Linear Technology LTM8052A Demo Board, 36Vin, 5A 2-Quadrant CVCC Step-Down µModule regulator w/o OVP DC1939A DC1939A Data Sheet

Product codes

DC1939A

LTM8052/LTM8052A

8052fc

For more information

www.linear.com/LTM8052

which the capacitor at the soft-start pin is charged with

an 11µA current source.
The LTM8052/LTM8052A is equipped with a thermal shut-

down to protect the device during momentary overload

conditions. It is set above the 125°C absolute maximum

internal temperature rating to avoid interfering with

normal specified operation, so internal device tempera-

tures will exceed the absolute maximum rating when the

operaTion

overtemperature protection is active. So, continuous or

repeated activation of the thermal shutdown may impair

device reliability. During thermal shutdown, all switching

is terminated and the SS pin is driven low.
The switching frequency is determined by a resistor at the

RT pin. The LTM8052/LTM8052A may also be synchronized

to an external clock through the use of the SYNC pin.

applicaTions inForMaTion

For most applications, the design process is straight

forward, summarized as follows:
1. Look at Table 1 and find the row that has the desired

input range and output voltage.

2. Apply the recommended C

, C

OUT

, R

ADJ

and R

values.

While these component combinations have been tested for

proper operation, it is incumbent upon the user to verify

proper operation over the intended system’s line, load and

environmental conditions. Bear in mind that the maximum

output current is limited by junction temperature, the

relationship between the input and output voltage mag-

nitude and polarity and other factors. Please refer to the

graphs in the Typical Performance Characteristics section

for guidance.
The maximum frequency (and attendant R

value) at which

the LTM8052/LTM8052A should be allowed to switch is

given in Table 1 in the f

MAX

column, while the recommended

frequency (and R

value) for optimal efficiency over the

given input condition is given in the f

OPTIMAL

column.

There are additional conditions that must be satisfied if

the synchronization function is used. Please refer to the

Synchronization section for details.

Capacitor Selection Considerations
The C

and C

OUT

capacitor values in Table 1 are the

minimum recommended values for the associated oper-

ating conditions. Applying capacitor values below those

indicated in Table 1 is not recommended, and may result

in undesirable operation. Using larger values is generally

acceptable, and can yield improved dynamic response, if

necessary. Again, it is incumbent upon the user to verify

proper operation over the intended system’s line, load and

environmental conditions.
Ceramic capacitors are small, robust and have very low ESR.

However, not all ceramic capacitors are suitable. X5R and

X7R types are stable over temperature, applied voltage and

give dependable service. Other types, including Y5V and

Z5U have very large temperature and voltage coefficients

of capacitance. In an application circuit they may have only

a small fraction of their nominal capacitance resulting in

much higher output voltage ripple than expected.
Many of the output capacitances given in Table 1 specify

an electrolytic capacitor. Ceramic capacitors may also be

used in the application, but it may be necessary to use

more of them. Many high value ceramic capacitors have a

large voltage coefficient, so the actual capacitance of the

component at the desired operating voltage may be only

a fraction of the specified value. Also, the very low ESR of

ceramic capacitors may necessitate additional capacitors

for acceptable stability margin.
A final precaution regarding ceramic capacitors concerns

the maximum input voltage rating of the LTM8052/

LTM8052A. A ceramic input capacitor combined with trace

or cable inductance forms a high Q (under damped) tank

circuit. If the LTM8052/LTM8052A circuit is plugged into a

live supply, the input voltage can ring to twice its nominal

value, possibly exceeding the device’s rating. This situa-

tion is easily avoided; see the Hot Plugging Safely section.