Diodes AP3602A/B - Manual (Page 7)

100mA REGULATED CHARGE PUMP AP3602A/B
7
Dec. 2012 Rev. 2. 0 BCD Semiconductor Manufacturing Limited
Data Sheet
Application Information
Operating Principles
The AP3602A/B use a switched capacitor charge
pump to boost the input voltage to a regulated output
voltage. Regulation is achieved by sensing the chip
output voltage through an internal resistor divider net-
work. Controlled by an internal comparator (refer to
the functional block diagram), the charge pump circuit
is enabled when the divided output voltage is below a
preset trip point .
The charge pump operates at 1.2MHz with 50% duty
cycle. Conversion consists of a two-phase operation. In
the first phase, switches S2 and S3 are opened and S1
and S4 are closed. During this time, C
FLY
charges to
the voltage on V
IN
and load current is supplied by
C
OUT
. During the second phase, S2 and S3 are closed,
and S1 and S4 are opened. This action connects C
FLY
low side to V
IN
, C
FLY
high side to V
OUT
, then a volt-
age about 2*V
IN
is used to charge C
OUT
and supply the
load current. For each cycle, charges is transported
from V
IN
to V
OUT
to maintain the output voltage in its
nominal value.
This process breaks when the V
OUT
is high enough for
the reason of higher input voltage or lower load, then
the divided voltage at the control comparator exceeds
the internal trip point high level, which compels the
charge pump circuit enter to the idle mode in which the
switching cycle stops (pulse skipping) and the output
voltage is continually decreased because it is main-
tained by the discharging of C
OUT
only. In idle mode,
the feedback circuit continues sensing V
OUT
. If the
divided voltage at the control comparator drops below
the preset trip point, the comparator will start the
switching cycle again.
In idle mode, the AP3602A/B's quiescent current is
about 13
μ A. In shutdown mode, all internal circuitry is
turned off and the AP3602A/B draw only leakage cur-
rent from V
IN
, which is less than 1 μ A. So, the shut-
down power loss for AP3602A/B is very low, that is
beneficial to the battery supplied systems.
Short Circuit and Thermal Protection
The AP3602A/B have a thermal protection and shut-
down circuit that continuously monitors the IC junc-
tion temperature.
When output short circuit occurs, the short circuit cur-
rent is about 300mA (Typical). Under this condition,
the I
IN
is about 2*Iout, which causes about 1.8W
instant power dissipation on AP3602A/B, that will
cause a rise in the internal IC junction temperature. If
the thermal protection circuit senses the junction tem-
perature exceeding approximately 160
o C , the thermal
shutdown circuit will disable the charge pump switch-
ing circuit. The thermal hysteresis is about 10
o C , which
means that the charge pump circuit can be active when
the short circuit is removed and the junction tempera-
ture drops below 150
o C .
The thermal shutdown protection will cycle on and off
if an output short circuit condition persists. This will
allow the AP3602A/B to operate on a short circuit con-
dition without latch up or damage to the device.