MP1605 – 2A, SYNCHRONOUS, STEP-DOWN SWITCHER WITH 11µA IQ
OPERATION
The MP1605 uses constant on-time control with
input voltage feed-forward to stabilize the
switching frequency over the full input range. It
achieves 2A of output current from a 2.3V to
5.5V input voltage range with excellent load and
line regulation. The output voltage can be
regulated as low as 0.6V.
reference voltage. Therefore, the average
output voltage is slightly higher than the output
voltage in DCM or CCM. The on-time pulse in
sleep mode is around 40% larger than that in
DCM or CCM. Figure 3 shows the average FB
voltage relationship with the internal reference
in sleep mode.
FB
Constant-On-Time Control
Average FB
Vref
Compared to fixed frequency PWM control,
constant-on-time control offers a simpler control
loop and faster transient response. By using
input voltage feed-forward, the MP1605
maintains a nearly constant switching frequency
across the input and output voltage ranges. The
switching pulse on time can be estimated with
Equation (1):
Figure 3: FB Average Voltage at Sleep Mode
When the MP1605 is in sleep mode, the
average output voltage is higher than the
internal reference voltage. The EAO is kept low
and clamped in sleep mode. When the load
increases, the PWM switching
period
decreases to keep the output voltage regulated,
and the output voltage ripple decreases
relatively. Once the EAO is higher than the
internal low threshold, the MP1605 exits sleep
mode and enters DCM or CCM depending on
the load. In DCM or CCM, the error amplifier
(EA) regulates the average output voltage to
the internal reference (see Figure 4).
VOUT
(1)
TON
0.454s
V
IN
To prevent inductor current runaway during the
load transient, the MP1605 has a fixed
minimum off time of 60ns.
Sleep Mode Operation
FB+Ramp
The MP1605 features sleep mode to achieve
high efficiency at extreme light-load. In sleep
mode, most of the circuit blocks are turned off
except for the error amplifier and PWM
comparator. The operation current is reduced to
a minimal value (see Figure 2).
Average FB= REF
EA out
Figure 4: DCM Control
There is always a loading hysteresis when
entering and exiting sleep mode due to the EA
clamping response time.
Bias
Soft start
&
AAM Operation at Light-Load Operation
Voltage
Reference
The MP1605 uses advanced asynchronous
modulation (AAM) power-save mode with zero-
current cross detection (ZCD) circuit for light
load.
0.6V
+
+
-
E.A.
Lo-Iq
+
+
-
FBCOMP
Lo-Iq
The MP1605 uses AAM power-save mode for
light load. The simplified AAM control theory is
shown in Figure 5. The AAM current (IAAM) is set
internally. The SW on pulse time is determined
by the on-time generator and AAM comparator.
At light-load condition, the SW on pulse time is
longer. If the AAM comparator pulse is longer
than the on-time generator, the operation mode
is as shown in Figure 6.
FB
Ramp
generator
SW
Figure 2: Operation Blocks at Sleep Mode
When the load becomes lighter, the ripple of the
output voltage becomes larger and drives the
error amplifier output (EAO) lower. When the
EAO reaches the internal low threshold, it is
clamped at that level, and the MP1605 enters
sleep mode. During sleep mode, the valley of
the FB voltage is regulated to the internal
MP1605 Rev. 1.0
6/17/2016
www.MonolithicPower.com
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2016 MPS. All Rights Reserved.
12
MPS [ MONOLITHIC POWER SYSTEMS ]
