MAX1870AETJ+ Maxim Integrated Products, MAX1870AETJ+ Datasheet - Page 18

• 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

Step-Up/Step-Down
Li+ Battery Charger
The input source current is the sum of the MAX1870A
quiescent current, the charger input current, and the
system load current. The MAX1870A’s 6mA maximum
quiescent current is minimal compared to the charge
and load currents. The actual wall adapter current is
determined as follows:
where η is the efficiency of the DC-DC converter (85%
to 95% typ), I
I
charge current.
By controlling the input current, the current require-
ments of the AC wall adapter are reduced, minimizing
system size and cost. Since charge current is reduced
to control input current, priority is given to system loads.
An internal amplifier compares the sum of (V
V
the CLS input. Drive V
voltage-divider between REF and GND. Connect CLS
to REF for the maximum input current limit of 105mV.
Sense resistors RS1a and RS1b set the maximum-
allowable wall adapter current. Use the same values for
RS1a, RS1b, and RS2. Calculate the maximum wall
adapter current as follows:
where V
age threshold, and is 105mV (typ). The internal error
amplifier (GMS) maintains input-current regulation (see
Figure 3 for the Functional Diagram). Typically, connect
a 0.01µF capacitor from CCS to GND to compensate
the source current loop (GMS). See the Charge-Current
and Wall-Adapter-Current Loop Compensation for more
information.
The MAX1870A includes an input-current monitor out-
put, IINP. IINP is a scaled-down replica of the system
load current plus the input-referred charge current. The
output voltage range for IINP is 0 to 3.5V. The voltage
of IINP is proportional to the output current by the fol-
lowing equation:
where I
AC adapter, G
(2.8µA/mV typ), and R7 is the resistor connected
between IINP and ground.
18
ADAPTER
CSSN
______________________________________________________________________________________
) and (V
CSST
ADAPTER
I
ADAPTER
V
IINP
is the adapter current, and I
I
ADAPTER MAX
is the full-scale source current-sense volt-
CSSP
= I
SYS_LOAD
IINP
ADAPTER
is the DC current supplied by the
=
_
Input Current Measurement
- V
I
is the transconductance of IINP
SYS LOAD
CLS
CSSS
_
=
is the system load current,
directly or set with a resistive
x RS1_ x G
V
V
) to a scaled voltage set by
CLS
REF
+
x
I
CHARGE
V
RS
CSST
IINP
1
_
V
CHARGE
IN
x R7
x
x V
η
BATT
CSSP
is the
-
In the Typical Application Circuit, the duty cycle and
AC load current affect the accuracy of V
Typical Operating Characteristics).
LDO provides a 5.4V supply derived from DCIN. The
low-side MOSFET driver is powered by DLOV, which
must be connected to LDO as shown in Figure 1. LDO
also supplies the 4.096V reference (REF) and most of
the internal control circuitry. Bypass LDO to GND with a
1µF or greater ceramic capacitor. Bypass DLOV to
PGND with a 1µF or greater ceramic capacitor.
The MAX1870A includes a logic output, ASNS, which
indicates AC adapter presence. When the system load
draws more than 1.5A (for 30mΩ sense resistors and
R7 is 10kΩ), the ASNS logic output pulls high.
When the AC adapter is removed, the MAX1870A shuts
down to a low-power state, and typically consumes less
than 1µA from the battery through the combined load of
the CSIP, CSIN, BLKP, and BATT inputs. The charger
enters this low-power state when DCIN falls below the
undervoltage-lockout (UVLO) threshold of 7.5V.
Alternatively, drive SHDN below 23.5% of V
drive ICTL below V
suspends switching and pulls CCI, CCS, and CCV to
ground. The LDO, input current monitor, and control
logic all remain active in this state.
The MAX1870A is a step-up/step-down DC-DC con-
troller. The MAX1870A controls a low-side n-channel
MOSFET and a high-side p-channel MOSFET to a con-
stant output voltage with input voltage variation above,
near, and below the output. The MAX1870A implements
a control scheme that delivers higher efficiency with
smaller components and less output ripple when com-
pared with other step-up/step-down control algorithms.
This occurs because the MAX1870A operates with
lower inductor currents, as shown in Figure 4.
The MAX1870A proprietary algorithm offers the follow-
ing benefits:
• Inductor current requirements are minimized.
• Low inductor-saturation current requirements allow
• Low inductor current improves efficiency by reducing
the use of physically smaller inductors.
I
resistors.
2
R losses in the MOSFETs, inductor, and sense
REFIN
Step-Up/Step-Down
/ 100 to inhibit charge. This
AC Adapter Detection
DC-DC Controller
LDO Regulator
IINP
Shutdown
REFIN
(see the
or