Linear Technology DC2117A Demo Manual

Description
Demonstration circuit 2117A is a single output high volt-
age nonisolated synchronous step-down converter that
drives all N-channel MOSFET power stage. It features the
LTC3895EFE, a high voltage step-down DC/DC controller
housed in a TSSOP-38 package with several pins removed
for high voltage spacing.
This DC2117A operates over an input voltage range from
14V to 130V, while the LTC
This demo board produces a 12V output voltage with up to
a 5A output current, and is configured with a sense resistor
for over current protection and has optional DCR sensing.
To prevent high on-chip power dissipation in high input
voltage applications, the LTC3895 includes an NDRV pin
which drives the gate of an optional external N-channel
MOSFET acting as a low dropout linear regulator to supply
IC power and is an option on this board.
An internal charge pump allows for 100% duty cycle op-
eration in dropout, a useful feature when powered from
a battery during discharge. The LTC3895's powerful 1Ω
performance summary
Table 1.
PARAMETER
Input Voltage Range
Output Voltage V
OUT
Maximum Output Current I
OUT(MAX)
Default Operating Frequency (Typical)
External Clock Sync Frequency Range
Typical Full Load Efficiency (See Figure 4)
*Important Note: 60V or higher voltage can result in an electric shock if care is not taken. Also, hot plugging the circuit to a power supply that has more
than 40V present at its output can produce a high voltage transient exceeding the absolute maximum input voltage which can damage the DC2117A
board.
3895 can operate up to 150V.
®
Specifications are at T
CONDITIONS
DC Up to 150V
V = 14~130V, I
IN
V = 14~130V
IN
V = 48V, V
IN OUT
DEMO MANUAL DC2117A
High Input Voltage
Synchronous Buck Converter
N-channel MOSFET gate drivers can be adjusted from
5V to 10V to enable the use of logic- or standard-level
MOSFETs to maximize efficiency. The EXTV
the LTC3895 to be powered from the output of the switch-
ing regulator or other available source, reducing power
dissipation and improving efficiency.
A mode selector allows the DC2117A to operate in forced
continuous operation, pulse-skipping or low ripple Burst
Mode operation during light loads. Additional features
®
include a power good output signal, a PLLIN, PHASEMD
and CLKOUT for multiphase operation.
The LTC3895 data sheet gives a complete description of
the part, operation and application information and must
be read in conjunction with this demo board manual.
Design files for this circuit board are available at
http://www.linear.com/demo/DC2117A
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
= 25°C
A
Transient
PK
= 0~5A, JP4: FCM
OUT
= 12V, I = 5A, f = 150kHz
OUT SW
LTC3895EFE
pin permits
CC
UNITS
14V ~ 130V
12V ± 2% (11.76V ~ 12.24V)
5A
150kHz
75kHz to 850kHz
94.9%
dc2117af
1