elm613da

ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter
■General description
ELM613DA is 550KHz fixed frequency PWM synchronous step-down regulator. ELM613DA is operated from
4.75V to 20V, the generated output is adjustable from 0.923V to 18V, and the output current can be up to 2A.
The integrated two MOSFET switches is with turn on resistance of 0.085Ω. Current mode control provides fast
transient response and cycle-by-cycle over current protection. The shutdown current is 1μA typical. Adjustable
soft start prevents inrush current at turn on. ELM613DA is with thermal shutdown.
■Features
■Application
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Programmable soft start
Short circuit protection
Thermal shutdown protection
Input voltage
: 4.75V to 20V
Output voltage
: 0.923V to 18V
Output current
: 2A
High efficiency
: Max.93%
Power MOSFET switches
: 85mΩ
Shutdown current
: Typ.1µA
Fixed frequency
: Typ.550kHz
Package
: SOP-8
Distributed power system
Network system
FPGA, DSP, ASIC power supply
Notebook computer
Green electronics and appliance
■Maximum absolute ratings
Parameter
VIN power supply voltage
Apply voltage to SW
Apply voltage to BS
Apply voltage to FB
Apply voltage to COMP
Apply voltage to EN
Apply voltage to SS
Power dissipation
Operating temperature range
Storage temperature range
Symbol
Vin
Vsw
Vbs
Vfb
Vcomp
Ven
Vss
Pd
Top
Tstg
Limit
-0.3 to +21
-0.3 to Vin+0.3
Vsw-0.3 to Vsw+6
-0.3 to +6
-0.3 to +6
-0.3 to +6
-0.3 to +6
630
-40 to +85
-65 to +150
Caution:Permanent damage to the device may occur when ratings above maximum absolute ones are used.
Unit
V
V
V
V
V
V
V
mW
°C
°C
■Selection guide
ELM613DA-N
Symbol
a
b
c
Package
Product version
Taping direction
D: SOP-8
A
N: Refer to PKG file
ELM613DA - N
↑↑ ↑
ab c
* Taping direction is one way.
11 - 1
Rev.1.3
ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter
■Pin configuration
SOP-8(TOP VIEW)
1
8
2
7
3
6
4
5
Pin No.
1
2
3
4
5
6
7
8
Pin name
BS
VIN
SW
GND
FB
COMP
EN
SS
Pin description
High-side gate drive boost input
Power input
Power switching output
Ground
Feedback input
Compensation node
Enable input
Soft start control input
■Standard circuit
Input
R4=100k
Cin=
10µF/25V
Ceramic
7
8
2
1
VIN
EN
BS
ELM613DA
SW
FB
COMP
SS
GND
4
C2=
0.1µF
C3=10nF
Output=
3.3V/2A
R1=12.1kΩ
5
1%
6
C1=3.3nF
C4
Option
L=10µH
3
Cout=
22µF/6.3V
Ceramic×2
R2=4.7kΩ
1%
R3=15kΩ
Note: EN pin is clamped to 5.6V. If EN pin needs to be pulled-up, EN input current has to
be lower than 200μA with R4 (about 100kΩ).
■Block diagram
1.1V
FB
5
0.3V
SS
OVP
+
-
Oscillator
170kHz &
550kHz
+
-
8
0.923V
+
+
Error
amplifier
Current sense
amplifier +
RAMP
CLK
+
Current
comparator
BS
R Q
3
SW
4
GND
M2
85mΩ
EN
6
1.2V
EN
1
M1
85mΩ
OVP
COMP
VIN
-
S Q
6µA
2
5V
7
1.5V
+
IN<4.10V
IN
Internal
regulators
Shutdown
comparator
11 - 2
5V
Rev.1.3
ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter
■Electrical characteristics
Parameter
Supply voltage
Output voltage
Output current
Shutdown current
Supply current
Feedback voltage
Feedback over-voltage threshold
Error amplifier voltage gain
Error amplifier transconductance
High-side switch-on resistance
Low-side switch-on resistance
High-side switch leakage current
Upper switch current limit
Lower switch current limit
COMP to current sense transconductance
Oscillation frequency
Short circuit oscillation frequency
Maximum duty cycle
Minimum on time
EN shutdown threshold voltage
EN shutdown threshold
voltage hysteresis
EN lockout threshold voltage
EN lockout hysteresis
Input under voltage lockout threshold
Input under voltage lockout threshold
hysteresis
Soft-start current
Soft-start period
Thermal shutdown
Symbol
Vin
Vout
Iout
Is
Iss
Vfb
Vfbo-th
Aea
Gea
Rds(on)1
Rds(on)2
Ileak
Ilim_usw
Ilim_lsw
Gcs
Fosc1
Fosc2
Dmax
To
Vens_th
Vin=+12V, Top=+25°C, unless otherwise noted.
Test condition
Min.
Typ.
Max. Unit
4.75
20.00
V
0.923
18.000 V
2.0
A
Ven=0V
1.0
3.0
µA
Ven=2.0V, Vfb=1.0V
1.3
1.5
mA
4.75V ≤ Vin ≤ 20V
0.900 0.923 0.946
V
1.1
V
400
V/V
∆Ic = ±10µA
800
µA/V
85
mΩ
85
mΩ
Ven = 0V, Vsw = 0V
10
µA
Minimum duty cycle
2.4
4.0
A
From drain to source
1.1
A
3.5
A/V
500
550
600
kHz
Vfb = 0V
120
170
220
kHz
Vfb = 0.78mV
90
%
140
ns
Ven falling
1.39
V
Vens_hys
210
mV
Venl_th
Venl_hys
Vth
Vin rising
1.64
210
4.10
V
mV
V
Vth_hys
210
mV
6
15
160
µA
ms
°C
Isoft
Psoft
Tsd
Vss = 0V
Vss = 0.1µF
11 - 3
Rev.1.3
ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter
■Application notes
ELM613DA is synchronous rectified, current-mode, step-down regulator. It regulates input voltages from 4.75V
to 20V down to an output voltage as low as 0.923V, and supplies up to 2A of load current. ELM613DA 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 transconductance error amplifier. The voltage at the COMP
pin is compared to the switch current measured internally to control the output voltage. 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 BS is needed to drive the high side gate. The boost capacitor is charged from the internal 5V rail when
SW is low. When ELM613DA FB pin exceeds 20% of the nominal regulation voltage of 0.923V, the over
voltage comparator is tripped and the COMP pin and the SS pin are discharged to GND, forcing the high-side
switch off.
1. Pin description
BS: High side gate drive boost input
BS supplies the drive for the high-side N-Channel MOSFET switch. Connect a 0.01μF or greater capacitor
from SW to BS to power the high side switch.
VIN: Power input
VIN supplies the power to the IC, as well as the step-down converter switches. Drive VIN with a 4.75V to 20V
power source. Bypass VIN to GND with a suitably large capacitor to eliminate noise on the input to the IC.
SW: Power switch 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 BS to power the high-side switch.
GND: Ground
Connect to PCB wiring which is lower than high frequency impedance.
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 0.923V.
COMP: Compensation node
COMP is used to compensate the regulation control loop. 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.
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. If EN pin needs to be pulled-up, EN input current has to be lower than 200μA with R4 (about
100kΩ).
SS: Soft-start control input
SS controls the soft start period. Connect a capacitor from 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.
2. Setting output voltage
The output voltage is set using a resistive voltage divider from the output voltage to FB pin. The voltage divider divides the output voltage down to the feedback voltage by the ratio:
Vfb = Vout × R2 / (R1 + R2)
11 - 4
Rev.1.3
ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter
Where Vfb is the feedback voltage and Vout is the output voltage. Thus the output voltage is:
Vout = 0.923 × (R1 + R2) / R2
R2 can be as high as 100kΩ, but a typical value is 10kΩ. Using the typical value for R2, R1 is determined by:
R1 = 10.83 × (Vout − 0.923) (kΩ)
3. 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-topeak 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.
4. 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 1 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 1: Diode selection guide.
5. 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 (Cin) absorbs
the input switching current it requires an adequate ripple current rating. The RMS current in the input capacitor
can be estimated by:
Icin = Iload × [ (Vout/Vin) × (1 − Vout/Vin) ]1/2
The worst-case condition occurs at Vin = 2Vout, where Icin = Iload/2. For simplification, choose the input capacitor whose RMS current rating greater than half of the maximum load current.
11 - 5
Rev.1.3
ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter
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/(Cin × fs) ] × (Vout/Vin) × (1 − Vout/Vin)
Where Cin is the input capacitance value.
6. 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 × Cout) ]
Where Cout 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/(8 × fs2 × L × Cout) ] × (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. ELM613DA can be
optimized for a wide range of capacitance and ESR values.
7. Compensation components
ELM613DA employs current mode control for easy compensation and fast transient response. The system stability and transient response are controlled through the COMP pin. COMP pin is the output of the internal transconductance error amplifier. A series capacitor and 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:
Avdc = Rload × Gcs × Aea × Vfb/Vout
Where Aea is the error amplifier voltage gain; Gcs is the current sense transconductance and Rload is the load
resistor value.
The system has two poles of importance. One is due to the compensation capacitor (C1) 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:
fp1 = Gea / (2π × C1 × Aea), fp2 = 1 / (2π × Cout × Rload)
Where Gea is the error amplifier transconductance.
The system has one zero of importance, due to the compensation capacitor (C1) and the compensation resistor
(R3). This zero is located at:
fz1 = 1 / (2π × C1 × R3)
The system may have another zero of importance, if the output capacitor has a large capacitance and/or a high
ESR value. The zero, due to the ESR and capacitance of the output capacitor, is located at:
fesr = 1 / (2π × Cout × Resr)
11 - 6
Rev.1.3
ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter
In this case, a third pole set by the compensation capacitor (C4) and the compensation resistor (R3) is used to
compensate the effect of the ESR zero on the loop gain. This pole is located at:
fp3 = 1 / (2π × C4 × R3)
The goal of compensation design is to shape the converter transfer function to get a desired loop gain. The system crossover frequency where the feedback loop has the unity 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 one-tenth of the switching frequency.
To optimize the compensation components, the following procedure can be used.
1) Choose the compensation resistor (R3) to set the desired crossover frequency.
Determine the R3 value by the following equation:
R3 = [ (2π × Cout × fc) / (Gea × Gcs) ] × (Vout/Vfb) < [ (2π × Cout × 0.1 × fs) / (Gea × Gcs) ] × (Vout/Vfb)
Where fC is the desired crossover frequency which is typically below one tenth of the switching frequency.
2) Choose the compensation capacitor (C1) to achieve the desired phase margin. For applications with typical
inductor values, setting the compensation zero, fz1, below one-forth of the crossover frequency provides sufficient phase margin. Determine the C1 value by the following equation:
C1 > 4 / (2π × R3 × fc)
Where R3 is the compensation resistor.
3) Determine if the second compensation capacitor (C4) is required. It is required if the ESR zero of the output
capacitor is located at less than half of the switching frequency, or the following relationship is valid:
1 / (2π × Cout × Resr) < fs/2
If this is the case, then add the second compensation capacitor (C4) to set the pole fP3 at the location of the
ESR zero. Determine the C4 value by the equation:
C4 = (Cout × Resr) / R3
8. External bootstrap diode
An external bootstrap diode may enhance the efficiency of the regulator, the applicable conditions of external
BS diode are:
Vout = 5V or 3.3V, and duty cycle is high: D = Vout/Vin > 65%
In these cases, an external BS diode is recommended from the output of the voltage regulator to BS pin, as
shown in Figure 1.
External BS
diode IN4148
BS
ELM613DA
SW
◄
Cbs
0.1 to 1µF
L
5V or 3.3V
Cout
Figure 1. Add optional external bootstrap diode to enhance efficiency.
The recommended external BS diode is IN4148, and the BS capacitor is 0.1 to 1μF.
11 - 7
Rev.1.3
ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter
when Vin≤ 6V, for the purpose of promote the efficiency, it can add an external Schottky diode between IN and
BS pins, as shown in Figure 2.
Schottky
(B0520LW) ▲
BS
VIN
5V to 6V
ELM613DA
Vout
SW
GND
Figure 2: Add a Schottky diode to promote efficiency when Vin ≤ 6V.
9. 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.
Table2 : BOM of ELM613DA
Vout=5.0V
L
10µH
R1
15K
R2
6.8K
R3
16K
Cout
22µF
C1
3.3nF
15K
Vout=3.3V
10µH
12K
100
4.7K
15K
22µF
3.3nF
Vout=2.5V
Vout=1.8V
Vout=1.2V
10µH
10µH
9.1K
6.8K
470
1K
5.6K
8.2K
13K
6.8K
22µF
22µF
3.3nF
3.3nF
4.7µH
1.5K
1.5K
10K
5.1K
22µF
3.3nF
Vout=1.0V
3.3µH
1K
1K
24K
4.7K
22µF
3.3nF
■Marking
SOP-8
LV1482SN
abcdef
ghijk
Mark
LV1482SN
Content
Product ID
a to k
Assembly lot No.:
0 to 9 & A to Z repeated
11 - 8
Rev.1.3
ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter
■Typical characteristics
• Vout=1.8V : Cin=10µF, Cout=22µF, L=10µH, R1=9.5k, R2=10k, R3=15k
C1=3.3nF, C2=0.1µF, C3=10nF, Top=25°C
• V=1.8V
EFFICIENCY-Iout
100
2
80
EFFICIENCY (%)
Vout (V)
Vout-Vin
2.5
1.5
Iout=10mA
1
Iout=1000mA
Iout=100mA
0.5
0
5
10
15
20
Vin (V)
60
Vin=12V
40
20
0
0.1
25
Vin=5V
1
10
100
Iout (mA)
Vout-Iout
1000
10000
Vfb-Top
2.5
Vin=12V, Iout=100mA)
0.95
2.4
2.3
0.94
2.1
Vfb (V)
Vout (V)
2.2
Vin=12V
2.0
1.9
0.93
0.92
1.8
1.7
1.6
1
10
100
Iout (mA)
1000
0.9
-40
10000
Start Response
0
20
Top (°C)
40
60
80
Load Transient Response
Vin=12V, Iout=1mA~1A
Vout (V)
Vin=12V, No load
1
2.5
2.0
1.5
0
1.0
2
1
0
0.5
Ven (V)
Vout (V)
2
-20
0
Time (4ms/div)
Iout (A)
1.5
0.1
0.91
Vin=5V
Time (100µs/div)
11 - 9
Rev.1.3
ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter
• Vout=3.3V : Cin=10µF, Cout=22µF, L=10µH, R1=12k, R2=4.7k, R3=15k
C1=3.3nF, C2=0.1µF, C3=10nF, Top=25°C
• V=3.3V
EFFICIENCY-Iout
Vout-Vin
100
4.0
3.5
2.5
Iout=1000mA
EFFICIENCY (%)
Vout (V)
3.0
Iout=10mA
2.0
1.5
1.0
Iout=100mA
5
1
60
Vin=12V
40
20
0.5
0
Vin=5V
80
15
2
Vin (V)
0
0.1
25
1
10
100
Iout (mA)
1000
10000
Vfb-Top
Vout-Iout
Vin=12V, Iout=100mA
0.95
3.50
3.45
3.40
3.35
3.30
Vfb (V)
Vout (V)
0.94
Vin=12V
3.25
3.20
3.15
Vin=5V
0.93
0.92
0.91
3.10
3.05
3.00
0.1
1
10
100
Iout (mA)
1000
0.9
-40
10000
Start Response
0
20
Top (°C)
40
60
80
Load Transient Response
Vin=12V, Iout=1mA~1A
Vout (V)
Vin=12V, No load
3
2
3.5
3.0
0
1.0
2
1
0
0.5
0
Time (4ms/div)
Iout (A)
1
Ven (V)
Vout (V)
4
-20
Time (100µs/div)
11 - 10
Rev.1.3
ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter
• Vout=5.0V : Cin=10µF, Cout=22µF, L=10µH, R1=30K R2=6.8K R3=15K
C1=3.3nF, C2=0.1µF, C3=10nF, Top=25°C
• V=5.0V
EFFICIENCY-Iout
100
80
EFFICIENCY (%)
Vout (V)
Vout-Vin
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
Iout=10mA
Iout=100mA
Iout=1000mA
5
0
10
15
Vin (V)
60
40
20
0
0.1
20
Vin=12V
1
10
100
Iout (mA)
Vout-Iout
1000
10000
Vfb-Top
5.5
Vin=12V, Iout=100mA
0.95
5.4
5.3
0.94
Vin=12V
5.1
Vfb (V)
Vout (V)
5.2
5.0
4.9
0.93
0.92
4.8
4.7
0.91
4.6
1
10
100
Iout (mA)
1000
0.90
-40
10000
Start Response
0
20
40
Top (°C)
60
80
Load Transient Response
Vin=12V, No load
Vout (V)
6.0
6
4
2
Vin=12V, Iout=1mA~1A
5.5
5.0
4.5
0
1.0
2
1
0
0.5
Ven (V)
Vout (V)
-20
0
Time (4ms/div)
Iout (A)
4.5
0.1
Time (100µs/div)
11 - 11
Rev.1.3