LTC1704 Просмотр технического описания (PDF) - Linear Technology

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LTC1704

550kHz Synchronous Switching Regulator Controller Plus Linear Regulator Controller

Linear Technology 

LTC1704/LTC1704B

PI FU CTIO S

compensation and soft-start connections should return to

GND. GND and PGND should connect only at a single

point, near the PGND pin and the negative plate of the VIN

bypass capacitor.

REGFB (Pin 9): Linear Regulator Controller Feedback

Input. REGFB should be connected through a resistor

divider network to VOUTREG to set the output voltage of the

linear regulator.

REGILM (Pin 10): Linear Regulator Controller Current

Limit Setting cum ON/OFF Control. This pin is internally

servoed to 0.8V. An external resistor RREGILM between VCC

and REGILM programs the REGILM pin input current. This

current determines the maximum pass transistor base

current and directly controls the linear regulator current

sourcing capabilitiy. An external capacitor, CDELAY is added

to this pin to control the turn-on time of the linear regula-

tor, the minimum value for this capacitor is 100pF. Refer

to the Linear Regulator Current Limit Programming sec-

tion for more information on choosing RREGILM and CDELAY.

Pulling REGILM to GND turns off the linear regulator. If

both RUN/SS and REGILM are pulled low, the LTC1704

enters shutdown mode.

VCC (Pin 11): Power Supply Input. All internal circuits

except the switcher output drivers are powered from this

pin. VCC should be connected to a low noise 5V supply, and

should be bypassed to GND with at least a 10µF capacitor

in close proximity to the LTC1704.

PGOOD (Pin 12): Power Good. PGOOD is an open-drain

logic output. PGOOD pulls low if any of the two supply

outputs are outside ±10% of their nominal levels. An

external pull-up resistor is required at PGOOD to allow it

to swing positive.

PGND (Pin 13): Power Ground. The BG driver returns to

this pin. Connect PGND to a high current ground node in

close proximity to the sources of external MOSFET QB,

and the VIN and VOUTSW bypass capacitors.

BG (Pin 14): Switcher Controller Bottom Gate Drive. The

BG pin drives the gate of the bottom N-channel synchro-

nous switch MOSFET, QB. BG is designed to typically drive

up to 10,000pF of gate capacitance.

PVCC (Pin 15): Switcher Controller Bottom Gate Driver Sup-

ply. PVCC provides power to the BG output driver. PVCC

must be connected to a voltage high enough to fully turn

on the external MOSFET, QB. PVCC should generally be con-

nected directly to VIN, the main system 5V supply. PVCC

requires at least a 10µF bypass capacitor directly to PGND.

BOOST (Pin 16): Switcher Controller Top Gate Driver

Supply. The BOOST pin supplies power to the floating TG

driver. Bypass BOOST to SW with a 1µF capacitor. An

external Schottky diode from VIN to BOOST creates a

complete floating charge-pumped supply at BOOST. No

other external supplies are required.

TEST CIRCUIT

fOSC

2000pF

2k

VFB

100Ω

1µF

1

TG

16

BOOST

2

SW

15

PVCC

3

14

IMAX LTC1704 BG

4

RUN/SS

13

PGND

5

COMP

12

PGOOD

6

FB

7

REGDR

11

VCC

10

REGILM

8

GND

9

REGFB

250k

IBOOST IPVCC IVCC

+

5V

10µF

2000pF

RREGILM

100k

80k

100pF

1704 TC

8

1704bfa

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