WEITRON
WT1117A
1.0A LOW DROPOUT PRECISION LINEAR REGULATORS
P b Lead(Pb)-Free
General Description:
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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Rev-A 18-Oct-06
WT1117A
Ordering Information
Ordering Number Output Voltage
Package
Shipping
WT1117AN-X
Adj
SOT-223
2,500 Units/Tape&Reel
WT1117AD-X
Adj
TO-252
2,500 Units/Tape&Reel
WT1117AN-15
1.5
SOT-223
2,500 Units/Tape&Reel
WT1117AD-15
1.5
TO-252
2,500 Units/Tape&Reel
WT1117AN-18
1.8
SOT-223
2,500 Units/Tape&Reel
WT1117AD-18
1.8
TO-252
2,500 Units/Tape&Reel
WT1117AN-25
2.5
SOT-223
2,500 Units/Tape&Reel
WT1117AD-25
2.5
TO-252
2,500 Units/Tape&Reel
WT1117AN-285
2.85
SOT-223
2,500 Units/Tape&Reel
WT1117AD-285
2.85
TO-252
2,500 Units/Tape&Reel
WT1117AN-30
3.0
SOT-223
2,500 Units/Tape&Reel
WT1117AD-30
3.0
TO-252
2,500 Units/Tape&Reel
WT1117AN-33
3.3
SOT-223
2,500 Units/Tape&Reel
WT1117AD-33
3.3
TO-252
2,500 Units/Tape&Reel
WT1117AN-50
5.0
SOT-223
2,500 Units/Tape&Reel
WT1117AD-50
5.0
TO-252
2,500 Units/Tape&Reel
Marking Information & PIN Configurtions (Top View)
TO-252 (DPAK)
SOT-223
1117-VV
1117-VV
YAWW
YAWW
VIN
VOUT
ADJ/GND*
VIN
VOUT
ADJ/ GND*
V V/VVV
A
Y
WW
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= Output Voltage (50 = 5.0V, 285= 2.85V ,X = ADJ )
= Assembly Location
= Year
= Weekly
2/11
On fixed versions Pin 1 = GND,
on adjustable versions Pin 1 = A DJ
Tab = VOUT
Rev-A 18-Oct-06
WT1117A
Typical Application
(Fixed Version)
(Adjustable Version)
VIN> 4.75V
3
WT1117A-Adj
2
VOUT
VIN
R1
133
1.0%
ADJ
+
C
10μF
Tant
1
VOUT= VREF X (1 +
Notes:
VIN> 4.75V
VOUT= 3.45V
R2
232
1.0%
3
WT1117A-3.3
VOUT 2
VIN
VOUT= 3.3V
GND
+
+
C2
10μF
Tant.Min
C1
10μF
Tant
1
+
C2
10μF
Tant.Min
R2
) + IADJ X R2
R1
1. C1 needed if device is far from filter capacitors
2. C2 minimum value required for stability
Block Diagram
(Fixed Version)
VOUT
VIN
Thermal
Shutdown
-
+
Error
Amplifier
Output
Current
Limit
Bandgap
Reference
GND
(Adjustable Version)
VOUT
VIN
Thermal
Shutdown
Bandgap
Reference
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+
Error
Amplifier
Output
Current
Limit
ADJ
3/11
Rev-A 18-Oct-06
WT1117A
Parameter
Value
Symbol
UNIT
Power Dissipation
PD
Internally limited
W
Input Voltage
V IN
7.0
V
T LEAD
300
°C
Lead Temperature(Soldering, 10sec)
Operating Junction Temperature Range
Control Section
Power Transistor
TJ
Storage Temperature Range
T STG
Thermal Characteristics
SOT-223
Thermal Resistance, Junction-to-Case
DPAK
Thermal Resistance, Junction-to-Case
R
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JC
-40 to 125
-40 to 150
°C
-65 to + 150
°C
15
°C / W
6.0
4/11
Rev-A 18-Oct-06
WT1117A
ELECTRICAL CHARACTERISTICS
Typicals and limits appearing in normal type apply for Tj 25°C
Reference Voltage
Min
Typ
Max
Unit
1.232
1.225
1.250
1.250
1.268
1.275
V
-1.5
-
+1.5
%
-2
-
+2
%
-
0.04
0.20
%
-
0.20
0.40
%
-
1.15
1.3
V
1.0
-
-
A
-
2
7
mA
-
7
13
mA
-
35
90
μA
VIN-VOUT=1.5V, ILoad=10mA
-
0.005
-
%/°C
Symbol
Parameter
WT1117A-Adj
Output Voltage
VREF
-
Condition
IOUT=10mA, VIN= 5V
10mA
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,
Line Regulation
All
REGLINE
Load Regulation
All
REGLOAD
Dropout Voltage
All
VD
IOUT=1.0A
Current Limit
All
ICL
VIN-VOUT=1.5V
Minimum Load Current
WT1117A-Adj
Ground Current
All Fixed
Versions
Adjust Pin Current
WT1117A-Adj
IO MIN
IQ
IADJ
(1.5 V +VOUT)
VOUT
7V
VIN =VOUT + 1.5V
ILoad =10mA to 1.0A
VIN=5V, Vadj=0V
VIN =VOUT + 1.5V
ILoad =10mA to 1.0A
ILoad=10mA, 2.65V
VIN
7V
Temp. Coefficient
All
Thermal Regulation
All
TC
TA=25℃, 30ms pulse
-
0.003
-
%/W
Ripple Rejection (Note 1)
All
RA
VIN-VOUT=1.5V, ILoad=1.0A
60
72
-
dB
Note 1: 120Hz input ripple (CADJ for ADJ =25μF)
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Rev-A 18-Oct-06
WT1117A
Typical Performance Characteristics
1.00
0.10
TCASE = 0°C
0.08
TCASE = 25°C
V DROPOUT
0.90
0.85
TCASE = 125°C
0.80
0.06
Output Voltage Deviation (%)
0.95
0.04
0.02
0.00
-0.02
-0.04
-0.06
-0.08
-0.10
0.75
0
200
400
600
800
-0.12
0
1000
10 20 30 40 50 60 70 80 90 100 110 120 130
IOUT(mA)
TJ (°C)
Fig.1 Dropout Voltage vs. Output Current
Fig.2 Reference Voltage vs. Temperature
70
75
IO = 10mA
Ripple Rejection(dB)
Adjust Pin Current(μA)
65
85
60
55
50
45
40
0 10
65
55
45
TCASE = 25°C
I
= 1.0A
35 OUT
(VIN-VOUT) = 3.0V
VRIPPLE = 1.0VP-P
25
Cadj =0.1μF
15
10
20 30 40 50 60 70 80 90 100 110 120 130
Temperature (°C)
10
2
10
3
10
4
5
10
6
Fig.4 Ripple Rejection vs. Frequency
300
3.5
200
3.3
3.1
100
2.9
0
I SC (A)
Load Step(mA) Voltage Deviation(mV)
10
Frequency(Hz)
Fig.3 Adjust Pin Current vs. Temperature
VOUT = 3.3V
COUT = CIN =22μF Tantalum
CAdj =0.1μF
-100
-200
2.7
2.5
2.3
2.1
1000
1.9
500
0
0
1
1.7
2
1
3
4
5
6
7
8
9
1.5
1.0
10
Fig.5 Transient Response
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1.5
2.0
2.5
3.0
3.5
4.0
VIN - VOUT(V)
Tim(μS)
Fig.6 Short Circuit Current vs. VIN- VOUT
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 35μA) 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 0.1μF tantalum capacitor is recommended for first
cut design. Type and value may be varied to obtainoptimum performance vs. price.
WT1117A
VIN
VIN
C1
VOUT
VOUT
VREF
Adj
R1
C2
IAdj
CAdj
R2
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 22µF 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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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
(b) Adjustable Version
IN4002
VIN
VIN
IN4002
VOUT
VIN
VOUT
VIN
WT1117A-Adj
WT1117A-3.3
GND
C1
VOUT
VOUT
ADJ
C1
C2
R1
CADJ
C2
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
VIN
(a) Fixed Version
VOUT
WT1117A-Adj
ADJ
WT1117A-3.3
GND
VIN
RLOAD
RC
R1
Conductor
Parasitic
Resistance
RLOAD
R2
(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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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 RθJA(°C/W)
The relationship of these four factors is expressed by equation (1):
TJ=TA + PD X RθJA ........(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 RθJA the total thermal resistance between the junction and the air.
This is expressed by equation (3):
RθJA=RθJC + RθCS X RθSA........(3)
Where all of the following are in °C/W
RθJC is thermal resistance of junction to case,
RθCS is thermal resistance of case to heat sink,
RθSA is thermal resistance of heat sink to ambient air
The value for RθJA is calculated using equation (3) and the result can be substituted in equation (1) .The value for RθJC is
3.5°C/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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Rev-A 18-Oct-06
WT1117A
TO-252-3 PACKAGE OUTLINE DIMENSIONS
6.50 0.10
2.30 0.10
5.30 0.10
0.51 0.005
1.40 0.10
5.50 0.10
9.50 0.25
1.00 0.10
0.80 0.05
2.30 0.05
1.20 0.25
0.60 0.05
0.51 0.05
4.60 0.10
Unit: mm
SOT-223 PACKAGE OUTLINE DIMENSIONS
6.50 0.20
0.325 0.005
3.00 0.10
3.50 0.15
7.00 0.15
1.75TYP
0~10
2.30 0.05
0.73 0.05
4.60 0.10
1.60 0.05
0.06 0.04
Unit: mm
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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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Rev-A 18-Oct-06