Datasheet

Current Limit
Threshold
Inductor
Current
Io
Normal Operation
Current Limited
Low Load Current
High Load Current
'I
I
OCL
I
PK
LM5010A
LM5010A-Q1
www.ti.com SNVS376E –OCTOBER 2005–REVISED FEBRUARY 2013
Figure 10. Inductor Current - Current Limit Operation
N-Channel Buck Switch and Driver
The LM5010A integrates an N-Channel buck switch and associated floating high voltage gate driver. The peak
current through the buck switch should not exceed 2A, and the load current should not exceed 1.5A. The gate
driver circuit is powered by the external bootstrap capacitor between BST and SW (C4), which is recharged each
off-time from V
CC
through the internal high voltage diode. The minimum off-time, nominally 260 ns, ensures
sufficient time during each cycle to recharge the bootstrap capacitor. A 0.022 µF ceramic capacitor is
recommended for C4.
Soft-start
The soft-start feature allows the regulator to gradually reach a steady state operating point, thereby reducing
startup stresses and current surges. At turn-on, while V
CC
is below the under-voltage threshold (t1 in Figure 7),
the SS pin is internally grounded, and V
OUT
is held at 0V. When V
CC
exceeds the under-voltage threshold
(UVLO) an internal 11.5 µA current source charges the external capacitor (C6) at the SS pin to 2.5V (t2 in
Figure 7). The increasing SS voltage at the non-inverting input of the regulation comparator gradually increases
the output voltage from zero to the desired value. The soft-start feature keeps the load inductor current from
reaching the current limit threshold during start-up, thereby reducing inrush currents.
An internal switch grounds the SS pin if V
CC
is below the under-voltage lock-out threshold, or if the circuit is
shutdown using the RON/SD pin.
Thermal Shutdown
The LM5010A should be operated below the Maximum Operating Junction Temperature rating. If the junction
temperature increases during a fault or abnormal operating condition, the internal Thermal Shutdown circuit
activates typically at 175°C. The Thermal Shutdown circuit reduces power dissipation by disabling the buck
switch and the on-timer. This feature helps prevent catastrophic failures from accidental device overheating.
When the junction temperature reduces below approximately 155°C (20°C typical hysteresis), normal operation
resumes.
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