ELM603GC 5V input 1.5A 1.5MHz synchronous step-down DC/DC converter
http://www.elm-tech.com■General description

ELM603GC is high efficiency 1.5A constant on-time (COT) controlled synchronous step-down DC/DC
converter. It can operate with input voltage from 2.5V to 6.0V and provide output range from 0.6V to
input level, thanks to its 100% duty cycle operation. The constant on-time control scheme simplifies loop
compensation and offers excellent load transient response. ELM603GC operates at fixed 1.5MHz acrossentire load range. The high gain error amplifier in the control loop provides excellent load and line regulation.
ELM603GC has cycle-by-cycle current limit and hiccup mode to protect over-load or short circuit fault
conditions.
ELM603GC is available in low profile 6 leads DFN 2mm×2mm packages.

■Features■Application• Proprietary fast transient constant on time architecture
stable with low ESR ceramic output capacitors• Thermal shutdown protection• Internal 1msec soft-start• Cycle-by-cycle current limit protection• Input under/over voltage lockout• Output discharging function in shutdown• Hiccup mode for short circuit and over-load protection• Output current: 1.5A• Wide input voltage range: 2.5V to 6.0V
• Switching frequency: Fixed 1.5MHz• Feedback voltage: 0.6V ±2%• Built-in power switches: 260mΩ/180mΩ
• Maximum duty cycle: 100%• Package: DFN6-2×2• Solid-state and hard disk drives• WiFi RF modules• DC/DC micro modules• Smart phone and tablets■Typical applications
Efficiency
100%
90%
VIN
2.5V~5.5V

CIN
10uF

C1
0.1uF

PGOOD
VIN

PG

RPG 100K
SW

FB

EN

EN

GND

VOUT
1.2V

L
2.2uH

R1
200K

CFF

68pF

COUT
10uF

80%
70%
60%
50%
40%

5Vin 3.3Vo
5Vin 2.5Vo
5Vin 1.8Vo
5Vin 1.2Vo

30%

R2
200K

20%
10%
0%
0.001

0.01

0.1

1

Iout (A)Rev.1.0
1 / 11

ELM603GC 5V input 1.5A 1.5MHz synchronous step-down DC/DC converter
http://www.elm-tech.com■Recommended operating conditions
Parameter
Input voltage
Output voltage
Operating temperature range

Symbol
Vin
Vout
Top

Limit
+2.5 to +6.0
+0.6 to Vin-40 to +85

Unit
V
V
°C

* Note: The device is not guaranteed to function outside of the recommended operating conditions.

■Maximum absolute ratings (*1)
Parameter
Input voltage
SW pin voltage
Dynamic Vsw
In 10ns duration
The other pins
Power dissipation at Ta=+25°C (* 2, 3)
Storage temperature range
Junction temperature range
Thermal resistance (* 2, 3)
Thermal resistance (* 2, 3)

SymbolVin
Vsw
Vother
Pd
Tstg
Tj
θja
θjc

Limit
-0.3 to +6.5
-0.3 to Vin+0.3-2.0 to Vin+2.0-0.3 to +6.5
1.3
-65 to +150
-40 to +150
75
20

Unit
V
V
V
V
W
°C
°C
°C/W
°C/W

* : 1. Stress exceeding those listed "Maximum absolute ratings" may damage the device.
2. Measured on JESD51-7, 4-Layer PCB.
3. The maximum allowable power dissipation is a function of the maximum junction temperature TJ_MAX, the junction toambient thermal resistance θja, and the ambient temperature Ta. The maximum allowable continuous power dissipation at any
ambient temperature is calculated by Pd_max= (Tj_max-Ta)/θja. Exceeding the maximum allowable power dissipation will cause
excessive die temperature, and the regulator will go into thermal shutdown. Internal thermal shutdown circuitry protects the device
from permanent damage.

■Selection guide
ELM603GC-N
Symbolabc

Package
Product version
Taping direction

G: DFN6-2×2
C
N: Refer to PKG file

ELM603GC - N
↑↑ ↑
ab c

* Taping direction is one way.

Rev.1.0
2 / 11

ELM603GC 5V input 1.5A 1.5MHz synchronous step-down DC/DC converter
http://www.elm-tech.com■Pin configuration
Top view

Pin No.

Pin name

1

PG

2

EN

3

VIN

Power good open-drain output. Connect a 100kΩ pull-up
resistor to Vin or Vout.
Regulator enable control input with accurate 1.21V enable
threshold which can be used to build precision R-C turn-on
delay and input under-voltage lockout. This pin has a pulldown resistor of typically 1MΩ to GND.
• Drive EN above 1.21V to turn on the converter• Drive EN below 1.11V to turn off the converter anddischarge output
Input supply voltage

4SW

Power switch node5

GND

GroundFB

Voltage feedback input. Connect a resistor divider between
output and FB to program the output voltage. VFB is regulated
to 0.6V

Exposed pad on backside

6

Description■Block diagram
Bandgap

EA
REFSS

-

Modulation
Ramp

PWM

-

FB

+
+

0.6V

REFSS

IN

SoftStart

+
+

EN

HSON

ON

Constant
On-time
IN

VIN

SW

SW

M1

Control
Logic
OVLD

SW
LSON

ILIMT

M2

GND

PG

+

-

Current
Limit&
Over-load
Detection

Comp

+

+

0.54V

Rev.1.0
3 / 11

ELM603GC 5V input 1.5A 1.5MHz synchronous step-down DC/DC converter
http://www.elm-tech.com■Electrical characteristics

Top=+25°C, Vin=5V, Unless otherwise noted. Typical values are at Vin=Ven=5V and Vout=1.8V.
Parameter
SymbolTest conditions
Min. Typ. Max.
Input voltage range
Vin
2.5
6.0
Shutdown current
Is
Ven=0V, Vin=5.5V
0.1
1.0
Input under voltage lockout threshold Vuvlo Vin Increasing
2.3
2.4
2.5
280
Input under voltage lockout hysteresis Vhysu
Input over voltage lockout threshold
Vovlo
6.4
6.6
6.8
Input over voltage lockout hysteresis
Vhyso
400
Quiescent current
Iq
Vfb=0.63V
500
650
Feedback regulation voltage
Vfbref591
600
609
Feedback current
Ifb
1
HS switch peak current limit
Ilim
2.8
3.5
4.2
HS main switch on resistance
Ron_H Vin=5V260
LS synchronous switch on resistance
Ron_L Vin=5V
180
HS leakage current
Ileak_H Vin=5.5V, Ven=Vsw=0V
0.1
2.0
LS leakage current
Ileak_L Vin=Vsw=5.5V, Ven=0V
0.1
2.0
PWM switching frequency
Fsw
Iout=1A
1.5
EN on threshold
Ven_on Ven ramp up
1.18
1.21
1.24
1.05
1.11
1.17
EN off threshold
Ven_off Ven ramp down
EN internal pull down resistor
Ren
700
1000 1300
PG output leakage current
Ileak_pg Vfb=0.63V, Vpg=Vin=5.5V
0.01
Vfb rising,
PG lower trip threshold
Vpg-10% with respec to Vfbref
PG hysteresis
Vpghys % with respect to Vfbref
5
PG delaytdpg
PG going high to low
20
Thermal shutdown
Tsd160
Thermal shutdown hysteresis
Tsdhys30
Output discharge resistance
Rdsc Ven=0V, Vsw=1V
200

Unit
V
μA
V
mV
V
mV
μA
mV
nA
A
mΩ
mΩ
μA
μA
MHz
V
kΩ
μA
%
%
μs
°C
°C
Ω

■Marking
Mark

Content

3120
a to eProduct code
Lot No.

Rev.1.0
4 / 11

ELM603GC 5V input 1.5A 1.5MHz synchronous step-down DC/DC converter
http://www.elm-tech.com■Typical characteristics• Cin=10µF, Cout=10µF, L=2.2µH, Top=25°C
Steady State Test

Steady State Test

Steady State Test

5Vin 3.3Vo 0mA

5Vin 3.3Vo 0.5A

5Vin 3.3Vo 1.5A

Vin
(10mV/div)Vin(20mV/div)Vin(50mV/div)

Vout(10mV/div)

Vout(10mV/div)

Vout(10mV/div)

SW(5V/div)

SW(5V/div)

SW(5V/div)

IL(0.5A/div)

IL(0.5A/div)IL(1A/div)(1uS/div)(1uS/div)(1uS/div)

Steady State Test

Steady State Test

Steady State Test

5Vin 1.2Vo 0mA

5Vin 1.2Vo 0.5A

5Vin 1.2Vo 1.5A

Vin
(10mV/div)Vin(20mV/div)Vin(50mV/div)

Vout(10mV/div)

Vout(10mV/div)

Vout(10mV/div)

SW(5V/div)

SW(5V/div)

SW(5V/div)

IL(0.5A/div)IL(1A/div)

IL(0.5A/div)(1uS/div)(1uS/div)(1uS/div)

Load Transient Response

Load Transient Response

Load Transient Response

5Vin 3.3Vo Io=0A to 0.5A

5Vin 3.3Vo Io=0.5A to 1A

5Vin 3.3Vo Io=0.5A to1.5A

Vout(20mV/div)

Vout(20mV/div)

Vout(50mV/div)

IL(0.5A/div)

IL(0.5A/div)IL(1A/div)(200uS/div)(200uS/div)(200uS/div)

Rev.1.0
5 / 11

ELM603GC 5V input 1.5A 1.5MHz synchronous step-down DC/DC converter
http://www.elm-tech.com

Load Transient Response

Load Transient Response

Load Transient Response

5Vin 1.2Vo Io=0A to 0.5A

5Vin 1.2Vo Io=0.5A to 1A

5Vin 1.2Vo Io=0.5A to1.5A

Vout(10mV/div)

Vout(20mV/div)

Vout(50mV/div)

IL(0.5A/div)

IL(0.5A/div)IL(1A/div)(200uS/div)(200uS/div)(200uS/div)

Vin Power On

Vin Power Off

Vin Power On

5Vin 3.3Vo 0A

5Vin 3.3Vo 0A

5Vin 1.2Vo 0A

Vin(2V/div)

Vin(2V/div)

Vin(2V/div)

Vout(2V/div)

Vout(2V/div)

Vout(0.5V/div)

SW(2V/div)

SW(2V/div)

SW(2V/div)

IL(0.5A/div)

IL(0.5A/div)

IL(0.5A/div)(2mS/div)(10mS/div)

Vin Power On

Vin Power Off

Vin Power Off

5Vin 3.3Vo 1.5A

5Vin 3.3Vo 1.5A

5Vin 1.2Vo 0A(2mS/div)Vin(2V/div)

Vin(2V/div)

Vin(2V/div)

Vout(2V/div)

Vout(2V/div)

Vout(0.5V/div)

SW(5V/div)

SW(5V/div)

SW(2V/div)

IL(1A/div)

IL(1A/div)

IL(0.5A/div)(2mS/div)(4mS/div)(10mS/div)

Rev.1.0
6 / 11

ELM603GC 5V input 1.5A 1.5MHz synchronous step-down DC/DC converter
http://www.elm-tech.com

Vin Power On

Vin Power Off

5Vin 1.2Vo 1.5A

5Vin 1.2Vo 1.5A

Vin
(2V/div)

Vin(2V/div)

Vout(0.5V/div)

Vout(0.5V/div)

SW(2V/div)

SW(2V/div)

IL(1A/div)

IL(1A/div)

Efficiency
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
0%
0.001

3.3Vin 2.5Vo
3.3Vin 1.8Vo
3.3Vin 1.2Vo

0.01

0.1

(2mS/div)(10mS/div)

EN On

EN Off

EN On

5Vin 3.3Vo 0A

5Vin 3.3Vo 0A

5Vin 1.2Vo 0A

Iout (A)Ven(1V/div)

Ven(1V/div)

Ven(2V/div)

Vout(2V/div)

Vout(2V/div)

Vout(0.5V/div)

SW(2V/div)

SW(2V/div)

SW(5V/div)

IL(0.5A/div)

IL(0.5A/div)

IL(0.5A/div)(2mS/div)(4mS/div)(2mS/div)

EN On

EN Off

EN Off5Vin 3.3Vo 1.5A

5Vin 3.3Vo 1.5A

5Vin 1.2Vo 0A

Ven(1V/div)

Ven(1V/div)

Ven(1V/div)

Vout(2V/div)

Vout(2V/div)

Vout(0.5V/div)

SW(5V/div)

SW(5V/div)

SW(5V/div)

IL(1A/div)

IL(1A/div)

IL(0.5A/div)(2mS/div)(4mS/div)

1(4mS/div)

Rev.1.0
7 / 11

ELM603GC 5V input 1.5A 1.5MHz synchronous step-down DC/DC converter
http://www.elm-tech.com

EN On

EN Off5Vin 1.2Vo 1.5A

5Vin 1.2Vo 1.5A

Ven
(1V/div)

Ven(1V/div)

Vout(0.5V/div)

Vout(0.5V/div)

SW(5V/div)

SW(5V/div)

IL(1A/div)

IL(1A/div)(2mS/div)(4mS/div)

Short Circuit Entry

Short Circuit Recovery

5Vin 3.3Vo 0A

5Vin 3.3Vo 0A

Vin(2V/div)

Vin(2V/div)

Vout(2V/div)(2V/div)

SW(5V/div)

SW(5V/div)

IL(2A/div)

IL(2A/div)

Vout(2mS/div)(2mS/div)

Short Circuit Entry

Short Circuit Recovery

5Vin 1.2Vo 0A

5Vin 1.2Vo 0A

Vin(2V/div)

Vin(2V/div)

Vout(0.5V/div)

Vout(0.5V/div)

SW(5V/div)

SW(5V/div)
IL(2A/div)

IL(2A/div)(2mS/div)(2mS/div)

Rev.1.0
8 / 11

ELM603GC 5V input 1.5A 1.5MHz synchronous step-down DC/DC converter
http://www.elm-tech.com■Theory of operation

ELM603GC is a constant on-time control synchronous step-down DC/DC converter that offers excellent transient response over a wide range of input voltage. It achieves superior light-load efficiency with extremely low
quiescent current.
Constant On-time Control
Constant on-time control step-down DC/DC converters turn on HS immediately when FB droops below reference. The HS is turned on for a pre-determined period (on-time) of time to ramp up the inductor current, andthen the LS will be turned on to ramp down the inductor current. The cycle repeats itself if FB droops below
reference again. ELM603GC uses proprietary technique to take into account the load current impact and adjusts
the on-time accordingly to achieve a constant switching frequency over entire load current range.
For ELM603GC, the on-time is approximately:Vout• 0.66μVin
Due to its immediate response on FB voltage droop and simplified loop compensation, constant on-time offers aTon =superior transient response compare to traditional fixed frequency PWM control step-down converters.
EnableWhen input voltage is above the under voltage lock-out threshold, ELM603GC can be enabled by pulling the
EN pin to above 1.21V. ELM603GC is disabled if the EN pin is pulled below 1.11V. The enable/disable threshold for EN pin is accurately designed to be 1.21V and 1.11V respectively, so one can also use external resistor
divider to program the desired input under-voltage lockout level.
Soft Start
ELM603GC has built-in soft start of 1ms. During the soft start period, output voltage is ramped up linearly tothe regulation voltage, independent of the load current level and output capacitor value.
Current Limit and Hiccup Mode
ELM603GC has cycle-by-cycle HS current limit protection to prevent inductor current from running away.
Once HS current limit is triggered, ELM603GC will turn on LS and wait for the inductor to drop down to a predetermined level before the HS can be turned on again. If this current limit condition is repeated for a sustained
long period of time, ELM603GC will consider it over-load or short circuit. Either way, ELM603GC will enterhiccup mode, where it stop switching for a pre-determined period of time before automatically re-try to start up
again. It always starts up with soft-start to limit inrush current and avoid output overshoot.

Rev.1.0
9 / 11

ELM603GC 5V input 1.5A 1.5MHz synchronous step-down DC/DC converter
http://www.elm-tech.com■Application information
Setting the output voltage

External feedback resistors are used to set the output voltage. Refer to typical application circuit on page1,
the top feedback resistor R1 has some impact on the loop stability, so its recommended range is between
100kΩ~300kΩ. For any chosen R1, the bottom feedback resistor R2 can be calculated as:
R1
R2 =
Vout
-1
0.6
Inductor Selection
The recommended inductor value for ELM603GC is between 1uH to 4.7uH. Usually the inductor value is chosen to satisfy a desired ripple current:
Vout • (Vin - Vout)L=
Vin • fsw • ∆I
where ∆I is the inductor ripple current.
With the chosen L , the peak inductor current will be:
1
Ipk = Iload + • ∆I
2
Input Bypass Capacitor Selection
The input current to the step-down converter is discontinuous with very sharp edges, therefore input bypass
ceramic capacitors are required and place them as close to the input pin as possible. For lowest temperature
variations, use X5R or X7R dielectric ceramic capacitors.
The RMS current of the input capacitor is approximately:
Icin_rms = Iout √ D(1 - D)
From the equation, it can be seen that the highest RMS current occurs when D is 0.5:
1
Icin_rms = Iout
2
Choose the capacitor with RMS current rating higher than 1/2 Iout. The power dissipation on the input capacitor can be estimated with the RMS current and the ESR resistor. Electrolytic or tantalum capacitors can also beused, but due to their significantly higher ESR, a small size ceramic capacitor should be placed as close to the
IC as possible.
The voltage ripple on the input capacitor, neglecting the ESR impact, can be calculated as:
Vout
Iload
Vout
∆Vcin =•• (1 )
fsw • Cin Vin
Vin
Output Capacitor Selection
An output capacitor is required to obtain a stable output voltage. To minimize the output voltage ripple, ceramic capacitors should be used, and the ripple voltage can be estimated as:
1
Vout
Vout
1
) •
∆Vout = • ( 1 •
2
8
Vin
L
(fsw) • CoutIf electrolytic or tantalum capacitors are used, the ESR will dominate the output voltage ripple:
Vout
Vout
∆Vout = ( 1 • Resr) •Vin
fsw • L

Rev.1.0
10 / 11

ELM603GC 5V input 1.5A 1.5MHz synchronous step-down DC/DC converter
http://www.elm-tech.com
PCB Layout recommendation
The physical design of the PCB is the final stage in the design of power converter. If designed improperly, thePCB could radiate excessive EMI and contribute instability to the power converter. Therefore, following the
PCB layout guidelines below can ensure better performance of ELM603GC.
(1). The loop (Vin-SW-L-Cout-GND) indicates a high current path. The traces within the loop should be kept as
wide and short as possible to reduce parasitic inductance and high-frequency loop area. It is also good for
efficiency improvement.
(2). Input capacitor as close as possible to the IC Pins (Vin and GND) and the input loop area should be as small
as possible to reduce parasitic inductance, input voltage spike and noise emission.
(3). Feedback components (R1, R2 and Cff) should be routed as far away from the inductor and the SW Pin as
possible to minimize noise and EMI issue.

■Application schematic

EVB BOM List
Qty
1
1
2
1
1

Ref
Cin
Cout
C1, Cen
Cff
L

1

R1

1

R2

2
1

Ren, Rpg
Power IC

Value
10µF
10µF
0.1µF
68pF
2.2µH
Vout=3.3V
200KΩ
Vout=2.5V
240KΩ
200KΩ
Vout=1.8V
Vout=1.2V
200KΩ
Vout=1.0V
100KΩ
43KΩ
Vout=3.3V
75KΩ
Vout=2.5V
Vout=1.8V
100KΩ
Vout=1.2V
200KΩ
Vout=1.0V
150KΩ
100KΩ
ELM603GC

Description
Ceramic capacitor, 10V, X5R
Ceramic capacitor, 10V, X5R
Ceramic capacitor, 10V, X5R
Ceramic capacitor, 10V, X5R
Inductor, Rated current 2.25A

Package
0805
0805
0603
0603
0805 SMD

Resistor, ±1%0603

Resistor, ±1%0603

Resistor, ±1%
Step-down DC/DC converter

0603
DFN6-2×2
Rev.1.0

11 / 11