ML4950

8

It is important to note that the accuracy of these resistors

directly affects the accuracy of the output voltage. The

SENSE pin threshold variation is ±3%, and the tolerance of

variation.

Under some circumstances, input ripple cannot be

reduced effectively. This occurs primarily in applications

where inductor currents are high, causing excess output

ripple due to “pulse grouping”, where the charge-

discharge pulses are not evenly spaced in time. In such

cases it may be necessary to add a small 20pF to 100pF

the SENSE pin. This is particularly true if the ripple voltage

SETTING THE

RESET THRESHOLD

To use the RESET comparator as an input voltage monitor,

it is necessary to use an external resistor divider tied to the

V

RR

R

IN MIN

AB

B

()

.

=™

+

(7)

equation:

RR

V

AB

IN MIN

=™

-









()

.

02

1

(8)

LAYOUT

Good PC board layout practices will ensure the proper

operation of the ML4950. Important layout considerations

include:

s

Use adequate ground and power traces or planes

s

Keep components as close as possible to the ML4950

s

s

Use a single point ground for the ML4950 PWR GND

pin and the input and output capacitors, and connect

GND to PWR GND with a separate trace

A typical PC board layout is shown in Figure 8.

Figure 8. Typical PC Board Layout

For 2V, R1 = 365k

W, R2 = 40.2kW

For 3V, R1 = 562k

W, R2 = 40.2kW

L = Sumida CD43, 22µH

80

60

40

20

0

VIN (V)

1.0

1.5

2.0

3.0

2.5

2V OUTPUT

3V OUTPUT

Figure 7. Battery Monitoring Circuit

VIN

RA

RB

1

DETECT

4

RESET

VREF

FROM

START-UP

CIRCUITRY

+

–

COMP

7