Evaluation board available.
NX2154/2154A
300kHz SYNCHRONOUS PWM CONTROLLER
PRELIMINARY DATA SHEET
Pb Free Product
DESCRIPTION
The NX2154/2154A controller IC is a synchronous Buck
controller IC designed for step down DC to DC con-
verter applications. It is optimized to convert bus volt-
ages from 2V to 40V to outputs as low as 0.8V voltage.
The NX2154/2154A operates at fixed 300kHz. The
NX2154/2154A employs fixed loss-less current limiting
by sensing the Rdson of synchronous MOSFET followed
by hiccup feature.NX2154A has higher current limit
threshold than NX2154. Feedback under voltage also
triggers hiccup.
Other features of the device are: 5V gate drive, Adaptive
deadband control, Internal digital soft start, Vcc
undervoltage lock out and shutdown capability via the
comp pin.
FEATURES
n
n
n
n
n
n
Bus voltage operation from 2V to 40V
Fixed 300kHz voltage mode controller
Internal Digital Soft Start Function
Prebias Startup
Less than 50 nS adaptive deadband
Current limit triggers hiccup by sensing Rdson of
Synchronous MOSFET
n
No negative spike at Vout during startup and
shutdown
n
Pb-free and RoHS compliant
APPLICATIONS
n
n
n
n
n
Graphic Card on board converters
Memory Vddq Supply in mother board applications
On board DC to DC such as
5V to 3.3V, 2.5V or 1.8V
Hard Disk Drive
Set Top Box
TYPICAL APPLICATION
Vin
+5V
MBR0530T1
1uF
50ME180WX
Vin
+33V
1uF
5
1
Vcc
7
BST
0.1uF
2
M1A STM6920
15uH
HI=SD
M3
12nF
82pF
13.3k
6
NX2154
Comp
Hdrv
SW
Ldrv
8
M1B
Vout
+5V,3A
6ME1000WG(1000uF,30mohm)
Fb
Gnd
3
4
1k
191
Figure1 - Typical application of 2154
ORDERING INFORMATION
Device
NX2154CSTR
NX2154ACSTR
Rev.1.2
02/26/07
Temperature
0 to 70
o
C
0 to 70
o
C
Package
SOIC-8L
SOIC-8L
Frequency
300kHz
300kHz
OCP Threshold
360mV
540mV
Pb-Free
Yes
Yes
1
NX2154/2154A
ABSOLUTE MAXIMUM RATINGS
(NOTE1)
Vcc to GND & BST to SW voltage ................... 6.5V
BST to GND Voltage ...................................... 50V
Storage Temperature Range ............................. -65
o
C to 150
o
C
Operating Junction Temperature Range ............. -40
o
C to 125
o
C
NOTE1: 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
8-PIN PLASTIC SOIC (S)
θ
JA
≈
130
o
C
/
W
BST
1
HDrv
2
Gnd
3
LDrv
4
8
SW
7
Comp
6
Fb
5
Vcc
ELECTRICAL SPECIFICATIONS
Unless otherwise specified, these specifications apply over Vcc = 5V, and T
A
= 0 to 70
o
C. Typical values refer to T
A
= 25
o
C. Low duty cycle pulse testing is used which keeps junction and case temperatures equal to the ambient
temperature.
PARAMETER
Reference Voltage
Ref Voltage
Ref Voltage line regulation
Supply Voltage(Vcc)
V
CC
Voltage Range
V
CC
Supply Current (Static)
V
CC
Supply Current
(Dynamic)
Supply Voltage(V
BST
)
V
BST
Supply Current (Static)
V
BST
Supply Current
(Dynamic)
Under Voltage Lockout
V
CC
-Threshold
V
CC
-Hysteresis
SYM
V
REF
Test Condition
4.5V<Vcc<5.5V
Min
TYP
0.8
0.4
4.5
5
3
5
5.5
MAX
Units
V
%
V
mA
mA
V
CC
I
CC
(Static) Outputs not switching
I
CC
C
LOAD
=3300pF F
S
=300kHz
(Dynamic)
I
BST
(Static) Outputs not switching
I
BST
C
LOAD
=3300pF
(Dynamic)
V
CC
_UVLO V
CC
Rising
V
CC
_Hyst V
CC
Falling
F
S
=300kHz
0.15
5
mA
mA
4.2
0.22
V
V
Rev.1.2
02/26/07
2
NX2154/2154A
PARAMETER
SS
Soft Start time
Oscillator (Rt)
Frequency
Ramp-Amplitude Voltage
Max Duty Cycle
Min Duty Cycle
Error Amplifiers
Transconductance
Input Bias Current
Comp SD Threshold
FBUVLO
Feedback UVLO threshold
High Side Driver(C
L
=2200pF)
Output Impedance , Sourcing
Output Impedance , Sinking
Sourcing Current
Sinking Current
Rise Time
Fall Time
Deadband Time
Low Side Driver (C
L
=2200pF)
Output Impedance, Sourcing
Current
Output Impedance, Sinking
Current
Sourcing Current
Sinking Current
Rise Time
Fall Time
Deadband Time
OCP
OCP voltage
R
source
(Ldrv)
R
sink
(Ldrv)
I
source
(Ldrv)
I
sink
(Ldrv)
TLdrv(Rise)
TLdrv(Fall)
Tdead(H to SW going Low to Ldrv
L)
going High, 10% to 10%
NX2154
NX2154A
I=200mA
I=200mA
1.9
1
1
2
13
12
10
ohm
ohm
A
A
ns
ns
ns
SYM
Tss
F
S
V
RAMP
Test Condition
Fsw=300Khz
Min
TYP
3.4
1.7
300
1.6
84
0
2000
10
0.3
percent of nominal
R
source
(Hdrv)
I=200mA
R
sink
(Hdrv)
I=200mA
I
source
(Hdrv)
I
sink
(Hdrv)
THdrv(Rise)
THdrv(Fall)
Tdead(L to Ldrv going Low to Hdrv
H)
going High, 10%-10%
65
70
1.9
1.7
1
1.2
14
17
30
75
MAX
Units
mS
kHz
V
%
%
umho
nA
V
%
ohm
ohm
A
A
ns
ns
ns
Ib
360
540
mV
Rev.1.2
02/26/07
3
NX2154/2154A
PIN DESCRIPTIONS
PIN #
1
PIN SYMBOL
BST
PIN DESCRIPTION
This pin supplies voltage to the high side driver. A high frequency
ceramic capacitor of 0.1 to 1 uF must be connected from this pin to SW pin.
High side MOSFET gate driver.
Ground pin.
Low side MOSFET gate driver. For the high current application, a 4.7nF capaci-
tor is recommend to placed on low side MOSFET's gate to ground. This is to
prevent undesired Cdv/dt induced low side MOSFET's turn on to happen, which
is caused by fast voltage change on the drain of low side MOSFET in synchro-
nous buck converter and lower the system efficiency.
Voltage supply for the internal circuit as well as the low side MOSFET gate
driver. A 1uF high frequency ceramic capacitor must be connected from this pin
to GND pin.
This pin is the error amplifier inverting input. This pin is also connected to the
output UVLO comparator. When this pin falls below 0.56V, both HDRV and
LDRV outputs are in hiccup.
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 also used as a shut
down pin. When this pin is pulled below 0.3V, both drivers are turned off and
internal soft start is reset.
This pin is connected to the source of the high side MOSFET and provides
return path for the high side driver. Also SW senses the low side MOSFETS
current, when the pin voltage is lower than 360mV for NX2154, 540mV for NX2154A,
hiccup will be triggered.
2
3
4
HDRV
GND
LDRV
5
Vcc
6
FB
7
COMP
8
SW
Rev.1.2
02/26/07
4
NX2154/2154A
BLOCK DIAGRAM
VCC
70%Vp
FB
Bias
Generator
1.25V
0.8V
UVLO
POR
START
Hiccup Logic
OC
BST
HDRV
COMP
0.3V
START 0.8V
OSC
Digital
start Up
ramp
S
R
FB
0.6V
CLAMP
COMP
START
GND
Q
PWM
OC
Control
Logic
VCC
SW
LDRV
1.3V
CLAMP
Hiccup Logic
360mV/540mV
OCP
comparator
Figure 2 - Simplified block diagram of the NX2154/NX2154A
Rev.1.2
02/26/07
5
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