LT3782AIFE データシートの表示（PDF） - Linear Technology

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LT3782AIFE

2-Phase Step-Up DC/DC Controller

Linear Technology 

LT3782A

APPLICATIONS INFORMATION

With a 200ns one-shot timer on chip, the LT3782A provides

flexibility on the external sync pulse width. The sync pulse

threshold is about 1.2V (Figure 1). This pin can be floated

when the sync function is not used.

Current Limit

Current limit is set by the 63mV threshold across SEN1P,

SEN1N for channel one and SEN2P, SEN2N for channel

two. By connecting an external resistor RS (see Block

Diagram), the current limit is set for 63mV/RS. RS should

be placed very close to the power switch with very short

traces. A low pass RC filter is needed across RS to filter out

the switching spikes. Good Kelvin sensing is required for

accurate current limit. The input bypass capacitor ground

should be at the same ground point of the current sense

resistor to minimize the ground current path.

Synchronous Rectifier Switches

For high output voltage applications, the power loss of the

catch diodes are relatively small because of high duty cycle.

If diodes power loss or heat is a concern, the LT3782A

provides PWM signals through SGATE1 and SGATE2 pins

to drive external MOSFET drivers for synchronous recti-

fier operation. Note that SGATE drives the top switch and

BGATE drives the bottom switch. To avoid cross conduction

between top and bottom switches, the BGATE turn-on is

delayed 100ns (when DELAY pin is tied to RSET pin) from

SGATE turn-off (see Figure 2). If a longer delay is needed

to compensate for the propagation delay of external gate

driver, a resistor divider can be used from RSET to ground to

program VDELAY for the longer delay needed. For example,

for a switching frequency of 250kHz and delay of 150ns,

5V TO 20V

5k

SYNC

LT3782A

VN2222

PULSE WIDTH > 200ns

3782A F01

Figure 1. Synchronizing with External Clock

BGATE1

SGATE1 DELAY

SET

3782A F02

Figure 2. Delay Timing

3782af

9

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