nx2116 Microsemi Corporation, nx2116 Datasheet - Page 13

• Manufacturer Part Number: nx2116
• Description: Synchronous Pwm Controller With Current Limit, Power Good & Over Voltage
• Manufacturer: Microsemi Corporation

tion temperature increases, K is R
dependency. As a result, R
the worst case, in which K approximately equals to 1.4
at 125
tion loss should not exceed package rating or overall
system thermal budget.
duction at the switching transition. The total switching
loss can be approximated.
and T
is switching frequency. Switching loss P
dependent.
ered when choosing the proper power MOSFET.
MOSFET gate driver loss is the loss generated by dis-
charg
circuits.It is proportional to frequency and is defined as:
charge,Q
side gate source voltage.
mum power dissipation of the driver device.
Soft Start and Enable
ler and has one enable pin for this start up. When the
Power Ready (POR) signal is high and the voltage at
enable pin is above 1.25V the internal digital counter
starts to operate and the voltage at positive input of Error
amplifier starts to increase, the feedback network will
force the output voltage follows the reference and starts
the output slowly. After 2048 cycles, the soft start is
complete and the output voltage is regulated to the de-
Rev. 3.0
03/14/06
is the high side gate source voltage, and V
P
where I
gate
where the R
Switching loss is mainly caused by crossover con-
Also MOSFET gate driver loss should be consid-
where Q
NX2116 has digital soft start for switching control-
P
P
P
F
i
P
This power dissipation should not exceed maxi-
ng the gate capacitor and is dissipated in driver
o
HCON
LCON
TOTAL
SW
which can be found in mosfet datasheet, and F
C according to IRFR3709Z datasheet
LGATE
(Q
=I
=I
=P
OUT
HGATE
1
2
OUT
OUT
is the low side MOSFETs gate charge,V
HCON
HGATE
is output current, T
2
2
V
IN
DS(ON)
(1 D) R
D R
V
P
is the high side MOSFETs gate
I
HGS
OUT
LCON
will increases as MOSFET junc-
DS(ON)
Q
T
DS(ON)
SW
LGATE
DS(ON)
K
F
should be selected for
S
V
SW
K
DS(ON)
LGS
is the sum of T
) F
SW
temperature
is frequency
LGS
S
.
is the low
Conduc-
.
...(22)
...(20)
..(21)
NX2116/2116A/2116B/2117/2117A
HGS
R
S
sired voltage decided by the feedback resistor divider.
with Enable pin.
resistor divider at Enable pin. For example, if the input
bus voltage is12V and we want NX2116 starts when Vbus
is above 9V. We can select using the following equa-
tion.
Enable pin by extra signal MOSFET as shown in the
above Figure. When Enable pin is below 1.25V
tal soft start is reset to zero. In addition, all the high side
and low side driver is off and no negative spike will be
generated during the turn off.
Over Current Protection
rent through the low side MOSFET. An internal current
source of 40uA flows through an external resistor con-
nected from OCP pin to SW node sets the over current
protection threshold. When synchronous FET is on, the
voltage at node SW is given as
occurss as shown in figure 10.
ON
Figure 9 - Enable and Shut down the NX2116
The start up of NX2116 can be programmed through
The NX2116 can be turned off by pulling down the
Over current protection is achieved by sensing cur-
The voltage at pin OCP is given as
When the voltage is below zero, the over current
I
OFF
R
V =-I
OCP
10k
SW
1
(9V 1.25V) R
R
L
OCP
R1
R2
R
+V
1.25V
DSON
Vbus
SW
1.25V/
1.15V
EN
2
POR
Digital
start
up
,
the digi-
13