Linear Technology LT3740EDHC Quick Start Manual

Wide operating range, valley mode, no rsense synchronous step-down controller

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No R
SENSE

DESCRIPTION

Demonstration circuit 947 is a Wide Operating
Range, Valley Mode, No R
Step-Down Controller featuring the LT3740EDHC.
It produces 1.8VDC for loads up to 10A from an
input range of 3-15VDC, switching at a fixed fre-
quency of 300KHz.
In order to operate from an input voltage as low as
3V, the circuit must provide adequate voltage to
drive the external power MOSFETs. To this end,
the LT3740 includes an on-chip step-up converter
to provide a bias about 7V above the input voltage
to power the top MOSFET gate driver. The stock
configuration of DC947 also uses this bias to
power the bottom gate drive circuit, but pads have
been added to the circuit board to power the bot-
tom gate drive from another source.
The LT3740 is equipped with an external reference
input that allows the user to override the 0.8V in-
ternal reference with any lower value, allowing full

PERFORMANCE SUMMARY

SYMBOL PARAMETER
V
Input Supply Range
IN
V
Output Voltage Range
OUT
I
Output current
OUT
V
Output Ripple
RIPPLE

QUICK START PROCEDURE

Demonstration circuit 947 is easy to set up to
evaluate the performance of the LT3740EDHC.
Wide Operating Range, Valley Mode,
™ Synchronous Step-Down Controller
™ Synchronous
SENSE
Specifications are at TA = 25° C
CONDITIONS
V
= 3.0 – 15.0V, I
IN
V
= 3.0 – 15.0V, V
IN
V
= 3.0 – 15.0V, I
IN
DEMO CIRCUIT 947
QUICK START GUIDE
control of the output voltage during operation, out-
put voltage tracking or soft-start.
In addition, the LT3740 has three current limit lev-
els that can be chosen by connecting the RANGE
pin to ground, leaving it open circuit, or tying to the
input.
DC947 is equipped with jumpers that allow the
user to select among soft-start options and refer-
ence voltage sources.
been added to DC947 in order to facilitate input
voltages higher than 15V and No R
tion.
Design files for this circuit board are available.
Call the LTC factory.
and LT are registered trademarks of Linear Technology Corporation. No R
is a trademark of Linear Technology Corporation. Other product names may be
trademarks of the companies that manufacture the products.
= 0-10A
LOAD
= 1.8V
OUT
= 0-10A
LOAD
Refer to Figure 1 for proper measurement equip-
ment setup and follow the procedure below:
LT3740EDHC
LT3740EDHC
Unpopulated pads have
™ opera-
SENSE
MIN
TYP
MAX
UNITS
3.0
15.0
1.76
1.84
0
10.0
20
SENSE
V
V
A
mV
1

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Summary of Contents for Linear Technology LT3740EDHC

  • Page 1 LT are registered trademarks of Linear Technology Corporation. No R SENSE is a trademark of Linear Technology Corporation. Other product names may be input that allows the user to override the 0.8V in- trademarks of the companies that manufacture the products.
  • Page 2 LT3740EDHC 4. Turn on the power at the input. Make sure that NOTE. When measuring the output voltage ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. the input voltage is between 3 and 15V.
  • Page 3 LT3740EDHC Figure 2. Measuring Input/Output Ripple OPERATION The LT3740 is a current-mode synchronous buck and thus save power. To do this, move the zero controller that can accept input voltages as low as ohm resistor at location R32 to R31 and add a 1uF 2.2V, and as high as 22V, but still provides at least...
  • Page 4 LT3740EDHC dominate the behavior of the demo board output. DC947A is equipped with many optional compo- To observe the behavior of the output when under nents to facilitate the implementation of many op- VOLTAGE_SS control, simply change the RC time tional functions.
  • Page 5 LT3740EDHC...
  • Page 6 Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Analog Devices Inc. DC947A...

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