View LT1173_126352.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

LT1173 Micropower DC/DC Converter Adjustable and Fixed 5V, 12V
FEATURES
s s s s s s s s s
DESCRIPTIO
Operates at Supply Voltages From 2.0V to 30V Consumes Only 110A Supply Current Works in Step-Up or Step-Down Mode Only Three External Components Required Low Battery Detector Comparator On-Chip User-Adjustable Current Limit Internal 1A Power Switch Fixed or Adjustable Output Voltage Versions Space Saving 8-Pin MiniDIP or SO8 Package
The LT1173 is a versatile micropower DC-DC converter. The device requires only three external components to deliver a fixed output of 5V or 12V. Supply voltage ranges from 2.0V to 12V in step-up mode and to 30V in step-down mode. The LT1173 functions equally well in step-up, stepdown or inverting applications. The LT1173 consumes just 110A supply current at standby, making it ideal for applications where low quiescent current is important. The device can deliver 5V at 80mA from a 3V input in step-up mode or 5V at 200mA from a 12V input in step-down mode. Switch current limit can be programmed with a single resistor. An auxiliary gain block can be configured as a low battery detector, linear post regulator, under voltage lockout circuit or error amplifier. For input sources of less than 2V, use the LT1073.
APPLICATI
s s s s s s s s s
S
Flash Memory Vpp Generators 3V to 5V, 5V to 12V Converters 9V to 5V, 12V to 5V Converters LCD Bias Generators Peripherals and Add-On Cards Battery Backup Supplies Laptop and Palmtop Computers Cellular Telephones Portable Instruments
and LTC are registered trademarks and LT is a trademark of Linear Technology Corporation.
TYPICAL APPLICATI
L1* 100H 5VIN 47 I LIM 10 F V IN SW1
S
VPP Output
12V 100mA
Logic Controlled Flash Memory VPP Generator
1N5818
VOUT 5V/DIV
1.07M
+
+
LT1173 FB SW2
SANYO OS-CON 100 F
0V
GND
124k
PROGRAM 5V/DIV 5ms/DIV
1173 TA02
1N4148 PROGRAM
LT1173 * TA01
*L1 = GOWANDA GA20-103K COILTRONICS CTX100-4 NO OVERSHOOT
EFFICIENCY = 81% = 1% METAL FILM
U
UO
UO
1
LT1 173 ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW ILIM 1 VIN 2 SW1 3 SW2 4 8 7 6 5 FB (SENSE)* SET AO GND
Supply Voltage (VIN) ................................................ 36V SW1 Pin Voltage (VSW1) .......................................... 50V SW2 Pin Voltage (VSW2) ............................. - 0.5V to VIN Feedback Pin Voltage (LT1173) ................................. 5V Sense Pin Voltage (LT1173, -5, -12) ....................... 36V Maximum Power Dissipation ............................. 500mW Maximum Switch Current ....................................... 1.5A Operating Temperature Range ..................... 0C to 70C Storage Temperature Range .................. -65C to 150C Lead Temperature, (Soldering, 10 sec.)................ 300C
Consult factory for Industrial and Military grade parts
ORDER PART NUMBER LT1173CN8 LT1173CN8-5 LT1173CN8-12
N8 PACKAGE 8-LEAD PLASTIC DIP *FIXED VERSIONS TJMAX = 90C, JA = 130C/W
TOP VIEW ILIM 1 VIN 2 SW1 3 SW2 4 8 FB (SENSE)* 7 SET 6 AO 5 GND
LT1173CS8 LT1173CS8-5 LT1173CS8-12 S8 PART MARKING 1173 11735 117312
S8 PACKAGE 8-LEAD PLASTIC SOIC *FIXED VERSIONS
TJMAX = 90C, JA = 150C/W
ELECTRICAL CHARACTERISTICS TA = 25C, VIN = 3V, unless otherwise noted.
SYMBOL IQ IQ VIN PARAMETER Quiescent Current Quiescent Current, Boost Mode Configuration Input Voltage Comparator Trip Point Voltage VOUT Output Sense Voltage Comparator Hysteresis Output Hysteresis fOSC tON Oscillator Frequency Duty Cycle Switch ON Time Feedback Pin Bias Current Set Pin Bias Current VOL Gain Block Output Low Reference Line Regulation VSAT SWSAT Voltage, Step-Up Mode Full Load ILIM tied to VIN LT1173, VFB = 0V VSET = VREF ISINK = 100A, VSET = 1.00V 2.0V VIN 5V 5V VIN 30V VIN = 3.0V, ISW = 650mA VIN = 5.0V, ISW = 1A
q
CONDITIONS Switch Off No Load Step-Up Mode Step-Down Mode LT1173 (Note 1) LT1173-5 (Note 2) LT1173-12 (Note 2) LT1173 LT1173-5 LT1173-12 LT1173-5 LT1173-12
q q q q q q q q q q q q q q q q q q
MIN
TYP 110 135 250
MAX 150
UNITS A A A
2.0 1.20 4.75 11.4 1.245 5.00 12.0 5 20 50 18 43 17 23 51 22 10 20 0.15 0.2 0.02 0.5 0.8
12.6 30 1.30 5.25 12.6 10 40 100 30 59 32 50 100 0.4 0.4 0.075 0.65 1.0 1.4
2
U
V V V V V mV mV mV kHz % s nA nA V %/V %/V V V V
W
U
U
WW
W
LT1173
ELECTRICAL CHARACTERISTICS TA = 25C, VIN = 3V, unless otherwise noted.
SYMBOL VSAT AV PARAMETER SWSAT Voltage, Step-Down Mode Gain Block Gain Current Limit Current Limit Temperature Coeff. Switch OFF Leakage Current VSW2 Maximum Excursion Below GND Measured at SW1 Pin ISW1 10A, Switch Off CONDITIONS VIN = 12V, ISW = 650mA
q
MIN
TYP 1.1
MAX 1.5 1.7
UNITS V V V/V mA %/C
RL = 100k (Note 3) 220 to ILIM to VIN
q
400
1000 400 - 0.3 1 - 400 10 - 350
q
A mV
The q denotes the specifications which apply over the full operating temperature range. Note 1: This specification guarantees that both the high and low trip points of the comparator fall within the 1.20V to 1.30V range.
Note 2: The output voltage waveform will exhibit a sawtooth shape due to the comparator hysteresis. The output voltage on the fixed output versions will always be within the specified range. Note 3: 100k resistor connected between a 5V source and the AO pin.
TYPICAL PERFOR A CE CHARACTERISTICS
Saturation Voltage Step-Up Mode (SW2 Pin Grounded)
1.2 1.0
SWITCH ON VOLTAGE (V)
1.4 1.3
SWITCH CURRENT (mA)
VIN= 3.0V 0.8
VCESAT (V)
0.6 0.4 0.2 0 0 0.2 0.4
VIN= 2.0V
0.6 ISWITCH (A)
0.8
1000 900 800
Maximum Switch Current vs RLIM Step-Down Mode
VOUT = 5V
SET PIN BIAS CURRENT (nA)
FEEDBACK PIN BIAS CURRENT (A)
SWITCH CURRENT (mA)
VIN = 24V L = 500H
700 600 500 400 300 200 100 0 100 R LIM ()
LT1173 * TPC09
VIN = 12V L = 250H
UW
VIN = 5.0V 1.0
LT1173 * TPC01
Switch ON Voltage Step-Down Mode (SW1 Pin Connected to VIN)
1200 1100 1000 900 800 700 600 500 400 300 200 100
Maximum Switch Current vs RLIM Step-Up Mode
2V VIN 5V
1.2 1.1 1.0 0.9 0.8 0.7 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 ISWITCH (A)
LT1173 * TPC02
1.2
10
100 R LIM ()
1000
LT1173 * TPC03
Set Pin Bias Current vs Temperature
20 VIN = 3V 15 18
Feedback Pin Bias Current vs Temperature
VIN = 3V
16
14
12
10
10
1000
5 -50
8 -25 0 25 50 75 100 125 -50 -25 0 25 50 75 100 TEMPERATURE (C)
LT1173 *TPC04
125
TEMPERATURE (C)
LT1173 *TPC05
3
LT1 173
TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current vs Temperature
120 VIN = 3V 110
SUPPLY CURRENT (mA)
FOSC (kHz)
IIN (A)
100
90 -50
-25
0
25
50
75
TEMPERATURE (C)
LT1173 *TPC06
PI FU CTI
S
GND (Pin 5): Ground. AO (Pin 6): Auxiliary Gain Block (GB) output. Open collector, can sink 100A. SET (Pin 7): GB input. GB is an op amp with positive input connected to SET pin and negative input connected to 1.245V reference. FB/SENSE (Pin 8): On the LT1173 (adjustable) this pin goes to the comparator input. On the LT1173-5 and LT1173-12, this pin goes to the internal application resistor that sets output voltage.
ILIM (Pin 1): Connect this pin to VIN for normal use. Where lower current limit is desired, connect a resistor between ILIM and VIN. A 220 resistor will limit the switch current to approximately 400mA. VIN (Pin 2): Input supply voltage. SW1 (Pin 3): Collector of power transistor. For step-up mode connect to inductor/diode. For step-down mode connect to VIN. SW2 (Pin 4): Emitter of power transistor. For step-up mode connect to ground. For step-down mode connect to inductor/diode. This pin must never be allowed to go more than a Schottky diode drop below ground.
BLOCK DIAGRA S
LT1173
SET
SET A2 V IN GAIN BLOCK/ ERROR AMP 1.245V REFERENCE A1 OSCILLATOR DRIVER GND FB COMPARATOR SW2
LT1173 * BD01
4
UW
100
Supply Current vs Switch Current
50
26.0 25.5
Oscillator Frequency
40
25.0
30
VIN = 5V
24.5 24.0 23.5 23.0 22.5
20
VIN = 2V
10
0 125 0 200 400 600 800 1000 SWITCH CURRENT (mA)
LT1173 *TPC07
22.0 0 5 10 15 VIN(V)
LT1173 * TPC08
20
25
30
W
UO
U
U
LT1173-5, -12
A2
AO
AO
V IN GAIN BLOCK/ ERROR AMP I LIM SW1
I LIM
SW1
1.245V REFERENCE A1 OSCILLATOR DRIVER COMPARATOR R1 GND R2 753k SW2 SENSE LT1173-5: R1 = 250k LT1173-12: R1 = 87.4k
LT1173 * BD02
LT1173
LT1173 OPERATI
The LT1173 is a gated oscillator switcher. This type architecture has very low supply current because the switch is cycled only when the feedback pin voltage drops below the reference voltage. Circuit operation can best be understood by referring to the LT1173 block diagram. Comparator A1 compares the feedback pin voltage with the 1.245V reference voltage. When feedback drops below 1.245V, A1 switches on the 24kHz oscillator. The driver amplifier boosts the signal level to drive the output NPN power switch. An adaptive base drive circuit senses switch current and provides just enough base drive to ensure switch saturation without overdriving the switch, resulting in higher efficiency. The switch cycling action raises the output voltage and feedback pin voltage. When the feedback voltage is sufficient to trip A1, the oscillator is gated off. A small amount of hysteresis built into A1 ensures loop stability without external frequency compensation. When the comparator is low the oscillator and all high current circuitry is turned off, lowering device quiescent current to just 110A, for the reference, A1 and A2. The oscillator is set internally for 23s ON time and 19s OFF time, optimizing the device for circuits where VOUT and VIN differ by roughly a factor of 2. Examples include a 3V to 5V step-up converter or a 9V to 5V step-down converter.
APPLICATI
S I FOR ATIO
Measuring Input Current at Zero or Light Load Obtaining meaningful numbers for quiescent current and efficiency at low output current involves understanding how the LT1173 operates. At very low or zero load current, the device is idling for seconds at a time. When the output voltage falls enough to trip the comparator, the power switch comes on for a few cycles until the output voltage rises sufficiently to overcome the comparator hysteresis. When the power switch is on, inductor current builds up to hundreds of milliamperes. Ordinary digital multimeters are not capable of measuring average current because of bandwidth and dynamic range limitations. A different approach is required to measure the 100A off-state and 500mA on-state currents of the circuit. Quiescent current can be accurately measured using the circuit in Figure 1. VSET is set to the input voltage of the LT1173. The circuit must be "booted" by shorting V2 to VSET. After the LT1173 output voltage has settled, disconnect the short. Input voltage is V2, and average input current can be calculated by this formula:
IIN = V2 - V1 100
U
W
UO
A2 is a versatile gain block that can serve as a low battery detector, a linear post regulator, or drive an under voltage lockout circuit. The negative input of A2 is internally connected to the 1.245V reference. A resistor divider from VIN to GND, with the mid-point connected to the SET pin provides the trip voltage in a low battery detector application. The gain block output (AO) can sink 100A (use a 47k resistor pull-up to + 5V). This line can signal a microcontroller that the battery voltage has dropped below the preset level. A resistor connected between the ILIM pin and VIN sets maximum switch current. When the switch current exceeds the set value, the switch cycle is prematurely terminated. If current limit is not used, ILIM should be tied directly to VIN. Propagation delay through the current limit circuitry is approximately 2s. In step-up mode the switch emitter (SW2) is connected to ground and the switch collector (SW1) drives the inductor; in step-down mode the collector is connected to VIN and the emitter drives the inductor. The LT1173-5 and LT1173-12 are functionally identical to the LT1173. The -5 and -12 versions have on-chip voltage setting resistors for fixed 5V or 12V outputs. Pin 8 on the fixed versions should be connected to the output. No external resistors are needed.
U
UO
(01)
5
LT1 173
APPLICATI
+12V
S I FOR ATIO
1M 1F*
- LTC1050 + V1
100 V2 1000F
LT1173 CIRCUIT
+
V SET
*NON-POLARIZED
LT1173 * TA06
Figure 1. Test Circuit Measures No Load Quiescent Current of LT1073 Converter
Inductor Selection A DC-DC converter operates by storing energy as magnetic flux in an inductor core, and then switching this energy into the load. Since it is flux, not charge, that is stored, the output voltage can be higher, lower, or opposite in polarity to the input voltage by choosing an appropriate switching topology. To operate as an efficient energy transfer element, the inductor must fulfill three requirements. First, the inductance must be low enough for the inductor to store adequate energy under the worst case condition of minimum input voltage and switch ON time. The inductance must also be high enough so that maximum current ratings of the LT1173 and inductor are not exceeded at the other worst case condition of maximum input voltage and ON time. Additionally, the inductor core must be able to store the required flux; i.e., it must not saturate. At power levels generally encountered with LT1173 based designs, small axial leaded units with saturation current ratings in the 300mA to 1A range (depending on application) are adequate. Lastly, the inductor must have sufficiently low DC resistance so that excessive power is not lost as heat in the windings. An additional consideration is Electro-Magnetic Interference (EMI). Toroid and pot core type inductors are recommended in applications where EMI must be kept to a minimum; for example, where there are sensitive analog circuitry or transducers nearby. Rod core types are a less expensive choice where EMI is not a problem. Specifying a proper inductor for an application requires first establishing minimum and maximum input voltage, output voltage, and output current. In a step-up converter,
6
U
the inductive events add to the input voltage to produce the output voltage. Power required from the inductor is determined by PL = (VOUT + VD - VIN) (IOUT) (02) where VD is the diode drop (0.5V for a 1N5818 Schottky). Energy required by the inductor per cycle must be equal or greater than
W
U
UO
PL FOSC
in order for the converter to regulate the output.
(03)
When the switch is closed, current in the inductor builds according to
-R't V IL t = IN 1 - e L R'
()
(04)
where R' is the sum of the switch equivalent resistance (0.8 typical at 25C) and the inductor DC resistance. When the drop across the switch is small compared to VIN, the simple lossless equation
V IL t = IN t L
()
(05)
can be used. These equations assume that at t = 0, inductor current is zero. This situation is called "discontinuous mode operation" in switching regulator parlance. Setting "t" to the switch ON time from the LT1173 specification table (typically 23s) will yield iPEAK for a specific "L" and VIN. Once iPEAK is known, energy in the inductor at the end of the switch ON time can be calculated as
EL = 12 Li 2 PEAK
(06)
EL must be greater than PL/FOSC for the converter to deliver the required power. For best efficiency iPEAK should be kept to 1A or less. Higher switch currents will cause excessive drop across the switch resulting in reduced efficiency. In general, switch current should be held to as low a value as possible in order to keep switch, diode and inductor losses at a minimum.
LT1173
APPLICATI S I FOR ATIO U
(07) In the negative-to-positive case, the switch saturates and the 0.8 switch ON resistance value given for Equation 04 can be used. In both cases inductor design proceeds from Equation 03. The step-down case is different than the preceeding three in that the inductor current flows through the load in a step-down topology (Figure 6). Current through the switch should be limited to ~650mA in step-down mode. This can be accomplished by using the ILIM pin. With input voltages in the range of 12V to 25V, a 5V output at 300mA can be generated with a 220H inductor and 100 resistor in series with the ILIM pin. With a 20V to 30V input range, a 470H inductor should be used along with the 100 resistor. Capacitor Selection
As an example, suppose 9V at 50mA is to be generated from a 3V input. Recalling Equation 02, PL = (9V + 0.5V - 3V) (50mA) = 325mW. Energy required from the inductor is
PL FOSC
=
325mW = 13.5J. 24kHz
Picking an inductor value of 100H with 0.2 DCR results in a peak switch current of
iPEAK =
3V 1
-1 *23 s 1 - e 100H = 616m A.
Substituting iPEAK into Equation 04 results in
EL =
2 1 100H 0.616 A = 19.0J. 2
(
)(
)
Since 19J > 13.5J the 100H inductor will work. This trial-and-error approach can be used to select the optimum inductor. Keep in mind the switch current maximum rating of 1.5A. If the calculated peak current exceeds this, consider using the LT1073. The 70% duty cycle of the LT1073 allows more energy per cycle to be stored in the inductor, resulting in more output power. An inductor's energy storage capability is proportional to its physical size. If the size of the inductor is too large for a particular application, considerable size reduction is possible by using the LT1111. This device is pin compatible with the LT1173 but has a 72kHz oscillator, thereby reducing inductor and capacitor size requirements by a factor of three. For both positive-to-negative (Figure 7) and negative-topositive configurations (Figure 8), all the output power must be generated by the inductor. In these cases PL = ( VOUT + VD) (IOUT). (11)
In the positive-to-negative case, switch drop can be modeled as a 0.75V voltage source in series with a 0.65 resistor so that VL = VIN - 0.75V - IL (0.65). (12)
W
U
UO
(08)
(09)
(10)
Selecting the right output capacitor is almost as important as selecting the right inductor. A poor choice for a filter capacitor can result in poor efficiency and/or high output ripple. Ordinary aluminum electrolytics, while inexpensive and readily available, may have unacceptably poor equivalent series resistance (ESR) and ESL (inductance). There are low-ESR aluminum capacitors on the market specifically designed for switch mode DC-DC converters which work much better than general-purpose units. Tantalum capacitors provide still better performance at more expense. We recommend OS-CON capacitors from Sanyo Corporation (San Diego, CA). These units are physically quite small and have extremely low ESR. To illustrate, Figures 2, 3, and 4 show the output voltage of an LT1173 based converter with three 100F capacitors. The peak switch current is 500mA in all cases. Figure 2 shows a Sprague 501D, 25V aluminum capacitor. VOUT jumps by over 120mV when the switch turns off, followed by a drop in voltage as the inductor dumps into the capacitor. This works out to be an ESR of over 240m. Figure 3 shows the same circuit, but with a Sprague 150D, 20V tantalum capacitor replacing the aluminum unit. Output jump is now about 35mV, corresponding to an ESR of 70m. Figure 4 shows the circuit with a 16V OS-CON unit. ESR is now only 20m.
7
LT1 173
APPLICATI
50mV/DIV
S I FOR ATIO
50mV/DIV
5s/DIV
50mV/DIV
LT1173 * TA07
Figure 2. Aluminum
In very low power applications where every microampere is important, leakage current of the capacitor must be considered. The OS-CON units do have leakage current in the 5A to 10A range. If the load is also in the microampere range, a leaky capacitor will noticeably decrease efficiency. In this type application tantalum capacitors are the best choice, with typical leakage currents in the 1A to 5A range. Diode Selection Speed, forward drop, and leakage current are the three main considerations in selecting a catch diode for LT1173 converters. General purpose rectifiers such as the 1N4001 are unsuitable for use in any switching regulator application. Although they are rated at 1A, the switching time of a 1N4001 is in the 10s-50s range. At best, efficiency will be severely compromised when these diodes are used; at worst, the circuit may not work at all. Most LT1173 circuits will be well served by a 1N5818 Schottky diode. The combination of 500mV forward drop at 1A current, fast turn ON and turn OFF time, and 4A to 10A leakage current fit nicely with LT1173 requirements. At peak switch currents of 100mA or less, a 1N4148 signal diode may be used. This diode has leakage current in the 1nA5nA range at 25C and lower cost than a 1N5818. (You can also use them to get your circuit up and running, but beware of destroying the diode at 1A switch currents.) In situations where the load is intermittent and the LT1173 is idling most of the time, battery life can sometimes be extended by using a silicon diode such as the 1N4933, which can handle 1A but has leakage current of less than 1A. Efficiency will decrease somewhat compared to a 1N5818 while delivering power, but the lower idle current may be more important.
8
U
5s/DIV
LT1173 * TA08
W
U
UO
5s/DIV
LT1173 * TA09
Figure 3. Tantalum
Figure 4. OS-CON
Step-Up (Boost Mode) Operation A step-up DC-DC converter delivers an output voltage higher than the input voltage. Step-up converters are not short circuit protected since there is a DC path from input to output. The usual step-up configuration for the LT1173 is shown in Figure 5. The LT1173 first pulls SW1 low causing VIN - VCESAT to appear across L1. A current then builds up in L1. At the end of the switch ON time the current in L1 is1:
i PEAK =
V IN R3* I LIM V IN SW1 FB R2
VIN L
t ON
L1 D1
(13)
V OUT
+
C1
LT1173
GND
SW2 R1
* = OPTIONAL
LT1173 * TA10
Figure 5. Step-Up Mode Hookup. Refer to Table 1 for Component Values
Immediately after switch turn off, the SW1 voltage pin starts to rise because current cannot instantaneously stop flowing in L1. When the voltage reaches VOUT + VD, the inductor current flows through D1 into C1, increasing VOUT. This action is repeated as needed by the LT1173 to
Note 1: This simple expression neglects the effect of switch and coil resistance. This is taken into account in the "Inductor Selection" section.
LT1173
APPLICATI S I FOR ATIO U W
+
C1 R1
keep VFB at the internal reference voltage of 1.245V. R1 and R2 set the output voltage according to the formula R2 VOUT = 1 + 1.245V . R1
(
Step-Down (Buck Mode) Operation A step-down DC-DC converter converts a higher voltage to a lower voltage. The usual hookup for an LT1173 based step-down converter is shown in Figure 6.
VIN R3 100
+
C2
I LIM
V IN
SW1 FB
LT1173 L1 SW2 GND D1 1N5818 R2 VOUT
Figure 6. Step-Down Mode Hookup
When the switch turns on, SW2 pulls up to VIN - VSW. This puts a voltage across L1 equal to VIN - VSW - VOUT, causing a current to build up in L1. At the end of the switch ON time, the current in L1 is equal to
i PEAK =
VIN - VSW - VOUT L
When the switch turns off, the SW2 pin falls rapidly and actually goes below ground. D1 turns on when SW2 reaches 0.4V below ground. D1 MUST BE A SCHOTTKY DIODE. The voltage at SW2 must never be allowed to go below -0.5V. A silicon diode such as the 1N4933 will allow SW2 to go to - 0.8V, causing potentially destructive power dissipation inside the LT1173. Output voltage is determined by R2 VOUT = 1 + 1.245 V . R1
(
U
UO
)
(14)
R3 programs switch current limit. This is especially important in applications where the input varies over a wide range. Without R3, the switch stays on for a fixed time each cycle. Under certain conditions the current in L1 can build up to excessive levels, exceeding the switch rating and/or saturating the inductor. The 100 resistor programs the switch to turn off when the current reaches approximately 800mA. When using the LT1173 in stepdown mode, output voltage should be limited to 6.2V or less. Higher output voltages can be accommodated by inserting a 1N5818 diode in series with the SW2 pin (anode connected to SW2). Inverting Configurations The LT1173 can be configured as a positive-to-negative converter (Figure 7), or a negative-to-positive converter (Figure 8). In Figure 7, the arrangement is very similar to a step-down, except that the high side of the feedback is referred to ground. This level shifts the output negative. As in the step-down mode, D1 must be a Schottky diode, and VOUTshould be less than 6.2V. More negative output voltages can be accomodated as in the prior section.
+VIN R3 I LIM V IN SW1 FB LT1173 L1 SW2 GND D1 1N5818 R1
LT1173 * TA11
+
C2
t ON.
(15)
+
C1 R2 -VOUT
LT1173 * F07
Figure 7. Positive-to-Negative Converter
)
(16)
In Figure 8, the input is negative while the output is positive. In this configuration, the magnitude of the input voltage can be higher or lower than the output voltage. A level shift, provided by the PNP transistor, supplies proper polarity feedback information to the regulator.
9
LT1 173
APPLICATI
S I FOR ATIO
L1 D1
+
C1 I LIM V IN SW1
+
C2 AO GND
LT1173 FB SW2 R2 VOUT =
SWITCH ON OFF
()
R1 1.245V + 0.6V R2
LT1173 * TA13
-VIN
Figure 8. Negative-to-Positive Converter
Using the ILIM Pin The LT1173 switch can be programmed to turn off at a set switch current, a feature not found on competing devices. This enables the input to vary over a wide range without exceeding the maximum switch rating or saturating the inductor. Consider the case where analysis shows the LT1173 must operate at an 800mA peak switch current with a 2.0V input. If VIN rises to 4V, the peak switch current will rise to 1.6A, exceeding the maximum switch current rating. With the proper resistor selected (see the "Maximum Switch Current vs RLIM" characteristic), the switch current will be limited to 800mA, even if the input voltage increases. Another situation where the ILIM feature is useful occurs when the device goes into continuous mode operation. This occurs in step-up mode when
IL
VOUT + VDIODE 1 < . VIN - VSW 1 - DC
When the input and output voltages satisfy this relationship, inductor current does not go to zero during the switch OFF time. When the switch turns on again, the current ramp starts from the non-zero current level in the inductor just prior to switch turn on. As shown in Figure 9, the inductor current increases to a high level before the comparator turns off the oscillator. This high current can cause excessive output ripple and requires oversizing the output capacitor and inductor. With the ILIM feature, however, the switch current turns off at a programmed level as shown in Figure 10, keeping output ripple to a minimum.
10
U
+VOUT R1 2N3906
IL
LT1173 * TA14
W
U
UO
Figure 9. No Current Limit Causes Large Inductor Current Build-Up
PROGRAMMED CURRENT LIMIT
SWITCH
ON OFF
LT1173 * TA15
Figure 10. Current Limit Keeps Inductor Current Under Control
(17)
Figure 11 details current limit circuitry. Sense transistor Q1, whose base and emitter are paralleled with power switch Q2, is ratioed such that approximately 0.5% of Q2's collector current flows in Q1's collector. This current is passed through internal 80 resistor R1 and out through the ILIM pin. The value of the external resistor connected between ILIM and VIN sets the current limit. When sufficient switch current flows to develop a VBE across R1 + RLIM, Q3 turns on and injects current into the oscillator, turning off the switch. Delay through this circuitry is approximately 2s. The current trip point becomes less accurate for switch ON times less than 4s. Resistor values programming switch ON time for 2s or less will cause spurious response in the switch circuitry although the device will still maintain output regulation.
RLIM (EXTERNAL) VIN Q3 DRIVER OSCILLATOR Q1 ILIM R1 80 (INTERNAL) SW1 Q2 SW2
LT1173 * TA28
Figure 11. LT1173 Current Limit Circuitry
LT1173
APPLICATI S I FOR ATIO U
+5V V IN LT1173 R1 VBAT 1.245V REF SET 100k
Using the Gain Block The gain block (GB) on the LT1173 can be used as an error amplifier, low battery detector or linear post regulator. The gain block itself is a very simple PNP input op amp with an open collector NPN output. The negative input of the gain block is tied internally to the 1.245V reference. The positive input comes out on the SET pin. Arrangement of the gain block as a low battery detector is straightforward. Figure 12 shows hookup. R1 and R2 need only be low enough in value so that the bias current of the SET input does not cause large errors. 100k for R2 is adequate. R3 can be added to introduce a small amount of hysteresis. This will cause the gain block to "snap" when the trip point is reached. Values in the 1M-10M range are optimal. The addition of R3 will change the trip point, however.
Table 1. Component Selection for Common Converters
INPUT VOLTAGE 2.0-3.1 2.0-3.1 2.0-3.1 2.0-3.1 5 5 5 5 6.5-9.5 12-20 20-30 5 12 -5 -5 OUTPUT VOLTAGE 5 5 12 12 12 12 15 30 5 5 5 -5 -5 5 12 OUTPUT CURRENT (MIN) 90mA 10mA 50mA 10mA 90mA 30mA 50mA 25mA 50mA 300mA 300mA 75mA 250mA 150mA 75mA CIRCUIT FIGURE 5 5 5 5 5 5 5 5 6 6 6 7 7 8 8 INDUCTOR VALUE 47H 220H 47H 150H 120H 150H 120H 100H 47H 220H 470H 100H 470H 100H 100H INDUCTOR PART NUMBER G GA10-472K, C CTX50-1 G GA10-223K, C CTX G GA10-472K, C CTX50-1 G GA10-153K G GA10-123K G GA10-153K G GA10-123K C CTX100-4 G GA10-103K, C CTX100-4 G GA10-472K, C CTX50-1 G GA20-223K G GA20-473K G GA10-103K, C CTX100-4 G GA40-473K G GA10-103K, C CTX100-4 G GA10-103K, C CTX100-4
G = Gowanda C = Coiltronics * Add 68 from ILIM to VIN ** Add 100 from ILIM to VIN
W
U
UO
-
AO TO PROCESSOR
+
R2
GND R3
V - 1.245V R1 = LB 11.7A VLB = BATTERY TRIP POINT R2 = 100k R3 = 4.7M
LT1173 * TA16
Figure 12. Setting Low Battery Detector Trip Point
CAPACITOR VALUE 100F 22F 47F 22F 100F 47F 47F 10F, 50V 100F 220F 470F 100F 220F 220F 47F
NOTES * *
**
** ** ** ** **
11
LT1 173
APPLICATI
MANUFACTURER
S I FOR ATIO
Table 2. Inductor Manufacturers
PART NUMBERS GA10 Series GA40 Series Gowanda Electronics Corporation 1 Industrial Place Gowanda, NY 14070 716-532-2234 Caddell-Burns 258 East Second Street Mineola, NY 11501 516-746-2310 Coiltronics International 984 S.W. 13th Court Pompano Beach, FL 33069 305-781-8900 Renco Electronics Incorporated 60 Jefryn Boulevard, East Deer Park, NY 11729 800-645-5828
7300 Series 6860 Series
Custom Toroids Surface Mount
RL1283 RL1284
TYPICAL APPLICATI
S
3V to -22V LCD Bias Generator
R1 100 ILIM 2 X 1.5V CELLS V IN SW1 3V LT1173 FB GND SW2
* L1 = GOWANDA GA10-103K COILTRONICS CTX100-4 FOR 5V INPUT CHANGE R1 TO 47. CONVERTER WILL DELIVER -22V AT 40mA.
12
U
Table 3. Capacitor Manufacturers
MANUFACTURER Sanyo Video Components 2001 Sanyo Avenue San Diego, CA 92173 619-661-6835 Nichicon America Corporation 927 East State Parkway Schaumberg, IL 60173 708-843-7500 Sprague Electric Company Lower Main Street Sanford, ME 04073 207-324-4140 PART NUMBERS OS-CON Series PL Series 150D Solid Tantalums 550D Tantalex
L1* 100H 1N4148 2.21M 1%
W
UO
U
UO
+
4.7F 118k 1% 1N5818 1N5818 0.1F
+
22F 220k -22V OUTPUT 7mA AT 2.0V INPUT 70% EFFICIENCY
LT1173 * TA19
LT1173
TYPICAL APPLICATI
3V to 5V Step-Up Converter
L1* 100 H
ILIM 2 X 1.5V CELLS
V IN SW1
LT1173-5 SENSE GND SW2
* L1 = GOWANDA GA10-103K COILTRONICS CTX100-1 (SURFACE MOUNT)
+5V to -5V Converter
+VIN 5V INPUT 100 ILIM V IN SW1 LT1173-5 SENSE GND SW2 L1* 100H
+
22F
1N5818
* L1 = GOWANDA GA10-103K COILTRONICS CTX100-1
44mH 48V DC 44mH *L1 = CTX110077 IQ = 120A
~ ~
+ -
UO
+
+
S
9V to 5V Step-Down Converter
100 ILIM 9V BATTERY V IN SW1
LT1173-5 SENSE
1N5818 5V OUTPUT 150mA AT 3V INPUT 60mA AT 2V INPUT 100 F
GND
SW2
L1* 47H
1N5818
+
5V OUTPUT 150mA AT 9V INPUT 50mA AT 6.5V INPUT 100 F
LT1173 * TA17
* L1 = GOWANDA GA10-472K COILTRONICS CTX50-1 FOR HIGHER OUTPUT CURRENTS SEE LT1073 DATASHEET
LT1173 * TA18
+20V to 5V Step-Down Converter
+VIN 12V-28V 100 ILIM V IN SW1 LT1173-5 SENSE GND SW2 L1* 220H
100 F
+
-5V OUTPUT 75mA
LT1173 * TA20
+
1N5818
5V OUTPUT 300mA 100 F
* L1 = GOWANDA GA20-223K
LT1173 * TA21
Telecom Supply
L1* 500H 47F 100V MUR110 +5V 100mA 390k
3.6M 10k VN2222 12V 100 15V 1N4148 ILIM V IN SW1 10F 16V LT1173 FB GND SW2
220F 10V
+
10nF
2N5400 IRF530
+
1N965B
110k
LT1173 * TA22
13
LT1 173
TYPICAL APPLICATI
4 X NICAD OR ALKALINE CELLS
470F
*L1 = COILTRONICS CTX100-4 GOWANDA GA20-103K
2V to 5V at 300mA Step-Up Converter with Under Voltage Lockout
L1* 20H, 5A 1N5820
47k 100k 2N3906 2 X NICAD
100k
*L1 = COILTRONICS CTX-20-5-52 1% METAL FILM
14
UO
S
"5 to 5" Step-Up or Step-Down Converter
L1* 100H 1N5818 SI9405DY
+5V OUTPUT
56 1 ILIM 2 V IN SW1 7 SET LT1173 AO FB GND 5 SW2 4 470k 3 6 8 75k
+
+
470F
+
470F
240
24k
VIN = 2.6V TO 7.2V VOUT = 5V AT 100mA
LT1173 * TA23
100k ILIM AO 2.2M SET GND LT1173 V IN SW1 100
220
2N4403 301k +5V OUTPUT 300mA LOCKOUT AT 1.85V INPUT
FB SW2 5
+
MJE200 100k 47
100F OS-CON
LT1173 * TA24
LT1173
TYPICAL APPLICATI
VIN 5V-12V
V IN
LT1173 FB GND SW2 LT1006
* L1 = GOWANDA GT10-101
High Power, Low Quiescent Current Step-Down Converter
0.22 L1* 25H, 2A
VIN 7V-24V
1N5818
18V 1W 100 1/2W
2k 2N3904
V IN
ILIM SW1 LT1173 FB
1N4148 121k
GND
SW2
40.2k * L1 = GOWANDA GT10-100 EFFICIENCY 80% FOR 10mA ILOAD 500mA STANDBY IQ 150A
LT1173 * TA26
OPERATE STANDBY
2 Cell Powered Neon Light Flasher
0.02F L1* 470H
1N4148
1N4148
ILIM
V IN SW1 0.02F 100M FB 0.02F
3V
LT1173
GND
SW2 1.3M 3.3M
*TOKO 262LYF-0100K
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.
-
+
UO
S
Voltage Controlled Positive-to-Negative Converter
MJE210 L1* 50H, 2.5A
0.22
+
1N5818 220 1N5820 100F -VOUT = -5.13 * VC 2W MAXIMUM OUTPUT 150 V IN 200k 39k VC (0V TO 5V)
ILIM SW1
LT1173 * TA25
MTM20P08
5V 500mA
51
1N5820
+
470F
1N4148
95V REGULATED
0.68F 200V
NE-2 BLINKS AT 0.5Hz
LT1173 * TA27
15
LT1 173
PACKAGE DESCRIPTIO
0.300 - 0.325 (7.620 - 8.255)
0.009 - 0.015 (0.229 - 0.381)
(
+0.025 0.325 -0.015 8.255 +0.635 -0.381
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTURSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm).
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
0.016 - 0.050 0.406 - 1.270
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm).
16
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
U
Dimensions in inches (milimeters) unless otherwise noted. N8 Package 8-Lead Plastic DIP
0.400* (10.160) MAX 8 7 6 5
0.255 0.015* (6.477 0.381)
1
2
3
4
0.045 - 0.065 (1.143 - 1.651)
0.130 0.005 (3.302 0.127)
0.065 (1.651) TYP 0.125 (3.175) MIN 0.015 (0.380) MIN
)
0.045 0.015 (1.143 0.381) 0.100 0.010 (2.540 0.254)
0.018 0.003 (0.457 0.076)
N8 0694
S8 Package 8-Lead Plastic SOIC
0.189 - 0.197* (4.801 - 5.004) 8 7 6 5
0.228 - 0.244 (5.791 - 6.197)
0.150 - 0.157* (3.810 - 3.988)
1
2
3
4
0.053 - 0.069 (1.346 - 1.752)
0.004 - 0.010 (0.101 - 0.254)
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) BSC
SO8 0294
LT/GP 0894 2K REV B * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1994

▲Up To Search▲

Price & Availability of LT1173

	To Download LT1173 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .