MAX8568AETE+ Maxim Integrated Products, MAX8568AETE+ Datasheet - Page 12

• Manufacturer Part Number: MAX8568AETE+
• Description: IC BATT MANAGE LITH 16-TQFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX8568AETE+

• Function: Back-Up Management
• Battery Type: Lithium-Ion (Li-Ion); Nickel-Metal Hydride (NiMH)
• Voltage - Supply: 2.8 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-TQFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Note that both V
2-resistor voltage-divider as shown in the typical applica-
tion circuit (see Figure 7) if the factory-set ratio between
the two thresholds is acceptable. In that case:
One 3-resistor-divider can be used to set both
V
the connections of R17, R18, and R19. Select R19 in
the 100kΩ to 1MΩ range. The equations for the two
upper divider-resistors are:
V
INOK connects to a resistor-divider between IN and
GND. The MAX8568 requires V
proper operation when not backing up, so the backup
threshold, V
2.8V. Once V
less than 2.8V. The resistor-divider for INOK is shown in
Figure 7 (R9 and R10). Select resistor R10 to be in the
100kΩ to 1MΩ range. Calculate R9 as follows:
where V
greater than 2.8V.
The step up DC-DC converter is most likely used with
NiMH backup batteries, but can also be used with
rechargeable lithium backup batteries. If the backup
battery voltage is greater than the set output voltage at
BKSU, the output voltage follows the backup battery
voltage. The voltage difference between the backup
battery and BKSU never exceeds a diode forward-volt-
age drop. If I/O OUT (Figure 7) is less than BK during
charge mode, no current flows from BK to I/O OUT.
Complete Backup-Management ICs
for Lithium and NiMH Batteries
12
BK(NILO)
INOK
______________________________________________________________________________________
sets the IN voltage at which backup mode starts.
R
INOK
17
and V
V
IN(BACKUP)
V
=
INOK
BK(NIMAX)
R
BK(NIHI)
R
= 2.43V, and V
Setting the Switchover Voltage
9
18
(
BK(NILO)
R
R
BK(NIHI)
6
18
=
drops below 2.43V (typ), V
=
=
R
+
10
R
R
= 1.163 x V
R
8
19
, must be set for no less than
= 1.283 x V
and V
independently. Figure 4 shows



19



V
V



)
IN BACKUP
BK NILO
V
V
(
BK NILO
V
×
REF
INOK
BK(NIHI)
(
V
IN(BACKUP)
REF



IN
Step-Up Converter
(
1 163
BK(NILO)
.
greater than 2.8V for
V
)
BK(NIHI)
BK NIHI
)
)
−
can be set with a
(
−
×
1
−



1
V
1



REF



must be set
)
IN
−
may be
1



Choose output capacitors to supply output peak cur-
rents with acceptable voltage ripple. Low equivalent-
series-resistance (ESR) capacitors are recommended.
Ceramic capacitors have the lowest ESR, but low-ESR
tantalum or polymer capacitors offer a good balance
between cost and performance.
Output voltage ripple has two components: variations in
the charge stored in the output capacitor with each LX
pulse and the voltage drop across the capacitor’s ESR
caused by the current into and out of the capacitor. The
equations for calculating output ripple are:
where I
Inductor Selection section). For ceramic capacitors, the
output voltage ripple is typically dominated by
V
Input capacitors connected to IN and BK should be
X5R or X7R ceramic capacitors. C
greater. C
step-up converter. If the step-up converter is not used,
then C
Capacitance and ESR variation with temperature should
be considered for best performance in applications with
wide operating temperature ranges.
Figure 4. 3-Resistor Divider Used to Set V
RIPPLE(C)
V
RIPPLE C
BK
PEAK
V
V
can be reduced to 1µF.
BK
.
( )
RIPPLE
RIPPLE(ESR)
should be 10µF or greater when using the
=
is the peak inductor current (see the
1
2



= V
(
V
BKSU
RIPPLE(C)
TERMV
STRTV
= I
REF
Step-Up Capacitor Selection
PEAK
−
16
15
14
L
V
BK
+ V
x R
)
C
IN
ESR(CBKSU)
RIPPLE(ESR)
BKSU
BK(NILO)
should be 4.7µF or



R17
R18
R19
I
PEAK
and V
2
BK(NIHI)