SC2604 [SEMTECH]
Simple PWM Boost Controller with Input Disconnect FET Drive; 简单的PWM升压控制器与输入断开FET驱动器
| 型号： | SC2604 |
| 厂家： | 
SEMTECH CORPORATION |
| 描述： | Simple PWM Boost Controller with Input Disconnect FET Drive |
| 文件： | 总14页 (文件大小：361K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
SC2604
Simple PWM Boost Controller
with Input Disconnect FET Drive
POWER MANAGEMENT
Features
Description
Input Voltage Range: 4.5V to ꢀ3.5V
ꢀ% Voltage Reference Accuracy
Up to 95% Efficiency
Input Disconnect FET Drive
In-rush Current Control
Internal Compensation
Programmable Current Limit
Programmable Soft Start
800mA Typical PWM Gate Drive
400kHz Switching Frequency
Under Voltage Lockout
<200uA Shutdown Current
-40oC to +85oC Temperature Range
MSOP-8 Package, Fully WEEE and RoHS Compliant
The SC2604 is a versatile, low-cost, voltage-mode PWM
controller designed for boost DC/DC power supply
applications. It features input disconnect FET driver
allowing power source and load separation at shutdown
mode, which eliminates possible leakage current from
source to load. Also, it prevents catastrophic failure when
output is shorted during operation.
The SC2604 also includes temperature compensated
voltage reference, internal ramp, current limit comparator,
internally compensated error amplifier, and floating driver
with charge pump. Programmable soft start controls
in-rush current and reduces output voltage overshoot.
Hiccup mode over-current protection allows system auto-
retry and ease of trouble shooting.
Applications
Internally compensated feedback loop makes power
supply design simple, and eliminates the need for external
compensation network.
Portable Devices
Flat Panel TV
TV Set Top Box
Auxiliary Supplies
Peripheral Card Supplies
Industrial Power Supply
High Density DC/DC Conversion
The SC2604 is available in MSOP-8 package with rated
temperature range of -40oC to +85oC.
Typical Application Circuit
Figure 1. 12V to 25V/1A Boost Converter with Over Current Protection
www.semtech.com
January 4, 2008
ꢀ
SC2604
Pin Configuration
Ordering Information
Device
Package
SC2604MSTRT(ꢀ)(2)
SC2604EVB
MSOP-8
Evaluation Board
Notes:
(ꢀ) Available in tape and reel only. A reel contains 2,500 devices.
(2) Available in lead-free package only. Device is fully WEEE and RoHS
compliant.
(8 - Pin MSOP)
Marking Information
Top Mark
Bottom Mark
nnnn=Part Number Code (Example AS00)
- Reference Part No. Code for MSOP
yyww=Date Code (Example: 0752)
xxxx = Semtech Lot No. (Example: E90ꢀ)
xxxx = Semtech Lot No. (Example: 0ꢀ-ꢀ)
© 2007 Semtech Corp.
www.semtech.com
2
SC2604
Absolute Maximum Ratings
Thermal Information
Junction to Ambient (ꢀ) ……………………………… ꢀ60°C/W
Junction to Case (ꢀ) ………………………………… 45°C/W
Maximum Junction Temperature……………………… ꢀ50°C
Storage Temperature ………………………… -45 to +ꢀ50°C
VIN Supply Voltage ……………………………… -0.3 to 20V
CS Pin Voltage………………………………………-0.3 to 20V
GATE Pin Voltage……………………………………-0.3 to 20V
DRV Pin Voltage ……………………………………-0.3 to 25V
Lead Temperature (Soldering) ꢀ0 sec ………………… 300°C
OCP/EN Pin Voltage …………………………………-0.3 to 7V
SS/VREF Pin Voltage …………………………………-0.3 to 7V
FB Pin Voltage ………………………………………-0.3 to 7V
Peak IR Reflow Temperature …………………………. 260°C
ESD Protection Level(2) ………………………………… 2000V
Recommended Operating Conditions
Input Voltage Range …………………………… 4.5V to ꢀ3.5V
Exceeding the above specifications may result in permanent damage to the device or device malfunction. Operation outside of the parameters specified in the
Electrical Characteristics section is not recommended.
NOTES-
(ꢀ) Calculated from package in still air, mounted to 3”x 4.5”, 4 layer FR4 PCB with thermal vias under the exposed pad per JESD5ꢀ standards.
(2) Tested according to JEDEC standard JESD22-Aꢀꢀ4-B.
Electrical Characteristics
Unless otherwise noted, VIN = ꢀ2V, VO = 25V, -40°C < TA = TJ < ꢀ25°C.
Parameter
Conditions
Min
Typ
Max
Units
Input Supply
VIN Supply Voltage
VIN Start Voltage
4.5
ꢀ3.5
4.5
V
VIN Rising
4.2
400
6.0
V
VIN Start Hysteresis
VIN Supply Current
VIN Shutdown Current
Error Amplifier
Feedback Voltage
Feedback Bias Current
Error Amplifier Gain (ꢀ)
Oscillator
mV
mA
µA
Switching, GATE pin floating
OCP/EN = Low
9.0
200
IO = ꢀ00mA
ꢀ.225
ꢀ.250
0.5
ꢀ.275
ꢀ.0
V
VIN = ꢀ2V, VFB = VSS/VREF
µA
90
V/V
Oscillator Frequency
Maximum Duty Cycle
Internal Ramp Peak (2)
Internal Ramp Valley (2)
Regulation
320
86
400
90
480
kHz
%
V
ꢀ.4
0.4
V
Load Regulation
Line Regulation
IO = 0.ꢀA to ꢀA
0.5
ꢀ.0
%
%
VIN = 5V to ꢀ3.5V, IO = 0.ꢀA
© 2007 Semtech Corp.
www.semtech.com
3
SC2604
Electrical Characteristics (Cont.)
Unless otherwise noted, VIN = ꢀ2V, VO = 25V, -40°C < TA = TJ < ꢀ25°C.
Parameter
Conditions
Min
Typ
Max
Units
PWM Switch Gate Drive
Gate Source Current
Gate Sink Current
VIN = ꢀ2V, CGATE = ꢀ0nF
VIN = ꢀ2V, CGATE = ꢀ0nF
0.5
0.5
0.8
0.8
A
A
PWM Switch Soft Start
Soft Start Charge Current
55
µA
Pull down below this level to
disable PWM Switch gate
SS/VREF Threshold to Shutdown Switch
SS/VREF Threshold to Turn-on Switch
ꢀ00
mV
Pull above this level to
enable PWM Switch gate
3ꢀ0
mV
Disconnect Switch Gate Drive
DRV Source Current
VIN = ꢀ2V, VDRV = ꢀ5.5V
VIN = ꢀ2V, VDRV = 8V
45
45
µA
µA
DRV Sink Current
Over Current Protection
Current Limit Threshold
VIN - CS
6ꢀ
72
83
mV
mV
Pull down below this level to
disable Disconnect FET gate
OCP/EN Threshold
520
590
660
OCP/EN Charge Current
OCP/EN Discharge Current
CS Input Current
37
ꢀ.0
0.2
µA
µA
µA
Note: (ꢀ). Guaranteed by Characterization
(2). Guaranteed by design
© 2007 Semtech Corp.
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4
SC2604
Pin Descriptions
Pin
Pin Name
Pin Function
ꢀ
2
3
4
5
6
CS
VIN
Current sense input (negative)
Device supply voltage (also positive current sense input)
PWM gate driver output for boost converter
Device ground
GATE
GND
SS/VREF
FB
Soft start and reference voltage pin
Error amplifier inverted input
When a capacitor is tied to this pin, the maximum inrush current is controlled during start-up. The capacitor value
also determines the off-time after the device has entered hiccup mode. Pulling this pin low can disable the linear
and the switcher to turn off the circuit.
7
8
OCP/EN
DRV
Gate drive of input disconnect FET limiting system input current
© 2007 Semtech Corp.
www.semtech.com
5
SC2604
Block Diagram
Figure 2. SC2604 Function Diagram
© 2007 Semtech Corp.
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6
SC2604
Typical Characteristics
© 2007 Semtech Corp.
www.semtech.com
7
SC2604
Typical Characteristics (Cont.)
© 2007 Semtech Corp.
www.semtech.com
8
SC2604
Applications Information
PWM Control Loop
allow a complete shutdown of the output. Pulling the SS/
VREF pin below 0.ꢀV only shuts the boost FET (Q2 in Figure
ꢀ) off and the output voltage will be (VIN-Vd).
The SC2604 is a voltage-mode PWM controller with a fixed
switching frequency of 400kHz for use in high efficiency,
boosted voltage, DC/DC power supplies.
As shown in Figure 2, the PWM control loop of the SC2604
consists of a 400kHz oscillator, a PWM comparator,
a voltage error amplifier, and a FET driver. The boost
converter output voltage is fed back to FB (error amplifier
negative) and is regulated to the reference voltage at
SS/VREF pin. The error amplifier output is compared
with the 400kHz ramp to generate a PWM wave, which
is amplified and used to drive the boost FET (Q2 in Figure
ꢀ) for the converter. The PWM controller works with soft
start and fault monitoring circuitry to meet application
requirements.
UVLO, Start-up, and Shutdown
To initiate the SC2604, a supply voltage is applied to VIN.
The DRV and GATE are held low. When VIN voltage exceeds
UVLO (Under Voltage Lockout) threshold, typically 4.2V,
an internal current source (37µA) begins to charge the
OCP/EN pin capacitor. The OCP/EN voltage ramps from
near ground to over ꢀ.25V but the voltage between
0.625V and ꢀ.25V provides the linear soft-start range for
the disconnect FET (Qꢀ). When the OCP/EN voltage is
over ꢀ.25V, the OCP hiccup is enabled, and SS/VREF pin is
released. At this moment, another internal current source
(55µA) begins to charge the SS/VREF pin capacitor. When
the SS/VREF pin voltage reaches 0.5V, the error amplifier
output will rise to 0.4V, then the PWM comparator begins
to switch. The switching regulator output is slowly
ramping up for a soft turn-on. The details of SC2604 start-
up timing is shown in Figure 3.
Figure 3. Start-up Timing Diagram
Hiccup Mode Short Circuit Protection
Hiccup mode over-current protection is utilized in the
SC2604. When an increasing load causes a voltage of
72mv to occur from VIN to CS then a current limit hiccup
sequence is started. The sequence starts by pulling DRV
low and discharging the OCP/EN pin with a ꢀµA current
source. When the OCP/EN pin falls below ꢀ.25V, the SS/
VREFpinisforcedtoground(similartotheUVLOshutdown
described in the last setion).
When the voltage on the OCP/EN pin falls to near zero
volt, the ꢀµA discharge current becomes a 37µA charging
current and the OCP/EN pin starts to charge and DRV is
enabled. When the OCP/EN voltage rises from 0.625V
to ꢀ.25V, the current in the disconnect FET is allowed to
increase from zero to a maximum of 72mV/(Current Sense
Resistor Value). If the over-current condition still exists
when OCP/EN crosses ꢀ.25V then the hiccup sequence
will re-start. If there is no over-current as OCP/EN crosses
ꢀ.25V then the SS/VREF pin is released to rise and allow a
If the supply voltage at VIN pin falls below UVLO threshold
(3.8V typically) during a normal operation, the DRV pin
is pulled low to cut off the supply power of the boost
converter, while the OCP/EN pin capacitor is discharged
with a ꢀµA internal current source. When the OCP/EN pin
falls below ꢀ.25V, the SS/VREF pin is forced to ground. This
completely shuts down the boost conveter.
Directly pulling the OCP/EN pin below 0.52V can also
© 2007 Semtech Corp.
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9
SC2604
Applications Information (Cont.)
soft-start of the switching boost regulator.
Capacitor at OCP/EN Pin - COCP/EN
The DRV pin of the SC2604 is meant to drive an N-Channel
FET that can disconnect the input supply in the event of an
over-current condition. The OCP/EN capacitor becomes
part of a hiccup oscillator that is charged with 37µA and
discharged with ꢀµA to provide a low duty cycle for the
FET Qꢀ.
Asthecurrentatstart-upmayhititscurrentlimitthreshold,
the ramp rate of the current must be slow enough to allow
the output capacitor to be fully charged to a voltage one
diode drop Vd less than input voltage VIN. To guarantee a
successful start-up at no load, the value of the capacitor at
the OCP/EN pin has to satisfy the following formula:
It should be understood that sufficiently fast ramp rates
on the OCP/EN pin and the SS/VREF pin can trigger a
hiccup event because of the charging current demanded
by the boost regulator output capacitor.
Disconnect FET Selection
Setting the Output Voltage
The floating driving voltage of DRV pin drops slightly as
the supply voltageVIN is below 7.5V (Typical Characteristics
on page 8), where a FET with low gate threshold voltage
(VGS(TH)) has to be used for the disconnect FET. In a 5V input
application, a FET with VGS(TH)=2V, such as FDD6672A from
Fairchild, is needed.
In Figure ꢀ, an external resistive divider R7 and R8 with its
center tap tied to the FB pin sets the output voltage.
In some applications, a RC branch (R6, Cꢀ2 in the Typical
Schematic on page ꢀ2) will be needed for loop stability.
Layout Guidelines
Careful attentions to layout requirements are necessary
for successful implementation of the SC2604 PWM
controller. High currents switching at 400kHz are present
in the application and their effect on ground plane voltage
differentials must be understood and minimized.
Maximum Duty Cycle
The maximum duty cycle, Dmax defines the upper limit of
power conversion ratio
ꢀ) The high power parts of the circuit should be laid out
first. A ground plane should be used, the number and
position of ground plane interruptions should be such as
to not unnecessarily compromise ground plane integrity.
Isolated or semi-isolated areas of the ground plane may
be deliberately introduced to constrain ground currents
to particular areas, for example the input capacitor and
bottom Schottky ground.
Calculating Current Sense Resistor
Current sense resistor is placed at the input to sense
inductor peak current of the boost regulator. The value of
the resistor can be calculated by
2) The loop formed by the output Capacitor(s) (COUT), the
FET (Qꢀ), the current sensing resistor, and the Schottky
(Dꢀ) must be kept as small as possible, as shown on the
layout diagram in Figure 4. This loop contains all the high
current, fast transition switching. Connections should
be as wide and as short as possible to minimize loop
inductance. Minimizing this loop area will reduce EMI,
where IPEAK is the allowed boost inductor peak current.
Inmanyapplications,anoisefiltercircuit(Rꢀ=200,Cꢀ0=ꢀ0nF
in the Typical Schematic on page ꢀ2) may be needed for
the input current sensing.
© 2007 Semtech Corp.
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ꢀ0
SC2604
Applications Information (Cont.)
lower ground injection currents, resulting in electrically
“cleaner” grounds for the rest of the system and minimize
source ringing, resulting in more reliable gate switching
signals.
5) The SC2604 is best placed over an isolated ground
plane area.The soft-start capacitor and theVin decoupling
capacitor should also connected to this ground pad
area. This isolated ground area should be connected to
the main ground by a trace that runs from the GND pin
to the ground side of the output capacitor. If this is not
possible, the GND pin may be connected to the ground
path between the Output Capacitor and the CIN, Qꢀ, Dꢀ
loop. Under no circumstances should GND be returned to
a ground inside the CIN, Qꢀ, Dꢀ loop.
3) The connection between the junction of Qꢀ, Dꢀ and the
output capacitor should be a wide trace or copper region.
It should be as short as practical. Since this connection
has fast voltage transitions, keeping this connection short
will minimize EMI.
4) The Output Capacitor(s) (COUT) should be located as
close to the load as possible, fast transient load currents
are supplied by COUT only, and connections between COUT
and the load must be short, wide copper areas to minimize
inductance and resistance.
6) Input voltage of the SC2604 should be supplied from
the power rail through a ꢀΩ resistor, the Vin pin should
be decoupled directly to GND by a 0.ꢀµF~ꢀµF ceramic
capacitor, trace lengths should be as short as possible.
Note: Heavy lines indicate the critical loop carrying high pulsating current.
The inductance of the loop needs to be minimized.
Figure 4. SC2604 Layout Diagram
© 2007 Semtech Corp.
www.semtech.com
ꢀꢀ
SC2604
Applications Information (Cont.)
Typical application schematic with 12V input and 25V/1.5A output
Note: A small Schottky diode (Da) may be required in some applications to clamp negative spike at the GATE pin.
Bill of materials
© 2007 Semtech Corp.
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ꢀ2
SC2604
Applications Information (Cont.)
Start up
Inductor current and DRV pin voltage at OCP
© 2007 Semtech Corp.
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ꢀ3
SC2604
Outline Drawing - MSOP-8
Land Pattern - MSOP-8
Contact Information
Semtech Corporation
Power Mangement Products Division
200 Flynn Road, Camarillo, CA 930ꢀ2
Phone: (805) 498-2ꢀꢀꢀ Fax: (805) 498-3804
© 2007 Semtech Corp.
www.semtech.com
ꢀ4
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