ILC6377 View Datasheet(PDF) - Impala Linear Corporation

Part Name

Description

Manufacturer

ILC6377

0.5A, 300kHz, SO-8 PWM/PFM Step Down Converter with Shutdown

Impala Linear Corporation 

0.5A, 300kHz, SO-8 PWM/PFM Step Down Converter with Shutdown

VI N

S/D

EXT1

*CI N +

1

8

2 ILC6377 7

3

6

(TOP VIE W)

4

5

CSS

SD1

L

+

CL

VO UT

Fig. 2: 1AmpFoigut.p2u1t Acumrrepnot uaptppluictatciounrruesnintgaepxptelrincaaltMioOnSFET

using external MOSFET

The EXT1 and EXT2 pins are provided so as to drive

external transistors; thus allowing design flexibility.

The EXT output drive signal has the same timing as

the gate drive to the internal P-channel MOSFET i.e.

EXT output is low as long as the internal MOSFET is

on. Both EXT1 and EXT2 pins are capable of driving

1000pF gate capacitance. For example, a high out-

put current application circuit using an external P-

channel MOSFET is shown in figure 2.

To pin 8

6 CF B

5

VOU T

RFB1

RFB 1 + RF B2 ≤ 2MΩ

RFB2

CF B

chosen

so that 1kHz

<

-------------------------1----------------------------

2 × π × CF B × RFB1

< 20kHz

Fig.4FigA.d4j:uAsdtajubstleaboleuotuptuptutuussiinngg IILLCC6367377S7OS-AOd-jAdj

( N(Nootete:: rreessttoof fcicrcirucituisit siasmseaamsefigausreF1i)g.1 )

Adjustable Output ( ILC6377SO-Adj )

For adjustable output voltage ILC6377SO-Adj should be

used. All connections to the ILC6377SO-Adj are the same

as ILC6377SO-XX, except for the feedback voltage divider

network shown in figure 4. The output voltage, VOUT, can be

calculated from the following equation:

VOUT = VFB ( 1 + RFB1/RFB2 ),

where VFB is approximately 1V and

RFB1 + RFB2 < 2MΩ

CBST

2200pF

SD1

MA729

Schottky

1

8

2 ILC6377 7

3

6

(TOP VI EW)

4

5

Voltage beettwweeeenn VVIiNnaannddP_BST

must be less than 10V.

FigFuirge. 33:. PP-C-hCahnannelnNeelgNateivgeative

P-Channel Boost Circuit

The ILC6377 includes a unique P-Channel MOSFET

architecture with built-in charge pump to maintain low

on-resistance even at low input voltages. As shown in

figure 3, a 2200pF ceramic capacitor and a schottky

diode ( MA729 or equivalent ) allows the gate voltage

of the internal P-Channel MOSFET to be driven neg-

ative; thus reducing the switch on-resistance. This

technique can be employed to increase efficiency at

low input voltages and high output currents.

Note that the voltage between VIN and P_BST should not

exceed 10V, otherwise damage to the device may occur.

For high input voltage applications the schottky diode

should be replaced by a low voltage zener diode so that the

P_BST pin is clamped to a safe negative voltage.

The feedback compensation capacitor should be chosen

such that the pole frequency f is between 1kHz and 20kHz:

1kHz<

1

<20kHz

2 x Π X CFB X RFB1

The pole frequency should generally be set at 5kHz. The

value of CFB calculated from the above equation may

require some adjustment depending on the output inductor

( L ) and output capacitor ( CL ) values chosen.

Example for 3V output :

RFB1 = 400kΩ

RFB2 = 200kΩ

CFB = 100pF

PC Board Layout

As with all switching DC-DC converter designs, good PC

board layout is critical for optimum performance. The heavy

lines indicated in figure 1 schematic should be wide

printed circuit board traces and should be kept as short

as is practical. A large ground plane with as much copper

area as is allowable should be used. All external compo-

nents should be mounted as close to the IC as possible. For

ILC6377SO-Adj, the feedback resistors and their associat-

ed wiring should be kept away from the inductor location

and the vicinity of inductive flux.

Impala Linear Corporation

ILC6377 1.3

(408) 574-3939 www.impalalinear.com

June 1999 6

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