E-CMOS EC3276NNMHR 2.2a/32v synchronous rectified step-down converter Datasheet

2.2A/32V Synchronous Rectified
Step-Down Converter
General Description
EC3276
Features
The EC3276 is a monolithic synchronous buck regulator. •
The device integrates two 90mΩ MOSFETs, and provides •
2.2A Output Current
2.2A of continuous load current over a wide input voltage •
•
of 4.75V to 32V. Current mode
•
control provides fast
transient
response
and
•
cycle-by-cycle current limit.
•
An adjustable soft-start prevents inrush current at turn-on,
•
and in shutdown mode the supply current drops to 1µA.
•
This
device, available in an SOP-8(Exposed PAD)
•
package, provides a very compact solution with minimal
Integrated 90mΩ Power MOSFET Switches
external components.
Wide 4.75V to 32V Operating Input Range
Output Adjustable from 0.923V to 30V
Up to 93% Efficiency
Programmable Soft-Start
Stable with Low ESR Ceramic Output Capacitors
Fixed 600KHz Frequency
Cycle-by-Cycle Over Current Protection
Input Under Voltage Lockout
Applications
•
•
Distributed Power Systems
Networking Systems
•
FPGA, DSP, ASIC Power Supplies
•
Green Electronics/ Appliances
•
Notebook Computers
Typical Application Circuit
Fig1. EC3276 with 5V Output, 470µF/16V Electrolytic Output Capacitor
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Page 1 of 12
3G16N-Rev.P001
2.2A/32V Synchronous Rectified
Step-Down Converter
EC3276
Pin Configurations
Figure 2 Pin Configuration of EC3276(Top View)
Pin Description
Pin Number
Pin Name
Description
High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N-Channel
1
BS
MOSFET switch. Connect a 0.01µF or greater capacitor from SW to BS to power the
high side switch.
Power Input. IN supplies the power to the IC, as well as the step-down converter
2
IN
switches. Drive IN with a 4.75V to 32V power source. Bypass IN to GND with a
suitably large capacitor to eliminate noise on the input to the IC. See Input Capacitor.
Power Switching Output. SW is the switching node that supplies power to the output.
3
SW
Connect the output LC filter from SW to the output load. Note that a capacitor is
required from SW to BS to power the high-side switch.
4
GND
5
FB
Ground.
Feedback Input. FB senses the output voltage to regulate that voltage. Drive FB
with a resistive voltage divider from the output voltage. The feedback threshold
is 0.923V. See Setting the Output Voltage.
Compensation Node. COMP is used to compensate the regulation control loop.
6
COMP
Connect a series RC network from COMP to GND to compensate the regulation
control loop. In some cases, an additional capacitor from COMP to GND is
required. See Compensation Components.
Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to
7
EN
turn on the regulator, drive it low to turn it off. Pull up with 100kΩ resistor for
automatic startup.
Soft-Start Control Input. SS controls the soft start period. Connect a capacitor from SS
8
SS
to GND to set the soft-start period. A 0.1µF capacitor sets the soft-start period to 15ms.
To disable the soft-start feature, leave SS unconnected.
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Page 2 of 12
3G16N-Rev.P001
2.2A/32V Synchronous Rectified
Step-Down Converter
EC3276
Ordering Information
Part Number
Package
Marking
EC3276NNMHR
SOP-8L
(Exposed PAD)
EC3276
LLLLL
YYWWT
Marking Information
LLLLL is Lot Number
YYWW is date code
T is internal tracking code
Package Types
Figure 3. Package Types of EC3276
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Page 3 of 12
3G16N-Rev.P001
2.2A/32V Synchronous Rectified
Step-Down Converter
EC3276
Function Block Diagram
Figure 4 Function Block Diagram of EC3276
Absolute Maximum Ratings
Parameter
Symbol
Value
Unit
Supply Voltage
VIN
-0.3 to 32
V
Switch Node Voltage
VSW
30
V
Boost Voltage
VBS
VSW – 0.3V to VSW +6V
V
Output Voltage
VOUT
0.923V to 30
V
–0.3V to +6V
V
TJ
150
ºC
Storage Temperature
TSTG
-65 to 150
ºC
Lead Temperature (Soldering, 10 sec)
TLEAD
260
ºC
2000
V
All Other Pins
Operating Junction Temperature
ESD (HBM)
MSL
Level3
RθJA
RθJC
Thermal Resistance-Junction to Ambient
Thermal Resistance-Junction to Case
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Page 4 of 12
90
45
ºC / W
ºC / W
3G16N-Rev.P001
2.2A/32V Synchronous Rectified
Step-Down Converter
EC3276
Electrical Characteristics
VIN = 12V, Ta = 25℃ unless otherwise specified.
Parameters
Symbol
Shutdown Supply Current
Min.
VEN = 0V
VEN = 2.0V; VFB =
Supply Current
Feedback Voltage
Test Condition
1.0V
VFB
4.75V ≤ VIN ≤ 23V
0.900
Feedback Overvoltage Threshold
Typ.
Max.
Unit
1
3.0
µA
1.3
1.5
mA
0.923
0.946
V
1.1
V
400
V/V
800
µA/V
Error Amplifier Voltage Gain *
AEA
Error Amplifier Trans-conductance
GEA
High-Side Switch On Resistance *
RDS(ON)1
90
mΩ
Low-Side Switch On Resistance *
RDS(ON)2
90
mΩ
High-Side Switch Leakage
∆IC = ±10µA
VEN = 0V, VSW = 0V
Current
Upper Switch Current Limit
Minimum Duty Cycle
Lower Switch Current Limit
From Drain to Source
COMP to Current Sense
Trans-conductance
Oscillation Frequency
Short Circuit Oscillation
Frequency
Maximum Duty Cycle
10
2.4
GCS
Fosc1
3.4
A
1.1
A
4.8
A/V
600
KHz
Fosc2
VFB = 0V
100
KHz
DMAX
VFB = 1.0V
90
%
220
ns
Minimum On Time *
EN Shutdown Threshold Voltage
µA
VEN Rising
1.1
1.5
2.0
V
EN Shutdown Threshold Voltage
Hysteresis
210
EN Lockout Threshold Voltage
2.2
EN Lockout Hysterisis
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2.5
210
Page 5 of 12
mV
2.7
V
mV
3G16N-Rev.P001
2.2A/32V Synchronous Rectified
Step-Down Converter
EC3276
Electrical Characteristics(Cont.)
VIN = 12V, Ta = 25℃ unless otherwise specified.
Parameters
Symbol
Input Under Voltage Lockout
Threshold
Test Condition
VIN Rising
Input Under Voltage Lockout
Min.
3.80
Typ.
4.10
Max.
4.40
Unit
V
210
mV
6
µA
Threshold Hysteresis
Soft-Start Current
VSS = 0V
Soft-Start Period
CSS = 0.1µF
Thermal Shutdown
*
15
ms
160
°C
Typical Performance Characteristics
Figure 5. Steady State Test
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Figure 6. Steady State Test
Page 6 of 12
3G16N-Rev.P001
2.2A/32V Synchronous Rectified
Step-Down Converter
Figure 7. Startup through Enable
EC3276
Figure 8. Startup through Enable
Figure 9. Shutdown through Enable
Figure 10. Shutdown through Enable
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Page 7 of 12
3G16N-Rev.P001
2.2A/32V Synchronous Rectified
Step-Down Converter
EC3276
Figure 12. Short Circuit Test
Figure 11. Load Transient Test
Figure 13. Short Circuit Recovery
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Page 8 of 12
3G16N-Rev.P001
2.2A/32V Synchronous Rectified
Step-Down Converter
EC3276
Function Description
Component Selection
Where VOUT is the output voltage, VIN is the input voltage,
fS is the switching frequency, and ΔIL is the peak-to-peak
Setting the Output Voltage
The output voltage is set using a resistive voltage divider
inductor ripple current.
Choose an inductor that will not saturate under the
from the output voltage to FB pin. The voltage divider
divides the output voltage down to the feedback voltage by
maximum inductor peak current. The peak inductor current
can be calculated by:
the ratio:
Where VFB is the feedback voltage and VOUT is the output
voltage. Thus the output voltage is:
Where ILOAD is the load current.
The choice of which style inductor to use mainly depends
on the price vs. size requirements and any EMI
requirements.
Optional Schottky Diode
R2 can be as high as 100kΩ, but a typical value is 10kΩ.
During the transition between high-side switch and low-side
switch, the body diode of the lowside power MOSFET
Using the typical value for R2, R1 is determined by:
conducts the inductor current. The forward voltage of this
body diode is high. An optional Schottky diode may be
For example, for a 3.3V output voltage, R2 is 10kΩ, and R1
paralleled between the SW pin and GND pin to improve
is 26.1kΩ.
overall efficiency. Table 1 lists example Schottky diodes
and their Manufacturers.
Inductor
The inductor is required to supply constant current to the
Table 1:
Part Number
Voltage/Current
Vendor
B140
40V, 1A
Diodes, Inc.
will result in lower output ripple voltage. However, the larger
SK14
40V, 1A
Diodes, Inc.
value inductor will have a larger physical size, higher series
MBRS140
40V, 1A
International Rectifier
output load while being driven by the switched input voltage.
A larger value inductor will result in less ripple current that
resistance, and/or lower saturation current. A good rule for
Input Capacitor
determining the inductance to use is to allow the
The input current to the step-down converter is
peak-to-peak ripple current in the inductor to be
discontinuous, therefore a capacitor is required to supply
approximately 30% of the maximum switch current limit.
the AC current to the step-down converter while maintaining
Also, make sure that the peak inductor current is below the
the DC input voltage. Use low ESR capacitors for the best
maximum switch current limit. The inductance value can be
performance. Ceramic capacitors are preferred, but
calculated by:
tantalum or low-ESR electrolytic capacitors may also
suffice. Choose X5R or X7R dielectrics when using ceramic
capacitors.
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Page 9 of 12
3G16N-Rev.P001
2.2A/32V Synchronous Rectified
Step-Down Converter
EC3276
Since the input capacitor (C1) absorbs the input switching
current it requires an adequate ripple current rating. The
RMS current in the input capacitor can be estimated by:
In the case of tantalum or electrolytic capacitors, the ESR
dominates the impedance at the switching frequency. For
simplification, the output ripple can be approximated to:
The worst-case condition occurs at VIN = 2VOUT,where
IC1 = ILOAD/2. For simplification, choose the input capacitor
whose RMS current rating greater than half of the maximum
The characteristics of the output capacitor also affect the
load current.
stability of the regulation system. The EC3276 can be
The input capacitor can be electrolytic, tantalum or ceramic.
optimized for a wide range of capacitance and ESR values.
When using electrolytic or tantalum capacitors, a small, high
Compensation Components
quality ceramic capacitor, i.e. 0.1μF, should be placed as
EC3276 employs current mode control for easy
close to the IC as possible. When using ceramic capacitors,
compensation and fast transient response. The system
make sure that they have enough capacitance to provide
stability and transient response are controlled through the
sufficient charge to prevent excessive voltage ripple at
COMP pin. COMP pin is the output of the internal
input. The input voltage ripple for low ESR capacitors can
trans-conductance error amplifier. A series
be estimated by:
capacitor-resistor combination sets a pole-zero combination
to control the characteristics of the control system.
The DC gain of the voltage feedback loop is given by:
Where C1 is the input capacitance value.
Output Capacitor
The output capacitor is required to maintain the DC output
Where AVEA is the error amplifier voltage gain; GCS is the
voltage. Ceramic, tantalum, or low ESR electrolytic
current sense transconductance and RLOAD is the load
capacitors are recommended. Low ESR capacitors are
resistor value.
preferred to keep the output voltage ripple low. The output
The system has two poles of importance. One is due to the
voltage ripple can be estimated by:
compensation capacitor (C3) and the output resistor of the
error amplifier, and the other is due to the output capacitor
and the load resistor. These poles are located at:
Where C2 is the output capacitance value and RESR is the
equivalent series resistance (ESR) value of the output
capacitor.
In the case of ceramic capacitors, the impedance at the
switching frequency is dominated by the capacitance. The
output voltage ripple is mainly caused by the capacitance.
Where GEA is the error amplifier transconductance.
For simplification, the output voltage ripple can be
estimated by:
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Page 10 of 12
3G16N-Rev.P001
2.2A/32V Synchronous Rectified
Step-Down Converter
The system has one zero of importance, due to the
EC3276
Determine the C3 value by the following equation:
compensation capacitor (C3) and the compensation resistor
(R3). This zero is located at:
Where R3 is the compensation resistor.
3. Determine if the second compensation capacitor (C6) is
The system may have another zero of importance, if the
required. It is required if the ESR zero of the output
output capacitor has a large capacitance and/or a high ESR
capacitor is located at less than half of the switching
value. The zero, due to the ESR and capacitance of the
frequency, or the following relationship is valid:
output capacitor, is located at:
If this is the case, then add the second compensation
capacitor (C6) to set the pole fP3 at the location of the ESR
In this case (as shown in Figure 14), a third pole set by the
zero. Determine the C6 value by the equation:
compensation capacitor (C6) and the compensation resistor
(R3) is used to compensate the effect of the ESR zero on
External Bootstrap Diode
the loop gain. This pole is located at:
An external bootstrap diode may enhance the efficiency
of the regulator, the applicable
The goal of compensation design is to shape the converter
conditions of external BST diode are:
transfer function to get a desired loop gain. The system

VOUT=5V or 3.3V; and
crossover frequency where the feedback loop has the unity

Duty cycle is high:
gain is important. Lower crossover frequencies result in
slower line and load transient responses, while higher
crossover frequencies could cause system instability. A
good rule of thumb is to set the crossover frequency below
In these cases, an external BST diode is recommended
one-tenth of the switching frequency.
from the output of the voltage regulator to BST pin, as
To optimize the compensation components, the following
shown in Fig.14
procedure can be used.
1. Choose the compensation resistor (R3) to set the desired
crossover frequency.
Determine the R3 value by the following equation:
Where fC is the desired crossover frequency which is
typically below one tenth of the switching frequency.
Figure14.Add Optional External Bootstrap Diode to Enhance
2. Choose the compensation capacitor (C3) to achieve the
Efficiency
desired phase margin. For applications with typical inductor
The recommended external BST diode is IN4148, and the
values, setting the compensation zero, fZ1, below one-forth
BST cap is 0.1~1μF.
of the crossover frequency provides sufficient phase
margin.
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Page 11 of 12
3G16N-Rev.P001
2.2A/32V Synchronous Rectified
Step-Down Converter
EC3276
Package Information
SOP-8(Exposed PAD) Package Outline Dimensions
E-CMOS Corp. (www.ecmos.com.tw)
Page 12 of 12
3G16N-Rev.P001
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