MC34717EP Freescale Semiconductor, MC34717EP Datasheet - Page 17

• Manufacturer Part Number: MC34717EP
• Description: IC CONVERTER DDR 26QFN
• Manufacturer: Freescale Semiconductor

Specifications of MC34717EP

• Applications: Converter, DDR
• Voltage - Input: 3 ~ 6 V
• Number Of Outputs: 2
• Voltage - Output: 0.7 ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 26-QFN
• Output Voltage: 0.7 V to 3.6 V
• Output Current: 5 A
• Input Voltage: 3 V to 6 V
• Switching Frequency: 1 MHz
• Operating Temperature Range: - 40 C to + 85 C
• Mounting Style: SMD/SMT
• No. Of Outputs: 2
• Power Dissipation Pd: 2.03W
• No. Of Pins: 26
• Filter Terminals: SMD
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

current that can result in an undesired voltage spike once the
capacitor is fully charged. The soft start is active each time
the IC goes out of standby or shutdown mode, power is
recycled, or after a fault retry.
enabled, no faults have occurred, and the output voltage has
reached its regulation point, the 34717 pulls the power good
output signal low after a 10 ms reset delay, to indicate to the
host that the device is in normal operation.
PROTECTION FUNCTIONS
conditions to protect the load from overstress. The reaction of
the IC to these faults ranges from turning off the outputs to
just alerting the host that something is wrong. In the following
paragraphs, each fault condition is explained:
Output Over-voltage
goes higher than the rising over-voltage threshold (V
this case, the power good output signal is pulled high, alerting
the host that a fault is present, but the output will stay active.
To avoid erroneous over-voltage conditions, a 20 µs filter is
implemented. The buck converter will use its feedback loop
to attempt to correct the fault. Once the output voltage falls
below the falling over-voltage threshold (V
cleared and the power good output signal is pulled low, the
device is back in normal operation.
Output Under-voltage
falls below the falling under-voltage threshold (V
case, the power good output signal is pulled high, alerting the
host that a fault is present, but the output will stay active. To
avoid erroneous under-voltage conditions, a 20 µs filter is
implemented. The buck converter will use its feedback loop
to attempt to correct the fault. Once the output voltage rises
above the rising under-voltage threshold (V
cleared and the power good output signal is pulled low, the
device is back in normal operation.
Output Over-current
the buck converter. It is comprised of a sense MOSFET and
a comparator. The sense MOSFET acts as a current
Analog Integrated Circuit Device Data
Freescale Semiconductor
After a successful start-up cycle where the device is
The 34717 monitors the application for several fault
An over-voltage condition occurs once the output voltage
An under-voltage condition occurs once the output voltage
This block detects over-current in the Power MOSFETs of
OVF
UVR
), the fault is
), the fault is
UVF
). In this
OVR
). In
detecting device by sampling a ratio of the load current. That
sample is compared via the comparator with an internal
reference to determine if the output is in over-current or not.
If the peak current in the output inductor reaches the over
current limit (I
operation to limit the current, and a 10 ms over-current limit
timer (t
operation until one of the following occurs:
Short-circuit Current Limit
the over-current limit detection block. If the load current
reaches the I
the output immediately. This is necessary to prevent damage
in case of a permanent short circuit. Then, at the end of a
timeout period of 100 ms (t
another soft start cycle.
Thermal Shutdown
the device and protects against excessive heating. If the
temperature reaches the thermal shutdown threshold
(T
good output signal indicates a fault by pulling high. The
device will stay in this state until the temperature has
decreased by the hysteresis value and then After a timeout
period (t
automatically and the output will go through a soft start cycle.
If successful normal operation is regained, the power good
output signal is asserted low to indicate it.
SDFET
• The current is reduced back to the normal level before
• t
• The device reaches the thermal shutdown limit (T
• The output current keeps increasing until it reaches the
This block uses the same current detection mechanism as
Thermal limit detection block monitors the temperature of
t
regained.
which point the device turns off the output and the
power good output signal is pulled high. At the end of a
time-out period of 100 ms (t
attempt another soft start cycle.
and turns off the output. The power good output signal
is pulled high.
short-circuit current limit (I
details.
LIM
LIM
LIM
), the converter output switches off and the power
TIMEOUT
expires, and in this case normal operation is
expires without regaining normal operation, at
) starts. The converter will stay in this mode of
SHORT
LIM
) of 100 ms, the device will retry
), the converter will start a cycle-by-cycle
value, the device reacts by shutting down
FUNCTIONAL DEVICE OPERATION
TIMEOUT
SHORT
TIMEOUT
), the device will attempt
OPERATIONAL MODES
). See below for more
), the device will
SDFET
34717
17
)