elm605da

ELM605DA 2A
synchronous step-down DC/DC converter
■General description
ELM605DA is low-input voltage and high-output current synchronous-buck PWM converter and integrates
with all required active components. Its' operating input voltage ranges from 2.5V to 6V and output voltage
ranges from Vin down to 0.8V. ELM605DA operates at a fixed switching frequency of 1.0MHz. In addition, it
provides internal soft-start to reduce inrush-current, current-limit and thermal shutdown, preventing IC from
being damaged and improving design reliability. Open-drain power good monitors the output voltage.
■Features
■Application
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Current mode operation
Power good function monitoring output voltage
Internal soft start
Thermal shutdown
Current-limit and short-circuit protection
Input voltage range
: 2.5V to 6.0V
Output current
: 2A
Low quiescent current (active mode) : 200μA
Output voltage range (adj.)
: 0.8V to Vin
Shutdown current
: 7μA
High efficiency
: 95%
Constant frequency operation
: 1.0MHz
Package
: SOP-8
ASIC/DSP/μP/FPGA core and I/O voltages
Networking and telecommunications
TV
Set top boxes
Cellular base stations
■Maximum absolute ratings
Parameter
VIN power supply voltage
Apply voltage to SW
Apply voltage to EN
Apply voltage to FB
Power dissipation
Operating temperature range
Storage temperature range
Symbol
Vin
Vsw
Ven
Vfb
Pd
Top
Tstg
Limit
-0.3 to +6.5
-0.3 to Vin+0.3
-0.3 to Vin
-0.3 to Vin
300
-40 to +150
-65 to +150
Caution:Permanent damage to the device may occur when ratings above maximum absolute ones are used.
Unit
V
V
V
V
mW
°C
°C
■Selection guide
ELM605DA-S
Symbol
a
b
c
Package
Product version
Taping direction
D: SOP-8
A
S: Refer to PKG file
ELM605DA - S
↑↑ ↑
ab c
* Taping direction is one way.
13 - 1
Rev.1.2
ELM605DA 2A 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
VCC
PG
GND
FB
EN
PGND
SW
VIN
Pin description
Supply voltage input
Power good
Ground
Feedback/Output voltage
Enable input
Power switch ground
Power switch output
Power switch supply voltage input
■Standard circuit
ELM605DA
Vin
8
10µF 100k
10
1
VIN
PG
100k
2.2µH
VCC
SW
0.1µF
5
PG
2
EN
PGND
FB
GND
6
Vout
7
22µF
4
R1
Cup*
(option)
R2
3
Vout=0.8V*(1+R1/R2)
■Block diagram
VCC
VIN
500k ohm
+
Current
sence
amplifier
Reference
0.8V
FB
+
-
+
Error
amplifier
Oscillator
0.72V
PWM
comparator
Clock
+
-
PWM
logic
SW
GND
13 - 2
M2
LG
DCC
PG
M1
UG
Zero-current
comparator
+
-
Slop comp
+
EN
PGND
Rev.1.2
ELM605DA 2A synchronous step-down DC/DC converter
■DC electrical characteristics
Vin=3.3V, Top=25°C, unless otherwise noted
Parameter
Symbol
Test condition
Min.
Typ.
Max. Unit
Supply voltage
Vin
2.5
6.0
V
Quiescent current
Iout=0mA, no switching
220
µA
Iq
Shutdown current
EN=GND
7
µA
Is
Adjustable output voltage range
0.8
Vin
V
Vout
Regulated feedback voltage
Top=+25°C
0.784 0.800 0.816 V
Vfb
Output voltage line regulation ΔVline-reg Vin=2.5V to 6.0V, Iout=0A to 2A
-2
2
%
Output voltage load regulation ΔVload-reg Vout=0.8V to 3.3V, Iout=0A to 2A -2
2
%
Vin rising
2.3
VIN under voltage
V
UVLO
lockout threshold
Vin falling
2.1
Feedback current
-30
30
nA
Ivfb
SW leakage current
Ileak(sw) Ven=0V, Vin=6V, Vsw=0V or 6V
-1
1
µA
PMOSFET on resistance
Vin=Vgs=5V,
Iout=100mA
130
mΩ
RdsonP
NMOSFET on resistance
100
mΩ
RdsonN Vin=Vgs=5V, Iout=100mA
PMOSFET current limit
IclP
3.2
A
Oscillator frequency
Fosc
1
MHz
Thermal shutdown threshold
Ts
150
°C
Soft-start time
Tss
1
mS
Power good threshold
Vpg
0.9*Vout
Power good current
Ipg
Vpg=0.3V
3
mA
EN high Level input voltage
Ven
-40°C≤Top≤+85°C
1.3
V
EN low level input voltage
Ven
0.3
V
■Marking
SOP-8
ELM
605DA
abc
Mark
ELM605DA
Content
Product name
a, b, c
Assembly lot No.:
000 to 999 repeated
13 - 3
Rev.1.2
ELM605DA 2A synchronous step-down DC/DC converter
■Functional description
ELM605DA is high-efficiency DC-to-DC step-down converter and capable of delivering up to 2A of output current. It
operates in pulse-width modulation at 1MHz fixed frequency with 2.5V to 6V input voltage and provides output voltage ranging from 0.8V to VIN. The high switching frequency allows for the use of smaller external components, and
internal synchronous rectifiers improve efficiency and eliminate external Schottky diode. Using the on-resistance of the
internal high-side MOSFET to sense switching currents eliminates current-sense resistors, further enhancing the efficiency and reducing the cost.
1. Current mode PWM control
Current mode PWM control provides stable switching and cycle-by-cycle current limit for superior load and line
response and protection of the internal main switch and synchronous rectifier. ELM605DA switches at 1MHz fixed
frequency and regulates the output voltage. The main switch is turned on for a certain period to ramp the inductor current at each rising edge of the internal oscillator under normal operation whereas switched off when the peak inductor
current is above the error voltage. When the main switch is off, the synchronous rectifier will be turned on immediately
and stay on until the next cycle starts.
2. Dropout operation
ELM605DA allows the main switch to remain on for more than one switching cycle and increases the duty
cycle while the input voltage decreases close to the output voltage. When the duty cycle reaches 100%, the main
switch still keeps on in order to deliver the current to the output up to the P MOSFET current limit. The output
voltage then is the input voltage minus the voltage drop across the main switch and the inductor.
3. Short Circuit Protection
ELM605DA features short circuit protection. When the output is shorted to ground, the oscillator’s frequency
is reduced to prevent the inductor’s current from increasing beyond the P-Channel MOSFET current limit. The
P-Channel MOSFET current is reduced to lower the short circuit current. The frequency and current limit will
return to the normal values once the short circuit condition is removed and the feedback voltage restores above
0.3V.
4. Internal soft-start
ELM605DA supports an internal soft-start function, which reduces inrush current and overshoot of the output
voltage. Soft-start is achieved by ramping up the reference voltage (Vref), which is applied to the input of the
error amplifier. The typical soft-start time is about 1 ms, and it depends on the component’s values on AP circuit.
5. Thermal Shutdown
As soon as the junction temperature exceeds the typical 150°C, the device goes into thermal shutdown. In this
mode, the P-Channel switch and N-Channel MOSFETs are latched off.
6. Under-voltage lockout
The under-voltage lockout circuit prevents mal-operation of the device at low input voltage. It prevents the converter from turning on the switch or MOSFET under undefined conditions.
7. Enable
Connect EN to ground forces the device into shutdown mode, whereas to VIN or floating enables the device
.Pulling the EN low forces the IC to enter the shutdown mode, in which the P-Channel MOSFET and N-Channel
MOSFETs are turned off and the whole device is shut down. If an output voltage is present during shut down,
this could be an external voltage source or super cap. The reverse leakage current is specified under electrical
parameter table. On the contrary, pulling the EN high starts up the ELM605DA in the way as described soft-start
section.
13 - 4
Rev.1.2
ELM605DA 2A synchronous step-down DC/DC converter
8. Power good
ELM605DA also includes an open-drain power good output that indicates when the regulator output is over
90%of its nominal output. If the output voltage is beyond this range, the power good output is pulled to ground.
Since this comparator has no hysteresis on either threshold, a 30μs delay time is added to prevent the power
good output from chattering between states. The power good should be pulled to VIN or another supply voltage
less than 5.5V through a resistor.
■Application notes
1.Input Capacitor Selection
It is necessary for the input capacitor to sustain the ripple current produced during the period of “on” state of
the upper MOSFET, so a low ESR is required to minimize the loss. The RMS value of this ripple can be obtained by the following:
IinRMS = Iout √ D × ( 1 - D )
where D is the duty cycle, IinRMS is the input RMS current, and Iout is the load current. The equation reaches
its maximum value with D = 0.5. The loss of the input capacitor can be calculated by the following equation:
Pcin = ESRcin × IinRMS2
where Pcin is the power loss of the input capacitor and ESRcin is the effective series resistance of the input capacitance. Due to large dI/dt through the input capacitor, electrolytic or ceramics should be used. If a tantalum is
required, it must be surge-protected. Otherwise, capacitor failure could occur.
2. Output inductor selection
The output inductor selection is to meet the requirements of the output voltage ripple and affects the load transient response. The higher inductance can reduce the inductor’s ripple current and induce the lower output ripple
voltage. The ripple voltage and current are approximated by the following equations:
Vin - Vout
Vout
∆I =
×
∆Vout = ∆I × ESR
Fs × L
Vin
Although the increase of the inductance reduces the ripple current and voltage, it contributes to the increase of
the response time for the regulator to load transient as well. Increasing the switching frequency (Fs) for a given
inductor also can reduce the ripple current and voltage but it will increase the switching loss of the power MOS.
The way to set a proper inductor value is to have the ripple current (∆I) be approximately 10%~50% of the
maximum output current. Once the value has been determined, select an inductor capable of carrying the required peak current without going into saturation. It is also important to have the inductance tolerance specified
to keep the accuracy of the system controlled. Using 20% for the inductance (at room temperature) is reasonable
tolerance able to be met by most manufacturers. For some types of inductors, especially those with core made of
ferrite, the ripple current will increase abruptly when it saturates, which will result in a larger output ripple voltage.
3. Output capacitor selection
An output capacitor is required to filter the output and supply the load transient current. The high capacitor value and low ESR will reduce the output ripple and the load transient drop. These requirements are met by a mix
of capacitors and careful layout.
13 - 5
Rev.1.2
ELM605DA 2A synchronous step-down DC/DC converter
In typical switching regulator design, the ESR of the output capacitor bank dominates the transient response.
The number of output capacitors can be determined by the following equations:
∆Vesr
ESRcap
ESRmax =
Number of capacitors =
∆Iout
ESRmax
∆Vser = change in output voltage due to ESR (assigned by the designer)
∆Iout = load transient
ESRcap = maximum ESR per capacitor (specified in manufacturer’s data sheet)
ESRmax = maximum allowable ESR
High frequency decoupling capacitors should be placed as closely to the power pins of the load as physically
possible. For the decoupling requirements, please consult the capacitor manufacturers for confirmation.
4. Output Voltage
The output voltage is set using the FB pin and a resistor divider connected to the output as shown in AP Circuit
below. The output voltage (Vout) can be calculated according to the voltage of the FB pin (Vfb) and ratio of the
feedback resistors by the following equation, where (Vfb) is 0.8V:
R2
Vfb = Vout ×
( R1 + R2 )
Thus the output voltage is:
( R1 + R2 )
Vout = 0.8 ×
R2
5. Layout consideration
The physical design of the PCB is the final stage in the design of power converter. If designed improperly, the
PCB could radiate excessive EMI and contribute instability to the power converter. Therefore, follow the PCB
layout guidelines below can ensure better performance of ELM605DA.
(1). The bold lines of AP Circuit below show the main power current paths. Keep the traces short and wide.
(2). To reduce resistive voltage drops and the number of via, ELM605DA and power components (Cin1, Cin2,
Cout and L) should be placed on the component side of the board and power current traces routed on its
component layer.
(3). SW node supports high frequency voltage swing (dv/dt). It should be routed small area.
(4). Place input capacitor CIN as close as possible to the IC pins (VIN and PGND).
(5). To avoid the switching noise from polluting the ELM605DA’s internal circuit, place a resistor between the
VIN and VCC pin. A bypass capacitor C8 (0.1µF) should be placed between analog ground pin (GND) and
VCC pin.
(6). Place feedback components (R1, R2 and C5 ) behind the output capacitor and near the ELM605DA. Keep
the feedback loop area small and away from SW node.
(7). To avoid PGND terminal is polluting the ELM605DA’s internal ground. The analog ground pin (GND)
should be connected to a clearer node as show in AP circuit below.
(8). To minimize parasitical capacitor couplings and magnetic field-to-loop couplings, the power converter
should be located away from other circuitry, especially from sensitive analog circuitry.
13 - 6
Rev.1.2
ELM605DA 2A synchronous step-down DC/DC converter
ELM605DA AP Circuit
AP circuit
Short and wide traces
R4
ELM605DA
CIN
C8
VIN
VCC
1
L
R6
VOUT
VIN
8
2
PG
3
GND
SW
7
PGND
6
VOUT
Cout
R1
PGND
4
EN
FB
5
C5
EN
SOP-8
TOP VIEW
R2
■Evaluation circuit
C1=10µF, C2=0.1µF, C3=22µF, C5=1nF, C7= NC, C8=0.1µF, R3=100KΩ, R4=10, R6=100K, L=2.2µH
Vout=3.3V
Vout=1.8V
Vout=1.2V
Vout=1.0V
R1
47K
R2
15K
12.5K
5K
10K
10K
24K
6K
R4
10 Ω
C8
0.1µF
U1
1
2
3
4
R6
Vout
VCC
VIN
PG
SW
7
6
GND PGND
5
EN
EN
FB
R3
Vin
8
ELM605DA
100K Ω
PG
C2
0.1µF
100KΩ
EN
C7
NC
13 - 7
Vin
C1
10µF
L=2.2µH
2
1
Vout=0.8~(R1+R2)/R2
Vout
C3
22µF
R1
C5
1nF
R2
Rev.1.2
ELM605DA 2A synchronous step-down DC/DC converter
■Typical characteristics
• Vin=3.3V, Vout=1.0V
• Vin=3.3V, Vout=1.0V, R1=6K, R2=24K, Top=25°C
Vout-Iout
1.15
90.0
1.1
80.0
1.05
1
0.95
0.9
70.0
60.0
50.0
40.0
30.0
20.0
0.85
10.0
0.8
0.1
1000
100
10
1
Iout (mA)
Vout-Vin
1.2
0.0
0.1
10000
1
10
100
Iout (mA)
1000
10000
Vout=1.0V
Iout=10mA
1.1
Vout (V)
Vin=3.3V, Vout=1.0V
100.0
Efficiency (%)
Vout (V)
Efficiency-Iout
Vin=3.3V, Vout=1.0V
1.2
1
0.9
Iout=100mA
Iout=1A
0.8
0.7
1
2
3
4
Vin (V)
5
6
7
13 - 8
Rev.1.2
ELM605DA 2A synchronous step-down DC/DC converter
• Vin=3.3V, Vout=1.8V
• Vin=3.3V, Vout=1.8V, R1=12.5K, R2=10K, Top=25°C
Vout-Iout
2.1
90.0
2
80.0
1.9
1.8
1.7
1.6
70.0
60.0
50.0
40.0
30.0
20.0
1.5
10.0
1.4
0.1
10
1
1000
100
Iout (mA)
Vout-Vin
1.9
0.0
0.1
10000
1
10
100
Iout (mA)
1000
10000
Vout=1.8V
2
Vout (V)
Vin=3.3V, Vout=1.8V
100.0
Efficiency (%)
Vout (V)
Efficiency-Iout
Vin=3.3V, Vout=1.8V
2.2
Iout=10mA
1.8
1.7
Iout=1A
1.6
Iout=100mA
1.5
0
1
2
3
4
Vin (V)
5
6
7
13 - 9
Rev.1.2
ELM605DA 2A synchronous step-down DC/DC converter
• Vin=5.0V, Vout=1.2V
• Vin=5.0V, Vout=1.2V, R1=5K, R2=10K, Top=25°C
Vout-Iout
Efficiency-Iout
Vin=5V, Vout=1.2V
1.5
1.45
90.0
1.4
80.0
Efficiency (%)
1.35
Vout (V)
Vin=5V, Vout=1.2V
100.0
1.3
1.25
1.2
1.15
70.0
60.0
50.0
40.0
30.0
1.1
20.0
1.05
10.0
1
0.1
10
1
1000
100
Iout (mA)
0.0
0.1
10000
1
10
100
Iout (mA)
1000
10000
Vout-Vin
Vin=5V, Vout=1.2V
1.4
Vout (V)
1.3
Iout=10mA
1.2
1.1
Iout=1A
1
0.9
Iout=100mA
0
1
2
3
4
Vin (V)
5
6
7
13 - 10
Rev.1.2
ELM605DA 2A synchronous step-down DC/DC converter
• Vin=5V, Vout=3.3V
• Vin=5.0V, Vout=3.3V, R1=47K, R2=15K, Top=25°C
Vout-Iout
3.5
3.45
90.0
3.4
80.0
3.35
70.0
3.3
3.25
3.2
3.15
60.0
50.0
40.0
30.0
3.1
20.0
3.05
10.0
3
0.1
10
1
1000
100
Iout (mA)
Vout-Vin
Vout (V)
0.0
0.1
10000
1
10
100
Iout (mA)
1000
10000
Vout=3.3V
3.5
3.4
Vin=5V, Vout=3.3V
100.0
Efficiency (%)
Vout (V)
Efficiency-Iout
Vin=5V, Vout=3.3V
Iout=10mA
3.3
3.2
Iout=100mA
3.1
3
0
1
2
Iout=1A
3
4
Vin (V)
5
6
7
13 - 11
Rev.1.2
ELM605DA 2A synchronous step-down DC/DC converter
■Dynamic load waveform
■Vin,Vout woveform
Dynamic
Dynamic load
load waveform
waveform
Steady
Steady state
state waveform
waveform
Iout=1A,
Iout=1A,Vout=3.3V
Vout=3.3V
Vout
Vout(AC)
(AC)
100mV/Div
100mV/Div
Vin=5V,Vout=3.3V,
Vin=5V,Vout=3.3V,Iout=1A
Iout=1A
Dynamic load waveform
Vin
Vin(AC)
(AC)
100mV/Div
100mV/Div
Iout=1A, Vout=3.3V
Steady state waveform
Vin=5V,Vout=3.3V, Iout=1A
Vin (AC)
100mV/Div
Vout (AC)
100mV/Div
Vout
Vout(AC)
(AC)
10mV/Div
10mV/Div
Iout
Iout
'0.5A/Div
'0.5A/Div
Iout
'0.5A/Div
Vout (AC)
10mV/Div
Time
Time (500µs/Div)
(500µs/Div)
Time
Time (1.0µs/Div)
(1.0µs/Div)
Time (500µs/Div)
Time (1.0µs/Div)
Power
Power
on/off
on/off
from
from EN
EN
■Power ON/OFF
from
EN
Vin=5V,
Vin=5V,Vout=3.3V,
Vout=3.3V,Iout=40mA
Iout=40mA
Ven
Ven
2V/Div
2V/Div
Power
Power on/off
on/off from
from EN
EN
Vin=5V,
Vin=5V,Vout=3.3V,
Vout=3.3V,Iout=1A
Iout=1A
Power on/off from EN
Ven
Ven
2V/Div
2V/Div
Vin=5V, Vout=3.3V, Iout=40mA
Ven
2V/Div
Vout
Vout
2V/Div
2V/Div
Ven
2V/Div
Vout
Vout
2V/Div
2V/Div
Vout
Iout
Iout
2V/Div
20mA/Div
20mA/Div
Vout
Iout
Iout
2V/Div
1A/Div
1A/Div
Iout
20mA/Div
Time
Time (1ms/Div)
(1ms/Div)
Iout
1A/Div
Time (1ms/Div)
Power on/off from EN
Vin=5V, Vout=3.3V, Iout=1A
Time
Time (1ms/Div)
(1ms/Div)
Time (1ms/Div)
13 - 12
Rev.1.2
ELM605DA 2A synchronous step-down DC/DC converter
■Fosc-Top
■Vfb-Top
■Switching temperature characteristics
■Fosc-Top
■Fosc-Top
■Vfb-Top
■Vfb-Top
Vfb-Top
Vin=5V, Vout=3.3V
0.82
Vfb-Top
Vfb-Top
Vin=5V,
Vin=5V,
Vout=3.3V
Vout=3.3V
0.82
0.82
Vin=5V, Vout=3.3V
Fosc-Top
Fosc-Top
Vin=5V,
Vin=5V,
Vout=3.3V
Vout=3.3V
1050.0
1050.0
1000.0
0.81
Fosc (KHz)
Fosc (KHz)
Fosc (KHz)
1000.0
1000.0
950.0
Vfb (V)
Vfb (V)
Vfb (V)
0.81
0.81
0.8
950.0
950.0
900.0
0.80.8
0.79
900.0
900.0
850.0
0.79
0.79
0.78
-40 -20
Fosc-Top
1050.0
0
20
40
60
Top (°C)
850.0
850.0
800.0
-40 -20
80 100 120
0
20
40
60
Top (°C)
80 100 120
800.0
800.0
120120
-40-40-20-20 0 0 20 2040 4060 6080 80100100
0.78
0.78
-40-40-20-20 0 0 20 2040 4060 6080 80100100
120120
Top
Top
(°C)
(°C)
Top
Top
(°C)
(°C)
■Iq-Top
■Iq-Top
■Iq-Top
Iq-Top
240
Vin=5V
Iq-Top
Iq-Top
240240
230
Vin=5V
Vin=5V
Iq (�A)
Iq (�A)
Iq (�A)
230230
220
220220
210
210210
200
200200
190
-40 -20
0
20
40
60
Top (°C)
80 100 120
190190
120120
-40-40-20-20 0 0 20 2040 4060 6080 80100100
Top
Top
(°C)
(°C)
13 - 13
Rev.1.2