MAX4921BETD+T Maxim Integrated Products, MAX4921BETD+T Datasheet - Page 13

• Manufacturer Part Number: MAX4921BETD+T
• Description: IC CTLR OVP/OCP BATT PWR 14-TDFN
• Manufacturer: Maxim Integrated Products

Specifications of MAX4921BETD+T

• Applications: *
• Mounting Type: Surface Mount
• Package / Case: 14-TDFN Exposed Pad
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 8. MAX4919B/MAX4920B/MAX4921B Power_Hold
Waveform When Voltage IN is Not Present
Figures 11 and 12 depict the MAX4919B/MAX4920B
being utilized in an application where the AC adapter
supplies the input voltage and the car adapter is not
plugged in. In this case, when the AC adapter (5V) is
plugged in, the voltage at IN initially makes sure that a
negative voltage is not present.
If V
ranges for more than 25ms (debouncer), the n-channel
MOSFET (N1) turns on and after 25ms, ACOK asserts
low, then a one-shot timer starts that turns P2 on for 1.2s.
During this duration, the µP needs to issue a PWR_HOLD
to keep P2 on before the one-shot period expires. The
adapter then powers the charger to charge the battery
and the battery supports the load.
PWR_HOLD
P2 STATUS
IN
ONE-SHOT
HP_PWR
HP_PWR
remains above the UVLO and below the OVLO
Additional Applications Information
OFF
Battery Power-Up Logic with Overvoltage
______________________________________________________________________________________
t
1SHHP
t
HPDBC
ON
Adapter Application
OFF
and Overcurrent Protection
Figure 11 shows an application where the external
p-channel MOSFET is added for reverse-polarity protec-
tion. The reverse-polarity protection works by turning off
the p-channel MOSFET when the adapter voltage is
below ground. The p-channel MOSFET only turns off if
the voltage at IN is less than the threshold voltage of the
p-channel MOSFET. Due to the body diode leakage
path through the external n-channel MOSFET, the
reverse-polarity protection operation requires a reverse
current-limited load. Figure 11 shows a battery charger
as the load connected to the source of n-channel MOS-
FET. If the voltage at the load connection (source of the
n-channel MOSFET) is greater than the drop across the
n-channel MOSFET’s body diode plus the p-channel
MOSFET threshold voltage, then the p-channel MOSFET
remains on if the adapter voltage is below ground. If the
load has reverse-current protection, the voltage at the
load pulls down and the p-channel MOSFET turns off
limiting reverse current. If the load allows a large reverse
current, then this current flows out of the adapter input
and the reverse-polarity protection is defeated.
Figures 13 and 14 illustrate the MAX4921B being uti-
lized when the car-kit adapter, with built-in charger, is
plugged in and connected directly to the battery.
HP_PWR goes through a 25ms debounce period and
then a 1.2s one-shot is issued.
During this one-shot period, the µP needs to issue a
PWR_HOLD to keep P2 on before the one-shot period
expires. The car kit then charges the battery and the
battery supports the load. Note that the reverse-polarity
protection p-channel MOSFET cannot be used in this
application due to the direct connection of the battery
to the source of the n-channel MOSFET.
Reverse-Polarity Protection
Car-Kit Application
13