Datasheet

Data Sheet ADP5023
Rev. D | Page 15 of 28
THEORY OF OPERATION
ENABLE
AND MODE
CONTROL
LDO
CONTROL
LDO
UNDERVOLTAGE
LOCK OUT
SOFT START
PWM/
PSM
CONTROL
BUCK2
DRIVER
AND
ANTISHOOT
THROUGH
SOFT START
PWM/
PSM
CONTROL
BUCK1
DRIVER
AND
ANTISHOOT
THROUGH
OSCILLATOR
THERMAL
SHUTDOWN
SYSTEM
UNDERVOLTAGE
LOCKOUT
PWM
COMP
GM ERROR
AMP
GM ERROR
AMP
PSM
COMP
PSM
COMP
LOW
CURRENT
I
LIMIT
PWM
COMP
LOW
CURRENT
I
LIMIT
R1
R2
ADP5023
V
OUT1 FB1 FB2
V
OUT2
VIN1
AVI N
SW1
PGND1
EN1
EN2
ENBK1
ENBK2
ENLDO
EN3
VDDA
VIN3 AGND
FB3 VOUT3
PGND2
MODE
SW2
VIN2
ENLDO
600Ω
ENBK2
75Ω
ENBK1
75Ω
B
A
Y
SEL
OPMODE
MODE2
09889-003
Figure 45. Functional Block Diagram
POWER MANAGEMENT UNIT
The ADP5023 is a micropower management unit (micro PMU)
combining two step-down (buck) dc-to-dc converters and one
low dropout linear regulator (LDO). The high switching
frequency and tiny 24-lead LFCSP package allows a small
power management solution.
To combine these high performance regulators into the micro
PMU, there is a system controller allowing them to operate
together.
The buck regulators can operate in forced PWM mode if the
MODE pin is at a logic high level. In forced PWM mode, the
buck switching frequency is always constant and does not
change with the load current. If the MODE pin is at a logic
low level, the switching regulators operate in auto PWM/PSM
mode. In this mode, the regulators operate at fixed PWM
frequency when the load current is above the PSM current
threshold. When the load current falls below the PSM current
threshold, the regulator in question enters PSM, where the
switching occurs in bursts. The burst repetition rate is a
function of the current load and the output capacitor value.
This operating mode reduces the switching and quiescent
current losses. The auto PWM/PSM mode transition is
controlled independently for each buck regulator. The two
bucks operate synchronized to each other.
The ADP5023 has individual enable pins (EN1 to EN3) control-
ling the activation of each regulator. The regulators are activated
by a logic level high applied to the respective EN pin. EN1 controls
BUCK1, EN2 controls BUCK2, and EN3 controls LDO.
Regulator output voltages are set through external resistor
dividers or can be optionally factory programmed to default
values (see the Ordering Guide section).
When a regulator is turned on, the output voltage ramp rate is
controlled though a soft start circuit to avoid a large inrush
current due to the charging of the output capacitors.
Thermal Protection
In the event that the junction temperature rises above 150°C,
the thermal shutdown circuit turns off all the regulators.
Extreme junction temperatures can be the result of high current