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PDF ELM621LA Data sheet ( Hoja de datos )
| Número de pieza | ELM621LA | |
| Descripción | High efficiency 30V step up DC/DC converter | |
| Fabricantes | ELM Technology | |
| Logotipo |  |
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ELM621LA High efficiency 30V step up DC/DC converter
■General description
ELM621LA is a high efficiency step-up DC/DC converter using a constant frequency, current mode
architecture. Featuring current-mode and fixed frequency operation, this device incorporates an integrated
main switch and the switching frequency is internally set at 1.3MHz, allowing the use of small surface mount
inductors and capacitor. As for the output voltage, it can be regulated ranging from 2.7V to 30V.
ELM621LA is available in a low profile TSOT-25 package.
■Features
• Current mode operation
• Thermal shutdown protection
• Undervoltage-lockout (UVLO)
• Input voltage range
• Internal current limit
• Shutdown current
• Constant frequency operation
• High efficiency
• Package
: 2.5V to 5.5V
: 1.45A
: < 0.1µA
: Typ.1.3MHz
: 90%
: TSOT-25
■Application
• Cellular telephones
• PDAs and smart phones
• MP3 players
• Wireless and DSL card
• Digital still cameras
• Slim-type DVD
• Portable instruments
■Maximum absolute ratings
Parameter
Symbol
Limit
VIN power supply voltage
Vin
GND-0.3 to +6.5
Apply voltage to EN
Ven GND-0.3 to +6.5
Apply voltage to FB
Vfb GND-0.3 to +6.5
Apply voltage to SW
Vsw GND-0.3 to +43
SW peak current
Isw 2
Power dissipation
Pd 200
Operating temperature range
Top
-20 to +85
Storage temperature range
Tstg
-65 to +150
Caution:Permanent damage to the device may occur when ratings above maximum absolute ones are used.
Unit
V
V
V
V
A
mW
°C
°C
■Selection guide
ELM621LA-S
Symbol
a Package
b Product version
c Taping direction
* Taping direction is one way.
L: TSOT-25
A
S: Refer to PKG file
ELM621LA - S
↑↑ ↑
ab c
9- 1
Rev.1.2
1 page  
ELM621LA High efficiency 30V step up DC/DC converter
■Application notes
1. Input and output capacitor selection
For the most optimized application of ELM621LA, 4.7µF of the input ceramic capacitor and 10µF of output
ceramic capacitor are recommended. Additionally, ceramic capacitors with low ESR are recommended for better
voltage filtering. Regarding the ceramic type, multi-layer ceramic (MLC) type such as X5R or X7R is recom-
mended to ensure good capacitance stability over the full operating temperature range.
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 can be met by
a mix of capacitors and careful layout. Assuming a capacitor with zero ESR, the minimum capacitance needed
for a given ripple can be obtained by the following formula:
Cout = (Vout - Vin) × Iout / (Vout × Fs × Vripple)
Vripple = Peak to peak output ripple
The additional output ripple component caused by ESR is calculated using:
Vripple_ESR = Iout × Resr
High frequency decoupling capacitors should be placed as close to the power pins of the load as physically
possible. For the decoupling requirements, please consult the capacitor manufacturers for confirmation.
2. Inductor selection
For the value of the inductor to achieve the most optimized application, it is recommended to select that rang-
ing from 4.7µH to 15µH. The small size as well as better efficiency are the main concern for portable devices
such as mobile phones. Therefore low core loss at 1.3MHz and low DCR are required for the inductor to have
better efficiency. Besides, the inductor saturation current rating should be considered to cover the inductor peak
current.
3. Diode selection
To get better efficiency, Schottky diode is a good choice for ELM621LA because of its low forward voltage
drop and fast reverse recovery. The high speed rectification is also a good characteristic of it for the high switch-
ing frequency. The current rating of the diode must meet the root mean square of the peak current and output
average current multiplication as the following: Id(RMS) ≈ (Iout × Ipeak)
The diode’s reverse breakdown voltage should be larger than the output voltage. 40V rated Schottky diodes are
recommended for outputs less than 30V, while 60V rated Schottky diodes are recommended for outputs greater
than 35V.
4. 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, following the
PCB layout guidelines below can ensure better performance of ELM621LA.
1) The bold lines of AP Circuit1 below show the main power current paths. Keep the traces short and wide.
2) To reduce resistive voltage drops and the number of via, ELM621LA and power components (Cin. 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 GND).
5) When laying out a board, minimize trace lengths between the IC and inductor, diode, input capacitor, and
out capacitor.
6) 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.
9- 5
Rev.1.2
5 Page | ||
| Páginas | Total 9 Páginas | |
| PDF Descargar | [ Datasheet ELM621LA.PDF ] | |
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