AAT3125 Datasheet, PDF (9/12 Pages) Advanced Analogic Technologies – USB OTG 5V Charge Pump

AAT3125
USB OTG 5V Charge Pump
Functional Block Diagram
C1+ C1- C2+ C2-
IN
5V Charge Pump
OC
10mA
4.0
SR
Control
EN
UVLO
OTMP
4.4
2.0
Voltage
Reference
0.6
OUTCP
OUT
POK1
POK2
SESDET
SRRDY
Functional Description
Charge Pump
The AAT3125 charge pump uses a 1.5X topology;
the two flying capacitors are charged in series and
discharged in parallel. Using this topology, output
current is approximately 2/3 input current. Since
the power bus in battery-operated devices that use
a single cell lithium-ion/polymer battery ranges
from 3V to 4.5V, an output voltage above 4.4V can
be maintained. Output voltage is regulated to 5V
and output current is limited by the value of R_CS.
The charge pump is designed to operate safely
with any combination of input and output voltages.
Current is not allowed to flow from OUT to IN.
10mA Current Source
A 10mA current source supplies current to OUT for
V_BUS pulsing during SRP. During V_BUS pulsing, the
length of time needed to charge capacitance con-
nected to OUT distinguishes between non-SRP
capable devices and SRP capable devices. Using
3125.2005.12.1.4
GND
10mA, SESDET should rise about 7ms after
SRRDY rises when an OTG device is connected.
With a non-OTG device connected, this period is at
least 70ms. 10mA should not damage non-SRP
capable hosts that allow reverse current flow from
the bus. Current is not allowed to flow from OUT
to IN through the current source.
SESDET MicroPower Voltage Detector
The SESDET open drain output signals the use of
SRP while the system is acting as the A device.
OUT powers this detector because the local 5V
bus may not be powered when the B device initi-
ates SRP. Since V_BUS provides no more than
150µA to OUT, the detector consumes only 7µA.
SRRDY Voltage Detector
The SRRDY open drain output signals that V_BUS is
ready for SRP. SRRDY is powered by IN and is
active as long as IN is above the UVLO level.
SRRDY is true (low) when OUT is below the
SRRDY threshold (0.6V nominal). SRRDY is false
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