Datasheet

MAX745
Switch-Mode Lithium-Ion
Battery Charger
6 _______________________________________________________________________________________
V
REF
/ 2, the voltage limit is 4.2V. Table 1 defines the
battery cell count.
The battery limit voltage is set by the following:
Solving for V
ADJ
, we get:
Set V
ADJ
by choosing a value for R11 (typically 100kΩ),
and determine R3 by:
R3 = [1 - (V
ADJ
/ V
REF
)] x R11 (Figure 1)
where V
REF
= 4.2V and cell count is 1, 2, 3, 4 (Table 1).
The voltage-regulation loop is compensated at the CCV
pin. Typically, a series-resistor-capacitor combination
can be used to form a pole-zero doublet. The pole
introduced rolls off the gain starting at low frequencies.
The zero of the doublet provides sufficient AC gain at
mid-frequencies. The output capacitor (C1) rolls off the
mid-frequency gain to below unity. This guarantees sta-
bility before encountering the zero introduced by the
C1’s equivalent series resistance (ESR). The GMV
amplifier’s output is internally clamped to between one-
fourth and three-fourths of the voltage at REF.
Current Control
The charging current is set by a combination of the cur-
rent-sense resistor value and the SETI pin voltage. The
current-sense amplifier measures the voltage across
the current-sense resistor, between CS and BATT. The
current-sense amplifier’s gain is 6. The voltage on SETI
is buffered and then divided by 4. This voltage is com-
pared to the current-sense amplifier’s output.
Therefore, full-scale current is accomplished by con-
necting SETI to REF. The full-scale charging current
(I
FS)
is set by the following:
I
FS
= 185mV / R1 (Figure 1)
V =
9.523 V
cell count
9.023V
ADJ
BATT
REF
()
−
V = cell count x V
V
1
2
V
9.523
BATT REF
ADJ REF
()
+
−




















CELL0 CELL1
GND GND 1
VL GND 2
GND VL 3
VL VL 4
CELL COUNT
REF
(UP TO 24V)
VL
DCIN
V
IN
BST
DHI
DLO
LX
PGND
CS
BATT
THM 1
VADJ
SETI
CCI
C3
47nF
R11
100kΩ
1%
R3
100kΩ
1%
R16
D2
C6
0.1µF
C7
0.1µF
M1A
1/2 IRF7303
M1B
D6
MBRS
340T3
D1
MBRS
340T3
R1
0.2Ω
C1
68µF
L1
22µH
1/2 IRF7303
IN4148
R12
R15
10kΩ
C4
0.1µF
C5
4.7µF
R2
C2, 0.1µF
10kΩ
GND
IBAT
CCV
MAX745
BATTERY
THM/SHDN
STATUS
Figure 1. Standard Application Circuit
Table 1. Cell-Count Programming Table