SGM61234 [SGMICRO]
28V, 2A, 5V Fixed Output, Non-Synchronous Buck Converter;
| 型号： | SGM61234 |
| 厂家： | 
Shengbang Microelectronics Co, Ltd |
| 描述： | 28V, 2A, 5V Fixed Output, Non-Synchronous Buck Converter |
| 文件： | 总16页 (文件大小：765K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
SGM61234
28V, 2A, 5V Fixed Output,
Non-Synchronous Buck Converter
GENERAL DESCRIPTION
FEATURES
The SGM61234 is a 5V fixed output, non-synchronous
Buck converter with a wide input voltage range from
6.5V to 28V and 2A output current capability. This
device uses peak current mode control with slope
compensation. Pulse skip mode (PSM) feature is included
to reduce losses at the light loads.
● Wide 6.5V to 28V Input Voltage Range
● 5V Fixed Output Voltage
● 2A Maximum Continuous Output Current
● PSM Feature for Improved Light Load Efficiency
● Peak Current Mode Control
● Cycle-by-Cycle Over-Current Protection
● Frequency Foldback Output Short Protection
● 50kHz to 1.1MHz Adjustable Switching Frequency
● 120kHz Default Frequency (No Set Resistor)
● Spread Spectrum to Reduce EMI Peaks
● Switching Node Anti-Ringing for EMI Reduction
● Adjustable Soft-Start
The switching frequency is adjustable from 50kHz to
1.1MHz with an external resistor (RT). Spread spectrum
technique is used for the switching frequency to avoid
high power peaks in EMI. For further reduction of the
EMI, an anti-ringing circuit is added on the switching
node (SW) to damp the oscillations in DCM.
● Available in a Green SOIC-8 (Exposed Pad)
Package
Natural cycle-by-cycle current limit and an included
frequency foldback mechanism protect the device against
over-current and short-circuit faults. Thermal shutdown
protection is also provided to save the device if the
junction temperature reaches +170℃.
APPLICATIONS
Home Appliances
Distributed Power Systems
CPE Equipment
The SGM61234 is available in a Green SOIC-8 (Exposed
Pad) package and can operate in the -40℃ to +125℃
ambient temperature range.
Set-Top Boxes
LCD Displays
Battery Chargers
TYPICAL APPLICATION
CBOOT
VIN
VIN
RT
BOOT
CIN
L
VOUT
SW
RT
SGM61234
COUT
D
COMP
SS
C5
R2
VSENSE
C6
CSS
GND
Figure 1. Typical Application Circuit
SG Micro Corp
JANUARY2022–REV. A
www.sg-micro.com
28V, 2A, 5V Fixed Output,
SGM61234
Non-Synchronous Buck Converter
PACKAGE/ORDERING INFORMATION
SPECIFIED
TEMPERATURE
RANGE
PACKAGE
DESCRIPTION
ORDERING
NUMBER
PACKAGE
MARKING
PACKING
OPTION
MODEL
SGM
61234XPS8
XXXXX
SOIC-8
(Exposed Pad)
SGM61234
SGM61234XPS8G/TR
Tape and Reel, 4000
-40℃ to +125℃
MARKING INFORMATION
NOTE: XXXXX = Date Code, Trace Code and Vendor Code.
X X X X X
Vendor Code
Trace Code
Date Code - Year
Green (RoHS & HSF): SG Micro Corp defines "Green" to mean Pb-Free (RoHS compatible) and free of halogen substances. If
you have additional comments or questions, please contact your SGMICRO representative directly.
OVERSTRESS CAUTION
ABSOLUTE MAXIMUM RATINGS
Stresses beyond those listed in Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to
absolute maximum rating conditions for extended periods
may affect reliability. Functional operation of the device at any
conditions beyond those indicated in the Recommended
Operating Conditions section is not implied.
VIN, SW Voltages.............................................. -0.3V to 30V
SW (Maximum withstand Voltage Transient < 20ns)
.............................................................................. -5V to 30V
BOOT to SW Voltage........................................... -0.3V to 6V
VSENSE Voltage................................................. -0.3V to 6V
SS, RT, COMP Voltages...................................... -0.3V to 3V
Package Thermal Resistance
SOIC-8 (Exposed Pad), θJA ....................................... 46℃/W
Junction Temperature.................................................+150℃
Storage Temperature Range.......................-65℃ to +150℃
Lead Temperature (Soldering, 10s)............................+260℃
ESD Susceptibility
ESD SENSITIVITY CAUTION
This integrated circuit can be damaged if ESD protections are
not considered carefully. SGMICRO recommends that all
integrated circuits be handled with appropriate precautions.
Failureto observe proper handlingand installation procedures
can cause damage. ESD damage can range from subtle
performance degradation tocomplete device failure. Precision
integrated circuits may be more susceptible to damage
because even small parametric changes could cause the
device not to meet the published specifications.
HBM.............................................................................3000V
CDM ............................................................................1000V
RECOMMENDED OPERATING CONDITIONS
Input Voltage Range............................................6.5V to 28V
Operating Ambient Temperature Range......-40℃ to +125℃
DISCLAIMER
SG Micro Corp reserves the right to make any change in
circuit design, or specifications without prior notice.
SG Micro Corp
www.sg-micro.com
JANUARY 2022
2
28V, 2A, 5V Fixed Output,
SGM61234
Non-Synchronous Buck Converter
PIN CONFIGURATION
(TOP VIEW)
BOOT
VIN
RT
1
2
3
4
8
7
6
5
SW
GND
GND
COMP
VSENSE
SS
SOIC-8 (Exposed Pad)
PIN DESCRIPTION
PIN
NAME
I/O
FUNCTION
Bootstrap Pin to Supply the Internal MOSFET Gate Driver. Place a 0.1μF bootstrap
capacitor (CBOOT) between the BOOT and SW pins. If the voltage between BOOT and SW
falls below the BOOT UVLO threshold (3V TYP), the high-side MOSFET will be turned off
to refresh CBOOT voltage.
1
BOOT
O
2
3
VIN
RT
P
I
Power Supply Input with 6.5V to 28V Range and 3.4V (TYP) UVLO Threshold.
Input Pin for Setting the Switching Frequency. Place a programming resistor between this
pin and GND to set the switching frequency from 50kHz to 1.1MHz. If this pin is left floating,
fSW will be set to 120kHz and if it is shorted to GND, the fSW will be around 70kHz.
Soft-Start Time Adjustment Pin. Place an external capacitor (CSS < 27nF) between this pin
and GND to adjust the output ramp-up time (10% to 90%) from 1ms to 10ms based on the
following equation. A 2µA current source charges the external capacitor (VREF = 0.8V).
4
SS
I
I
CSS (nF)× VREF (V)
tSS (ms) =
ISS (μA)
5
6
7
8
VSENSE
Output Voltage Feedback Input Pin. Connect this pin to the output regulation point.
Transconductance Error-Amplifier Output and the Input to the PWM Comparator. A
frequency compensation network is placed between this pin and GND. The COMP pin
voltage (VCOMP) determines the required output current for the PWM regulation.
COMP
GND
SW
O
G
P
Ground Pin.
Converter Switching Node. It connects to the external power diode cathode pin, the
external inductor switching terminal and one terminal of the bootstrap capacitor.
Exposed
Pad
Exposed Pad. It helps cooling the device junction and must be connected to GND pin for
proper operation.
GND
G
NOTE: I = input, O = output, P = power, G = ground.
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28V, 2A, 5V Fixed Output,
SGM61234
Non-Synchronous Buck Converter
ELECTRICAL CHARACTERISTICS
(VIN = 12V, TJ = -40℃ to +125℃, typical values are at TJ = +25℃, unless otherwise noted.)
PARAMETER
SYMBOL
TEST CONDITIONS
MIN
TYP
MAX
UNITS
Input Supply
Input Voltage Range
VIN
6.5
28
V
µA
V
TJ = +25℃
Non-Switching Quiescent Supply Current
IDDQ_NSW VSENSE = 6V, not switching
105
3.4
Rising VIN
VUVLO
VIN Under-Voltage Lockout
Hysteresis
220
mV
Feedback and Error Amplifier
Regulated Output Voltage
Error Amplifier Transconductance (1)
Error Amplifier Source/Sink Current (1)
Inductor Current to Comp Voltage Gain Gm
PSM and Soft-Start
VSENSE
Gm_EA
Igm
VIN = 12V
4.87
5.02
92
±7
9
5.23
V
-2µA < ICOMP < 2µA, VCOMP = 1V
VCOMP = 1V, with 100mV overdrive
VIN = 12V
µA/V
µA
(1)
Gm_SRC
A/V
Switch Current Threshold to Enter Pulse Skip
Mode
ITH
ISS
VIN = 12V
200
2
mA
µA
SS Pin Charge Current Source
Internal Switching Oscillator
Switching Frequency Range
fSW_BK
50
1100
kHz
kHz
Set by external resistor RT, TJ = +25℃
RT = open
RT = short
RT = 85.5kΩ
VIN = 12V
VIN = 12V
VIN = 12V
VIN = 12V
120
70
Programmable Frequency
fSW
340
±6
Frequency Spread Spectrum in % of fSW
Jittering Swing Frequency
fJITTER
fSWING
tMIN_ON
DMAX
%
kHz
ns
fSW/512
200
93
MOSFET Switch Minimum On-Time
Maximum Duty Cycle
%
Current Limit
Peak Inductor Current Limit
MOSFET On-Resistance
ILIMIT
VIN = 12V
4.2
A
On-Resistance of the MOSFET Switch
Thermal Shutdown
RDSON_HS VIN = 12V
125
265
mΩ
Thermal Shutdown Trip Temperature
Thermal Shutdown Hysteresis
TTRIP
THYS
Rising temperature
170
35
℃
℃
NOTE:
1. Guaranteed by design. Not production tested.
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28V, 2A, 5V Fixed Output,
SGM61234
Non-Synchronous Buck Converter
TYPICAL PERFORMANCE CHARACTERISTICS
TA = +25℃, VIN = 12V, fSW = 340kHz, unless otherwise noted.
Output Voltage Ripple
Output Voltage Ripple
AC Coupled
AC Coupled
VOUT
VOUT
VIN
VIN
VSW
VSW
IL
IL
VIN = 12V, VOUT = 5V, IOUT = 0A
VIN = 12V, VOUT = 5V, IOUT = 2A
Time (1ms/div)
Time (2μs/div)
Startup through VIN
Startup through VIN
VOUT
VIN
VOUT
VIN
VSW
VSW
IL
IL
VIN = 12V, VOUT = 5V, IOUT = 0A
VIN = 12V, VOUT = 5V, IOUT = 2A
Time (2ms/div)
Time (2ms/div)
Shutdown through VIN
Shutdown through VIN
VOUT
VOUT
VIN
VSW
IL
VIN
VSW
IL
VIN = 12V, VOUT = 5V, IOUT = 0A
VIN = 12V, VOUT = 5V, IOUT = 2A
Time (200ms/div)
Time (20ms/div)
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28V, 2A, 5V Fixed Output,
SGM61234
Non-Synchronous Buck Converter
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
TA = +25℃, VIN = 12V, fSW = 340kHz, unless otherwise noted.
Short-Circuit Recovery
Short-Circuit Entry
VOUT
VOUT
VIN
VIN
VSW
IL
VSW
IL
VIN = 12V, VOUT = 5V, IOUT = 2A
VIN = 12V, VOUT = 5V, IOUT = 2A
Time (5ms/div)
Time (100μs/div)
Pre-biased Startup
Load Transient Response
AC Coupled
VOUT
VOUT
VIN
VSW
IL
IL
VIN = 12V, VPre-biased = 2.5V
VIN = 12V, VOUT = 5V, IOUT = 200mA to 2A, SR = 2.5A/μs
Time (2ms/div)
Time (200μs/div)
Efficiency vs. Load Current
Load Regulation
100
90
80
70
60
50
40
30
20
10
0
1.0
0.5
0.0
-0.5
-1.0
VIN = 12V
OUT = 5V
VIN = 12V
OUT = 5V
V
V
f
SW = 340kHz
f
SW = 340kHz
0
0.5
1
1.5
2
0.0
0.5
1.0
1.5
2.0
Output Current (A)
Output Current (A)
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28V, 2A, 5V Fixed Output,
SGM61234
Non-Synchronous Buck Converter
FUNCTIONAL BLOCK DIAGRAM
TJ > 170℃
VIN
UVLO & Thermal
Shutdown Logic
Boot Bias
VSENSE
Shutdown
Boot
UVLO
BOOT
gm = 92μA/V
PSM Mode
-
-
0.8V
+
+
R
S
Q
PWM
+
2μA
Control
SW
Oscillator
& Slope
SS
+
Shutdown
+
Discharge
Logic
GND
Frequency
Fold-back
VSENSE
9A/V Current
Sense
COMP
RT
Figure 2. SGM61234 Block Diagram
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28V, 2A, 5V Fixed Output,
SGM61234
Non-Synchronous Buck Converter
DETAILED DESCRIPTION
800
700
600
500
400
300
200
100
0
Overview
The SGM61234 is a fixed 5V output Buck converter with
a wide input voltage range from 6.5V to 28V and 2A
continuous output current capability. It is
a
non-synchronous regulator and requires an external
high frequency power diode to complete the converter.
The integrated high-side switch (HS) is a 125mΩ
N-MOSFET. This device operates at fixed frequency
(with spread spectrum jittering) and uses current mode
control for better line and load transient responses.
These features allow reduced output capacitance and
simple compensation network.
0.0
0.2
0.4
0.6
0.8
1.0
1.2
Switching Frequency (MHz)
An external resistor connected between the RT pin and
GND sets the switching frequency. If the RT is open, the
default switching frequency is 120kHz.
Figure 3. RT and Switching Frequency Relationship
Bootstrap Voltage (BOOT)
Use a 0.1μF boot capacitor (X5R or X7R recommended)
to provide the MOSFET gate drive voltage. If CBOOT
voltage falls below BOOT UVLO threshold (3V), the
MOSFET will be turned off to refresh the boot capacitor
charge.
Switching can start when VIN exceeds 3.4V. The no
switching quiescent current is 105μA.
The diode for recharging the external bootstrap
capacitor (CBOOT) is integrated. The bootstrap circuit
provides the supply voltage for driving the N-MOSFET
that needs to be higher than VIN. If CBOOT voltage falls
below BOOT UVLO threshold (3V), the MOSFET will
be turned off to refresh the boot capacitor charge.
SS Pin and Soft-Start Adjustment
It is recommended to add a soft-start capacitor (CSS)
between SS pin and GND to set the soft-start time
between 1ms to 10ms for a proper startup. The lower of
the SS voltage (VSS) and VREF is applied to the error
amplifier to regulate the output. The internal ISS = 2μA
current charges the CSS and provides a linear voltage
ramp on the SS pin. Use Equation 2 to calculate the
soft-start time (10% to 90% rise). It is recommended
that CSS be less than 27nF. (VREF = 0.8V).
The soft-start time can be set by an external capacitor
(CSS) placed between SS and GND pins. Adjustable
soft-start time provides more flexibility in selection of
the output filter.
Light load losses are reduced when the inductor peak
current falls below 200mA (TYP) and the device enters
in its unique pulse skip mode (PSM).
CSS (nF)× VREF (V)
ISS (μA)
(2)
tSS (ms) =
The peak current control naturally limits the current in
each cycle. However it may not be sufficient during
startup or an over-current event. The frequency
foldback feature reduces the switching frequency to
give enough time to the controller for limiting the
inductor current, especially in short-circuit conditions.
Error Amplifier (EA)
This device uses a transconductance error amplifier
(EA) to compare the sensed output voltage (VSENSE
and the internal reference. The gain of EA amplifier in
normal operation is 92μA/V. The output current is
injected into the frequency compensation network
(between COMP and GND pins) to produce the control
signal (VCOMP) for the PWM comparator.
)
Thermal shutdown is an additional protection for the
device against overheating caused by the faults.
Switching Frequency
The external resistor between the RT and GND sets the
Slope Compensation
Without slope compensation, when the duty cycle is
above 50%, the PWM pulse-widths will be unstable
with subharmonic oscillation. To avoid such oscillations
in the SGM61234, a compensation ramp is added to
the measured switch current before it is compared with
the control signal by the PWM comparator.
switching frequency (Equation 1) as shown in Figure 3.
If RT is shorted, fSW = 70kHz, and if it is open, fSW
=
120kHz. For fSW = 340kHz, set RT = 85.5kΩ.
-1.12
(1)
R kΩ = 25.5×f
MHz
(
)
(
)
T
SW
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28V, 2A, 5V Fixed Output,
SGM61234
Non-Synchronous Buck Converter
DETAILED DESCRIPTION (continued)
to 0V, the frequency will be divided by 1, 2, 4, and 8
depending on the drop as shown in Table 1.
Pulse Skip Mode (PSM)
To improve light load efficiency, the pulse skip mode
(PSM) feature is included in the SGM61234. The
device enters in PSM if VCOMP < 0.65V (TYP) at light
load (the peak inductor current falls below 200mA at VIN
= 12V). In PSM, the COMP voltage is internally
clamped at 0.65V to inhibit MOSFET from switching.
The device can exit PSM if VCOMP rises above the
clamp level. Since the peak inductor current is the
sensed parameter for entering the PSM, the actual load
current (DC) threshold for PSM will depend on the
output filter.
Table 1. Frequency Foldback with VOUT Drop
Switching Frequency
VSENSE Pin Voltage
VSENSE ≥ 3.75V
fSW
fSW/2
fSW/4
fSW/8
3.75V > VSENSE ≥ 2.5V
2.5V > VSENSE ≥ 1.25V
1.25V > VSENSE
Spread Spectrum Switching
Spread spectrum technique is used in the SGM61234
to flatten the generated EMI spectrum and reduce the
large EMI peaks. The switching frequency is
periodically varied between -6% and +6% of the
nominal value at the jittering frequency of fSW/512.
Over-Current and Frequency Foldback
Over-current protection (OCP) is naturally provided by
current mode control. In each cycle, the control voltage
(VCOMP) is compared with the sensed switch current
(that is equivalent to the inductor current during on-time)
and when the peak inductor current reaches to the
control signal level, the switch is turned off. This
technique reduces the duty cycle and hence the output
voltage in the over-current conditions. Normally, if the
output voltage drops, the EA will increase VCOMP to
expand the duty cycle and increase the output current
to bring the output back to regulation. However, the
COMP pin has an internal maximum clamp and cannot
request more than a certain level of current for the
output. In other words, the OCP current limit is
determined by the COMP pin clamp voltage.
Anti-Ringing at the Switching Node
A high-Q LC resonant circuit is formed by the filter
inductor and the parasitic capacitances (such as diode)
at the switching node. In DCM, the parasitic energy
stored in the parasitic elements causes high frequency
oscillations (ringing) on the SW pin after the diode is
turned off. This ringing is not quickly damped due to the
high-Q (low loss) resonance. The high frequency
ringing may radiate EMI at levels that is not acceptable
in some systems. To stop such oscillations, an
anti-ringing circuit that includes an auxiliary MOSFET
between SW and VSENSE pins is integrated in the
device. This switch is turned on when the inductor
current crosses zero and the SW voltage starts to rise
above VSENSE. This will kill the ringing by shorting those
two pins that increases the damping (reduces Q).
The natural OCP in the peak current mode control may
not be able to provide a complete protection when an
output short-circuit occurs, so an extra protection for
short-circuit is needed. During an output short, inductor
current may runaway above over-current limits. Current
runaway can saturate the inductor and the current may
increase until the device is damaged. It occurs since
the inductor current cannot reset (volt-second balance)
during the off-times. During an output-short, only the
small negative diode forward voltage appears across
the inductor in the off-time. Note that the minimum
on-time is limited, and in each cycle, all input voltage
appears on the inductor during the minimum on-time.
The circuit delays and reaction times make these
conditions even worse, and in each cycle the current is
increased to a higher level. In the SGM61234 this
problem is effectively solved by increasing the off-time
by reducing the switching frequency which is called
frequency foldback. As the VSENSE voltage falls from 5V
Over-Voltage Transient Protection (OVTP)
When an overload or an output fault condition is
cleared, large overshoot voltages may appear on the
output. The SGM61234 includes a protection circuit to
reduce such over-voltage transients. If the VSENSE
voltage exceeds 108% of the VREF threshold, the HS
MOSFET is turned off and when it returns below 105%
of the VREF, the HS MOSFET is released for turn-on.
Thermal Shutdown
If the device junction temperature exceeds +170℃, the
thermal shutdown protection trips the device, and the
switching will stop. When the temperature falls below
+135℃, the device will automatically recover with a
power-up and soft-start sequence.
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28V, 2A, 5V Fixed Output,
SGM61234
Non-Synchronous Buck Converter
APPLICATION INFORMATION
Equation 6, Equation 7 and Equation 8 to calculate the
inductor peak-to-peak, RMS and peak currents
respectively.
Input Capacitor Design
It is recommended to use at least a 10μF X5R or better
ceramic capacitor between VIN and GND pins, placed
as close as possible to the device. The converter AC
(RMS) input current that is given in Equation 3, is
provided by this capacitor.
V - VOUT
VOUT
IN
(5)
L =
×
×
IOUT ×K
V ×fSW
IN
V - VOUT
VOUT
IN
(6)
ΔIL =
In this example VIN_MIN = 6.5V, that results in IIN_RMS
1A. The input capacitor RMS rating should be above
1A.
≈
L
V ×fSW
IN
2
ΔIL
IRMS = IO2 UT
+
+
(7)
12
V
IN_MIN - VOUT
(
×
)
VOUT
(3)
I
= IOUT
×
IN_RMS
ΔIL
V
V
IN_MIN
IN_MIN
(8)
=
IPEAK = IOUT
2
The main requirement that determines the input
capacitance is the converter input voltage ripple given
in Equation 4. In this design, the choosing CIN = 10μF
results in 147mV input voltage ripple.
For a design with IOUT_MAX = 2A, VOUT = 5V, fSW
340kHz and VIN = 12V parameters, and by choosing K
= 0.3, the calculated inductance will be 14.3μH. A 15μH
standard inductor can be selected that results in about
29% peak-to-peak current ripple.
IOUT_MAX ×0.25
(4)
∆V =
IN
CIN ×fSW
External Diode
An external power diode between the SW and GND
pins is needed for the SGM61234 to complete the
converter. This diode must tolerate the application’s
absolute maximum ratings. The reverse blocking
voltage must be higher than VIN_MAX and its peak
current must be above the maximum inductor current.
Choose a diode with small forward voltage drop for
higher efficiency. Typically, diodes with higher voltage
and current ratings have higher forward voltages. A
diode with a minimum of 30V reverse voltage is
preferred to allow input voltage transients up to the
rated voltage of the SGM61234.
The input capacitor also provides the high frequency
switching transient currents. So, choosing a low-ESR
and small size capacitor with high self-resonance
frequency and sufficient RMS rating is necessary.
Inductor Selection
Higher operating frequency allows the designer to
choose smaller inductor and capacitor values, however,
the switching and gate losses are increased. On the
other hand, at lower frequencies the current ripple (∆IL)
is higher, which results in higher light load losses.
Use Equation 5 to calculate the required inductance. K
is the ratio of the inductor peak-to-peak ripple (∆IL) to
the DC current (IOUT). The recommended selection
range for K is between 0.2 ~ 0.4. Choosing a higher K
value reduces the selected inductance, but a too high K
factor may result in insufficient slope compensation.
Equation 6 shows that ∆IL is inversely proportional to
fSW × L and is increased at higher input voltages (VIN).
Therefore by accepting larger ∆IL values, smaller
inductances can be chosen but the cost is higher output
voltage ripple and increased core losses.
Output Capacitor Design
The main two factors for designing the output
capacitance are output voltage ripple and the transient
response (peak or valley) to load steps (up or down).
The minimum required capacitance to keep the output
transient overshoot below ∆VOUT in response to a load
step (drop) with the magnitude of ∆IOUT, is given in
Equation 9. In this example (L = 15μH), if ΔIOUT = 1A -
0A = 1A, the required peak voltage deviation (overshoot)
is ΔVOUT = 500mV (10% of the VOUT = 5V), which results
in 3μF minimum calculated output capacitance.
If the peak current exceeds the saturation current, the
current ripple increases abruptly (and hence the output
voltage ripple). So, it is important to make sure that
inductor does not saturate even in the worst conditions.
To select the inductor, the RMS current ratings, DCR
and temperature rise must also be considered. Use
∆IO2 UT ×L
2× VOUT ×∆VOUT
(9)
COUT
>
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28V, 2A, 5V Fixed Output,
SGM61234
Non-Synchronous Buck Converter
APPLICATION INFORMATION (continued)
The other factor is the required maximum output
voltage ripple. This requirement limits both COUT and its
ESR, because they individually contribute to the output
voltage ripple. Capacitor charge and discharge during
switching cycles and the ESR × ∆IL voltage ripple are
two main components of this ripple. Use Equation 10 to
calculate the minimum output capacitance required to
keep the output voltage ripple below ΔVOUT. In this
example, the ∆IL is 0.57A from Equation 6. If the
in series with C4 to slow down switch-on speed of the
HS switch and improve radiated EMI problems. The R4
value depends on the size of the HS switch. For most
applications, it’s approximately 5Ω ~ 10Ω. Too high
values for R4 may cause insufficient C4 charging in high
duty-cycle applications. Slower switch-on will also
increase switch losses and reduce efficiency.
Soft-Start Capacitor Selection
The soft-start capacitor programs the ramp-up time of
the output voltage during power-up. Due to the limited
voltage slew rate required by the load or limited
available input current, a ramp is needed in many
applications to avoid input voltage sag during startup
(UVLO) or to avoid over-current protection that can
occur during output capacitor charging. Soft-start will
solve all these issues by limiting the output voltage slew
rate.
maximum acceptable ripple is 50mV (1% of the VOUT
=
5V), and ESR = 3mΩ, the minimum output capacitance
to satisfy the output ripple requirement is 4.4μF.
1
1
(10)
COUT
>
×
∆VOUT
∆IL
8×fSW
−ESR
Considering both conditions and the required derating
and tolerances, a 10μF/6.3V/X7R capacitor with ESR ≤
3mΩ can be chosen.
Equation 2 (with ISS = 2μA and VREF = 0.8V) can be
used to calculate the soft-start capacitor for a required
soft-start time (tSS). It is recommended that CSS be less
than 27nF.
Bootstrap Capacitor Selection
Use a 0.1μF high-quality ceramic capacitor (X7R or
X5R) with 10V or higher voltage rating for the bootstrap
capacitor (C4). It is recommended to add a resistor R4
Typical Application
C4
R4
VIN
VIN
RT
BOOT
C1
L
VOUT
SW
R1
SGM61234
C2
D
COMP
SS
C5
R2
VSENSE
C6
C3
GND
Figure 4.SGM61234 Typical Application Circuit
SG Micro Corp
www.sg-micro.com
JANUARY 2022
11
28V, 2A, 5V Fixed Output,
SGM61234
Non-Synchronous Buck Converter
APPLICATION INFORMATION (continued)
Layout Considerations
A PCB layout example is provided in Figure 5 and Figure 6. This layout has been proved to bring good results
although other layout designs may also obtain good performance.
• Bypass the VIN pin to GND pin (where it connects to the anode pin of the power diode) with low-ESR ceramic
capacitors and place them as close as possible to the device.
• Connect the diode as close as possible to SW and GND pins.
• Minimize VSENSE trace length. Connect the VSENSE trace from the point where VOUT accuracy is important
and keep it away from the noisy nodes (SW), preferably through another layer that is on the other side of a shield
layer.
• Share the same GND connection point with the input and output capacitors.
• Minimize the length and the area of the connection route from SW pin to the cathode of the diode and the inductor
to reduce the noise coupling from this area.
• Consider sufficient ground plane area on the top side for proper heat dissipation. Connect the large internal or
back-side ground planes to the top-side ground near the device with thermal vias for better heat dissipation.
Figure 5.Top Layer
Figure 6.Bottom Layer
SG Micro Corp
www.sg-micro.com
JANUARY 2022
12
28V, 2A, 5V Fixed Output,
SGM61234
Non-Synchronous Buck Converter
REVISION HISTORY
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Original (JANUARY 2022) to REV.A
Page
Changed from product preview to production data.............................................................................................................................................All
SG Micro Corp
www.sg-micro.com
JANUARY 2022
13
PACKAGE INFORMATION
PACKAGE OUTLINE DIMENSIONS
SOIC-8 (Exposed Pad)
D
e
3.22
E1
E
E2
2.33 5.56
1.91
b
D1
1.27
0.61
RECOMMENDED LAND PATTERN (Unit: mm)
L
A
A1
c
θ
A2
Dimensions
In Millimeters
Symbol
MIN
MOD
MAX
1.700
0.150
1.650
0.510
0.250
5.100
3.420
4.000
6.200
2.530
A
A1
A2
b
0.000
1.250
0.330
0.170
4.700
3.020
3.800
5.800
2.130
-
-
-
c
-
D
-
D1
E
-
-
E1
E2
e
-
-
1.27 BSC
L
0.400
0°
-
-
1.270
8°
θ
NOTES:
1. Body dimensions do not include mode flash or protrusion.
2. This drawing is subject to change without notice.
SG Micro Corp
TX00013.002
www.sg-micro.com
PACKAGE INFORMATION
TAPE AND REEL INFORMATION
REEL DIMENSIONS
TAPE DIMENSIONS
P2
P0
W
Q2
Q4
Q2
Q4
Q2
Q4
Q1
Q3
Q1
Q3
Q1
Q3
B0
Reel Diameter
P1
A0
K0
Reel Width (W1)
DIRECTION OF FEED
NOTE: The picture is only for reference. Please make the object as the standard.
KEY PARAMETER LIST OF TAPE AND REEL
Reel Width
Reel
Diameter
A0
B0
K0
P0
P1
P2
W
Pin1
Package Type
W1
(mm)
(mm) (mm) (mm) (mm) (mm) (mm) (mm) Quadrant
SOIC-8
(Exposed Pad)
13″
12.4
6.40
5.40
2.10
4.0
8.0
2.0
12.0
Q1
SG Micro Corp
TX10000.000
www.sg-micro.com
PACKAGE INFORMATION
CARTON BOX DIMENSIONS
NOTE: The picture is only for reference. Please make the object as the standard.
KEY PARAMETER LIST OF CARTON BOX
Length
(mm)
Width
(mm)
Height
(mm)
Reel Type
Pizza/Carton
13″
386
280
370
5
SG Micro Corp
www.sg-micro.com
TX20000.000
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