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National Semiconductor Electronic Components Datasheet

LM25115MT Datasheet

Secondary Side Post Regulator Controller

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LM25115MT pdf
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November 2005
LM25115
Secondary Side Post Regulator Controller
General Description
The LM25115 controller contains all of the features neces-
sary to implement multiple output power converters utilizing
the Secondary Side Post Regulation (SSPR) technique. The
SSPR technique develops a highly efficient and well regu-
lated auxiliary output from the secondary side switching
waveform of an isolated power converter. Regulation of the
auxiliary output voltage is achieved by leading edge pulse
width modulation (PWM) of the main channel duty cycle.
Leading edge modulation is compatible with either current
mode or voltage mode control of the main output. The
LM25115 drives external high side and low side NMOS
power switches configured as a synchronous buck regulator.
A current sense amplifier provides overload protection and
operates over a wide common mode input range. Additional
features include a low dropout (LDO) bias regulator, error
amplifier, precision reference, adaptive dead time control of
the gate signals and thermal shutdown.
Features
n Self-synchronization to main channel output
n Free-run mode for buck regulation of DC input
n Leading edge pulse width modulation
n Voltage-mode control with current injection and input line
feed-forward
n Operates from AC or DC input up to 42V
n Wide 4.5V to 30V bias supply range
n Wide 0.75V to 13.5V output range.
n Top and bottom gate drivers sink 2.5A peak
n Adaptive gate driver dead-time control
n Wide bandwidth error amplifier (4MHz)
n Programmable soft-start
n Thermal shutdown protection
n TSSOP-16 or thermally enhanced LLP-16 packages
Typical Application Circuit
FIGURE 1. Simplified Multiple Output Power Converter Utilizing SSPR Technique
20172601
© 2005 National Semiconductor Corporation DS201726
www.national.com


National Semiconductor Electronic Components Datasheet

LM25115MT Datasheet

Secondary Side Post Regulator Controller

No Preview Available !

LM25115MT pdf
Connection Diagram
20172602
16-Lead TSSOP, LLP
See NS Package Numbers MTC16 and SDA16A
Ordering Information
Ordering Number
LM25115MT
LM25115MTX
LM25115SD
LM25115SDX
Package Type
TSSOP-16
TSSOP-16
LLP-16
LLP-16
NSC Package Drawing
MTC16
MTC16
SDA16A
SDA16A
Supplied As
92 Units Per Anti-Static Tube
2500 shipped as Tape & Reel
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Pin Descriptions
Pin Name
Description
Application Information
1 CS Current Sense amplifier positive input A low inductance current sense resistor is connected between
CS and VOUT. Current limiting occurs when the differential
voltage between CS and VOUT exceeds 45mV (typical).
2 VOUT Current sense amplifier negative input Connected directly to the output voltage. The current sense
amplifier operates over a voltage range from 0V to 13.5V at the
VOUT pin.
3 AGND Analog ground
Connect directly to the power ground pin (PGND).
4 CO Current limit output
For normal current limit operation, connect the CO pin to the
COMP pin. Leave this pin open to disable the current limit
function.
5
COMP Compensation. Error amplifier output
COMP pin pull-up is provided by an internal 300uA current
source.
6 FB Feedback. Error amplifier inverting input Connected to the regulated output through the feedback resistor
divider and compensation components. The non-inverting input
of the error amplifier is internally connected to the SS pin.
7 SS Soft-start control
An external capacitor and the equivalent impedance of an
internal resistor divider connected to the bandgap voltage
reference set the soft-start time. The steady state operating
voltage of the SS pin equal to 0.75V (typical).
8 RAMP PWM Ramp signal
An external capacitor connected to this pin sets the ramp slope
for the voltage mode PWM. The RAMP capacitor is charged
with a current that is proportional to current into the SYNC pin.
The capacitor is discharged at the end of every cycle by an
internal MOSFET.
www.national.com
2


Part Number LM25115MT
Description Secondary Side Post Regulator Controller
Maker National Semiconductor
Total Page 17 Pages
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