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AQ1541
Low Dropout 1 Amp Voltage Regulator with Enable Function
Product Specification Revision 2.2 September 13, 2006
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 AcuRefTM 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. The AQ1541 is featured in the new SOT223 4-lead TetraPackTM package.
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
Typical Application
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Pin Configuration
Pin Descriptions
Pin Name VIN VOUT Ground/Adjust ENABLE Function Accepts + VCC Regulated Output - 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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AQ1541
Ordering Information
Device AQ1541 AQ1541 AQ1541 AQ1541 AQ1541 AQ1541 AQ1541 AQ1541
Note: The
Operating Tj 0C 125C 0C 125C 0C 125C 0C 125C 0C 125C 0C 125C 0C 125C 0C 125C
%Tol 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0
PKG Type SOT-223-4 SOT-223-4 SOT-223-4 SOT-223-4 SOT-223-4 SOT-223-4 SOT-223-4 SOT-223-4
VOUT 1.8V 1.8V 2.5V 2.5V 3.3V 3.3V ADJ ADJ
Wrap T&R T&R T&R T&R T&R T&R T&R T&R
Ordering Number AQ1541CY-S4-18-TR AQ1541CY-S4-18-TRL AQ1541CY-S4-25-TR AQ1541CY-S4-25-TRL AQ1541CY-S4-33-TR AQ1541CY-S4-33-TRL AQ1541CY-S4-AJ-TR AQ1541CY-S4-AJ-TRL
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 Maximum VIN Maximum VEN Maximum IEN Power Dissipation (Internally limited) Maximum Junction Temperature Operating Junction Temperature Range Storage Temperature Range Lead Temperature (Soldering, 10 sec.) TO packages Lead Temperature (Soldering, 4sec.) SOT- 223 package 150 0 to 125 -65 to 150 300 300 C C C C C Value 18 18 10 Units Volts Volts mA
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) www.acutechnology.com 3 Typical Value 15 Typical Value 46 Rev. 2.2 Units C/W Units C/W September 13, 2005
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AQ1541
Electrical Specifications
Electrical characteristics are guaranteed over the full temperature range 0C ENABLE = ENABLE =
Typ VOUT VOUT 0.035 0.2 0.91 0.93 0.95
Max +1 +1.5 0.2 0.4 0.95 0.95 1.0
Units % % % % V V V A
-1.5
1.1
1.5 7.5 9.0 10 0.1 0.1 0.5 1.0
mA mA A A V
IQOFF VIL VIH IIL IIH VADJ IADJ IADJ IQMIN TC TS VN PSRR TSD TSDHYST
Quiescent Current Off Enable Pin Voltage (OFF) Enable Pin Voltage (ON) Enable Pin Current (OFF) Enable Pin Current (ON) Reference Voltage Adjust Pin Current (5) Adjust Pin Current (5) Change Minimum Load Current (5) Temperature Coefficient Temperature Stability RMS Output Noise (3) Ripple Rejection Ratio (4) Thermal Shutdown TSD Hysteresis
0.25
0.45 0.5 0.1 10 0.8 1.0 25 1.232 1.238 20 0.2 0.5 0.005 0.5 0.003 40 5.0 2.0
V A A V V A A mA %/C %/C % VOUT dB C C
0V, VIN = 5V VIN = 5V 1.208 1.202
Adjustable version only 0C Tj 125C Adjustable version only 10mA IOUT 1Amp 1.4 VIN 18V To Maintain regulation
1.220
Vin = 5V Junction Temperature
60
72 150 25
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 www.acutechnology.com 4 Rev. 2.2 September 13, 2005
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AQ1541
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 1.0F. 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 1.0F 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/(2*fRIPPLE* CADJ) < R1 R1 is normally in the range of 1K. 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 www.acutechnology.com 6 Rev. 2.2 September 13, 2005
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AQ1541
current (I1). The current from the adjust terminal could introduce error to the output, but since it is very small (< 20A) 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 www.acutechnology.com 7 Rev. 2.2 September 13, 2005
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AQ1541
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 K and 100 nF. The output is in regulating 13 ms after the input supply is applied.
FIG. 4 Enable circuit delays output www.acutechnology.com 8 Rev. 2.2 September 13, 2005
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AQ1541
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 125C. 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 (125C), 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 (JA) can be calculated: JA=T(max)/ PD If the maximum allowable value for JA 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
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.
TEL: FAX: website:
(408) 259-2300 (408) 259-9160 www.acutechnology.com
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 www.acutechnology.com 10 Rev. 2.2 September 13, 2005

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