LTC3728LEGN-1#PBF Linear Technology, LTC3728LEGN-1#PBF Datasheet - Page 22

• Manufacturer Part Number: LTC3728LEGN-1#PBF
• Description: IC REG SYNC DUAL 28-SSOP
• Manufacturer: Linear Technology
• Series: PolyPhase®r
• Type: Step-Down (Buck)r

Specifications of LTC3728LEGN-1#PBF

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 0.8 ~ 7 V
• Current - Output: 3A
• Frequency - Switching: 250kHz ~ 550kHz
• Voltage - Input: 4.5 ~ 28 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -

APPLICATIONS INFORMATION
LTC3728L-1
If V
temporary continuous switching operation until V
again above its minimum.
In order to prevent erratic operation if no external connec-
tions are made to the FCB pin, the FCB pin has a 0.18μA
internal current source pulling the pin high. Include this
current when choosing resistor values R5 and R6.
The following table summarizes the possible states avail-
able on the FCB pin:
Table 1
FCB PIN
0V to 0.75V
0.85V < V
Feedback Resistors
>4.8V
Voltage Positioning
Voltage positioning can be used to minimize peak-to-peak
output voltage excursions under worst-case transient
loading conditions. The open-loop DC gain of the control
loop is reduced depending upon the maximum load step
specifi cations. Voltage positioning can easily be added
to either or both controllers by loading the I
a resistive divider having a Thevenin equivalent voltage
source equal to the midpoint operating voltage range of
the error amplifi er, or 1.2V (see Figure 8).
The resistive load reduces the DC loop gain while main-
taining the linear control range of the error amplifi er.
The maximum output voltage deviation can theoretically
be reduced to half or alternatively the amount of output
22
SEC
FCB
drops below this level, the FCB voltage forces
< 4.3V
CONDITION
Forced Continuous Both Controllers
(Current Reversal Allowed—
Burst Inhibited)
Minimum Peak Current Induces
Burst Mode Operation
No Current Reversal Allowed
Regulating a Secondary Winding
Burst Mode Operation Disabled
Constant Frequency Mode Enabled
No Current Reversal Allowed
No Minimum Peak Current
TH
pin with
SEC
is
capacitance can be reduced for a particular application. A
complete explanation is included in Design Solutions 10.
(See www.linear.com)
Effi ciency Considerations
The percent effi ciency 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 effi ciency and which change would
produce the most improvement. Percent effi ciency can
be expressed as:
where L1, L2, etc. are the individual losses as a percent-
age of input power.
Although all dissipative elements in the circuit produce
losses, four main sources usually account for most of the
losses in LTC3728L-1 circuits: 1) IC V
loading on the 3.3V internal regulator), 2) INTV
tor current, 3) I
losses.
1. The V
supply current given in the Electrical Characteristics table,
which excludes MOSFET driver and control currents; the
second is the current drawn from the 3.3V linear regulator
output. V
loss.
%Effi ciency = 100% – (L1 + L2 + L3 + ...)
IN
IN
Figure 8. Active Voltage Positioning
Applied to the LTC3728L-1
current has two components: the fi rst is the DC
INTV
current typically results in a small (<0.1%)
CC
R
R
2
T2
T1
R losses, 4) Topside MOSFET transition
R
C
C
C
I
TH
LTC3728L-1
3728L1 F08
IN
current (including
CC
regula-
3728l1fc