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150mA Ultra Low Dropout Regulator with Adjustable Output
POWER MANAGEMENT Description
The SC553 is a low dropout linear regulator that operates from a +2.25V to +6.5V input range and delivers up to 150mA. A PMOS pass transistor allows the low 75A supply current to remain independent of load, making these devices ideal for battery operated portable equipment such as cellular phones, cordless phones and personal digital assistants. The SC553 has an adjust pin (ADJ) enabling the user to set the output voltage anywhere from 1.25V to 6V. For a low noise version, see SC1453 and for an error flag see SC1457. Other features include low powered shutdown, short circuit protection, thermal shutdown protection and reverse battery protection. The SC553 comes in the tiny 5 lead SOT-23 package.
SC553
Features
! "5205" compatible pinout ! 2% output accuracy guaranteed over line, load and ! ! ! ! ! ! ! ! ! ! ! ! ! ! ! !
temperature Guaranteed 150 mA output current Very small external components - designed to work with ceramic capacitors Output adjustable from 1.25V to 6V Very low supply current Thermal overload protection Reverse battery protection Low power shutdown Full industrial temperature range Surface mount packaging (5 pin SOT-23)
Applications
Battery Powered Systems Cellular Telephones Cordless Telephones Personal Digital Assistants Portable Instrumentation Modems PCMCIA cards
Typical Application Circuit
U1 VIN C1 1uF 1 3 IN EN SC553 OUT GND ADJ 2 5 4 R1
VOUT C2 1uF
R1 VOUT = 1.250 * 1 + R2
R2
Revision: April 20, 2004
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SC553
POWER MANAGEMENT Absolute Maximum Ratings
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied.
Parameter Input Supply Voltage Enable Voltage Output Pin Voltage Adjust Pin Voltage Thermal Resistance Junction to Ambient Thermal Resistance Junction to Case Operating Ambient Temperature Range Operating Junction Temperature Range Storage Temperature Range Lead Temperature (Soldering) 10 Sec.
Symbol VIN V EN VOUT V AD J J A J C TA TJ TSTG TLEAD
Maximum -0.6 to +7 -0.6 to VIN -0.6 to +7 -0.6 to +7 256 81 -40 to +85 -40 to +125 -65 to 150 300
Units V V V V C/W C/W C C C C
Electrical Characteristics
Unless specified: VIN = 2.25V, VEN = VIN, IOUT = 100A, CIN = COUT = 1F, TA = 25C. Values in bold apply over full operating ambient temperature range.
Parameter IN Supply Voltage Range Supply Current
Symbol
Conditions
Min
Typ
Max
Units
VIN IQ IOUT = 0mA to150mA, 2.25V VIN 6.5V
2.25 75
6.50 130 160
V A
Off-State Supply Current
IQ(OFF)
VIN = 6.5V, VEN = 0V
0.1
1.0 1.5
A
ADJ Adjust Pin Voltage (1) V AD J IOUT = 1mA 0mA IOUT 150mA, 2.25V VIN 5.5V Adjust Pin Input Current (2) IADJ VADJ = 1.3V -1.5% -2.0% 0.015 1.250 +1.5% +2.0% 2.500 5.000 OUT Line Regulation (1) REG(LINE) VIN = 2.25V to 5.5V, IOUT = 1mA, VADJ = VOUT 1.5 10 12 Load Regulation (1) REG(LOAD) IOUT = 0.1mA to 150mA, VIN = 2.25V, VADJ = VOUT
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V
nA
mV
-1
-10 -20
mV
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SC553
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: VIN = 2.25V, VEN = VIN, IOUT = 100A, CIN = COUT = 1F, TA = 25C. Values in bold apply over full operating ambient temperature range.
Parameter OUT (Cont.) Current Limit Dropout Voltage(1)(3)
Symbol
Conditions
Min
Typ
Max
Units
ILIM VD IOUT = 1mA IOUT = 50mA
400 1 50 65 75 IOUT = 100mA 100 125 155 IOUT = 150mA 150 190 230
mA mV mV
mV
mV
EN Enable Input Threshold VIH VIL Enable Input Bias Current (2) Over Temperature Protection High Trip Level Hysteresis THI THYST 150 15 C C IEN 2.25V VIN 6.5V 2.25V VIN 6.5V 0V VEN VIN -0.5 0 1.6 0.4 +0.5 A V
Notes: (1) Low duty cycle pulse testing with Kelvin connections required. (2) Guaranteed by design. (3) VOUT = 3.3V. Defined as the input to output differential at which the output voltage drops 100mV below the value measured at a differential of 1V. Not measurable on outputs set below 2.25V due to minimum VIN constraints. See Typical Characteristics for typical dropout voltage at other output voltage settings.
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SC553
POWER MANAGEMENT Pin Configuration
Top View
Ordering Information
Part Number (1) SC553ISKTR SC553ISKTRT(2) P ackag e SOT-23-5
SOT-23-5L
Notes: (1) Only available in tape and reel packaging. A reel contains 3000 devices. (2) Lead free product. This product is fully WEEE and RoHS compliant.
Pin Descriptions
Pin # 1 2 3 4 Pin Name IN GND EN AD J Pin Function Input pin. Ground pin. Can be used for heatsinking if needed. Active high enable pin. Connect to IN if not being used. Adjust pin. Connecting this pin to an external resistor divider (see Typical Application Circuit on page 1) sets VOUT to: R1 VOUT = 1.250 * 1 + R2 Regulator output, sourcing up to 150mA.
5
OUT
Block Diagram
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SC553
POWER MANAGEMENT Marking Information
Top Mark Bottom Mark
553
Applications Information
Theory Of Operation The SC553 is intended for applications where very low dropout voltage, low supply current and low output noise are critical. It provides a very simple, low cost solution that uses very little pcb real estate. Only two external capacitors are required for operation. The SC553 contains a bandgap reference trimmed for optimal temperature coefficient which is fed into the inverting input of an error amplifier. The output voltage of the regulator is divided down externally using a resistor divider and compared to the bandgap voltage via the adjust pin (ADJ). The error amplifier drives the gate of a low RDS(ON) P-channel MOSFET pass device to maintain VOUT such that VADJ = VREF. An active high enable pin (EN) allows the regulator to be shut down. Pulling this pin low causes the device to enter a very low power shutdown mode, where it will draw typically 0.1A from the input supply. The regulator has its own current limit circuitry to ensure that the output current will not damage the device during output short, overload or start-up. The current limit is guaranteed to be greater than 400mA to allow fast charging of the output capacitor and high initial currents for DSP initialization. The SC553 includes thermal shutdown circuitry to turn off the device if T J exceeds 150C (typical), with the device remaining off until TJ drops by 15C (typical). Reverse battery protection circuitry ensures that the device cannot be damaged if the input supply is accidentally reversed, limiting the reverse current to less than 1.5mA.
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Component Selection - General Output capacitor - Semtech recommends a minimum capacitance of 1F at the output with an equivalent series resistance (ESR) of < 1 over temperature. While the SC553 has been designed to be used with ceramic capacitors, it does not have to be used with ceramic capacitors, allowing the designer a choice. Increasing the bulk capacitance will further reduce output noise and improve the overall transient response. Input capacitor - Semtech recommends the use of a 1F ceramic capacitor at the input. This allows for the device being some distance from any bulk capacitance on the rail. Additionally, input droop due to load transients is reduced, improving overall load transient response. External voltage selection resistors - the use of 1% resistors, and designing for a current flow 10A is recommended to ensure a well regulated output (thus R2 125k). The output voltage (referring to Figure 1 below) will be:
R1 VOUT = 1.250 * 1 + R2
VIN C1 1uF
1 3
U1 IN EN
SC553 OUT GND ADJ 2
5 4 R1
VOUT C2 1uF
R2
Figure 1
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SC553
POWER MANAGEMENT Applications Information (Cont.)
Thermal Considerations The worst-case power dissipation for this part is given by:
PD(MAX ) = (VIN(MAX) - VOUT(MIN) ) * IOUT(MAX ) + VIN(MAX ) * IQ(MAX )
Layout Considerations While layout for linear devices is generally not as critical as for a switching application, careful attention to detail will ensure reliable operation. 1) Attaching the part to a larger copper footprint will enable better heat transfer from the device, especially on PCBs where there are internal ground and power planes. 2) Place the input and output capacitors close to the device for optimal transient response and device behaviour. 3) While the external resistor divider does not need to be close to the device, care should be taken to avoid routing the connections next to any lines carrying large amounts of noise. The simplest solution is to place these resistors close to the device and routing the top of R1 to the load if not adjacent to the part. 4) Connect all ground connections directly to the ground plane. If there is no ground plane, connect to a common local ground point before connecting to board ground.
(1)
For all practical purposes, equation (1) can be reduced to the following expression: (2) Looking at a typical application, 3.3V to 2.8V at 150mA: VIN(MAX) = 3.3 + 5% = 3.465V VOUT(MIN) = 2.8V - 2% = 2.744V IOUT = 150mA TA = 85C Inserting these values into equation (2) gives us:
Using this figure, we can calculate the maximum thermal impedance allowable to maintain TJ 125C:
JA (MAX ) =
(T
J(MAX )
- TA (MAX ) )
Typical Characteristics
Dropout Voltage vs. Output Voltage vs. Output Current
250 225 200 175 VD (mV) 150 125 100 75 50 25 0 2.0 2.5 3.0 3.5 4.0 VOUT (V) 4.5 5.0 5.5 6.0 TA = 25C
PD(MAX )
=
(125 - 85) = 370C / W
0.108
With the standard SOT-23-5 Land Pattern shown at the end of this datasheet, and minimum trace widths, the thermal impedance junction to ambient for SC553 is 256C/W. Thus no additional heatsinking is required for this example. The junction temperature can be reduced further (or higher power dissipation can be allowed) by the use of larger trace widths and connecting PCB copper to the GND pin (pin 2), which connects directly to the device substrate. Adding approximately one square inch of PCB copper to pin 2 will reduce JA to approximately 130C/W and T J(MAX) for the example above to approximately 100C. The use of multi layer boards with internal ground/power planes will lower the junction temperature and improve overall output voltage accuracy.
Top to bottom: IOUT = 150mA IOUT = 100mA IOUT = 50mA
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SC553
POWER MANAGEMENT Outline Drawing - SOT-23-5
Land Pattern - SOT-23-5
This land pattern is for reference only. Consult your manufacturing group to ensure you meet your company's manufacturability guidelines.
Contact Information
Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804
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