DC1307A Linear Technology, DC1307A Datasheet - Page 13

• Manufacturer Part Number: DC1307A
• Description: BOARD EVAL LTM8027
• Manufacturer: Linear Technology
• Series: LTM®, uModule®r

Specifications of DC1307A

• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Power - Output: 48W
• Current - Output: 4A
• Voltage - Input: 16 ~ 60 V
• Regulator Topology: Buck
• Frequency - Switching: 300kHz
• Board Type: Fully Populated
• Utilized Ic / Part: LTM8027
• Lead Free Status / RoHS Status: Not applicable / Not applicable
• Voltage - Output: -

APPLICATIONS INFORMATION
Table 1 lists typical resistor values for common operating
frequencies.
Table 1. R
It is recommended that the user apply the R
in Table 2 for the input and output operating condition.
System level or other considerations, however, may ne-
cessitate another operating frequency. While the LTM8027
is flexible enough to accommodate a wide range of oper-
ating frequencies, a haphazardly chosen one may result
in undesirable operation under certain operating or fault
conditions. A frequency that is too high can damage the
LTM8027 if the output is overloaded or short circuited. A
frequency that is too low can result in a final design that has
too much output ripple or too large of an output capacitor.
The maximum frequency (f
should be allowed to switch and the minimum frequency
set resistor value that should be used for a given set of
input and output operating condition is given in Table 2
as R
satisfied if the synchronization function is used. Please
refer to the Synchronization section for details.
Output Voltage Programming
The LTM8027 regulates its ADJ pin to 1.23V. Connect the
adjust resistor from this pin to ground. The value of R
is given by the equation R
where R
T(MIN)
ADJ
T
Resistor Values vs Frequency
. There are additional conditions that must be
R
63.4k
48.7k
40.2k
31.6k
27.4k
23.7k
T
82.5
187
118
is in kΩ.
(kΩ)
ADJ
MAX
= 613.77/(V
) at which the LTM8027
f
SW
100
150
200
250
300
350
400
450
500
(kHz)
T
OUT
value given
– 1.23),
ADJ
RUN Control
The LTM8027 RUN pin uses a reference threshold of 1.4V.
This precision threshold allows use of the RUN pin for both
logic-level controlled applications and analog monitor-
ing applications such as power supply sequencing. The
LTM8027 operational status is primarily controlled by a
UVLO circuit on internal power source. When the LTM8027
is enabled via the RUN pin, only the internal regulator
(INTV
the UVLO threshold is achieved at the BIAS1 pin, when
the remainder of the LTM8027 is enabled and switching
commences.
Because the LTM8027 high power converter is a power
transfer device, a voltage that is lower than expected on
the input supply could require currents that exceed the
sourcing capabilities of that supply, causing the system
to lock up in an undervoltage state. Input supply start-
up protection can be achieved by enabling the RUN pin
using a resistive divider from the V
Setting the divider output to 1.4V when that supply is at
an adequate voltage prevents an LTM8027 converter from
drawing large currents until the input supply is able to
provide the required power. 200mV of input hysteresis on
the RUN pin allows for about 15% of input supply droop
before disabling the converter.
Input UVLO and RUN
The RUN pin has a precision voltage threshold with hys-
teresis which can be used as an undervoltage lockout
threshold (UVLO) for the power supply. Undervoltage
lockout keeps the LTM8027 in shutdown until the supply
input voltage is above a certain voltage programmed by
the user. The hysteresis voltage prevents noise from falsely
tripping UVLO. Resistors are chosen by first selecting R
(refer to Figure 2). Then:
where V
age lockout is disabled and the supply turns on.
R
A
CC
= R
) is enabled. Switching remains disabled until
IN(ON)
B
•



is the input voltage at which the undervolt-
V
1.4V
IN(ON)
– 1



IN
supply to ground.
LTM8027
13
8027fa
B