AAT3236IGV3.3-T1 operates at a continuous 100mA load current
level and has short 500mA current peaks. The current peak occurs for 378µs out of a 4.61ms period.
It will be assumed the input voltage is 4.2V.
First, the current duty cycle in percent must be
calculated:
% Peak Duty Cycle: X/100 = 378µs/4.61ms
% Peak Duty Cycle = 8.2%
The LDO regulator will be under the 100mA load
for 91.8% of the 4.61ms period and have 500mA
peaks occurring for 8.2% of the time. Next, the
continuous nominal power dissipation for the
100mA load should be determined and then multiplied by the duty cycle to conclude the actual
power dissipation over time.
PD(MAX) = (VIN - VOUT)IOUT + (VIN x IGND)
PD(100mA) = (4.2V - 3.3V)100mA + (4.2V x 150µA)
PD(100mA) = 90.6mW
PD(91.8%D/C) = %DC x PD(100mA)
PD(91.8%D/C) = 0.918 x 90.6mW
PD(91.8%D/C) = 83.2mW
The power dissipation for 100mA load occurring for
91.8% of the duty cycle will be 83.2mW. Now the
power dissipation for the remaining 8.2% of the
duty cycle at the 500mA load can be calculated:
PD(MAX) = (VIN - VOUT)IOUT + (VIN x IGND)
PD(500mA) = (4.2V - 3.3V)500mA + (4.2V x 150µA)
PD(500mA) = 450.6mW
PD(8.2%D/C) = %DC x PD(500mA)
PD(8.2%D/C) = 0.082 x 450.6mW
PD(8.2%D/C) = 37mW
3236.2007.03.1.4
The power dissipation for 500mA load occurring for
8.2% of the duty cycle will be 37mW. Finally, the two
power dissipation levels can summed to determine
the total true power dissipation under the varied load.
PD(total) = PD(100mA) + PD(500mA)
PD(total) = 83.2mW + 37mW
PD(total) = 120.2mW
The maximum power dissipation for the AAT3236
operating at an ambient temperature of 25°C is
526mW. The device in this example will have a
total power dissipation of 120.2mW. This is well
within the thermal limits for safe operation of the
device.
Printed Circuit Board Layout
Recommendations
In order to obtain the maximum performance from
the AAT3236 LDO regulator, very careful attention
must be considered in regard to the printed circuit
board (PCB) layout. If grounding connections are
not properly made, power supply ripple rejection,
low output self noise, and transient response can
be compromised.
Figure 1 shows a common LDO regulator layout
scheme. The LDO regulator, external capacitors
(CIN, COUT and CBYP), and the load circuit are all
connected to a common ground plane. This type of
layout will work in simple applications where good
power supply ripple rejection and low self noise are
not a design concern. For high performance applications, this method is not recommended.
The problem with the layout in Figure 1 is that the
bypass capacitor and output capacitor share the
same ground path to the LDO regulator ground pin,
along with the high-current return path from the load
back to the power supply. The bypass capacitor
node is connected directly to the LDO regulator
internal reference, making this node very sensitive
to noise or ripple. The internal reference output is
fed into the error amplifier, thus any noise or ripple
from the bypass capacitor will be subsequently
amplified by the gain of the error amplifier. This
effect can increase noise seen on the LDO regulator
output, as well as reduce the maximum possible
power supply ripple rejection. There is PCB trace
impedance between the bypass capacitor connec13
AAT3236
300mA CMOS High Performance LDO
tion to ground and the LDO regulator ground connection. When the high load current returns through
this path, a small ripple voltage is created, feeding
into the CBYP loop.
any load noise or ripple current feedback through
the LDO regulator.
Evaluation Board Layout
Figure 2 shows the preferred method for the
bypass and output capacitor connections. For low
output noise and highest possible power supply
ripple rejection performance, it is critical to connect
the bypass and output capacitor directly to the LDO
regulator ground pin. This method will eliminate
VIN
LDO
Regulator
EN
DC INPUT
Note: Board layout shown is not to scale.
ILOAD
IIN
VIN
The AAT3236 evaluation layout (Figures 3, 4, and
5) follows the recommend printed circuit board layout procedures and can be used as an example for
good application layouts.
VOUT
BYP
GND
CIN
CBYP
IGND
IRIPPLE
IBYP + noise
COUT
RLOAD
CBYP
GND
LOOP
GND
RTRACE
RTRACE
RTRACE
RTRACE
ILOAD return + noise and ripple
Figure 1: Common LDO Regulator Layout with CBYP Ripple Feedback Loop.
ILOAD
IIN
VIN
VIN
LDO
Regulator
EN
VOUT
BYP
GND
DC INPUT
CIN
IGND
CBYP
COUT
RLOAD
IBYP only
IRIPPLE
GND
RTRACE
RTRACE
RTRACE
RTRACE
ILOAD return + noise and ripple
Figure 2: Recommended LDO Regulator Layout.
14
3236.2007.03.1.4
AAT3236
300mA CMOS High Performance LDO
Figure 3: Evaluation Board
Component Side Layout.
Figure 4: Evaluation Board
Solder Side Layout.
Figure 5: Evaluation Board Top Side
Silk Screen Layout / Assembly Drawing.
3236.2007.03.1.4
15
AAT3236
300mA CMOS High Performance LDO
Ordering Information
Output Voltage
Package
Marking1
Part Number (Tape and Reel)2
2.5V
SOT23-5
BRXYY
AAT3236IGV-2.5-T1
2.7V
SOT23-5
CPXYY
AAT3236IGV-2.7-T1
2.8V
SOT23-5
CQXYY
AAT3236IGV-2.8-T1
2.85V
SOT23-5
CRXYY
AAT3236IGV-2.85-T1
3.0V
SOT23-5
CSXYY
AAT3236IGV-3.0-T1
3.1V
SOT23-5
GAXYY
AAT3236IGV-3.1-T1
3.3V
SOT23-5
CDXYY
AAT3236IGV-3.3-T1
3.5V
SOT23-5
CUXYY
AAT3236IGV-3.5-T1
3.6V
SOT23-5
2.5V
SC70JW-8
BRXYY
AAT3236IJS-2.5-T1
2.7V
SC70JW-8
CPXYY
AAT3236IJS-2.7-T1
2.8V
SC70JW-8
CQXYY
AAT3236IJS-2.8-T1
2.85V
SC70JW-8
CRXYY
AAT3236IJS-2.85-T1
2.9V
SC70JW-8
3.0V
SC70JW-8
CSXYY
AAT3236IJS-3.0-T1
3.1V
SC70JW-8
GAXYY
AAT3236IJS-3.1-T1
3.3V
SC70JW-8
CDXYY
AAT3236IJS-3.3-T1
3.5V
SC70JW-8
AAT3236IJS-3.5-T1
3.6V
SC70JW-8
AAT3236IJS-3.6-T1
AAT3236IGV-3.6-T1
AAT3236IJS-2.9-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.
1. XYY = assembly and date code.
2. Sample stock is generally held on all part numbers listed in BOLD.
16
3236.2007.03.1.4
AAT3236
300mA CMOS High Performance LDO
Package Information
SOT23-5
2.85 ± 0.15
1.90 BSC
10° ± 5°
0.40 ± 0.10
0.075 ± 0.075
0.15 ± 0.07
4° ± 4°
1.10 ± 0.20
0.60 REF
1.20 ± 0.25
2.80 ± 0.20
1.575 ± 0.125
0.95
BSC
GAUGE PLANE
0.45 ± 0.15
0.60 REF
0.10 BSC
SC70JW-8
2.20 ± 0.20
1.75 ± 0.10
0.50 BSC 0.50 BSC 0.50 BSC
0.225 ± 0.075
2.00 ± 0.20
0.100
7° ± 3°
0.45 ± 0.10
4° ± 4°
0.05 ± 0.05
0.15 ± 0.05
1.10 MAX
0.85 ± 0.15
0.048REF
2.10 ± 0.30
All dimensions in millimeters
3236.2007.03.1.4
17
AAT3236
300mA CMOS High Performance LDO
© Advanced Analogic Technologies, Inc.
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18
3236.2007.03.1.4