MAX1870AETJ+ Maxim Integrated Products, MAX1870AETJ+ Datasheet - Page 21

• 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

signal based on the integrated error of the input cur-
rent, charge current, and battery voltage. The error sig-
nal, determined by the lowest voltage clamp (LVC),
sets the threshold for current-mode regulation. The fol-
lowing comparators are used for regulation:
•
Figure 6. MAX1870A Step-Down Inductor Current Waveform
Figure 7. Step-Up Inductor-Current Waveform
IMIN: The MAX1870A operates in discontinuous
conduction if LVC is below 0.15V, and does not ini-
tiate another step-down on-time. In discontinuous
step-up conduction, the peak current is set by
STATE C
STATE B
______________________________________________________________________________________
V
IN
STATE B
> 0.9 x V
BATT
STATE A
V
IN
> 1.4 x V
BATT
dl
dt
PRECALCULATED STEP-DOWN ON-TIME
=
V
OUT
L
dl
dt
=
DUTY = 1 - V
V
IN
dl
dt
- V
L
=
OUT
V
IN
IN
DUTY = V
- V
L
/ V
OUT
OUT
IMIN. The peak inductor current in discontinuous
step-up mode is:
where VIMIN is the IMIN comparator threshold,
0.15V, and ACSI is the charge current-sense ampli-
fier gain, 18V/V.
IN
/ V
Li+ Battery Charger
OUT
Step-Up/Step-Down
I
PK
dl
dt
>
=
V
A
OUT
VALLEY REGULATED OFF-TIME
L
CSI
PRECALCULATED OFF-TIME
PEAK REGULATED ON-TIME
V
IMIN
x RS
2
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