參數(shù)資料
型號(hào)： LTC3890IGN-1#TRPBF
廠商： LINEAR TECHNOLOGY CORP
元件分類： 穩(wěn)壓器
英文描述： SWITCHING CONTROLLER, PDSO28
封裝： LEAD FREE, PLASTIC, SSOP-28
文件頁(yè)數(shù)： 10/36頁(yè)
文件大?。?/td> 498K
代理商： LTC3890IGN-1#TRPBF
LTC3890-1
18
38901f
APPLICATIONS INFORMATION
The peak-to-peak drive levels are set by the INTVCC
voltage. This voltage is typically 5.1V during start-up
(see EXTVCC Pin Connection). Consequently, logic-level
threshold MOSFETs must be used in most applications.
Pay close attention to the BVDSS specication for the
MOSFETs as well.
Selection criteria for the power MOSFETs include the
on-resistance, RDS(ON), Miller capacitance, CMILLER, input
voltage and maximum output current. Miller capacitance,
CMILLER, can be approximated from the gate charge curve
usually provided on the MOSFET manufacturers’ data
sheet. CMILLER is equal to the increase in gate charge
along the horizontal axis while the curve is approximately
at divided by the specied change in VDS. This result is
then multiplied by the ratio of the application applied VDS
to the Gate charge curve specied VDS. When the IC is
operating in continuous mode the duty cycles for the top
and bottom MOSFETs are given by:
Main Switch Duty Cycle
V
Synchronous S
OUT
IN
=
w
witch Duty Cycle
VV
V
IN
OUT
IN
=
The MOSFET power dissipations at maximum output
current are given by:
PMAIN =
VOUT
VIN
IMAX
()
2 1+
()RDS(ON) +
VIN
()
2
IMAX
2
RDR
() CMILLER
()
1
VINTVCC –VTHMIN
+
1
VTHMIN
f
()
PSYNC =
VIN –VOUT
VIN
IMAX
()
2 1+
()RDS(ON)
where δ is the temperature dependency of RDS(ON) and
RDR (approximately 2Ω) is the effective driver resistance
at the MOSFET’s Miller threshold voltage. VTHMIN is the
typical MOSFET minimum threshold voltage.
Both MOSFETs have I2R losses while the topside N-channel
equation includes an additional term for transition losses,
which are highest at high input voltages. For VIN < 20V
the high current efciency generally improves with larger
MOSFETs, while for VIN > 20V the transition losses rapidly
increase to the point that the use of a higher RDS(ON) device
with lower CMILLER actually provides higher efciency. The
synchronous MOSFET losses are greatest at high input
voltage when the top switch duty factor is low or during
a short-circuit when the synchronous switch is on close
to 100% of the period.
The term (1+ δ) is generally given for a MOSFET in the
form of a normalized RDS(ON) vs Temperature curve, but
δ = 0.005/°C can be used as an approximation for low
voltage MOSFETs.
The optional Schottky diodes D3 and D4 shown in
Figure 11 conduct during the dead-time between the
conduction of the two power MOSFETs. This prevents
the body diode of the bottom MOSFET from turning on,
storing charge during the dead-time and requiring a
reverse recovery period that could cost as much as 3%
in efciency at high VIN. A 1A to 3A Schottky is generally
a good compromise for both regions of operation due
to the relatively small average current. Larger diodes
result in additional transition losses due to their larger
junction capacitance.
CIN and COUT Selection
The selection of CIN is simplied by the 2-phase architec-
ture and its impact on the worst-case RMS current drawn
through the input network (battery/fuse/capacitor). It can
beshown that theworst-case capacitorRMScurrentoccurs
when only one controller is operating. The controller with
the highest (VOUT)(IOUT) product needs to be used in the
formula shown in Equation 1 to determine the maximum
相關(guān)PDF資料
PDF描述
LTC3890IGN-1#PBF SWITCHING CONTROLLER, PDSO28
LTC3890MPUH#TRPBF DUAL SWITCHING CONTROLLER, 585 kHz SWITCHING FREQ-MAX, PQCC32
LTC3890EUH#PBF DUAL SWITCHING CONTROLLER, 585 kHz SWITCHING FREQ-MAX, PQCC32
LTC3890IUH#TRPBF DUAL SWITCHING CONTROLLER, 585 kHz SWITCHING FREQ-MAX, PQCC32
LTC3890HUH#PBF DUAL SWITCHING CONTROLLER, 585 kHz SWITCHING FREQ-MAX, PQCC32
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