參數(shù)資料
型號(hào): LTC3608IWKG#TRPBF
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: 8 A SWITCHING REGULATOR, PQCC52
封裝: 8 X 7 MM, LEAD FREE, PLASTIC, QFN-52
文件頁數(shù): 9/26頁
文件大?。?/td> 464K
代理商: LTC3608IWKG#TRPBF
LTC3608
3608fc
applications inForMation
EfficiencyConsiderations
The percent efficiency of a switching regulator is equal to
the output power divided by the input power times 100%.
It is often useful to analyze individual losses to determine
what is limiting the efficiency and which change would
produce the most improvement. Although all dissipative
elements in the circuit produce losses, four main sources
account for most of the losses in LTC3608 circuits:
1. DC I2R losses. These arise from the resistance of the
internal resistance of the MOSFETs, inductor and PC
board traces and cause the efficiency to drop at high
outputcurrents.Incontinuousmodetheaverageoutput
currentflowsthroughL,butischoppedbetweenthetop
and bottom MOSFETs. The DC I2R loss for one MOSFET
can simply be determined by [RDS(ON) + RL] IO.
2. Transition loss. This loss arises from the brief amount
of time the top MOSFET spends in the saturated re-
gion during switch node transitions. It depends upon
the input voltage, load current, driver strength and
MOSFET capacitance, among other factors. The loss
is significant at input voltages above 20V and can be
estimated from:
Transition Loss
(1.7A–1) VIN2 IOUT CRSS f
3. INTVCC current. This is the sum of the MOSFET driver
and control currents. This loss can be reduced by sup-
plying INTVCC current through the EXTVCC pin from a
high efficiency source, such as an output derived boost
network or alternate supply if available.
4. CIN loss. The input capacitor has the difficult job of
filtering the large RMS input current to the regulator. It
must have a very low ESR to minimize the AC I2R loss
and sufficient capacitance to prevent the RMS current
from causing additional upstream losses in fuses or
batteries.
Other losses, including COUT ESR loss, Schottky diode D1
conduction loss during dead time and inductor core loss
generally account for less than 2% additional loss.
When making adjustments to improve efficiency, the input
current is the best indicator of changes in efficiency. If you
make a change and the input current decreases, then the
efficiency has increased. If there is no change in input
current, then there is no change in efficiency.
CheckingTransientResponse
The regulator loop response can be checked by looking
at the load transient response. Switching regulators take
several cycles to respond to a step in load current. When
a load step occurs, VOUT immediately shifts by an amount
equal to
ΔILOAD (ESR), where ESR is the effective series
resistance of COUT. ΔILOAD also begins to charge or dis-
chargeCOUTgeneratingafeedbackerrorsignalusedbythe
regulator to return VOUT to its steady-state value. During
this recovery time, VOUT can be monitored for overshoot
or ringing that would indicate a stability problem. The ITH
pin external components shown in Figure 6 will provide
adequate compensation for most applications. For a
detailed explanation of switching control loop theory see
Application Note 76.
3.3V OR 5V
RUN/SS
VIN
INTVCC
RUN/SS
D1
(5a)
(5b)
D2*
CSS
RSS*
CSS
*OPTIONAL TO OVERRIDE
OVERCURRENT LATCHOFF
RSS*
3608 F05
2N7002
Figure5.RUN/SSPinInterfacingwithLatchoffDefeated
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