LTM8026 LINER [Linear Technology], LTM8026 Datasheet - Page 15

• Manufacturer Part Number: LTM8026
• Description: 36VIN, 5A, 2-Quadrant CVCC Step-Down
• Manufacturer: LINER [Linear Technology]

applicaTions inForMaTion
must have a logic low below 0.6V, a logic high greater
than 1.2V and frequency between 100kHz and 1MHz. The
input frequency must be 20% higher than the frequency
determined by the resistor at the RT pin. Input signals
outside of these specified parameters may cause erratic
switching behavior and subharmonic oscillations. The
SYNC pin must be tied to GND if synchronization to an
external clock is not required. When SYNC is grounded,
the switching frequency is determined by the resistor at
the RT pin.
Switching Mode
The LTM8052 operates in forced continuous mode. This
means that the part will not skip cycles when the load
approaches zero amps. This may be particularly useful in
applications where the synchronization function is used,
or any time discontinuous switching is undesirable. The
LTM8052 will not operate in forced continuous mode
when an input UVLO, output OVLO or minimum duty cycle
violation occurs.
Soft-Start
The soft-start function controls the slew rate of the power
supply output voltage during start-up. A controlled output
voltage ramp minimizes output voltage overshoot, reduces
inrush current from the V
sequencing. A capacitor connected from the SS pin to
GND programs the slew rate. The capacitor is charged
from an internal 11µA current source to produce a ramped
output voltage.
Maximum Output Current Adjust
To adjust the regulated load current, an analog voltage
is applied to the CTL_I pin or CTL_T pins. Varying the
voltage between 0V and 1.5V adjusts the maximum
current between the minimum and the maximum current,
typically 5.6A positive and 7.7A negative. Graphs of the
output current vs CTL_I and CTL_T voltages are given
in the Typical Performance Characteristics section. The
LTM8052 provides a 2V reference voltage for conveniently
applying resistive dividers to set the current limit. The
IN
supply, and facilitates supply
current limit can be set as shown in Figure 1 with the
following equation:
Load Current Derating Using the CTL_T Pin
In high current applications, derating the maximum current
based on operating temperature may prevent damage to the
load. In addition, many applications have thermal limitations
that will require the regulated current to be reduced based
on the load and/or board temperature. To achieve this,
the LTM8052 uses the CTL_T pin to reduce the effective
regulated current in the load. While CTL_I programs the
regulated current in the load, CTL_T can be configured to
reduce this regulated current based on the analog voltage
at the CTL_T pin. The load/board temperature derating is
programmed using a resistor network with a temperature
dependant resistance (Figure 2). When the board/load
temperature rises, the CTL_T voltage will decrease. To
reduce the regulated current, the CTL_T voltage must be
lower than the voltage at the CTL_I pin. V
higher than V
R1
I
I
R2
(OPTION A TO D)
MAX
MAX
V
CTL_T
REF
=
= −
LTM8052
Figure 1. Setting the Output Current Limit
7.467 • R2
R1+R2
Figure 2. Load Current Derating vs
Temperature Using NTC Resistor
CTL_I
7.467 • R2
R1+R2
, but then it will have no effect.
CTL_I OR CTL_T
R
NTC
LTM8052
Amps Positive Current
A
+ 2.1 Amps Negative Current
R
V
REF
NTC
(
B
R1
R2
8052 F01
R
X
2V
R
(
LTM8052
NTC
C
CTL_T
R
V
)
R
NTC
may be
15
D
R
8052 F02
V
8052fa
R
)
X