DC-DC

Converter

Linear

Regulator

SW

PGND

FB

SGND

EN_DCDC

EN_LIN

Startup LDO

Mode Switch

200 mV

LM3687

SNVS473B – DECEMBER 2007 – REVISED MAY 2013

www.ti.com

Electrical Characteristics: External Components, Recommended Specification

(1) (2) (3)

Limit

Symbol

Parameter

Conditions

Value

Units

Min

Max

Output Capacitance for

linear regulator

2.2

1.5

10

µF

Input Capacitance for

linear regulator

post regulation application)

1.0

0.47

µF

Input Capacitance for DC-

DC converter

4.7

µF

DC-DC converter output

filter capacitor

10

µF

ESR of all capacitors

0.003

0.300

Ω

Inductance

2.2

µH

L

1.6

A

DCR

200

m

Ω

(1)

All voltages are with respect to the potential at the SGND pin.

(2)

Min and Max limits are guaranteed by design, test, or statistical analysis. Typical numbers are not guaranteed, but do represent the

(3)

The capacitor tolerance should be 30% or better over temperature. The full operating conditions for the application should be considered

when selecting a suitable capacitor to ensure that the minimum value of capacitance is always met. Recommended capacitor type is

X7R. However, dependent on application, X5R, Y5V, and Z5U can also be used. The shown minimum limit represents real minimum

capacitance, including all tolerances and must be maintained over temperature and dc bias voltage (See CAPACITOR

CHARACTERISTICS)

BLOCK DIAGRAM

Figure 4. Simplified Block Diagram

8

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