LTM4609V Просмотр технического описания (PDF) - Linear Technology

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LTM4609V

36VIN, 34VOUT High Efficiency Buck-Boost DC/DC µModule Regulator

Linear Technology 

LTM4609

Applications Information

In buck mode, the allowed maximum average load cur-

rent is:

IOUT(MAX,BUCK)

=

130mV

RSENSE

+

∆IL

2

The maximum current sensing RSENSE value for the boost

mode is:

RSENSE(MAX,BOOST) =

2 •160mV • VIN

2 •IOUT(MAX,BOOST) • VOUT + ∆IL • VIN

The maximum current sensing RSENSE value for the buck

mode is:

RSENSE(MAX,BUCK)

=

2

2 •130mV

•IOUT(MAX,BUCK)

–

∆IL

A 20% to 30% margin on the calculated sensing resistor

is usually recommended. Please refer to Table 3 for the

recommended sensing resistors for different applications.

Run Enable

The RUN pin is used to enable the power module. The pin

can be driven with a logic input, not to exceed 6V.

The RUN pin can also be used as an undervoltage lockout

(UVLO) function by connecting a resistor from the input

supply to the RUN pin. The equation:

V_UVLO= R1+R2 •1.6V

R2

Power Good

The PGOOD pin is an open drain pin that can be used to

monitor valid output voltage regulation. This pin monitors

a ±7.5% window around the regulation point.

COMP Pin

This pin is the external compensation pin. The module

has already been internally compensated for most output

voltages. A spice model is available for other control loop

optimization.

Soft-Start

The SS pin provides a means to soft-start the regulator.

A capacitor on this pin will program the ramp rate of the

output voltage. A 1.7µA current source will charge up the

external soft-start capacitor. This will control the ramp of

the internal reference and the output voltage. The total

soft-start time can be calculated as:

tSOFTSTART

=

2.4V •CSS

1.7µA

When the RUN pin falls below 1.6V, then the soft-start

pin is reset to allow for proper soft-start control when

the regulator is enabled again. Current foldback and force

continuous mode are disabled during the soft-start process.

Do not apply more than 6V to the SS pin.

Fault Conditions: Current Limit and Overcurrent

Foldback

LTM4609 has a current mode controller, which inherently

limits the cycle-by-cycle inductor current not only in steady

state operation, but also in transient. Refer to Table 3.

To further limit current in the event of an overload condi-

tion, the LTM4609 provides foldback current limiting. If the

output voltage falls by more than 70%, then the maximum

output current is progressively lowered to about 30% of

its full current limit value for boost mode and about 40%

for buck mode.

Standby Mode (STBYMD)

The standby mode (STBYMD) pin provides several choices

for start-up and standby operational modes. If the pin is

pulled to ground, the SS pin is internally pulled to ground,

preventing start-up and thereby providing a single control

4609ff

12

For more information www.linear.com/LTM4609

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