LX2750
SINGLE INPUT SUPPLY PWM CONTROLLER WITH LDO
CONTROLLER
PRODUCTION DATA SHEET
Pb Free Product
DESCRIPTION
The LX2750 controller IC is a compact synchronous
Buck controller IC with 16 lead MLPQ package de-
signed for step-down DC to DC converter applications.
Selectable feedforward voltage mode control or con-
stant on time control provides fast dynamic response.
Selectable diode emulation mode greatly improves the
light load efficiency. The LX2750 controller is optimized
to convert single supply 12V bus voltage to as low as
0.8V output voltage. An internal regulator converts bus
voltage to 5V, which provides voltage supply to inter-
nal logic and driver circuit. The LX2750 employs pro-
grammable loss-less current limiting by sensing the
Rdson of synchronous MOSFET followed by hiccup
feature. Feedback under voltage also triggers hiccup.
Internal UVLO keeps the controller off until the bus
supply voltage exceeds 9V where internal digital soft
starts get initiated to ramp up output. The LX2750 em-
ploys NMOS LDO controller. Other features include:
5V gate drive for HDRV signal, 12V gate drive for LDRV
signal, programmable frequency, adaptive deadband
control.
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FEATURES
Single Input 12V Bus Voltage
Excellent Dynamic Response with Selectable
Feedforward Voltage Mode Control or Constant On
Time Control
Diode Emulation Mode Available
Programmable Switching Frequency Up to 2MHz
Internal Digital Soft Start Function
Programmable Over Current Protection Triggers
Hiccup
NMOS LDO Controller Available
FB UVLO Followed by Hiccup Feature in Both
Controllers
5V High Side Driver and 12 V Low Side Driver
Pb-free and RoHS Compliant
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APPLICATIONS
Graphic Card on Board Converters
On Board DC to DC such as
12V to 3.3V, 2.5V or 1.8V
Set Top Box and LCD Display
ASIC Power Supplies
TYPICAL APPLICATION
VIN1
+12V
15
7 VIN
10
BST
VCC
HDRV 14
SW 13
12
Connected to 5VREG Voltage mode
Connected to GND Constant on time mode
Connected to 5VREG synchronous mode
Connected to GND Diode emulation mode
VOUT1
+1.8V@8A
PGOOD
9 FCCM
16 RT
LX2750
8 MODE
LDRV 11
2
FB
COMP
6
VREF_OC
LDO_DRV
1
3
5 REFIN
GPIO
17
GND(PAD)
LDO_FB 4
VOUT2
+1.1V
Figure1 - Typical application of LX2750
ORDERING INFORMATION
Device
LX2750CLQ
Temperature
0 to 70
o
C
Package
3X3 MLPQ-16L
Frequency
200kHz to 2MHz
Pb-Free
Yes
Note: Available in Tape & Reel. Append the letters "TR" to the part number. (i.e. LX2750CLQ-TR)
Rev. 1.0a
07/14/10
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
1
LX2750
ABSOLUTE MAXIMUM RATINGS
5VREG to GND & BST to SW voltage ................ -0.3V to 6V
VIN, LDO_DRV to GND ...................................... -0.3V to 16V
BST,HDRV to GND Voltage .............................. -0.3V to 21V
SW to GND ....................................................... -2V to 16V
LDRV to GND .................................................... -0.3V to VIN+0.3V
All other pins ..................................................... -0.3V to VCC+0.3V
Storage Temperature Range ............................... -65
o
C to 150
o
C
Operating Junction Temperature Range ...............-40
o
C to 125
o
C
ESD Susceptibility .............................................. 1000V
CAUTION: Stresses above those listed in "ABSOLUTE MAXIMUM RATINGS", may cause permanent
damage to the device. This is a stress only rating and operation of the device at these or any other conditions
above those indicated in the operational sections of this specification is not implied.
PACKAGE INFORMATION
3x3 16-LEAD PLASTIC MLPQ
θ
JA
≈ 46
o
C
/
W
SW
13
12 PGOOD
17
GND
11 LDRV
10 VCC
9 FCCM
5
REFIN
6
VREF_OC
7
VIN
8
MODE
SYM
V
REF
V
IN
from 10V to 16V
V
in
No switching,COMP=0.8V
Switching with HDRV and
LDRV open,COMP=1.8V
16
COMP 1
FB
2
15
14
LDO_DRV 3
LDO_FB 4
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over VIN=12V and T
A
= 0 to 70
o
C. Typical values refer to
T
A
= 25
o
C.
PARAMETER
REFOUT_OC Voltage
REFOUT_OC Voltage
Accuracy
Supply Voltage(Vin)
V
in
Voltage Range
Input Voltage Current(Static)
Input Voltage Current
(Dynamic)
Rev. 1.0a
07/14/10
HDRV
BST
RT
Test Condition
Min
2.45
-0.3
10
TYP
2.5
MAX
2.55
0.3
16
Units
V
%
V
mA
mA
7
9
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
2
LX2750
PARAMET ER
VIN UVL O
V
in
-Threshold
V
in
-Hysteresis
5V REG
5VREG Output
5VREG Max Current
SS
Soft Start time
Oscillator (Rt)
Frequency
Ramp-feedforward gain
Ramp Offset
Max Duty Cycle
Min Off Tim e
Min Controlable On Time
Rt Disable threshold
Error Amplifiers
Open Loop Gain (Note1)
Gain Bandwidth (Note1)
Input Bias Current
Max Sourcing Current
Max Sinking Current
COMP High Voltage
COMP Low Voltage
SW zero cross comparator
Offset voltage
High Side Driver
N
Output Impedance , Sourcing
Current (Note1)
Output Impedance , Sinking
Current (Note1)
Low Side Driver
Output Impedance, Sourcing
Current (Note1)
SYM
V
in
_UVLO
V
in
_Hyst
Test Condition
V
in
Rising
V
in
Falling
No switching
Min
TYP
9
8
5.4
50
5.2
1.3
MAX
Units
V
V
V
mA
mS
mS
30
Tss_pwm
Tss_con
F
S
V
RAMP
F
S
=300kHz
F
S
=350kHz,MODE=5V
F
S
=350kHz,MODE=0V
Rt=110k,MODE=5V
245
300
0.1
1
80
560
200
0.3
80
10
1
3
0.4
4.4
0.1
-2
359
kHz
V/V
V
%
nS
nS
V
dB
MHz
nA
mA
mA
V
V
mV
ohm
ohm
Ib
FB=0.7V, comp>=3V
FB=0.9V,com p<=0.3V
FB=0.7V, source 80uA
FB=0.9V, sink 40uA
100
R
source
(Hdrv) BST to SW=5V,
I=200mA
R
sink
(Hdrv) BST to SW=5V,
I=200mA
R
source
(Ldrv) PVCC=12V
R
sink
(Ldrv)
PVCC=12V
1
0.8
6
2
ohm
ohm
Output Impedance, Sinking
Current (Note1)
MODE,FCCM thresho ld
High T hreshold
Low Threshold
Internal Schottky Diode
Forward voltage drop
Power Good
T hreshold Voltage as % of Vref
Hysteresis
FBUVL O
Feedback UVLO threshold
Rev. 1.0a
07/14/10
2
0.8
Forward current=20mA
FB ram ping up
450
85
5
percent of nom inal
60
V
V
mV
%
%
%
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
3
LX2750
PARAMETER
LDO Controller
Open Loop Gain(Note1)
Gain Bandwidth(Note1)
FB Pin- Bias Current
LDO FB Voltage
LDO FB UVLO
High Output Voltage
Low Output Voltage
Max Sourcing Current
Min Sinking Current
0.772
percent of nom inal
VIN=12V,LDOFB=0.7V,
source 1.4mA
LDOFB=0.9V,sink
1.4mA
LDOFB=0.7V,
LDODRV>8V
LDOFB=0.9V,
LDODRV<1V
SYM
Test Condition
Min
TYP
100
2
1
0.8
60
11.5
0.4
2
8
100
0.828
MAX
Units
dB
MHz
nA
V
%
V
V
mA
mA
Note1: Design Guaranteed.
Note
Rev. 1.0a
07/14/10
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
4
LX2750
PIN DESCRIPTIONS
PIN SYMBOL
VCC
PIN DESCRIPTION
This pin is internal 5V regulator output and supplies the internal 5V bias circuit. A high
freq 1uF ceramic capacitor is recommended to connect this pin to ground.
This pin supplies voltage to high side FET driver. A high freq minimum 0.1uF ceramic
capacitor is placed as close as possible to and connected to this pin and SW pin.
Ground pin.
This pin is the error amplifiers inverting input. This pin is connected via resistor divider to
the output of the switching regulator to set the output DC voltage.
This pin is the output of the error amplifier and together with FB pin is used to compensate
the voltage control feedback loop.
This pin is connected to source of high side FETs and provide return path for the high
side driver.
High side gate driver output.
Low side gate driver output.
Voltage supply for the internal 5V regulator, LDO controller and low side driver.
Oscillator's frequency can be set by using an external resistor from this pin to GND.
Pulling this pin down below 0.3V shuts down both controllers.
LDO controller feedback input. This pin is connected via resistor divider to the output of
the LDO to set the output DC voltage.
LDO controller output. This pin is controlling the gate of an external NCH MOSFET. The
maximum rating of this pin is 16V.
Connecting this pin to 5VREG voltage control mode will be chosen.
Connecting this pin to ground, constant on time control mode will be chosen.
Connecting this pin to 5VREG, synchronous mode will be chosen.
Connecting this pin to ground, diode emulation mode will be chosen, LDRV will be off
when inductor current becomes negative current.
Reference input voltage for error amplifier.
2.5V external reference. OCP trigger level is set by connect resistor from this pin to
ground.
PGOOD indicator for switching regulator. It requires a pull up resistor to Vcc or lower
voltage. When FB pin reaches 85% of the reference voltage PGOOD transitions from LO
to HI state.
BST
GND
FB
COMP
SW
HDRV
LDRV
VIN
RT
LDO_FB
LDO_DRV
MODE
FCCM
REFIN
VREF_OC
PGOOD
Rev. 1.0a
07/14/10
Microsemi
Analog Mixed Signal Group
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570
5
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