Data Sheet
MP2636 –3.0A SINGLE CELL SW MODE BATTERY CHARGER WITH PPM AND 3.0A BOOST
MP2636 Rev.1.01 www.MonolithicPower.com 34
9/16/2015 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2015 MPS. All Rights Reserved.
BOOST MODE OPERATION
Low Voltage Start-Up
The minimum battery voltage required to start up
the circuit in boost mode is 2.9V. Initially, when
V
SYS
< V
BATT
, the MP2636 works in down mode.
In this mode, the synchronous P-MOSFET stops
switching and its gate connects to V
BATT
statically.
The P_MOSFET keeps off as long as the voltage
across the parasitic C
DS
(V
SW
) is lower than V
BATT
.
When the voltage across C
DS
exceeds V
BATT
, the
synchronous P-MOSFET enters linear mode
allowing the inductor current to decrease and
flowing into the SYS pin. Once V
SYS
exceeds
V
BATT
, the P-MOSFET gate is released and
normal close-loop PWM operation is initiated. In
boost mode, the battery voltage can drop to as
low as 2.5V without affecting circuit operation.
SYS Disconnect and Inrush Limiting
The MP2636 allows for true output disconnection
by eliminating body diode conduction of the
internal P-MOSFET rectifier. V
SYS
can go to 0V
during shutdown, drawing no current from the
input source. It also allows for inrush current
limiting at start-up, minimizing surge currents
from the input supply. To optimize the benefit of
output disconnect, avoid connecting an external
Schottky diode between the SW and SYS pins.
Board layout is extremely critical to minimize
voltage overshoot at the SW pin due to stray
inductance. Keep the output filter capacitor as
close as possible to the SYS pin and use very
low ESR/ESL ceramic capacitors tied to a good
ground plane.
Boost Output Voltage Setting
In boost mode, the MP2636 programs the output
voltage via the external resistor divider at FB pin,
and provides built-in output over-voltage
protection (OVP) to protect the device and other
components against damage when V
SYS
goes
beyond 6V. Once the output over voltage occurs,
the MP2636 turns off the boost converter. When
the voltage at SYS pin drops to a normal level,
the boost converter restarts as long as the
MODE pin remains in active status.
Boost Output Current Limiting
The MP2636 integrates a programmable output
current limit function in boost mode. When the
boost output current exceeds the programmable
limit, the MP2636 will regulate the output current
at this limit and the SYS voltage will start to drop
down. The OLIM pin programs the current limit
threshold up to 3.0A as the following equation:
OLIM
OLIM
2400 0.92
I(A)
R(k)RS1(m)
×
=
Ω× Ω
(10)
SYS Output Over-Current Protection
The MP2636 integrates three-phase output over-
current protection.
Phase one (boost mode output current limit):
when the output current exceeds the
programmed output current limit, the output
constant current loop controls the output current,
the output current remains at its limit of I
OLIM
, and
V
SYS
decreases.
Phase two (down mode): when V
SYS
drops below
V
BATT
+100mV and the output current loop
remains in control, the boost converter enters
down mode and shutdown after a 120s blanking
time. Then the boost converter will try to restart
after 1ms. At this time, the peak current limit will
be cut by half.
Phase three (short circuit mode): when V
SYS
drops below 3.8V (will be 2.1V during boost soft
start), the boost converter shuts down
immediately once the inductor current hits the
fold-back peak current limit of the low side N-
MOSFET. The boost converter can also recover
automatically after a 1ms period. At this time, the
peak current limit will be cut by half.
Thermal Shutdown Protection
The thermal shutdown protection is also active in
boost mode. Once the junction temperature rises
higher than 150°C, the MP2636 enters thermal
shutdown. It will not resume normal operation
until the junction temperature drops below 120ºC.