NCP81038MNTWG

NCP81038
http://onsemi.com
10
DCR
L
Rs1
Rs2
C
Vin
Vout
Vc
+
Figure 3. X
DCR
L
R
R1
RNTC
C
R2
Vin
Vout
Vc
+
Figure 4. X + 1
R
THE
The Rs1, Rs2 and C can be calculated as:
C @
ǒ
R
S1
ńńR
S2
Ǔ
+
L
DCR
The inductor peak current limit is:
I
LIM(Peak)
+
V
th_DC
k @ DCR
,where k +
R
S2
R
S1
) R
S2
The DC current limit is:
I
LIM
+ I
LIM(Peak)
*
V
O
@ (V
in
* V
O
)
2 @ V
in
@ f
SW
@ L
where Vin is the input supply voltage of the power stage, and
fsw is normal switching frequency.
Fig. X+1 shows NTC resistor network to compensate the
temperature drift of DCR.
If inductor current exceeds the current threshold, the
highside gate driver will be turned off cyclebycycle. In
the mean time, an internal OC fault timer will be triggered.
If the fault still exists after 16 clocks, the part latches off,
both the highside MOSFET and the lowside MOSFET are
turned off. If the sensed current reaches 60 mV, the part will
latch off right away. The fault remains set until the system
has shutdown and reapplied VCC and/or the enable signal
EN is toggled.
PreBias Startup
In some applications the controller will be required to start
switching when its output capacitors are charged anywhere
from slightly above 0 V to just below the regulation voltage.
This situation occurs for a number of reasons: the
converters output capacitors may have residual charge on
them or the converters output may be held up by a low
current standby power supply. NCP81038 supports prebias
start up by holding Low side FETs off till soft start ramp
reaches the FB pin voltage.
Thermal Shutdown
The NCP81038 protects itself from over heating with an
internal thermal monitoring circuit. If the junction
temperature exceeds the thermal shutdown threshold the
voltage at the COMP pin will be pulled to GND and both the
upper and lower MOSFETs will be shut OFF.
NCP81038
http://onsemi.com
11
PACKAGE DIMENSIONS
QFN28 4x4, 0.4P
CASE 485AR
ISSUE A
NOTES:
1. DIMENSIONING AND TOLERANCING PER ASME
Y14.5M, 1994.
2. CONTROLLING DIMENSION: MILLIMETERS.
3. DIMENSION b APPLIES TO PLATED TERMINAL
AND IS MEASURED BETWEEN 0.15 AND 0.30 MM
FROM THE TERMINAL TIP.
4. COPLANARITY APPLIES TO THE EXPOSED PAD
AS WELL AS THE TERMINALS.
A
D
E
B
C0.10
PIN ONE
REFERENCE
TOP VIEW
SIDE VIEW
BOTTOM VIEW
A
K
D2
E2
C
C0.10
C0.10
C0.08
A1
SEATING
PLANE
e
28X
NOTE 3
b
28X
0.07 C
0.05 C
A
BB
DIM MIN MAX
MILLIMETERS
A 0.80 1.00
A1 0.00 0.05
b 0.15 0.25
D 4.00 BSC
D2 2.50 2.70
E 4.00 BSC
E2 2.50 2.70
e 0.40 BSC
K
L 0.30 0.50
8
15
22
28X
0.40
PITCH
4.30
0.62
4.30
DIMENSIONS: MILLIMETERS
0.26
28X
1
L
A3 0.20 REF
MOUNTING FOOTPRINT
NOTE 4
A3
PIN 1
INDICATOR
2.71
2.71
1
PACKAGE
OUTLINE
L1
DETAIL A
L
ALTERNATE TERMINAL
CONSTRUCTIONS
L
DETAIL B
MOLD CMPDEXPOSED Cu
ALTERNATE
CONSTRUCTION
DETAIL B
DETAIL A
0.10 C A
BB
0.10 C A
BB
L1 −−− 0.15
0.30 REF
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NCP81038/D
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NCP81038MNTWG

Mfr. #:
Manufacturer:
ON Semiconductor
Description:
Switching Controllers SYNCHRONOUS BUCK CONTROLL
Lifecycle:
New from this manufacturer.
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