LM25069MM-2EVAL National Semiconductor, LM25069MM-2EVAL Datasheet - Page 16

• Manufacturer Part Number: LM25069MM-2EVAL
• Description: BOARD EVALUATION LM25069
• Manufacturer: National Semiconductor

Specifications of LM25069MM-2EVAL

• Main Purpose: Power Management, Hot Swap Controller
• Embedded: No
• Utilized Ic / Part: LM25069-2
• Primary Attributes: High Side MOSFET Driver, Inrush Current Limiting
• Secondary Attributes: Auto Restart, 2.9 V ~ 17 V Supply
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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the required capacitor value for the LM25069-2 is calculated
using this shorter time period:
For example, if the desired Fault Timeout Period is 17 ms,
C
the LM25069-2 expires, a restart sequence starts as de-
scribed below (Restart Timiing). Since the LM25069 normally
operates in power limit and/or current limit during a power-up
sequence, the Fault Timeout Period MUST be longer than the
time required for the output voltage to reach its final value.
See the Turn-on Time section
C) Restart Timing For the LM25069-2, after the Fault Time-
out Period described above, C
current sink to 1.0V. The TIMER pin then cycles through sev-
en additional charge/discharge cycles between 1V and 1.72V
as shown in
pin voltage reaches 0.3V during the final high-to-low ramp.
The restart time, after the Fault Timeout Period, is equal to:
For example, if C
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 0.67% in this mode.
UVLO, OVLO
By programming the UVLO and OVLO thresholds the
LM25069 enables the series pass device (Q1) when the input
supply voltage (V
If V
threshold, Q1 is switched off, denying power to the load. Hys-
teresis is provided for each threshold.
Option A: The configuration shown in
three resistors (R1-R3) to set the thresholds.
The procedure to calculate the resistor values is as follows:
UVLO threshold (V
FIGURE 11. UVLO and OVLO Thresholds Set By R1-R3
T
- Choose the upper UVLO threshold (V
- Choose the upper OVLO threshold (V
calculates to 0.96 µF. When the Fault Timeout Period of
SYS
is below the UVLO threshold, or above the OVLO
Figure
SYS
T
= 0.8 µF, t
UVL
5. The restart time ends when the TIMER
) is within the desired operational range.
= C
).
T
x 2.65 x 10
RESTART
T
is discharged by the 2.5 µA
= 2.12 seconds. At the
6
Figure 11
UVH
OVH
), and the lower
).
requires
30086729
(4)
16
advance in this case, but is determined after the values for
R1-R3 are determined. If V
addition to the other three thresholds, see Option B below.
The resistors are calculated as follows:
The lower OVLO threshold is calculated from:
As an example, assume the application requires the following
thresholds: V
The lower OVLO threshold calculates to 13.9V, and the OVLO
hysteresis is 1.1V. Note that the OVLO hysteresis is always
slightly greater than the UVLO hysteresis in this configuration.
When the R1-R3 resistor values are known, the threshold
voltages and hysteresis are calculated from the following:
Option B: If all four thresholds must be accurately defined,
the configuration in
- The lower OVLO threshold (V
UVH
V
= 8V, V
OV(HYS)
V
Figure 12
UV(HYS)
= (R1 + R2) x 20 µA
UVL
OVL
= R1 x 20 µA
= 7V, V
can be used.
must be accurately defined in
OVL
OVH
) cannot be chosen in
= 15V.