MAX846AEEE Maxim Integrated Products, MAX846AEEE Datasheet - Page 7

• Manufacturer Part Number: MAX846AEEE
• Description: Battery Management Multichemistry Bat Charger System
• Manufacturer: Maxim Integrated Products

Specifications of MAX846AEEE

• Battery Type: Li-Ion, Li-Polymer, NiCd, NiMH
• Output Voltage: 3.3 V
• Operating Supply Voltage: 3.7 V to 20 V
• Supply Current: 5 mA
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 40 C
• Package / Case: QSOP-16
• Mounting Style: SMD/SMT

The voltage/current regulator consists of a precision
attenuator, voltage loop, current-sense amplifier, and
current loop. The attenuator can be pin programmed to
set the regulation voltage for one or two Li-Ion cells
(4.2V and 8.4V, respectively). The current-sense ampli-
fier is configured to sense the battery current on the
high side. It is, in essence, a transconductance amplifi-
er converting the voltage across an external sense
resistor (R
an external load resistor (R
by selecting R
also be adjusted by varying the voltage at the low side
of R
ISET node (Figure 5). The voltage and current loops are
individually compensated using external capacitors at
CCV and CCI, respectively. The outputs of these two
loops are OR’ed together and drive an open-drain,
internal N-channel MOSFET transistor sinking current to
ground. An external P-channel MOSFET or PNP transis-
tor pass element completes the loop.
The Typical Operating Characteristics show the loop
gains for the current loop and voltage loop. The domi-
nant pole for each loop is set by the compensation
capacitor connected to each capacitive compensation
pin (CCI, CCV). The DC loop gains are about 50dB for
the current loop and about 33dB for the voltage loop,
for a battery impedance of 250mΩ.
The CCI output impedance (50kΩ) and the CCI capaci-
tor determine the current-loop dominant pole. In Figure
2, the recommended C
dominant pole at 300Hz. There is a high-frequency
pole, due to the external PNP, at approximately f
This pole frequency (on the order of a few hundred kilo-
hertz) will vary with the type of PNP used. Connect a
10nF capacitor between the base and emitter of the
Table 1. Float-Voltage Accuracy
Internal-reference accuracy
VSET error due to external divider. Calculated from a 2% internal 20kΩ resistor tolerance and
a 1% external R
adjustment range of 5%.
VSET amplifier and divider accuracy
TOTAL
ISET
or by summing/subtracting current from the
CS
) to a current, and applying this current to
CS
VSET
_______________________________________________________________________________________
and R
Voltage/Current Regulator
resistor tolerance. The total error is 3% x (adjustment). Assume max
CCV
ISET
ISET
. The charge current can
is 10nF, which places a
). Set the charge current
ERROR SOURCE
Stability
Cost-Saving Multichemistry
T
/ß.
Battery-Charger System
PNP to prevent self-oscillation (due to the high-imped-
ance base drive).
Similarly, the CCV output impedance (150kΩ) and the
CCV capacitor set the voltage-loop dominant pole. In
Figure 2, the compensation capacitance is 10nF, which
places a dominant pole at 200Hz.
The battery impedance directly affects the voltage-loop
DC and high-frequency gain. At DC, the loop gain is
proportional to the battery resistance. At higher fre-
quencies, the AC impedance of the battery and its con-
nections introduces an additional high-frequency zero.
A 4.7µF output capacitor in parallel with the battery,
mounted close to BATT, minimizes the impact of this
impedance. The effect of the battery impedance on DC
gain is noticeable in the Voltage-Loop-Gain graph (see
Typical Operating Characteristics ). The solid line repre-
sents voltage-loop gain versus frequency for a fully
charged battery, when the battery energy level is high
and the ESR is low. The charging current is 100mA. The
dashed line shows the loop gain with a 200mA charg-
ing current, a lower amount of stored energy in the bat-
tery, and a higher battery ESR.
Figure 2 shows the stand-alone configuration of the
MAX846A. Select the external components and pin
configurations as follows:
• Program the number of cells: Connect CELL2 to GND
• Program the float voltage: Connect a 1% resistor from
__________Applications Information
for one-cell operation, or to VL for two-cell operation.
VSET to GND to adjust the float voltage down, or to
VL to adjust it up. If VSET is unconnected, the float
voltage will be 4.2V per cell. Let the desired float volt-
age per cell be V
as follows:
F
Stand-Alone Li-Ion Charger
, and calculate the resistor value
ERROR
±0.15%
±0.25%
±0.5%
±0.9%
7