ltc4264cde-trpbf Linear Technology Corporation, ltc4264cde-trpbf Datasheet - Page 13

• Manufacturer Part Number: ltc4264cde-trpbf
• Description: High Power Pd Interface Controller With 750ma Current Limit
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
During the inrush event as C1 is being charged, a large
amount of power is dissipated in the MOSFET. The LTC4264
is designed to accept this load and is thermally protected
to avoid damage to the onboard power MOSFET. If a
thermal overload does occur, the power MOSFET turns
off, allowing the die to cool. Once the die has returned to
a safe temperature, the LTC4264 automatically switches
to I
The LTC4264 has the option of disabling the normal operat-
ing input current limit, I
PoE applications. To disable the current limit, connect
I
the normal current limit is disabled, a safeguard current
limit, I
levels, typically 1.4A. Note that continuous operation at
or near the safeguard current limit will rapidly overheat
the LTC4264, engaging the thermal protection circuit. For
normal operations, fl oat the I
maintains the I
the load capacitor regardless of the state of I
operation of the I
LIM_EN
LIMIT_LOW
LIMIT_DISA
to V
V
V
IN
IN
IN
, and load capacitor C1 charging resumes.
. To protect the LTC4264 from damage when
LIMIT_LOW
5
6
LTC4264
BOLD LINE INDICATES HIGH CURRENT PATH
THERMAL SD
LIM_EN
keeps the current below destructive
UVLO
LIMIT_HIGH
REF
pin is summarized in Table 3.
inrush current limit for charging
CONTROL
CIRCUIT
LIM_EN
Figure 8. LTC4264 Power Good Functional and State Diagram
, for custom high power
pin. The LTC4264
LIM_EN
. The
4264 BD
10
9
8
7
Table 3. Current Limit as a Function of I
POWER GOOD
The LTC4264 includes complementary power good outputs
(Figure 8) to simplify connection to any DC/DC converter.
Power Good is asserted at the end of the inrush event when
load capacitor C1 is fully charged and the DC/DC converter
can safely begin operation. The power good signal stays
active during normal operation and is de-asserted at power
off when the port drops below the UVLO threshold or in
the case of a thermal overload event.
For PD designs that use a large load capacitor and also
consume a lot of power, it is important to delay activa-
tion of the DC/DC converter with the power good signal.
If the converter is not disabled during the current-limited
turn-on sequence, the DC/DC converter will rob current
intended for charging up the load capacitor and create a
slow rising input, possibly causing the LTC4264 to go into
thermal shutdown.
PWRGD
PWRGD
V
V
STATE OF I
OUT
OUT
Tied to V
Floating
LIM_EN
IN
POWER
GOOD
AND NOT IN THERMAL SHUTDOWN
NOT
INRUSH CURRENT
OR THERMAL SHUTDOWN
I
I
LIMIT_LOW
LIMIT_LOW
INRUSH COMPLETE
LIMT
V
IN
< UVLO OFF
LIM_EN
POWER
LTC4264
GOOD
OPERATING INPUT
CURRENT LIMIT
I
I
LIMIT_DISA
LIMT_HIGH
13
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