LT1961IMS8E-PBF データシートの表示（PDF） - Linear Technology

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LT1961IMS8E-PBF

1.5A, 1.25MHz Step-Up Switching Regulator

Linear Technology 

LT1961

PIN FUNCTIONS

FB: The feedback pin is used to set output voltage using an

external voltage divider that generates 1.2V at the pin with

the desired output voltage. If required, the current limit

can be reduced during start up when the FB pin is below

0.5V (see the Current Limit Foldback graph in the Typical

Performance Characteristics section). An impedance of

less than 5kΩ at the FB pin is needed for this feature to

operate.

VIN: This pin powers the internal circuitry and internal

regulator. Keep the external bypass capacitor close to this

pin.

GND: Short GND pins 3 and 4 and the exposed pad on the

PCB. The GND is the reference for the regulated output, so

load regulation will suffer if the “ground” end of the load

is not at the same voltage as the GND of the IC. This

condition occurs when the load current flows through the

metal path between the GND pins and the load ground

point. Keep the ground path short between the GND pins

and the load and use a ground plane when possible. Keep

the path between the input bypass and the GND pins short.

The exposed pad should be attached to a large copper area

to improve thermal resistance.

VSW: The switch pin is the collector of the on-chip power

NPN switch and has large currents flowing through it.

Keep the traces to the switching components as short as

possible to minimize radiation and voltage spikes.

SYNC: The sync pin is used to synchronize the internal

oscillator to an external signal. It is directly logic compat-

ible and can be driven with any signal between 20% and

80% duty cycle. The synchronizing range is equal to initial

operating frequency, up to 2MHz. See Synchronization

section in Applications Information for details. When not

in use, this pin should be grounded.

SHDN: The shutdown pin is used to turn off the regulator

and to reduce input drain current to a few microamperes.

The 1.35V threshold can function as an accurate under-

voltage lockout (UVLO), preventing the regulator from

operating until the input voltage has reached a predeter-

mined level. Float or pull high to put the regulator in the

operating mode.

VC: The VC pin is the output of the error amplifier and the

input of the peak switch current comparator. It is normally

used for frequency compensation, but can do double duty

as a current clamp or control loop override. This pin sits

at about 0.3V for very light loads and 0.9V at maximum

load.

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