ELM605DA 2A synchronous step-down DC/DC … Rev.1.2 SOP-8(TOP VIEW) Pin configuration Block diagram Pin No. Pin name Pin description 1 VCC Supply voltage input 2 PG Power good 3 GND

1 Rev.1.2

Parameter Symbol Limit UnitVIN power supply voltage Vin -0.3 to +6.5 VApply voltage to SW Vsw -0.3 to Vin+0.3 VApply voltage to EN Ven -0.3 to Vin VApply voltage to FB Vfb -0.3 to Vin VPower dissipation Pd 300 mWOperating temperature range Top -40 to +150 °CStorage temperature range Tstg -65 to +150 °C

ELM605DA 2A synchronous step-down DC/DC converter

■General description

■Features

■Maximum absolute ratings

• ASIC/DSP/μP/FPGA core and I/O voltages• Networking and telecommunications• TV• Set top boxes• Cellular base stations

■Application

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• 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

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.

Caution:Permanent damage to the device may occur when ratings above maximum absolute ones are used.

* Taping direction is one way.

ELM605DA-SSymbol

a Package D: SOP-8b Product version Ac Taping direction S: Refer to PKG file

ELM605DA - S ↑ ↑ ↑ a b c

■Selection guide

2 Rev.1.2

SOP-8(TOP VIEW)

■Pin configuration

■Block diagram

Pin No. Pin name Pin description1 VCC Supply voltage input2 PG Power good3 GND Ground4 FB Feedback/Output voltage5 EN Enable input 6 PGND Power switch ground7 SW Power switch output8 VIN Power switch supply voltage input

VCC

EN

+-

0.8VFB

+-0.72V

PG

Oscillator

+-

+

Erroramplifier

Slop comp

PWMcomparator

PWMlogic

GND

Clock

+-

PGND

SW

+-

VIN500k ohm

UG

LG

M1

M2

Currentsence

amplifier

DCCZero-currentcomparator

Reference

4

3

2

1

5

6

7

8


■Standard circuitELM605DA

VIN

VCC

ENPGND GND

FB

SW

PG8

1

5

2

7

4

6 3

10100k

0.1µF

10µF

Vin PG

2.2µH 100k

22µF R1

R2

Vout

Cup*(option)

Vout=0.8V*(1+R1/R2)

13 -

3 Rev.1.2

Parameter Symbol Test condition Min. Typ. Max. UnitSupply voltage Vin 2.5 6.0 VQuiescent current Iq Iout=0mA, no switching 220 µAShutdown current Is EN=GND 7 µAAdjustable output voltage range Vout 0.8 Vin VRegulated feedback voltage Vfb Top=+25°C 0.784 0.800 0.816 VOutput 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 under voltagelockout threshold UVLO

Vin rising 2.3 VVin falling 2.1Feedback current Ivfb -30 - 30 nASW leakage current Ileak(sw) Ven=0V, Vin=6V, Vsw=0V or 6V -1 1 µAPMOSFET on resistance RdsonP Vin=Vgs=5V, Iout=100mA 130 mΩNMOSFET on resistance RdsonN Vin=Vgs=5V, Iout=100mA 100 mΩPMOSFET current limit IclP 3.2 AOscillator frequency Fosc 1 MHzThermal shutdown threshold Ts 150 °CSoft-start time Tss 1 mSPower good threshold Vpg 0.9*VoutPower good current Ipg Vpg=0.3V 3 mAEN high Level input voltage Ven -40°C≤Top≤+85°C 1.3 VEN low level input voltage Ven 0.3 V

■DC electrical characteristicsVin=3.3V, Top=25°C, unless otherwise noted


SOP-8

■Marking

ELM605DAabc

Mark ContentELM605DA Product name

a, b, cAssembly lot No.:

000 to 999 repeated

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4 Rev.1.2

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 volt-age 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 effi-ciency 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 cur-rent 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 con-verter 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.


■Functional description

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5 Rev.1.2

■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 ob-tained 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 ca-pacitance. 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 tran-sient 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:

∆I = Vin - Vout

× Vout

∆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 re-quired 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 volt-age.3. Output capacitor selection An output capacitor is required to filter the output and supply the load transient current. The high capacitor val-ue 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.


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.

13 -

6 Rev.1.2

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:

ESRmax = ∆Vesr

Number of capacitors = ESRcap

∆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:

Vfb = Vout × R2

( R1 + R2 )

Thus the output voltage is:

Vout = 0.8 × ( R1 + R2 )

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 -

7 Rev.1.2

AP circuit

ELM605DA 2A synchronous step-down DC/DC converterELM605DA AP Circuit

4

PG

FB

GND

1

2

3

VCC

SOP-8TOP VIEW

5

8

6

EN

SW 7

PGND

VIN

ELM605DA

L

Cout

VOUT

EN

VIN

R6VOUT

R2

R1 C5

CIN

PGND

R4

C8

Short and wide traces

■Evaluation circuit

GND

VCC

FB

PGND

EN

VIN

PG SW

ELM605DA

EN

Vin 100K

R3

EN

L=2.2µH

C322µF

R1

R2

C51nF

VoutVout=0.8~(R1+R2)/R2

R6

100K

Vout

4 5

3 6

2 7

1 8U1

PG

Vin

C110µF

R4

10C80.1µF

1 2

C20.1µF

C7NC

R1 R2Vout=3.3V 47K 15KVout=1.8V 12.5K 10KVout=1.2V 5K 10KVout=1.0V 6K 24K

C1=10µF, C2=0.1µF, C3=22µF, C5=1nF, C7= NC, C8=0.1µF, R3=100KΩ, R4=10, R6=100K, L=2.2µH

Ω

Ω

Ω

13 -

8 Rev.1.2


• Vin=3.3V, Vout=1.0V

0.1 1 10 100 1000 100000.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

Iout (mA)

Effic

ienc

y (%

)

Efficiency-IoutVin=3.3V, Vout=1.0V

0.1 1 10 100 1000 100000.8

0.85

0.9

0.95

1

1.05

1.1

1.15

1.2Vout-Iout

Vin=3.3V, Vout=1.0V

Iout (mA)

Vou

t (V

)

1 2 3 4 5 6 70.7

0.8

0.9

1

1.1

1.2Vout-Vin

Vout=1.0V

Vin (V)

Vou

t (V

)

Iout=1A

Iout=10mA

Iout=100mA

■Typical characteristics

• Vin=3.3V, Vout=1.0V, R1=6K, R2=24K, Top=25°C

13 -

9 Rev.1.2


0.1 1 10 100 1000 100000.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

Iout (mA)

Effic

ienc

y (%

)

Efficiency-IoutVin=3.3V, Vout=1.8V

0.1 1 10 100 1000 100001.4

1.5

1.6

1.7

1.8

1.9

2

2.1

2.2Vout-Iout

Vin=3.3V, Vout=1.8V

Iout (mA)

Vou

t (V

)

0 1 2 3 4 5 6 71.5

1.6

1.7

1.8

1.9

2Vout-Vin

Vout=1.8V

Vin (V)

Vou

t (V

)

Iout=1A

Iout=10mA

Iout=100mA

• Vin=3.3V, Vout=1.8V, R1=12.5K, R2=10K, Top=25°C


13 -

10 Rev.1.2


0.1 1 10 100 1000 100000.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

Iout (mA)

Effic

ienc

y (%

)

Efficiency-IoutVin=5V, Vout=1.2V

0.1 1 10 100 1000 100001

1.05

1.1

1.15

1.2

1.25

1.3

1.35

1.4

1.45

1.5Vout-Iout

Vin=5V, Vout=1.2V

Iout (mA)

Vou

t (V

)

0 1 2 3 4 5 6 70.9

1

1.1

1.2

1.3

1.4Vout-Vin

Vin=5V, Vout=1.2V

Vin (V)

Vou

t (V

)

Iout=1A

Iout=10mA

Iout=100mA


13 -


11 Rev.1.2

• Vin=5V, Vout=3.3V

0.1 1 10 100 1000 100000.0

10.0

20.0

30.0

40.0

50.0

60.0

70.0

80.0

90.0

100.0

Iout (mA)

Effic

ienc

y (%

)

Efficiency-IoutVin=5V, Vout=3.3V

0.1 1 10 100 1000 100003

3.05

3.1

3.15

3.2

3.25

3.3

3.35

3.4

3.45

3.5

Iout (mA)

Vou

t (V

)

Vout-IoutVin=5V, Vout=3.3V

0 1 2 3 4 5 6 73

3.1

3.2

3.3

3.4

3.5Vout-Vin

Vout=3.3V

Vin (V)

Vou

t (V

)

Iout=1A

Iout=10mA

Iout=100mA


13 -


12 Rev.1.2

■Dynamic load waveform

Vout (AC)100mV/Div

Iout'0.5A/Div

Iout=1A, Vout=3.3V Vin=5V,Vout=3.3V, Iout=1A

Vin (AC)100mV/Div

Vout (AC)10mV/Div

Ven2V/Div

Vout2V/Div

Iout1A/Div

Ven2V/Div

Vout2V/Div

Iout20mA/Div

Power on/off from EN

Steady state waveformDynamic load waveform

Vin=5V, Vout=3.3V, Iout=1APower on/off from EN

Vin=5V, Vout=3.3V, Iout=40mA

Time (500µs/Div) Time (1.0µs/Div)

Time (1ms/Div) Time (1ms/Div)

■Vin,Vout woveform

■Power ON/OFF from EN

Vout (AC)100mV/Div

Iout'0.5A/Div


Vin (AC)100mV/Div

Vout (AC)10mV/Div

Ven2V/Div

Vout2V/Div

Iout1A/Div

Ven2V/Div

Vout2V/Div

Iout20mA/Div







Vout (AC)100mV/Div

Iout'0.5A/Div


Vin (AC)100mV/Div

Vout (AC)10mV/Div

Ven2V/Div

Vout2V/Div

Iout1A/Div

Ven2V/Div

Vout2V/Div

Iout20mA/Div







13 -


13 Rev.1.2

■Switching temperature characteristics■Vfb-Top

-40 -20 0 20 40 60 80 100 120800.0

850.0

900.0

950.0

1000.0

1050.0Fosc-Top

Vin=5V, Vout=3.3V

Top (°C)Fo

sc (K

Hz)

-40 -20 0 20 40 60 80 100 1200.78

0.79

0.8

0.81

0.82Vfb-Top

Vin=5V, Vout=3.3V

Top (°C)

Vfb

(V)

-40 -20 0 20 40 60 80 100 120190

200

210

220

230

240Iq-Top

Vin=5V

Top (°C)

Iq (�

A)

■Iq-Top

■Fosc-Top■Vfb-Top

-40 -20 0 20 40 60 80 100 120800.0

850.0

900.0

950.0

1000.0

1050.0Fosc-Top

Vin=5V, Vout=3.3V

Top (°C)

Fosc

(KH

z)

-40 -20 0 20 40 60 80 100 1200.78

0.79

0.8

0.81

0.82Vfb-Top

Vin=5V, Vout=3.3V

Top (°C)

Vfb

(V)

-40 -20 0 20 40 60 80 100 120190

200

210

220

230

240Iq-Top

Vin=5V

Top (°C)

Iq (�

A)

■Iq-Top

■Fosc-Top

■Vfb-Top

-40 -20 0 20 40 60 80 100 120800.0

850.0

900.0

950.0

1000.0

1050.0Fosc-Top

Vin=5V, Vout=3.3V

Top (°C)

Fosc

(KH

z)

-40 -20 0 20 40 60 80 100 1200.78

0.79

0.8

0.81

0.82Vfb-Top

Vin=5V, Vout=3.3V

Top (°C)

Vfb

(V)

-40 -20 0 20 40 60 80 100 120190

200

210

220

230

240Iq-Top

Vin=5V

Top (°C)

Iq (�

A)

■Iq-Top

■Fosc-Top

13 -


Documents

ELM605DA 2A synchronous step-down DC/DC … Rev.1.2 SOP-8(TOP VIEW) Pin configuration Block diagram Pin No. Pin name Pin description 1 VCC Supply voltage input 2 PG Power good 3 GND