Datasheet

LTM8020
10
8020fd
High Temperature Considerations
The die temperature of the LTM8020 must be lower than
the maximum rating of 125°C, so care should be taken
in the layout of the circuit to ensure good heat sinking of
the LTM8020. To estimate the junction temperature, ap-
proximate the power dissipation within the LTM8020 by
applying the typical efficiency stated in this data sheet to
the desired output power, or, if you have an actual module,
by taking a power measurement. Then calculate the inter-
nal temperature rise of the LTM8020 above the surface
of the printed circuit board by multiplying the module’s
power dissipation by the thermal resistance. The actual
thermal resistance of the LTM8020 to the printed circuit
board depends upon the layout of the circuit board, but the
thermal resistance given in the Pin Configuration, which is
based upon a 25cm
2
4-layer FR4 PC board, and the Typical
Performance Characteristics can be used a guide.
Finally, be aware that at high ambient temperatures the
internal Schottky diode will have significant leakage current
increasing the quiescent current of the LTM8020.
BIAS Pin Considerations
The BIAS pin is used to provide drive power for the internal
power switching stage and operate internal circuitry. For
proper operation, it must be powered by at least 3V. If the
output voltage is programmed to be 3V or higher, simply
tie BIAS to V
OUT
. If V
OUT
is less than 3V, BIAS can be tied
to V
IN
or some other voltage source. In all cases, ensure
that the maximum voltage at the BIAS pin is both less than
25V and the sum of V
IN
and BIAS is less than 47V. If BIAS
power is applied from a remote or noisy voltage source, it
may be necessary to apply a decoupling capacitor locally
to the LTM8020.
APPLICATIONS INFORMATION
Figure 4. A Well Chosen Input Network Prevents Input Voltage Overshoot and Ensures
Reliable Operation When the LTM8020 is Connected to a Live Supply
+
LTM8020
2.2μF
V
IN
10V/DIV
I
IN
10A/DIV
V
IN
10V/DIV
I
IN
10A/DIV
V
IN
10V/DIV
I
IN
10A/DIV
10μs/DIV
10μs/DIV
10μs/DIV
V
IN
CLOSING SWITCH
SIMULATES HOT PLUG
I
IN
(4a)
(4b)
(4c)
LOW
IMPEDANCE
ENERGIZED
24V SUPPLY
STRAY
INDUCTANCE
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR
+
LTM8020
2.2μF
10μF
35V
AI.EI.
LTM8020
2.2μF0.1μF
1Ω
8020 F04