LM5067 Datasheet, PDF (20/35 Pages) National Semiconductor (TI) – Negative Hot Swap / Inrush Current Controller with Power Limiting

LM5067
SNVS532C – OCTOBER 2007 – REVISED MARCH 2013
www.ti.com
For example, if C_T = 0.33 µF, t_RESTART = 3.1 seconds. At the end of the restart time, Q1 is switched on. If the fault
is still present, the fault timeout and restart sequence repeats. The on-time duty cycle of Q1 is approximately
0.5% in this mode.
UVLO, OVLO
By programming the UVLO and OVLO thresholds the LM5067 enables the series pass device (Q1) when the
input supply voltage (V_SYS) is within the desired operational range. If V_SYS is below the UVLO threshold, or above
the OVLO threshold, Q1 is switched off, denying power to the load. Hysteresis is provided for each threshold.
NOTE
All voltages are with respect to Vee in the discussions below. Use absolute values in the
equations.
Option A: The configuration shown in Figure 14 requires three resistors (R1-R3) to set the thresholds.
GND
To Load
R_IN
C_IN
VEE
VCC
R1
UVLO/EN _2.50V
Vee
R2
OVLO _2.50V
Vee
22 PA
LM5067
TIMER AND GATE
LOGIC CONTROL
Vee
R3
VEE
22 PA
V_SYS
Figure 14. UVLO and OVLO Thresholds Set By R1-R3
The procedure to calculate the resistor values is as follows:
• Determine the upper UVLO threshold (V_UVH) to enable Q1, and the lower UVLO threshold (V_UVL) to disable
Q1.
• Determine the upper OVLO threshold (V_OVH) to disable Q1.
• The lower OVLO threshold (V_OVL), to enable Q1, cannot be chosen in advance in this case, but is determined
after the values for R1-R3 are determined. If V_OVL must be accurately defined in addition to the other three
thresholds, see Option B below.
The resistors are calculated as follows:
V_UVH - V_UVL
R1 =
V_UV(HYS)
=
22 PA
22 PA
R3 = ^{2.5V x R1 x VUVL}
V_OVH x (V_UVL - 2.5V)
2.5V x R1
R2 =
- R3
V_UVL - 2.5V
(10)
The lower OVLO threshold is calculated from:
V_OVL = [(R1 + R2) x ((2.5V) - 22 PA)] + 2.5V
R3
(11)
20
Submit Documentation Feedback
Product Folder Links: LM5067
Copyright © 2007–2013, Texas Instruments Incorporated