MAX1870AETJ+ Maxim Integrated Products, MAX1870AETJ+ Datasheet - Page 19

• 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

• Continuous output current for V
The MAX1870A uses the state machine shown in Figure
5. The controller switches between the states A, B, and C,
depending on V
operation during light loads. Under moderate and heavy
loads the MAX1870A operates in PWM.
During medium and heavy loads when V
V
state B, keeping MOSFET M2 off (Figure 5). Figure 6
shows the inductor current in step-down operation.
During this mode, the MAX1870A regulates the step-
down off-time. Initially, DHI switches M1 off (state A) and
the inductor current ramps down with a dI/dt of V
until a target current is reached (determined by the error
integrator). After the target current is reached, DHI
switches M1 on (state B), and the inductor current ramps
Table 2. MAX1870A H-Bridge Controller Advantages
Figure 4. Inductor Current for V
•
•
BATT
reduces output ripple.
A) CONVENTIONAL
Only 1 MOSFET switched per cycle
Continuous output current in step-down mode
B) MAX1870A
, the MAX1870A alternates between state A and
ALGORITHM
ALGORITHM
MAX1870A H-BRIDGE CONTROLLER
IN
______________________________________________________________________________________
and V
BATT
IN
Step-Down Operation
= V
. State D provides PFM
(V
BATT
IN
> 1.4 x V
IN
> 1.4 x V
IN
> 1.4 x
BATT
BATT
OUT
/ L
)
TIME
•
•
up with a dI/dt of (V
step-down on-time timer expires. This on-time is calculat-
ed based on the input and output voltage to maintain
pseudo-fixed-frequency 400kHz operation. At the end of
state B, another step-down off-time (state A) is initiated
and the cycle repeats. The off-time is valley regulated
according to the error signal. The error signal is set by
the charge current or source current if either is at its limit,
or the battery voltage if both charge current and source
current are below their respective current limits.
During light loads, when the inductor current falls to
zero during state A, the controller switches to state D to
reduce power consumption and avoid shuttling current
in and out of the output.
When V
between state B and state C, keeping MOSFET M1 on.
In this mode, the controller looks like a simple step-up
controller. Figure 7 shows the inductor current in step-
2 MOSFETs switched per cycle
Always discontinuous output current
(requires higher inductor currents)
Step-Up Operation (V
Li+ Battery Charger
IN
TRADITIONAL H-BRIDGE CONTROLLER
Step-Up/Step-Down
< 0.9 x V
IN
BATT
- V
BATT
, the MAX1870A alternates
) / L. M1 remains on until a
IN
2 x I
SHADED REGIONS REPRESENT
CHARGE DELIVERED
CHARGE
< 0.9 x V
BATT
19
)