LT3582 datasheet(15/28 Pages) LINER

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LT3582/LT3582-5/LT3582-12

3582512f

disconnect current limit being reached D) additional ring-

ing occurs when the CAPP pin starts charging E) output

voltage overshoot occurs because the inductor currents

are maximized during the output ramp up.

In some cases it may be desirable to use only one RAMP

pin capacitor. In cases where PUSEQ = 11 (see Power-Up

Sequencing section) the RAMPP & RAMPN pins can be

connected together and to a single capacitor. In this case

the capacitor will charge with twice the current conﬁgured

by the IRMP bits.

Ramping VOUTP from Ground: The LT3582 series has

the unique ability to generate a smooth VOUTP voltage

ramp starting from ground and continuing all the way up

to regulation (see Figure 6). This ability is not possible

with typical Boost converters in which the output is taken

from the cathode of the Schottky diode (CAPP node in

Figure 5).

The LT3582 series incorporates an output disconnect

PMOS allowing VOUTP to be grounded during shutdown.

SWP

VOUTP

VIN

CAPP

LT3582

SERIES

DISCONNECT

CONTROL

LOAD

3582512 F05

APPLICATIONS INFORMATION

Once enabled, the Disconnect Control circuit actively

drives the PMOS gate allowing VOUTP to ramp up linearly

as shown in Figure 6. Once VOUTP reaches regulation,

the PMOS is fully turned “on” to reduce resistance and

improve efﬁciency.

Power-Up Sequencing (PUSEQ bits)

Once enabled, the part requires a delay of TSTARTUP (64μs

typ) to properly conﬁgure itself. Once conﬁgured, the order

in which VOUTP and VOUTN ramp to regulation is controlled

by the PUSEQ bits. The combinations available for the

LT3582 are shown in Table 2. The LT3582-5/LT3582-12

are pre-conﬁgured with the 11 combination.

Table 2. Power-Up Sequences

PUSEQ[1:0]

Power-Up Sequence

Outputs are disabled, neither output ramps up

VOUTN ramps up 1st, followed by VOUTP

VOUTP ramps up 1st, followed by VOUTN

Both VOUTP & VOUTN ramp up starting at the

same time.

Selecting the 01 or 10 combinations cause one of the out-

puts to start ramping shortly after SHDN rises. The ramp

rate of VOUT is controlled by the RAMP pin as discussed in

the Soft-Start section. After VOUT nears its target regula-

tion voltage, the remaining output is activated and ramps

Figure 5: Boost Converter Topology

Figure 6: VOUTP Soft-Start Ramping from Ground

Figure 7: VOUTP Soft-Start with Excessive Ramp Rate

3582512 F06

CAPP

2V/DIV

IL2

0.2A/DIV

VRAMPP

0.2V/DIV

VOUTP

2V/DIV

5μs/DIV

3582512 F07

VOUTP

3V/DIV

VRAMPP

0.5V/DIV

CAPP

3V/DIV

IL2

0.2A/DIV

50μs/DIV

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