ILC6376/77

7

©2001 Fairchild Semiconductor Corporation

1kHz <

< 20kHz

The EXT1 and EXT2 pins are provided so as to drive exter-

nal transistors; thus allowing design flexibility. The EXT1

output drive signal has the same timing as the gate drive to

the internal P-channel MOSFET i.e. EXT1 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 output current application circuit using an

external P-channel MOSFET is shown in figure 2.

P-Channel Boost Circuit

The ILC6376/77 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 (MBR0520L

or equivalent) allows the gate voltage of the internal P-Chan-

nel MOSFET to be driven negative; thus reducing the switch

on-resistance. This technique can be employed to increase

efficiency at low input voltages and high output currents.

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.

Adjustable Output (ILC6376/77SOADJ)

For adjustable output voltage ILC6376/77SOADJ should be

used. All connections to the ILC6376/77SOADJ are the

same as ILC6376/77SOXX, except for the feedback voltage

divider network shown in figure 4. The output voltage,

1V and RFB1 + RFB2 < 2M

Ω

The feedback compensation capacitor should be chosen such

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

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

some adjustment depending on the output inductor (L) and

output capacitor (CL) values chosen.

Example for 3V output:

RFB1 = 400k

Ω

RFB2 = 200k

Ω

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 components

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

ILC6376/77SOADJ, the feedback resistors and their associ-

ated wiring should be kept away from the inductor location

and the vicinity of inductive flux.

ILC6376/77

(TOP VIEW)

3

4

5

1

2

6

7

8

+

+

S/D

SD1

L

EXT1

Fig.2 1Amp output current application

using external MOSFET

5

6

To pin 8

(Note: rest of circuit is same as Fig.1)

2 x

π x CFB x RFB1

1kHz <

1

< 20kHz

Fig.4 Adjustable output using ILC6376/77SOADJ

Figure 3. P-Channel Negative

Voltage between Vin and

P_BST must be less than 10V.

ILC6376/77

(TOP VIEW)

3

4

5

1

2

6

7

8

SD2

Boost Circuit

2200pF

Schottky

MBR0520L

2 x

π x CFB x RFB1

1