PI3749-X0 Datasheet, PDF (15/26 Pages) Vicor Corporation – 16V to 34VIN, 12V to 28VOUT, 240W Cool-Power ZVS Buck-Boost

Functional Description
The PI3749-x0 is part of a family of highly integrated ZVS Buck-
Boost regulators. The PI3749-x0 has a variable output voltage
that is set with a resistive divider. Performance and maximum
output current are characterized with a specific external power
inductor as defined in electrical specifications, with Inductor
Pairing section.
Vin
Cin
L1
Vin
PGND
VS1
VS2
VOUT
PGND
ISP
VDR
PGD
EN
SYNCO
PI3749-00
SYNCI
TRK
SGND
ISN
IMON
VSN
VSP
VDIFF
EAIN
EAO
COMP
Cout
Vout
R1
R2
Figure 24 — ZVS Buck-Boost with required components
For basic operation, Figure 24 shows the minimum connections
and components required.
Enable
The EN pin of the regulator is referenced to SGND and permits
the user to turn the regulator on or off. The EN polarity is a
positive logic assertion. If the EN pin is left floating or asserted
high, the regulator output is enabled. Pulling the EN pin below
0.8V_DC with respect to SGND will discharge the SS/TRK pin until
the output reaches zero or the EN pin is released.
Switching Frequency Synchronization
The SYNCI input allows the user to synchronize the controller
switching frequency to the falling edge of an external clock
referenced to SGND. The external clock can synchronize the
unit between 50% and 110% of the preset switching frequency
(FSW). The SYNCI pin should be connected to SGND when not in
use, and should never be left floating.
Soft-Start and Tracking
The PI3749-x0 provides a soft start and tracking feature using
the TRK pin. Programmable Soft Start requires an external
capacitor from the TRK pin to SGND in addition to the internal
47nF soft-start capacitor to set the start-up ramp period greater
then t_SS. The PI3749-x0 output will proportionately follow the
TRK pin when it is below 1.7V_DC. If the TRK pin is goes below the
disable threshold, the regulator will finish the current switching
cycle and then stop switching.
Remote Sensing Differential Amplifier
A general purpose operational amplifier is provided to assist
with differential remote sensing and or level shifting of the
output voltage. The VDIFF pin can be connected to the
transconductance error amplifier input EAIN pin, or with proper
Cool-Power^® ZVS Switching Regulators
Page 15 of 26
Rev 1.6
09/2016
PI3749-x0
configuration can also be connected to the EAO pin to drive the
modulator directly.
Power Good
The PI3749-x0 PGD pin functions as a power good indicator and
pulls low when the regulator is not operating or if EAIN is less
than 1.4V.
Output Current Limit Protection
PI3749-x0 has three methods implemented to protect from
output short circuit or over current condition.
Slow Current Limit protection: prevents the output load from
sourcing current higher than the maximum rated regulator
current. If the output current exceeds the Vout Slow Current
Limit (V_{OUT_SCL}) a slow current limit fault is initiated and the
regulator is shutdown which eliminates output current flow.
After Fault Restart Delay (t_{FR_DLY}), a soft-start cycle is initiated.
This restart cycle will be repeated indefinitely until the excessive
load is removed.
Fast Current Limit protection: monitors the regulator inductor
current pulse-by-pulse to prevent the output from supplying
very high current. If the regulator senses a high inductor current
pulse, it will initiate a fault and stop switching. After Fault Restart
Delay (t_{FR_DLY}), a soft-start cycle is initiated. This restart cycle will
be repeated indefinitely until the excessive load is removed.
Overload Timeout protection: If the regulator is providing
maximum output power for longer than the Overload Timeout
delay (T_OL), it will initiate a fault and stop switching. After Fault
Restart Delay (t_{FR_DLY}), a soft-start cycle is initiated. This restart
cycle will be repeated indefinitely until the overload load
is removed.
Input Undervoltage Lockout
If V_IN falls below the input Under Voltage Lockout (UVLO)
threshold, the PI3749-x0 will complete the current cycle and
stop switching. The system will restart once the input voltage is
reestablished and after the Fault Restart Delay.
Input Overvoltage Lockout
If V_IN rises above the input Overvoltage Lockout (OVLO)
threshold, the PI3749-x0 will complete the current cycle and
stop switching. The system will restart once the input voltage is
reestablished and after the Fault Restart Delay.
Output Overvoltage Protection
The PI3749-x0 family is equipped with two methods of detecting
an output overvoltage condition. Output Overvoltage Protection
(OVP) to prevent damage to input voltage sensitive devices. If
the output voltage exceeds 20% of its set regulated value as
measured by the EAIN pin (V_{EAIN_OV}), the regulator will complete
the current cycle, stop switching and issue an OVP fault. Also if
the output voltage of the regulator exceeds the V_OUT Overvoltage
Threshold (V_{OUT_OVT}) then the regulator will complete the current
cycle, stop switching and issue an OVP fault. The system will
resume operation once the output voltage falls below the OVP
threshold and after Fault Restart Delay.
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