LTC3728LEGN Linear Technology, LTC3728LEGN Datasheet - Page 27
![IC REG SW DUAL 2PH STPDWN 28SSOP](/photos/6/59/65971/161-28-ssop_sml.jpg)
LTC3728LEGN
Manufacturer Part Number
LTC3728LEGN
Description
IC REG SW DUAL 2PH STPDWN 28SSOP
Manufacturer
Linear Technology
Series
PolyPhase®r
Type
Step-Down (Buck)r
Datasheet
1.LTC3728LXCUHPBF.pdf
(36 pages)
Specifications of LTC3728LEGN
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
Contains lead / RoHS non-compliant
Power - Output
-
Available stocks
Company
Part Number
Manufacturer
Quantity
Price
Company:
Part Number:
LTC3728LEGN
Manufacturer:
LINEAR
Quantity:
84
Part Number:
LTC3728LEGN
Manufacturer:
LINEAR
Quantity:
20 000
Company:
Part Number:
LTC3728LEGN#2CQPBF
Manufacturer:
LT
Quantity:
3 048
Company:
Part Number:
LTC3728LEGN#PBF
Manufacturer:
KEC
Quantity:
1 130
Part Number:
LTC3728LEGN#PBF
Manufacturer:
LINEAR/凌特
Quantity:
20 000
Company:
Part Number:
LTC3728LEGN#TRPBF
Manufacturer:
LT
Quantity:
3 048
Part Number:
LTC3728LEGN#TRPBF
Manufacturer:
LT/凌特
Quantity:
20 000
Company:
Part Number:
LTC3728LEGN-1#PBF
Manufacturer:
LT
Quantity:
189
APPLICATIONS INFORMATION
of full-load current having a rise time of 1μs to 10μs will
produce output voltage and I
give a sense of the overall loop stability without break-
ing the feedback loop. Placing a power MOSFET directly
across the output capacitor and driving the gate with an
appropriate signal generator is a practical way to produce
a realistic load step condition. The initial output voltage
step resulting from the step change in output current may
not be within the bandwidth of the feedback loop, so this
signal cannot be used to determine phase margin. This
is why it is better to look at the I
in the feedback loop and is the fi ltered and compensated
control loop response. The gain of the loop will be in-
creased by increasing R
will be increased by decreasing C
the same factor that C
will be kept the same, thereby keeping the phase shift the
same in the most critical frequency range of the feedback
loop. The output voltage settling behavior is related to the
stability of the closed-loop system and will demonstrate
the actual overall supply performance.
A second, more severe transient is caused by switching
in loads with large (>1μF) supply bypass capacitors. The
discharged bypass capacitors are effectively put in parallel
with C
alter its delivery of current quickly enough to prevent this
sudden step change in output voltage if the load switch
resistance is low and it is driven quickly. If the ratio of
C
should be controlled so that the load rise time is limited
to approximately 25 • C
require a 250μs rise time, limiting the charging current
to about 200mA.
LOAD
OUT
to C
, causing a rapid drop in V
OUT
is greater than 1:50, the switch rise time
C
LOAD
is decreased, the zero frequency
C
and the bandwidth of the loop
. Thus a 10μF capacitor would
TH
pin waveforms that will
C
TH
. If R
OUT
pin signal, which is
. No regulator can
Figure 9. Automotive Application Protection
C
12V
TRANSIENT VOLTAGE
SUPPRESSOR
GENERAL INSTRUMENT
1.5KA24A
is increased by
50A I
PK
RATING
V
Automotive Considerations: Plugging into the
Cigarette Lighter
As battery-powered devices go mobile, there is a natural
interest in plugging into the cigarette lighter in order to
conserve or even recharge battery packs during operation.
But before you connect, be advised: you are plugging
into the supply from hell. The main power line in an
automobile is the source of a number of nasty potential
transients, including load-dump, reverse-battery and
double-battery.
Load-dump is the result of a loose battery cable. When the
cable breaks connection, the fi eld collapse in the alterna-
tor can cause a positive spike as high as 60V which takes
several hundred milliseconds to decay. Reverse-battery is
just what it says, while double-battery is a consequence of
tow truck operators fi nding that a 24V jump start cranks
cold engines faster than 12V.
The network shown in Figure 9 is the most straightforward
approach to protect a DC/DC converter from the ravages of
an automotive power line. The series diode prevents current
from fl owing during reverse-battery, while the transient
suppressor clamps the input voltage during load-dump.
Note that the transient suppressor should not conduct
during double-battery operation, but must still clamp the
input voltage below breakdown of the converter. Although
the LTC3728L/LTC3728LX have a maximum input voltage
of 30V, most applications will also be limited to 30V by
the MOSFET BVD
IN
LTC3728LX
LTC3728L/
3728 F09
LTC3728L/LTC3728LX
SS
.
27
3728lxfe