lt3782aeufd Linear Technology Corporation, lt3782aeufd Datasheet - Page 9

• Manufacturer Part Number: lt3782aeufd
• Description: 2-phase Step-up Dc/dc Controller
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
With a 200ns one-shot timer on chip, the LT3782A provides
fl exibility on the external sync pulse width. The sync pulse
threshold is about 1.2V (Figure 1). This pin can be fl oated
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 R
Diagram), the current limit is set for 63mV/R
be placed very close to the power switch with very short
traces. A low pass R
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.
C
fi lter is needed across R
Figure 1. Synchronizing with External Clock
PULSE WIDTH > 200ns
S
S
S
. R
(see Block
to fi lter out
SGATE1
S
Figure 2. Delay Timing
should
BGATE1
SET
5V TO 20V
DELAY
VN2222
5k
Synchronous Rectifi er 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-
fi er 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 R
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 R
program V
for a switching frequency of 250kHz and delay of 150ns,
SYNC
3782A F02
LT3782A
DELAY
3782A F01
for the longer delay needed. For example,
LT3782A
SET
SET
to ground to
pin) from
3782af
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