LTM8026 LINER [Linear Technology], LTM8026 Datasheet - Page 16

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

LTM8052
applicaTions inForMaTion
Voltage Regulation and Output Overvoltage Protection
The LTM8052 uses the ADJ pin to regulate the output
voltage and to provide a high speed overvoltage lockout
to avoid high voltage conditions. If the output voltage
exceeds 125% of the regulated voltage level (1.5V at the
ADJ pin), the LTM8052 terminates switching and shuts
down switching for a brief time before restarting. The
regulated output voltage must be greater than 1.19V and
is set by the equation:
where R
In situations where the output of the LTM8052 is required
to sink current (that is, the load is driving current into the
LTM8052 output), the μModule regulator will maintain
voltage regulation as long as the negative current limit is
not exceeded. If the current limit is exceeded, the output
voltage may begin to rise. If the output voltage rises more
than 125% of the target regulation voltage, the output
overvoltage protection will engage, and the LTM8052 will
stop switching. In this situation, the load will be free to
pull up the LTM8052 output. If the voltage exceeds the
LTM8052 input, an internal power diode will clamp the
output to a diode drop above the input.
Thermal Shutdown
If the part is too hot, the LTM8052 engages its thermal
shutdown, terminates switching and discharges the soft-
start capacitor. When the part has cooled, the part automati-
cally restarts. This thermal shutdown is set to engage at
temperatures above the 125°C absolute maximum internal
operating rating to ensure that it does not interfere with
16
V
Figure 3. Voltage Regulation and Overvoltage Protection
Feedback Connections
OUT
ADJ
= 1.19V 1+
is shown in Figure 3.

 
LTM8052
R
10k
ADJ
V
ADJ
OUT

 
V
R
8052 F03
OUT
ADJ
functionality in the specified operating range. This means
that internal temperatures will exceed the 125°C absolute
maximum rating when the overtemperature protection is
active, possibly impairing the device’s reliability.
UVLO and Shutdown
The LTM8052 has an internal UVLO that terminates switch-
ing, resets all logic, and discharges the soft-start capacitor
when the input voltage is below 6V. The LTM8052 also has
a precision RUN function that enables switching when the
voltage at the RUN pin rises to 1.68V and shuts down the
LTM8052 when the RUN pin voltage falls to 1.55V. There
is also an internal current source that provides 5.5μA of
pull-down current to program additional UVLO hysteresis.
For RUN rising, the current source is sinking 5.5µA until
RUN = 1.68V, after which the current source turns off.
For RUN falling, the current source is off until the RUN =
1.55V, after which it sinks 5.5µA. The following equations
determine the voltage divider resistors for programming
the falling UVLO voltage and rising enable voltage (V
as configured in Figure 4.
The RUN pin has an absolute maximum voltage of 6V.
To accommodate the largest range of applications, there
is an internal Zener diode that clamps this pin, so that it
can be pulled up to a voltage higher than 6V through a
resistor that limits the current to less than 100µA. For
applications where the supply range is greater than 4:1,
size R2 greater than 375k.
R1=
R2 =
UVLO– 1.55V
V
1.55V •R2
ENA
– 1.084 •UVLO
Figure 4. UVLO Configuration
5.5µA
LTM8052
RUN
V
IN
R2
R1
8052 F04
V
IN
ENA
8052fa
)