Download

PDF Abstract Text:

LT1764 Series 3A, Fast Transient Response, Low Noise, LDO Regulators

DESCRIPTIO

LT1764 Series 3A, Fast Transient Response, Low Noise, LDO Regulators
FEATURES
DESCRIPTIO
APPLICATIO S
, LTC and LT are registered trademarks of Linear Technology Corporation.
3.3V to 2.5V Logic Power Supply Post Regulator for Switching Supplies
TYPICAL APPLICATIO
3.3VIN to 2.5VOUT Regulator
DROPOUT VOLTAGE (mV)
350 300 250 200 150 100 50 0 0 0.5 1.0 1.5 2.0 LOAD CURRENT (A) 2.5 3.0
1764 TA02
OUT LT1764-2.5
2.5V 3A
SHDN SENSE GND
1764 TA01
Dropout Voltage
1764fa
LT1764 Series
ABSOLUTE MAXIMUM RATINGS (Note 1)
PACKAGE / ORDER INFORMATION
FRONT VIEW 5 4 TAB IS GND 3 2 1 Q PACKAGE 5-LEAD PLASTIC DD SENSE / ADJ OUT GND IN SHDN
ORDER PART NUMBER LT1764EQ LT1764EQ-1.5 LT1764EQ-1.8 LT1764EQ-2.5 LT1764EQ-3.3
TAB IS GND
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
Regulated Output Voltage (Note 4)
FRONT VIEW 5 4 3 2 1 T PACKAGE 5-LEAD PLASTIC TO-220 GND IN SHDN SENSE / ADJ OUT
ORDER PART NUMBER LT1764ET LT1764ET-1.5 LT1764ET-1.8 LT1764ET-2.5 LT1764ET-3.3
1764fa
LT1764 Series
ELECTRICAL CHARACTERISTICS
MAX 10 10 10 10 10 7 23 23 8 25 25 10 30 30 12 40 40 5 20 20 0.05 0.10 0.13 0.18 0.20 0.27 0.33 0.40 0.66 0.45 0.66 1.5 1.6 5 18 75 200 200 10 2 1 30 1
Load Regulation
LT1764-1.8
LT1764-2.5
LT1764-3.3
Output Voltage Noise ADJ Pin Bias Current Shutdown Threshold SHDN Pin Current (Note 9) Quiescent Current in Shutdown Ripple Rejection
1764fa
LT1764 Series
ELECTRICAL CHARACTERISTICS
TYPICAL PERFOR A CE CHARACTERISTICS
Typical Dropout Voltage
GUARANTEED DROPOUT VOLTAGE (mV)
500 TJ 125°C 400 300 TJ 25°C 200 100 0 0 0.5
DROPOUT VOLTAGE (mV)
1.0 1.5 2.0 OUTPUT CURRENT (A)
1764 G01
Guaranteed Dropout Voltage
Dropout Voltage
2.0 1.5 1.0 OUTPUT CURRENT (A)
1764 G02
50 25 75 0 TEMPERATURE (°C)
1764 G03
1764fa
LT1764 Series TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current
QUIESCENT CURRENT (mA)
LT1764-1.8 / 2.5 / 3.3
1.0 LT1764 0.8 0.6 0.4 0.2
OUTPUT VOLTAGE (V)
LT1764-3.3 Output Voltage
OUTPUT VOLTAGE (V)
QUIESCENT CURRENT (mA)
ADJ PIN VOLTAGE (V)
3.34 3.32 3.30 3.28 3.26 3.24 3.22 - 50 - 25 0 75 50 25 TEMPERATURE (°C) 100 125
LT1764-2.5 Quiescent Current
QUIESCENT CURRENT (mA)
1764 G04 1756 G07 1764 G10
LT1764-1.8 Output Voltage
LT1764-2.5 Output Voltage
75 50 25 TEMPERATURE (°C)
1756 G05
1756 G06
LT1764 ADJ Pin Voltage
1.230 1.225 1.220 1.215 1.210 1.205 1.200 1.195 1.190 - 50 - 25 0 75 50 25 TEMPERATURE (°C) 100 125
LT1764-1.8 Quiescent Current
1756 G08
1764 G09
LT1764-3.3 Quiescent Current
LT1764 Quiescent Current
6 8 10 12 14 16 18 20 INPUT VOLTAGE (V)
1764 G12
1764 G11
1764fa
LT1764 Series TYPICAL PERFOR A CE CHARACTERISTICS
LT1764-1.8 GND Pin Current
GND PIN CURRENT (mA)
LT1764 GND Pin Current
GND PIN CURRENT (mA)
3 4 5 6 7 INPUT VOLTAGE (V)
LT1764-3.3 GND Pin Current
GND PIN CURRENT (mA)
3 4 5 6 7 INPUT VOLTAGE (V)
1764 G13
LT1764-2.5 GND Pin Current
LT1764-3.3 GND Pin Current
3 4 5 6 7 INPUT VOLTAGE (V)
1764 G14
1764 G15
LT1764-1.8 GND Pin Current
LT1764-2.5 GND Pin Current
3 4 5 6 7 INPUT VOLTAGE (V)
1764 G16
1764 G17
1764 G18
LT1764 GND Pin Current
GND Pin Current vs ILOAD
3 4 5 6 7 INPUT VOLTAGE (V)
1.0 2.0 1.5 OUTPUT CURRENT (A)
1764 G21
1764 G19
1764 G20
1764fa
LT1764 Series TYPICAL PERFOR A CE CHARACTERISTICS
SHDN Pin Threshold (On-to-Off)
SHDN PIN THRESHOLD (V)
0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 -50 -25 50 25 0 75 TEMPERATURE (°C) 100 125
SHDN PIN THRESHOLD (V)
SHDN PIN INPUT CURRENT (µA)
SHDN Pin Input Current
SHDN PIN INPUT CURRENT (µA)
ADJ PIN BIAS CURRENT (µA)
8 7 6 5 4 3 2 1 0 -50 -25 50 25 0 75 TEMPERATURE (°C) 100 125
CURRENT LIMIT (A)
Current Limit
CURRENT LIMIT (A)
REVERSE OUTPUT CURRENT (mA)
50 25 75 0 TEMPERATURE (°C)
1764 G22 1764 G25
SHDN Pin Threshold (Off-to-On)
10 9 8 7 6 5 4 3 2 1 0 50 25 0 75 TEMPERATURE (°C) 100 125
SHDN Pin Input Current
6 8 10 12 14 16 18 20 SHDN PIN VOLTAGE (V)
1764 G24
1764 G23
ADJ Pin Bias Current
Current Limit
75 50 25 TEMPERATURE (°C)
4 6 8 10 12 14 16 18 20 INPUT / OUTPUT DIFFERENTIAL (V)
1764 G27
1756 G26
Reverse Output Current
1764 G28
1764 G29
1764 G30
1764fa
LT1764 Series TYPICAL PERFOR A CE CHARACTERISTICS
Ripple Rejection
RIPPLE REJECTION (dB)
MINIMUM INPUT VOLTAGE (V)
Load Regulation
OUTPUT NOISE SPECTRAL DENSITY (µV / Hz)
LOAD REGULATION (mV)
OUTPUT NOISE (µVRMS)
LT1764
LT1764-3.3 10Hz to 100kHz Output Noise
OUTPUT VOLTAGE DEVIATION (V)
0.1 0 -0.1 -0.2 1.00 0.75 0.50 0.25 0 0 2 4 6 8 10 12 14 16 18 20 TIME (µs)
1764 G38
OUTPUT VOLTAGE DEVIATION (V)
VOUT 100µV / DIV
LOAD CURRENT (A)
1ms / DIV
1764 G31 1764 G34
Ripple Rejection
LT1764 Minimum Input Voltage
50 25 0 75 TEMPERATURE (°C)
50 25 75 0 TEMPERATURE (°C)
1764 G32
1764 G33
Output Noise Spectral Density
RMS Output Noise vs Load Current (10Hz to 100kHz)
LT1764-3.3 0.1
LT1764-2.5
LT1764
LT1764-1.8
1k 10k FREQUENCY (Hz)
1764 G35
0.01 0.1 LOAD CURRENT (A)
1764 G36
LT1764-3.3 Transient Response
1764 G39
1764 G37
1764fa
LT1764 Series
PI FU CTIO S
IN LT1764
SENSE GND 3
1764 F01
Figure 1. Kelvin Sense Connection
1764fa
LT1764 Series
APPLICATIO S I FOR ATIO
The LT1764 series are 3A low dropout regulators optimized for fast transient response. The devices are capable of supplying 3A at a dropout voltage of 340mV. The low operating quiescent current (1mA) drops to less than 1µA in shutdown. In addition to the low quiescent current, the LT1764 regulators incorporate several protection features which make them ideal for use in battery-powered systems. The devices are protected against both reverse input and reverse output voltages. In battery backup applications where the output can be held up by a backup battery when the input is pulled to ground, the LT1764-X acts like it has a diode in series with its output and prevents reverse current flow. Additionally, in dual supply applications where the regulator load is returned to a negative supply, the output can be pulled below ground by as much as 20V and still allow the device to start and operate. Adjustable Operation The adjustable version of the LT1764 has an output voltage range of 1.21V to 20V. The output voltage is set by the ratio of two external resistors as shown in Figure 2. The device servos the output to maintain the voltage at the ADJ pin at 1.21V referenced to ground. The current in R1 is then equal to 1.21V / R1 and the current in R2 is the current in R1 plus the ADJ pin bias current. The ADJ pin bias current, 3µA at 25°C, flows through R2 into the ADJ pin. The output voltage can be calculated using the formula in Figure 2. The value of R1 should be less than 4.17k to minimize errors in the output voltage caused by the ADJ pin bias current. Note that in shutdown the output is turned off and the divider current will be zero.
IN VIN LT1764 ADJ GND R1
1764 F02
Figure 2. Adjustable Operation
1764fa
LT1764 Series
APPLICATIO S I FOR ATIO
20 0 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10µF X5R -20 -40 -60 Y5V -80 -100
8 6 4 10 12 DC BIAS VOLTAGE (V)
1764 F03
Figure 3. Ceramic Capacitor DC Bias Characteristics
0 -20 -40 -60 -80 BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10µF 50 25 75 0 TEMPERATURE (°C) Y5V
1764 F04
Figure 4. Ceramic Capacitor Temperature Characteristics
voltage across its terminals due to mechanical stress, similar to the way a piezoelectric accelerometer or microphone works. For a ceramic capacitor the stress can be induced by vibrations in the system or thermal transients. Overload Recovery Like many IC power regulators, the LT1764-X has safe operating area protection. The safe area protection decreases the current limit as input-to-output voltage increases and keeps the power transistor inside a safe operating region for all values of input-to-output voltage. The protection is designed to provide some output current at all values of input-to-output voltage up to the device breakdown.
When power is first turned on, as the input voltage rises, the output follows the input, allowing the regulator to start up into very heavy loads. During the start-up, as the input voltage is rising, the input-to-output voltage differential is small, allowing the regulator to supply large output currents. With a high input voltage, a problem can occur wherein removal of an output short will not allow the output voltage to recover. Other regulators, such as the LT1085, also exhibit this phenomenon, so it is not unique to the LT1764 series. The problem occurs with a heavy output load when the input voltage is high and the output voltage is low. Common situations are immediately after the removal of a short circuit or when the SHDN pin is pulled high after the input voltage has already been turned on. The load line for such a load may intersect the output current curve at two points. If this happens, there are two stable output operating points for the regulator. With this double intersection, the input power supply may need to be cycled down to zero and brought up again to make the output recover. Output Voltage Noise The LT1764 regulators have been designed to provide low output voltage noise over the 10Hz to 100kHz bandwidth while operating at full load. Output voltage noise is typically 50nVHz over this frequency bandwidth for the LT1764 (adjustable version). For higher output voltages (generated by using a resistor divider), the output voltage noise will be gained up accordingly. This results in RMS noise over the 10Hz to 100kHz bandwidth of 15µVRMS for the LT1764 increasing to 37µVRMS for the LT1764-3.3. Higher values of output voltage noise may be measured when care is not exercised with regards to circuit layout and testing. Crosstalk from nearby traces can induce unwanted noise onto the output of the LT1764-X. Power supply ripple rejection must also be considered the LT1764 regulators do not have unlimited power supply rejection and will pass a small portion of the input noise through to the output.
1764fa
LT1764 Series
APPLICATIONS INFORMATION
Thermal Considerations The power handling capability of the device is limited by the maximum rated junction temperature (125°C). The power dissipated by the device is made up of two components: 1. Output current multiplied by the input / output voltage differential: (IOUT)(VIN - VOUT), and 2. GND pin current multiplied by the input voltage: (IGND)(VIN). The GND pin current can be found using the GND Pin Current curves in the Typical Performance Characteristics. Power dissipation will be equal to the sum of the two components listed above. The LT1764 series regulators have internal thermal limiting designed to protect the device during overload conditions. For continuous normal conditions, the maximum junction temperature rating of 125°C must not be exceeded. It is important to give careful consideration to all sources of thermal resistance from junction to ambient. Additional heat sources mounted nearby must also be considered. For surface mount devices, heat sinking is accomplished by using the heat spreading capabilities of the PC board and its copper traces. Surface mount heatsinks and plated through-holes can also be used to spread the heat generated by power devices. The following table lists thermal resistance for several different board sizes and copper areas. All measurements were taken in still air on 1 / 16" FR-4 board with one ounce copper.
Table 1. Q Package, 5-Lead DD
COPPER AREA TOPSIDE 2500mm2 1000mm2 125mm
BACKSIDE 2500mm2 2500mm2 2500mm
BOARD AREA 2500mm2 2500mm2 2500mm
THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 23°C / W 25°C / W 33°C / W
Device is mounted on topside.
1764fa
LT1764 Series
APPLICATIONS INFORMATION
5.0 REVERSE OUTPUT CURRENT (mA) 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0
1764 F05
LT1764
LT1764-1.8
LT1764-3.3
3 4 5 6 7 8 OUTPUT VOLTAGE (V)
Figure 5. Reverse Output Current
1764fa
LT1764 Series
TYPICAL APPLICATIO S
SCR Preregulator Provides Efficiency Over Line Variations
L1 500µH 1N4148 1k 10V AC AT 115VIN 12.1k NTE5437 1N4002 "SYNC" 1N4002 TO ALL "V +" POINTS 2.4k 1N4002 V+
L2 10V AC AT 115VIN
90V AC TO 140V AC
22µF 750
C1 10µF
C2 3.3µF
NTE5437
LT1764-3.3
10000µF 34k
IN SHDN GND
OUT FB
VOUT 3.3V 3A
C1A 1 / 2 LT1018
1N4148
200k 0.1µF
V+ 0.033µF 750
C1B 1 / 2 LT1018 1N4148
A1 LT1006 10k 10k V+
10k 1µF
LT1004 1.2V
1764 TA03
Adjustable Current Source
R5 0.01 R1 1k R4 2.2k R6 2.2k IN OUT LT1764-1.8 SHDN FB GND R8 100k
LT1004-1.2
R2 40.2k R3 2k
C3 1µF
R7 470
ADJUST R1 FOR 0A TO 3A CONSTANT CURRENT 2 8 1
1764 TA04
1764fa
LT1764 Series
PACKAGE DESCRIPTION
Q Package 5-Lead Plastic DD Pak
(LTC DWG # 05-08-1461)
0.060 (1.524) TYP
0.075 (1.905) 0.300 (7.620) BOTTOM VIEW OF DD PAK HATCHED AREA IS SOLDER PLATED COPPER HEAT SINK +0.012 0.143 -0.020 0.067 (1.70) 0.028 - 0.038 BSC (0.711 - 0.965) 0.013 - 0.023 (0.330 - 0.584)
0.230 - 0.270 (5.842 - 6.858) 0.460 - 0.500 (11.684 - 12.700) 0.570 - 0.620 (14.478 - 15.748) 0.330 - 0.370 (8.382 - 9.398) 0.700 - 0.728 (17.78 - 18.491) 0.620 (15.75) TYP
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
0.390 - 0.415 (9.906 - 10.541) 15° TYP
0.059 (1.499) TYP
Q(DD5) 1098
T Package 5-Lead Plastic TO-220 (Standard)
(LTC DWG # 05-08-1421)
0.147 - 0.155 (3.734 - 3.937) DIA
SEATING PLANE 0.152 - 0.202 0.260 - 0.320 (3.861 - 5.131) (6.60 - 8.13)
MEASURED AT THE SEATING PLANE
T5 (TO-220) 0399
1764fa
LT1764 Series
TYPICAL APPLICATIO U
Paralleling of Regulators for Higher Output Current
R1 0.01
C1 100µF
IN OUT LT1764-3.3 SHDN FB GND R2 0.01 IN OUT LT1764 ADJ GND
3.3V 6A C2 22µF
R6 6.65k R7 4.12k
R3 2.2k
R4 2.2k
8 1 C3 0.01µF
1764 TA05
RELATED PARTS
PART NUMBER LT1120 LT1121 LT1129 LT1175 LT1374 LT1521 LT1529 LT1573 LT1575 LT1735 LT1761 Series LT1762 Series LT1763 Series LT1962 LT1963 DESCRIPTION 125mA Low Dropout Regulator with 20µA IQ 150mA Micropower Low Dropout Regulator 700mA Micropower Low Dropout Regulator 500mA Negative Low Dropout Micropower Regulator 4.5A, 500kHz Step-Down Converter 300mA Low Dropout Micropower Regulator with Shutdown 3A Low Dropout Regulator with 50µA IQ UltraFast Transient Response Low Dropout Regulator UltraFast Transient Response Low Dropout Regulator Synchronous Step-Down Converter 100mA, Low Noise, Low Dropout Micropower Regulators in SOT-23 150mA, Low Noise, LDO Micropower Regulators 500mA, Low Noise, LDO Micropower Regulators 300mA, Low Noise, LDO Micropower Regulator 1.5A, Low Noise, Fast Transient Response LDO COMMENTS Includes 2.5V Reference and Comparator 30µA IQ, SOT-223 Package 50µA Quiescent Current 45µA IQ, 0.26V Dropout Voltage, SOT-223 Package 4.5A, 0.07 Internal Switch, SO-8 Package 15µA IQ, Reverse Battery Protection 500mV Dropout Voltage Drives External PNP Drives External N-Channel MOSFET High Efficiency, OPTI-LOOP Compensation 20µA Quiescent Current, 20µVRMS Noise, SOT-23 Package 25µA Quiescent Current, 20µVRMS Noise, MSOP Package 30µA Quiescent Current, 20µVRMS Noise, SO-8 Package 20µVRMS Noise, MSOP Package 40µVRMS Noise, SOT-223 Package
UltraFast and OPTI-LOOP are trademarks of Linear Technology Corporation.
1764fa
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
LT / TP 0602 1.5K REV A · PRINTED IN USA
www.linear.com