uP1723
Functional Description
Output Voltage Setting and Feedback Network
Over Voltage Protection
For the adjustable output version, the output voltage can The uP1723 continuously monitors FB voltage for over
be set from VREF to VIN by a voltage divider as:
voltage protection. When VFB > 1.1V (typical), the uP1723
triggers over voltage protection and the low-side MOSFET
is turned on while high-side MOSFET is turned off to
discharge the output voltage. At any time if the OVP
condition is relieved, the uP1723 will restart the soft start
0.925 ×
(
R1+ R2
)
VOUT
=
R2
The internal VREF is 0.925V with 1.5% accuracy. In real
applications, a 22pF feed-forward ceramic capacitor is
recommended in parallel with R1 for better transient
response.
sequence.
Over Temperature Protection
The OTP is triggered and shuts down the uP1723 if the
junction temperature is higher than 150OC. The OTP is a
non-latch type protection. The uP1723 automatically
initiates another soft start cycle if the junction temperature
drops below 120OC.
Current Limit Function
The uP1723 continuously monitors the inductor current
for current limit by sensing the voltage drop across the
upper switch when it turns on. When the inductor current
is higher than current limit threshold (4A typical), the
current limit function activates and forces the upper switch
turning off to limit inductor current cycle by cycle. If the
load continuously demands more current than what
uP1723 could provide, uP1723 will not be able to regulate
the output voltage, and the output voltage will drop
accordingly. Eventually, under voltage protection will be
triggered if VFB is lower than UVP threshold.
When the output is shorted to ground, the current limit
function activates immediately, and VOUT will be pulled
down very fast. Eventually the under voltage protection
will be triggered, and the IC will shut down to protect
external components. The IC will restart after the UVP
retry delay, and the above behavior may repeat if the output
short condition is not released. This is the so-called Short
Circuit Protection (SCP).
Under Voltage Protection
The uP1723 continuously monitors FB voltage for under
voltage protection. When VFB < 0.4V (typical), the uP1723
triggers under voltage protection and enters frequency
decay mode which the switching frequency of the
uP1723 will decrease linearly according to the FB voltage
drop. Eventually when VFB = 0V, the switching frequency
of the uP1723 will be clamped at 100kHz. After triggering
UVP, the SS voltage is also discharged to 0V. After VSS
=
0V, the uP1723 will try to re-soft-start to establish the
output voltage once again. In the end of re-soft-start (VSS
= 1.2V), if the UVP condition is still not relieved, the
uP1723 will turn-off all high-side and low-side MOSFETs
and re-try to soft start every 8ms.
uP1723-DS-P0001, Jan. 2015
www.upi-semi.com
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