AAT3685IWP-4.2-1-T1 データシートの表示（PDF） - Analog Technology Inc

部品番号

コンポーネント説明

メーカー

AAT3685IWP-4.2-1-T1

Lithium-Ion/Polymer Battery Charger

Analog Technology Inc 

BatteryManagerTM

The maximum ambient temperature before the AAT3685

thermal limit protection will shut down charging can now

be calculated using Equation 5:

Eq. 7: TA = 140°C - (50°C/W · 1.00375W)

= 89.81°C

Therefore, under the stated conditions for this worst

case power dissipation example, the AAT3685 will sus-

pend charging operations when the ambient operating

temperature rises above 89.81°C.

Capacitor Selection

Input Capacitor

In general, it is good design practice to place a decou-

pling capacitor between the ADP/USB pin and ground. An

input capacitor in the range of 1μF to 22μF is recom-

mended. If the source supply is unregulated, it may be

necessary to increase the capacitance to keep the input

voltage above the under-voltage lockout threshold during

device enable and when battery charging is initiated.

If the AAT3685 input is to be used in a system with an

external power supply source rather than a USB port

VBUS, such as a typical AC-to-DC wall adapter, then a CIN

capacitor in the range of 10μF should be used. A larger

input capacitor in this application will minimize switching

or power bounce effects when the power supply is “hot

PRODUCT DATASHEET

AAT3685

Lithium-Ion/Polymer Battery Charger

plugged” in. Likewise, a 10μF or greater input capacitor

is recommended for the USB input to help buffer the

effects of USB source power switching noise and input

cable impedance.

Output Capacitor

The AAT3685 only requires a 1μF ceramic capacitor on

the BAT pin to maintain circuit stability. This value

should be increased to 10μF or more if the battery con-

nection is made any distance from the charger output.

If the AAT3685 is to be used in applications where the

battery can be removed from the charger, such as in the

case of desktop charging cradles, an output capacitor

greater than 10μF may be required to prevent the device

from cycling on and off when no battery is present.

Printed Circuit Board

Layout Considerations

For the best results, it is recommended to physically

place the battery pack as close as possible to the

AAT3685 BAT pin. To minimize voltage drops on the PCB,

keep the high current carrying traces adequately wide.

For maximum power dissipation of the AAT3685 3x3mm

TDFN package, the metal substrate should be solder

bonded to the board. It is also recommended to maxi-

mize the substrate contact to the PCB ground plane layer

to further increase local heat dissipation. Refer to the

AAT3685 evaluation board for a good layout example

(see Figures 5 and 6).

18

www.analogictech.com

3685.2007.12.1.4

Share Link: