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LT1305 Micropower High Power DC/DC Converter with Low-Battery Detector
FEATURES
s s s s s s s
DESCRIPTIO
5V at 400mA from 2V Input Supply Voltage As Low As 1.8V 120A Quiescent Current Low-Battery Detector Low VCESAT Switch: 310mV at 2A Typ Uses Inexpensive Surface Mount Inductors 8-Lead SO Package
The LT (R)1305 is a micropower step-up DC/DC converter that uses Burst ModeTM operation. Similar to the LT1303, the LT1305 features a 2A internal low-loss switch and can deliver up to four times the output power of the LT1303. Quiescent current is only 120A and the Shutdown pin further reduces current to 10A. A low-battery detector provides an open-collector output that goes low when the input voltage drops below a preset level. The LT1305 is available in an 8-pin SO, easing board space requirements.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode is a trademark of Linear Technology Corporation
APPLICATI
s s s
S
2-Cell and 3-Cell to 5V Conversion EL Panel Drivers Portable Instruments
TYPICAL APPLICATI
2-Cell and 3-Cell to 5V/400mA DC/DC Converter with Low-Battery Detect
L1 10H 316k 1% 2 TO 3 CELLS
90
D1 LOW BATTERY GOES LOW AT VBAT = 2.2V
VIN = 4.00V
EFFICIENCY (%)
VIN LBI LT1305 SHDN GND
SW LBO
100k 301k 1%
+ C1
220F
412k 1% SHUTDOWN
FB PGND
C2 100k 220F 1%
+
VOUT 5V 400mA
C1, C2: AVX TPSE227010R0100 D1: MOTOROLA MBRS130LT3 L1: COILCRAFT D03316-103
LT1305 * TA03
U
Efficiency
80 VIN = 3.00V VIN = 2.00V VIN = 2.50V 70 60 1 10 100 LOAD CURRENT (mA) 1000
LT1305 * TA02
UO
UO
1
LT1305 ABSOLUTE AXI U RATI GS
PACKAGE/ORDER I FOR ATIO
TOP VIEW GND 1 LBO 2 SHDN 3 FB 4 8 7 6 5 PGND SW VIN LBI
VIN Voltage .............................................................. 10V SW1 Voltage ............................................................ 25V FB Voltage ............................................................... 10V Shutdown Voltage ................................................... 10V LBO Voltage ............................................................. 10V LBI Voltage .............................................................. 10V Maximum Power Dissipation ............................. 500mW Operating Temperature Range ..................... 0C to 70C Storage Temperature Range ................. - 65C to 150C Lead Temperature (Soldering, 10 sec).................. 300C
ORDER PART NUMBER LT1305CS8 S8 PART MARKING 1305
S8 PACKAGE 8-LEAD PLASTIC SO
TJMAX = 100C, JA = 80C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL IQ VIN PARAMETER Quiescent Current Input Voltage Range CONDITIONS
TA = 25C, VIN = 2.0V, unless otherwise noted.
MIN
q q q
TYP 120 7
MAX 200 15
UNITS A A V V
VSHDN = 0.5V, VFB = 2V VSHDN = 1.8V
1.8 2.0 1.22
1.55 1.24 6 7 1.26 12.5 20 185 95 0.15 280 10 2.35 2.50 2.15 1.24 7 0.11 0.1 1.27 20 0.4 5 0.5
Feedback Voltage Comparator Hysteresis Feedback Pin Bias Current Oscillator Frequency Oscillator TC DC tON VCESAT Maximum Duty Cycle Switch On Time Output Line Regulation Switch Saturation Voltage Switch Leakage Current Peak Switch Current Current Limit Not Asserted 1.8V < VIN < 6V ISW = 1A VSW = 5V, Switch Off VIN = 2V VFB = 1V Current Limit Not Asserted
q q q
120
q
155 0.2 86 5.6 0.06 140 0.1
%/C % s %/V mV A A A A V nA V A V V A A A
75
q q q q
1.35 1.20 1.15 1.21
2
VIN = 5V LBI Trip Voltage LBI Input Bias Current LBO Output Low LBO Leakage Current VSHDNH VSHDNL ISHDN Shutdown Pin High Shutdown Pin Low Shutdown Pin Bias Current VSHDN = 5V VSHDN = 2V VSHDN = 0V
q q q
(Note 2) VLBI = 1V ILOAD = 100A VLBI = 1.3V, VLBO = 5V
q q q q q
1.8 8.0 3.0 0.1 20 1
The q denotes specifications which apply over the 0C to 70C operating temperature range. Note 1: Hysteresis specified is DC. Output ripple may be higher if output capacitance is insufficient or capacitor ESR is excessive.
Note 2: Low-battery detector comparator is inoperative when device is in shutdown.
2
U
V mV nA kHz
W
U
U
WW
W
LT1305 TYPICAL PERFORMANCE CHARACTERISTICS
Switch On Time
8 7
160 150 140 130 120 110
DUTY CYCLE (%)
ON TIME (s)
6 5 4 3 2 -50
FREQUENCY (kHz)
- 25
0 25 50 TEMPERATURE (C)
Quiescent Current
200 190
SWITCH OFF VIN = 2V
QUIESCENT CURRENT (A)
QUIESCENT CURRENT (A)
180 170 160 150 140 130 120 110 100 -50
PEAK SWITCH CURRENT (A)
-25
25 50 0 TEMPERATURE (C)
LBI Pin Bias Current
20 18 16
14 12 10 8 6 4 2 0 -50 -25 25 50 0 TEMPERATURE (C) 75 100
14 12 10 8 6 4 2 0 -50 -25 25 50 0 TEMPERATURE (C) 75 100
FEEDBACK VOLTAGE (V)
BIAS CURRENT (nA)
BIAS CURRENT (nA)
UW
75
LT1305 * G01
Oscillator Frequency
200 190 180 170 100 95 90 85 80 75 70 65 60 55 -25 25 50 0 TEMPERATURE (C) 75 100
Maximum Duty Cycle
100
100 -50
50 -50
-25
25 50 0 TEMPERATURE (C)
75
100
LT1305 * G02
LT1305 * G03
Quiescent Current
500 TA = 25C SWITCH OFF 400
2.4 2.2 2.0 1.8 1.6 1.4 1.2
Current Limit
300
200
100
0
75 100
0
2
6 4 INPUT VOLTAGE (V)
8
10
LT1305 * G05
1.0 - 50
-25
50 25 0 TEMPERATURE (C)
75
100
LT1305 * G04
LT1305 * G06
FB Pin Bias Current
20 18 16
1.250 1.245 1.240 1.235 1.230 1.225 1.220 1.215 1.210 1.205
FB Voltage
1.200 -50
-25
25 50 0 TEMPERATURE (C)
75
100
LT1305 * G07
LT1305 * G08
LT1305 * G09
3
LT1305 TYPICAL PERFORMANCE CHARACTERISTICS
Low-Battery Detect Trip Point
1.250 1.245 1.240
SWITCH SATURATION VOLTAGE (mV)
350 300 250 200 150 100 50 0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 SWITCH CURRENT (A)
LT1305 * F12
SWITCH SATURATION VOLTAGE (mV)
LBI VOLTAGE (V)
1.235 1.230 1.225 1.220 1.215 1.210 1.205 1.200 -50 -25 25 50 0 TEMPERATURE (C) 75 100
PI FU CTIO S
GND (Pin 1): Signal Ground. Tie to PGND under the package. LBO (Pin 2): Open-Collector Output of Comparator C3. Can sink 100A. High impedance when device is in shutdown. SHDN (Pin 3): Shutdown. Pull high to shut down the LT1305. Ground for normal operation. FB (Pin 4): Feedback Input. Connects to main comparator C1 input. LBI (Pin 5): Low-Battery Comparator Input. When voltage on this pin is below 1.24V, LBO is low. VIN (Pin 6): Supply Pin. Must be bypassed with a large value capacitor to gound. Keep bypass within 0.2" of the device. SW (Pin 7): Switch Pin. Connect inductor and diode here. Keep layout short and direct to minimize radio frequency interference. PGND (Pin 8): Power Ground. Tie to signal ground (pin 1) under the package. Bypass capacitor from VIN should be tied directly to PGND within 0.2" of the device.
4
UW
LT1305 * G10
Switch Saturation Voltage
400 TA = 25C
300
Switch Saturation Voltage
ISW = 1A 250 200 150 100 50 0 - 50
- 25
0 25 50 TEMPERATURE (C)
75
100
LT1305 * G13
U
U
U
LT1305
BLOCK DIAGRAM
VIN
+
C5 6
C2
4
FB
-
C1
OFF OSCILLATOR A3 DRIVER Q2 1x Q1 160x
R2
REFERENCE 1.24V
+ -
C3
+
GND 1 5 LBI 2 LBO SHUTDOWN 3 8 PGND
Figure 1. LT1305 Block Diagram
OPERATION
Operation of the LT1305 is best understood by referring to the Block Diagram in Figure 1. When C1's negative input, related to the output voltage by the appropriate resistordivider ratio, is higher than the 1.24V reference voltage, C1's output is low. C2, A3 and the oscillator are turned off, drawing no current. Only the reference and C1 consume current, typically 120A. When C1's negative input drops below 1.24V and overcomes C1's 6mV hysteresis, C1's output goes high, enabling the oscillator, current comparator C2 and driver A3. Quiescent current increases to 2mA as the device goes into active switching mode. Q1 then turns on in controlled saturation for nominally 6s or until current comparator C2 trips, whichever comes first. The switch then turns off for approximately 1.5s, then turns on again. The LT1305's switching causes current to alternately build up in L1 and dump into output capacitor C4 via D1, increasing the output voltage. When the output is high enough to cause C1's output to go high, switching action ceases. Capacitor C4 is left to supply current to the load until VOUT decreases enough to force C1's output high, and the entire cycle repeats. Figure 2 details relevant waveforms. C1's cycling causes low-to-mid-frequency ripple voltage on the output. Ripple can be reduced by making the output capacitor large. The 220F unit specified results in ripple of 50mV to 100mV on the 5V output. Paralleling two capacitors will decrease ripple by approximately 50%.
VOUT 100mV/DIV AC COUPLED VSW 5V/DIV
IL 1A/DIV
Figure 2. Burst Mode Operation
-
R1
HYSTERETIC COMPARATOR
+
W
L1 VIN SW D1
+
C4
7 CURRENT COMPARATOR 36mV R1 3
LT1305 * F01
U
50s/DIV
LT1305 * F02
5
LT1305
OPERATION
If switch current reaches 2A, causing C2 to trip, switch on time is reduced and off time increases slightly. This allows continuous operation during bursts. C2 monitors the voltage across 3 resistor R1 which is directly related to the switch 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 36mV, corresponding to 2A switch current, C2's output goes high, truncating the on time portion of the oscillator cycle and increasing off time to about 2s. Response time of C2, which determines minimum on time, is approximately 300ns. Low-Battery Detector The low-battery detector is enabled when SHDN is low and disabled when SHDN is high. The comparator has no hysteresis built in, but hysteresis can be added by connecting a high-value resistor from LBI to LBO as shown in Figure 3. The internal reference can be accessed via the comparator as shown in Figure 4.
VBAT LT1305 5V R4 47k LBO
R1
1.24V LBI
R2 49.9k 1% R1 = (VTRIP -1.24V) (43.5k) HYSTERESIS 30mV
Figure 3. R3 Adds Hysteresis to Low-Battery Detector
VIN 100k 2N3906 R2 VIN LBO LT1305 VREF OUTPUT
+
2.2F
VREF = 1.24V 1 + R2 R1 VIN VREF + 200mV R1 + R2 33k
Figure 4. Accessing Internal Reference
6
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Inductor Selection Inductors used with the LT1305 must fulfill two requirements. First, the inductor must be able to handle current of 2A to 2.5A without runaway saturation. Rod or drum core units usually saturate gradually and it is acceptable to exceed manufacturer's published saturation current by 20% or so. Second, the unit must have low DCR, under 0.05 so that copper loss is kept low and excess heating is avoided. Inductance value is not critical. Generally, for low voltage inputs below 3V a 10H inductor is recommended (such as Coilcraft DO3316-103). For inputs above 4V to 5V use a 22H unit (such as Coilcraft DO3316-223). Switching frequency can reach up to 300kHz so the core material should be able to operate at high frequency without excessive core loss. Ferrite or molypermalloy cores are a better choice than powdered iron. If EMI is a concern, a toroidal inductor is suggested, such as Coiltronics CTX20-4. Capacitor Selection Output and input capacitors should have low ESR for best performance. Inexpensive aluminum electrolytics sometimes have ESR above 1, even for relatively large values such as 100F, 16V units. Since the LT1305 has a 2A current limit, 2V of ripple voltage would result with such a capacitor at the output. Keep ESR below 0.05 to 0.1 for reasonable ripple voltage. Tantalum capacitors such as AVX TPS series or Sprague 593D have low ESR and are surface mount components. For lowest ESR, use Sanyo OS-CON units (OS-CON is also available from Vishay). These capacitors have superior ESR, small size and perform well at cold temperatures. Diode Selection A 2A Schottky diode such as Motorola MBRS130LT3 is a good choice for the rectifier diode. A 1N5821 or MBRS130T3 are suitable as well. Do not use "general purpose" diodes such as 1N4001. They are much too slow for use in switching regulator applications.
- +
R3 2M
LT1305 * F03
LBI R1 GND
()
LT1305 * F04
LT1305
TYPICAL APPLICATIONS N
Setting Output Voltage
L1 VIN VIN SW VOUT LT1305 GND FB PGND R2 1N5817
3.5V to 6.5V
+
100F 4 CELLS
VIN LT1305
SW 5V 400mA 309k FB PGND 22H* 100k
+
100F
+
220F
SHDN GND SHUTDOWN
R1
VOUT = 1.24V 1 + R2 R1
()
LT1305 * TA03
* COILCRAFT DO3316-223 OR SUMIDA CD105-220 ** SANYO OS-CON
5V Step-Up Converter with Reference Output
1.8V TO 4.5V INPUT 100k 2N3906 VREF OUTPUT 1.24V VIN 10H* MBRS130LT3
SW LT1305 309k FB PGND 100k
+
100F
LBO
5V 400mA
+
2.2F 33k
LBI GND
+
220F
*COILCRAFT DO3316-103
LT1305 * TA06
EL Panel Driver
VIN 1.5V TO 8V 10 T1** 1:15 *6 4, 5 * 1, 2 10 1N5818 4.7F 160V MUR160 C1* 50pF
+
VIN 47F 0.1F CERAMIC LT1305 SHDN GND SHUTDOWN
SW
3.3M 3.3M 1N4148
1k 1/2W 10k ZETEX FZT658
FB PGND R1 25k
51k
100Hz TO 1000Hz SQUARE WAVE DRIVE
*ADD C1 FOR OPEN-PANEL PROTECTION **DALE LPE5047-A132 1:15 TURNS RATIO 10H PRIMARY INDUCTANCE (605) 666-9301 R1 ADJUSTS VOUT 83VRMS TO 115VRMS AVX TPS OR SANYO OS-CON MUST HAVE ESR 0.15
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.
+
3.3M
LT1305 * TA04
+
U
4-Cell-to-5V Converter
L1* 22H 100F** MBRS130LT3
+
150F**
LT1305 * TA05
EL PANEL
CPANEL 100nF
7
LT1305
PACKAGE DESCRIPTION U
Dimensions in inches (millimeters) unless otherwise noted. 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 0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254) 0- 8 TYP
2
3
4
0.053 - 0.069 (1.346 - 1.752)
0.004 - 0.010 (0.101 - 0.254)
0.016 - 0.050 0.406 - 1.270
0.014 - 0.019 (0.355 - 0.483)
0.050 (1.270) BSC
SO8 0294
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS. MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006 INCH (0.15mm).
RELATED PARTS
PART NUMBER LT1129 LT1182/83/84 LT1301 LT1302 LT1303 LT1372 LTC (R)1472 DESCRIPTION Micropower Low Dropout Regulator LCD and CCFL Backlight Controller 5V to 12V/200mA Step-Up DC/DC Converter 2-Cell to 5V/600mA Step-Up DC/DC Converter Micropower DC/DC Converter with Low-Battery Detect 500kHz Step-Up PWM, 1.5A Switch PCMCIA Host Switch with Protection COMMENTS 700mA Output Current in SO-8 Package High Efficiency and Excellent Backlight Control Range 120A Quiescent Current 200A Quiescent Current 2V to 5V at 200mA Low Noise, Fixed Frequency Operation Includes Current Limit and Thermal Shutdown
8
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 q FAX: (408) 434-0507 q TELEX: 499-3977
LT/GP 0595 10K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1995

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