High Efficiency Linear Regulators Post Regulators for Switching Supplies Microprocessor Supply
Description
GM1117 of positive adjustable and fixed regulators is de-signed to provide 1.0A output with low dropout voltage per-formance. O n-chip trimming adjusts the reference voltage to 1%. For usage on working in post regulators or micro-processor power supplies, low voltage operation and fast transient response are required.
Pin-to-pin compatible with the LT1086 family of regulators, GM1117 is available in surface-mount SO T-223 and TO -252 packages.
Application
Features
Adjustable or Fixed Output
Output Current of 1.0A
Dropout Voltage (T ypical) 1.15V @ 1.0A Line Regulation 0.2% max. Load Regulation 0.4% max. Fast Transient Response Current Limit Protection Thermal Shutdown Protection
TYPICAL APPLICATION CIRCUITS
Hard Drive Controllers Battery Chargers Adjustable Power Supply
(Adjustable Version)
(Fixed Version)
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Notes:
1. C1 needed if device is far from filter capacitors
2. C2 minimum value required for stability
V V R2
= X (1 + ) + I X O
UT REF ADJ R2
R1
MARKING INFORMATION & PIN CONFIGURA TIONS (Top View)
TO-252 (DPAK)
On fixed versions Pin 1 = GND,on adjustable versions Pin 1 = A Tab = V OUT
DJ
V V/VVV = Output Voltage (50 = 5.0V , 285= 2.85V ,A =Adj )A = Assembly Location Y = Y ear W W = Weekly
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V IN
V O UT
ADJ/ GND*
GM1117
VVAYWW
SOT-223
IN
TO-220
IN GM1117
VVAYWW
2
TO-263-2 (D PAK)
V IN V OUT
ADJ/ GND*
ORDERING INFORMATION
* For detail Ordering Number identification, please see last page.
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ORDERING INFORMATION (Continued)
* For detail Ordering Number identification, please see last page.
BLOCK DIAGRAM V IN
V OUT
GND
T hermal Shutdown
Bandgap Reference
Output Current Limit
Error Amplifier +
-ABSOLUTE MAXIMUM RATINGS
V IN
V OUT
ADJ
T hermal Shutdown
B
andgap Reference
Output Current Limit
Error Amplifier +
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(Adjustable Version)
(Fixed Version)
ELECTRICAL CHARACTERISTICS
(Typicals and limits appearing in normal type apply for T = 25°C)
J
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APPLICATION INFORMA TION
GM1117 linear regulators provide fixed and adjustable output voltages at currents up to 1.0A. These regula-tors are protected against overcurrent conditions and in-clude thermal shutdown protection. The GM1117's have a composite PNP-NPN output transistor and re-quire an output capacitor for stability. A detailed proce-dure for selecting this capacitor follows.
Adjustable Operation
The GM1117 has an output voltage range of 1.25 V to 5.5 V. An external resistor divider sets the output volt-age 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 1.25 V across R1 and sets the overall output voltage. The adjust pin current (typically 50 μA) also flows through R2 and adds a small error that should be taken into account if precise adjustment of V is OUT necessary.
The output voltage is set according to the formula:
The term I Adj × R2 represents the error added by the adjust pin current.
R1 is chosen so that the minimum load current is at least 2.0 mA. 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 0.1 μF tantalum capacitor is recommended for “first cut” design. Type and value may be varied to obtain optimum performance vs. price.
Stability Considerations
The output compensation capacitor helps to deter-mine three main characteristics of a linear regula-tor's performance: start-up delay, load transient re-sponse, and loop stability. The capacitor value and type is based on cost, availability, size and tempera-ture constraints. A tantalum or aluminum electrolytic capacitor is preferred, as a film or ceramic capacitor with almost zero ESR can cause instability. An alu-minum electrolytic capacitor is the least expensive type, but when the circuit operates at low tempera-tures, both the value and ESR of the capacitor will vary widely. 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 GM1117 higher capacitance values will improve the transient response and stability. Most ap-plications for the GM1117's involve large changes in load current, so the output capacitor must supply in-stantaneous load current. The ESR of the output ca-pacitor causes an immediate drop in output voltage given by:
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 volt-age 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 the input voltage is instantaneously shorted to ground, damage can occur. In this case, a diode connected as shown above in Figure 1.
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V = V X ( ) + I X R2
OUT REF Adj R1 + R2
R1
D V = I x ESR
D
V OUT
Figure 1. Resistor Divider Scheme
Output Voltage Sensing
The GM1117 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 GM1117 should be connected are as shown in Figure 3.
Calculating Power Dissipation and Heat Sink Requirements
The GM1117 precision linear regulators include thermal shutdown and current limit circuitry to protect the de-vices. However, high power regulators normally oper-ate at high junction temperatures. It is important to cal-culate the power dissipation and junction temperatures accurately to be sure that you use and adequate heat sink. The case is connected to V on the GM1117, O UT and electrical isolation may be required for some appli-cations. Thermal compound should always be used with high current regulators like the GM1117.
LO AD
Conductor
LO AD
(a),(b)
Figure 3Conductor Parasitic Resistance Effects are
Minimized by this Grounding Scheme For Fixed
and Adjustable Output Regulators
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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 out-put capacitor will discharge into the output of the reg-ulator. The discharge current depends on the value of capacitor, output voltage, and rate at which V IN drops.
In the GM1117 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.
(a),(b)
Figure 2 Protection Diode Scheme for
Large Output Capacitors (a) Fixed Version
(b) Adjustable Version
V IN
V OUT
C ADJ
GM1117-Adj
ADJ
V IN
V OUT
C1
C2
R1
R2
GM1117-3.3
GND
V IN
V OUT
C1
IN4002
C2
V IN
V OUT
IN4002
Conductor
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The thermal characteristics of an IC depend four fac-tors:
1. Maximum Ambient T emperature T (°C)A
2. Power Dissipation P (Watts)
D 3. Maximum Junction T emperature T (°C)
J 4. Thermal Resistance Junction to ambient R JA Q (°C/W)
The relationship of these four factors is expressed by equation (1):
Maximum ambient temperature and power dissipa-tion 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 ex-pressed by equation (2):
where:
V is the maximum input voltage,IN(max)V is the minimum output voltage,OUT(min)I is the maximum output current
OUT(max)I is the maximum quiescent current at I .Q OUT(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 re-sistance. Like series electrical resistances, these re-sistance are summed to determine R ,
the total Q JA thermal resistance between the junction and the air. This is expressed by equation (3):
Where all of the following are in °C/W:
R is thermal resistance of junction to case, Q JC R is thermal resistance of case to heat sink,
Q CS R is thermal resistance of heat sink to ambient air
Q SA The value for R is calculated using equation (3) Q JA and the result can be substituted in equation (1). The value for R is 3.5°C/W for a given package type Q JC based on an average die size. For a high current reg-ulator such as the GM1117 the majority of the heat is generated in the power transistor section.
T = T + P X R ........J A D JA
(1)
Q P = { V - V } I + V I ) D(max)IN(max)O UT(min)O
UT(max IN(max)Q (2)
R = R + R + R JA JC CS SA (3)
Q Q Q Q
Typical Performance Characteristics
0 200 400 600 800 1000
I (mA)
OUT V D R O P O U T
Figure 3. Dropout Voltage vs. Output Current 0.10
0.080.060.040.020.00-0.02-0.04
-0.06-0.08-0.10
-0.12
0 10 20 30 40 50 60 70 80 90 100 110 120 130
T (°C)
J O u t p u t V o l t a g e D e v i a t i o n (%)
Figure 4. Reference Voltage vs. T emperature
0 10 20 30 40 50 60 70 80 90 100 110 120 130
Temperature (°C)
A d j u s t P i n C u r r e n t (μA )
Frequency(Hz)
R i p p l e R e j e c t i o n (d B )
Figure 5. Adjust Pin Current vs. Temperature
Figure 6. Ripple Rejection vs. Frequency
Time(μS)
L o a d S t e p (m A ) V o l t a g e D e v i a t i o n (m V )
Figure 7. Transient Response
3.53.33.12.9
2.72.52.32.11.91.7
1.5
1.0 1.5
2.0 2.5
3.0 3.5
4.0
V -
V IN O UT(V)
I (A )
S C Figure 8. Short Circuit Current vs. V -V IN OUT
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SOT- 223 PACKAGE OUTLINE DIMENSIONS
Unit: mm
TO-252-3 PACKAGE OUTLINE DIMENSIONS
Unit: mm
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TO-220 PACKAGE OUTLINE DIMENSIONS
Unit: mm
+0.1
-0.05
TO-263-2 PACKAGE OUTLINE DIMENSIONS
(2.54 ± 0.20)
Unit: mm
R 0.3
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ORDERING NUMBER
1.0A LOW DROPOUT PRECISION LINEAR REGULATORS
A
A MICROELECTRONICS
GM1117
1.0A LOW DROPOUT PRECISION LINEAR REGULATORS
Power Management
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