IRPLLED1 International Rectifier, IRPLLED1 Datasheet - Page 7

• Manufacturer Part Number: IRPLLED1
• Description: BOARD EVALUATION FOR IRS2540PBF
• Manufacturer: International Rectifier

Specifications of IRPLLED1

• Current - Output / Channel: 1.5A
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 24V
• Features: Dimmable
• Voltage - Input: 50 ~ 170V
• Utilized Ic / Part: IRS2540PBF
• Core Chip: IRS2540, IRS2541, IRS25401
• Topology: Buck (Step Down)
• No. Of Outputs: 1
• Output Current: 1.5A
• Output Voltage: 500mV
• Dimming Control Type: PWM
• Development Tool Type: Hardware - Eval/Demo Board
• Lead Free Status / RoHS Status: Contains lead / RoHS compliant by exemption

Functional Description
www.irf.com
Operating Mode
The IRS254(0,1) operates as a time-delayed
hysteritic buck controller. During normal operating
conditions the output current is regulated via the IFB
pin voltage (nominal value of 500 mV).
feedback is compared to an internal high precision
bandgap voltage reference. An on-board dV/dt filter
has
transitioning.
Once the supply to the IC reaches V
output is held high and the HO output low for a
predetermined period of time. This initiates charging
of the bootstrap capacitor, establishing the V
floating supply for the high-side output. The IC then
begins toggling HO and LO outputs as needed to
regulate the current.
As long as V
by the watchdog timer described below, the load is
receiving current from V
stores energy in the inductor, as V
unless the load is open. Once V
the control loop switches HO off after the delay
t
deadtime (DT), the inductor releases the stored
energy into the load and V
When V
switches HO on after the delay t
after the delay t
to regulate the current at an average value
determined as follows. When the inductance value
HO,OFF
. Once HO is off, LO will turn on after the
also
Fig.1 IRS254(0,1) Control Signals, Iavg=1.2 A
IFB
crosses V
IFB
been
is below V
HO,ON
used
+ DT. The switching continues
IFBTH
BUS
IFBTH
again, the control loop
to
, which simultaneously
IFB
, HO is on, modulated
ignore
starts decreasing.
IFB
HO,ON
crosses V
CCUV+
IFB
and LO off
increases,
erroneous
,
the LO
Iout
HO
LO
IFBTH
This
BS
,
is large enough to maintain a low ripple on I
can be calculated:
The control method is based upon a free running
frequency, in constrast to a more widely used fixed
frequency regulation. This reduces the part count
since there is no need for frequency setting
components and also provides an inherently stable
sytem, which acts as a current source.
A deadtime of approximately 140 ns between the
two gate drive signals is necessary to prevent a
“shoot-through” condition. At higher frequencies, the
switching losses become very large in the absence
of this deadtime. The deadtime has been adjusted to
maintain precise current regulation, while still
preventing shoot-through.
IFB
HO
LO
IFBTH
Fig.3 IRS254(0,1) Time Delayed Hysterisis
50%
(B) Releasing Inductor Stored Energy
Fig.2 (A) Storing Energy in Inductor
(A)
Iout
(
avg
IRS254(0,1)(S)PbF
t_HO_off
t_LO_on
)
=
50%
DT1
VIFBTH
50%
t_LO_off
t_HO_on
RCS
50%
50%
DT2
Page 7
(B)
FB
, I
out,avg