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Final Electrical Specifications
LTC1844 Series 150mA, Micropower, Low Noise, VLDO Linear Regulator
May 2003
FEATURES
s
DESCRIPTIO
s s s s
s s s s s s s s s s s
Very Low Dropout: 90mV at 150mA 30mV at 50mA (LTC1844-3.3) Wide Input Voltage Range: 1.6V to 6.5V Low 35A Supply Current, Even in Dropout Low Noise: 30VRMS (10Hz to 100kHz) 1.75% Voltage Accuracy Over Temperature, Voltage and Current Ranges Fast Transient Response 10nA Supply Current in Shutdown Fixed Output Voltages: 1.5V, 1.8V, 2.5V, 2.8V, 3.3V Adjustable Output Voltage: 1.25V to 6V Output Current Limit Reverse-Battery and Reverse-Current Protection No Protection Diodes Needed Stable with 1F Output Capacitor Stable with Ceramic Capacitors Short-Circuit and Thermal Overload Protection Low Profile (1mm) SOT-23 Package
The LTC(R)1844 Series are low noise VLDOTM (very low dropout) linear regulators designed for low power/portable applications. These regulators can operate from input voltages as low as 1.6V. Typical output noise is only 30VRMS and typical dropout for the LTC1844-3.3 is just 90mV at the maximum load current of 150mA, reducing to 30mV at 50mA. The internal P-channel MOSFET pass transistor requires no base current, allowing the device to draw only 35A during normal operation, independent of the dropout voltage and load current. The quiescent current falls to a negligible 10nA during shutdown. Other features include high output voltage accuracy, excellent transient response, stablity with ultralow ESR ceramic capacitors as small as 1F, reverse-battery and reverse-current protection, short-circuit and thermal overload protection and output current limiting. The LTC1844 regulators are available in a low profile (1mm) SOT-23 (ThinSOTTM) package.
, LTC and LT are registered trademarks of Linear Technology Corporation. VLDO and ThinSOT are trademarks of Linear Technology Corporation.
APPLICATIO S
s s s s
Bluetooth/802.11 Cards PDAs and Notebook Computers Portable Instruments and Battery-Powered Systems Cellular Phones
TYPICAL APPLICATIO
VIN 3.3V TO 6.5V 1F OFF ON 3 1
LTC1844-3.3 Dropout Voltage vs Load Current
120 100
Fixed Voltage Low Noise, VLDO Linear Regulator
DROPOUT VOLTAGE (mV)
IN OUT LTC1844-3.3 BYP SHDN GND 2 4 0.1F
1844 TA01
5 1F
VOUT 3.3V
80 60 40 20 0
0
25
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.
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50 75 100 IOUT (mA) 125 150
1844 TA02
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U
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1
LTC1844 Series
ABSOLUTE AXI U RATI GS (Note 1)
Output Short-Circut Duration .......................... Indefinite Operating Junction Temperature Range (Notes 2, 10) .....................................-40C to 125C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C Supply Voltage (IN) ....................................... - 7V to 7V Input Voltage SHDN, BYP, ADJ .................................... - 0.3V to 7V Output Voltage OUT ........................................................ - 0.3V to 7V OUT to IN .................................................. - 7V to 7V
PACKAGE/ORDER I FOR ATIO
TOP VIEW IN 1 GND 2 SHDN 3 4 BYP 5 OUT
IN 1 GND 2 SHDN 3
S5 PACKAGE 5-LEAD PLASTIC TSOT-23
S5 PACKAGE 5-LEAD PLASTIC TSOT-23
TJMAX = 150C, JA = 250C/ W, JC = 90C/ W SEE THE APPLICATIONS INFORMATION SECTION
TJMAX = 150C, JA = 250C/ W, JC = 90C/ W SEE THE APPLICATIONS INFORMATION SECTION
ORDER PART NUMBER LTC1844ES5-1.5 LTC1844ES5-1.8 LTC1844ES5-2.5 LTC1844ES5-2.8 LTC1844ES5-3.3
S5 PART MARKING LTF1 LTF2 LTF3 LTQK LTF4
ORDER PART NUMBER LTC1844ES5-SD
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
SYMBOL VIN IIN IINSHDN VOUT% PARAMETER Input Voltage Quiescent Current VIN Shutdown Supply Current Regulated Output Voltage (Notes 3, 4, 5) SHDN = VIN CONDITIONS
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = VOUT + 0.5V, unless otherwise noted. (Note 2)
MIN
q q
SHDN = 0V LTC1844-3.3 LTC1844-3.3 LTC1844-2.8 LTC1844-2.8 LTC1844-2.5 LTC1844-2.5 LTC1844-1.8 LTC1844-1.8 VIN = 3.8V to 6.5V, IOUT = 0mA to 150mA VIN = 3.8V to 6.5V, IOUT = 0mA to 150mA VIN = 3.3V to 6.5V, IOUT = 0mA to 150mA VIN = 3.3V to 6.5V, IOUT = 0mA to 150mA VIN = 3.0V to 6.5V, IOUT = 0mA to 150mA VIN = 3.0V to 6.5V, IOUT = 0mA to 150mA VIN = 2.3V to 6.5V, IOUT = 0mA to 150mA VIN = 2.3V to 6.5V, IOUT = 0mA to 150mA
2
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U
W
WW U
W
TOP VIEW 5 OUT IN 1 GND 2 4 ADJ BYP 3
TOP VIEW 5 OUT
4 ADJ
S5 PACKAGE 5-LEAD PLASTIC TSOT-23
TJMAX = 150C, JA = 250C/ W, JC = 90C/ W SEE THE APPLICATIONS INFORMATION SECTION
S5 PART MARKING LTE8
ORDER PART NUMBER LTC1844ES5-BYP
S5 PART MARKING LTE9
TYP 35
MAX 6.5 55 80 1 1.50 1.75 1.50 1.75 1.50 1.75 1.50 1.75
UNITS V A A A %VOUT %VOUT %VOUT %VOUT %VOUT %VOUT %VOUT %VOUT
1.6
q q q q q
0.01 -1.50 -1.75 -1.50 -1.75 -1.50 -1.75 -1.50 -1.75
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LTC1844 Series
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS LTC1844-1.5 LTC1844-1.5 LTC1844-1.5 LTC1844-BYP LTC1844-BYP LTC1844-BYP LTC1844-SD LTC1844-SD LTC1844-SD VLNR Line Regulation (Notes 3, 5) LTC1844-3.3 LTC1844-2.8 LTC1844-2.5 LTC1844-1.8 VIN = 2.0V to 6.5V, IOUT = 0mA to 150mA VIN = 2.2V to 6.5V, IOUT = 0mA to 150mA VIN = 2.0V to 6.5V, IOUT = 0mA to 150mA VIN = 1.75V to 6.5V, IOUT = 0mA to 150mA VIN = 2.2V to 6.5V, IOUT = 0mA to 150mA VIN = 1.75V to 6.5V, IOUT = 0mA to 150mA VIN = 1.75V to 6.5V, IOUT = 0mA to 150mA VIN = 2.2V to 6.5V, IOUT = 0mA to 150mA VIN = 1.75V to 6.5V, IOUT = 0mA to 150mA VIN = 3.4V to 6.5V, IL = 1mA VIN = 2.9V to 6.5V, IL = 1mA VIN = 2.6V to 6.5V, IL = 1mA VIN = 2.2V to 6.5V, IL = 1mA VIN = 1.9V to 6.5V, IL = 1mA VIN = 1.9V to 6.5V, IL = 1mA VIN = 2.2V to 6.5V, IL = 1mA VIN = 1.6V to 6.5V, IL = 1mA VIN = 1.6V to 6.5V, IL = 1mA VIN = 2.2V to 6.5V, IL = 1mA VIN = 1.6V to 6.5V, IL = 1mA VIN = 1.6V to 6.5V, IL = 1mA VIN = 2.2V to 6.5V, IL = 1mA VIN = 1.6V to 6.5V, IL = 1mA VIN = 1.6V to 6.5V, IL = 1mA VIN = 3.8V, IOUT = 0mA to 150mA VIN = 3.3V, IOUT = 0mA to 150mA VIN = 3.0V, IOUT = 0mA to 150mA VIN = 2.3V, IOUT = 0mA to 150mA VIN = 2.2V, IOUT = 0mA to 150mA VIN = 2.0V, IOUT = 0mA to 150mA VIN = 2.2V, IOUT = 0mA to 150mA VIN = 1.75V, IOUT = 0mA to 150mA VIN = 2.2V, IOUT = 0mA to 150mA VIN = 1.75V, IOUT = 0mA to 150mA IOUT = 50mA IOUT = 150mA IOUT = 50mA IOUT = 150mA IOUT = 50mA IOUT = 150mA IOUT = 50mA IOUT = 150mA IOUT = 50mA IOUT = 150mA IOUT = 50mA IOUT = 150mA IOUT = 50mA IOUT = 150mA
q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q q
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = VOUT + 0.5V, unless otherwise noted. (Note 2)
MIN -1.50 -2.00 -2.50 -1.50 -1.75 -3.50 -1.50 -1.75 -3.50 4 4 4 4 4 4 4 4 4 4 4 4 4 4 4 9 9 9 9 9 9 9 9 9 9 30 90 35 105 45 135 85 230 115 350 45 135 45 135 TYP MAX 1.50 2.00 2.00 1.50 1.75 1.75 1.50 1.75 1.75 20 20 20 20 20 30 20 20 80 20 20 80 20 20 80 20 20 20 20 20 40 20 50 20 50 55 150 60 165 75 200 120 300 160 450 75 200 75 200 UNITS %VOUT %VOUT %VOUT %VOUT %VOUT %VOUT %VOUT %VOUT %VOUT mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV mV
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LTC1844-1.5
LTC1844-BYP
LTC1844-SD
VLDR
Load Regulation (Notes 3, 5)
LTC1844-3.3 LTC1844-2.8 LTC1844-2.5 LTC1844-1.8 LTC1844-1.5 LTC1844-BYP LTC1844-SD
VDO
Dropout Voltage (Notes 6, 7)
LTC1844-3.3 LTC1844-2.8 LTC1844-2.5 LTC1844-1.8 LTC1844-1.5 LTC1844-BYP LTC1844-SD
3
LTC1844 Series
ELECTRICAL CHARACTERISTICS
SYMBOL ILIM en VSHDN tDELAY TSHDN TSHDN IADJ IIRL PARAMETER Output Current Limit Output Voltage Noise SHDN Input Threshold Shutdown Exit Delay Thermal Shutdown Limit Thermal Shutdown Hysteresis ADJ Pin Bias Current Input Reverse Leakage Current (Notes 3, 8) LTC1844-3.3, LTC1844-2.8, LTC1844-2.5, LTC1844-1.8, LTC1844-1.5, VIN = -5V, VOUT = 0V LTC1844-BYP, LTC1844-SD, VIN = -5V, VOUT = 0V IORL VOSH VRP Output Reverse Leakage Current (Note 9) Start-Up Overshoot Output Ripple Rejection VIN = 0V, VOUT = VOUT(NOMINAL) VIN = 0V, VOUT = VOUT(NOMINAL) RL = 1k, SHDN Rise Time 1s (VIN - VOUT) = 1V (Avg), VRIPPLE = 0.5VP-P, fRIPPLE = 120Hz, ILOAD = 100mA
q q q q
The q denotes specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25C. VIN = VOUT + 0.5V, unless otherwise noted. (Note 2)
CONDITIONS
q
MIN 160
TYP 350 35 30
MAX
UNITS mA VRMS VRMS
f = 10Hz to 100kHz, CBP = 0.1F, COUT = 1F, IL = 150mA f = 10Hz to 100kHz, CBP = 0.1F, COUT = 10F, IL = 150mA
q
0.35
0.65 70
0.9 100 200
V s s C C
CBP = 0.01F, COUT = 1F, No load CBP = 0.01F, COUT = 1F, No load
q
155 10 30 200 1000 0.01 2 60 100 500 1500 0.1 1.2
nA A A A A %VOUT dB
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: The LTC1844 is tested and specified under pulse load conditions such that TJ TA. The LTC1844E is guaranteed to meet performance specifications from 0C to 70C. Specifications over the - 40C to 125C operating junction temperature range are assured by design, characterization and correlation with statistical process controls. Note 3: The LTC1844 adjustable versions are tested and specifed for these conditions with the ADJ pin connected to the OUT pin for a VOUT(NOMINAL) of 1.252V. Note 4: Operating conditions are limited by maximum junction temperature. The regulated output voltage specification will not apply for all possible combinations of input voltage and output current. When operating at maximum input voltage, the output current range must be limited. When operating at maximum output current, the input voltage range must be limited. Note 5: The LTC1844's high precision degrades slightly at high temperatures (TJ > 70C) with input voltages below 2.2V. The lower output voltage versions have been split into higher and lower accuracy input voltage ranges to reflect this.
Note 6: To ensure adequate input supply voltage, the LTC1844 adjustable versions are tested and specified for these conditions with an external resistor divider (two 100k resistors) for an output voltage of 2.504V. The external resistor divider will add a 5A load on the output. Note 7: Dropout voltage is (VIN - VOUT) when VOUT falls to 100mV below its nominal value measured at VIN = VOUT + 0.5V. For example, the LTC1844-3.3 is tested by measuring the VOUT at VIN = 3.8V, then VIN is lowered until VOUT falls 100mV below the measured value. The difference (VIN - VOUT) is then measured and defined as VDO. Note 8: ADJ pin bias current flows into the ADJ pin. Note 9: Output reverse leakage current is tested with the IN pin grounded and the OUT pin forced to the rated output voltage. Note 10: This IC includes overtemperature protection that is intended to protect the device during momentary overload conditions. Junction temperature will exceed 125C when overtemperature protection is active. Continuous operation above the specified maximum operating junction temperature may impair device reliability.
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LTC1844 Series
PI FU CTIO S
IN (Pin 1): Power for LTC1844 and Load. Power is supplied to the device through the IN pin. The IN pin should be locally bypassed to ground if the LTC1844 is more than a few inches away from another source of bulk capacitance. In general, the output impedance of a battery rises with frequency, so it is usually adviseable to include an input bypass capacitor in battery-powered circuits. A capacitor in the range of 0.1F to 1F is usually sufficient. The LTC1844 is designed to withstand reverse voltages on the IN pin with respect to both ground and the output pin. In the case of a reversed input, which can happen if a battery is plugged in backwards, the LTC1844 will act as if there is a large resistor in series with its input with only a small amount of current flow. GND (Pin 2): Ground and Heat Sink. Solder to a ground plane or large pad to maximize heat dissipation. SHDN (Pin 3, Fixed and SD Devices): Shutdown, Active Low. This pin is used to put the LTC1844 into shutdown. The SHDN pin current is typically less than 10nA. The SHDN pin cannot be left floating and must be tied to the input pin if not used. If reverse-battery protection is desired, the SHDN pin must be tied to the input pin through a large value resistor (10k to 1M). ADJ (Pin 4, Adjustable Devices): Output Adjust. For the adjustable versions of the LTC1844, this is the input to the error amplifier. It has a typical bias current of 30nA flowing into the pin. The ADJ pin reference voltage is 1.25V referenced to ground. The output voltage range is 1.25V to 6V and is typically set by connecting ADJ to a resistor divider from OUT to GND. See Figure 2. BYP (Pin 4, Fixed/Pin 3, BYP Devices): Noise Bypass. The BYP pin is used to augment the internal noise filter to improve low noise performance. A small low leakage bypass capacitor from this pin to ground will filter the input of the error amplifier to lower the output voltage noise. Any value may be used; larger values will result in lower output noise, but will increase initial power-up time. Shutdown exit delay time after a brief shutdown (<10ms) will not be affected. If not used, this pin must be left unconnected. OUT (Pin 5): Voltage Regulated Output. The OUT pin supplies power to the load. A minimum output capacitor of 1F is required to ensure stability. Larger output capacitors may be required for applications with large transient loads to limit peak voltage transients. See the Applications Information section for more information on output capacitance.
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LTC1844 Series
APPLICATIO S I FOR ATIO
The LTC1844 family are a series of 150mA ultralow dropout regulators with micropower quiescent current and shutdown. The devices are capable of supplying 150mA at a dropout voltage of 90mV (LTC1844-3.3, see Electrical Characteristics for dropout voltage of other versions). Output voltage noise is as low as 30VRMS over a 10Hz to 100kHz bandwidth with the addition of a 0.1F bypass capacitor. The low operating quiescent current (35A) drops to 10nA in shutdown. In addition to the low quiescent current, the LTC1844 regulators incorporate several protection features which make them ideal for use in battery-powered systems. The devices are protected against both reverse input voltages and reverse voltages from output to input (reverse current protection). The devices also include current limit and thermal overload protection, and will survive an output short circuit indefinitely. The fast transient response overcomes the traditional tradeoff between dropout voltage, quiescent current and load transient response inherent in most regulators by using a proprietary new architecture (see Figure 1).
OUTPUT VOLTAGE DEVIATION (V)
0.04 0.02 0 -0.02 -0.04
VIN = 3V CIN = 1F COUT = 1F
LOAD CURRENT (mA)
50 0 0 10 20 30 40 50 60 70 80 90 100 TIME (s)
1844 F01
Figure 1. LTC1844-2.5 Transient Response 1mA to 50mA to 1mA
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Adjustable Operation The adjustable version of the LTC1844 has an output voltage range of 1.25V to 6V. 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 ADJ pin voltage at 1.25V (referenced to ground). The current in R1 is then equal to 1.25V/R1 and the current in R2 is the current in R1 plus the ADJ pin bias current. The ADJ pin bias current, 30nA at 25C, 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 no greater than 1M 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 once COUT is discharged. Adjustable devices are tested and specified with the ADJ pin tied to the OUT pin for an output voltage of 1.25V. Specifications for output voltages greater than 1.25V will be proportional to the ratio of the desired output voltage to 1.25V: VOUT/1.25V. For example, load regulation for an
IN VIN OUT LTC1844 ADJ GND R1
1844 F02
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VOUT R2 CFF
+
R2 VOUT = 1.25V 1 + + (IADJ )(R2) R1 VADJ = 1.25V IADJ = 30nA AT 25C OUTPUT RANGE = 1.25V TO 6V CFF OPTIONAL
Figure 2. Adjustable Operation
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LTC1844 Series
APPLICATIO S I FOR ATIO
(5V/1.25V)(- 4mV) = -16mV
output current change of 1mA to 100mA is - 4mV typical at VOUT = 1.25V. At VOUT = 5V, load regulation is: Because the ADJ pin is relatively high impedance (depending on the resistor divider used), stray capacitance at this pin can introduce significant phase shift in the error amplifier loop. The PCB layout should be designed to absolutely minimize the capacitance seen at the ADJ pin. To ensure stability over all operating conditions when utilizing large divider resistors, it may be necessary to use a small ceramic feedforward capacitor (~1000pF) in parallel with the upper divider resistor (see CFF in Figure 2). As an added bonus, this capacitor will improve transient response. Bypass Capacitance and Low Noise Performance A bypass capacitor can optionally be connected from the BYP pin to ground to lower output voltage noise. A good quality low leakage capacitor is recommended. This capacitor will bypass the input of the error amplifier, providing a low frequency noise pole. The noise pole provided by this bypass capacitor will lower the output voltage noise to as low as 30VRMS with the addition of a 0.1F capacitor. Initial regulator power-up time is inversely proportional to the size of the bypass capacitor, slowing to 10ms with a 0.1F capacitor and 10F output capacitor. However, the LTC1844 does not discharge the bypass capacitor when
0.40 0.35 0.30
ESR ()
0.25 0.20 STABLE REGION 0.15 0.10 0.05 0 0.33 1 3.3 10 33 OUTPUT CAPACITANCE (F) 100
1844 F03
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put into shutdown and thus the shutdown exit delay can be much shorter (70s) than initial power-up time if the shutdown duration is brief (<10ms). The maximum shutdown duration required to allow fast shutdown exit is determined by the capacitor leakage current, thus a low leakage bypass capacitor is recommended. Output Capacitance and Transient Response The LTC1844 regulators are designed to be stable with a wide range of output capacitors. The ESR of the output capacitor affects stability, most notably with small capacitors. A minimum output capacitor of 1F with an ESR of 0.3 or less is recommended to ensure stability. The LTC1844 is a micropower device and output transient response will be a function of output capacitance. Larger values of output capacitance decrease the peak deviations and provide improved transient response for larger load current changes. Note that bypass capacitors used to decouple individual components powered by the LTC1844 will increase the effective output capacitor value. The shaded region of Figure 3 defines the region over which the LTC1844 regulators are stable. The maximum ESR allowed is 0.3. High ESR tantalum and electrolytic capacitors may be used, but a low ESR ceramic capacitor must be in parallel at the output. There is no minimum ESR requirement. Extra consideration must be given to the use of ceramic capacitors. Ceramic capacitors are manufactured with a variety of dielectrics, each with different behavior across
Figure 3. Stability
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LTC1844 Series
APPLICATIONS INFORMATION
temperature and applied voltage. The most common dielectrics used are Z5U, Y5V, X5R and X7R. The Z5U and Y5V dielectrics are good for providing high capacitances in a small package, but exhibit strong voltage and temperature coefficients as shown in Figures 4 and 5. When used with a 5V regulator, a 10F Y5V capacitor can exhibit an effective value as low as 1F to 2F over the operating temperature range. The X5R and X7R dielectrics result in more stable characteristics and are more suitable for use as the output capacitor. The X7R type has better stability across temperature, while the X5R is less expensive and is available in higher values.
20 0
BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10F X5R
CHANGE IN VALUE (%)
-20 -40 -60 Y5V -80
-100
0
2
4
8 6 10 12 DC BIAS VOLTAGE (V)
14
16
1844 F04
Figure 4. Ceramic Capacitor DC Bias Characteristics
40 20
CHANGE IN VALUE (%)
0 -20 -40 -60 -80 Y5V
X5R
BOTH CAPACITORS ARE 16V, 1210 CASE SIZE, 10F -100 50 25 75 -50 -25 0 TEMPERATURE (C)
100
125
1844 F05
Figure 5. Ceramic Capacitor Temperature Characteristics
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Additionally, some ceramic capacitors have a piezoelectric response. A piezoelectric device generates 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. The resulting voltages produced can cause appreciable amounts of noise, especially when a ceramic capacitor is used for noise bypassing. A ceramic capacitor produced Figure 6's trace in response to light tapping from a pencil. Similar vibrationinduced behavior can masquerade as increased output voltage noise.
LTC1844-2.8 COUT = 10F CBYP = 0.01F ILOAD = 100mA
VOUT 500V/DIV
100ms/DIV
1844 F06
Figure 6. Noise Resulting from Tapping on a Ceramic Capacitor
Thermal Considerations The power handling capability of the device will be limited by the maximum rated junction temperature (125C). The power dissipated by the device will be the output current multiplied by the input/output voltage differential: (IOUT)(VIN - VOUT). The LTC1844 series regulators have internal thermal limiting designed to protect the device during momentary overload conditions. For continuous normal conditions, the maximum junction temperature rating of 125C 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.
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LTC1844 Series
APPLICATIONS INFORMATION
For surface mount devices, heat sinking is accomplished by using the heat-spreading capabilities of the PC board and its copper traces. Copper board stiffeners and plated through holes can also be used to spread the heat generated by power devices. Table 1 lists thermal resistance for several different board sizes and copper areas. All measurements were taken in still air on 3/32" FR-4 board with one ounce copper.
Table 1. Measured Thermal Resistance
COPPER AREA TOPSIDE* BACKSIDE 2500mm 1000mm 100mm 50mm
2 2
BOARD AREA 2500mm 2500mm 2500mm 2500mm
2 2
THERMAL RESISTANCE (JUNCTION-TO-AMBIENT) 125C/W 125C/W 130C/W 135C/W 150C/W
2500mm 2500mm 2500mm 2500mm
2 2
225mm2
2 2
2500mm2
2 2
2500mm2
2 2
*Device is mounted on topside.
Calculating Junction Temperature Example: Given an output voltage of 3.3V, an input voltage of 4V to 6V, an output current range of 0mA to 50mA and a maximum ambient temperature of 50C, what will the maximum junction temperature be? The power dissipated by the device will be equal to: IOUT(MAX)(VIN(MAX) - VOUT) where: IOUT(MAX) = 50mA VIN(MAX) = 6V So: P = 50mA(6V - 3.3V) = 0.135W The power dissipated by the LTC1844's quiescent current (240W) is insignificant. The thermal resistance will be in the range of 125C/W to 150C/W depending on the
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copper area. The junction temperature rise above ambient will be approximately equal to: 0.135W(150C/W) = 20.3C The maximum junction temperature will then be equal to the maximum junction temperature rise above ambient plus the maximum ambient temperature or: T = 50C + 20.3C = 70.3C Protection Features The LTC1844 regulators incorporate several protection features which make them ideal for use in battery-powered circuits. In addition to the usual protection features associated with monolithic regulators, such as current limiting and thermal limiting, the devices are protected against reverse input voltages and reverse voltages from output to input. Current limit protection and thermal overload protection are intended to protect the device against current overload conditions at the output of the device. For normal operation, the junction temperature should not exceed 125C. The input of the device will withstand input voltages of - 7V. Current flow into the device will be limited to less than 500A (typically less than 200A) and only a small negative voltage will appear at the output (~ -300mV with no load). The LTC1844 will protect both itself and the load against batteries plugged in backward. In circuits where a backup battery is required, several different input/output conditions can occur. The output voltage may be held up externally while the input is either pulled to ground, pulled to some intermediate voltage or left open circuit. The LTC1844 features reverse current protection to limit current draw from any supplementary power source at the output. When VIN is pulled to ground or is left open circuit, IIN and IOUT are less than 0.1A for VOUT = 0V to 7V.
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LTC1844 Series
APPLICATIONS INFORMATION
When VIN is held constant and VOUT varied, current flow will follow the curves shown in Figure 7. With VOUT held below VOUT(NOM), the LTC1844 will be in current limit trying to pull VOUT up. With VOUT held between VOUT(NOM) and VIN, IIN will be at the normal quiescent current level and IOUT will be 1A to 2A. As VOUT is pulled above VIN, IOUT temporarily increases to 30A until the reverse current protection circuitry activates and reduces IOUT to less than 10A.
50 45 40 35 LTC1844-2.8 TJ = 25C VIN = 3.3V CURRENT FLOWS INTO PINS
CURRENT (A)
30 25 20 15 10 5 0 0
CURRENT (A)
IN CURRENT LIMIT BELOW 2.8V
IOUT
IIN
1
4 3 2 5 OUTPUT VOLTAGE (V)
6
7
1844 F07
Figure 7. Reverse Current vs Output Voltage
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Alternatively, when VOUT is held constant and VIN varied, current flow will follow Figure 8's curves. IOUT will be less than 10A at all times except for a brief spike just below 2.7V before the reverse current protection circuitry activates.
100 90 80 70 60 50 40 30 20 10 0 0 0.5 1.5 2.0 1.0 INPUT VOLTAGE (V) 2.5 3.0
1844 F08
LTC1844-2.8 TJ = 25C VOUT = 2.7V CURRENT FLOW INTO PINS
IN CURRENT LIMIT ABOVE 2.7V
IIN IOUT
Figure 8. Reverse Current vs Input Voltage
1844ia
LTC1844 Series
PACKAGE DESCRIPTIO
0.62 MAX
0.95 REF
3.85 MAX 2.62 REF
RECOMMENDED SOLDER PAD LAYOUT PER IPC CALCULATOR
0.20 BSC 1.00 MAX DATUM `A'
0.30 - 0.50 REF 0.09 - 0.20 (NOTE 3) NOTE: 1. DIMENSIONS ARE IN MILLIMETERS 2. DRAWING NOT TO SCALE 3. DIMENSIONS ARE INCLUSIVE OF PLATING 4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR 5. MOLD FLASH SHALL NOT EXCEED 0.254mm 6. JEDEC PACKAGE REFERENCE IS MO-193
U
S5 Package 5-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1635)
2.90 BSC (NOTE 4) 1.22 REF 1.4 MIN 2.80 BSC 1.50 - 1.75 (NOTE 4) PIN ONE 0.30 - 0.45 TYP 5 PLCS (NOTE 3) 0.95 BSC 0.80 - 0.90 0.01 - 0.10 1.90 BSC
S5 TSOT-23 0302
1844ia
11
LTC1844 Series RELATED PARTS
PART NUMBER LT1761 LT1762 LT1763 LT1764A LT1962 LT1963A LT1964 LT3150 DESCRIPTION 100mA, Low Noise LDO in ThinSOT 150mA, Low Noise LDO 500mA, Low Noise LDO 3A, Fast Transient Response, Low Noise LDO 300mA, Low Noise LDO 1.5A Low Noise, Fast Transient Response LDO 200mA, Low Noise, Negative LDO Fast Transient Response, VLDO Regulator Controller COMMENTS 300mV Dropout Voltage, Low Noise: 20VRMS, VIN = 1.8V to 20V, ThinSOT 300mV Dropout Voltage, Low Noise: 20VRMS, VIN = 1.8V to 20V, MS8 Package 300mV Dropout Voltage, Low Noise: 20VRMS, VIN = 1.8V to 20V, SO-8 Package 340mV Dropout Voltage, Low Noise: 40VRMS, VIN = 2.7V to 20V, TO-220 and DD Packages 270mV Dropout Voltage, Low Noise: 20VRMS, VIN = 1.8V to 20V, MS8 Package 340mV Dropout Voltage, Low Noise: 40VRMS, VIN = 2.5V to 20V, TO-220, DD, SOT-223 and SO-8 Packages 340mV Dropout Voltage, Low Noise 30VRMS, VIN = -1.8V to - 20V, ThinSOT 0.035mV Dropout Voltage via External FET, VIN: 1.3V to 10V
1844ia
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 q FAX: (408) 434-0507
q
LT/TP 0503 1K REV A * PRINTED IN USA
www.linear.com
(c) LINEAR TECHNOLOGY CORPORATION 2003

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