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PDF LP6342 Data sheet ( Hoja de datos )
| Número de pieza | LP6342 | |
| Descripción | 2A Step-down Converter | |
| Fabricantes | Lowpowersemi | |
| Logotipo |  |
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Preliminary Datasheet
LP6342
1.5MHz, 2A Step-down Converter
General Description
The LP6342 is a 1.5MHz constant frequency current
mode PWM step-down converter. It is ideal for portable
equipment requiring very high current up to 2A from
single-cell Lithium-ion batteries while still achieving
over 90% efficiency during peak load conditions. The
LP6342 also can run at 100% duty cycle for low dropout
operation, extending battery life in portable systems
while light load operation provides very low output
ripple for noise sensitive applications.
The LP6342 can supply up to 2A output load current
from a 2.5V to 5.5V input voltage and the output voltage
can be regulated as low as 0.6V. The high switching
frequency minimizes the size of external components
while keeping switching losses low. The internal slope
compensation setting allows the device to operate with
smaller inductor values to optimize size and provide
efficient operation.
The LP6342 is available with adjustable (0.6V to VIN)
output voltage. The device is available in a Pb-free, 3mm
x 3mm 10-lead TDFN or MSOP-10,SOP8(EP) package
and is rated over the-40°C to +85°C temperature range.
Order Information
LP6342 □ □ □
F: Pb-Free
Package Type
QV: TDFN-10
MS: MSOP-10
SP:SOP8(EP)
Features
Input Voltage Range: 2.5V to 5.5V
Output Voltage Range: 0.6V to VIN
2A Output Current
Low R(DSON) Internal Switches:130mΩ
High Efficiency :Up to 95%
100% Duty Cycle in Dropout
Low Shutdown Current: < 1 u A
1.5MHz Switching Frequency
Soft star Function
Short Circuit Protection
Thermal Fault Protection
3 m m × 3 m m TDFN-10 or MSOP-10,SOP8(EP)
Package
RoHS Compliant and 100% Lead (Pb)-Free
Applications
Portable Instruments
DSP Core Supplies
Cellular Phone and Smart mobile phone
PDA
GPS Applications
Marking Information
Please see website:www.lowpowersemi.com.
Typical Application Circuit
VIN
C1
10uF
2 Vin LP6342 SW 7
3 Vin
SW 8
1 EN
FB 5
L1
2.2uH
Vout=(R1/R2+1)*VFB
Vout_2A
R1 C2
22uF
R2
LP6342-03 Version 1.3 Datasheet Oct.-2011
www.lowpowersemi.com
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1 page  
Preliminary Datasheet
LP6342
LP6342-03 Version 1.3 Datasheet Oct.-2011
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5 Page 
Preliminary Datasheet
LP6342
A low ESR input capacitor sized for maximum RMS
cur-rent must be used. Ceramic capacitors with X5R or
X7R dielectrics are highly recommended because of their
low ESR and small temperature coefficients. A 22μF
ceramic capacitor for most applications is sufficient. A
large value may be used for improved input voltage
filtering. The maximum input capacitor RMS current is:
The input capacitor RMS ripple current varies with the
input and output voltage and will always be less than or
equal to half of the total DC load current.
current increases to match the load current demand. The
relationship of the output voltage droop during the three
switching cycles to the output capacitance can be estimated
by:
In many practical designs, to get the required ESR, a
capacitor with much more capacitance than is needed must
be selected. For both continuous or discontinuous inductor
current mode operation, the ESR of the COUT needed to
limit the ripple to ∆VO, V peak-to-peak is:
To minimize stray inductance, the capacitor should be
placed as closely as possible to the IC. This keeps the high
frequency content of the input current localized,
minimizing EMI and input voltage ripple. The proper
placement of the input capacitor (C1) can be seen in the
evaluation board layout in Figures 2.
A laboratory test set-up typically consists of two long wires
running from the bench power supply to the evaluation
board input voltage pins. The inductance of these wires,
along with the low-ESR ceramic input capacitor, can create
a high Q network that may affect converter performance.
This problem often becomes apparent in the form of
excessive ringing in the output voltage during load
transients. Errors in the loop phase and gain measurements
can also result.
Since the inductance of a short PCB trace feeding the input
voltage is significantly lower than the power leads from the
bench power supply, most applications do not exhibit this
problem. In applications where the input power source lead
inductance cannot be reduced to a level that does not affect
the converter performance, a high ESR tantalum or
aluminum electrolytic should be placed in parallel with the
low ESR, ESL bypass ceramic. This dampens the high Q
network and stabilizes the system.
Ripple current flowing through a capacitor’s ESR causes
power dissipation in the capacitor. This power dissipation
causes a temperature increase internal to the capacitor.
Excessive temperature can seriously shorten the expect-ed
life of a capacitor. Capacitors have ripple current rat-ings
that are dependent on ambient temperature and should not
be exceeded. The output capacitor ripple cur-rent is the
inductor current, IL, minus the output current, IO. The
RMS value of the ripple current flowing in the output
capacitance (continuous inductor current mode operation) is
given by:
ESL can be a problem by causing ringing in the low
megahertz region but can be controlled by choosing low
ESL capacitors, limiting lead length (PCB and capacitor),
and replacing one large device with several smaller ones
connected in parallel. In conclusion, in order to meet the
requirement of out-put voltage ripple small and regulation
loop stability, ceramic capacitors with X5R or X7R
dielectrics are recommended due to their low ESR and high
ripple current ratings. The output ripple VOUT is
determined by:
Output Capacitor Selection
The function of output capacitance is to store energy to
attempt to maintain a constant voltage. The energy is stored
in the capacitor’s electric field due to the voltage applied.
The value of output capacitance is generally selected to
limit output voltage ripple to the level required by the
specification. Since the ripple current in the output inductor
is usually determined by L, VOUT and VIN, the series
impedance of the capacitor primarily determines the out-put
voltage ripple. The three elements of the capacitor that
contribute to its impedance (and output voltage ripple) are
equivalent series resistance (ESR), equivalent series
inductance (ESL), and capacitance (C). The output voltage
droop due to a load transient is dominated by the
capacitance of the ceramic output capacitor. During a step
increase in load current, the ceramic output capacitor alone
supplies the load current until the loop responds. Within
three switching cycles, the loop responds and the inductor
LP6342-03 Version 1.3 Datasheet Oct.-2011
A 22μF ceramic capacitor can satisfy most applications.
Thermal Calculations
There are three types of losses associated with the LP6342
step-down converter: switching losses, conduction losses,
and quiescent current losses. Conduction losses are
associated with the RDS(ON) characteristics of the power
output switching devices. Switching losses are dominated
by the gate charge of the power output switching devices.
At full load, assuming continuous conduction mode (CCM),
a simplified form of the losses is given by:
IQ is the step-down converter quiescent current. The term
Tsw is used to estimate the full load step-down converter
switching losses.
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