LTC3442EDE-TRPBF Просмотр технического описания (PDF) - Linear Technology

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LTC3442EDE-TRPBF

Micropower Synchronous Buck-Boost DC/DC Converter with Automatic Burst Mode Operation

Linear Technology 

LTC3442

TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise specified).

Transition from Burst Mode

Operation to Fixed Frequency Mode

VOUT

50mV/DIV

INDUCTOR

CURRENT

0.5A/DIV

200µs/DIV

COUT = 100µF

LOW ESR TANTALUM

3442 G22

Pulsed Overload Using Average Input

Current Limit

VOUT

2V/DIV

RLIM PIN

0.5V/DIV

INDUCTOR

CURRENT

0.5A/DIV

RLIM = 133k

CLIM = .001µF

1ms/DIV

3442 G23

PIN FUNCTIONS

SHDN/SS (Pin 1): Combined Soft-Start and Shutdown.

Applied voltage <0.4V shuts down the IC. Tie to >1.4V to

enable the IC and >2.4V to ensure the error amp is not

clamped from soft-start. For Burst Mode operation, this

pin must be pulled up to within 0.5V of VIN. An RC network

from the shutdown command signal to this pin will provide

a soft-start function by limiting the rise time of the VC pin.

RT (Pin 2): Programs the Frequency of the Internal Os-

cillator. Place a resistor from this pin to ground. See the

Applications Information section for component value

selection.

SGND (Pin 3): Signal Ground for the IC.

SW1 (Pin 4): Switch Pin Where Internal Switches A and B

Are Connected. Connect inductor from SW1 to SW2. An

optional Schottky diode can be connected from SW1 to

ground for a moderate efficiency improvement. Minimize

trace length to reduce EMI.

PGND (Pin 5, 13): Power Ground for the Internal NMOS

Power Switches. The exposed pad must be soldered to

PCB ground to provide both electrical contact and a good

thermal contact to the PCB.

SW2 (Pin 6): Switch Pin Where Internal Switches C

and D Are Connected. An optional Schottky diode can be

connected from SW2 to VOUT for a moderate efficiency

improvement. Minimize trace length to reduce EMI.

BURST (Pin 7): Used to Set the Automatic Burst Mode Op-

eration Threshold. Place a resistor and capacitor in parallel

from this pin to ground. See the Applications Information

section for component value selection. For manual control,

ground the pin to force Burst Mode operation, connect to

VOUT to force fixed frequency mode.

VOUT (Pin 8): Output of the Synchronous Rectifier. A filter

capacitor is placed from VOUT to GND. A ceramic bypass

capacitor is recommended as close to the VOUT and GND

pins as possible.

VIN (Pin 9): Input Supply Pin. Internal VCC for the IC. A

10µF ceramic capacitor is recommended as close to VIN

and SGND as possible.

RLIM (Pin 10): Sets the Average Input Current Limit

Threshold. Place a resistor and capacitor in parallel from

this pin to ground. See the Applications Information sec-

tion for component value selection.

VC (Pin 11): Error Amp Output. A frequency compensation

network is connected from this pin to FB to compensate

the loop. During Burst Mode operation, VC is internally

connected to a hold circuit.

FB (Pin 12): Feedback Pin. Connect resistor divider tap

here. The output voltage can be adjusted from 2.4V to

5.25V. The feedback reference voltage is typically 1.22V.

3442fb

6

For more information www.linear.com/LTC3442

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