Electronic Components Datasheet Search
Selected language     English  ▼
Part Name
         Description

LTC4268-1 Datasheet (HTML) - Linear Technology

Part No. LTC4268-1
Description  High Power PD with Synchronous NoOpto Flyback Controller
Download  48 Pages
Scroll/Zoom Zoom In 100% Zoom Out
Maker  LINER [Linear Technology]
Homepage  http://www.linear.com
Logo 
 19 page
background image
LTC4268-1
19
42681fa
UNDERVOLTAGE LOCKOUT
The IEEE 802.3af specification dictates a maximum turn-on
voltage of 42V and a minimum turn-off voltage of 30V for
the PD. In addition, the PD must maintain large on-off
hysteresis to prevent current-resistance (I-R) drops in the
wiring between the PSE and the PD from causing start-up
oscillation. The LTC4268-1 incorporates an undervoltage
lockout (UVLO) circuit that monitors line voltage at
VPORTN to determine when to apply power to the PD load
(Figure 7). Before power is applied to the load, the VNEG
pin is high impedance and there is no charge on capacitor
C1. When the input voltage rises above the UVLO turn-on
threshold, the LTC4268-1 removes the classification load
current and turns on the internal power MOSFET. C1
charges up under LTC4268-1 inrush current limit control
and the VNEG pin transitions from 0V to VPORTN as shown
in Figure 3. The LTC4268-1 includes a hysteretic UVLO
circuit on VPORTN that keeps power applied to the load
until the magnitude of the input voltage falls below the
UVLO turn-off threshold. Once VPORTN falls below UVLO
turn-off, the internal power MOSFET disconnects VNEG
from VPORTN and the classification current is re-enabled.
C1 will discharge through the PD circuitry and the VNEG
pin will go to a high impedance state.
INPUT CURRENT LIMIT
IEEE 802.3af specifies a maximum inrush current and also
specifies a minimum load capacitor between the VPORTP
and VNEG pins. To control turn-on surge currents in the
system the LTC4268-1 integrates a dual current limit circuit
using an onboard power MOSFET and sense resistor to
provide a complete inrush control circuit without additional
external components. At turn-on, the LTC4268-1 will limit
the inrush current to ILIMIT_LOW, allowing the load capaci-
tor to ramp up to the line voltage in a controlled manner
without interference from the PSE current limit. By keeping
the PD current limit below the PSE current limit, PD power
up characteristics are well controlled and independent of
PSE behavior. This ensures interoperability regardless of
PSE output characteristics.
After load capacitor C1 is charged up, the LTC4268-1
switches to the high input current limit, ILIMIT_HIGH. This
allows the LTC4268-1 to deliver up to 35W to the PD load
for high power applications. To maintain compatibility
with IEEE 802.3af power levels, it is necessary for the PD
designer to ensure the PD steady-state power consumption
remains below the limits shown in Table 2. The LTC4268-1
maintains the high input current limit until the port voltage
drops below the UVLO turn-off threshold.
APPLICATIONS INFORMATION
VPORTP
C1
5μF
MIN
VPORTN
VNEG
VIN
LTC4268-1
42681 F07
TO
PSE
UNDERVOLTAGE
LOCKOUT
CIRCUIT
CURRENT-LIMITED
TURN ON
+
VPORT
LTC4268-1
VOLTAGE
POWER MOSFET
0V TO UVLO*
OFF
>UVLO*
ON
*UVLO INCLUDES HYSTERESIS
RISING INPUT THRESHOLD
–38.9V
FALLING INPUT THRESHOLD
–30.6V
Figure 7. LTC4268-1 Undervoltage Lockout



Html Pages

1  2  3  4  5  6  7  8  9  10  11  12  13  14  15  16  17  18  19  20  21  22  23  24  25  26  27  28  29  30  31  32  33  34  35  36  37  38  39  40  41  42  43  44  45  46  47  48 


Datasheet Download



Related Electronics Part Number

Part NumberComponents DescriptionHtml ViewManufacturer
RJK6014DPPSilicon N Channel MOS FET High Speed Power Switching 1 2 3 4 Renesas Technology Corp
IR3629HIGH FREQUENCY SYNCHRONOUS PWM BUCK CONTROLLER WITH POWER GOOD OUTPUT 1 2 3 4 5 MoreInternational Rectifier
IR3622AMPBFHIGH FREQUENCY 2-PHASE SINGLE OR DUAL OUTPUT SYNCHRONOUS STEP DOWN CONTROLLER WITH OUTPUT TRACKING AND SEQUENCING 1 2 3 4 5 MoreInternational Rectifier
TPS61058SYNCHRONOUS BOOST CONVERTER WITH DOWN MODE HIGH POWER WHITE LED DRIVER 1 2 3 4 5 MoreTexas Instruments
TPS610501.2-A HIGH POWER WHITE LED DRIVER 2-MHz SYNCHRONOUS BOOST CONVERTER WITH I2C COMPATIBLE INTERFACE 1 2 3 4 5 MoreTexas Instruments
R2J20701NPPeak Current Mode Synchronous Buck Controller with Power MOSFETs 1 2 3 4 5 MoreRenesas Technology Corp
CS51665−Bit Synchronous CPU Controller with Power Good and Current Limit 1 2 3 4 5 MoreON Semiconductor
SP6120_05Low Voltage AnyFETTM Synchronous Buck Controller Ideal for 2A to 10A High Performance DC-DC Power Converters 1 2 3 4 5 MoreSipex Corporation
TPS61054HIGH POWER WHITE LED DRIVER 2-MHz SYNCHRONOUS BOOST CONVERTER WITH STANDARD LOGIC INTERFACE 1 2 3 4 5 MoreTexas Instruments
LT3825Isolated No-Opto Synchronous Flyback Controller with Wide Input Supply Range 1 2 3 4 5 MoreLinear Technology

Link URL

Does ALLDATASHEET help your business so far?  [ DONATE ]  

About Alldatasheet   |   Advertisement   |   Partner program   |   Contact us   |   Privacy Policy   |   Bookmark   |   Link Exchange   |   Manufacturer List
All Rights Reserved© Alldatasheet.com 2003 - 2014    


Mirror Sites
English : Alldatasheet.com  , Alldatasheet.net  |   Chinese : Alldatasheetcn.com  |   German : Alldatasheetde.com  |   Japanese : Alldatasheet.jp  |   Russian : Alldatasheetru.com
Korean : Alldatasheet.co.kr   |   Spanish : Alldatasheet.es  |   French : Alldatasheet.fr  |   Italian : Alldatasheetit.com  |   Portuguese : Alldatasheetpt.com  |   Polish : Alldatasheet.pl