SD6251 [SHOUDING]
5V, 2.5A 550KHz High Efficiency Low Ripple Synchronous Step-Up Converter;
| 型号： | SD6251 |
| 厂家： | 
SHOUDING Shouding Semiconductor |
| 描述： | 5V, 2.5A 550KHz High Efficiency Low Ripple Synchronous Step-Up Converter |
| 文件： | 总9页 (文件大小：576K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
SD6251
2.5A 55
5V,
0KHz High Efficiency Low Ripple
Synchronous Step-Up Converter
Description
Features
The SD6251 is a high efficiency, fixed frequency
550KHz, current mode PWM boost DC/DC converter
which could operate battery such as input voltage
down to 2.5V. The converter output voltage can be
adjusted to a maximum of 5.25V by an external
resistor divider. Besides the converter includes a
0.08Ω N-channel MOSFET switch and 0.12Ω
P-channel synchronous rectifier. So no external
Schottky diode is required and could get better
efficiency near 93%.
High Efficiency up to 93%
Low RDS(ON) Integrated Power MOSFET
NMOS 80mΩ / PMOS120mΩ
Wide Input Voltage Range: 2.5V to 5.5V
Fixed 550KHz Switching Frequency
Low-Power Mode for Light Load Conditions
±2.0% Voltage Reference Accuracy
PMOS Current Limit for Short Circuit Protection
Low Quiescent Current
Output Ripple under 200mV. (Scope Full
Bandwidth)
Fast Transient Response
The converter is based on a fixed frequency, current
mode, pulse-width-modulation PWM controller that
goes automatically into PSM mode at light load.
Built-In Soft Start Function
Over-Temperature Protection with Auto Recovery
Output Overvoltage Protection
Space-Saving SOT-23-6 Package
When converter operation into discontinuous mode,
the internal anti-ringing switch will reduce
interference and radiated electromagnetic energy.
Applications
The SD6251 is available in a space-saving SOT-23-6
package for portable application.
Portable Power Bank
Wireless Equipment
Handheld Instrument
GPS Receiver
Pin Assignments
Ordering Information
SD6251□□□ □
Package (SOT-23-6)
R: Tape/Reel
VIN
OUT EN
G: Green
6
5
4
3
(Marking)
1
2
Package Type
D6: SOT-23-6 and marking
LX GND FB
Figure 1. Pin Assignment of SD6251
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SD6251
Typical Application Circuit
L1
VIN
VOUT
5V/1A
10μH
2.5V to 5.5V
C1
10μF
C2
0.1μF
R1
525K
C4, C6
0.1μF
C3, C5
22μF
6
2
4
1
5
3
VIN
LX
OUT
FB
SD6251
GND
R2
100K
EN
ON
OFF
Figure 2. Typical Application Circuit
Functional Pin Description
Pin Name
Pin No.
Pin Function
EN
4
2
1
6
5
3
Logic Controlled Shutdown Input.
Ground Pin.
GND
LX
Power Switching Connection. Connect LX to the inductor and output rectifier.
Power Supply Input Pin.
VIN
OUT
FB
Output of the Synchronous Rectifier.
Voltage Feedback Input Pin.
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SD6251
Block Diagram
VIN
LX
PMOS
OUT
ANTI-RING
On/Off
Control
EN
NMOS
Body-Diode
Switch
Anti-Reverse
Comparator
Isense/Current Limit
Slope Comp.
PFM
Control
PWM
Control
Logic
OSC
OVP
COMP
FB
Error
Amp
Bandgap
Reference
UVLO
VIN
OTP
GND
Figure 3. Block Diagram of SD6251
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SD6251
Absolute Maximum Ratings (Note 1)
● Supply Voltage VIN --------------------------------------------------------------------------------------------- -0.3V to +6.5V
● LX Voltage VLX -------------------------------------------------------------------------------------------------- -0.3V to +6.5V
● All Other Pins Voltage ----------------------------------------------------------------------------------------- -0.3V to +6.5V
● Maximum Junction Temperature (TJ) --------------------------------------------------------------------- +150°C
● Storage Temperature (TS) ----------------------------------------------------------------------------------- -65°C to +150°C
● Lead Temperature (Soldering, 10sec.) ------------------------------------------------------------------- +260°C
● Package Thermal Resistance (θJA)
SOT-23-6 ---------------------------------------------------------------------------------------------- +250°C/W
● Package Thermal Resistance (θJC)
SOT-23-6 ---------------------------------------------------------------------------------------------- +130°C/W
Note 1：Stresses beyond this listed under “Absolute Maximum Ratings" may cause permanent damage to the device.
Recommended Operating Conditions
● Supply Voltage VIN --------------------------------------------------------------------------------------------- +2.5V to +5.5V
● Output Voltage Range ---------------------------------------------------------------------------------------- up to +5.25V
● Operation Temperature Range ------------------------------------------------------------------------------ -40°C to +85°C
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SD6251
Electrical Characteristics
(VIN=3.3V, TA=25°C, unless otherwise specified.)
Parameter
VIN Input Supply Voltage
Input UVLO Threshold
Symbol
Conditions
Min
Typ
Max
Unit
V
VIN
2.5
5.5
VIN Rising
1.85
0.2
V
Under Voltage Lockout Threshold
Hysteresis
VIN Falling
V
VIN=3.3V, VFB=0.8V
Measure VIN
VIN Supply Current (Switching)
300
500
μA
VIN Supply Current (No switching)
Feedback Voltage
VFB=1V
25
μA
V
2.5V≦VIN≦5.5V
VFB
0.784
0.8
120
80
0.816
High-Side PMOSFET RDS(ON)
Low-Side NMOSFET RDS(ON)
mΩ
mΩ
High-Side MOSFET Leakage
Current
ILX(leak)
VLX=5.5V, VOUT=0V
VLX=5.5V
10
μA
Low-Side MOSFET Leakage Current
Oscillation Frequency
Switch Current Limit
10
μA
KHz
A
FOSC
450
2.5
550
650
VIN=3.3V
Short Circuit Trip Point
Short Circuit Current Limit
Maximum Duty Cycle
Line Regulation
Monitored FB voltage
VIN = 3.3V
0.3
50
90
V
mA
%
DMAX
VIN=3.3V
85
VIN=2.5V to 5.5V, IOUT=100mA
IOUT=0A to 1A
1
%
Load Regulation
0.5
6
%
OVP Threshold Voltage on OUT Pin
OVP Threshold Hysteresis
Internal Soft-Start Time
EN Input Low Voltage
EN Input High Voltage
EN Input Current
V
500
1
mV
ms
V
3
VEN (L)
VEN (H)
IEN
0.4
1.4
V
VIN=3.3V
2
μA
Thermal Shutdown Threshold
(Note 2)
TSD
150
30
°C
°C
Thermal Shutdown Hysteresis
Note 2：Not production tested.
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SD6251
Application Information
Controller Circuit
Device Enable
The device is based on a current-mode control
The device will be shut down when EN is set to
GND. In this mode, the regulator stops switching,
all internal control circuitry including the low-battery
comparator will be switched off, and the load will be
disconnected from the input (as described in above
synchronous rectifier section). This also means
that the output voltage may drop below the input
voltage during shutdown.
topology and uses
a
constant frequency
pulse-width modulator to regulate the output
voltage. The controller limits the current through
the power switch on a pulse by pulse basis. The
current sensing circuit is integrated in the device;
therefore, no additional components are required.
Due to the nature of the boost converter topology
used here, the peak switch current is the same as
the peak inductor current, which will be limited by
the integrated current limiting circuits under normal
operating conditions.
The device is put into operation when EN is set
high. During start-up of the converter, the duty
cycle is limited in order to avoid high peak currents
drawn from the battery. The limit is set internally
by the current limit circuit.
Synchronous Rectifier
Anti-Ringing Switch
The device integrates an N-channel and a P-
channel MOSFET transistor to realize
synchronous rectifier. There is no additional
Schottky diode required. Because the device
uses a integrated low RDS(ON) PMOS switch for
rectification, the power conversion efficiency
reaches 93%.
a
The device integrates a circuit which removes
the ringing that typically appears on the SW node
when the converter enters the discontinuous
current mode. In this case, the current through
the inductor ramps to zero and the integrated
PMOS switch turns off to prevent a reverse
current from the output capacitors back to the
battery. Due to remaining energy that is stored
in parasitic components of the semiconductors
and the inductor, a ringing on the SW pin is
A special circuit is applied to disconnect the load
from the input during shutdown of the converter.
In conventional synchronous rectifier circuits, the
backgate diode of the high-side PMOS is forward
biased in shutdown and allows current flowing from
the battery to the output. This device, however,
uses a special circuit to disconnect the backgate
diode of the high-side PMOS and so, disconnects
the output circuitry from the source when the
regulator is not enabled (EN=low).
induced.
The integrated anti-ringing switch
clamps this voltage internally to VIN; therefore,
dampens this ringing.
Adjustable Output Voltage
The accuracy of the output voltage is determined by
the accuracy of the internal voltage reference, the
controller topology, and the accuracy of the external
resistor. The reference voltage has an accuracy of
PSM Mode
The SD6251 is designed for high efficiency over
wide output current range. Even at light load, the
efficiency stays high because the switching losses
of the converter are minimized by effectively
reducing the switching frequency. The controller
will enter a power saving mode if certain conditions
are met. In this mode, the controller only switches
on the transistor if the output voltage trips below a
set threshold voltage. It ramps up the output
voltage with one or several pulses, and goes again
into PSM mode once the output voltage exceeds a
set threshold voltage.
± 2%.
The controller switches between fixed
frequency and PSM mode, depending on load
current. The tolerance of the resistors in the
feedback divider determines the total system
accuracy.
Design Procedure
The SD6251 boost converter family is intended for
systems that are powered by a single-cell Ion
battery with a typical terminal voltage between 3V
to 4.2V.
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SD6251
Application Information (Continued)
(3) Capacitor Selection
(1) Programming the Output Voltage
The major parameter necessary to define the
output capacitor is the maximum allowed output
voltage ripple of the converter. This ripple is
determined by two parameters of the capacitor,
the capacitance and the ESR. It is possible to
calculate the minimum capacitance needed for
the defined ripple, supposing that the ESR is zero,
by using Equation 3.
The output voltage of the SD6251 can be
adjusted with an external resistor divider. The
typical value of the voltage on the FB pin is
800mV in fixed frequency operation.
The
maximum allowed value for the output voltage is
5.5V. The current through the resistive divider
should be about 100 times greater than the
current into the FB pin. The typical current into
the FB pin is 0.01µA, and the voltage across R2
is typically 800mV. Based on those two values,
the recommended value for R2 is in the range of
800kΩ in order to set the divider current at 1µA.
From that, the value of resistor R1, depending
on the needed output voltage (VO), can be
calculated using Equation 1.
ꢁꢁꢂ -ꢂ ꢂ
OꢃT ꢆN
ꢉMꢆNꢀ ꢆ
…..(3)
OꢃT
ꢈꢁꢇꢂꢁꢂ
OꢃT
Parameter f is the switching frequency and △V is
the maximum allowed ripple.
The total ripple is larger due to the ESR of the
output capacitor. This additional component of
the ripple can be calculated using Equation 4.
ꢂ
ꢂ
OꢃT
OꢃT
ꢀ ꢀ
-1 ꢀ800kΩꢁ 800mꢂ -1 …..(1)
R1ꢀR2ꢁ
ꢂ
Fꢄ
ꢇꢂESRꢀꢆOꢃTꢁRESR …..(4)
(2) Inductor Selection
The total ripple is the sum of the ripple caused by
the capacitance and the ripple caused by the ESR
of the capacitor. It is possible to improve the
design by enlarging the capacitor or using smaller
capacitors in parallel to reduce the ESR or by using
better capacitors with lower ESR, like ceramics.
Tradeoffs must be made between performance and
costs of the converter circuit.
A boost converter normally requires two main
passive components for storing energy during
the conversion. A boost inductor is required
and a storage capacitor at the output. To select
the boost inductor, it is recommended to keep
the possible peak inductor current below the
current limit threshold of the power switch in the
chosen configuration.
A 10µF input capacitor is recommended to
The second parameter for choosing the inductor
is the desired current ripple in the inductor.
Normally, it is advisable to work with a ripple of
less than 20% of the average inductor current.
A smaller ripple reduces the magnetic hysteresis
losses in the inductor, as well as output voltage
ripple and EMI. But in the same way, regulation
time at load changes rises. In addition, a larger
inductor increases the total system cost. With
those parameters, it is possible to calculate the
value for the inductor by using Equation 2.
improve transient behavior of the regulator.
ceramic or tantalum capacitor with a 100nF in
parallel placed close to the IC is recommended.
A
ꢁꢁꢂ -ꢂ ꢂ
OꢃT ꢆN
ꢅꢀꢂ
…..(2)
ꢆN
ꢇꢆ ꢁꢈꢁꢂ
OꢃT
ꢅ
Parameter ꢈ is the switching ꢈrequency and ΔꢆL is
the ripple current in the inductor, i.e, 20% x IL.
With this calculated value and currents, it is
possible to choose a suitable inductor. Care must
be taken that load transients and losses in the
circuit can lead to higher currents. Also, the
losses in the inductor caused by magnetic
hysteresis losses and copper losses are a major
parameter for total circuit efficiency.
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SD6251
Application Information (Continued)
Layout Considerations
As for all switching power supplies, the layout is an
important step in the design, especially at high peak
currents and high switching frequencies. If the
layout is not carefully done, the regulator could
show stability problems as well as EMI problems.
Therefore, use wide and short traces for the main
current path as indicated in bold in Figure 4. The
input capacitor, output capacitor and the inductor
should be placed as close to the IC as possible.
Use a common ground node as shown in Figure 4
to minimize the effects of ground noise. The
feedback divider should be placed as close to the IC
as possible.
VOUT
VIN
C3 C5
C1
6
1
5
GND
2
4
GND
L1
3
LX
R2
R1
Figure 4. Layout Diagram
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SD6251
Outline Information
SOT-23-6 Package (Unit: mm)
DIMENSION IN MILLIMETER
SYMBOLS
UNIT
MIN
0.90
0.00
0.90
0.30
2.80
MAX
1.45
0.15
1.30
0.50
3.00
A
A1
A2
B
D
E
2.60
1.50
0.90
1.80
0.30
3.00
1.70
1.00
2.00
0.60
E1
e
e1
L
Note：Followed From JEDEC MO-178-C.
Carrier Dimensions
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