MAX8814 MAXIM [Maxim Integrated Products], MAX8814 Datasheet - Page 7

• Manufacturer Part Number: MAX8814
• Description: 28V Linear Li+ Battery Charger with Smart Autoboot Assistant
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 2. Charge-State Diagram
The MAX8814 contains an active-low logic input (EN)
used to enable the charger. Drive EN low, leave uncon-
nected, or connect to GND to enable the charger-
control circuitry. Drive EN high to disable the charger-
control circuitry. EN has an internal 200kΩ pull-down
resistor.
The open-drain POK output asserts low when V
4.25V and (V
requires an external pullup resistor (1MΩ typ) to an
external power supply. POK is high impedance when
V
The MAX8814 contains an autobooting assistant circuit
that generates an enable signal for system booting
(ABO). The booting assistant functions as an internal
“OR” gate (Figure 1). The first input is dependent on
the input voltage (V
external signal applied to ABI. The first input (POK) is
driven high once V
(typ, V
The second input signal (ABI) is driven by an external
source. ABI enables an autoboot signal (ABO high)
when a battery is connected at BATT and is independent
of POK. If POK is pulled low, the booting assistant
always drives ABO high, regardless of ABI (see Table 1).
ABI is pulled to GND through an internal 200kΩ resistor.
BATT
IN
≥ (V
rising).
IN
IN
- 40mV).
- V
_______________________________________________________________________________________
_______________________________________________________________________________________
IN
BATT
IN
≥ 4.25V and (V
), and the second input is an
) ≥ 40mV (typ, V
V
BATT
CONSTANT-CURRENT CHARGE
Autobooting Assistant
10% CHARGE CURRENT
< 2.4V
100% CHARGE CURRENT
Charger Enable Input
28V Linear Li+ Battery Charger with
V
FAST-CHARGE
BATT
PRECHARGE
< 2.5V
IN
V
BATT
- V
POK Output
IN
≥ 2.5V
BATT
(V
IN
rising). POK
- V
BATT
) ≥ 40mV
) < 30mV
IN
(V
V
V
BATT
BATT
IN
Smart Autoboot Assistant
- V
≥
V
≥ 4.2V
< 4.2V
IC ENABLED
BATT
IN
< 7V, AND
) ≥ 40mV, AND
If ABI is driven externally, a RC filter (R1 and C2 of
Figure 3) is required for ESD protection and noise filter-
ing. If ABI is supplied by a system’s internal GPIO, or
logic, the RC filter is not required.
The soft-start algorithm activates when entering fast-
charge mode. In the MAX8814, when the prequalifica-
tion state is complete (V
current ramps up in 250µs to the full charging current.
This reduces the inrush current on the input supply.
Table 1. ABO and POK States
X = Don’t care.
CHARGER = DISABLED
High
Low
ABI
X
X
SHUTDOWN
CONSTANT VOLTAGE CHARGE
VOLTAGE REGULATION
REGULATED 4.2V AT BATT
(V
Not present
IN
- V
Present
Present
Present
IC DISABLED
BATT
V
BATT
IN
> 7V, OR
) < 30mV, OR
(V
POK
Hi-Z
Hi-Z
Low
Low
IN
FROM ANYWHERE
ASYNCHRONOUS
- V
IC DISABLED
V
BATT
IN
BATT
> 7V, OR
) < 30mV, OR
Fast-charge/voltage
Fast-charge/voltage
CHARGER STATE
≥ 2.5V), the charging
Shutdown
Shutdown
regulation
regulation
Soft-Start
ABO
High
High
High
Low
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