LT1300 Micropower High Efficiency 3.3/5V Step-Up DC/DC Converter U
DESCRIPTION
FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■
Up to 220mA Output Current at 5V from 2V Supply Supply Voltage as Low as 1.8V Up to 88% Efficiency Small Inductor –10µH 120µA Quiescent Current Shutdown to 10µA Programmable 3.3V or 5V Output ILIM Pin Programs Peak Switch Current Low VCESAT Switch: 170mV at 1A Typical Uses Inexpensive Surface Mount Inductors 8-Lead DIP or SOIC Package
U APPLICATIONS ■ ■ ■ ■ ■ ■
Palmtop Computers Portable Instruments Bar-Code Scanners DC/DC Converter Module Replacements Battery Backup Supplies Personal Digital Assistants PCMCIA Cards
Burst Mode is a trademark of Linear Technology Corporation.
U
■
The LT1300 is a micropower step-up DC/DC converter that utilizes Burst Mode™ operation. The device can deliver 5V or 3.3V from a two-cell battery input. It features programmable 5V or 3.3V output via a logic-controlled input, noload quiescent current of 120µA and a shutdown pin which reduces supply current to 10µA. The on-chip power switch has a low 170mV saturation voltage at a switch current of 1A, a four-fold reduction over prior designs. A 155kHz internal oscillator allows the use of extremely small surface mount inductors and capacitors. Operation is guaranteed at 1.8V input. This allows more energy to be extracted from the battery increasing operating life. The ILIM pin can be used to program peak switch current with a single resistor allowing the use of less expensive and smaller inductors and capacitors in lighter load applications. The LT1300 is available in an 8-lead SOIC package, minimizing board space requirements. For a 5V/12V Selectable Output Converter see the LT1301. For increased output current see the LT1302.
TYPICAL APPLICATIONS N Two-Cell to 3.3V/5V Step-Up Converter L1 10µH
2× AA CELL
+ C1
SENSE
3
88
ILIM
PGND
GND 1
8
VIN = 4.0V
86
+ C1
SHDN
90
4
LT1300
100µF
5V/3.3V OUTPUT
7 SW
VIN 5V/3.3V 2 SELECT SELECT
SHUTDOWN
D1
5
N/C
100µF
EFFICIENCY (%)
6
5V Output Efficiency
VIN = 3.0V
84
VIN = 2.5V
82
VIN = 2.0V
80 78
L1 = COILCRAFT DO1608-103 OR SUMIDA CD54-100 C1 = AVX TPSD107M010R0100 OR SANYO OS-CON 16SA100M D1 = MBRS130LT3 OR 1N5817
LT1300 TA1
76 74 1
10 100 LOAD CURRENT (mA)
500 LT1300 TA2
1
LT1300
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ABSOLUTE MAXIMUM RATINGS
PACKAGE/ORDER INFORMATION
VIN Voltage .............................................................. 10V SW1 Voltage ............................................................ 20V Sense Voltage .......................................................... 10V SHUTDOWN Voltage................................................ 10V SELECT Voltage ....................................................... 10V ILIM Voltage ............................................................ 0.5V Maximum Power Dissipation ............................. 500mW Operating Temperature Range ..................... 0°C to 70°C Storage Temperature Range ................. – 65°C to 150°C Lead Temperature (Soldering, 10 sec).................. 300°C
ORDER PART NUMBER
TOP VIEW GND 1
8
PGND
SEL 2
7
SW
SHDN 3
6
VIN
SENSE 4
5
ILIM
N8 PACKAGE 8-LEAD PLASTIC DIP
LT1300CN8 LT1300CS8
S8 PACKAGE 8-LEAD PLASTIC SOIC
S8 PART MARKING 1300
TJMAX = 100°C, θJA = 150°C/ W
Consult factory for Industrial grade parts.
ELECTRICAL CHARACTERISTICS SYMBOL PARAMETER Quiescent Current IQ VIN
TA = 25°C, VIN = 2V unless otherwise noted.
CONDITIONS VSHDN = 0.5V, VSEL = 5V, VSENSE = 5.5V VSHDN = 1.8V
MIN ● ●
Input Voltage Range ●
VOUT
DC tON VCESAT
VSHDNH VSHDNL VSELH VSELL ISHDN
ISEL
Output Sense Voltage Output Referred Comparator Hysteresis Oscillator Frequency Oscillator TC Maximum Duty Cycle Switch On Time Output Line Regulation Switch Saturation Voltage Switch Leakage Current Peak Switch Current (Internal Trip Point) Shutdown Pin High Shutdown Pin Low Select Pin High Select Pin Low Shutdown Pin Bias Current
Select Pin Bias Current
VSEL = 5V VSEL = 0V VSEL = 5V (Note 1) VSEL = 0V (Note 1) Current Limit not Asserted. See Test Circuit.
● ●
120 75
Current Limit not Asserted. 1.8V < VIN < 6V ISW = 700mA VSW = 5V, Switch Off ILIM Floating (See Typical Application) ILIM Grounded
● ● ●
0.75 ●
1.8
●
1.5
MAX 200 15
5.0 3.3 22 14 155 0.2 86 5.6 0.06 130 0.1 1.0 0.4
5.20 3.45 50 35 185 95 0.15 200 10 1.25
0.5 ●
VSHDN = 5V VSHDN = 2V VSHDN = 0V 0V < VSEL < 5V
The ● denotes specifications which apply over the 0°C to 70°C temperature range.
2
● ●
1.8 2.0 4.80 3.15
TYP 120 7
● ● ● ●
9 3 0.1 1
0.8 20 1 3
Note 1: Hysteresis specified is DC. Output ripple may be higher if output capacitance is insufficient or capacitor ESR is excessive. See applications section.
UNITS µA µA V V V V mV mV kHz %/ °C % µs %/V mV µA A A V V V V µA µA µA µA
LT1300 U W
TYPICAL PERFORMANCE CHARACTERISTICS Efficiency 170
VOUT = 3.3V L = 10µH
86
165
84 EFFICIENCY (%)
82
VIN = 3V
80
INPUT CURRENT (µA)
160
VIN = 2.5V
78
VIN = 2V
76 74 72
150 145 140
68
125
10 100 LOAD CURRENT (mA)
VOUT = 3.3V
135 130
1
70
VOUT = 5V
155
70 66
80
ISHDN + IVIN + ISENSE (µA)
88
Total Quiescent Current in Shutdown
No-Load Battery Current
50 40 30 20 10 0
120 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4 INPUT VOLTAGE (V)
1000
60
1
0
2
4 5 6 3 INPUT VOLTAGE (V)
7
8
LT1300 G1 LT1300 G2
20
700
250 TA = 25°C
225 200
14
175 VCESAT (mV)
16
12 10 8
150 125 100
6
75
4
50
2
25
0 0
1
6 4 3 2 5 SHUTDOWN VOLTAGE (V)
7
0
8
600
OUTPUT CURRENT (mA)
18 SHUTDOWN CURRENT (µA)
Maximum Output Current vs Input Voltage
VCESAT vs ISW
Shutdown Pin Bias Current
800
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 SWITCH CURRENT (A)
300
L = 10µH
ILOAD
500
L = 10µH COILCRAFT DO1608-103
200
0 1.5
2
3.5 3 2.5 INPUT VOLTAGE (V)
4
4.5
LT1300 G6
Startup Response
VOUT 100mV/DIV AC COUPLED
700 600
400
Transient Response VIN = 2V, VOUT = 5V
VOUT = 3.3V ILIM FLOATING
L = 22µH COILCRAFT DO3316-223
500
LT1300 G5
Maximum Output Current vs Input Voltage 900
VOUT = 5V, ILIM FLOATING
100
LT1300 G4
LOAD CURRENT (mA)
LT1300 G3
VOUT 1V/DIV
200mA
VSHDN 10V/DIV
0
400
200µs/DIV
300 200
LT1300 G8
500µs/DIV VOUT = 5V RLOAD = 20Ω
LT1300 G9
100 0 1.5
2
3 2.5 INPUT VOLTAGE (V)
3.5 LT1300 G7
3
LT1300
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PIN FUNCTIONS GND (Pin 1): Signal Ground. Sel (Pin 2): Output Select. When tied to VIN or VOUT converter regulates at 5V. When grounded converter regulates at 3.3V. SHDN (Pin 3): Shutdown. Pull high to effect shutdown. Tie to ground for normal operation. Sense (Pin 4): “Output” Pin. ILIM (Pin 5): Float for 1A switch current limit. Tie to ground for approximately 400mA. A resistor between ILIM and ground sets peak current to some intermediate value (see Figure 5).
VIN (Pin 6): Supply Pin. Must be bypassed with a large value electrolytic to ground. A 0.1µF ceramic capacitor close to the pin may be needed in some cases. SW (Pin 7): Switch Pin. Connect inductor and diode here. Keep layout short and direct to minimize electronic radiation. PGND (Pin 8): Power Ground. Tie to signal ground (pin 1) under the package. Bypass capacitor from VIN should be tied directly to the pin.
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BLOCK DIAGRAM VIN
D1
L1
VOUT
+
+
C2
C1
VIN
SENSE 4
SW
2
7
18mV A2 CURRENT COMPARATOR
R1 3Ω
+ R2 730Ω
500k
– A1 COMPARATOR
OFF
+
1.25V REFERENCE
ENABLE OSCILLATOR 155kHZ
144k
A3 DRIVER
Q2 1x
–
Q1 160x
BIAS
161k
Q3 8.5k
GND 1
SELECT 2
SHUTDOWN 3
5
ILIM
PGND 8
LT1300 F1
Figure 1.
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LT1300
TEST CIRCUITS
Oscillator Test Circuit 5V 2V 100Ω VIN
IL
SEL 100µF
SW
fOUT
LT1300
SENSE
SHDN
GND
PGND
U OPERATION Operation of the LT1300 is best understood by referring to the Block Diagram in Figure 1. When A1’s negative input, related to the Sense pin voltage by the appropriate resistor-divider ratio, is higher that the 1.25V reference voltage, A1’s output is low. A2, A3 and the oscillator are turned off, drawing no current. Only the reference and A1 consume current, typically 120µA. When the voltage at A1’s negative input decreases below 1.25V, overcoming A1’s 6mV hysteresis, A1’s output goes high, enabling the oscillator, current comparator A2, and driver A3. Quiescent current increases to 2mA as the device prepares for high current switching. Q1 then turns on in a controlled saturation for (nominally) 5.3µs or until current comparator A2 trips, whichever comes first. After a fixed off-time of (nominally) 1.2µs, Q1 turns on again. The LT1300’s switching causes current to alternately build up in L1 and dump into capacitor C2 via D1, increasing the output voltage. When the output is high enough to cause A1’s output to go to low, switching action ceases. C2 is left to supply current to the load until VOUT decreases enough to force A1’s output high, and the entire cycle repeats. If switch current reaches 1A, causing A2 to trip, switch ontime is reduced and off-time increases slightly. This allows continuous mode operation during bursts. Current comparator A2 monitors the voltage across 3Ω resistor R1 which is directly related to inductor L1’s current. Q2’s collector current is set by the emitter-area ratio to 0.6% of Q1’s collector current. When R1’s voltage drop exceeds 18mV, corresponding to 1A inductor current, A2’s output goes high, truncating the on-time portion of the oscillator cycle and increasing off-time to about 2µs as shown in Figure 2, trace A. This programmed peak current can be
TRACE A 500mA/DIV ILIM PIN OPEN
TRACE B 500mA/DIV ILIM PIN GROUNDED 20µs/DIV
LT1300 F2
Figure 2. Switch Pin Current With ILIM Floating or Grounded
reduced by tying the ILIM pin to ground, causing 15µA to flow through R2 into Q3’s collector. Q3’s current causes a 10.4mV drop in R2 so that only an additional 7.6mV is required across R1 to turn off the switch. This corresponds to a 400mA switch current as shown in Figure 2, trace B. The reduced peak switch current reduces I2R loses in Q1, L1, C1 and D1. Efficiency can be increased by doing this provided that the accompanying reduction in full load output current is acceptable. Lower peak currents also extend alkaline battery life due to the alkaline cell’s high internal impedance. Typical operating waveforms are shown in Figure 3. VOUT 20mV/DIV AC COUPLED
VSW 5V/DIV
ISW IA/DIV 20µS/DIV
LT1300 F2
Figure 3. Burst Mode Operation in Action
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LT1300
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APPLICATIONS INFORMATION Output Voltage Selection The LT1300 can be selected to 3.3V or 5V under logic control or fixed at either by tying SELECT to ground or VIN respectively. It is permissible to tie SELECT to a voltage higher than VIN as long as it does not exceed 10V. Efficiency in 3.3V mode will be slightly less that in 5V mode due to the fact that the diode drop is a greater percentage of 3.3V than 5V. Since the bipolar switch in the LT1300 gets its base drive from VIN, no reduction in switch efficiency occurs when in 3.3V mode. When VIN exceeds the programmed output voltage the output will follow the input. This is characteristic of the simple step-up or “boost” converter topology. A circuit example that provides a regulated output with an input voltage above or below the output (called a buck-boost or SEPIC) is shown in the Typical Applications section.
L1 10µH
D1
SW
VIN
+
C1 100µF
5V/3.3V OUTPUT
SENSE
SELECT LT1300 SHDN
ILIM
PGND
GND
+
C2 100µF
C3 0.1µF
R1 1M
Figure 4. Addition of R1 and C3 Limit Input Current at Startup
VOUT 2VDIV
Shutdown
ILIM Function The LT1300’s current limit (ILIM) pin can be used for soft start. Upon start-up, switching regulators require maximum current from the supply. The high currents flowing can create IR drops along supply and ground lines and are especially demanding on alkaline batteries. By installing an R1 and C3 as shown in Figure 4, the switch current in the LT1300 is limited to 400mA until the 15µA flowing out of the ILIM pin charges up the 0.1µF capacitor. Input current is held to under 500mA while the output voltage ramps up to 5V as shown in Figure 5. The 1Meg resistor provides a discharge path for the capacitor without appreciably decreasing peak switch current. When the full capability of the LT1300 is not required, peak current can be reduced by changing the value of R3 as shown in Figure 6. With R3 = 0, switch current is limited to approximately 400mA.
6
IBATTERY 500mA/DIV
VSHDN 10V/DIV 500µs/DIV REP RATE = 1Hz
LT1300 F5
Figure 5. Startup Waveforms using Soft-Start Circuitry ILOAD = 100mA, VOUT = 5V
1100 1000
SWITCH CURRENT (mA)
The converter can be turned off by pulling SHDN (pin 3) high. Quiescent current drops to 10µA in this condition. Bias current of 3µA to 5µA flows into the pin (at 2.5V input). It is recommended that SHDN not be left floating. Tie the pin to ground if the feature is not used.
1.6V ≤ VIN ≤ 5V
900 800 700 600 500 400 300 100
1k
10k RLIM (Ω)
100k
1M LT1300 F1B
Figure 6. Peak Switch Current vs. RLIM
LT1300
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APPLICATIONS INFORMATION Table 1. Recommended Inductors PART NUMBER DO1608-103 DO3316-223 DO1608-223 CTX10-1 CTX20-1 LQH3C2204K0M00 CD54-100M CDRH62-220M CDRH62-100M GA10-102K
VENDOR Coilcraft Coilcraft Coilcraft Coiltronics Coiltronics Murata-Frie Sumida Sumida Sumida Gowanda
L (µH) 10 22 22 10 20 22 10 22 10 10
DCR (Ω) 0.11 0.050 0.31 0.038 0.175 0.7 0.11 0.38 0.17 0.038
ILIM PIN Float Float Ground Float Ground Ground Float Ground Float Float
EFFICIENCY 2.5VIN, 5VOUT 50mA LOAD 200mA LOAD 83 83 85 85 85 — 85 85 86 — 81 — 85 85 84 — 81 82 85 86
COMPONENT HEIGHT (mm) 3.5 5.5 3.5 4.2 4.2 2.0 4.5 3.0 3.0 6.6 Through-Hole
Inductor Selection
Table 2. Recommended Capacitors
For full output power, the inductor should have a saturation current rating of 1.25A for worst-case current limit, although it is acceptable to bias an inductor 20% or more into saturation. Smaller inductors can be used in conjunction with the ILIM pin. Efficiency is significantly affected by inductor DCR. For best efficiency limit the DCR to 0.03Ω or less. Toroidal types are preferred in some cases due to their closed design and inherent EMI/RFI superiority. Recommended inductors are listed in Table 1.
VENDOR AVX Sanyo Panasonic
Capacitor Selection Low ESR capacitors are required for both input and output of the LT1300. ESR directly affects ripple voltage and efficiency. For surface mount applications AVX TPS series tantalum capacitors are recommended. These have been specially designed for SMPS and have low ESR along with high surge current ratings. For through-hole application Sanyo OS-CON capacitors offer extremely low ESR in a small size. Again, if peak switch current is reduced using the ILIM pin, capacitor requirements can be relaxed and smaller, higher ESR units can be used. Low frequency output ripple can be reduced by adding multiple output capacitors. If capacitance is reduced, output ripple will increase. Suggested capacitor sources are listed in Table 2.
SERIES TPS OS-CON HFQ
TYPE Surface Mount Through-Hole Through-Hole
PHONE NUMBER (708) 639–6400
(407) 241–7876 (404) 436–1300 (708) 956–0666
(716) 532–2234
PHONE# (803)448–9411 (619) 661–6835 (201) 348–5200
Diode Selection Best performance is obtained with a Schottky rectifier diode such as the 1N5817. Phillips Components makes this in surface mount as the PRLL5817. Motorola makes the MBRS130LT3 which is slightly better and also in surface mount. For lower output power a 1N4148 can be used although efficiency will suffer substantially. Layout Considerations The LT1300 is a high speed, high current device. The input capacitor must be no more than 0.2" from VIN (pin 6) and ground. Connect the PGND and GND (pins 8 and 1) together under the package. Place the inductor adjacent to SW (pin 7) and make the switch pin trace as short as possible. This keeps radiated noise to a minimum.
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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LT1300 U
TYPICAL APPLICATIONS N Four-Cell to 5V/3.3V Up-Down Converter L1* 27µH
2.5V ≤ VIN ≤ 8V
LCD Contrast Supply
C2** 100µF
VIN 1.8V TO 6V
+
4
N/C
4× AA CELL
ILIM
+
5V/3.3V
SELECT
C1** 100µF
L2* 27µH
VIN
1
7 3
10
8 2
1N5817
SHDN
SENSE
GND
PGND
5V/3.3V 220mA 80% EFFICIENT
+
9
C3** 100µF
N/C
+
*L1, L2 = GOWANDA GA20-272K COILCRAFT DO3316-273K SUMIDA CD73-270K **C1, C2, C3 = SANYO OS-CON 16SA100M
VIN
SW
SENSE
SHDN
N/C LT1300 TA3
SHUTDOWN
GND
12K
T1 = DALE LPE-5047-AO45 (605) 665-9301
470Ω
12K
+ 2.2µF
PWM IN 0% TO 100% CMOS DRIVE 0V TO 5V
2N4403
1N5817
1N5819
ILIM
SELECT PGND
Step-Up Converter with Automatic Output Disconnect
+ 35V
LT1300
100µF
L1* 10µH
22µF
150K
SW LT1300
SHUTDOWN
CONTRAST VOUT –4V TO –29V 12mA MAXIMUM FROM 1.8V SUPPLY (77% EFFICIENT) 20mA MAXIMUM FROM 3V SUPPLY (83% EFFICIENT)
T1
LT1300 TA6
5V, 200mA
2× AA CELL
+
SHUTDOWN
SELECT
VIN
SHDN
SW
100µF
+ 100µF
LT1300 NC
ILIM
SENSE PGND
GND
0.1µF
*SUMIDA CD54-100LC COILCRAFT DO3316-223
LT1300 TA5
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PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
0.300 – 0.320 (7.620 – 8.128)
N8 Package 8-Lead Plastic DIP
0.045 – 0.065 (1.143 – 1.651)
(
+0.025 0.325 –0.015 +0.635 –0.381
)
0.125 (3.175) MIN
0.100 ± 0.010 (2.540 ± 0.254)
0.008 – 0.010 (0.203 – 0.254)
6
5
1630 McCarthy Blvd., Milpitas, CA 95035-7487 (408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977
2
3
4
N8 0392
0.189 – 0.197* (4.801 – 5.004) 7
6
5
0.004 – 0.010 (0.101 – 0.254)
0.050 (1.270) BSC
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm).
Linear Technology Corporation
1
8
0°– 8° TYP
0.014 – 0.019 (0.355 – 0.483)
0.020 (0.508) MIN
0.018 ± 0.003 (0.457 ± 0.076)
0.053 – 0.069 (1.346 – 1.752)
0.016 – 0.050 0.406 – 1.270
8
7
0.250 ± 0.010 (6.350 ± 0.254)
0.045 ± 0.015 (1.143 ± 0.381)
0.010 – 0.020 × 45° (0.254 – 0.508)
S8 Package 8-Lead Plastic S0IC
8
0.065 (1.651) TYP
0.009 – 0.015 (0.229 – 0.381)
8.255
0.130 ± 0.005 (3.302 ± 0.127)
0.400 (10.160) MAX
0.150 – 0. (3.810 – 3.
0.228 – 0.244 (5.791 – 6.197)
1
2
3
4
SO8 0294
LT/GP 0394 10K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1994
