Datasheet

Threshold
I
PK
'I
I
OCL
I
O
Inductor Current
Load Current
Increases
Normal Operation
Current Limited
LM5010
www.ti.com SNVS307F –SEPTEMBER 2004–REVISED FEBRUARY 2013
Figure 12. Inductor Current - Current Limit Operation
The current limit threshold can be increased by connecting an external resistor (R
CL
) between S
GND
and I
SEN
. The
external resistor typically is less than 1Ω, and its calculation is explained in the Applications Information section.
The peak current out of SW and I
SEN
must not exceed 3.5A. The average current out of SW must be less than
3A, and the average current out of I
SEN
must be less than 2A.
N-Channel Buck Switch and Driver
The LM5010 integrates an N-Channel buck switch and associated floating high voltage gate driver. The peak
current through the buck switch must not be allowed to exceed 3.5A, and the average current must be less than
3A. The gate driver circuit is powered by the external bootstrap capacitor between BST and SW (C4). During
each off-time, the SW pin is at approximately -1V, and C4 is re-charged from V
CC
through the internal high
voltage diode. The minimum off-time of 265 ns ensures a minimum time 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 converter to gradually reach a steady state operating point, thereby reducing
startup stresses and current surges. Upon turn-on, after V
CC
reaches the under-voltage threshold (t1 in Figure 8),
an internal 11.5 µA current source charges the external capacitor at the Softstart pin to 2.5V (t2 in Figure 8). The
ramping voltage at SS (and at the non-inverting input of the regulation comparator) ramps up the output voltage
in a controlled manner. This feature keeps the load current from going to current limit during startup, thereby
reducing inrush currents.
An internal switch grounds the Softstart pin if V
CC
is below the under-voltage lockout threshold, if a thermal
shutdown occurs, or if the circuit is shutdown using the R
ON
/SD pin.
Thermal Shutdown
The LM5010 should be operated so the junction temperature does not exceed 125°C. If the junction temperature
increases above that, an internal Thermal Shutdown circuit activates (typically) at 175°C, taking the controller to
a low power reset state by disabling the buck switch and the on-timer, and grounding the Softstart pin. This
feature helps prevent catastrophic failures from accidental device overheating. When the junction temperature
reduces below 155°C (typical hysteresis = 20°C), the Softstart pin is released and normal operation resumes.
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