LX1562IDM Microsemi Analog Mixed Signal Group, LX1562IDM Datasheet - Page 15

• Manufacturer Part Number: LX1562IDM
• Description: IC CONTROLLER PFC 13.1V 8SOIC
• Manufacturer: Microsemi Analog Mixed Signal Group

Specifications of LX1562IDM

• Mode: Discontinuous Conduction (DCM)
• Frequency - Switching: 1.7MHz
• Current - Startup: 200µA
• Voltage - Supply: 11 V ~ 25 V
• Operating Temperature: 0°C ~ 100°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Copyright © 1996
Rev. 1.3a
MULTIPLIER
The LX1562/63 features a one quadrant multiplier stage having
two inputs. One (V
which is the difference of E.A. output and V
is connected to an external resistor divider monitoring the rec-
tified AC line. The output of the multiplier which is a function
of both inputs, controls inductor peak current during each cycle
of operation. This allows the inductor peak current to follow
the AC line thus forcing the average input current to be sinu-
soidal.
to less than 2V and the E.A. output is kept below 3.5V under all
line and load conditions. The output is internally clamped to
1.24V typically to limit the MOSFET peak current during turn on
or under excessive load conditions. The equation below de-
scribes the relationship between multiplier output voltage and
the its inputs.
CURRENT SENSE COMPARATOR
Current sense comparator is configured as a PNP input differ-
ential stage with one input internally tied to the multiplier out-
put and the other available for current sensing. Current is con-
verted to voltage using an external sense resistor in series with
the external power MOSFET. When sense voltage exceeds the
threshold set by the multiplier output, the current sense com-
parator terminates the gate drive to the MOSFET and resets the
PWM latch. The latch insures that the output remains in a low
state after the switch current falls back to zero. The LX1562/63
features a leading edge blanking circuit that eliminates the need
The multiplier is in the linear region if the V
V
where: K = Multiplier gain (typ. 0.65)
8/30
M0
V
= K * V
INPUT
AC
INV.
R1
R2
V
V
V
1
3
M1
EA0
M0
M1
2.5V
V
= Multiplier output voltage
= Voltage at pin3 (0 to 2V)
REF
* (V
= Error amp output voltage (2.5 to 3.5V)
FIGURE 28 — MULTIPLIER SECTION
EA0
M2
- V
V
) is internally driven by a DC voltage
M1
REF
)
OUTPUT
E.A.
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
2
V
S
EA
E C O N D
P
V
-G
R O D U C T I O N
M2
REF
M1
. The other (V
E N E R AT I O N
input is limited
V
OUTPUT
MULT.
M0
I C D E S C R I P T I O N
INPUT
C.S.
4
M1
P
),
O W E R
D
for an external RC filter otherwise required for proper opera-
tion of the circuit. This function is described in detail under
“current detect logic” section.
nal 1.24V (typ.) voltage clamp of the multiplier output. There-
fore maximum switch current is typically given by:
Maximum switch peak current happens at full load and mini-
mum line conditions.
CURRENT DETECT LOGIC
The function of “current detect logic” is to sense the operating
state of the boost inductor and to enable the output driver
accordingly. To achieve this, the downward slope of the in-
ductor current is indirectly detected by monitoring the voltage
across a separate winding and connecting it to the detector
input “I
level, the voltage across the winding reverses polarity and
changes the “I
state (See Figure 30). When comparator changes state, it sets
the latch and turns on the output driver for a period of 1µs
(typ.) regardless of any changes in the latch output (Q) within
this period. This ensures that if the C.S. comparator changes
state due to any turn-on spike, the driver output remains on
and does not turn off prematurely.
turns off and the MOSFET stops conducting. This type of digi-
tal current sense blanking which is not amplitude dependent
has higher noise immunity than the commonly used external
RC filtering, allowing for more flexibility in board layout.
internal voltage clamping is provided to protect the IC. The
PIN 7
A T A
TO
F
The current sense comparator voltage is limited by an inter-
However if the spike lasts longer than 1µs, the output driver
Since inductor voltage swings both positive and negative,
A C T O R
DET
S
” pin. Once the inductor current reaches ground
R
C
S
H E E T
FIGURE 29 — CURRENT SENSE SECTION
O N T R O L L E R
DET
” input and the comparator output to the low
I
PK (MAX)
3
5
= 1.24V / R
V
M0
LX1562/1563
S
Circuit
R
1µsec
Logic
Blank
15
7