Datasheet > LTC1265-5_15

LTC1265-5_15

更新时间： 2022-02-26 11:51:49

品牌	Logo	应用领域
凌特 - Linear		/
页数	文件大小	规格书
16页	243K
描述
1.2A, High Efficiency Step-Down DC/DC Converter

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LTC1265-5_15 数据手册

LTC1265/LTC1265-3.3/LTC1265-5

FU CTIO AL DIAGRA

(Pin 9 connection shown for LTC1265-3.3 and LTC1265-5; change create LTC1265)

PWR V

1, 13

–

SENSE

14 SW

12 PGND

–

ADJUSTABLE

VERSION

–

SLEEP

25mV TO 150mV

5pF

–

13k

TH2

100k

–

TH1

0UT

–

REFERENCE

SHDN

OFF-TIME

CONTROL

–

SENSE

1265 FD

11 SGND

OPERATIO

(Refer to Functional Diagram)

The LTC1265 uses a constant off-time architecture to

switch its internal P-channel power MOSFET. The off time

is set by an external timing capacitor at C_T(Pin 5). The

operatingfrequencyisthendeterminedbytheofftimeand

the voltage across the shunt reaches the comparator’s

threshold value, its output signal will change state, setting

theflipflopandturningtheinternalP-channelMOSFEToff.

The timing capacitor connected to Pin 5 is now allowed to

discharge at a rate determined by the off-time controller.

the difference between V_INand V_OUT

The output voltage is set by an internal resistive divider

(LTC1265-3.3 and LTC1265-5) connected to SENSE^–

(Pin 7) or an external divider returned to V_FB(Pin 9 for

LTC1265). A voltage comparator V, and a gain block G,

compare the divided output voltage with a reference

voltage of 1.25V.

When the voltage on the timing capacitor has discharged

past V_TH1, comparator T trips, sets the flip flop and causes

the switch to turn on. Also, the timing capacitor is re-

charged. The inductor current will again ramp up until the

current comparator C trips. The cycle then repeats.

When the load current increases, the output voltage de-

creases slightly. This causes the output of the gain stage

(Pin 6) to increase the current comparator threshold, thus

tracking the load current.

Tooptimizeefficiency,theLTC1265automaticallyswitches

between continuous and Burst Mode operation. The volt-

age comparator is the primary control element when the

device is in Burst Mode operation, while the gain block

controls the output voltage in continuous mode.

When the load is relatively light, the LTC1265 automati-

cally goes into Burst Mode operation. The current loop is

interrupted when the output voltage exceeds the desired

regulated value. The hysteretic voltage comparator V trips

when V_OUTis above the desired output voltage, shutting

off the switch and causing the capacitor to discharge. This

When the load is heavy, the LTC1265 is in continuous

operation. During the switch ON time, current comparator

C monitors the voltage between Pins 7 and 8 connected

across an external shunt in series with the inductor. When

1 2 3 456 7 8...16

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