LTC4264IDE datasheet(19/24 Pages) LINER

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LTC4264

4264f

APPLICATIONS INFORMATION

RCLASS from Table 2. If a unique load current is required,

the value of RCLASS can be calculated as:

RCLASS = 1.237V/(ILOAD – IIN_CLASS)

IIN_CLASS is the LTC4264 IC supply current during clas-

siﬁcation given in the electrical speciﬁcations. The RCLASS

resistor must be 1% or better to avoid degrading the overall

accuracy of the classiﬁcation circuit. Resistor power dissi-

pation will be 100mW maximum and is transient so heating

is typically not a concern. In order to maintain loop stabil-

ity, the layout should minimize capacitance at the RCLASS

node. The classiﬁcation circuit can be disabled by ﬂoating

the RCLASS pin. The RCLASS pin should not be shorted to

VIN as this would force the LTC4264 classiﬁcation circuit

to attempt to source very large currents. In this case, the

LTC4264 will quickly go into thermal shutdown.

GND

10k

R10

100k

PWRGD

MMBD4148

FMMT2222

–54V

4264 F11

PSE

LTC4264

ACTIVE-LOW ENABLE

VIN

VOUT

V+

LOAD

GND

10k

100k

PWRGD

5.1V

MMBZ5231B

–54V

PSE

LTC4264

ACTIVE-LOW ENABLE

VIN

VOUT

LOAD

–54V

PSE

ACTIVE-HIGH ENABLE

LOAD

RUN

SHDN

GND

PWRGD

LTC4264

VIN

VOUT

Power Good Interface

The LTC4264 provides complimentary power good signals

to simplify the DC/DC converter interface. Using the power

good signal to delay converter operation until the load

capacitor is fully charged is recommended as this will help

ensure trouble free start up. The active high PWRGD pin

is controlled by an open collector transistor referenced to

VOUT while the active low PWRGD pin is controlled by a

high voltage, open-drain MOSFET referenced to VIN. The

designer has the option of using either of these signals to

enable the DC/DC converter and example interface circuits

are shown in Figure 11. When using PWRGD, diode D9

and resistor RS protects the converter shutdown pin from

excessive reverse voltage.

Figure 11. Power Good Interface Examples

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