參數資料
型號: LTC3714EG
廠商: LINEAR TECHNOLOGY CORP
元件分類: 穩(wěn)壓器
英文描述: Intel Compatible, Wide Operating Range, Step-Down Controller with Internal Op Amp
中文描述: 2 A SWITCHING CONTROLLER, PDSO28
封裝: 5.30 MM, PLASTIC, SSOP-28
文件頁數: 16/28頁
文件大?。?/td> 345K
代理商: LTC3714EG
LTC3714
16
3714f
APPLICATIOU
Fault Conditions: Current Limit and Foldback
The maximum inductor current is inherently limited in a
current mode controller by the maximum sense voltage. In
the LTC3714, the maximum sense voltage is controlled by
the voltage on the V
RNG
pin. With valley current control,
the maximum sense voltage and the sense resistance
determine the maximum allowed inductor valley current.
The corresponding output current limit is:
W
U
U
I
V
R
*
I
LIMIT
SNS MAX
(
DS ON
(
T
L
=
+
)
)
ρ
1
2
The current limit value should be checked to ensure that
I
LIMIT(MIN)
> I
OUT(MAX)
. The minimum value of current limit
generally occurs with the lowest V
IN
at the highest ambient
temperature. Note that it is important to check for self-
consistency between the assumed junction temperature
and the resulting value of I
LIMIT
which heats the MOSFET
switches.
Caution should be used when setting the current limit
based upon the R
DS(ON)
of the MOSFETs. The maximum
current limit is determined by the minimum MOSFET on-
resistance. Data sheets typically specify nominal and
maximum values for R
DS(ON)
, but not a minimum. A
reasonable assumption is that the minimum R
DS(ON)
lies
the same amount below the typical value as the maximum
lies above it. Consult the MOSFET manufacturer for further
guidelines.
To further limit current in the event of a short circuit to
ground, the LTC3714 includes foldback current limiting. If
the output falls by more than 50%, then the maximum
sense voltage is progressively lowered to about one sixth
of its full value.
Minimum Off-Time and Dropout Operation
The minimum off-time t
OFF(MIN)
is the smallest amount of
time that the LTC3714 is capable of turning on the bottom
MOSFET, tripping the current comparator and turning the
MOSFET back off. This time is generally about 250ns. The
minimum off-time limit imposes a maximum duty cycle of
t
ON
/(t
ON
+ t
OFF(MIN)
). If the maximum duty cycle is reached,
due to a dropping input voltage for example, then the
output will drop out of regulation. The minimum input
voltage to avoid dropout is:
V
V
t
t
t
IN MIN
(
OUT
ON
OFF MIN
(
ON
)
)
=
+
Output Voltage Programming
The output voltage is digitally set to levels between 0.6V
and 1.75V using the voltage identification (VID) inputs
VID0-VID4. An internal 5-bit DAC configured as a preci-
sion resistive voltage divider sets the output voltage in
increments according to Table 1. The VID codes are
compatible with Intel Mobile Pentium
III processor speci-
fications. Each VID input is pulled up by an internal 2.5
μ
A
current source from the INTV
CC
supply and includes a
series diode to prevent damage from VID inputs that
exceed the supply.
*Use R
SENSE
value here if a sense resistor is connected between SENSE and PGND.
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