PI3741-0X datasheet(21/38 Pages) VICOR

21 / 38 page

Cool-Power® ZVS Switching Regulators

Rev 1.1

vicorpower.com

Page 21 of 38

08/2016

800 927.9474

PI3741-0x

Functional Description

The PI3741-0x is a family of highly integrated ZVS Buck-Boost

regulators. The PI3741-0x 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.

For basic operation, Figure 30 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

0.8VDC with respect to SGND will discharge the SS/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 960uA

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

(FSW). The SYNCI pin should be connected to SGND when not in

use, and should never be left floating.

Soft-Start and Tracking

The PI3741-0x 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

than tSS. The PI3741-0x internal reference and regulated output

will proportionally follow the TRK ramp when it is below 1.7VDC.

When the ramp is greater than 1.7VDC, the internal reference will

remain at 1.7VDC while the TRK ramp rises and clamps at 2.5VDC.

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 PI3741-0x 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

PI3741-0x 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 VOUT Slow Current

Limit (VOUT_SCL) a slow current limit fault is initiated and the

regulator is shutdown, which eliminates output current flow.

After the Fault Restart Delay (tFR_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 (tFR_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 (TOL), it will initiate a fault and stop

switching. After Fault Restart Delay (tFR_DLY), a soft-start cycle is

initiated. This restart cycle will be repeated indefinitely until the

overload load is removed.

Input Undervoltage Lockout

If VIN falls below the input Undervoltage Lockout (UVLO)

threshold, the PI3741-0x 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 VIN rises above the input Overvoltage Lockout (OVLO)

threshold, the PI3741-0x will complete the current cycle and

stop switching. The system will restart once the input voltage is

reestablished and after the Fault Restart Delay.

SGND

OUT

PGND

COMP

ISP

ISN

IMON

EAO

OUT

PGND

VS1

VS2

VSN

VSP

VDIFF

EAIN

SYNCI

VDR

SYNCO

TRK

PGD

PI3741

10k

4700pF

COMP

Figure 30 — ZVS Buck-Boost with required components

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