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SC4806
Multiple Function
Double Ended PWM Controller
POWER MANAGEMENT
Description
The SC4806 is a double ended, high speed, highly integrated PWM controller optimized for applications requiring minimum space. The device is easily configurable for current mode or voltage mode operation and contains all the control circuitry required for isolated applications, where a secondary side error amplifier is used.
Designed for simplicity, the SC4806 is fully featured and requires only a few external components. It features a programmable frequency up to 1MHZ, external programmable soft start, pulse-by-pulse current limit and over current protection for both voltage and current modes, as well as a line monitoring input with hysteresis to reduce stress on the power components. A ramp pin allows for slope compensation to be programmed by external resistors for current mode. This also allows for operation in voltage mode with voltage feed forward.
A unique oscillator is utilized which allows two SC4806 to be synchronized together and work out-of-phase. This feature minimizes the input and output ripples, and reduces stress and size on input/output filter components.
The outputs are configured for push-pull format, dead time between the 2 outputs is programmable depending on the size of the timing components.
The SC4806 features a turn on threshold of 8 volts .
The device is available at a MLP-12 package.
Typical Application Circuit
Features
90 µA starting current
Pulse-by-pulse current limit for both voltage/current modes
Programmable operating frequency up to 1MHz
Programmable external soft start
Programmable line undervoltage lockout
Programmable external slope compensation
Over current shutdown with separate pin
Dual output drive stages on push-pull configuration
Programmable mode of operation (peak current mode or voltage mode)
External frequency synchronization
Bi-phase mode of operation
Lead free MLP-12 package,WEEE and RoHS compliant
-40 to 105 °C operating temperature
Applications
Telecom equipment and power supplies
Networking power supplies
Industrial power supplies
Push-pull converter
Half bridge converter
Full bridge converter
Isolated VRMs
+VIN +Vo
+ +
-VIN
ON/OFF
REF SYNC
4
RC
5
ILIM
6
RAMP
I sense
Vcc
SC4806
Vcc
VCC
12
OUTA
11
OUTB
10
SC1301A
Rsense
SC1301A
FB
REF
SC431
-Vo
REF
FB
I sense
Revision: October 13, 2006 1 www.semtech.com
SC4806
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.
P a r a m e t e r S y m b o l M a x i m u m U n i t s
V
C C
I
C C
S u p p l y V o tl a g e
S u p p l y C u r r e n t
S Y N C , R C , R A M P , L U V L O , R E F , I L M , S S t o G N D
F B t o G N D
R E F C u r r e n t
O U T A / O U T B t o G N D
O U T A / O U T B S o u r c e C u r r e n t ( p e a k )
O U T A / O U T B S i n k C u r r e n t ( p e a k )
T h e r m a l R e s i s t a n c e , J u n c it o n t o A m b i e n t
T h e r m a l R e s i s t a n c e , J u n c it o n t o C a s e
J u n c it o n T e m p e r a t u r e
S t o r a g e T e m p e r a t u r e R a n g e
P e a k I R R e lf o w T e m p e r a t u r e 1 0 4 0 s
E S D R a it n g ( H u m a n B o d y M o d e )l
Electrical Characteristics
Unless specified: VCC = 12V; CL = 100pF; T
A
= -40°C to 105°C
P a r a m e t e r
V
F B
I
R E F
V
O U T A / B
I s o u r c e
I s i n k
θ
J A
θ
J C
T
J
T
S T G
T
P K G
E S D
T e s t C o n d i t i o n s
0 .
5 t o 1 8
2 0
0 .
5 t o 7
0 .
5 t o ( V
R E F
+ 0 .
5 )
1 0
0 .
5 t o 1 8
2 5 0
2 5 0
3 2
3
5 5 t o 1 5 0
6 5 t o 1 5 0
2 6 0
2
M i n
45455
T y p
V m A
V
V m A
V m A m A
° C / W
° C / W
° C
° C
° C k V
M a x U n i t s
V C C S u p p l y
V
C C
S t a r t T h r e s h o l d
H y s t e r e s i s
S t a r t u p C u r r e n t
O p e r a it n g S u p p l y C u r r e n t
V C C Z e n e r S h u n t V o tl a g e
P W M
M a x i m u m D u t y C y c l e
M i n i m u m D u t y C y c l e
V C C < s t a r t t h r e s h o l d
F B = 0 V , R A M P = 0 V
I D D = 1 0 m A
M
F e a o s s c u r e
= d
5 0 a t k H z ,
O U
F
T A
B o r
= 5 V ,
O U T B
M
F o s e a s c = u r e
5 0 d k a t
H
O z ,
U
F B
T A
= o r
1 .
5 V ,
O U T B
7 .
4
1 .
1 7
1 6
4 8
8
1 .
5
4 9
8 .
6
1 .
8 3
1 5 0
7
5 0
0
V
V
µ A m A
V
%
%
C u r r e n t S e n s e / L i m i t
I L M C y c l e b y C y c l e C u r r e n t L i m ti T h r e s h o l d
I L M t o O u t p u t D e l a y
I L M A u t o R e s t a r t O v e r C u r r e n t T h r e s h o l d
F B t o R A M P O ff s e t
4 5 0
7 5 0
1 .
2 0
5 2 5
5 0
8 5 0
1 .
4 0
6 0 0
9 5 0
1 .
6 0 m V n s m V
V
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SC4806
POWER MANAGEMENT
Electrical Characteristics (Cont.)
Unless specified: VCC = 12V; CL = 100pF; T
A
= -40°C to 105°C
P a r a m e t e r T e s t C o n d i t i o n s
L i n e U n d e r V o l t a g e L o c k o u t
S t a r t T h r e s h o l d R h i g h = 1 4 k
Ω
, R l o w = 1 0 k
Ω
H y s t e r e s i s R h i g h = 1 4 k
Ω
, R l o w = 1 0 k
Ω
S o f t S t a r t
I n t e r n a l
C u r r e n t
S o
( I
S S
) tf S t a r t C h a r g e
I n t e r n a l D i s c h a r g e C u r r e n t
O s c i ll a t o r
O s c i ll a t o r F r e q u e n c y
O s c i ll a t o r R a m p
V
S S
= 1 .
5 V
V
S S
= 1 .
5 V
R o s c
= 1 0 k
Ω
, C o s c
= 2 0 0 p F
O s c i ll a t o r F a ll T i m e
R C p i n t o G N D C a p a c ti a n c e
O s c i ll a t o r F r e q u e n c y R a n g e
S y n c / C L O C K
C l o c k S Y N C T h r e s h o l d
S y n c F r e q u e n c y R a n g e
B a n d g a p
R e f e r e n c e V o tl a g e
R e f e r e n c e L o a d R e g u l a it o n
R e f e r e n c e L i n e R e g u l a it o n
O u t p u t
O U T L o w L e v e l
O U T H i g h L e v e l
R i s e T i m e
F a ll T i m e
M i n i m a l D e a d T i m e
T h e r m a l S h u t d o w n
T h e
T h r e r m s a h o l l
S h u t d o d T
S D w n
T h e r m a l
H y s t e r e s
S i s h u t d o w n
2006 Semtech Corp.
G u a r a n t e e d b y c h a r a c t e ir z a it o n
G u a r a n t e e d b y c h a r a c t e ir z a it o n
G u a r a n t e e d b y c h a r a c t e ir z a it o n
I
R E F
= 0 5 m A
V
C C
= 8 .
5 V t o 1 5 V
V
C C
= 1 2 V
L o a d 1 n F
L o a d 1 n F
3
M i n T y p M a x
3 % V R E F
5 .
5 %
V R E o
F f
+ 3 %
U
V m
n
V
i
2 5 3 5
1 0
4 5
4 5 0 5 0 0
V R E F / 2
+ 0 .
2 5
2 0 0
2 2
5 0
5
2
5
5
0
0
1 0 0 0
µ A
µ A
K H z
V n s p F
K H z
t
4 .
7 5
1 0 .
8 5
0 .
5
1 1 .
2 0
3 5
3 5
2 0 0
1 .
7 5
F
O S C
* 1 .
3
V
K H z
5 .
0
1 0
0 .
3
5 .
2 5 V m V / m A m V / V
0 .
7
2 5 0
V
V n s n s n s
1 7 5
1 5
° C
° C www.semtech.com
POWER MANAGEMENT
Pin Configuration
TOP VIEW
VCC OUTA OUTB
LUVLO
SS
SYNC
1
12
2
3
4
11 10
9
8
5 6
7
RC ILIM RAMP
SYNC
SS
LUVLO
BOTTOM VIEW
RC ILIM RAMP
3
4 5 6
7
2
1
12
GND
11
8
10
9
VCC OUTA OUTB
(MLPQ-12 4x4)
FB
REF
GND
GND
REF
FB
SC4806
Ordering Information
D E V I C E ( 1 )
S C 4 8 0 6 M L T R T
( 2 )
P A C K A G E
M L P Q 1 2
T e m p .
R a n g e ( T
J
)
4 0 ° C t o 1 0 5 ° C
Notes:
(1) Only available in tape and reel packaging. A reel contains 3000 devices.
(2) Lead free product. This product is fully WEEE and
RoHS compliant.
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SC4806
POWER MANAGEMENT
Pin Descriptions
LUVLO (Pin 1): RC (Pin 4):
Line undervoltage lockout pin. An external resistive divider from the Input supply will program the undervoltage lockout level. The external divider should be referenced to the quiet analog ground. During the LUVLO, the driver outputs are disabled. This pin can also function as an
Enable/Disable.
SS (Pin 2):
The oscillator programming pin. The oscillator should be referenced to a stable reference voltage for an accurate and stable frequency. Only two components are required to program the oscillator, a resistor (tied to Vref and RC), and a capacitor (tied to the RC and GND). The following formula can be used for a close approximation of the oscillator frequency.
F
OSC
≅
1
R
OSC
C
TOT
An internal 35µA current source charges the external capacitor connected to this pin. This pin is connected to one of the inputs of the PWM comparator. When the voltage on this SS pin increases, but less than 1/3 of the feedback voltage V
FB
, the pulse width of OUTA and OUTB gradually increases to achieve soft start. As the output voltage increases and feedback loop enters regulation, the PWM modulator is controlled by V
FB
. At normal operation, the voltage at SS pin is clamped at Vref.
where:
C
TOT
=
C
OSC
+
C
SC4806
+
C
Circuit
C
SC4806
≅
22pF
When the Over Current is tripped, both OUTA and OUTB are pulled low after a typical time delay (Typ. 100ns). At the same time, the SS cap is gradually discharged via an equivalent 10µA internal current source. When the voltage on SS pin is dropped below 0.8V, a new SS cycle is initiated while the SS cap is charged with 35µA again.
The recommended range of timing resistors is between
10kohm and 200kohm and range of timing capacitors is between 100pF and 1000pF. Timing resistors less than 10kohm should be avoided.
Refer to layout guidelines in Application Information section to achieve best results.
The internal thermal protection circuit monitors the die temperature. If the temperature exceeds 175 o
C, the controller is completely shutdown. When the temperature is dropped below 160 o
C, defined by the hysteresis, the controller re-starts with soft start process.
SYNC (Pin 3):
SYNC is a positive edge triggered input with a threshold set to 1.75V. In a single controller operation, SYNC could be grounded or connected to an external synchronization clock within the SYNC frequency range. In Bi-Phase operation mode SYNC pins could be connected to the
Cosc (Timing Capacitors) of the other controller. This will force an out-of-phase operation (see Application Information part).
ILim (Pin 5):
The current signal from a sense resistor is applied to peak current and overcurrent comparators through ILM pin.
Under normal operation condition, the comparators are not trigged. When the current signal sensed at ILM pin exceeds the first threshold -- pulse-by-pulse current limit, the corresponding on-time is terminated for the remainder of the switching cycle. In this case, the circuit output voltage loses regulation even though it continues to provide full load current.
When the load current continuously increases and the sensed signal at ILM pin reaches the second threshold -
- over current limit, the controller turns off both OUTA and OUTB. At the same time, the SS cap is discharged with equivalent 10uA current source. When the voltage at SS pin is below 0.5V, the controller initiates re-start.
The pins Ramp and ILM are discharged by the internal
FETs at the end of each switching cycle.
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SC4806
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Pin Descriptions (Cont.)
Ramp (Pin 6):
GND (Pin 9):
The signal at this pin will be used as the PWM ramp signal that will be compared to the FB to achieve regulation. The modes of operation can be programmed depending on how this pin is configured (For more details see Application section).
Device power and analog ground. The exposed paddle area on the back of the package must be connected to the GND (pin9). Careful attention should be paid to the layout of the ground planes.
For voltage mode control, the PWM ramp is generated via external RC circuit connected from a voltage source to the Ramp pin. Connection to a fixed voltage source
(REF) will provide a constant peak ramp with a frequency set by the internal oscillator frequency programed at the RC pin. Connection to a variable source such as the
VIN will provide the added benefit of the feed forward function enhancing the converter static and dynamic performance.
OUTB (Pin 10) and OUTA (Pin 11):
Out of phase gate drive stages. The driver’s peak source and sink current drive capability of 100mA, enables the use of an external MOSFET driver or a NPN/PNP transistor totem pole driver.
The oscillator RC network programs the oscillator frequency, which is twice the OUTA/OUTB frequency. To insure that the outputs do not overlap, a dead time can be generated between the two outputs by sizing the oscillator timing capacitor (see Application Information section).
For Current mode control the current information from the ILim pin can be directly connected to the Ramp pin without the need for the external RC circuit at the Ramp pin.
VCC (Pin 12):
If current mode of operation with slope compensation is required, an external resistor connected from the ILim pin to the Ramp pin will provide the slope compensation. The percentage of the slope compensation will be inversely proportional to the value of the resistor ( the higher resistor lower slope compensation, the lower resistor higher slope compensation). 1/3 of external feedback signal to FB pin by an internal 3 to 1 resistor divider compares to the combined current signal to generate PWM control signal.
The supply input for the device. Once VCC has exceeded the UVLO limit, the internal reference, oscillator, drivers and logic are powered up. A low ESR capacitor, should be placed right at the pin to minimize noise problems. It is recommended that the V
CC be smaller than 10V/mS.
rising rate during start-up
THERMAL PAD:
Pad for heatsinking purposes. Connect to ground plane using multiple thermal vias. Not connected internally.
FB (Pin 7):
The inverting input to the PWM comparator through an internal 3 to 1 resistor divider. Stray inductances and parasitic capacitance should be minimized by utilizing ground planes and correct layout guidelines.
REF (Pin 8):
Bandgap reference output. It is recommended by placing a minimum 2.2uF low ESR capacitor right at the pin.
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SC4806
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Block Diagram
RAMP
ABOA
Marking Information
Top View
35uA
10uA yyww = Date Code (Example: 0012) xxxxxx = Semtech Lot #
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SC4806
POWER MANAGEMENT
Application Information
SC4806 is a versatile double ended, high speed, low power, pulse width modulator optimized for applications requiring minimum space.
The device contains all of control and drive circuity required for isolated or non isolated power supplies where an external error amplifier is used. A fixed oscillator frequency (up to 1MHz) can be programmed by an external
RC network.
SC4806 also provides flexibility with programmable
LUVLO thresholds, with built-in hysteresis.
To generate PWM control signal, 1/3 of external feedback signal to FB pin by an internal 3 to 1 resistor divider compares to the combined current signal if an external resistor is connected from ILIM to RAMP. The value of the resistor will determine the level of slope compensation. The slope signal to RAMP is generated from either input voltage or VREF with external RC. Voltage mode of operation can be achieved if the slope signal is only used.
SC4806 is a peak current or voltage mode controller, depending on the amount of slope compensation, programmable with only one external resistor. The cycle by cycle peak current limit prevents core saturation when a transformer is used for isolation while the auto-restart over-current circuitry initiates the soft-start cycle.
SC4806 dual output drive stages are arranged for double ended configurations. Both outputs switch at half the oscillator frequency using a toggle flip flop. The dead time between the two outputs is programmable depending on the values of the timing capacitor and resistors, thus limiting each output stage duty cycle to less than 50%.
Two levels of undervoltage lockout are also available.
The LUVLO (line under voltage lockout) pin via an external resistive divider programs input voltage turn-on level.
During the LUVLO, the driver outputs are disabled and the soft-start is reset.
The VCC UVLO (under voltage lockout) determines VCC voltage turn-on level. Once VCC exceeds the UVLO limit, the internal reference, oscillator, drivers and logic are powered up.
PO WER SUPPL
A single supply, VCC is used to provide the bias for the internal reference, oscillator, drivers, and logic circuitry of SC4806.
SYNC is a positive edge triggered input with a threshold set to 1.75V. By connecting an external control signal to the SYNC pin, the internal oscillator frequency will be synchronized to the positive edge of the external control signal. In a single controller operation, SYNC should be grounded or connected to an external synchronization clock within the SYNC frequency range. In the Bi-phase operation mode, a very unique oscillator is utilized to allow two SC4806s to be synchronized together and work out of phase. This feature is set up by simple connection of the SYNC input of one part to the RC pin of the other.
The master oscillator forces the two PWMs to operate out of phase. This feature minimizes the input and output ripples, and may reduce input and output capacitors.
SC4806 is a double ended PWM controller that can be used in voltage or current mode applications. The oscillator frequency is programmed by a resistor and a capacitor network connected to an external reference provided by the SC4806. The two outputs, OUTA and OUTB, are 180 degrees out-of-phase and run at half of the oscillator frequency.
CC UNDER V
OL
Depending on the application and the voltages available, the SC4806 (UVLO = 8V) can be used to provide the VCC undervoltage lock out function to ensure the converters controlled start up.
A GE L
An external error amplifier will provide the error signal to the FB pin of the SC4806. The current limit input and external slope compensation are provided separately via the ILIM and RAMP pins. The current limit signal from a sense resistor or a current sense transformer is used for the peak current and auto-restart overcurrent comparators.
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Before the VCC UVLO has been reached, the internal reference, oscillator, OUTA/OUTB drivers, and logic are disabled.
LINE UNDER V OL A
GE L
OCK OUT
The SC4806 also provides a line undervoltage (LUVLO =
Vref) function. The LUVLO pin is programmed via an exwww.semtech.com
SC4806
POWER MANAGEMENT
Application Information (Cont.)
ternal resistor divider connected as shown below. The actual start-up voltage can be calculated by using the equation below:
V
Startup
=
V
REF
×
(1
+
R1
R2
)
+VIN
-VIN
ON/OFF
+
R1
R2
The oscillator has a ramp voltage of about Vref/2. The oscillator frequency is twice the frequency of the OUTA and OUTB gate drive controls.
The oscillator capacitor CT is charged from the Vref through RT. Once the RC pin reaches about Vref/2, the capacitor is discharged internally by the SC4806. It should be noted that larger capacitor values will result in a longer dead time during the down slope of the ramp.
The following equation can be used as an approximation of the oscillator frequency and the Dead time:
F
OSC
≅
R
OSC
1
C
TOT
REF SYNC
4
RC
5
ILim
6
RAMP
SC4806
Vcc
VCC
12
OUTA
11
OUTB
10 where:
C
TOT
=
C
OSC
C
SC4806
≅
22pF
+
C
SC4806
T deadtime
+
C
Circuit
≅
C
OSC
3
×
⋅
V
REF
10
−
3
×
0.5
REF
FB
I sense
The recommended range of timing resistors is between
10 kohm and 200kohm, range of timing capacitors is between 100pF and 1000pF. Timing resistors less than
10 kohm should be avoided.
A 5V reference voltage is available that can be used to source a typical current of 5mA to the external circuitry.
The Vref can be used to provide the oscillator RC network with a regulated bias.
OSCILLA TOR
The oscillator frequency is set by connecting a RC network as shown below.
+VIN
In noise sensitive applications where synchronization of the oscillator frequency to a reference frequency may be required, the SYNC pin can accept the external clock.
By connecting an external control signal to the SYNC pin, the internal oscillator frequency will be synchronized to the positive edge of the external control signal. SYNC is a positive edge triggered input with a threshold set to
1.75V.
REF
RT
CT
SYNC
4
RC
5
ILIM
6
RAMP
SC4806
Vcc
VCC
12
OUTA
11
OUTB
10
REF
FB
I sense
In a single controller operation, SYNC should be grounded or connected to an external synchronization clock within the SYNC frequency range.
In the Bi-phase operation mode a very unique oscillator is utilized to allow two SC4806’s to be synchronized together and work out of phase. This feature is set up by a simple connection of the SYNC input to the RC pin of the other part. The master oscillator forces two
PWMs to operate out of phase. This feature minimizes the input and output ripples, and may reduce input and output capacitors.
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SC4806
POWER MANAGEMENT
Application Information (Cont.)
REF
S la v e
S C 4 8 0 6
Rosc1
4
Cosc1
5
RC
ILIM
6
RAMP
VCC
12
OUTA
11
OUTB
10
Vcc
REF
M a s te r
S C 4 8 0 6
Rosc2
4
Cosc2
5
RC
ILIM
6
RAMP
VCC
12
OUTA
11
OUTB
10
Vcc
The signal at the FB pin is then compared to the 3X signal from the current sense/ slope compensation RAMP pin. Matched out of phase signals are generated to control the OUTA and OUTB gate drives of the two phases. A single ramp signal is used to generate the control signals for both phases, hence achieving a tightly matched per phase operation.
Voltages below 1.5V at the FB pin, will produce a 0% duty cycle at the OUTA/OUTB gate drives. This offset is to provide enough head room for the opto coupler used in isolated applications.
G A TE DRIVERS
OUTA (PWM1)
OUTB (PWM1)
OUTA (PWM2)
OUTB (PWM2)
OUTA and OUTB are out of phase bipolar gate drive output stages, that are supplied from VCC and provide a peak source/sink current of about 100mA. Both stages are capable of driving the logic input of external MOSFET drivers or a NPN/PNP transistor buffer. The output stages switch at half the oscillator frequency. When the voltage on the RC pin is rising, one of the two outputs is high, but during fall time, both outputs are off. This “dead time” between the two outputs, along with a slower output rise and fall time, insures that the two outputs can not be on at the same time. The dead time is programmable and depends upon the timing capacitor.
The error signal from output of an external error amplifier such as SC431 or SC4431 is applied to the inverting input of the PWM comparator at the FB pin either directly or via an opto-coupler for the isolated applications.
For best stability, keep the FB trace length as short as possible.
It should be noted that if high speed/high current drivers such as the SC1301 are used, careful layout guide lines must be followed in order to minimize stray inductance, which might cause negative voltages at the output of the drivers. This negative voltage can be clamped to a reasonable level by placing a small Schottky diode directly at the output of the driver as shown below:
+Vo
Lo1
+
Co1
VCC
-Vo
REF
4
RC
5
ILIM
6
RAMP
S C 4 8 0 6
VCC
12
OUTA
11
OUTB
10
1
VCC
4
D_B1
Gate_A
D_B2
SC1301A
FB
SC431
1 4
D_A1
Gate_B
D_A2
SC1301A
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SC4806
POWER MANAGEMENT
Application Information (Cont.)
OPERA TION MODE
SC4806 can be configured in either voltage mode or current mode. In voltage mode, a ramp is externally generated by RC network. The R can be connected to Vref or other fixed voltage source as shown below. By comparing control signal to the ramp, PWM duty cycle is derived.
SC4806 Voltage mode (Non-Feed Forward)
Vref or other fixed Voltage source
R1
Ramp
In current mode control, the ramp voltage is not derived artificially from a ramp generator. It is instead provided from a power converter inductor current by a current sensing transformer or resistor. Thus a second, inner control loop is formed by comparing the inductor current ramp to control voltage from outer voltage loop. Now the control voltage programs the inductor current via the inner loop and no longer controls the duty cycle directly.
The current mode control corrects most of problems with direct duty cycle control in voltage mode. The chief advantage of the methods its inherent feed-forward characteristics and simplified loop dynamics. An added benefits is the reduction or elimination of transformer saturation problems in full-bridge or push-pull isolated converters. The current mode configuration with SC4806 is as shown below:
C1
SC4806 100% Current mode (No Slope Compensation)
R3
Isense
ILIM
Ramp
C2
R3
Isense
ILIM
Voltage mode with feed-forward operation is implemented if the R is connected to input voltage as shown below. With this implementation, the ramp amplitude varies directly with input voltage. If control signal to FB is constant, the duty cycle varies inversely with input voltage. Thus the volt-second product, Vin*D, remains constant without any control change. Open loop line regulation better than direct duty cycle control as shown above.
Good dynamic response is achieved with less closed loop gain required.
C2
The current mode control ling the peak inductor current results in circuit instability whenever the steady state duty cycle is greater than 0.5. An artificial slope has to be added to avoid such problem. Power transformer magnetizing current riding on the reflected inductor current acts to provide some slope compensation, but the amount is rather variable and indeterminate. The current mode with slope compensation is as shown below:
SC4806 Voltage mode (Feed Forward)
Vin
SC4806 Current mode (With Slope Compensation)
Vref or other fixed Voltage source
R1
C1
Ramp
Isense
R3
C2
ILIM
RC
Ramp
ILIM
Isense
2006 Semtech Corp.
11 www.semtech.com
SC4806
POWER MANAGEMENT
Application Information (Cont.)
During start up of the converter, the discharged output capacitor and the load current have large supply current requirements. To avoid this a soft start scheme is usually implemented where the duty cycle of the regulator is gradually increased from 0% until the soft start duration is elapsed.
Careful attention to layout requirements are necessary for successful implementation of the SC4806 PWM controller.
High current switching is present in the application and their effect on ground plane voltage differentials must be understood and minimized.
SC4806 has soft start circuit with an external capacitor that limits the duty cycle for a duration approximated by the formula below. Also the soft start circuitry is activated if an over current condition occurs. After an over current condition, OUTA and OUTB are disabled and kept low. After the delay, the OUTA and OUTB are enabled while the soft start limits the duty cycle. If the over current condition persists, the soft start cycle repeats indefinitely.
1) 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, such as the input capacitor and FET ground.
Initially during the power up, the SC4806 is in under voltage lock out condition. As the Vcc supply exceeds the
UVLO limit of the SC4806, the internal reference, oscillator, and logic circuitry are powered up.
2) In the loop formed by the Input Capacitor(s) (Cin), the
FET must be kept as small as possible. 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 a) reduce
EMI, b) lower ground injection currents, resulting in electrically “cleaner” grounds for the rest of the system and c) minimize source ringing, resulting in more reliable gate switching signals.
The OUTA and OUTB drivers are not enabled until the line under voltage lock out limit is reached. At that point, once the FB pin is above 1.5V, soft start circuitry starts the output drivers, and gradually increases the duty cycle from
0%.
3) The connection between FETs and the Transformer 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.
As the output voltage starts to increase, the error signal from the error amplifier starts to decrease. If isolation is required, the error amplifier output can drive the LED of the opto isolator. The output of the opto is connected in a common emitter configuration with a pull-up resistor to a reference voltage connected to the FB pin of the
SC4806. The voltage level at the FB pin provides the duty cycle necessary to achieve regulation.
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.
If an over current condition occurs, the outputs are disabled and after a soft start delay time of about 100µs, the soft-start sequence mentioned above is repeated.
5) A SC4806 is best placed over a quiet ground plane area. Avoid pulse currents in the Cin FET loop flowing in this area. GND should be returned to the ground plane close to the package and close to the ground side of
(one of) the VCC supply capacitor(s). Under no circumstances should GND be returned to a ground inside the
Cin, Q1, Q2 loop. Avoid making a star connection be-
2006 Semtech Corp.
12 www.semtech.com
SC4806
POWER MANAGEMENT
Application Information (Cont.)
tween the quiet GND planes that the SC4806 will be connected to and the noisy high current GND planes connected to the FETs.
6) The feed back connection between the error amplifier and the FB pin should be kept as short as possible
The GND connections should be connected to the quiet
GND used for the SC4806.
7) If an Opto isolator is used for isolation, quiet primary and secondary ground planes should be used. The same precautions should be followed for the primary GND plane as mentioned in item 5 mentioned above. For the secondary GND plane, the GND plane method mentioned in item
4 should be followed.
8) All the noise sensitive components such as LUVLO resistive divider, reference by pass capacitor, Vcc bypass capacitor, current sensing circuitry, feedback circuitry, and the oscillator resistor/capacitor network should be connected as close as possible to the SC4806. The GND return should be connected to the quiet SC4806 GND plane.
9) The connection from the OUTA and OUTB of the
SC4806 should be minimized to avoid any stray inductance. If the layout can not be optimized due to constraints, a small Schottky diode may be connected from the OUTA/B pins to the ground directly at the IC. This will clamp excessive negative voltages at the IC. If drivers are used, the Schottky diodes should be connected directly at the IC from the output of the driver to the driver ground.
10) If the SYNC function is not used, the SYNC pin should be grounded at the SC4806 GND to avoid noise pick up.
2006 Semtech Corp.
13 www.semtech.com
SC4806
POWER MANAGEMENT
Push Pull Evaluation Board Sch
C30
82pF
7
REF
8
0
9
FB
REF
GND(heatsink)
GND
SYNC
3
SS
2
LUVLO
1
2
A A C
CMOSH-3 CMOSH-3
3
5
C
0.1u,25V
C29
VCC
2
A A C
CMOSH-3 CMOSH-3
3
5
C
A
D4
ZM4743A
C
C11
.1u,16V
C12
10u,16V
E
C8 1u,100V
C9 1u,100V
C
C10 1u,100V
R_GS_MA1
2 3
R_GS_MB1
2 3
1
N = 100
3
8
7
1
2
4
3
A C
2
Vref
1 2
Vref
1
C
CMOSH-3
A
CMOSH-3
A C
A
CMOSH-3
C C
CMOSH-3
A
C16
22u,6.3V
C17
22u,6.3V
C18
22u,6.3V
C19
22u,6.3V
C20
22u,6.3V
C21
22u,6.3V
C22
0.1u
C14
0.1u
2006 Semtech Corp.
14 www.semtech.com
SC4806
POWER MANAGEMENT
Evaluation Board Bill of Materials
SC4806 Slope Compensation Current Mode Push Pull 3.3V 35W non Synchronous
SC4806EVB__non_sync Revision: 1.1
Bill Of Materials March 30,2005 11:27:17
49
50
51
52
53
54
40
41
42
43
44
45
46
47
48
34
35
36
37
38
39
29
30
31
32
33
68
69
70
71
64
65
66
67
55
56
57
58
59
60
61
62
63
Item Quantity
1 1
19
20
21
22
23
24
13
14
15
16
17
18
7
8
9
10
11
12
4
5
6
2
3
1
2
1
1
1
1
1
1
1
1
2
1
6
6
2
2
2
1
2
3
1
1
1
25
26
27
28
8
8
1
14
CON1
CON2
C2
C23,C7
C8,C9,C10
C11
Reference
T1
T3
T4
U1
U2
U6,U3
U5,U8
U7
R42,R23
R24
R25,R38,R41
R37,R28
R30
R32
R36
R39
R43
C24,C12
C13,C15
C14,C22,C27,C33,C34,C43
C16,C17,C18,C19,C20,C21
C41,C25
C26
C28
C29
C30
C31
C44,C35
C36
C37
C40
C42
D2,D1
D3
D4
D5,D6,R12,R13,R19,R20,
R26,R31
D7,D8,D9,D10,D11,D12,D13,
D14
D15
J2
J3
J4
J5
JP1,JP2,JP3,JP4,JP5,JP6,
JP7,JP8,JP9,JP10,JP11,
JP12,JP25,JP28
J1
J6
J7
L1
L2
MB1,MA1
Q_Slope_Comp
Q2
R_GS_MB1,R_GS_MA1,R3
R_Pull_Up
R_Slope_I
R_Slope_V
R1,R33
R4
R8
R9
R10,R15
R17,R11
R16,R14
R18
R21
R22
2
1
2
2
1
1
2
1
1
1
1
1
1
3
1
1
2
1
1
1
1
1
1
1
1
1
1
2
2
1
1
1
1
1
1
1
2
1
1
1
2
1
3
Part
3input_half_brick
5output_half_brick
82p
100p
1u,100V
.1u,16V
10u,16V
2.2n
0.1u
22u,6.3V
1nF
0.1uF 16V
22nF
0.1u,25V
82pF
1u,16V
22n
2.2u,16V
.1uF
100pF
470pF
MBRB2535CTL
LS4448
ZM4743A
0
CMOSH-3
1N5819HW short
SS
Vcc
SYNC
OUTA
OUTB
REF
FB
0.9uH
LQH43MN102K011
SUD19N20-90
FMMT718
FZT853
10k
3.01k
301
20k
1k
15
49.9k
250
100
2.2
10
16.2
56.2k
10k
TBD
10
15k
2.2k
37.4k
18.2k
11.5k
25.5k
100
PA0810
P8208T
PE-68386
SC4806
RH02
SC1301A
SC4431
MOCD207
Manufacturer #
GRM44-1X7R105K250AL(muRata)
GRM32DR61C106KA01(muRata)
GRM32DR60J226KA01(muRata)
GRM32RR71H105KA011(muRata)
CMOSH-3 (Central Semiconductor)
PG0006.102(Pulse)
LQH43MN102K01L(muRata)
SUD19N20-90(vishay)
FMMT718 (Zetex)
FZT853 (Zetex)
PA0810(Pulse)
P8208T(Pulse)
PE-68386(Pulse)
SC4806(Semtech)
RH02(Diodes Inc.)
SC1301A(Semtech)
SC4431(Semtech)
Foot Print
CON\3INPUT_HALF_BRICK
CON\5OUTPUT_HALF_BRICK
SM/C_0805
SM/C_1206
SM/C_2220
SM/C_0805
SM/C_1210_GRM
SM/C_1206
SM/C_0805
SM/C_1210_GRM
SM/C_0805
SM/C_0603
SM/C_1206
SM/C_1206
SM/C_0805
SM/C_1210_GRM
SM/C_0805
SM/C_1206
SM/C_0805
SM/C_0805
SM/C_0805
DIODE_D2PAK
SM/DO213AC
SMB/DO214
SM/R_0805
SOD523
SOD123
VIA\2P
ED5052
ED5052
ED5052
ED5052
ED5052
ED5052
ED5052
PG0006
SDIP0302
DPAKFET
SM/SOT23_BEC
SM/SOT223_BCEC
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_1206
SM/R_1210_MCR
SM/R_1206
SM/R_0805
SM/R_1206
SM/R_0805
SM/R_1206
SM/R_1206
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
PA0810
P8208T
PE-68386
MLPQ-12 (4X4)
RH02
SOT23_5PIN
SOT23_5PIN
SO-8
2006 Semtech Corp.
15 www.semtech.com
POWER MANAGEMENT
Evaluation Board Gerber Plots
SC4806
Board Layout Assembly TOP Board Layout Assembly Bottom
2
1
2006 Semtech Corp.
Board Layout Top
16
Board Layout Bottom
www.semtech.com
POWER MANAGEMENT
Evaluation Board Gerber Plots (Cont.)
SC4806
Board Layout Inner1
Evaluation Board Modifications
1
R Slope I
Board Layout Inner2
Q Slope Comp
D15
R43
R Pull up
2006 Semtech Corp.
R Slope V
Board Layout Bottom
17
2
www.semtech.com
POWER MANAGEMENT
HB Evaluation Board Schematics
C32
82pF
C30
82pF
R4 15
7
REF 8
0
9
FB
REF
GND(heatsink)
GND
SYNC
3
SS
2
LUVLO
1
2 3
5
A A C C
CMOSH-3 CMOSH-3
0.1u,25V
C29
VCC
2 3
5
A A C C
CMOSH-3 CMOSH-3
C8 1u,100V
C9 1u,100V
A
D4
ZM4743A
C
C11
.1u,16V
C12
10u,16V
E
Q2 F
C
C10 1u,100V
C6
2.2u,50V
C4
2.2u,50V
1
6
2
5
4
3
R_GS_MA1
2 3
R_GS_MB1
2
C7 100p
3
1
N = 100
3
8
7
1
2
4
3
C
CMOSH-3
A
CMOSH-3
A C
A
CMOSH-3
C C
CMOSH-3
A
SC4806
A C
2
Vref
1 2
Vref
1
C16
47u,6.3V
C17
47u,6.3V
C18
47u,6.3V
C19
47u,6.3V
C20
47u,6.3V
C21
47u,6.3V
C22
0.1u
C14
0.1u
2006 Semtech Corp.
18 www.semtech.com
SC4806
POWER MANAGEMENT
Evaluation Board Bill of Materials
SC4806 Feed Forward Half bridge 3.3V 35W non Synchronous
SC4806EVB__non_sync Revision: 1.1
Bill Of Materials March 30,2005 10:47:27
52
53
54
55
56
57
58
45
46
47
48
49
50
51
38
39
40
41
42
43
44
32
33
34
35
36
37
65
66
67
68
69
70
71
59
60
61
62
63
64
72
73
74
Item Quantity
21
22
23
24
25
26
27
14
15
16
17
18
19
20
7
8
9
10
11
12
13
4
5
6
1
2
3
1
1
2
1
1
1
1
1
2
1
1
2
1
1
6
6
1
2
2
3
1
1
2
2
1
1
2
28
29
30
31
8
8
1
14
Reference
R35
R36
R39,R38
R43
T1
T2
T3
T4
U1
U4,U2
U6,U3
U5,U8
U7
CON1
CON2
C1,C5
C2
C4,C6
C23,C7
C8,C9,C10
C11
C12,C24
C15,C13
C14,C22,C27,C33,C34,C43
C16,C17,C18,C19,C20,C21
C25
C26
C28
C29
C32,C30
C31
C44,C35
C36
C37
C39
C40
C41
C42
D1,D2
D4
D5,D6,R12,R13,R19,R20,
R26,R31
D7,D8,D9,D10,D11,D12,D13,
D14
D15
JP13,JP14,JP15,JP16,JP17,
JP18,JP19,JP20,JP21,JP22,
JP23,JP24,JP25,JP26
J1
J2
J3
R15,R10
R17,R11
R16,R14
R18
R21
R22
R23,R42
R41,R25
R27
R28
R30
R32
R33,R37
J4
J5
J6
J7
L1
L2
MB1,MA1
Q2
R_GS_MB1,R_GS_MA1
R1
R4
R6,R7,R24
R8
R9
1
1
2
2
1
1
1
2
2
2
1
1
1
3
1
2
1
1
2
1
1
1
1
1
1
1
1
1
1
2
1
1
1
1
2
2
1
1
1
2
1
1
2
CMOSH-3
1N5819HW short
SS
Vcc
SYNC
OUTA
OUTB
REF
FB
1.9uH
LQH43MN102K011
SUD19N20-90
FZT853
10k
1k
16.2
56.2k
10k
TBD
15k
316k
2.2k
15
10
49.9k
250
100
2.2
10
37.4k
18.2k
1.1k
0
1.62k
25.5k
100
PA0801
PA0264
P8208T
PE-68386
SC4806
RH02
SC1301A
SC4431
MOCD207
Part
3input_half_brick
5output_half_brick
2.2n
82p
2.2u,50V
100p
1u,100V
.1u,16V
10u,16V
2.2n
0.1u
47u,6.3V
1nF
0.1uF 16V
22nF
0.1u,25V
82pF
1u,16V
22n
2.2u,16V
.1uF
6.8nF
47pF
2.2nF
680pF
MBRB2535CTL
ZM4743A
0
Manufacturer #
GRM44-1X7R105K250AL(muRata)
GRM32DR61C106KA01(muRata)
GRM43-2X5R476K6.3(muRata)
GRM32RR71H105KA011(muRata)
CMOSH-3 (Central Semiconductor)
PG0006.212(Pulse)
LQH43MN102K01L(muRata)
SUD19N20-90(vishay)
FZT853 (Zetex)
PA0801(Pulse)
PA0264 (Pulse)
P8208T(Pulse)
PE-68386(Pulse)
SC4806(Semtech)
RH02(Diodes Inc.)
SC1301A(Semtech)
SC4431(Semtech)
2006 Semtech Corp.
19
SOD523
SOD123
VIA\2P
ED5052
ED5052
ED5052
ED5052
ED5052
ED5052
ED5052
PG0006
SDIP0302
DPAKFET
SM/SOT223_BCEC
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_1206
SM/R_1210_MCR
SM/R_1206
SM/R_0805
SM/R_1206
SM/R_0805
SM/R_1206
SM/R_1206
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0805
SM/R_0603
SM/R_0805
SM/R_0805
SM/R_0805
PA0805
PE-68386
P8208T
PE-68386
MLPQ-12 (4X4)
RH02
SOT23_5PIN
SOT23_5PIN
SO-8
Foot Print
CON\3INPUT_HALF_BRICK
CON\5OUTPUT_HALF_BRICK
SM/C_0805
SM/C_0805
SM/C_2220
SM/C_1206
SM/C_2220
SM/C_0805
SM/C_1210_GRM
SM/C_1206
SM/C_0805
SM/C_1210_GRM
SM/C_0805
SM/C_0603
SM/C_1206
SM/C_1206
SM/C_0805
SM/C_1210_GRM
SM/C_0805
SM/C_1206
SM/C_0805
SM/C_0603
SM/C_0805
SM/C_0805
SM/C_0805
DIODE_D2PAK
SMB/DO214
SM/R_0805 www.semtech.com
SC4806
POWER MANAGEMENT
Evaluation Board Gerber Plots
Board Layout Assembly TOP Board Layout Assembly Bottom
2
Board Layout Top
2006 Semtech Corp.
20
Board Layout Bottom
www.semtech.com
POWER MANAGEMENT
Evaluation Board Gerber Plots (Cont.)
SC4806
Board Layout Inner1
Evaluation Board Modifications
D15
R43
2006 Semtech Corp.
2
Board Layout Bottom
21
Board Layout Inner2
www.semtech.com
SC4806
POWER MANAGEMENT
Outline Drawing - MLPQ-12, 4 x 4
PIN 1
INDICATOR
(LASER MARK)
A aaa C
A
A1
D
B
E
A2
C
SEATING
PLANE
D
D1
E
E1 e
A
A1
A2 b
L
N aaa bbb
DIM
MIN
.031
DIMENSIONS
INCHES MILLIMETERS
NOM
-
MAX
.040
MIN
0.80
NOM
-
MAX
1.00
.000
-
.010
.153
-
(.008)
.012
.157
.002
-
.014
.161
0.00
-
0.25
3.90
-
(0.20)
0.30
4.00
0.05
-
0.35
4.10
.074
.085
.089
1.90
2.15
2.25
.153
.157
.161
3.90
4.00
4.10
.074
.018
.085
.031 BSC
.022
.089
.026
12
.003
.004
1.90
0.45
2.15
0.80 BSC
0.55
12
0.08
0.10
2.25
0.65
D1
LxN
E/2
E1
2
1
N
D/2 e bxN bbb C A B
NOTES:
1.
CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
2.
COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS THE TERMINALS.
Land Pattern - MLPQ-12, 4 x 4
K
2x (C)
H
2x G
2x Z
Y
DIM
C
G
P
X
Y
Z
H
K
X
P
NOTES:
1.
THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY.
CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR
COMPANY'S MANUFACTURING GUIDELINES ARE MET.
DIMENSIONS
INCHES MILLIMETERS
(.148)
.106
.091
.091
.031
.016
.041
.189
(3.75)
2.70
2.30
2.30
0.80
0.40
1.05
4.80
Contact Information
2006 Semtech Corp.
Semtech Corporation
Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805)498-2111 FAX (805)498-3804
22 www.semtech.com
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