PI3740-00 Datasheet, PDF (20/48 Pages) Vicor Corporation – Parallel capable with single wire current sharing

Functional Description
The PI3740-00 is a highly integrated ZVS Buck-Boost regulator.
The PI3740-00 has an adjustable 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 the electrical specifications, and in the inductor
pairing section.
VIN VS1
C_IN
PGND
VS2 VOUT
PGND
C_OUT
R1
ISP
R2
ISN
10kΩ
VDR
PI3740-00
IMON
VSN
VSP
PGD
VDIFF
EN
LGH
SYNCO
EAIN
SYNCI
EAO
TRK
SGND
COMP
C_HF
C_TRK
C_COMP
Figure 37 — PI3740-00 with required components
For basic operation, Figure 37 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 TRK pin until
the output reaches zero or the EN pin is released. When the
converter is disabled via the EN pin or due to a fault mode, the
internal gate driver high side charge pumps are enabled as long
as there is enough input voltage for the internal VDR supply
voltage to be available. The return path for this charge pump
supply is through the output. If the output load is disconnected
or high impedance, the output capacitors will float up to
about 3.4V maximum, sourced by 960µA of leakage current.
This pre-biased condition poses no issue for the converter.
The 960µA leakage current may be safely bypassed to SGND.
A simple application circuit is available to bypass this current
in a non-dissipative manner. Please contact Applications
Engineering for details.
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
(F_SW). The SYNCI pin should be connected to SGND when not in
use, and should never be left floating.
Soft-Start and Tracking
The PI3740-00 provides a soft start and tracking feature using
the TRK pin. Programmable Soft Start requires an external
Cool-Power^® ZVS Switching Regulators
Page 20 of 48
Rev 1.4
04/2017
PI3740-00
capacitor from the TRK pin to SGND in addition to the internal
56pF soft-start capacitor to set the start-up ramp period equal
to t_SS. The recommended value is 47nF. The PI3740-00 internal
reference and regulated output will proportionally follow the
TRK ramp when it is below 1.7V_DC. When the ramp is greater
than 1.7V_DC, the internal reference will remain at 1.7V_DC while
the TRK ramp rises and clamps at 2.5V_DC. If the TRK pin 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
configuration can also be connected to the EAO pin to drive the
modulator directly. If unused, connect in unity gain with VSP
connected to SGND.
Power Good
The PI3740-00 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
PI3740-00 has three methods implemented to protect from
output short circuit or over current condition.
Slow Current Limit protection: prevents the regulator load
from sourcing current higher than the maximum rated regulator
current. If the output current exceeds the V_OUT Slow Current
Limit (V_{OUT_SCL}) a slow current limit fault is initiated and the
regulator is shutdown, which eliminates output current flow.
After the 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 external inductor
current pulse-by-pulse to prevent the output from supplying
saturation current. If the regulator senses a high inductor
current pulse, it will initiate a fault and stop switching. After
the 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
greater than the 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 Undervoltage Lockout (UVLO)
threshold, the PI3740-00 will complete the current cycle and
stop switching. The system will restart once the input voltage
is reestablished.
Input Overvoltage Lockout
If V_IN rises above the input Overvoltage Lockout (OVLO)
threshold, the PI3740-00 will complete the current cycle and
stop switching. The system will restart once the input voltage is
reestablished and after the Fault Restart Delay.
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