3A, 18V, 500KHz,
Synchronous Step Down DC/DC Converter
EC3293A
General Description
The EC3293A is a high-frequency, synchronous, rectified, step-down, switch-mode converter with
internal power MOSFETs. It offers a very compact solution to achieve a 3A continuous output current over a wide input supply range, with excellent load and line regulation.
The EC3293A has synchronous-mode operation for higher efficiency over the output current-load range.
Current-mode operation provides fast transient response and eases loop stabilization. Protection features include over-current protection and thermal shutdown.
The EC3293A requires a minimal number of readily available, standard external components and is available in a space-saving TSOT23-6L package.
Features
● 4.7V to 18V input voltage
● Output adjustable from 0.8V to 15V
● Output current up to 3A
● Integrated 110mΩ/58mΩ power MOSFET switches
● Shutdown current 3μA typical
● Efficiency up to 95%
● Fixed frequency 500KHz
● Internal soft start
● Over current protection and Hiccup
● Over temperature protection
● RoHS Compliant and 100% Lead (Pb) Free
Applications
● Distributed power systems
● Networking systems
● FPGA, DSP, ASIC power supplies
● Notebook computers
● Green electronics or appliance
Pin Assignments
Pin Description
TSOT23-6L | Symbol | Description |
1 | GND | Ground. |
2 | SW | Power switching output. |
3 | IN | Power input. |
4 | FB | Feedback input. |
5 | EN | Enable input. |
6 | BOOT | High-side gate drive boost input. |
Application Information
Note: R5 and C7 are optional.
R3=40.2KΩ for T-type
R3=0Ω for voltage division
Ordering Information
Functional Block Diagram
Absolute Maximum Ratings
Supply Voltage VIN ……………………–0.3V to +20V
Switch Node VSW ……………… –0.3V to VIN+0.3V
Boost VBOOT ………………… VSW–0.3V to VSW+6V
All Other Pins ………………………… –0.3V to +6V
Junction Temperature ………………………+150°C
Lead Temperature ………………………… +260°C
Storage Temperature Range ……–65°C to +150°C
CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent
damage to the device. This is a stress only rating and operation of the device at these or any other conditions
above those indicated in the operational sections of this specification is not implied.
Recommended Operating Conditions
Supply Voltage VIN ……...…………...…….…4.75V to 18V
Output Voltage VOUT ……...…………... 0.923V to VIN–3V
Operating Temperature Range ……...…–40°C to +125°C
Package Thermal Characteristics
TSOT23-6L:
Thermal Resistance, θJA ………………………100°C/W
Thermal Resistance, θJC ………………………… 55°C/W
Electrical Characteristics
(TA = +25°C, VIN = +12V, unless otherwise noted.)
PARAMETER | Symbol | TEST CONDITIONS | MIN | TYP | MAX | UNIT |
Supply Voltage | VIN |
| 4.7 |
| 18 | V |
Output Voltage | VOUT |
| 0.8 |
| 15 | V |
Shutdown Supply Current |
| VEN = 0V |
| 3 | 6 | µA |
Supply Current |
| VEN = 2.0V,VFB =1V |
| 0.7 |
| mA |
Feedback Voltage | VFB | 4.75V ≤ VIN ≤ 18V | 0.776 | 0.8 | 0.824 | V |
Feedback Over-voltage Threshold |
|
|
| 0.88 |
| V |
Error Amplifier Voltage Gain * | AEA |
|
| 1000 |
| V/V |
High-Side Switch-On Resistance * | RDS(ON)1 |
|
| 110 |
| mΩ |
Low-side Switch-On Resistance * | RDS(ON)2 |
|
| 58 |
| mΩ |
High-Side Switch Leakage Current |
| VEN = 0V, VSW = 0V, TA = +125°C |
|
| 10 | µA |
Upper Switch Current Limit |
| Minimum Duty Cycle | 3.7 | 4.3 |
| A |
Lower Switch Current Limit |
| From Drain to Source |
| 0 |
| A |
Oscillation Frequency | FOSC1 | | 400 | 500 | 600 | KHz |
Short Circuit Oscillation Frequency | FOSC2 | VFB = 0V | 100 | 125 | 150 | KHz |
Maximum Duty Cycle | DMAX | VFB = 0.5V |
| 90 |
| % |
Minimum On Time * |
|
|
| 120 |
| ns |
EN Falling Threshold Voltage |
| VEN Falling |
| 1.22 |
| V |
EN Rising Threshold Voltage |
| VEN Rising |
| 1.32 |
| V |
Input Under Voltage Lockout Threshold |
| VIN Rising |
| 3.75 |
| V |
Input Under Voltage Lockout Threshold Hysteresis |
|
|
| 200 |
| mV |
Soft-Start Period |
| |
| 1 |
| ms |
Thermal Shutdown * |
|
|
| 150 |
| °C |
* Guaranteed by design, not tested.
Typical Characteristics
VIN = 12V, VO = 3.3V, L1 = 4.7μH, C1 = 10μF, C2 = 22μF x 2, TA = +25°C, unless otherwise noted.
Start UP & Inrush Current 12V→3.3V (Load 1A) Shut Down (Iout 1A→Shut down)
Output Ripple (12V => 3.3V, Load=2A) Output Ripple (12V => 3.3V, Load=1A)
Output Ripple (12V => 3.3V, Load=0A) Dynamic Load (Iload=0.2A_1.2A;Vout=3.3V)
Short Circuit Protection
Efficiency Efficiency
Application Information
Overview
The EC3293A is a synchronous rectified, current-mode, step-down regulator. It regulates input voltages from
4.7V to 18V down to an output voltage as low as 0.8V, and supplies up to 3A of load current.
The EC3293A uses current-mode control to regulate the output voltage. The output voltage is measured at FB through a resistive voltage divider and amplified through the internal trans-conductance error amplifier.
The converter uses internal N-Channel MOSFET switches to step-down the input voltage to the regulated output
voltage. Since the high side MOSFET requires a gate voltage greater than the input voltage, a boost capacitor connected between SW and BOOT is needed to drive the high side gate. The boost capacitor is charged from the internal 5V rail when SW is low.
When the EC3293A FB pin exceeds 10% of the nominal regulation voltage of 0.8V, the over voltage comparator is tripped forcing the high-side switch off.
Pins Description
BOOT: High-Side Gate Drive Boost Input. BOOT supplies the drive for the high-side N-Channel MOSFET switch. Connect a 0.1μF or greater capacitor from SW to BOOT to power the high side switch.
IN: Power Input. IN supplies the power to the IC, as well as the step-down converter switches. Drive IN with a 4.7V to 18V power source. Bypass IN to GND with a suitably large capacitor to eliminate noise on the input to the IC.
SW: Power Switching Output. SW is the switching node that supplies power to the output. Connect the output
LC filter from SW to the output load. Note that a capacitor is required from SW to BOOT to power the high-side switch.
GND: Ground.
FB: 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 0.8V.
EN: Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to turn on the regulator, drive it low to turn it off. Pull up with 100kΩ resistor for automatic startup.
Setting the Output Voltage
The external resistor divider sets output voltage. The feedback resistor R1 also sets the feedback loop bandwidth through the internal compensation capacitor.
(see the typical application circuit). Choose the R1 around 10KΩ,and R2 by R2=R1/(Vout/0.8V-1)
Use T-type network for when Vout is low.
Figure 1：T-type network
Table 1 lists the recommended T-type resistors value for common output voltages.
VOUT (V) | R1 (KΩ) | R2 (KΩ) | Rt (KΩ) | LOUT (μH) | COUT (μF) |
1.05 | 10 | 32.4 | 150 | 2.2 | 44 |
1.2 | 20.5 | 41.2 | 120 | 2.2 | 44 |
1.8 | 40.2 | 32.4 | 75 | 3.3 | 44 |
2.5 | 40.2 | 19.1 | 59 | 4.7 | 44 |
3.3 | 40.2 | 13 | 40.2 | 6.8 | 44 |
5 | 40.2 | 7.68 | 24.9 | 6.8 | 44 |
Table 1: Resistor selection for common output voltages.
Inductor
The inductor is required to supply constant current to the output load while being driven by the
Switched input voltage. A larger value inductor will result in less ripple current that will result in lower
output ripple voltage. However, the larger value inductor will have a larger physical size, higher series
resistance, and/or lower saturation current. A good rule for determining the inductance to use is to allow the
peak-to-peak ripple current in the inductor to be approximately 30% of the maximum switch current limit. Also,
make sure that the peak inductor current is below the maximum switch current limit.
The inductance value can be calculated by:
L = [ VOUT / (fS × ΔIL) ] × (1 − VOUT/VIN)
Where VOUT is the output voltage, VIN is the input voltage, fS is the switching frequency, and ΔIL is the peak-to-peak inductor ripple current. Choose an inductor that will not saturate under the maximum inductor peak current. The peak inductor current can be calculated by:
ILP = ILOAD + [ VOUT / (2 × fS × L) ] × (1 − VOUT/VIN)
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
During the transition between high-side switch and low-side switch, the body diode of the low-side power MOSFET conducts the inductor current. The forward voltage of this body diode is high. An optional Schottky diode may be paralleled between the SW pin and GND pin to improve overall efficiency. Table 2 lists example Schottky diodes and their Manufacturers.
Part Number | Voltage and Current Rating | Vendor |
B130 | 30V, 1A | Diodes Inc. |
SK13 | 30V, 1A | Diodes Inc. |
MBRS130 | 30V, 1A | International Rectifier |
Table 2: Diode selection guide.
Input Capacitor
The input current to the step-down converter is discontinuous, therefore a capacitor is required to
supply the AC current to the step-down converter while maintaining the DC input voltage. Use low ESR
capacitors for the best performance. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also suffice. Choose X5R or X7R dielectrics when using ceramic capacitors.
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:
IC1 = ILOAD × [ (VOUT/VIN) × (1 − VOUT/VIN) ]1/2
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 load current.
The input capacitor can be electrolytic, tantalum or ceramic. When using electrolytic or tantalum capacitors, a small, high quality ceramic capacitor, i.e. 0.1μF, should be placed as close to the IC as possible. When using ceramic capacitors, make sure that they have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at input. The input voltage ripple for low ESR capacitors can be estimated by:
ΔVIN = [ ILOAD/(C1 × fS) ] × (VOUT/VIN) × (1 − VOUT/VIN)
Where C1 is the input capacitance value.
Output Capacitor
The output capacitor is required to maintain the DC output voltage. Ceramic, tantalum, or low ESR
electrolytic capacitors are recommended. Low ESR capacitors are preferred to keep the output voltage ripple low. The output voltage ripple can be estimated
by:
ΔVOUT = [ VOUT/(fS × L) ] × (1 − VOUT/VIN)× [ RESR + 1 / (8 × fS × C2) ]
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. For simplification, the output voltage ripple can be estimated by:
ΔVOUT = [ VOUT/(8xfS2 xLxC2)] × (1 − VOUT/VIN)
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:
ΔVOUT = [ VOUT/(fS × L) ] × (1 − VOUT/VIN) × RESR
The characteristics of the output capacitor also affect the stability of the regulation system. The EC3293A can be optimized for a wide range of capacitance and ESR values.
External Bootstrap Diode
An external bootstrap diode may enhance the efficiency of the regulator, the applicable conditions of external
BOOT diode are:
● VOUT = 5V or 3.3V; and
● Duty cycle is high: D = VOUT/VIN > 65%
Figure 2: Add optional external bootstrap diode to enhance efficiency.
In these cases, an external BOOT diode is recommended from the output of the voltage regulator to BOOT pin, as shown in Figure 2.
The recommended external BOOT diode is IN4148, and the BOOT capacitor is 0.1 ~ 1μF.
When VIN ≤ 6V, for the purpose of promote the Efficiency ,it can add an external Schottky diode
between IN and BOOT pins, as shown in Figure 3.
Figure 3: Add a Schottky diode to promote efficiency when VIN ≤ 6V.
PCB Layout Guide
PCB layout is very important to achieve stable operation.
Please follow the guidelines below.
1) Keep the path of switching current short and minimize the loop area formed by Input capacitor,
high-side MOSFET and low-side MOSFET.
2) Bypass ceramic capacitors are suggested to be put close to the VIN Pin.
3) Ensure all feedback connections are short and direct.
Place the feedback resistors and compensation components as close to the chip as possible.
4) Rout SW away from sensitive analog areas such as FB.
5) Connect IN, SW, and especially GND respectively to a
large copper area to cool the chip to improve thermal performance and long-term reliability.
BOM of EC3293A
Please refer to the Typical Application Circuit.
Item | Reference | Part |
1 | C1 | 10μF |
2 | C5 | 100nF |
3 | C7 | 0.1μF |
4 | R4 | 100K |
Table 3: BOM selection table I.
Package Information
TSOT23-6L
Symbol | Dimensions in mm | Dimensions in Inch | ||
Min | Max | Min | Max | |
A | 0.700 | 0.900 | 0.028 | 0.035 |
A1 | 0.000 | 0.100 | 0.000 | 0.004 |
B | 1.600 | 1.700 | 0.063 | 0.067 |
b | 0.350 | 0.500 | 0.014 | 0.020 |
C | 2.650 | 2.950 | 0.104 | 0.116 |
D | 2.820 | 3.020 | 0.111 | 0.119 |
e | 0.950 BSC | 0.037 BSC | ||
H | 0.080 | 0.200 | 0.003 | 0.008 |
L | 0.300 | 0.600 | 0.012 | 0.024 |
