NX2113A MICROSEMI [Microsemi Corporation], NX2113A Datasheet - Page 15

• Manufacturer Part Number: NX2113A
• Description: 300kHz & 600kHz SYNCHRONOUS PWM CONTROLLER WITH PROGRAMMABLE BUS UVLO
• Manufacturer: MICROSEMI [Microsemi Corporation]

loss: conduction loss, switching loss and gate driver loss.
ing the gate capacitor and is dissipated in driver circuits.
It is proportional to frequency and is defined as:
charge,Q
power dissipation should not exceed maximum power
dissipation of the driver device.
tion temperature increases, K is R
dependency. As a result, R
the worst case, in which K equals to 1.4 at 125
cording to IRFR3706 datasheet
the result of P
not exceed package rating or overall system thermal
budget.
duction at the switching transition. The total switching
loss can be approximated.
where I
which can be found in mosfet datasheet, and F
ing frequency. The result of P
P
Soft Start, Enable and shut Down
digital counter with 1024 cycles. For NX2113 with 300kHz
operation, the start up time is about 3.5ms. For NX2113A
with 600kHz operation, the start up time is about half of
NX2113, 1.75mS.
Rev. 2.0
11/18/05
is the high side gate source voltage, and V
the low side gate source voltage.
SW
P
gate
is frequency dependent.
Gate driver loss is the loss generated by discharg-
where Q
According to equation (20), P
Conduction loss is simply defined as:
where the R
Switching loss is mainly caused by crossover con-
The NX2113 has a digital start up. It is based on
P
P
P
P
There are three factors causing the MOSFET power
HCON
LCON
TOTAL
SW
OUT
LGATE
(Q
is output current, T
=I
=I
=P
HGATE
2
1
OUT
OUT
is the low side MOSFETs gate charge,V
HCON
TOTAL
HGATE
2
2
V
IN
DS(ON)
(1 D) R
D R
V
is 0.54W. Conduction loss should
is the high side MOSFETs gate
P
HGS
I
OUT
LCON
will increases as MOSFET junc-
DS(ON)
Q
T
DS(ON)
SW
LGATE
DS(ON)
SW
SW
K
is the sum of T
.
F
should be selected for
S
Using equation (21),
is 3W. Swithing loss
V
K
LGS
DS(ON)
GATE
) F
=0.14W. This
temperature
S
LGS
S
is switch-
.
..(22)
R
...(21)
is
...(20)
o
and T
C ac-
HGS
F
pulling down EN pin.
through resistor divider at Enable pin. For example, if
the input bus voltage is 12V and we want NX2113 starts
when Vbus is above 8V. We can select
ENable pin by extra signal MOSFET or NPN transistor
such as 2N3904 as shown in the above Figure. When
Enable pin is below 1.15V, the digital soft start is reset
to zero. In addition, all the high side is off and output
voltage is turned off.
leakage current from FB pin charging the output capaci-
tors.
Feedback Under Voltage Shut Down
Out (FB UVLO ) to provide short circuit protection. Ba-
sically, NX2113 has a comparator compares the feed-
back voltage with the FB UVLO threshold 0.4V.
the feedback voltage will be lower than 0.4V and com-
parator will change the state. After certain internal delay,
both high side and low side driver will be turned off. The
output will be latched. The normal operation should be
achieved by removing the short and recycle the VCC.
charged to zero by the synchronous FET. FB voltage
starts increase from zero when digital start block
Figure 14 - Enable and Shut down NX2113 by
The start up of NX2113/2113A can be programmed
R2=1.24k
The NX2113 can be turned off by pulling down the
A resistor should be added as preload to prevent
NX2113 relies on the Feedback Under Voltage Lock
During the normal operation, if the output is short,
R
ON
1
During the start up, the output voltage is dis-
OFF
10k
(8V 1.25V) R
1.25V
R1
R2
Vbus
1.25/1.15
EN
NX2113/2113A
2
6.8k
POR
Digital
start
up
15