NCP346SN1T1G ON Semiconductor, NCP346SN1T1G Datasheet - Page 7

• Manufacturer Part Number: NCP346SN1T1G
• Description: Supervisory Circuits 4.45V Overvoltage Supervisor
• Manufacturer: ON Semiconductor

Specifications of NCP346SN1T1G

• Number Of Voltages Monitored: 1
• Monitored Voltage: 4.45 V
• Overvoltage Threshold: Adjustable, 4.55 V
• Output Type: PFET Driver
• Manual Reset: Resettable
• Watchdog: No Watchdog
• Supply Voltage (max): 25 V
• Supply Voltage (min): 2.5 V
• Supply Current (typ): 650 uA
• Maximum Power Dissipation: 216 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: SOT-23-5 Thin (TSOP-5)
• Minimum Operating Temperature: - 40 C
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Normal Operation
adapter provides power to the protection system so the
circuitry is only active when the adapter is connected. The
OVP monitors the voltage from the charger and if the
voltage exceeds the overvoltage threshold, V
signal drives the gate of the MOSFET to within 1.0 V of
V
from the load. The nominal time it takes to drive the gate to
this state is 400 nsec (1.0 msec maximum for gate
capacitance of < 12 nF). The CNTRL input can be used to
interrupt charging and allow the microcontroller to measure
the cell voltage under a normal condition to get a more
accurate measure of the battery voltage. Once the
overvoltage is removed, the NCP346 will turn on the
MOSFET. The turn on circuitry is designed to turn on the
MOSFET more gradually to limit the in−rush current. This
characteristic is a function of the threshold of the MOSFET
and will vary depending on the device characteristics such
as the gate capacitance.
gate of the FET to a HIGH state.
•
•
Adjusting the Overvoltage Detection Point with
External Resistors
overvoltage threshold, V
divider with the tap at the IN pin. However, R
significant role in the calculation since it is several
10’s of kW. The following equation shows the effects of R
Figure 4. Voltage divider input to adjust overvoltage
CC
Figure 1 illustrates a typical configuration. The external
There are two events that will cause the OVP to drive the
The separate IN and V
Voltage on IN Rises Above the Overvoltage Detection
Threshold
CNTRL Input is Driven to a Logic HIGH
, thus turning off the FET and disconnecting the source
V CC + V x (1 ) R 1 (R 2 R in ))
R
R
1
2
V
detection point
CC
CC
th
, upwards by adding a resistor
pins allow the user to adjust the
GND
I
N
R
in
in
th
does play a
, the OUT
(eq. 1)
http://onsemi.com
in
NCP346
.
7
which equates to:
So, as R
accordance to the ratio of R
this shift can be minimized. The following steps show this
procedure.
Designing around the Maximum Voltage Rating
Requirements, V(V
pins V
the design does not exceed this voltage. Normally, the
designer shorts V
there is no issue. However, one must take care when
adjusting the overvoltage threshold.
the V(V
equals 30 V, therefore, one must ensure that:
maximum overvoltage thresholds which are less than 15 V.
If greater thresholds are desired than can be accommodated
by the NCP346, ON Semiconductor offers the NCP345
which can withstand those voltages.
This shows that R
The NCP346’s maximum breakdown voltage between
In Figure 4, the R1 resistor of the voltage divider divides
V(V
Where 0.5 = V(V
Therefore, the NCP346 should only be adjusted to
CC
CC
(V CC , IN) + V CC * (R1 (R1 ) (R2
CC
in
, IN) worst case equals 15 V, and V
and IN is 15 V. Therefore, care must be taken that
approaches infinity:
, IN) voltage to a given voltage threshold equal to:
V CC + V x (1 ) R 1 R 2 ) R 1 R in )
V CC + V x (1 ) R 1 R 2)
R1 (R1 ) (R2
CC
CC
CC
to IN, V(V
in
, IN)max/V
, IN)
shifts the V
1
/ R
CC
R in )) t 0.5
in
, IN) is shorted to 0 V, so
CCmax
. However, if R
th
detection point in
CC
R in )))
worst case
1
<< R
(eq. 2)
(eq. 3)
(eq. 4)
(eq. 5)
in
,