MC34652EF Freescale Semiconductor, MC34652EF Datasheet - Page 19

• Manufacturer Part Number: MC34652EF
• Description: IC CTRLR HOT SWAP NEG V 16-SOIC
• Manufacturer: Freescale Semiconductor
• Type: Hot-Swap Switchr

Specifications of MC34652EF

• Applications: General Purpose
• Internal Switch(s): Yes
• Current Limit: 2.0A
• Voltage - Supply: 15 V ~ 80 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

timer initiates. The UV and OV detection circuits are
equipped with a 1.0 ms filter to filter out momentary input
supply dips. Filter capacitors between the UV and VIN pins
and between the OV and VIN pins could also be added to
adjust the UV/OV filter time and prevent more transients from
affecting the device’s operation, especially if the input supply
has a lot of noise.
Guidelines for Choosing Resistor Divider Values
supply voltage divided by the total series resistance. The
supply voltage can reach up to 80 V and the device will still
be in normal operation, the resistors connected and drawing
current. So the resistor values should be chosen high enough
to allow for a reasonable current to pass through them and
not dissipate a lot of power or cause input noise that would
trip the UV / OV detection circuit.
resistors are readily available. The tolerance of the resistors
should be 1% or better to get an accurate reading.
resistors, let’s look at a system with an operating range of
40 V for UV falling to 75 V for OV rising as an example. This
operating range will be scaled down for the device’s internal
circuitry to operate the UV/OV detection circuits. The scale
factor is 31.6 for UV and 57.1 for the OV. Taking overvoltage
as an example, this means that every 5.0 mV change on the
OV pin represents a 0.29 V change for the OV trip point on
the supply. Which says that an error of 5.0 mV due to the
resistors not being accurate will result in an error of 0.29 V for
the trip point, and depending on how close we are operating
to the OV rising threshold the device might detect an OV
condition and turn off the Power MOSFET prematurely. The
same argument applies to the UV pin.
Example of Calculations for Resistor Values
resistor values using the same operating range as in the
previous paragraph:
Where V
values and also standard resistor values. The recommended
maximum value of the series resistance between the UV/OV
pins and VPWR pin is 500 kΩ.
select a value for R
and the closest 1% standard resistor value is 8.66 kΩ.
and the closest 1% standard resistor value is 7.15 kΩ.
Analog Integrated Circuit Device Data
Freescale Semiconductor
R
The total current flowing in the resistors is equal to the
Another consideration is whether or not the values of the
Note Accuracy requirements are application dependent.
To demonstrate the importance of the accuracy of the
The following equations are examples of calculating
Note Some iteration may be required to get the right
Here we have two equations and three unknowns. If we
Now, from the second equations we can solve for R
3
= 1.3
OV (RISING)
*
R
R
1
2
*
= R
V
UV (RISING)
3
= 75 V and V
1
(V
of 487 kΩ, then from the first equation:
OV (RISING)
R
R
3
2
= 8.72 kΩ
= 7.18 kΩ
/ (
V
OV (RISING)
UV (RISING)
/
V
UV (RISING)
(
V
= 41 V
UV (RISING)
- 1)
- 1.3))
2
:
TIMER and VIN pins, as shown in
default value of 200 ms.
approach, could not produce acceptable resistor values, the
user can consider two separate resistor dividers, one divider
for each pin from VPWR to VIN. An advantage of the two-
resistor dividers approach is that the user can set the trip
points of the UV and OV thresholds independently.
TIMER
the time base used to generate the timing sequences at start-
up. The same timer controls the retry delay when the device
experiences any fault. The TIMER pin can be left
unconnected for a default timer value of 200 ms or the user
can connect an external resistor (R
TIMER and VIN pins, as shown in
the timer value externally.
continuously after that, the 34652 checks the TIMER pin for
any external components to determine the value of the timer.
During start-up and if any fault occurred, this timer value is
used when initiating a start-up sequence.
Choosing the External Resistor R
Timer (t
timer value ranges between 100 ms and 1000 ms, with a
different values of the t
a plot of R
closest 1% standard resistor value to the actual value be
chosen.
following equations:
Table 6. R
t
If the three-resistor divider, which is the recommended
The TIMER pin on the 34652 gives the user control over
After the device passes the UVLO threshold and
The user can change the value of the Start-Up Delay
Note Accuracy requirements are application dependent.
To calculate the value of the R
TIMER
t
TIMER
R
100
150
200
250
300
350
400
450
500
500
TIMER
TIMER
(ms)
TIMER
(ms) = 20 (ms) + 2.0
TIMER
(kΩ) = [t
) by adding a resistor (R
versus t
R
Values for Some Desired t
TIMER
114
139
164
189
214
239
264
TIMER
39
64
89
TIMER
(kΩ)
Table 6
TIMER
(ms) - 20 (ms) ] / 2.0 - 1.0 kΩ
and
. It is recommended that the
*
t
lists examples of R
Figure
TIMER
TIMER
[R
Figure
Figure
T
1000
TIMER
TIMER
600
650
700
750
800
850
900
950
IMER
TYPICAL APPLICATIONS
—
TIMER
(ms)
resistor we use the
20,
) between the
19,
19,
(kΩ) + 1.0 kΩ]
Value
) between the
page
page
page
TIMER
R
TIMER
20, shows
18, to set
18. The
289
314
339
364
389
414
439
464
489
TIMER
—
Values
(kΩ)
34652
for
19