LTC1479IG データシートの表示（PDF） - Linear Technology

部品番号

コンポーネント説明

メーカー

LTC1479IG

PowerPath Controller for Dual Battery Systems

Linear Technology 

LTC1479

U

OPERATION

The LTC1479 is responsible for low-loss switching at the

“front end” of the power management system, where up

to two battery packs and a DC power source can be

indiscriminately connected and disconnected. Smooth

switching between input power sources is accomplished

with the help of low-loss N-channel switches driven by

special gate drive circuitry which limits the inrush current

in and out of the battery packs and the system power

supply capacitors.

All N-Channel Switching

The LTC1479 drives external back-to-back N-channel

MOSFET switches to direct power from the three main

power sources: the external DC power source, the pri-

mary battery and the secondary battery connected to the

main supply pins—DCIN, BAT1 and BAT2 respectively.

(N-channel MOSFET switches are more cost effective

and provide lower voltage drops than their P-channel

counterparts.)

Gate Drive (VGG) Power Supply

The gate drive for the low-loss N-channel switches is

supplied by a micropower boost regulator which is regu-

lated at approximately 36.5V. The VGG supply provides

sufficient headroom above the maximum 28V operating

voltage of the three main power sources to ensure that the

MOSFET switches are fully enhanced.

The power for this inductor based regulator is taken from

three internal diodes as shown in Figure 1. The three

DCIN BAT1 BAT2

LTC1479

V+

TO GATE

DRIVERS

(36.5V)

VGG

SWITCHING

REGULATOR

L1

1mH

VGG

+ C2 + C1

SW

1µF

1µF

50V

35V

GND

1479 F01

Figure 1. VGG Switching Regulator

diodes are connected to each of the three main power

sources, DCIN, BAT1 and BAT2. The highest voltage

potential is directed to the top of the boost regulator

inductor to maximize regulator efficiency. C1 provides

filtering at the top of the 1mH switched inductor, L1, which

is housed in a small surface mount package.

A fourth internal diode directs the current from the 1mH

inductor to the VGG output capacitor, C2, further reducing

the external parts count. In fact, as demonstrated in Figure

1, only three external components are required by the VGG

regulator, L1, C1 and C2.

Inrush Current Limiting

The LTC1479 uses an adaptive inrush current limiting

scheme to reduce current flowing in and out of the three

main power sources and the DC/DC converter input ca-

pacitor during switch-over transitions. The voltage across

a single small-valued resistor, RSENSE, is measured to

ascertain the instantaneous current flowing through the

three main switch pairs, SW A/B, SW C/D, and SW E/F

during the transitions.

Figure 2 is a block diagram showing only the DCIN switch

pair, SW A/B. (The gate drive circuits for switch pairs SW

C/D and SW E/F are identical). A bidirectional current

sensing and limiting circuit determines when the voltage

drop across RSENSE reaches plus or minus 200mV. The

gate-to-source voltage, VGS, of the appropriate switch is

limited during the transition period until the inrush current

subsides, generally within a few milliseconds, depending

upon the value of the DC/DC converter input capacitor.

DCIN

SW A

SW B

GA SAB GB

LTC1479 6V 6V

RSENSE

VSENSE +

+

VSENSE –

OUTPUT

TO DC/DC

CONVERTER

COUT

± 200mV

THRESHOLD

SW A/B

VGG

GATE

DRIVERS

BIDIRECTIONAL

INRUSH CURRENT

SENSING AND

LIMITING

1479 F02

Figure 2. SW A/B Inrush Current Limiting

10

Share Link: