Datasheet
Table Of Contents

Charge
Pump
GATEVIN OUT
V
SYS
V
OUT
SENSE
R
S
Q1
12V
C
L
2 mA
Gate
Control
16
PA
time
Insertion
OVLO
/
UVLO
/
Fault
/
Power Limit
Control
Current Limit
/
230
mA
Initial Hold - down
Circuit Breaker /
LM5069
SNVS452D –SEPTEMBER 2006–REVISED MAY 2013
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If the in-rush limiting condition persists such that the TIMER pin reached 4V during t2, the GATE pin is then
pulled low by the 2 mA pull-down current. The GATE pin is then held low until either a power up sequence is
initiated (LM5069-1), or until the end of the restart sequence (LM5069-2). See the Fault Timer & Restart section.
If the system input voltage falls below the UVLO threshold, or rises above the OVLO threshold, the GATE pin is
pulled low by the 2 mA pull-down current to switch off Q1.
Figure 25. Gate Control
Current Limit
The current limit threshold is reached when the voltage across the sense resistor R
S
(VIN to SENSE) reaches 55
mV. In the current limiting condition, the GATE voltage is controlled to limit the current in MOSFET Q1. While the
current limit circuit is active, the fault timer is active as described in the Fault Timer & Restart section. If the load
current falls below the current limit threshold before the end of the Fault Timeout Period, the LM5069 resumes
normal operation. For proper operation, the R
S
resistor value should be no larger than 100 mΩ.
Circuit Breaker
If the load current increases rapidly (e.g., the load is short-circuited) the current in the sense resistor (R
S
) may
exceed the current limit threshold before the current limit control loop is able to respond. If the current exceeds
twice the current limit threshold (105 mV/R
S
), Q1 is quickly switched off by the 230 mA pull-down current at the
GATE pin, and a Fault Timeout Period begins. When the voltage across R
S
falls below 105 mV the 230 mA pull-
down current at the GATE pin is switched off, and the gate voltage of Q1 is then determined by the current limit
or the power limit functions. If the TIMER pin reaches 4.0V before the current limiting or power limiting condition
ceases, Q1 is switched off by the 2 mA pull-down current at the GATE pin as described in the Fault Timer &
Restart section.
Power Limit
An important feature of the LM5069 is the MOSFET power limiting. The Power Limit function can be used to
maintain the maximum power dissipation of MOSFET Q1 within the device SOA rating. The LM5069 determines
the power dissipation in Q1 by monitoring its drain-source voltage (SENSE to OUT), and the drain current
through the sense resistor (VIN to SENSE). The product of the current and voltage is compared to the power
limit threshold programmed by the resistor at the PWR pin. If the power dissipation reaches the limiting threshold,
the GATE voltage is modulated to reduce the current in Q1. While the power limiting circuit is active, the fault
timer is active as described in the Fault Timer & Restart section.
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