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LTC4089/LTC4089-5

40895fb

USB and 5V Wall Adapter Power

Although the LTC4089/LTC4089-5 is designed to draw

power from a USB port, a higher power 5V wall adapter

can also be used to power the application and charge the

battery (higher voltage wall adapters can be connected

directly to HVIN). Figure 5 shows an example of combining

a 5V wall adapter and a USB power input. With its gate

grounded by 1k, P-channel MOSFET MP1 provides USB

power to the LTC4089/LTC4089-5 when 5V wall power is

not available. When 5V wall power is available, D1 both

supplies power to the LTC4089, pulls the gate of MN1 high

to increase the charge current (by increasing the input

current limit), and pulls the gate of MP1 high to disable it

and prevent conduction back to the USB port.

MN1

2.87k

59k

PROG

CLPROG

LTC4089

BAT

MP1

ICHG

Li-Ion

BATTERY

5V WALL

ADAPTER

850mA ICHG

USB POWER

500mA ICHG

4089 F05

Inductor Selection and Maximum Output Current

A good choice for the inductor value is L = 10µH. With this

value the maximum load current will be 1A. The RMS current

rating of the inductor must be greater than the maximum

load current and its saturation current should be about

30% higher. Note that the maximum load current

will be the programmed charge current plus the largest

expected application load current. For robust operation in

fault conditions, the saturation current should be ~2.3A. To

keep efﬁciency high, the series resistance (DCR) should

be less than 0.1 . Table 1 lists several vendors and types

that are suitable.

Table 1: Inductor Vendors

VENDOR

URL

PART

SERIES

INDUCTANCE

(µH)

SIZE

(mm)

Sumida

www.sumida.com CDRH5D28

8.2, 10

CDRH6D38

TDK

www.tdk.com

SLF6028T

2.8

Toko

www.toko.com

D63LCB

6.3

Catch Diode

Depending on load current, a 1A to 2A Schottky diode is

recommended for the D1 catch diode. The diode must

have a reverse voltage rating equal to, or greater than,

the maximum input voltage. The ON Semiconductor

MBRM140 and the Diodes Inc. DFLS140/160/240 are

good choices.

High Voltage Regulator Capacitor Selection

Bypass the HVIN pin of the LTC4089/LTC4089-5 circuit

with a 1µF, or higher value ceramic capacitor of X7R or

X5R type. Y5V types have poor performance over tempera-

ture and applied voltage and should not be used. A 1µF

ceramic is adequate to bypass the high voltage input and

will easily handle the ripple current. However, if the input

power source has high impedance, or there is signiﬁcant

inductance due to long wires or cables, additional bulk

capacitance may be necessary. This can be provided with

a low performance electrolytic capacitor.

APPLICATIO S I FOR ATIO

Figure 5. USB or 5V Wall Adapter Power

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