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WEITRON
1.0A LOW DROPOUT PRECISION LINEAR REGULATORS P b Lead(Pb)-Free
General Description:
WT1117A
WT1117A of positive adjustable and fixed regulators is designed to provide 1.0A output with low dropout voltage performance. On-chip trimming adjusts the reference voltage to 1.5%. For usage on working in post regulators or microprocessor power supplies, low voltage operation and fast transient response are required. WT1117A is available in surface-mount SOT-223 and TO-252 packages.
Features:
* Adjustable or Fixed Output * Output Current of 1.0A * Dropout Voltage(Typical) 1.15V @1.0A * Line Regulation 0.2% max. * Load Regulation 0.4% max. * Fast Transient Response * Current Limit Protection * Thermal Shutdown Protection
Applications:
* High Efficiency Linear Regulators * Post Regulators for Switching Supplies * Microprocessor Supply * Hard Drive Controllers * Battery Chargers * Adjustable Power Supply
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1/11
Rev-A 18-Oct-06
WT1117A
Ordering Information
Ordering Number Output Voltage WT1117AN-X WT1117AD-X WT1117AN-15 WT1117AD-15 WT1117AN-18 WT1117AD-18 WT1117AN-25 WT1117AD-25 WT1117AN-285 WT1117AD-285 WT1117AN-30 WT1117AD-30 WT1117AN-33 WT1117AD-33 WT1117AN-50 WT1117AD-50 Adj Adj 1.5 1.5 1.8 1.8 2.5 2.5 2.85 2.85 3.0 3.0 3.3 3.3 5.0 5.0 Package SOT-223 TO-252 SOT-223 TO-252 SOT-223 TO-252 SOT-223 TO-252 SOT-223 TO-252 SOT-223 TO-252 SOT-223 TO-252 SOT-223 TO-252 Shipping 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel 2,500 Units/Tape&Reel
Marking Information & PIN Configurtions (Top View)
TO-252 (DPAK) SOT-223
1117-VV
YAWW
YAWW
1117-VV
VOUT ADJ/ GND*
VIN
VIN VOUT ADJ/GND*
V V/VVV A Y WW
= Output Voltage (50 = 5.0V, 285= 2.85V ,X = ADJ ) = Assembly Location = Year = Weekly
On fixed versions Pin 1 = GND, on adjustable versions Pin 1 = A DJ Tab = VOUT
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2/11
Rev-A 18-Oct-06
WT1117A
Typical Application
(Adjustable Version) (Fixed Version)
VOUT= 3.45V
VIN> 4.75V
3
WT1117A-Adj 2 VOUT VIN
ADJ
VIN> 4.75V
3
WT1117A-3.3 VOUT 2 VIN
GND
VOUT= 3.3V
+
C 10F Tant
1
R1 133 1.0% R2 232 1.0% R2 ) + IADJ X R2 R1
+
C2 10F Tant.Min
+
C1 10F Tant
1
+
C2 10F Tant.Min
VOUT= VREF X (1 +
Notes:
1. C1 needed if device is far from filter capacitors 2. C2 minimum value required for stability
Block Diagram
(Fixed Version)
VIN Output Current Limit
VOUT
Thermal Shutdown Bandgap Reference +
Error Amplifier
GND
(Adjustable Version)
VIN Output Current Limit
VOUT
Thermal Shutdown Bandgap Reference +
Error Amplifier
ADJ
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3/11
Rev-A 18-Oct-06
WT1117A
Parameter
Power Dissipation
Input Voltage Lead Temperature(Soldering, 10sec)
Symbol
PD V IN T LEAD TJ T STG
Value
Internally limited 7.0 300 -40 to 125 -40 to 150 -65 to + 150
UNIT
W V C C C
Operating Junction Temperature Range Control Section Power Transistor Storage Temperature Range
Thermal Characteristics SOT-223 Thermal Resistance, Junction-to-Case DPAK Thermal Resistance, Junction-to-Case
R
JC
15 6.0
C / W
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4/11
Rev-A 18-Oct-06
WT1117A
ELECTRICAL CHARACTERISTICS
Typicals and limits appearing in normal type apply for Tj 25C Parameter
Reference Voltage WT1117A-Adj
Symbol
VREF
10mA
Condition
IOUT=10mA, VIN= 5V IOUT 1.0A, 2.65V VIN 7V IOUT=10mA, VIN=VOUT+1.5V VIN=VOUT+1.5V to 7 V 0 IOUT 1.0A ILoad =10mA, (1.5 V +VOUT) VOUT 7V
Min
1.232 1.225 -1.5 -2 1.0 VIN 7V 60
Typ
1.250 1.250 0.04
Max
1.268 1.275 +1.5 +2
0.20
Unit
V % %
%
Output Voltage
-
Line Regulation
All
REGLINE REGLOAD VD ICL IO MIN IQ IADJ
Load Regulation Dropout Voltage Current Limit Minimum Load Current Ground Current Adjust Pin Current Temp. Coefficient Thermal Regulation Ripple Rejection (Note 1)
All All All WT1117A-Adj All Fixed Versions WT1117A-Adj All All All
VIN =VOUT + 1.5V ILoad =10mA to 1.0A
0.20 1.15 2 7 35 0.005 0.003 72
0.40 1.3
%
IOUT=1.0A VIN-VOUT=1.5V VIN=5V, Vadj=0V
VIN =VOUT + 1.5V ILoad =10mA to 1.0A ILoad=10mA, 2.65V
V A mA mA A %/C %/W dB
7 13 90
VIN-VOUT=1.5V, ILoad=10mA TC RA TA=25, 30ms pulse VIN-VOUT=1.5V, ILoad=1.0A
-
Note 1: 120Hz input ripple (CADJ for ADJ =25F)
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5/11
Rev-A 18-Oct-06
WT1117A
Typical Performance Characteristics
1.00
0.10
TCASE = 0C
Output Voltage Deviation (%)
0.08 0.06 0.04 0.02 0.00 -0.02 -0.04 -0.06 -0.08 -0.10 -0.12 0
0.95 0.90 0.85 0.80 0.75 0
V DROPOUT
TCASE = 25C
TCASE = 125C
200
400
600
800
1000
10 20 30 40 50 60 70 80 90 100 110 120 130 TJ (C)
IOUT(mA)
Fig.1 Dropout Voltage vs. Output Current
70 65 85
Fig.2 Reference Voltage vs. Temperature
Adjust Pin Current(A)
IO = 10mA
Ripple Rejection(dB)
75 65 55 45
60 55 50 45 40 0 10
TCASE = 25C I = 1.0A 35 OUT (VIN-VOUT) = 3.0V VRIPPLE = 1.0VP-P 25 Cadj =0.1F
15
20 30 40 50 60 70 80 90 100 110 120 130 Temperature (C)
10
1
10
2
10
3
10
4
10
5
10
6
Frequency(Hz)
Fig.3 Adjust Pin Current vs. Temperature
300
Load Step(mA) Voltage Deviation(mV)
Fig.4 Ripple Rejection vs. Frequency
3.5 3.3 3.1 2.9 2.7 2.5 2.3 2.1 1.9 1.7 1 2 3 4 5
Tim(S)
200 100
I SC (A)
0 -100 -200
VOUT = 3.3V COUT = CIN =22F Tantalum CAdj =0.1F
1000 500 0 0 6 7 8 9 10
1.5 1.0
1.5
2.0
2.5
3.0
3.5
4.0
Fig.5 Transient Response
VIN - VOUT(V)
Fig.6 Short Circuit Current vs. VIN- VOUT
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6/11
Rev-A 18-Oct-06
WT1117A
APPLICATION INFORMATION
WT1117A linear regulators provide fixed and adjustable output voltages at currents up to 1.0A. These regulators are protected against overcurrent conditions and include thermal shutdown protection. The WT1117A's have a composite PNP-NPN output transistorand require an output capacitor for stability. A detailed procedure for selecting this capacitor follows.
Adjustable Operation
The WT1117A has an output voltage range of 1.25 V to 5.5 V. An external resistor divider sets the output voltage as shown in Figure 1. The regulator maintains a fixed 1.25V (typical) reference between the output pin and the adjust pin. A resistor divider network R1 and R2 causes a fixed current to flow to ground. This current creates a voltage across R2 that adds to the 1.25V across R1 and sets the overall output voltage. The adjust pin current (typically 35A) also flows through R2 and adds a small error that should be taken into account if precise adjustment of VOUT is necessary. The output voltage is set according to the formula:
V OUT = VREF X (
R1 + R2 ) + IAdj X R2 R1
The term IAdj R2 represents the error added by the adjust pin current. R1 is chosen so that the minimum load current is at least 2.0mA R1 and R2 should be the same type e.g. metal film for best tracking over temperature. While not required, a bypass capacitor from the adjust pin to ground will improve ripple rejection and transient response. A 0.1F tantalum capacitor is recommended for first cut design. Type and value may be varied to obtainoptimum performance vs. price.
WT1117A VIN C1 VIN VOUT Adj VREF IAdj CAdj R2 R1 C2 VOUT
Figure1. Resistor Divider Scheme
Stability Considerations
The output compensation capacitor helps to determine three main characteristics of a linear regulator's performance: start-up delay,load transient response, and loop stability. The capacitor value and type is based on cost, availability, size and temperature constrains, A tantalum or aluminum electrolytic capacitor is preferred, as a film or ceramic capacitor with almost zero ESR can cause Instability. An aluminum electrolytic capacitor is the least expensive type. but when the circuit operates at low temperatures, both the value and ESR of the capacitor will vary widelt.For optimum performance over the full operating temperature range, a tantalum capacitor is best, A 22F tantalum capacitor will work fine in most applications, but with high current regulators such as the WT1117A higher capacitance values will improve the transient response and stability. Most applications for the WT1117A's involve large changes in load current, so the output capacitor must supply instantaneous load current. The ESR of the output capacitor causes an immediate drop in output voltage given by:
V = I x ESR
In microprocessor applications an output capacitor network of several tantalum and ceramic capacitors in parallel is commonly used. This reduces overall ESR and minimizes the instantaneous output voltage drop under transient load conditions. The output capacitor network should be placed as close to the load as possible for the best results. Used with large output capacitance values and theinput voltage is instantaneously shorted to ground, damage can occur. In this case, a diode connected as shown above in Figure1.
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7/11
Rev-A 18-Oct-06
WT1117A
Protection Diodes
When large external capacitors are used with most linear regulator, it is wise to add protection diodes. If the input voltage of the regulator is shorted, the output capacitor will discharge into the output of the regulator. The discharge current depends on the value of capacitor, output voltage, and rate at which VIN drops.
Figure2 (a),(b) Protection Diode Scheme for Large Output Capacitors (a) Fixed Version IN4002 VIN VIN VOUT VOUT VIN VIN (b) Adjustable Version IN4002 VOUT VOUT WT1117A-Adj C2 C1 ADJ R1 CADJ C2
WT1117A-3.3
C1 GND
R2
In the WT1117A linear regulators, the discharge path is through a large junction, and protection diodes are normally not needed. However, damage can occur if the regulator is used with large output capacitance values and the input voltage is instantaneously shorted to ground. In this case, a diode connected as shown above in Figure 2.
Output Voltage Sensing
The WT1117A are three terminal regulators. For which, they cannot provide true remote load sensing. Load regulation is limited by the resistance of the conductors connecting the regulator to the load. For best results the WT1117A should be connected are as shown in Figure 3.
Figure3 (a),(b) Conductor Parasitic Resistance Effects are Minimized by this Grounding Scheme For Fixed and Adjustable Output Regulators
VIN
VIN
VOUT
RC
Conductor Parasitic Resistance RLOAD
VIN
VIN
VOUT
RC R1 R2
Conductor Parasitic Resistance RLOAD
WT1117A-3.3 GND (a) Fixed Version
WT1117A-Adj ADJ
(b) Adjustable Version
Calculating Power Dissipation and Heat Sink Requirements
The WT1117A precision linear regulators include thermal shutdown and current limit circuitry to protect the devices. However, high power regulators normally operate at high junction temperatures. It is important to calculate the power dissipation and junction temperatures accurately to be sure that you use and adequate heat sink. The case is connected to VOUT on the WT1117A, and electrical isolation may be required for some applications. Thermal compound should always be used with high current regulators like the WT1117A.
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8/11
Rev-A 18-Oct-06
WT1117A
The thermal characteristics of an IC depend four factors: 1. Maximum Ambient Temperature TA(C) 2. Power Dissipation PD (Watts) 3. Maximum Junction Junction Temperature TJ(C) 4. Thermal Resistance Junction to ambient RJA(C/W) The relationship of these four factors is expressed by equation (1):
TJ=TA + PD X RJA ........(1)
Maximum ambient temperature and power dissipation are determined by the design while the maximum junction temperature and thermal resistance depend on the manufacturer and the package type. The maximum power dissipation for a regulator is expressed by equation (2):
PD(max) = { VIN(max)- VOUT(min) } IOUT(max) + VIN(max)IQ ........(2)
where: VIN(max) is the maximum input voltage, VOUT(min) is the minimum output voltage, IOUT(max) is the maximum output current IQ is the maximum quiescent current at IOUT(max) . A heat sink effectively increases the surface area of the package to improve the flow of heat away from the IC into the air. Each material in the heat flow path between the IC and the environment has a thermal resistance. Like series electrical resistances, these resistance are summed to determine RJA the total thermal resistance between the junction and the air. This is expressed by equation (3):
RJA=RJC + RCS X RSA........(3)
Where all of the following are in C/W RJC is thermal resistance of junction to case, RCS is thermal resistance of case to heat sink, RSA is thermal resistance of heat sink to ambient air The value for RJA is calculated using equation (3) and the result can be substituted in equation (1) .The value for RJC is 3.5C/W for a given package type based on an average die size. For a high current regulator such as the WT1117A the majority of the heat is generated in the power transistor section.
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9/11
Rev-A 18-Oct-06
WT1117A
TO-252-3 PACKAGE OUTLINE DIMENSIONS
6.50 0.10 5.30 0.10 1.40 0.10 2.30 0.10 0.51 0.005
5.50 0.10 9.50 0.25 1.00 0.10 0.80 0.05 2.30 0.05 4.60 0.10 0.60 0.05 1.20 0.25 0.51 0.05
Unit: mm
SOT-223 PACKAGE OUTLINE DIMENSIONS
6.50 0.20 3.00 0.10 0.325 0.005
7.00 0.15
3.50 0.15
1.75TYP
0~10
2.30 0.05 4.60 0.10
0.73 0.05
1.60 0.05 0.06 0.04
Unit: mm
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10/11
Rev-A 18-Oct-06
WT1117A
ORDERING NUMBER
WT1117 A X - XX
Output Voltage - X : Adj - 15 : 1.5V - 18 : 1.8V - 25 : 2.5V - 285 : 2.85V - 30 : 3.0V - 33 : 3.3V - 50 : 5.0V
Circuit Type
Output Current = 1.0A Package N : SOT-223 D : TO-252
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11/11
Rev-A 18-Oct-06

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