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Very Low Dropout 1 Amp Regulator With Enable
POWER MANAGEMENT Description
The SC4205 is a high performance positive voltage regulator designed for use in applications requiring very low dropout voltage at up to 1 Amp. Since it has superior dropout characteristics compared to regular LDOs, it can be used to supply 2.5V on motherboards or 2.8V on peripheral cards from the 3.3V supply thus allowing the elimination of costly heatsinks. Additionally, the SC4205 has an enable pin to further reduce power dissipation while shut down. The SC4205 provides excellent regulation over variations in line, load and temperature. The SC4205 is available in the SOIC-8EDP package with internally preset outputs that are also adjustable using external resistors.
SC4205
Features
350mV dropout @ 1A Adjustable output from 1.2V to 4.8V 2.5V and 1.8V options (adjustable externally using resistors) Over current and over temperature protection Enable pin 10A quiescent current in shutdown Low reverse leakage (output to input) Surface mount and through-hole packages Full industrial temperature range Available in SOIC-8EDP package
Applications
Battery powered systems Motherboards Peripheral cards Network cards Set Top Boxes Medical Equipment Notebook Computers
Typical Application Circuits
SC4205
4 NC VIN EN NC NC VO ADJ GND 5 6 7 8
VIN ENABLE
3 2 1
VO
R1
VO
C2
=
1.2 (R1 + R2) R2
Volts
C1
U1
R2
SC4205
4 NC VIN EN NC NC VO ADJ GND 5 6 7 8 4 NC VIN EN NC
SC4205
NC VO ADJ GND 5 6 7 8
VIN ENABLE
3 2 1
VO
VIN ENABLE
3 2 1
VO
C1
U1
C2
C1
U1
C2
Notes: (1) Maximum VO setpoint for 1.8V parts = 5.4V. (2) This device is designed to operate with ceramic input and output capacitors.
Revision: June 28, 2004 1 www.semtech.com
SC4205
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 Voltage Power Dissipation Thermal Resistance Junction to Ambient SOIC-8EDP(1) Thermal Resistance Junction to Case SOIC-8EDP(1) Operating Ambient Temperature Range Operating Junction Temperature Range Storage Temperature Range Lead Temperature (Soldering) 10 Sec. ESD Rating (Human Body Model)
Note: (1) 1 square inch of FR-4, double sided, 1 oz. minimum copper weight.
Symbol VIN PD JA JC TA TJ TSTG TLEAD V ESD
Max 7 Internally Limited 36 5.5 -40 to +85 -40 to +150 -65 to +150 300 4
Units V W C/W C/W C C C C kV
Electrical Characteristics
Unless specified: VEN = VIN. Adjustable Option (VADJ > VTH(ADJ)): VIN = 2.2V to 5.5V and IO = 10A to 1A. Fixed Options (VADJ = GND): VIN = (VO + 0.5V) to 5.5V and IO = 0A to 1A. Values in bold apply over TJ = -40C to 125C
Parameter VIN Operating Voltage Range Quiescent Current
Symbol
Test Conditions
Min
Typ
Max
Units
VIN IQ VIN = 3.3V VIN = 5.5V, VEN = 0V
2.2 0.75 10
5.5 1.75 35
V mA A
VO Output Voltage(1) (Internal Fixed Voltage) Line Regulation(1) Load Regulation(1) Dropout Voltage(1)(2) VO REG(LINE) REG(LOAD) VD IO = 10mA IOUT = 10mA IOUT = 10mA to 1A IO = 10mA -1% -2% 0.035 0.2 2.5 VO +1% +2% 0.3 0.4 10 20 IO = 500mA 90 300 400 IO = 1A 180 400 500 % % mV V
mV
mV
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SC4205
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: VEN = VIN. Adjustable Option (VADJ > VTH(ADJ)): VIN = 2.2V to 5.5V and IO = 10A to 1A. Fixed Options (VADJ = GND): VIN = (VO + 0.5V) to 5.5V and IO = 0A to 1A. Values in bold apply over TJ = -40C to 125C
Parameter VO (Cont.) Minimum Load Current(3) Current Limit ADJ Reference Voltage(1)
Symbol
Test Conditions
Min
Typ
Max
Units
IO ICL 1.6
1 1.33
10 3.5
A A
VREF
VIN = 2.2V, VADJ = VOUT, IO = 10mA
1.188 1.176
1.200
1.212 1.224
V
Adjust Pin Current(4) Adjust Pin Threshold(5) EN Enable Pin Current Enable Pin Threshold
IADJ VTH(ADJ)
VADJ = VREF 0.05
30 0.20
200 0.40
nA V
IEN VIH VIL
VEN = 0V, VIN = 3.3V VIN = 3.3V VIN = 3.3V 1.6
1.5
10
A V
0.4
Over Temperature Protection High Trip level Hysteresis THI THYST 170 20 C C
Notes: (1) Low duty cycle pulse testing with Kelvin connections required. (2) Defined as the input to output differential at which the output voltage drops to 1% below the value measured at a differential of 0.7V. (3) Required to maintain regulation. Voltage set resistors R1 and R2 are usually utilized to meet this requirement. Adjustable versions only. (4) Guaranteed by design. (5) When VADJ exceeds this threshold, the "Sense Select" switch disconnects the internal feedback chain from the error amplifier and connects VADJ instead.
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SC4205
POWER MANAGEMENT Ordering Information
Part Number SC4205IS-X.XTR
(1)(2)
P ackag e SOIC-8EDP
Temp. Range (TA) -40 to +85 OC
SC4205IS-X.XTRT(1)(2)(3) S C 4205E V B
Evaluation Board
Notes: (1) Where -X.X denotes voltage options. Available voltages are: 2.5V and 1.8V. Output voltage can be adjusted using external resistors, see Pin Descriptions on page 5. (2) Only available in tape and reel packaging. A reel contains 2500 devices. (3) Lead free product
Pin Configuration
Top View Bottom View
GND
NC EN VIN NC
SOIC-8EDP
GND ADJ VO NC
GND ADJ VO NC
8 7 6 5
Exposed Die Pad
1 2 3 4
NC EN VIN NC
SOIC-8EDP
Pin Descriptions
Pin N ame Pin D esciption AD J Thi s pi n, when grounded, sets the output voltage to that set by the i nternal feedback resi stors. If external feedback resi stors are used, the output voltage wi ll be (See Appli cati on C i rcui ts on page 1):
VO = 1.200 (R1 + R2) R2 Volts
EN GND VIN VO
Enable Input. Pulli ng thi s pi n below 0.4V turns the regulator off, reduci ng the qui escent current to a fracti on of i ts operati ng value. The devi ce wi ll be enabled i f thi s pi n i s left open. C onnect to VIN i f not bei ng used. Reference ground. Note: The GND pi n and the exposed di e pad must be connected together at the IC pi n. Use the exposed di e pad on the devi ce for heatsi nki ng. Input voltage. For regulati on at full load, the i nput to thi s pi n must be between (VO + 0.5V) and 5.5V. Mi ni mum VIN = 2.2V. The pi n i s the power output of the devi ce.
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SC4205
POWER MANAGEMENT Block Diagram
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SC4205
POWER MANAGEMENT Applications Information
Introduction The SC4205 is intended for applications such as graphics cards where high current capability and very low dropout voltage are required. It provides a very simple, low cost solution that uses very little pcb real estate. Additional features include an enable pin to allow for a very low power consumption standby mode, and a fully adjustable output. Component Selection Input capacitor: a 4.7F ceramic capacitor is recommended. 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 load transient response. Additional capacitance may be added if required by the application. Output capacitor: a minimum bulk capacitance of 2.2F, along with a 0.1F ceramic decoupling capacitor is recommended. Increasing the bulk capacitance will improve the overall transient response. The use of multiple lower value ceramic capacitors in parallel to achieve the desired bulk capacitance will not cause stability issues. Although designed for use with ceramic output capacitors, the SC4205 is extremely tolerant of output capacitor ESR values and thus will also work comfortably with tantalum output capacitors. For reference, the phase-margin contour of Figure 1 can be used to choose an appropriate output capacitor for a given stability requirement. Noise immunity: in very electrically noisy environments, it is recommended that 0.1F ceramic capacitors be placed from IN to GND and OUT to GND as close to the device pins as possible. 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 120k). Thermal Considerations The power dissipation in the SC4205 is approximately equal to the product of the output current and the input to output voltage differential:
PD (VIN - VOUT )* I O
The absolute worst-case dissipation is given by:
PD ( MAX ) = ( ( MAX ) - VOUT( MIN ) )* I O ( MAX ) + VIN ( MAX ) * I Q ( MAX ) VIN
For a typical scenario, VIN = 3.3V 5%, VOUT = 2.8V and IO = 1A, therefore: VIN(MAX) = 3.465V, VOUT(MIN) = 2.744V and IQ(MAX) = 1.75mA, Thus PD(MAX) = 727mW. Using this figure, and assuming TA(MAX) = 70C, we can calculate the maximum thermal impedance allowable to maintain TJ 150C:
RTH ( J - A)( MAX ) =
(T
J ( MAX )
- TA( MAX ) )
PD ( MAX )
=
(150 - 70) = 110C / W
.727
This should be achievable for the SOIC-8EDP package using pcb copper area to aid in conducting the heat away, such as one square inch of copper connected to the pins of the device. Internal ground/power planes and air flow will also assist in removing heat. For higher ambient temperatures it may be necessary to use additional copper area.
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SC4205
POWER MANAGEMENT Outline Drawing - SOIC-8EDP
Land Pattern - SOIC-8EDP
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SC4205
POWER MANAGEMENT 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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