View SC140805_4123862.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

Low Voltage, Boost DC-DC Controller
POWER MANAGEMENT Description
The SC1408 is a low voltage boost controller that operates from a 1.8V to 16.5V input range. The SC1408 was designed for two cell Alkaline or single cell Lithium Ion battery applications. With the proper external components it can be used as a boost converter or a buck/boost converter. A Shutdown pin allows the user to turn the controller off, reducing supply current to less than 2A typical. Output voltage can be preset to 5V or is adjustable from 3V to 16.5V with a resistor divider. The controller changes frequency in light load conditions to improve efficiency.
SC1408
Features
1.8V to 16.5V input range Preset (5V) or adjustable output Ground referenced current limit On chip precision reference Up to 300kHz switching frequency 10A max shutdown current Industrial temperature range SO-8 and MSOP-8 packages. Lead free packages available are fully WEEE and RoHS compliant
Applications
PDA Power supplies Battery powered applications Positive LCD Bias generator Portable communications (cellular phones) Peripheral card supplies Industrial power supplies
Typical Application Circuit
Vin (1.8V to 16.5V)
L1
D1
Vout (3V to 16.5V)
U1 2 4 + C1 5 7
BST GATE
Q1 1 8 3 6 R2
R3
SHDN ISENSE REF GND FB AGND
+
C2
R4
C3
SC1408
Revision: November 23, 2005
1
www.semtech.com
SC1408
POWER MANAGEMENT Absolute Maximum Ratings
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied. Exposure to Absolute Maximum rated conditions for extended periods of time may affect device reliability.
Parameter Input Voltage Small Si gnal Ground to Power Ground GATE to GND FB, SHD N, REF, ISENSE to GND Operati ng Temperature Juncti on Temperature Range Storage Temperature Range Lead Temperature (Solderi ng) 10 Sec. Thermal Resi stance, Juncti on to Ambi ent SO-8 MSOP-8 Thermal Resi stance, Juncti on to C ase SO-8 MSOP-8
Symbol BST to GND GND to AGND
Maximum -0.3 to 18 +0.1 -0.3 to VBST +0.3 or 5 -0.3 to mi n. of VBST +0.3 or 5
U nits V V V V C C C C C /W
TA TJ TSTG TL J A
-40 to +85 -40 to +150 -65 to +160 +300 128 216 50 70
J C
C /W
Electrical Characteristics
Unless specified: VOUT = 5V; ILOAD = 0mA; TA = +25C
Parameter Input Voltage
Sym VIN
Conditions TA = 25oC TA = -40oC to +85oC
Min 1.8 1.8
Typ
Max 16.5 16.5
Units V V A
Supply Current
VOUT=16.5V,SHDN < 0.4V VOUT=10V, 1.6V < SHDN < 5V
TA = -40oC to +85oC TA = -40oC to +85oC TA = -40oC to +85oC 4,800
110 2 5.0 60 7
140 10 5.200
Output Voltage Load Regulation Line Regulation Minimum Start Up Voltage Minimum Switch On Time Minimum Switch Off Time Efficiency Reference Voltage Reference Load Regulation Reference Line Regulation
2005 Semtech Corp.
VOUT
VIN = 2.0V to 5.0V
V mV/A mV/V
VIN = 2.0V, VOUT = 5V, ILOAD = 0mA to 500mA VIN = 2.7V to 4.0V, VOUT = 5V, ILOAD = 500mA No load tON(Max) tOFF(Min) VIN = 4V, VOUT = 5V, ILOAD = 0mA to 500mA VREF IREF =0A TA = -40oC to +85oC 1.176 9.6 1.4
1.8 16 2.3 87 1.200 -4 40 1.224 10 100 22.4 3.2
V s s % V mV V/V
0A < IREF < 100A 5V < VOUT < 16.5V
2
www.semtech.com
SC1408
POWER MANAGEMENT Electrical Characteristics (Cont.)
Unless specified: VOUT = 5V; ILOAD = 0mA; TA = +25C
Parameter FB Trip Point Voltage FB Input Current SHDN Input High Voltage SHDN Input Low Voltage SHDN Input Current Current Limit Trip Level ISENSE Input Current GATE Rise Time GATE Fall Time GATE On Resistance
Sym VFB IFM VIN VIL
Conditions TA = 25oC TA = -40oC to +85oC TA = 25oC TA = -40oC to +85oC VOUT = 2.7V to 16.5V VOUT = 2.7V to 16.5V VOUT = 16.5V, SHDN = 0V or 5V
Min 1.176
Typ 1.200
Max 1.224
Units V nA
-4 40 1.6 0.4 1 85 80 100 0.01 115 120 1
V V A mV A ns
VCS
VOUT = 3V to 16.5V
TA = 25oC TA = -40oC to +85oC
VOUT = 5V, InF from GATE to GND VOUT = 5V, InF from GATE to GND GATE = high or low
50 50 15 30
NOTE: (1) This device is ESD sensitive. Use of standard ESD handling precautions is required.
2005 Semtech Corp.
3
www.semtech.com
SC1408
POWER MANAGEMENT Pin Configuration
TOP VIEW
GATE BST FB SHDN 1 2 3 4 8 7 6 5 ISENSE GND AGND REF
Ordering Information
Part Number SC1408IS.TR SC1408ISTRT(2) SC1408IMS.TR SC1408IMSTRT(2) MSOP-8(3) SO-8 -40 to +85C P ackag e
(1)
Temp Range (TA)
(SO-8/MSOP-8)
Pin Descriptions
Pin # 1 2 3 4 5 6 7 8 Pin Name GATE BST FB SHDN REF AGND GND ISENSE Gate drive output. Supply voltage. Voltage feedback
Notes: (1) Only available in tape and reel packaging. A reel contains 2500 devices. (2) Lead free product. This product is fully WEEE and RoHS compliant. (3) Contact factory for MSOP availability
Pin Function
Logic high shuts down the converter. Reference output pin. Small signal analog and digital ground. Power ground. Current sense pin.
Block Diagram
REF FB
MODE DETECT ERROR COMP
1.20V REFERENCE
+
VDD
+ -
50mV BIAS
SHDN
MIN OFF TIME ONE SHOT START UP COMP
Q
TRIG 2.3uS
+ 2.5V
BST
S TRIG Q 16uS MAX ON TIME ONE SHOT Q R
GATE GND
LOW VOLTAGE OSCILLATOR
CURRENT SENSE AMP
+ 0.1V
ISENSE
AGND
2005 Semtech Corp.
4
www.semtech.com
SC1408
POWER MANAGEMENT Applications Information
Theory of Operation The SC1408 is a modified hysteretic boost converter controller. The power switch is turned on when the output voltage falls slightly below it's setpoint. It remains on for approximately 16s, or until the inductor current reaches limit, whichever occurs first. The power switch is then turned off for 2.3 s, or until the output voltage once again falls below setpoint, whichever occurs last. The SC1408 is normally powered from the output voltage. Internal circuitry, such as the bandgap, comparators and one shots, will not function properly until the BST pin voltage reaches 2.5V. To ensure start-up at low input voltages, the normal control circuitry is disabled and a special, low voltage start up oscillator generates an approximate square wave at the GATE pin, initiating boost action. When the output voltage reaches 2.5V, the normal control circuitry is enabled and the start up oscillator shuts down. To conserve power, a SHDN pin is provided which, when pulled high, shuts down most internal circuitry. The output voltage will then be 1 diode drop below the input. COMPONENT SELECTION Boost Converter RSENSE The value of the sense resistor is the primary determining factor for maximum output current. The SC1408 has a fixed current limit voltage threshold, which is developed by the peak inductor current flowing through RSENSE. RSENSE may be determined either from the maximum output current curves or from the equation below:
IO (MAX ) = - V + VF - VIN VCS 1 - O VO + VF - VFET R SENSE
The bottom resistor in the divider chain (R4 in the typical application circuits) should be 300k or less and the top resistor (R3 in the application circuits) can be calculated from
V R 3 = R 4 O - 1 V REF
Inductor The SC1408 will work with a wide range of inductor values. A good choice for most applications is 22H. Smaller inductor values result in higher peak currents and increase output ripple, while larger values will result in slower loop response. Transistor selection Normally the power switch will be an N-channel MOSFET, although in certain circumstances an NPN bipolar may be substituted. The choice of FET can be critical, especially in battery powered applications where the converter must be able to use all of the available energy in the battery. This requires that the converter be capable of starting up from very low input voltages. For example a two cell alkaline system's terminal voltage will drop to 1.8V as it approaches full discharge. For these demanding applications, a FET with low VGS(th) is required. A good rule of thumb is that VGS(th) should be at least 0.5V less than the minimum input voltage. Diode For most applications, a Schottky diode should be used as the output rectifier. It will be subjected to reverse voltages of at least VO , and average current will be somewhat less than the Inductor peak current. Industry standard 1N5817 series or an equivalent surface mount part would be suitable. Output Capacitors Output capacitors should be low ESR to minimize ripple voltage and maximize efficiency. Low ESR tantalum or OSCON capacitors should be used. Ripple voltage will be approximately: Input Capacitors Input capacitors on a boost converter are less critical than the output capacitors, since there are no fast current pulses drawn from the input supply. A 100F tantalum will be adequate for most applications.
www.semtech.com
t off (VIN - VFET )(VO + VF - VIN ) 2L VO + VF - VFET
Where : VF = Output Diode Forward Voltage Drop VFET = Voltage across FET, RSENSE and Inductor DCR
In the equation above, the use of 2.3s for toff may lead to slightly optimistic current values for low VO/VIN ratios. The theoretical curves use the actual value of toff, VF=0.5V, VFET=0.3V and VCS=0.08V and are generated for L=22H. Output Voltage Output voltage can be set to 5V by connecting the FB pin to GND, or to any voltage in the 3.0V to 16.5V range using external divider resistors.
2005 Semtech Corp. 5
SC1408
POWER MANAGEMENT Applications Information (Cont.)
COMPONENT SELECTION SEPIC Converter RSENSE Again, with the SEPIC topology, the value of the sense resistor is the primary determining factor for maximum output current. The simplest approach to select RSENSE is to add Vin to Vo and use this value as the output voltage in the output current curves or in the equation for Boost converter. Output Voltage Output voltage setting works exactly the same in SEPIC topology as in Boost, including the ability to set to 5V by connecting the FB pin to GND. Care must be taken to ensure that the IC supply (pin2; BST) does not exceed its 16.5V rating. In the circuit of Fig.2: This requires maximum output voltage to be limited to 16.5V-Vin. Higher output voltages are possible with different IC supply strategies. Inductor The SEPIC topology requires a coupled inductor. Again A good choice for most applications is 22H. Smaller inductor values result in higher peak currents and increase output ripple, while larger values will result in slower loop response. Transistor selection The choice of FET can be critical, especially in battery powered applications where the converter must be able to use all of the available energy in the battery. This requires that the converter be capable of starting up from very low input voltages. For example a two cell alkaline system's terminal voltage will drop to 1.8V as it approaches full discharge. For these demanding applications, a FET with low VGS(th) is required. A good rule of thumb is that VGS(th) should be at least 0.5V less than the minimum input voltage. Diode For most applications, a Schottky diode should be used as the output rectifier. It will be subjected to reverse voltages of at least VO +VIN and average current will be somewhat less than the Inductor peak current. Industry standard 1N5817 series or an equivalent surface mount part would be suitable. Output Capacitors Output capacitors should be low ESR to minimize ripple voltage and maximize efficiency. Low ESR tantalums, OSCONs or the newer Polymer capacitors should be used. Input Capacitors Input capacitors on a SEPIC converter are less critical than the output capacitors, since there are no fast current pulses drawn from the input supply. A 100F tantalum will be adequate for most applications. Series Capacitors The Series capacitor(s) must be capable of handling an RMS current given by:IRMS = IO VO + 0 .5 VIN
2005 Semtech Corp.
6
www.semtech.com
SC1408
POWER MANAGEMENT Typical Characteristics
Figs.5 - 8: Maximum output current vs. input voltage and sense resistor value. (Boost Mode)
3.5 3.0 2.5 Io (A) 2.0 1.5 1.0 0.5 0.0 2.0
3.5 3.0 2.5 Io (A) 2.0 1.5 1.0 0.5 0.0 2.0 4.0 6.0 Vin (V) 8.0 10.0 12.0 35mOhm 50mOhm 100mOhm Vo=3.3V L=22uH 3.5 Vo=5V L=22uH
20mOhm 25mOhm
Io (A)
3.0 2.5 2.0 1.5 1.0 0.5 0.0
20mOhm 25mOhm
35mOhm 50mOhm 100mOhm 2.2 2.4 2.6 Vin (V) 2.8 3.0 3.2
35mOhm 50mOhm 100mOhm 2.0 2.5 3.0 3.5 Vin (V) 4.0 4.5 5.0
Vo=12V L=22uH 20mOhm 25mOhm Io (A)
4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 0.0 2.0
Vo=15V L=22uH 20mOhm 25mOhm 35mOhm 50mOhm 100mOhm 4.0 6.0 8.0 10.0 Vin (V) 12.0 14.0 16.0
Figs.9-11:Efficiency in the Boost Application circuit of Fig.1
100% Vo=5V
100% Vo=12V
90%
90% Efficiency (%)
Efficiency (%)
80%
Vin=5.0V Vin=4.0V Vin=3.3V Vin=3.0V
80%
70%
70%
Vin=5.0V Vin=3.0V Vin=1.8V
60% 1 10 Io (mA) 100 1000
60% 1 10 Io (mA) 100 1000
100% Vo=15V
90% Efficiency (%)
80%
Vin=12V Vin=9.0V Vin=5.0V Vin=3.0V Vin=1.8V
70%
60% 1 10 Io (mA) 100 1000
2005 Semtech Corp.
7
www.semtech.com
SC1408
POWER MANAGEMENT Typical Characteristics
Output Ripple Voltage; Vin=3V, Vo=5V, Io=470mA Ch1 = Output Ripple Ch2 = Voltage at GATE pin Output Ripple Voltage; Vin=3V, Vo=5V, Io=810mA Ch1 = Output Ripple Ch2 = Voltage at GATE pin
Load Transient; Vin=3V, Vo=5V, Io=0 to 500mA Ch1 = Output Voltage Ch2 = Load Current (0.5A/div)
Load Transient; Vin=2V, Vo=5V, Io=0 to 500mA Ch1 = Output Voltage Ch2 = Load Current (0.5A/div)
2005 Semtech Corp.
8
www.semtech.com
SC1408
POWER MANAGEMENT Typical Application Circuit (Cont.)
Fig.1: Typical Application - Boost Configuration
1.8V-16.5V IN
L1
22uH
D1 B130T R3 See Table
Vin to 16.5V OUT
Coilcraft DO3316P-223 U1 2 C2 100uF + 4 5 7 BST GATE EN ISENSE REF FB 1 8 3 6
Q1 IRLR024N
C9 See Text
+
C8 100uF
+ R2 0.1Ohm R4 10.0k C3 100uF
GND AGND SC1408CS
C5 0.1uF
Fig.2: Typical Application - Buck/Boost (SEPIC) Configuration
D2 1N4148
1.8V TO 5V IN
2
L1A 22uH
1
C1 +
100uF
D1 B130T
0V TO (16.5V-Vin) OUT
U1 2 C2 100uF + C4 0.1uF C5 0.1uF 4 5 7 BST GATE EN ISENSE REF FB 1 8 3 6 Q1 IRLL3303
R3 See Table
C9 See Text
+
C8 100uF
+ R2 0.1Ohm 4 L1B 22uH R4 10.0k C3 100uF
GND AGND SC1408CS
3 L1A/L1B IS COUPLED INDUCTOR PULSE PE-53718 OR EQUIVALENT
2005 Semtech Corp.
9
www.semtech.com
SC1408
POWER MANAGEMENT Typical Application Circuit (Cont.)
Fig.3: Achieving output voltages greater than 16.5V
D4 1N4148 3.3V IN R6 470
L1
22uH
D1 B130T
25V OUT
U1 2 C4 0.1uF 4 5 7 BST GATE EN ISENSE REF FB 1 8 3 6
Q1 IRL3103S
R3 200k + C8 100uF
C2 100uF +
+ R2 0.05Ohm R4 10.0k C3 100uF
GND AGND SC1408CS
D3 12V
C5 0.1uF
Fig.4: Implementing shutdown with input/output isolation
3.3V IN R5 5.1k
Q2 Si2301DS
L1
22uH
D1 B130T
12V OUT
2 C4 0.1uF 4 5 7
U1 BST GATE EN ISENSE REF FB
1 8 3 6
Q1 IRLL3303
R3 90k + C8 100uF
SHORT = RUN OPEN = SHUTDOWN
J1 1 2
C2 100uF +
+ R2 0.05Ohm R4 10.0k C3 100uF
GND AGND SC1408CS
C5 0.1uF
2005 Semtech Corp.
10
www.semtech.com
SC1408
POWER MANAGEMENT Outline Drawing - SO-8
A N 2X E/2 E1 E 1 ccc C 2X N/2 TIPS 2 e/2 B D aaa C SEATING PLANE A2 A C bxN bbb A1 C A-B D GAGE PLANE 0.25 SEE DETAIL SIDE VIEW
NOTES: 1. 2. 3. 4. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). DATUMS -A- AND -B- TO BE DETERMINED AT DATUM PLANE -HDIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. REFERENCE JEDEC STD MS-012, VARIATION AA.
e
D
DIM
A A1 A2 b c D E1 E e h L L1 N 01 aaa bbb ccc
DIMENSIONS MILLIMETERS INCHES MIN NOM MAX MIN NOM MAX
.069 .053 .010 .004 .065 .049 .020 .012 .010 .007 .189 .193 .197 .150 .154 .157 .236 BSC .050 BSC .010 .020 .016 .028 .041 (.041) 8 0 8 .004 .010 .008 1.75 1.35 0.25 0.10 1.65 1.25 0.31 0.51 0.17 0.25 4.80 4.90 5.00 3.80 3.90 4.00 6.00 BSC 1.27 BSC 0.25 0.50 0.40 0.72 1.04 (1.04) 8 8 0 0.10 0.25 0.20
h h
H
c
A
L (L1) DETAIL
01
A
Minimum Land Pattern - SO-8
X
DIM
(C) G Z C G P X Y Z
DIMENSIONS INCHES MILLIMETERS
(.205) .118 .050 .024 .087 .291 (5.20) 3.00 1.27 0.60 2.20 7.40
Y P
NOTES: 1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET.
2. REFERENCE IPC-SM-782A, RLP NO. 300A.
2005 Semtech Corp.
11
www.semtech.com
SC1408
POWER MANAGEMENT Outline Drawing - MSOP-8
e/2 A N 2X E/2 PIN 1 INDICATOR ccc C 2X N/2 TIPS 12 e B E1 E D
DIM
A A1 A2 b c D E1 E e L L1 N 01 aaa bbb ccc
DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX
.043 .000 .006 .030 .037 .009 .015 .003 .009 .114 .118 .122 .114 .118 .122 .193 BSC .026 BSC .016 .024 .032 (.037) 8 0 8 .004 .005 .010 1.10 0.00 0.15 0.75 0.95 0.38 0.22 0.08 0.23 2.90 3.00 3.10 2.90 3.00 3.10 4.90 BSC 0.65 BSC 0.40 0.60 0.80 (.95) 8 0 8 0.10 0.13 0.25
aaa C SEATING PLANE
D A2 A GAGE PLANE 0.25
H c
C
A1 bxN bbb C A-B D
L (L1) DETAIL
01
A
SIDE VIEW
NOTES: 1.
SEE DETAIL
A
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). -B- TO BE DETERMINED AT DATUM PLANE -H-
2. DATUMS -A- AND
3. DIMENSIONS "E1" AND "D" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. 4. REFERENCE JEDEC STD MO-187, VARIATION AA.
Land Pattern - MSOP-8
X
DIM
(C) G Z C G P X Y Z
DIMENSIONS INCHES MILLIMETERS
(.161) .098 .026 .016 .063 .224 (4.10) 2.50 0.65 0.40 1.60 5.70
Y P
NOTES: 1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET.
Contact Information
Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805)498-2111 FAX (805)498-3804
2005 Semtech Corp. 12 www.semtech.com

▲Up To Search▲

Price & Availability of SC140805

	To Download SC140805 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .