ACUTECH AQ1541 Low dropout 1 amp voltage regulator with enable function Datasheet

AQ1541
Low Dropout
1 Amp Voltage Regulator
with Enable Function
Product Specification
Revision 2.2
General Description
The AQ1541 is a low dropout three terminal
voltage regulator, offered in popular fixed options
or an adjustable version that can set a precise
voltage from 1.22V to 12V with two external
resistors.
It drops into the footprint of the popular LM1117
SOT-223 and provides a true fourth pin
separated from the output tab. The extra pin
allows for an enable function that provides a
remote turn-off for low power consumption. It
draws virtually zero current in shutdown mode.
The Enable pin implements Sequential, Ratiometric, or Simultaneous sequencing schemes.
To assure accuracy within 1.5% over
temperature the heart of the AQ1541 is a selfcorrecting AcuRef™ bandgap reference.
On-chip current limit and thermal shutdown with
hysteresis protects against any combination of
overload and ambient temperature that might
cause the junction temperature to exceed safe
limits.
September 13, 2006
Applications
• Graphic cards
• PC motherboards
• Switching power supply post-regulation
• Telecom equipment
• DVD video player
Features
• Enable pin implements sequencing in
•
•
•
•
•
•
•
•
SOT223-3 footprint
Vout tolerance 1.5% over temperature
Eliminates expensive components
Stable with low cost 1uF capacitor
Low dropout voltage (1V at 1 Amp)
Thermal protection with hysteresis
Short circuit protection
Offered with 1.8V, 2.5V, and 3.3V fixed or
adjustable output
RoHS compliant available
The AQ1541 is featured in the new
SOT223 4-lead TetraPackTM package.
Typical Application
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AQ1541
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Pin Configuration
Pin Descriptions
Pin Name
Function
VIN
Accepts + VCC
VOUT
Regulated Output
Ground/Adjust
ENABLE
- VCC for fixed option / Adjust pin for adjustable option
Active high, ENABLE > (0.5V + VOUT). Connect to VIN when not in use.
Functional Block Diagram
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Ordering Information
Device
Operating Tj
%Tol
PKG Type
VOUT
Wrap
AQ1541
0C˚ ≤ 125C˚
1.0
SOT-223-4
1.8V
T&R
AQ1541CY-S4-18-TR
AQ1541
0C˚ ≤ 125C˚
1.0
SOT-223-4
1.8V
T&R
AQ1541CY-S4-18-TRL
AQ1541
0C˚ ≤ 125C˚
1.0
SOT-223-4
2.5V
T&R
AQ1541CY-S4-25-TR
AQ1541
0C˚ ≤ 125C˚
1.0
SOT-223-4
2.5V
T&R
AQ1541CY-S4-25-TRL
AQ1541
0C˚ ≤ 125C˚
1.0
SOT-223-4
3.3V
T&R
AQ1541CY-S4-33-TR
AQ1541
0C˚ ≤ 125C˚
1.0
SOT-223-4
3.3V
T&R
AQ1541CY-S4-33-TRL
AQ1541
0C˚ ≤ 125C˚
1.0
SOT-223-4
ADJ
T&R
AQ1541CY-S4-AJ-TR
AQ1541
0C˚ ≤ 125C˚
1.0
SOT-223-4
ADJ
T&R
AQ1541CY-S4-AJ-TRL
Note: The
Ordering Number
TRL parts are Lead Free and RoHS compliant.
Absolute Maximum Ratings
Stress greater than those listed under “Absolute Maximum Ratings” may cause permanent damage to the
device. These stress ratings only, and functional operation of the device at these or any conditions beyond
those indicated under recommended Operating Conditions is not implied. Exposure to “Absolute Maximum
Rating” for extended periods may affect device reliability. Use of standard ESD handling precautions is
required.
Parameter
Value
Units
Maximum VIN
18
Volts
Maximum VEN
18
Volts
Maximum IEN
10
mA
150
°C
0 to 125
°C
-65 to 150
°C
Lead Temperature (Soldering, 10 sec.) TO packages
300
°C
Lead Temperature (Soldering, 4sec.) SOT- 223 package
300
°C
Typical Value
Units
15
°C/W
Typical Value
Units
46
°C/W
Power Dissipation (Internally limited)
Maximum Junction Temperature
Operating Junction Temperature Range
Storage Temperature Range
Thermal Management
Thermal Resistance (Junction to TAB)
SOT-223
Thermal Resistance (Junction to Ambient)
SOT-223 (tab soldered to 1 in2 1 oz. copper PCB)
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Electrical Specifications
Electrical characteristics are guaranteed over the full temperature range 0ºC <Tj< 125ºC. Ambient temperature
must be de-rated based upon power dissipation and package thermal characteristics. Unless otherwise
specified: VENABLE = VIN = (VOUT + 1.5V), IOUT = 10 mA, Tj = 25C. All values in bold are over the full
temperature range.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
-1
VOUT
+1
%
-1.5
VOUT
+1.5
%
0.035
0.2
%
VOUT
Output Voltage (1)
LNREG
Line Regulation (1)
∆VIN = VOUT + (1.5V to 10V)
LDREG
Load Regulation (1)
∆IOUT = (10mA to 1 Amp)
0.2
0.4
%
IOUT = 100 mA
0.91
0.95
V
IOUT = 500 mA
0.93
0.95
V
IOUT = 1 Amp
0.95
1.0
V
VD
ISC
Drop out Voltage (1, 2)
Current Limit (1)
IQON
Quiescent Current ON
IQOFF
Quiescent Current Off
0°C ≤Tj ≤ 125°C
VIN-VOUT = 2V
1.1
VIN = VENABLE = 5V
1.5
7.5
0°C ≤Tj ≤ 125°C
A
9.0
mA
10
mA
VIN = 5V VENABLE = GND
0.1
0.5
µA
0°C ≤Tj ≤ 125°C
0.1
1.0
µA
VIL
Enable Pin Voltage (OFF)
With respect to GND
VIH
Enable Pin Voltage (ON)
With respect to VOUT
0.5
0.8
V
IIL
Enable Pin Current (OFF)
ENABLE =
0V, VIN = 5V
0.1
1.0
µA
IIH
Enable Pin Current (ON)
ENABLE =
VIN = 5V
10
25
µA
1.220
1.232
V
1.238
V
0.25
Adjustable version only
1.208
0°C ≤Tj ≤ 125°C
1.202
0.45
V
VADJ
Reference Voltage
IADJ
Adjust Pin Current (5)
Adjustable version only
20
40
µA
∆ IADJ
Adjust Pin Current (5)
Change
10mA ≤ IOUT≤ 1Amp
1.4 ≤ VIN ≤ 18V
0.2
5.0
µA
Minimum Load Current (5)
To Maintain regulation
0.5
2.0
mA
IQMIN
TC
Temperature Coefficient
TS
VN
PSRR
TSD
TSDHYST
0.005
%/°C
Temperature Stability
0.5
RMS Output Noise (3)
0.003
%/°C
%
VOUT
Ripple Rejection Ratio (4)
Vin = 5V
Thermal Shutdown
Junction Temperature
60
TSD Hysteresis
72
dB
150
°C
25
°C
Notes: (1) Low duty cycle pulse testing with Kelvin connections required.
(2) Measure (VIN - VOUT) when ∆VOUT, OR ∆VREF = 1%
(3) Bandwidth of 10Hz to 10kHz
(4) 120Hz input ripple
(5) Adjustable version only
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Typical Response Curves
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Application Notes
1. Typical Application
Notes:
1. Output voltage is 1.22V * (R2 +R1)/R1
2. Input and output capacitors should be located close to the device.
3. The AQ1541 will remain stable with C1 and C2 as low as 1.0µF. Overall transient
performance is improved with increased capacitance.
4. The output is fully enabled when EN is 800 mV above the expected output. EN should
not be pulled substantially above Vin. EN may be driven by either a digital or analog
signal to control either turn-on time or to give full control of risetime.
2. Stability
An input capacitor is recommended. A 1.0µF capacitor on the input is a suitable input
bypassing for almost all applications. A larger capacitor is also suitable. In the adjustable
version the “adjust” terminal can be bypassed to ground with a bypass capacitor (CADJ) to
improve ripple rejection. This bypass capacitor prevents ripple from being amplified as the
output voltage is increased. At any ripple frequency, the impedance of the CADJ should be
less than R1 (being R1 the resistor between the output and the adjust pin) to prevent the
ripple from being amplified:
Z = 1/(2π*fRIPPLE* CADJ) < R1
R1 is normally in the range of 1KΩ.
The output capacitor is critical in maintaining regular stability. The AQ1541 is stable with an
output capacitor greater than 1uF. Of course any increase of the output capacitor will merely
improve the loop stability and the load transient response. In the case of the adjustable
regulator, when the CADJ is used, a larger output capacitance may be required. Tantalum
Capacitors exhibit the best stability over a wide range of loads and are recommended.
3. Output Voltage
The AQ1541 adjustable version develops a 1.22V reference voltage between the output and
the adjust pin terminal. This voltage is applied across the resistor R1 to generate a constant
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current (I1). The current from the adjust terminal could introduce error to the output, but since
it is very small (< 20µA) compared with the current I1 and very constant with line and load
changes, the error can be ignored. The constant current I1 then flows through resistor R2
and sets the output voltage to the desired level.
For fixed voltages the resistor R1 and R2 are integrated inside the devices.
The AQ1541 regulates the voltage that appears between its output and ground pins or
between its output and adjust pins. In some cases, line resistances can introduce errors to
the voltage across the load. To obtain the best load regulation a few precautions are needed.
For example it is important to minimize the line resistances to the load, so the load itself
should be tied directly to the output terminal on the positive side and directly to the ground
terminal on the negative side.
When the adjustable regulator is used, the best performance is obtained with the positive
side of the resistor R1 tied directly to the output terminal of the regulator rather than near the
load. This will eliminate line drops from appearing effectively in series with the reference and
degrading regulation. In addition the ground side of the resistor R2 can be returned near the
ground of the load to provide remote ground sensing and improve load regulation. A
capacitor (470pF) between the ADJ pin and system ground will enhance stability.
4. Enable/Sequencing
The AQ1541 provides an enable function. The EN pin has to be at least 800 mV higher than
the output voltage for the device to be fully turned on. When the voltage of the EN pin is low
the device is in shutdown mode and it will not draw any current from the VIN terminal.
ENABLE
OUT
0
FIG.2 ENABLE 0-5V, Output follows to 3.3V out
(1V/div vertical, 200us/div horizontal)
In addition the enable function includes a sequencing feature, because when the enable pin
ramps in voltage the output voltage follows (it will be around 800 mV less than the enable
voltage until it reaches the regulation voltage) as shown in Fig. 2 above.
In applications where multiple regulated supply rails are required, it is often required that the
relationship between the various supply voltages be controlled during start-up and
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shutdown. To this end, the AQ1541 allows for an analog control of the output voltage via the
ENBL pin. This allows for sequential, ratio-metric and simultaneous sequencing schemes.
In a simple sequencing scheme, the output voltage can be delayed with respect to the
application of Vin by connecting an RC network as shown in figure 3 below. This RC
generates a slow ramp at the enable pin; the output follows 800 mV below this ramp until the
output reaches regulation.
Virtually no current flows into the enable pin until it reaches the enable voltage which is
equal to Vout + 800 mV. Therefore, the time delay can be reliably set by using the time
constant of a known RC to slow the of the enable pin.
FIG.3 Enable delay circuit
The Enable and Output raise with respect to a Vin is shown in Fig.3 below. Vin = 5V, Vout =
2.5V, RC = 100 KΩ and 100 nF. The output is in regulating 13 ms after the input supply is
applied.
FIG. 4 Enable circuit delays output
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5. Protection Diodes
Unlike older regulators, the AQ1541 family does not need any protection diodes between
the adjustment pin and output or from the output to the input to prevent over-stressing the
die. Internal resistors are limiting the internal current paths on the adjustment pin.
Therefore, even with capacitors on the adjustment pin, no protection diode is needed to
ensure device safety under short circuit conditions. External diodes between the input and
output are not usually needed. Only if high value output capacitors are used (> 1000uF)
and the input is instantaneously shorted to ground, can damage occur.
6. Thermal Considerations
When an integrated circuit operates with an appreciable current, its junction temperature is
elevated. It is important to quantify its thermal limits in order to achieve acceptable
performance and reliability. This limit is determined by summing the individual parts
consisting of a series of temperature rises from the semiconductor junction to the operating
environment. The heat generated at the device junction flows through the die to the die
attach pad, through the lead frame to the surrounding case material, to the printed circuit
board, and eventually to the ambient environment.
The AQ1541 regulators have internal thermal shutdown to protect the device from overheating. Under all possible operating conditions, the junction temperature of the AQ1541
must be lower than 125°C. A heatsink may be required depending on the maximum power
dissipation and maximum ambient temperature of the application.
To determine if a heatsink is needed, the power dissipated by the regulator, PD, must be
calculated:
PD= (VIN-VOUT) IL
where the IL is the load current.
The next parameter which must be calculated is the maximum allowable temperature rise,
T(max):
T(max)=TJ(max)-TA(max)
where TJ(max) is the maximum allowable junction temperature (125°C), and TA(max) is the
maximum ambient temperature which will be encountered in the application.
Using the calculated values for T(max) and PD, the maximum allowable value for the
junction to ambient thermal resistance (θJA) can be calculated:
θJA=T(max)/ PD
If the maximum allowable value for θJA is found to be greater than the junction to ambient
thermal resistance for the package used, no heatsink is needed since the package alone will
dissipate enough heat to satisfy these requirements.
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Package Dimensions
SOT223-4 TetraPackTM
Contact Information
Acutechnology Semiconductor Inc.
3487 McKee Rd. Suite 52
San Jose CA , USA 95127
TEL:
FAX:
website:
(408) 259-2300
(408) 259-9160
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Disclaimer
The information furnished by Acutechnology in this data sheet is believed to be accurate and reliable. However,
Acutechnology assumes no responsibility for its use. Acutechnology reserves the right to change circuitry and specifications
at any time without notification to the customer.
Life Support Policy
Acutechnology Products are not designed or authorized for use as components in life support devices or systems where
malfunction of a product can reasonably be expected to result in personal injury. Life support devices or systems are
devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to
perform can be reasonably expected to result in a significant injury to the user.
TetraPack and AcuRef are trademarks of Acutechnology Semiconductor Inc
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