MP9928
4V-60V Input, Current Mode,
Synchronous Step-Down Controller
The Future of Analog IC Technology
DESCRIPTION
The MP9928 is a high-voltage, synchronous
step-down switching regulator controller that
can directly step down voltages from up to 60V.
The MP9928 uses PWM current control
architecture with accurate cycle-by-cycle
current limiting. It is capable of driving dual Nchannel MOSFET switches.
AAM Mode (Advanced asynchronous mode)
enables non-synchronous operation and PFM
mode to optimize light load efficiency.
The operating frequency of MP9928 can be
programmed by an external resistor or
synchronized to an external clock for noisesensitive applications. Fault protections are
available including a precision output over
voltage protection (OVP), output over current
protection (OCP), and thermal shutdown.
The MP9928 is available in TSSOP20-EP
package and QFN-20 (3mmx4mm) package.
FEATURES
Wide 4V to 60V Operating Input Range
Dual N-Channel MOSFET Driver
Low Dropout Operation: Maximum Duty
Cycle at 99.5%
Programmable Frequency Range: 100kHz 1000kHz
180º Out-of-Phase SYNCO
External Soft-Start and PG Pin
Selectable Cycle-by-Cycle Current Limit
Output Over Voltage Protection
Internal LDO with Externally Power Supply
Option
Programmable CCM and AAM PulseSkipping Mode
Accuracy Over Temperature Protection
TSSOP20-EP package and QFN-20
(3mmx4mm) Package
APPLICATIONS
PD Power Supply in PoE System
USB Dedicated Charging Port (DCP)
Industrial Control Systems
Power Supply for Linear Chargers
All MPS parts are lead-free, halogen-free, and adhere to the RoHS
directive. For MPS green status, please visit the MPS website under quality
assurance. “MPS” and “The Future of Analog IC Technology” are
registered trademarks of Monolithic Power Systems, Inc.
TYPICAL APPLICATION
Efficiency
VOUT=5V, AAM
100
VIN=12V
90
80
VIN=24V
70
60
50
0.01
MP9928 Rev. 1.1
8/24/2018
VIN=48V
0.1
1
OUTPUT CURRENT(A)
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10
1
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
ORDERING INFORMATION
Part Number
MP9928GF*
MP9928GL**
Package
TSSOP-20 EP
QFN-20 (3mmx4mm)
Top Marking
See Below
See Below
* For Tape & Reel, add suffix –Z (e.g. MP9928GF–Z)
** For Tape & Reel, add suffix –Z (e.g. MP9928GL–Z)
TOP MARKING (MP9928GF)
MP9928: product code of MP9928GF;
MPS: MPS prefix;
YY: year code;
WW: week code:
LLLLLLLLL: lot number;
TOP MARKING (MP9928GL)
9928: product code of MP9928GL;
MP: MPS prefix;
Y: year code;
W: week code:
LLL: lot number;
MP9928 Rev. 1.1
8/24/2018
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© 2018 MPS. All Rights Reserved.
2
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
PACKAGE REFERENCE
TOP VIEW
TOP VIEW
TSSOP-20 EP
QFN-20 (3mmx4mm)
ABSOLUTE MAXIMUM RATINGS (1)
Input supply voltage (VIN) ................ -0.3V to 65V
EN/SYNC ........................................ -0.3V to 50V
SW...........................-0.3V(-4V for 5V for startup, and after start up MP9928 can
work down to 4V input voltage.
5) Measured on JESD51-7, 4-layer PCB.
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3
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
ELECTRICAL CHARACTERISTICS
VIN = 24V, TJ = -40C to 125C, EN = 2V, VILIMIT = 75mV, unless otherwise noted.
Parameters
Symbol
Condition
Min
Typ
Max
Units
Input Supply
VIN UVLO threshold (rising)
INUV_RISING
4.5
5
V
VIN UVLO threshold (falling)
INUV_FALLING
3.7
3.95
V
800
25
40
mV
μA
750
1000
μA
250
350
μA
0.5
3
μA
VIN UVLO hysteresis
VIN supply current with VCC2 bias
VIN supply current without VCC2
bias
VIN AAM current
INUV_HYS
IQ_VCC2
IQ
IQ_AAM
VIN shutdown current
ISHDN
VCC2 = 12V, external bias
VCC2 = 0, VFB = 0.84V, VAAM = 5V,
SENSE+ = SENSE- = 0.3V
VAAM=0.6V, VFB=0.84V,
SENSE+ = SENSE- = 0.3V
VEN = 0V
VCC Regulator
VCC1 regulator output voltage
from VIN
VCC1 regulator load regulation
from VIN
VCC1 regulator output voltage
from VCC2
VCC1_VIN
VCC1_VCC2
VCC1 regulator load regulation
from VCC2
VIN > 6V
5
V
Load = 0 to 50mA,
VCC2 floating or connects to GND
1
VCC2 > 6V
5
Load = 0 to 50mA, VCC2 = 12V
1
3
%
4.92
V
3
%
V
VCC2 UVLO threshold (rising)
VCC2_RISING
4.7
VCC2 UVLO threshold (falling)
VCC2_FALLING
4.45
V
VCC2_HYS
250
mV
VCC2 threshold hysteresis
VCC2 supply current
IVCC2
VAAM = 5V, VFB = 0.84V,
VCC2 = 12V
VAAM = 0.6V,
VFB = 0.84V, VCC2 = 12V
800
1200
μA
200
300
μA
0.792 0.800
0.808
V
4V VIN 60V, TJ=-40C to 125C 0.788 0.800
0.812
V
Feedback (FB)
Feedback voltage
Feedback current
VFB
IFB
4V VIN 60V, TJ=25C
VFB = 0.84V
10
nA
Enable (EN)
Enable threshold (rising)
VEN_RISING
1.16
1.22
1.28
V
Enable threshold (falling)
VEN_FALLING
1.03
1.09
1.15
V
Enable threshold hysteresis
EN input current
Enable turn-off delay
MP9928 Rev. 1.1
8/24/2018
VEN_TH
IEN
TOFF
VEN = 2V
10
130
mV
2
μA
15
μs
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4
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
ELECTRICAL CHARACTERISTICS (continued)
VIN = 24V, TJ = -40C to 125C, EN = 2V, VILIMIT = 75mV, unless otherwise noted.
Parameters
Symbol
Condition
Min
Typ
Max
Units
R Freq = 65kΩ
240
300
360
kHz
Oscillator and Sync
Operating frequency
FSW
Foldback operating frequency
Maximum programmable
frequency
Minimum programmable
frequency
Sync/EN frequency range
FSW_FOLDBACK VFB = 0.1V
50%
FSYNC
100
Sync/EN voltage rising threshold
VSYNC_RISING
2
FSW
1000
FSWH
kHz
FSWL
100
kHz
1000
kHz
V
Sync/EN voltage falling threshold VSYNC_FALLING
0.35
V
24
V
35
60
85
mV
mV
mV
Current Sense
Current sense common mode
voltage range
Current limit sense voltage
Reverse
voltage
current
limit
VILIMIT
sense
Valley current limit
Input current of sensor
0
VSENSE+/-
VREV_ILIMIT
VVAL_ILIMIT
ISENSE
ILIM = GND, VSENSE+ = 3.3V
ILIM = VCC1, VSENSE+ = 3.3V
ILIM = FLOAT, VSENSE+ = 3.3V
15
40
65
25
50
75
ILIM = GND, VSENSE+ = 3.3V
8
ILIM = VCC1, VSENSE+ = 3.3V
ILIM = FLOAT, VSENSE+ = 3.3V
17
24
ILIM = GND, VSENSE+ = 3.3V
22.5
ILIM = VCC1, VSENSE+ = 3.3V
ILIM = FLOAT, VSENSE+ = 3.3V
VSENSE+/-(CM) = 0V
VSENSE+/-(CM) = 3.3V
VSENSE+/-(CM) > 5V
47.5
72.5
-45
115
150
mV
mV
μA
μA
μA
Soft Start (SS)
Soft-start source current
ISS
SS = 0.5V
Error amp transconductance
Gm
ΔV = 5mV
Error amp open loop DC gain(6)
AO
Error amp sink/source current
IEA
2
4
6
μA
Error Amplifier
FB = 0.7/0.9V
500
μA/V
70
dB
±30
μA
Protection
Over-voltage threshold
Over-voltage hysteresis
VOV
VOV_HYS
110% 115%
10%
120%
VFB
VFB
Thermal shutdown(7)
170
°C
Thermal shutdown hysteresis(7)
20
°C
MP9928 Rev. 1.1
8/24/2018
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5
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
ELECTRICAL CHARACTERISTICS (continued)
VIN = 24V, TJ = -40C to 125C, EN = 2V, VILIMIT = 75mV, unless otherwise noted.
Parameters
Symbol
Condition
Min
Typ
Max
Units
Gate Driver
TG pull-up resistor
RTG_PULLUP
Source 20mA
2
Ω
TG pull-down resistor
RTG_PULLDN
Sink 20mA
1
Ω
BG pull-up resistor
RBG_PULLUP
Source 20mA
3
Ω
BG pull-down resistor
RBG_PULLDN
Sink 20mA
1
Ω
60
ns
99.5
%
ns
Dead time
TDead
CLoad = 3.3nF
TG maximum duty cycle
Dmax
VFB = 0.7V
98
TG minimum on time(7)
TON_MIN_TG
92
BG minimum on time
TON_MIN_BG
175
250
ns
0.1
0.3
V
Power Good
Power good low
VPG_Low
PG rising threshold
PGVth_RSING
PG falling threshold
PGVth_FALLING
PG threshold hysteresis
Power good leakage
Power good delay
ISINK = 4mA
VOUT rising
VOUT falling
VOUT falling
VOUT rising
85% 90% 96.5%
VFB
101% 107% 112.5%
81% 87% 92.5%
VFB
105% 110% 116.5%
PGVth_HYS
IPG_LK
TPG_delay
3%
PG = 5V
VFB
2
μA
PG rising and falling
25
μs
RFreq = 65 kΩ
9.2
μA
AAM/CCM
AAM output current
CCM required AAM threshold
voltage
IAAM
VCCM_TH
2.3
V
NOTES:
6) Guaranteed by design, not tested.
7) Guaranteed by characterization, not production tested.
MP9928 Rev. 1.1
8/24/2018
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6
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
TYPICAL CHARACTERISTICS
VIN = 24V, VOUT = 5V, L = 4.7µH, TA = +25°C, unless otherwise noted.
Shutdown Current vs.
Input Voltage
Frequency vs. Resistor
0.500
0.400
900
FREQUENCY (kHz)
1200
Quiescent Current vs.
Input Voltage
0.300
600
0.200
300
0.100
0
10
20
30
40
50
VIN (V)
60
70
0.000
10
Quiescent Current
vs. Temperature
20
30
40
50
VIN (V)
60
70
Shutdown Current
vs. Temperature
0.9
700
0.8
0.7
IQ without VCC2
600
FREQUENCY (kHz)
600
800
0.6
500
0.5
400
0.4
300
0.3
200
0.2
100
0.1
0
-50
0
50
100
0
-50
150
VIN UVLO vs.
Temperature
2
0
50
100
EN UVLO vs.
Temperature
1.6
VIN UVLO Falling
2
0
-50
MP9928 Rev. 1.1
8/24/2018
EN UVLO Falling
0.4
1
0
50
100
150
0
-50
200
250
200
0
50
100
150
VCC2 UVLO vs.
Temperature
5.5
EN UVLO Rising
1.2
0.8
150
400
6
VCC2 (V)
3
EN (V)
VIN (V)
4
100
RFRQ=65k
0
-50
150
VIN UVLO Rising
5
50
Frequency vs.
Temperature
900
6
1100
1000
900
800
700
600
500
400
300
200
100
0
0
5
VCC2 UVLO Rising
4.5
4
VCC2 UVLO Falling
3.5
0
50
100
150
3
-50
0
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50
100
150
7
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
TYPICAL CHARACTERISTICS (continued)
VIN = 24V, VOUT = 5V, L = 4.7µH, TA = +25°C, unless otherwise noted.
OVP vs. Temperature
120%
120%
115%
115%
OVP Trigger Threshold
OVP Recover Threshold
95%
FB REFERENCE VOLTAGE (V)
95%
PG RISING @ VOUT RISING
85%
100
150
FB Reference Voltage vs.
Temperature
800
8
700
7
600
6
500
5
400
4
300
3
200
2
100
1
MP9928 Rev. 1.1
8/24/2018
50
100
150
1
10
9
0
2
PG FALLING @ VOUT FALLING
80%
-50
0
50
100
150
900
0
-50
3
PG RISING @ VOUT FALLING
85%
50
4
100%
90%
0
PG FALLING @ VOUT RISING
105%
90%
80%
-50
5
0
-50
0
50
100
150
0
-50
CURRENT LIMIT SENSE VOLTAGE (V)
105%
100%
Soft Start Source Current
vs. Temperature
110%
UNIT (Vfb-ref)
UNIT (Vfb-ref)
110%
1000
PG Threshold vs.
Temperature
0
50
100
150
Internal Current Limit
vs. Temperature
0.1
0.09
ILIM=FLOAT
0.08
0.07
ILIM=VCC1
0.06
0.05
0.04
ILIM=GND
0.03
0.02
0.01
0
-50
0
50
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100
150
8
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VIN = 24V, VOUT = 5V, L = 4.7µH, TA = +25°C, unless otherwise noted.
Efficiency
Load Regulation
AAM Mode
100
0.3
VIN=12V
AAM Mode
0.1
0.08
0.2
90
0.06
0.04
VIN=24V
0.1
80
VIN=24V
VIN=48V
0.1
1
OUTPUT CURRENT (A)
-0.06
-0.08
-0.3
0
10
1
2
3
4
5
6
7
8
LOOP GAIN (dB)
0
-1
-2
10
MP9928 Rev. 1.1
8/24/2018
20 30 40 50
CURRENT (mA)
60
108
72
12
36
0
45
55
65
0
Gain
-36
40
20
-72
-36
-108
10
-48
-144
-180
1000
0
10
100
FREQUENCY (kHz)
VIN=24V
30
-24
-60
1
35
144
24
-12
25
Package TSSOP-20 EP
50
180
Phase
36
1
15
Case Temp Rise
IOUT=7A
48
2
IOUT=7A
INPUT VOLTAGE (V)
Bode Plot
60
0
-0.1
5
OUTPUT CURRENT (A)
3
IOUT=0A
-0.04
-0.2
VCC1 Load Regulation
-3
-0.02
PHASE MARGIN (DEG)
50
0.01
0
VIN=48V
-0.1
IOUT=3.5A
0.02
VIN=12V
0
70
60
Line Regulation
AAM Mode
VIN=48V
VIN=12V
0
2
4
LOAD (A)
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6
8
9
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VIN = 24V, VOUT = 5V, L = 4.7µH, AAM Mode, TA = +25°C, unless otherwise noted.
Steady State
Steady State
IOUT=0, AAM Mode
VOUT/AC
20mV/div.
IL
500mA/div.
VSW
10V/div.
Steady State
IOUT=0, Forced CCM Mode
IOUT=7A
VOUT/AC
20mV/div.
VOUT/AC
20mV/div.
IL
2A/div.
IL
2A/div.
VSW
10V/div.
VSW
10V/div.
Start-Up Through VIN
Start-Up Through VIN
Shutdown Through VIN
IOUT=0
IOUT=7A
IOUT=0
VIN
10V/div.
VIN
10V/div.
VIN
10V/div.
VOUT
2V/div.
VOUT
2V/div.
IL
1A/div.
IL
5A/div.
IL
500mA/div.
VSW
20V/div.
VSW
20V/div.
VSW
10V/div.
VOUT
2V/div.
Shutdown Through VIN
Start-Up Through EN
Start-Up Through EN
IOUT=7A
IOUT=0
IOUT=7A
VIN
10V/div.
VOUT
2V/div.
IL
5A/div.
VSW
20V/div.
MP9928 Rev. 1.1
8/24/2018
VEN
2V/div.
VEN
2V/div.
VOUT
2V/div.
VOUT
2V/div.
IL
2A/div.
IL
5A/div.
VSW
20V/div.
VSW
20V/div.
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10
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VIN = 24V, VOUT = 5V, L = 4.7µH, AAM mode, TA = +25°C, unless otherwise noted.
Shutdown Through EN
Shutdown Through EN
IOUT=0
VEN
2V/div.
SCP Entry
IOUT=7A
IOUT=0 to short circuit
VEN
2V/div.
VPOK
2V/div.
IL
2A/div.
VOUT
2V/div.
VOUT
2V/div.
IL
5A/div.
IL
10A/div.
VSW
5V/div.
VSW
20V/div.
VSW
20V/div.
VOUT
2V/div.
SCP Entry
SCP Steady State
SCP Recovery
IOUT=7A to short circuit
short circuit to IOUT=0
VOUT
1V/div.
VPOK
2V/div.
VSS
1V/div.
VPOK
2V/div.
VOUT
2V/div.
VOUT
2V/div.
IL
10A/div.
IL
5A/div.
IL
10A/div.
VSW
20V/div.
VSW
20V/div.
VSW
20V/div.
SCP Recovery
SYNC Function
short circuit to IOUT=7A
VIN=24V/VOUT=5V/7A, FSYN=100kHz
VOUT
1V/div.
VPOK
2V/div.
VOUT
2V/div.
IL
10A/div.
VSW
20V/div.
MP9928 Rev. 1.1
8/24/2018
VOUT/AC
100mV/div.
IL
5A/div.
VSW
20V/div.
VSYNC CLK
2V/div.
IL
2A/div.
VSW
20V/div.
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11
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
TYPICAL PERFORMANCE CHARACTERISTICS (continued)
VIN = 24V, VOUT = 5V, L = 4.7µH, AAM Mode, TA = +25°C, unless otherwise noted.
SYNC Function
VIN=24V/VOUT=5V/7A, FSYN=1MHz
VOUT
1V/div.
VSYNC CLK
2V/div.
IL
2A/div.
VSW
20V/div.
MP9928 Rev. 1.1
8/24/2018
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12
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
PIN FUNCTIONS
TSSOP
Pin #
QFN
Pin #
1
19
2
20
3
1
4
2
5
3
6
4
7
5
8
6
9
7
10
8
11
9
12
10
13
11
14
12
15
13
16
14
MP9928 Rev. 1.1
8/24/2018
Name
Description
Input supply. The MP9928 operates from a 4V to 60V input. Ceramic
capacitor is needed to prevent large voltage spikes from appearing at the
input.
Enable input. The threshold is 1.22V with 130mV of hysteresis, and it is
used to implement an input under voltage lockout (UVLO) function
EN/SYNC
externally. If an external sync clock is applied to this pin, internal clock will
follow the sync frequency.
External power supply for the internal VCC1 regulator. It will disable the
power from VIN as long as VCC2 is higher than 4.7V. Do not connect >12V
VCC2
power supply to this pin. Connecting VCC2 pin to external power supply
will reduce power dissipation and thus increases efficiency.
Internal bias supply. Decouple with a 1µF ceramic capacitor or greater
VCC1
ceramic capacitor. But the capacitance should be no more than 4.7µF.
SGND
Low noise signal ground reference.
Soft-start control input. This pin is used to program the soft-start period
SS
with an external capacitor between SS to SGND.
COMP is used to compensate the regulation control loop. Connect an RC
COMP
network from COMP to GND to compensate for the regulation control loop.
Feedback. This is the input to the error amplifier. An external resistive
FB
divider connected between the output and GND is compared to the internal
+0.8V reference to set the regulation voltage.
Continuous conduction mode/advanced asynchronous mode set pin.
Connect this pin to VCC1 pin or float can set the part operates in CCM
CCM/AAM mode. Connecting an appropriate external resistor from this pin to GND to
make AAM at low level, can set the part operates in AAM. The AAM
voltage should be no less than 480mV.
Connect a resistor between FREQ and GND to set the switching
FREQ
frequency.
PG
Power good output. The output of this pin is open drain.
Current sense voltage limit set. The voltage at this pin sets the nominal
ILIM
sense voltage at maximum output current. There are three fixed options
(float, connect to VCC1 or connect to GND.)
outputs a clock which are 180° out-of-phase with internal Oscillator Clock
or external Synchronize Clock when part works in CCM or DCM(but not
SYNCO
Sleep mode) for dual channel co-pack. SYNCO outputs DC voltage in
other cases(Sleep mode, Low Dropout mode, Fault protections, etc.).
Negative input for the current sense. The sensed inductor current limit
SENSEthreshold is determined by status of ILIM pin.
Positive input for the current sense. The sensed inductor current limit
SENSE+
threshold is determined by status of ILIM pin.
Power ground reference for the internal low side switch driver and the
PGND
VCC1 regulator circuit. Connect this pin directly to the negative terminal of
the VCC1 decoupling capacitor.
IN
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13
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
PIN FUNCTIONS (continued)
TSSOP
Pin #
QFN
Pin #
Name
17
15
BG
18
16
SW
19
17
TG
20
18
BST
MP9928 Rev. 1.1
8/24/2018
Description
Bottom gate driver output. Connect this pin to the gate of the synchronous
N-channel MOSFET.
Switch node. Reference for the VBST supply and high current returns for
bootstrapped switch.
Top gate drive. The TG pin drives the gate of the top N-channel MOSFET.
The TG driver draws power from the BST capacitor and returns to SW pin,
providing a true floating drive to the top N-channel MOSFET.
Bootstrap. This pin is the positive power supply for the internal floating high
side MOSFET driver. Connect a bypass capacitor between this pin and
SW pin.
A diode from VCC1 to this pin charges the BST capacitor when the low
side switch is off.
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14
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
BLOCK DIAGRAM
SYNCO
ILIM
IN
4.7V
VCC
Regulator
VCC2
VCC1
VCC1
BOOST
Regulator
FREQ
Oscillator
BST
HS
Driver
VCC1
EN/SYNC
Current Limit
Comparator
Reference
Control
Vref Error Amplifier
LS
Driver
TG
SW
BG
SS
SS
PGND
FB
12X
PG
V PG
Current Sense
Amplifer
SENSE+
SENSE-
SGND
COMP
CCM/AAM
Figure 1: Block Diagram
MP9928 Rev. 1.0
8/24/2018
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15
MP9928—4V TO 60V SYNCHRONOUS STEP-DOWN CONTROLLER
OPERATION
Overview
The MP9928 is a high-performance, step down,
synchronous DC/DC converter controller IC
with a wide input range. It implements current
mode, switching frequency programmable
control architecture to regulate the output
voltage with external N-channel MOSFET
switches.
The MP9928 senses the voltage at FB pin. The
difference between the voltage on this pin and
an internal 0.8V reference is amplified to
generate an error voltage on COMP pin which
is used as a threshold for the current sense
comparator with a slope compensation ramp.
Under normal load condition, the controller
operates in full PWM mode. At the beginning of
each oscillator cycle, the top gate driver is
enabled. Top gate turns on for a period
determined by the duty cycle. When the top
gate turns off, the bottom gate turns on after a
dead time and stays on until the beginning of
the next clock cycle.
There is an optional power save mode for light
load or no load conditions, and see details in
the following section.
AAM Mode
MP9928 employs AAM mode functionality to
optimize the efficiency during light-load or noload conditions. This AAM mode can be
optional enabled when CCM/AAM pin is at a
low level by connecting an appropriate resistor
to GND to make sure that VAAM is no less than
480mV.
VAAM (mV) = IAAM (μA) x RAAM (kΩ)
Where, IAAM is AAM pin output current, it can be
shown below.
IAAM (μA) = 600 (mV) / RFREQ (kΩ)
RFREQ is the resistor from FREQ to SGND, for
given operating frequency, and its value is
shown in ‘Programmable Switching Frequency’
section.
AAM is disabled when CCM/AAM pin is floating
or connected to VCC1.
inductor current approaches zero at light-load. If
the load is further decreased or even no load
that make COMP voltage below the voltage of
AAM threshold at about VAAM+VOFFSET, MP9928
enters AAM mode, where VAAM is the voltage of
CCM/AAM pin and VOFFSET is about 720mV. In
AAM mode, the internal clock is reset every
time when VCOMP crosses over AAM threshold,
and the crossover time is taken as benchmark
of the next clock. When the load increases and
the DC value of VCOMP is higher than AAM
threshold, the operation mode is DCM or CCM
which has a constant switching frequency.
Inductor
Current
AAM Mode
(AAM=Low)
Inductor
Current
PWM Mode
(AAM=High)
t
Load
Decreased
t
Load
t Decreased
t
t
t
Figure 2: AAM and PWM
Floating Driver and Bootstrap Charging
The floating top gate driver is powered by an
external bootstrap capacitor (CBST), which is
normally refreshed when the high-side
MOSFET (HS-FET) turns off. This floating
driver has its own UVLO protection. This
UVLO’s rising threshold is 3.05V with a
hysteresis of 170mV.
VCC1 Regulator and VCC2 Power Supply
Both high-side and low-side MOSFET drivers
and most of the internal circuitries are powered
from the VCC1 regulator. An internal low
dropout linear regulator supplies VCC1 power
from VIN, usually a 1μF to 4.7μF ceramic
capacitor is recommended from VCC1 to GND.
If VCC2 pin is left open or connected to a
voltage 4.7V, the 5V regulator is disabled and
another 5V regulator is triggered that supplies
VCC1 power from VCC2. If 4.5V
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