MAX1870AETJ+ Maxim Integrated Products, MAX1870AETJ+ Datasheet - Page 28

• Manufacturer Part Number: MAX1870AETJ+
• Description: Battery Management Li+ Step Up/Step Down Battery Charger
• Manufacturer: Maxim Integrated Products

Specifications of MAX1870AETJ+

• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Table 5. MOSFET Resistive and Switching Losses
Step-Up/Step-Down
Li+ Battery Charger
Note: C LX is the total parasitic capacitance at the drain terminals of M1 and M2. I GATE is the peak gate-drive source/sink current of
M1 or M2.
CON) are preferred due to their resilience to power-up
surge currents.
The input capacitors should be sized so that the temper-
ature rise due to ripple current in continuous conduction
does not exceed approximately 10°C. Choose a capaci-
tor with a ripple current rating higher than 0.5 x I
The output capacitor absorbs the inductor ripple current
in step-down mode, or a peak-to-peak ripple current
equal to the inductor current when in step-up or hybrid
mode. As such, both capacitance and ESR are impor-
tant parameters in specifying the output capacitor. The
actual amplitude of the ripple is the combination of the
two. Ceramic devices are preferable because of their
resilience to surge currents. The worst-case output ripple
occurs during hybrid mode when the input voltage is at
its minimum. See the Typical Operating Characteristics.
Select a capacitor that can handle 0.5 x I
V
than 10°C. Also, select the output capacitor to tolerate
the surge current delivered from the battery when it is
initially plugged into the charger.
28
IN
DESIGNATION
while keeping the rise in capacitor temperature less
______________________________________________________________________________________
M1
D4
M2
D3
M1
D4
M2
D3
Output-Capacitor Selection
V
DCIN MAX
⎛
⎜
⎝
⎛
⎜
⎝
1 −
V
V
BATT
DCIN
(
STEP-DOWN MODE
V
V
BATT
DCIN
I
CHG
⎞
⎟
⎠
) 2
x I
I
x C
GATE
⎞
⎟
⎠
x V
CHG
0
0
0
0
CHG
x I
LX
DIODE
2
CHG
x f
x R
x V
CHG
SW CHG
V
DS ON
BATT
Diode
I
.
(
)
/
SWITCHING LOSSES
Upon battery removal, the MAX1870A continues to reg-
ulate a constant inductor current until the battery volt-
age, V
MAX1870A’s response time depends on the bandwidth
of the CCV loop, f
Compensation section). For applications where battery
overshoot is critical, either increase C
f
Removal in the Typical Operating Characteristics.
The MAX1870A battery charger features a very fast
response time to system load transients. Since the
input current loop is configured as a single-pole sys-
tem, the MAX1870A responds quickly to system load
transients (see the System Load-Transient Response
graph in the Typical Operating Characteristics). This
reduces the risk of tripping the overcurrent threshold of
the wall adapter and minimizes requirements for
adapter oversizing.
DC LOSSES
CO
by increasing R
BATT
⎛
⎜
⎝
Battery-Removal Response
, exceeds the regulation threshold. The
1
−
V
V
V
⎛
⎜
⎝
DCIN
BATT
BATT MAX
V
V
BATT
DCIN
(
I
⎞
⎟
⎠
CV
GATE
STEP-UP MODE
CO
I
x
CHG
. See Battery Insertion and
System Load Transient
x I
)
⎛
⎜
⎝
3
x V
V
V
(see the Voltage Loop
x C
CHG
BATT
DCIN
x V
0
0
0
0
DCIN MAX
LX
⎞
⎟
⎠
DIODE
2
x I
x f
(
x R
CHG
SW CHG
DS ON
)
OUT
(
⎞
⎟
⎠
I
2
)
x R
or increase
DS ON
(
)