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PDF LMR62014 Data sheet ( Hoja de datos )
| Número de pieza | LMR62014 | |
| Descripción | Step-Up Voltage Regulator | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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LMR62014
October 5, 2011
SIMPLE SWITCHER® 20Vout, 1.4A Step-Up Voltage
Regulator in SOT-23
Features
■ Input voltage range of 2.7V to 14V
■ Output voltage up to 20V
■ Switch current up to 1.4A
■ 1.6 MHz switching frequency
■ Low shutdown Iq, <1 µA
■ Cycle-by-cycle current limiting
■ Internally compensated
■ SOT23-5 packaging (2.92 x 2.84 x 1.08mm)
■ Fully enabled for WEBENCH® Power Designer
Performance Benefits
■ Extremely easy to use
■ Tiny overall solution reduces system cost
Applications
■ Boost Conversions from 3.3V, 5V, and 12V Rails
■ Space Constrained Applications
■ Embedded Systems
■ LCD Displays
■ LED Applications
30167410
System Performance
Efficiency vs Load Current
VIN = 3.3V, VOUT = 12V
30167439
Efficiency vs Load Current
VIN = 5V, VOUT = 12V
© 2011 National Semiconductor Corporation 301674
30167457
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1 page  
Typical Performance Characteristics Unless otherwise specified: VIN = 5V, SHDN pin tied to VIN.
Iq Vin (Active) vs Temperature
Oscillator Frequency vs Temperature
30167402
Max. Duty Cycle vs Temperature
30167405
Iq Vin (Idle) vs Temperature
30167407
Feedback Bias Current vs Temperature
30167425
Feedback Voltage vs Temperature
30167426
5
30167427
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5 Page 
30167450
Switch Current Limit vs Duty Cycle
CALCULATING LOAD CURRENT
As shown in the figure which depicts inductor current, the load
current is related to the average inductor current by the rela-
tion:
ILOAD = IIND(AVG) x (1 - DC)
Where "DC" is the duty cycle of the application. The switch
current can be found by:
ISW = IIND(AVG) + ½ (IRIPPLE)
Inductor ripple current is dependent on inductance, duty cy-
cle, input voltage and frequency:
IRIPPLE = DC x (VIN-VSW) / (f x L)
combining all terms, we can develop an expression which al-
lows the maximum available load current to be calculated:
The equation shown to calculate maximum load current takes
into account the losses in the inductor or turn-OFF switching
losses of the FET and diode. For actual load current in typical
applications, we took bench data for various input and output
voltages that displayed the maximum load current available
for a typical device in graph form:
30167448
Max. Load Current (typ) vs VIN
DESIGN PARAMETERS VSW AND ISW
The value of the FET "ON" voltage (referred to as VSW in the
equations) is dependent on load current. A good approxima-
tion can be obtained by multiplying the "ON Resistance" of
the FET times the average inductor current.
FET on resistance increases at VIN values below 5V, since
the internal N-FET has less gate voltage in this input voltage
range (see Typical performance Characteristics curves).
Above VIN = 5V, the FET gate voltage is internally clamped to
5V.
The maximum peak switch current the device can deliver is
dependent on duty cycle. For higher duty cycles, see Typical
performance Characteristics curves.
THERMAL CONSIDERATIONS
At higher duty cycles, the increased ON time of the FET
means the maximum output current will be determined by
power dissipation within the LMR62014 FET switch. The
switch power dissipation from ON-state conduction is calcu-
lated by:
P(SW) = DC x IIND(AVE)2 x RDS(ON)
There will be some switching losses as well, so some derating
needs to be applied when calculating IC power dissipation.
INDUCTOR SUPPLIERS
Recommended suppliers of inductors for this product include,
but are not limited to Sumida, Coilcraft, Panasonic, TDK and
Murata. When selecting an inductor, make certain that the
continuous current rating is high enough to avoid saturation
at peak currents. A suitable core type must be used to mini-
mize core (switching) losses, and wire power losses must be
considered when selecting the current rating.
SHUTDOWN PIN OPERATION
The device is turned off by pulling the shutdown pin low. If this
function is not going to be used, the pin should be tied directly
to VIN. If the SHDN function will be needed, a pull-up resistor
must be used to VIN (approximately 50k-100kΩ recommend-
ed). The SHDN pin must not be left unterminated.
11 www.national.com
Free Datasheet http://www.datasheet4u.com/
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet LMR62014.PDF ] | |
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