AD IRF7811 Synchronous buck controller Datasheet

FEATURES
Power input voltage range: 2.95 V to 20 V
On-board bias regulator
Minimum output voltage: 0.6 V
0.6 V reference voltage with ±1.0% accuracy
Supports all N-channel MOSFET power stages
Available in 300 kHz, 600 kHz, and 1.0 MHz options
No current sense resistor required
Power saving mode (PSM) for light loads (ADP1879 only)
Resistor programmable current limit
Power good with internal pull-up resistor
Externally programmable soft start
Thermal overload protection
Short-circuit protection
Standalone precision enable input
Integrated bootstrap diode for high-side drive
Starts into a precharged output
Available in a 14-lead LFCSP_WD package
TYPICAL APPLICATIONS CIRCUIT
VIN = 2.95V TO 20V
VIN
CC
RC
VREG
VOUT
CC2
10kΩ
RTOP
RBOT
CVREG2
CVREG
RRES
ADP1878/
ADP1879
COMP
CIN
BST
EN
CBST
DRVH
FB
L
VOUT
COUT
Q2
SW
GND
Q1
LOAD
DRVL
VREG
RPGD
PGOOD
RES
SS
VEXT
CSS
PGND
09441-001
Data Sheet
Synchronous Buck Controller with
Constant On Time and Valley Current Mode
ADP1878/ADP1879
Figure 1.
APPLICATIONS
Telecommunications and networking systems
Mid-to-high end servers
Set-top boxes
DSP core power supplies
The ADP1879 is the power saving mode (PSM) version of the
device and is capable of pulse skipping to maintain output
regulation while achieving improved system efficiency at light
loads (see the ADP1879 Power Saving Mode (PSM) section for
more information).
Available in three frequency options (300 kHz, 600 kHz, and
1.0 MHz) plus the PSM option, the ADP1878/ADP1879 are well
suited for a wide range of applications that require a single input
power supply range from 2.95 V to 20 V. Low voltage biasing is
supplied via a 5 V internal low dropout regulator (LDO). In
addition, soft start programmability is included to limit input
inrush current from the input supply during startup and to
provide reverse current protection during precharged output
The ADP1878/ADP1879 operate over the −40°C to +125°C
junction temperature range and are available in a 14-lead
LFCSP_WD package.
100
95
VIN = 5V (PSM)
90
85
80
75
VIN = 16.5V
70
65
VIN = 13V
60
55
VIN = 13V (PSM)
50
45
40 VIN = 16.5V (PSM)
35
30
25
10
100
TA = 25°C
VOUT = 1.8V
fSW = 300kHz
WÜRTH INDUCTOR:
744325120, L = 1.2µH, DCR = 1.8mΩ
INFINEON FETs:
BSC042N03MS G (UPPER/LOWER)
1k
LOAD CURRENT (mA)
10k
100k
09441-102
The ADP1878/ADP1879 are versatile current-mode, synchronous
step-down controllers. They provide superior transient response,
optimal stability, and current-limit protection by using a constant
on time, pseudo fixed frequency with a programmable current-limit,
current control scheme. These devices offer optimum performance
at low duty cycles by using a valley, current-mode control architecture allowing the ADP1878/ADP1879 to drive all N-channel power
stages to regulate output voltages to as low as 0.6 V.
conditions. The low-side current sense, current gain scheme and
integration of a boost diode, together with the PSM/forced
pulse-width modulation (PWM) option, reduce the external
device count and improve efficiency.
EFFICIENCY (%)
GENERAL DESCRIPTION
Figure 2. ADP1878/ADP1879 Efficiency vs. Load Current (VOUT = 1.8 V, 300 kHz)
Rev. A
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ADP1878/ADP1879
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Pseudo Fixed Frequency............................................................ 22
Applications ....................................................................................... 1
Power-Good Monitoring ........................................................... 23
Typical Applications Circuit............................................................ 1
Applications Information .............................................................. 24
General Description ......................................................................... 1
Feedback Resistor Divider ........................................................ 24
Revision History ............................................................................... 2
Inductor Selection ...................................................................... 24
Specifications..................................................................................... 3
Output Ripple Voltage (ΔVRR) .................................................. 24
Absolute Maximum Ratings ....................................................... 5
Output Capacitor Selection....................................................... 24
Thermal Resistance ...................................................................... 5
Compensation Network ............................................................ 25
ESD Caution .................................................................................. 5
Efficiency Consideration ........................................................... 26
Pin Configuration and Function Descriptions ............................. 6
Input Capacitor Selection .......................................................... 27
Typical Performance Characteristics ............................................. 7
Thermal Considerations............................................................ 27
Theory of Operation ...................................................................... 17
Design Example .......................................................................... 29
Block Diagram ............................................................................ 17
External Component Recommendations .................................... 31
Startup .......................................................................................... 18
Layout Considerations ................................................................... 33
Soft Start ...................................................................................... 18
IC Section (Left Side of Evaluation Board) ............................. 35
Precision Enable Circuitry ........................................................ 18
Power Section ............................................................................. 35
Undervoltage Lockout ............................................................... 18
Differential Sensing .................................................................... 36
On-Board Low Dropout (LDO) Regulator ............................. 18
Typical Application Circuits ......................................................... 37
Thermal Shutdown..................................................................... 19
12 A, 300 kHz High Current Application Circuit .................. 37
Programming Resistor (RES) Detect Circuit .......................... 19
5.5 V Input, 600 kHz Current Application Circuit ................ 37
Valley Current-Limit Setting .................................................... 19
300 kHz High Current Application Circuit ............................ 38
Hiccup Mode During Short Circuit ......................................... 21
Packaging and Ordering Information ......................................... 39
Synchronous Rectifier ................................................................ 21
Outline Dimensions ................................................................... 39
ADP1879 Power Saving Mode (PSM) ...................................... 21
Ordering Guide .......................................................................... 40
Timer Operation ......................................................................... 22
REVISION HISTORY
6/12—Rev. 0 to Rev. A
Changes to Table 1 ............................................................................. 3
7/11—Revision 0: Initial Version
Rev. A | Page 2 of 40
Data Sheet
ADP1878/ADP1879
SPECIFICATIONS
All limits at temperature extremes are guaranteed via correlation using standard statistical quality control (SQC). VREG = 5 V,
BST − SW = VREG − VRECT_DROP (see Figure 40 to Figure 42). VIN = 12 V. The specifications are valid for TJ = −40°C to +125°C,
unless otherwise specified.
Table 1.
Parameter
POWER SUPPLY CHARACTERISTICS
High Input Voltage Range
Quiescent Current
Shutdown Current
Undervoltage Lockout
UVLO Hysteresis
INTERNAL REGULATOR
CHARACTERISTICS
VREG Operational Output Voltage
Symbol
Test Conditions/Comments
Min
Typ
Max
Unit
VIN
CVIN = 22 μF(25 V rating) right at Pin 1 to PGND (Pin 11)
ADP1878ACPZ-0.3-R7/ADP1879ACPZ-0.3-R7 (300 kHz)
ADP1878ACPZ-0.6-R7/ADP1879ACPZ-0.6-R7 (600 kHz)
ADP1878ACPZ-1.0-R7/ADP1879ACPZ-1.0-R7 (1.0 MHz)
FB = 1.5 V, no switching
2.95
2.95
3.25
12
12
12
1.1
20
20
20
V
V
V
mA
EN < 600 mV
140
225
μA
Rising VIN (see Figure 35 for temperature variation)
Falling VIN from operational state
Do not load VREG externally because it is intended to
bias internal circuitry only
CVREG = 4.7 μF to PGND, 0.22 μF to GND, VIN = 2.95 V to 20 V
ADP1878ACPZ-0.3-R7/ADP1879ACPZ-0.3-R7 (300 kHz)
ADP1878ACPZ-0.6-R7/ADP1879ACPZ-0.6-R7 (600 kHz)
ADP1878ACPZ-1.0-R7/ADP1879ACPZ-1.0-R7 (1.0 MHz)
VIN = 7 V, 100 mA
VIN = 12 V, 100 mA
0 mA to 100 mA, VIN = 7 V
0 mA to 100 mA, VIN = 20 V
VIN = 7 V to 20 V, 20 mA
VIN = 7 V to 20 V, 100 mA
100 mA out of VREG, VIN ≤ 5 V
VIN = 20 V
Connect external capacitor from SS pin to GND,
CSS = 10 nF/ms
2.65
178
IQ_REG +
IQ_BST
IREG,SD +
IBST,SD
UVLO
VREG
VREG Output in Regulation
Load Regulation
Line Regulation
VIN to VREG Dropout Voltage
Short VREG to PGND
SOFT START
Soft Start Period Calculation
ERROR AMPLIFER
FB Regulation Voltage
Transconductance
FB Input Leakage Current
CURRENT SENSE AMPLIFIER GAIN
Programming Resistor (RES)
Value from RES to PGND
SWITCHING FREQUENCY
ADP1878ACPZ-0.3-R7/
ADP1879ACPZ-0.3-R7
On Time
Minimum On Time
Minimum Off Time
VFB
Gm
IFB, LEAK
TJ = 25°C
TJ = −40°C to +85°C
TJ = −40°C to +125°C
2.75
2.75
3.05
4.82
4.83
5
5
5
4.981
4.982
32
34
1.8
2.0
306
229
V
mV
5.5
5.5
5.5
5.16
5.16
415
320
10
V
V
V
V
V
mV
mV
mV
mV
mV
mA
nF/ms
596
594.2
320
600
600
600
496
1
604
605.8
670
50
mV
mV
mV
μS
nA
RES = 47 kΩ ± 1%
2.7
3
3.3
V/V
RES = 22 kΩ ± 1%
RES = none
RES = 100 kΩ ± 1%
Typical values measured at 50% time points with 0 nF at
DRVH and DRVL; maximum values are guaranteed by
bench evaluation1
5.5
11
22
6
12
24
6.5
13
26
V/V
V/V
V/V
FB = 0.6 V, EN = VREG
300
VIN = 5 V, VOUT = 2 V, TJ = 25°C
VIN = 20 V
84% duty cycle (maximum)
Rev. A | Page 3 of 40
1120
1200
145
340
kHz
1345
190
400
ns
ns
ns
ADP1878/ADP1879
Data Sheet
Parameter
ADP1878ACPZ-0.6-R7/
ADP1879ACPZ-0.6-R7
On Time
Minimum On Time
Minimum Off Time
ADP1878ACPZ-1.0-R7/
ADP1879ACPZ-1.0-R7
On Time
Minimum On Time
Minimum Off Time
OUTPUT DRIVER CHARACTERISTICS
High-Side Driver
Output Source Resistance
Output Sink Resistance
Rise Time2
Fall Time2
Low-Side Driver
Output Source Resistance
Output Sink Resistance
Rise Time2
Fall Time2
Propagation Delays
DRVL Fall to DRVH Rise2
DRVH Fall to DRVL Rise2
SW Leakage Current
Integrated Rectifier
Channel Impedance
PRECISION ENABLE THRESHOLD
Logic High Level
Enable Hysteresis
COMP VOLTAGE
COMP Clamp Low Voltage
Symbol
Test Conditions/Comments
Min
Typ
600
Max
Unit
kHz
VIN = 5 V, VOUT = 2 V, TJ = 25°C
VIN = 20 V, VOUT = 0.8 V
65% duty cycle (maximum)
500
540
82
340
1.0
605
110
400
ns
ns
ns
MHz
VIN = 5 V, VOUT = 2 V, TJ = 25°C
VIN = 20 V
45% duty cycle (maximum)
285
312
52
340
360
85
400
ns
ns
ns
2.20
0.72
25
11
3
1
tr, DRVH
tf, DRVH
ISOURCE = 1.5 A, 100 ns, positive pulse (0 V to 5 V)
ISINK = 1.5 A, 100 ns, negative pulse (5 V to 0 V)
BST − SW = 4.4 V, CIN = 4.3 nF (see Figure 59)
BST − SW = 4.4 V, CIN = 4.3 nF (see Figure 60)
Ω
Ω
ns
ns
1.5
0.7
18
16
2.2
1
tr,DRVL
tf,DRVL
ISOURCE = 1.5 A, 100 ns, positive pulse (0 V to 5 V)
ISINK = 1.5 A, 100 ns, negative pulse (5 V to 0 V)
VREG = 5.0 V, CIN = 4.3 nF (see Figure 60)
VREG = 5.0 V, CIN = 4.3 nF (see Figure 59)
Ω
Ω
ns
ns
ttpdhDRVH
ttpdhDRVL
ISWLEAK
BST − SW = 4.4 V (see Figure 59)
BST − SW = 4.4 V (see Figure 60)
BST = 25 V, SW = 20 V, VREG = 5 V
15.7
16
ISINK = 10 mA
22.3
COMP Clamp High Voltage
COMP Zero Current Threshold
THERMAL SHUTDOWN
Thermal Shutdown Threshold
Thermal Shutdown Hysteresis
CURRENT LIMIT
Hiccup Current-Limit Timing
OVERVOLTAGE AND POWERGOOD THRESHOLDS
FB Power-Good Threshold
FB Power-Good Hysteresis
FB Overvoltage Threshold
FB Overvoltage Hysteresis
PGOOD Low Voltage During Sink
PGOOD Leakage Current
VCOMP(HIGH)
VCOMP_ZCT
TTMSD
VCOMP(LOW)
110
VIN = 2.9 V to 20 V, VREG = 2.75 V to 5.5 V
VIN = 2.9 V to 20 V, VREG = 2.75 V to 5.5 V
605
Tie EN pin to VREG to enable device
(2.75 V ≤ VREG ≤ 5.5 V)
(2.75 V ≤ VREG ≤ 5.5 V)
(2.75 V ≤ VREG ≤ 5.5 V)
0.47
634
31
ns
ns
μA
Ω
663
mV
mV
V
1.10
2.55
V
V
Rising temperature
155
15
°C
°C
COMP = 2.4 V
6
ms
FBPGD
VFB rising during system power up
FBOV
VFB rising during overvoltage event, IPGOOD = 1 mA
VPGOOD
IPGOOD = 1 mA
PGOOD = 5 V
542
34
691
35
143
1
PGOOD
1
566
55
710
55
200
100
mV
mV
mV
mV
mV
nA
The maximum specified values are with the closed loop measured at 10% to 90% time points (see Figure 59 and Figure 60), CGATE = 4.3 nF, and the high- and low-side
MOSFETs being Infineon BSC042N03MS G.
2
Not automatic test equipment (ATE) tested.
Rev. A | Page 4 of 40
Data Sheet
ADP1878/ADP1879
ABSOLUTE MAXIMUM RATINGS
THERMAL RESISTANCE
Table 2.
Parameter
VREG to PGND, GND
VIN, EN, PGOOD to PGND
FB, COMP, RES, SS to GND
DRVL to PGND
SW to PGND
BST to SW
BST to PGND
DRVH to SW
PGND to GND
PGOOD Input Current
θJA (14-Lead LFCSP_WD)
4-Layer Board
Operating Junction Temperature Range
Storage Temperature Range
Soldering Conditions
Maximum Soldering Lead Temperature
(10 sec)
Rating
−0.3 V to +6 V
−0.3 V to +28 V
−0.3 V to (VREG + 0.3 V)
−0.3 V to (VREG + 0.3 V)
−2.0 V to +28 V
−0.6 V to (VREG + 0.3 V)
−0.3 V to +28 V
−0.3 V to VREG
±0.3 V
35 mA
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Boundary Condition
In determining the values given in Table 2 and Table 3, natural
convection is used to transfer heat to a 4-layer evaluation board.
Table 3. Thermal Resistance
Package Type
θJA (14-Lead LFCSP_WD)
4-Layer Board
ESD CAUTION
30°C/W
−40°C to +125°C
−65°C to +150°C
JEDEC J-STD-020
300°C
Stresses a bove those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Absolute maximum ratings apply individually only, not in
combination. Unless otherwise specified, all other voltages are
referenced to PGND.
Rev. A | Page 5 of 40
θJA
Unit
30
°C/W
ADP1878/ADP1879
Data Sheet
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
ADP1878/ADP1879
VIN 1
14
BST
COMP 2
13
SW
EN 3
12
DRVH
FB
11 PGND
4
GND 5
10
RES 6
9
DRVL
PGOOD
VREG 7
8
SS
NOTES
1. CONNECT THE EXPOSED PAD TO THE
ANALOG GROUND PIN (GND).
09441-003
TOP VIEW
(Not to Scale)
Figure 3. Pin Configuration
Table 4. Pin Function Descriptions
Pin
No.
1
2
Mnemonic
VIN
COMP
3
4
5
EN
FB
GND
6
7
RES
VREG
8
SS
9
PGOOD
10
DRVL
11
12
13
14
PGND
DRVH
SW
BST
EP
Description
High-Side Input Voltage. Connect VIN to the drain of the high-side MOSFET.
Output of the Error Amplifier. Connect compensation network between this pin and AGND to achieve stability (see
the Compensation Network section).
IC Enable. Connect EN to VREG to enable the IC. When pulled down to AGND externally, EN disables the IC.
Noninverting Input of the Internal Error Amplifier. This is the node where the feedback resistor is connected.
Analog Ground Reference Pin of the IC. Connect all sensitive analog components to this ground plane (see the Layout
Considerations section).
Current Sense Gain Resistor (External). Connect a resistor between the RES pin and GND (Pin 5).
Internal Regulator Supply Bias Voltage for the ADP1878/ADP1879 Controller (Includes the Output Gate Drivers).
Connecting a bypass capacitor of 1 μF directly from this pin to PGND and a 0.1 μF capacitor across VREG and GND are
recommended.
Soft Start Input. Connect an external capacitor to GND to program the soft start period. There is a capacitance value
of 10 nF for every 1 ms of soft start delay.
Open-Drain Power-Good Output. PGOOD sinks current when FB is out of regulation or during thermal shutdown.
Connect a 3 kΩ resistor between PGOOD and VREG. Leave PGOOD unconnected if it is not used.
Drive Output for the External Low-Side, N-Channel MOSFET. This pin also serves as the current sense gain setting pin
(see Figure 69).
Power Ground. Ground for the low-side gate driver and low-side N-channel MOSFET.
Drive Output for the External High-Side N-Channel MOSFET.
Switch Node Connection.
Bootstrap for the High-Side N-Channel MOSFET Gate Drive Circuitry. An internal boot rectifier (diode) is connected
between VREG and BST. A capacitor from BST to SW is required. An external Schottky diode can also be connected
between VREG and BST for increased gate drive capability.
Exposed Pad. Connect the exposed pad to the analog ground pin (GND).
Rev. A | Page 6 of 40
Data Sheet
ADP1878/ADP1879
VIN = 16.5V
VIN = 13V
TA = 25°C
VOUT = 0.8V
fSW = 300kHz
WÜRTH INDUCTOR:
744325072, L = 0.72µH, DCR = 1.3mΩ
INFINEON FETs:
BSC042N03MS G (UPPER/LOWER)
100k
EFFICIENCY (%)
09441-005
EFFICIENCY (%)
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = 16.5V
TA = 25°C
VOUT = 7V
fSW = 300kHz
WÜRTH INDUCTOR:
7443551200, L = 2.0µH, DCR = 2.6mΩ
INFINEON FETs:
BSC042N03MS G (UPPER/LOWER)
100k
09441-006
EFFICIENCY (%)
100
1k
10k
100k
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
10
VIN = 13V
VIN = 13V (PSM)
VIN = 16.5V
VIN = 16.5V (PSM)
TA = 25°C
VOUT = 1.8V
fSW = 600kHz
WÜRTH INDUCTOR:
744325072, L = 0.72µH, DCR = 1.3mΩ
INFINEON FETs:
BSC042N03MS G (UPPER/LOWER)
100
1k
10k
100k
Figure 8. Efficiency—600 kHz, VOUT = 1.8 V
VIN = 13V
10k
WÜRTH INDUCTOR:
744355147, L = 0.47µH, DCR = 0.67mΩ
INFINEON FETs:
BSC042N03MS G (UPPER/LOWER)
LOAD CURRENT (mA)
Figure 5. Efficiency—300 kHz, VOUT = 1.8 V
1k
TA = 25°C
VOUT = 0.8V
fSW = 600kHz
VIN = 16.5V
(PSM)
Figure 7. Efficiency—600 kHz, VOUT = 0.8 V
100
95
VIN = 5V (PSM)
90
85
80
75
70
VIN = 16.5V
65
VIN = 13V (PSM)
60
55
VIN = 13V
50
45
40 VIN = 16.5V (PSM)
35
TA = 25°C
30
VOUT = 1.8V
25
fSW = 300kHz
20
WÜRTH INDUCTOR:
15
744325120, L = 1.2µH, DCR = 1.8mΩ
10
INFINEON FETs:
5
BSC042N03MS G (UPPER/LOWER)
0
10
100
1k
10k
100k
LOAD CURRENT (mA)
VIN = 16.5V
LOAD CURRENT (mA)
Figure 4. Efficiency—300 kHz, VOUT = 0.8 V
100
95 VIN = 16.5V (PSM)
90
85
80
75 V = 13V (PSM)
IN
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
10
100
VIN = 13V (PSM)
09441-008
10k
VIN = 13V
Figure 6. Efficiency—300 kHz, VOUT = 7 V
100
VIN = 13V (PSM)
95
90 V = 16.5V (PSM)
IN
85
80
75
70
65
VIN = 16.5V
60
55
50
VIN = 20V (PSM)
VIN = 20V
45
40
35
TA = 25°C
30
VOUT = 5V
25
fSW = 600kHz
20
WÜRTH INDUCTOR:
15
744318180, L = 1.4µH, DCR = 3.2mΩ
10
INFINEON FETs:
5
BSC042N03MS G (UPPER/LOWER)
0
10
100
1k
10k
100k
LOAD CURRENT (mA)
Figure 9. Efficiency—600 kHz, VOUT = 5 V
Rev. A | Page 7 of 40
09441-009
1k
LOAD CURRENT (mA)
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
10
09441-007
EFFICIENCY (%)
100
95
90
VIN = 13V (PSM)
85
80
75
70
65
60
55
50
45
40
35 V = 16.5V (PSM)
IN
30
25
20
15
10
5
0
10
100
09441-004
EFFICIENCY (%)
TYPICAL PERFORMANCE CHARACTERISTICS
Data Sheet
0.807
100
95
90
85
80
75
70
65 VIN = 13V (PSM)
60
55
50
45
40
35
30
VIN = 16.5V (PSM)
25
20
15
10
5
0
10
100
0.806
VIN = 13V
0.805
VIN = 16.5V
TA = 25°C
VOUT = 0.8V
fSW = 1.0MHz
10k
100k
LOAD CURRENT (mA)
0.798
0.797
0.796
0.792
VIN = 13V
+125°C
+25°C
–40°C
0
2000
VIN = 16.5V
+125°C
+25°C
–40°C
4000
6000
8000
10,000
LOAD CURRENT (mA)
1.821
VIN = 13V
VIN = 16.5V
TA = 25°C
VOUT = 1.8V
fSW = 1.0MHz
WÜRTH INDUCTOR:
744303022, L = 0.22µH, DCR = 0.33mΩ
INFINEON FETs:
BSC042N03MS G (UPPER/LOWER)
10k
100k
1.786
TA = 25°C
VOUT = 5V
fSW = 1.0MHz
100k
09441-012
WÜRTH INDUCTOR:
744355090, L = 0.9µH, DCR = 1.6mΩ
INFINEON FETs:
BSC042N03MS G (UPPER/LOWER)
10k
VIN = 5.5V
+125°C
+25°C
–40°C
0
1500
3000
4500
VIN = 13V
+125°C
+25°C
–40°C
6000
7500
VIN = 16.5V
+125°C
+25°C
–40°C
9000 10,500 12,000 13,500 15,000
LOAD CURRENT (mA)
OUTPUT VOLTAGE (V)
VIN = 16.5V
1k
1.796
Figure 14. Output Voltage Accuracy—300 kHz, VOUT = 1.8 V
VIN = 13V
LOAD CURRENT (mA)
1.801
1.791
VIN = 13V (PSM)
VIN = 16.5V (PSM)
1.806
7.100
7.095
7.090
7.085
7.080
7.075
7.070
7.065
7.060
7.055
7.050
7.045
7.040
7.035
7.030
7.025
7.020
7.015
7.010
7.005
7.000
+125°C
+25°C
–40°C
0
1000
2000
VIN = 13V
VIN = 16.5V
3000
4000
5000
6000
7000
8000
LOAD CURRENT (mA)
Figure 15. Output Voltage Accuracy—300 kHz, VOUT = 7 V
Figure 12. Efficiency—1.0 MHz, VOUT = 5 V
Rev. A | Page 8 of 40
9000
09441-015
1k
1.811
09441-014
OUTPUT VOLTAGE (V)
1.816
09441-011
EFFICIENCY (%)
EFFICIENCY (%)
0.799
0.793
Figure 11. Efficiency—1.0 MHz, VOUT = 1.8 V
100
0.800
Figure 13. Output Voltage Accuracy—300 kHz, VOUT = 0.8 V
LOAD CURRENT (mA)
100
95
90
85
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
10
0.801
0.794
Figure 10. Efficiency—1.0 MHz, VOUT = 0.8 V
100
95
90
85
80
VIN = 13V (PSM)
75
70
65
60
55
50
45
40 V = 16.5V (PSM)
IN
35
30
25
20
15
10
5
0
10
100
0.802
0.795
WÜRTH INDUCTOR:
744303012, L = 0.12µH, DCR = 0.33mΩ
INFINEON FETs:
BSC042N03MS G (UPPER/LOWER)
1k
0.803
09441-013
OUTPUT VOLTAGE (V)
0.804
09441-010
EFFICIENCY (%)
ADP1878/ADP1879
Data4heet
ADP1878/ADP1879
0.808
0.807
0.805
0.806
0.803
OUTPUT VOLTAGE (V)
FREQUENCY (kHz)
0.804
0.802
0.800
0.798
0.801
0.799
0.797
0.795
0.793
0.796
0.791
0.792
0
1000 2000 3000 4000 5000 6000 7000 8000 9000 10,000
LOAD CURRENT (mA)
0.787
0
4000
6000
8000
10,000
Figure 19. Output Voltage Accuracy—1.0 MHz, VOUT = 0.8 V
1.820
1.818
1.816
1.814
1.812
1.810
1.808
1.806
1.804
1.802
1.800
1.798
1.796
1.794
1.792
1.790
1.788
1.786
1.784
1.782
1.780
1.778
1.776
1.774
1.772
1.770
VIN = 13V
+125°C
+25°C
–40°C
0
1500
3000
4500
VIN = 16.5V
+125°C
+25°C
–40°C
6000
7500
9000
1.810
1.805
1.800
VIN = 13V
+125°C
+25°C
–40°C
1.795
10,500 12,000
LOAD CURRENT (mA)
VIN = 16.5V
+125°C
+25°C
–40°C
1.790
0
1000 2000 3000 4000 5000 6000 7000 8000 9000 10,000
LOAD CURRENT (mA)
Figure 17. Output Voltage Accuracy—600 kHz, VOUT = 1.8 V
Figure 20. Output Voltage Accuracy—1.0 MHz, VOUT = 1.8 V
5.030
5.04
5.025
5.03
5.020
5.02
5.01
5.010
5.005
5.000
4.995
4.990
4.985
5.00
4.99
4.98
4.97
4.96
4.95
4.94
4.93
4.980
4.970
0
1000 2000 3000 4000 5000 6000 7000 8000 9000 10,000
LOAD CURRENT (mA)
VIN = 13V
+125°C
+25°C
–40°C
4.92
VIN = 13V
VIN = 16.5V
VIN = 20V
4.91
09441-018
+125°C
+25°C
–40°C
4.975
Figure 18. Output Voltage Accuracy—600 kHz, VOUT = 5 V
VIN = 16.5V
+125°C
+25°C
–40°C
4.90
0
800 1600 2400 3200 4000 4800 5600 6400 7200 8000 8800 9600
LOAD CURRENT (mA)
Figure 21. Output Voltage Accuracy—1.0 MHz, VOUT = 5 V
Rev. A | Page 9 of 40
09441-021
OUTPUT VOLTAGE (V)
5.015
09441-020
OUTPUT VOLTAGE (V)
1.815
09441-017
OUTPUT VOLTAGE (V)
2000
VIN = 16.5V
+125°C
+25°C
–40°C
LOAD CURRENT (mA)
Figure 16. Output Voltage Accuracy—600 kHz, VOUT = 0.8 V
OUTPUT VOLTAGE (V)
VIN = 13V
+125°C
+25°C
–40°C
0.789
VIN = 13V
VIN = 16.5V
09441-019
+125°C
+25°C
–40°C
09441-016
0.794
ADP1878/ADP1879
Data4heet
900
601.0
599.5
VREG = 5V, VIN = 13V
599.0
598.5
598.0
840
820
800
780
760
740
597.5
–7.5
25.0
57.5
90.0
700
13.0
09441-022
597.0
–40.0
122.5
TEMPERATURE (°C)
+125°C
+25°C
–40°C
14.5
15.0
15.5
16.0
16.5
Figure 25. Switching Frequency vs. High Input Voltage, 1.0 MHz,
VIN Range = 13 V to 16.5 V
280
NO LOAD
VIN = 13V
VIN = 20V
VIN = 16.5V
265
+125°C
+25°C
–40°C
305
FREQUENCY (kHz)
SWITCHING FREQUENCY (kHz)
315
14.0
VIN (V)
Figure 22. Feedback Voltage vs. Temperature
325
13.5
09441-025
720
295
285
250
235
220
275
205
265
VIN (V)
190
09441-023
255
10.8 11.0 11.2 11.4 11.6 11.8 12.0 12.2 12.4 12.6 12.8 13.0 13.2
0
+125°C
+25°C
–40°C
4000
6000
8000
10,000
LOAD CURRENT (mA)
Figure 26. Frequency vs. Load Current, 300 kHz, VOUT = 0.8 V
Figure 23. Switching Frequency vs. High Input Voltage, 300 kHz, ±10% of 12 V
650
2000
09441-026
FEEDBACK VOLTAGE (V)
860
SWITCHING FREQUENCY (kHz)
VREG = 5V, VIN = 20V
600.0
330
NO LOAD
VIN = 20V
VIN = 13V
VIN = 16.5V
320
600
+125°C
+25°C
–40°C
310
FREQUENCY (kHz)
SWITCHING FREQUENCY (kHz)
+125°C
+25°C
–40°C
880
600.5
550
500
300
290
280
270
260
450
13.4
13.8
14.2
14.6
15.0
VIN (V)
15.4
15.8
16.2
Figure 24. Switching Frequency vs. High Input Voltage, 600 kHz, VOUT = 1.8 V,
VIN Range = 13 V to 16.5 V
Rev. A | Page 10 of 40
240
0
1500
3000
4500
6000
7500
9000 10,500 12,000 13,500 15,000
LOAD CURRENT (mA)
Figure 27. Frequency vs. Load Current, 300 kHz, VOUT = 1.8 V
09441-027
400
13.0
09441-024
250
Data4heet
+125°C
+25°C
–40°C
VIN = 13V
VIN = 16.5V
334
326
FREQUENCY (kHz)
FREQUENCY (kHz)
330
322
318
314
310
306
302
0
09441-028
298
800 1600 2400 3200 4000 4800 5600 6400 7200 8000 8800
LOAD CURRENT (mA)
510
+125°C
+25°C
–40°C
800 1600 2400 3200 4000 4800 5600 6400 7200 8000 8800 9600
LOAD CURRENT (mA)
Figure 31. Frequency vs. Load Current, 600 kHz, VOUT = 5 V
850
+125°C
+25°C
–40°C
VIN = 13V
VIN = 16.5V
VIN = 13V
VIN = 16.5V
0
Figure 28. Frequency vs. Load Current, 300 kHz, VOUT = 7 V
540
740
733
726
719
712
705
698
691
684
677
670
663
656
649
642
635
628
621
09441-031
338
ADP1878/ADP1879
VIN = 13V
VIN = 16.5V
+125°C
+25°C
–40°C
775
FREQUENCY (kHz)
FREQUENCY (kHz)
480
450
420
390
700
625
550
360
0
1200
2400
3600
4800
6000
7200
8400
9600 10,800 12,000
LOAD CURRENT (mA)
400
09441-029
300
0
6000
8000
10,000
12,000
Figure 32. Frequency vs. Load Current, VOUT = 1.0 MHz, 0.8 V
1225
675
VIN = 13V
VIN = 16.5V
655
4000
LOAD CURRENT (mA)
Figure 29. Frequency vs. Load Current, 600 kHz, VOUT = 0.8 V
VIN = 13V
VIN = 16.5V
1150
+125°C
+25°C
–40°C
1075
FREQUENCY (kHz)
635
615
595
575
555
1000
925
850
775
700
535
495
0
1000 2000 3000 4000 5000 6000 7000 8000 9000 10,000
LOAD CURRENT (mA)
Figure 30. Frequency vs. Load Current, 600 kHz, VOUT = 1.8 V
550
0
1200
2400
3600
4800
6000
7200
8400
9600 10,800 12,000
LOAD CURRENT (mA)
Figure 33. Frequency vs. Load Current, 1.0 MHz, VOUT = 1.8 V
Rev. A | Page 11 of 40
09441-033
625
+125°C
+25°C
–40°C
515
09441-030
FREQUENCY (kHz)
2000
09441-032
475
330
ADP1878/ADP1879
Data4heet
1450
82
VIN = 13V
VIN = 16.5V
1400
+125°C
+25°C
–40°C
MAXIMUM DUTY CYCLE (%)
1300
1250
1200
1150
1100
76
74
72
70
68
66
1050
800
1600 2400 3200 4000 4800 5600 6400 7200 8000
LOAD CURRENT (mA)
62
5.5
09441-034
7.9
9.1
10.3
11.5
12.7
13.9
15.1
16.3
VIN (V)
Figure 34. Frequency vs. Load Current, 1.0 MHz, VOUT = 5 V
Figure 37. Maximum Duty Cycle vs. High Voltage Input (VIN)
2.658
680
2.657
630
VREG = 2.7V
VREG = 3.6V
VREG = 5.5V
580
MINiMUM OFF TIME (ns)
2.656
2.655
2.654
2.653
2.652
530
480
430
380
330
2.651
280
2.650
230
–20
0
20
40
60
80
100
120
TEMPERATURE (°C)
180
–40
09441-035
2.649
–40
6.7
20
40
60
80
100
120
Figure 38. Minimum Off Time vs. Temperature
680
+125°C
+25°C
–40°C
90
0
TEMPERATURE (°C)
Figure 35. UVLO vs. Temperature
95
–20
09441-038
0
09441-037
64
1000
UVLO (V)
78
+125°C
+25°C
–40°C
630
580
MINIMUM OFF TIME (ns)
85
80
75
70
65
530
480
430
380
330
280
60
230
400
500
600
700
800
900
FREQUENCY (kHz)
1000
09441-036
55
300
Figure 36. Maximum Duty Cycle vs. Frequency
180
2.7
3.1
3.5
3.9
4.3
4.7
5.1
VREG (V)
Figure 39. Minimum Off Time vs. VREG (Low Input Voltage)
Rev. A | Page 12 of 40
5.5
09441-039
FREQUENCY (kHz)
1350
MAXIMUM DUTY CYCLE (%)
+125°C
+25°C
–40°C
80
Data4heet
80
+125°C
+25°C
–40°C
RECTIFIER DROP (mV)
640
560
480
400
320
240
160
400
500
600
700
800
900
1000
FREQUENCY (kHz)
1200
1120
VIN = 5.5V
VIN = 13V
VIN = 16.5V
1MHz
300kHz
48
40
32
24
16
3.1
3.5
3.9
4.3
4.7
5.1
5.5
VREG (V)
Figure 43. Low-Side MOSFET Body Diode Conduction Time vs. VREG
TA = 25°C
OUTPUT VOLTAGE
1
1040
RECTIFIER DROP (mV)
56
8
2.7
Figure 40. Internal Rectifier Drop vs. Frequency
1280
+125°C
+25°C
–40°C
64
09441-040
80
300
300kHz
1MHz
72
09441-043
720
VREG = 2.7V
VREG = 3.6V
VREG = 5.5V
BODY DIODE CONDUCTION TIME (ns)
800
ADP1878/ADP1879
960
880
800
INDUCTOR CURRENT
720
2
640
560
SW NODE
480
400
3
320
240
LOW SIDE
160
3.5
3.9
4.3
4.7
5.1
5.5
VREG (V)
Figure 41. Internal Boost Rectifier Drop vs. VREG (Low Input Voltage)
Over VIN Variation
720
640
300kHz
1MHz
CH1 50mV BW
CH3 10V BW
CH2 5A Ω
CH4 5V
M400ns
T 35.8%
A CH2
3.90A
09441-044
3.1
09441-041
80
2.7
4
Figure 44. Power Saving Mode (PSM) Operational Waveform, 100 mA
+125°C
+25°C
–40°C
OUTPUT VOLTAGE
INDUCTOR CURRENT
480
2
400
320
SW NODE
240
3
160
LOW SIDE
80
2.7
3.1
3.5
3.9
4.3
4.7
5.1
VREG (V)
5.5
CH1 50mV BW
CH3 10V BW
CH2 5A Ω
CH4 5V
M4.0µs
T 35.8%
A CH2
Figure 45. PSM Waveform at Light Load, 500 mA
Figure 42. Internal Boost Rectifier Drop vs. VREG
Rev. A | Page 13 of 40
3.90A
09441-045
4
09441-042
RECTIFIER DROP (mV)
1
560
ADP1878/ADP1879
Data Sheet
OUTPUT VOLTAGE
2
4
OUTPUT VOLTAGE
INDUCTOR CURRENT
12A NEGATIVE STEP
1
SW NODE
1
3
SW NODE
LOW SIDE
3
M400ns
CH4 100mV
B
A CH3
2.20V
W T 30.6%
CH1 10A Ω
CH3 20V
CH2 200mV
CH4 5V
B
W M20µs
A CH1
3.40A
T 48.2%
09441-049
CH1 5A Ω
CH3 10V
09441-046
4
Figure 49. Negative Step During Heavy Load Transient Behavior—PSM Enabled,
12 A (See Figure 95 Application Circuit)
Figure 46. CCM Operation at Heavy Load, 12 A
(See Figure 95 for Application Circuit)
OUTPUT VOLTAGE
2
4
OUTPUT VOLTAGE
12A STEP
12A STEP
LOW SIDE
1
1
SW NODE
3
2
SW NODE
LOW SIDE
4
B
W
M2ms
T 75.6%
A CH1
3.40A
CH1 10A Ω
CH3 20V
CH2 5V
CH4 200mV
B
W
M2ms
T 15.6%
A CH1
6.20A
09441-050
CH2 200mV
CH4 5V
09441-047
3
CH1 10A Ω
CH3 20V
Figure 50. Load Transient Step—Forced PWM at Light Load, 12 A
(See Figure 95 Application Circuit)
Figure 47. Load Transient Step—PSM Enabled, 12 A
(See Figure 95 Application Circuit)
OUTPUT VOLTAGE
OUTPUT VOLTAGE
2
4
12A POSITIVE STEP
12A POSITIVE STEP
SW NODE
1
LOW SIDE
1
3
2
SW NODE
LOW SIDE
4
B
W M20µs
T 30.6%
A CH1
3.40A
CH1 10A Ω
CH3 20V
Figure 48. Positive Step During Heavy Load Transient Behavior—PSM Enabled,
12 A, VOUT = 1.8 V (See Figure 95 Application Circuit)
CH2 5V
CH4 200mV
M20µs
B
W T 43.8%
A CH1
6.20A
09441-051
CH2 200mV
CH4 5V
09441-048
3
CH1 10A Ω
CH3 20V
Figure 51. Positive Step During Heavy Load Transient Behavior—Forced PWM
at Light Load, 12 A, VOUT = 1.8 V (See Figure 95 Application Circuit)
Rev. A | Page 14 of 40
Data Sheet
ADP1878/ADP1879
OUTPUT VOLTAGE
OUTPUT VOLTAGE
2
1
INDUCTOR CURRENT
12A NEGATIVE STEP
1
2
SW NODE
LOW SIDE
4
3
SW NODE
LOW
SIDE
CH2 200mV
CH4 5V
B
W M10µs
A CH1
5.60A
T 23.8%
CH1 2V BW CH2 5A Ω
CH3 10V
CH4 5V
Figure 52. Negative Step During Heavy Load Transient Behavior—Forced PWM
at Light Load, 12 A (See Figure 95 Application Circuit)
M2ms
T 32.8%
A CH1
720mV
09441-055
CH1 10A Ω
CH3 20V
3
09441-052
4
Figure 55. Start-Up Behavior at Heavy Load, 12 A, 300 kHz
(See Figure 95 Application Circuit)
OUTPUT VOLTAGE
OUTPUT VOLTAGE
1
1
INDUCTOR CURRENT
2
LOW SIDE
INDUCTOR CURRENT
2
LOW SIDE
4
4
SW NODE
SW NODE
3
M4ms
T 49.4%
A CH1
920mV
CH1 2V BW CH2 5A Ω
CH3 10V
CH4 5V
Figure 53. Output Short-Circuit Behavior Leading to Hiccup Mode
1
M4ms
T 41.6%
A CH1
720mV
09441-056
CH1 2V BW CH2 5A Ω
CH3 10V
CH4 5V
09441-053
3
Figure 56. Power-Down Waveform During Heavy Load
OUTPUT VOLTAGE
OUTPUT VOLTAGE
1
INDUCTOR CURRENT
INDUCTOR CURRENT
2
2
SW NODE
SW NODE
3
3
LOW SIDE
LOW SIDE
4
CH2 10A Ω
CH4 5V
M10µs
T 36.2%
A CH2
8.20A
CH1 50mV BW
CH3 10V BW
Figure 54. Magnified Waveform During Hiccup Mode
CH2 5A Ω
CH4 5V
M2µs
T 35.8%
A CH2
3.90A
09441-057
CH3 10V
09441-054
4
CH1 5V BW
Figure 57. Output Voltage Ripple Waveform During PSM Operation
at Light Load, 2 A
Rev. A | Page 15 of 40
ADP1878/ADP1879
Data Sheet
TA = 25°C
VREG = 5.5V
VREG = 3.6V
VREG = 2.7V
570
TRANSCONDUCTANCE (µS)
LOW SIDE
4
HIGH SIDE
SW NODE
3
2
550
530
510
490
470
HS MINUS
SW
M40ns
T 29.0%
A CH2
4.20V
430
–40
09441-058
CH3 5V
MATH 2V 40ns
CH2 5V
CH4 2V
20
40
60
80
100
680
+125°C
+25°C
–40°C
TRANSCONDUCTANCE (µS)
630
22ns (tpdhDRVH )
HIGH SIDE
25ns (tr,DRVH )
SW NODE
3
2
530
480
430
380
HS MINUS
SW
CH2 5V
CH3 5V
CH4 2V
MATH 2V 40ns
M40ns
T 29.0%
A CH2
4.20V
330
2.7
09441-059
M
580
3.0
3.3
3.6
3.9
4.2
4.5
4.8
5.1
5.4
VREG (V)
09441-062
4
120
Figure 61. Transconductance vs. Temperature
TA = 25°C
16ns (tf,DRVL )
0
TEMPERATURE (°C)
Figure 58. Output Drivers and SW Node Waveforms
LOW SIDE
–20
09441-061
450
M
Figure 62. Transconductance vs. VREG
Figure 59. High-Side Driver Rising and Low-Side Falling Edge Waveforms (CIN =
4.3 nF (High-/Low-Side MOSFET), QTOTAL = 27 nC (VGS = 4.4 V (Q1), VGS = 5 V (Q3))
1.30
18ns (tr,DRVL )
LOW SIDE
1.25
QUIESCENT CURRENT (mA)
1.20
4
24ns (tpdh,DRVL )
HIGH SIDE
HS MINUS
SW
11ns (tf,DRVH)
3
2
SW NODE
1.15
+125°C
1.10
1.05
+25°C
1.00
0.95
–40°C
0.90
0.85
0.80
M
M20ns
T 39.2%
A CH2
4.20V
0.70
2.7
09441-060
CH3 5V
MATH 2V 20ns
CH2 5V
CH4 2V
3.1
3.5
3.9
4.3
4.7
VREG (V)
Figure 60. High-Side Driver Falling and Low-Side Rising Edge Waveforms (CIN =
4.3 nF (High-/Low-Side MOSFET), QTOTAL = 27 nC (VGS = 4.4 V (Q1), VGS = 5 V (Q3))
Rev. A | Page 16 of 40
Figure 63. Quiescent Current vs. VREG
5.1
5.5
09441-063
0.75
TA = 25°C
Data Sheet
ADP1878/ADP1879
THEORY OF OPERATION
BLOCK DIAGRAM
PGOOD
690mV
FB
600mV
ADP1878/ADP1879
530mV
VREG
tON TIMER
PRECISION
ENABLE
EN
C
TO ENABLE
ALL BLOCKS
THRESHOLD/
HYSTERESIS
630mV
VIN
I
SW
INFORMATION
LDO
VREG
R (TRIMMED)
tON = 2RC(VOUT/VIN)
REF
SW FILTER
BIAS BLOCK
AND REFERENCE
TON
BG_REF
ISS
SS
COMP
BST
STATE
MACHINE
REF_ZERO
SS
COMP
VREG
PSM
IN_PSM
IN_SS
DRVH
300kΩ
HS_0
HS
LEVEL
SHIFT
SS_REF
COMP
PWM
FB
SW
IREV
SW
8kΩ
LS
LS_0
VREG
LS
ERROR
AMP
0.6V
HS
IN_HICCUP
DRVL
800kΩ
PGND
PWM
IREV
COMP
CS
AMP
REF_ZERO
CS GAIN SET
GND
ADC
RES DETECT AND
GAIN SET
0.4V
RES
09441-064
LOWER
COMP
CLAMP
Figure 64. ADP1878/ADP1879 Block Diagram
The ADP1878/ADP1879 are versatile current-mode, synchronous
step-down controllers that provide superior transient response,
optimal stability, and current-limit protection by using a constant
on time, pseudo fixed frequency with a programmable current
sense gain, current control scheme. In addition, these devices offer
optimum performance at low duty cycles by using a valley, currentmode control architecture. This allows the ADP1878/ADP1879
to drive all N-channel power stages to regulate output voltages
to as low as 0.6 V.
Rev. A | Page 17 of 40
ADP1878/ADP1879
Data Sheet
STARTUP
PRECISION ENABLE CIRCUITRY
Each ADP1878/ADP1879 has an internal regulator (VREG)
for biasing and supplying power for the integrated N-channel
MOSFET drivers. Place a bypass capacitor directly across the
VREG (Pin 7) and PGND (Pin 13) pins. Included in the powerup sequence is the biasing of the current sense amplifier, the
current sense gain circuit (see the Programming Resistor (RES)
Detect Circuit section), the soft start circuit, and the error
amplifier.
The ADP1878/ADP1879 have precision enable circuitry. The
precision enable threshold is 630 mV including 30 mV of
hysteresis (see Figure 66). Connecting the EN pin to GND
disables the ADP1878/ADP1879, reducing the supply current
of the device to approximately 140 μA.
The soft start and error amplifier blocks determine the rise time
of the output voltage (see the Soft Start section). At the beginning
of a soft start, the error amplifier charges the external compensation capacitor, causing the COMP pin to rise (see Figure 65).
Tying the VREG pin to the EN pin via a pull-up resistor causes
the voltage at the EN pin to rise above the enable threshold of
630 mV, thereby enabling the ADP1878/ADP1879.
COMP
>2.4V
2.4V
HICCUP MODE INITIALIZED
MAXIMUM CURRENT (UPPER CLAMP)
10kΩ
PRECISION
ENABLE COMP.
EN
TO ENABLE
ALL BLOCKS
630mV
09441-065
The current sense blocks provide valley current information
(see the Programming Resistor (RES) Detect Circuit section)
and they are a variable of the compensation equation for loop
stability (see the Compensation Network section). In a process
performed by the RES detect circuit, the valley current information is extracted by forcing 0.4 V across the RES and PGND pins
generating current. The current through the RES resistor is used
to set the current sense amplifier gain (see the Programming
Resistor (RES) Detect Circuit section). This process takes approximately 800 μs, after which time the drive signal pulses appear at
the DRVL and DRVH pins synchronously, and the output voltage
begins to rise in a controlled manner through the soft start
sequence.
VREG
Figure 66. Connecting EN Pin to VREG via a Pull-Up Resistor to Enable the
ADP1878/ADP1879
UNDERVOLTAGE LOCKOUT
The undervoltage lockout (UVLO) feature prevents the device
from operating both the high- and low-side N-channel MOSFETs
at extremely low or undefined input voltage (VIN) ranges.
Operation at an undefined bias voltage can result in the
incorrect propagation of signals to the high-side power switches.
This, in turn, results in invalid output behavior that can cause
damage to the output devices, ultimately destroying the device
tied at the output. The UVLO level is set at 2.65 V (nominal).
ON-BOARD LOW DROPOUT (LDO) REGULATOR
The ADP1878/ADP1879 use an on-board LDO to bias the
internal digital and analog circuitry. With proper bypass
capacitors connected to the VREG pin (output of the internal
LDO), this pin also provides power for the internal MOSFET
drivers. It is recommended to float VREG if VIN is used for
greater than 5.5 V operation. The minimum voltage at which
bias is guaranteed to operate is 2.75 V at VREG (see Figure 67).
ON-BOARD REGULATOR
VREG
1.0V
ZERO CURRENT
USABLE RANGE ONLY AFTER SOFT START
PERIOD IF CONTINUOUS CONDUCTION
MODE OF OPERATION IS SELECTED.
REF
09441-067
500mV
VIN
LOWER CLAMP
Figure 67. On-Board Regulator
09441-066
For applications where VIN is decoupled from VREG, the
minimum voltage at VIN must be 2.9 V. It is recommended to tie
VIN and VREG together if the VIN pin is subjected to a 2.75 V rail.
0V
Figure 65. COMP Voltage Range
SOFT START
The ADP1878 employs externally programmable, soft start
circuitry that charges up a capacitor tied to the SS pin to GND.
This prevents input inrush current through the external MOSFET
from the input supply (VIN). The output tracks the ramping voltage
by producing PWM output pulses to the high-side MOSFET. The
purpose is to limit the inrush current from the high voltage
input supply (VIN) to the output (VOUT).
Rev. A | Page 18 of 40
Data Sheet
ADP1878/ADP1879
Table 5. Power Input and LDO Output Configurations
VREG
Float
Connect to VIN
<5.5 V
VIN ranging
above and
below 5.5 V
Float
Float
PGND
ADC
CS GAIN
SET
0.4V
RES
Figure 69. RES Detect Circuit for Current Sense Gain Programming
THERMAL SHUTDOWN
Thermal shutdown is a protection feature that prevents the IC
from damage caused by a very high operating junction temperature. If the junction temperature of the device exceeds 155°C,
the device enters the thermal shutdown state. In this state, the
device shuts off both the high- and low-side MOSFETs and disables
the entire controller immediately, thus reducing the power consumption of the IC. The device resumes operation after the
junction temperature of the device cools to less than 140°C.
PROGRAMMING RESISTOR (RES) DETECT CIRCUIT
Upon startup, one of the first blocks to become active is the RES
detect circuit. This block powers up before soft start begins. It
forces a 0.4 V reference value at the RES pin (see Figure 68) and is
programmed to identify four possible resistor values: 47 kΩ, 22 kΩ,
open, and 100 kΩ.
The RES detect circuit digitizes the value of the resistor at the
RES pin (Pin 6). An internal ADC outputs a 2-bit digital code
that is used to program four separate gain configurations in the
current sense amplifier (see Figure 69). Each configuration corresponds to a current sense gain (ACS) of 3 V/V, 6 V/V, 12 V/V, or
24 V/V, respectively (see Table 6 and Table 7). This variable is used
for the valley current-limit setting, which sets up the appropriate
current sense gain for a given application and sets the compensation
necessary to achieve loop stability (see the Valley Current-Limit
Setting section and the Compensation Network section).
Q1
DRVH
SW
Q2
CS GAIN
PROGRAMMING
09441-068
DRVL
RES
SW
CS
AMP
Comments
Must use the LDO
LDO drop voltage is not
realized (that is, if VIN = 2.75 V,
then VREG = 2.75 V)
LDO drop is realized
LDO drop is realized, minimum
VIN recommendation is 2.95 V
09441-069
VIN
>5.5 V
<5.5 V
Table 6. Current Sense Gain Programming
Resistor
47 kΩ
22 kΩ
Open
100 kΩ
ACS
3 V/V
6 V/V
12 V/V
24 V/V
VALLEY CURRENT-LIMIT SETTING
The architecture of the ADP1878/ADP1879 is based on valley
current-mode control. The current limit is determined by three
components: the RON of the low-side MOSFET, the output voltage
swing of the current sense amplifier, and the current sense gain.
The output range of the current sense amplifier is internally
fixed at 1.4 V. The current sense gain is programmable via an
external resistor at the RES pin (see the Programming Resistor
(RES) Detect Circuit section). The RON of the low-side MOSFET
can vary over temperature and usually has a positive TC (meaning
that it increases with temperature); therefore, it is recommended to
program the current sense, gain resistor based on the rated RON of
the MOSFET at 125°C.
Because the ADP1878/ADP1879 are based on valley current
control, the relationship between ICLIM and ILOAD is
1
2
where:
KI is the ratio between the inductor ripple current and the
desired average load current (see Figure 70).
ICLIM is the desired valley current limit.
ILOAD is the current load.
Establishing KI helps to determine the inductor value (see the
Inductor Selection section), but in most cases, KI = 0.33.
Figure 68. Programming Resistor Location
RIPPLE CURRENT =
ILOAD
3
VALLEY CURRENT LIMIT
Figure 70. Valley Current Limit to Average Current Relation
Rev. A | Page 19 of 40
09441-070
LOAD CURRENT
ADP1878/ADP1879
Data Sheet
1.4 V
where:
RON is the channel impedance of the low-side MOSFET.
ACS is the current sense gain multiplier (see Table 6 and Table 7).
Although the ADP1878/ADP1879 have only four discrete current
sense gain settings for a given RON variable, Table 7 and Figure 71
outline several available options for the valley current setpoint
based on various RON values.
The valley current limit is programmed as listed in Table 7 and
shown in Figure 71. The inductor that is chosen must be rated
to handle the peak current, which is equal to the valley current
from Table 7 plus the peak-to-peak inductor ripple current (see
the Inductor Selection section). In addition, the peak current
value must be used to compute the worst-case power dissipation
in the MOSFETs (see Figure 72).
49A
MAXIMUM DC LOAD
CURRENT
39.5A
INDUCTOR
CURRENT
Table 7. Valley Current Limit Program (See Figure 71)
∆I = 33%
OF 30A
1
RON
(mΩ)
1.5
2
2.5
3
3.5
4.5
5
5.5
10
15
18
39.0
33.4
26.0
23.4
21.25
11.7
7.75
6.5
23.3
15.5
13.0
31.0
26.0
100 kΩ,
ACS = 24 V/V
38.9
29.2
23.3
19.5
16.7
13
11.7
10.6
5.83
7.5
3.25
CS AMP
OUTPUT
SWING
0A
RES = 22kΩ
ACS = 6V/V
RES = 100kΩ
ACS = 24V/V
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
RON (mΩ)
1V
Figure 72. Valley Current-Limit Threshold in Relation to Inductor Ripple Current
RES = 47kΩ
ACS = 3V/V
RES = NO RES
ACS = 12V/V
∆I = 45% 32.25A
OF 32.25A
30A
VALLEY CURRENT-LIMIT
THRESHOLD (SET FOR 25A)
09441-071
39
37
35
33
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
37A
CURRENT
SENSE
AMPLIFIER
OUTPUT
2.4V
Blank cells are not applicable.
VALLEY CURRENT LIMIT (A)
1
Valley Current Level (A)
22 kΩ,
Open,
ACS = 6 V/V
ACS = 12 V/V
47 kΩ,
ACS = 3 V/V
35A
∆I = 65%
OF 37A
09441-072
When the desired valley current limit (ICLIM) has been determined,
the current sense gain can be calculated as follows:
Figure 71. Valley Current-Limit Value vs. RON of the Low-Side MOSFET
for Each Programming Resistor (RES)
Rev. A | Page 20 of 40
Data Sheet
ADP1878/ADP1879
REPEATED CURRENT-LIMIT
VIOLATION DETECTED
HS
A PREDETERMINED NUMBER SOFT START IS
OF PULSES IS COUNTED TO REINITIALIZED TO
ALLOW THE CONVERTER MONITOR IF THE
TO COOL DOWN
VIOLATION
STILL EXISTS
09441-073
CLIM
ZERO
CURRENT
Figure 73. Idle Mode Entry Sequence Due to Current-Limit Violation
HS
A current-limit violation occurs when the current across the
source and drain of the low-side MOSFET exceeds the currentlimit setpoint. When 32 current-limit violations are detected,
the controller enters idle mode and turns off the MOSFETs for
6 ms, allowing the converter to cool down. Then, the controller
reestablishes soft start and begins to cause the output to ramp
up again (see Figure 73). While the output ramps up, the current
sense amplifier output is monitored to determine if the violation is
still present. If it is still present, the idle event occurs again, followed
by the full chip, power-down sequence. This cycle continues
until the violation no longer exists. If the violation disappears,
the converter is allowed to switch normally, maintaining
regulation.
tON
HS AND LS ARE OFF
OR IN IDLE MODE
LS
tOFF
AS THE INDUCTOR
CURRENT APPROACHES
ZERO CURRENT, THE STATE
MACHINE TURNS OFF THE
LOWER-SIDE MOSFET.
ILOAD
0A
09441-074
HICCUP MODE DURING SHORT CIRCUIT
Figure 74. Discontinuous Mode of Operation (DCM)
The ADP1878/ADP1879 employ internal MOSFET drivers for
the external high- and low-side MOSFETs. The low-side
synchronous rectifier not only improves overall conduction
efficiency, but it also ensures proper charging of the bootstrap
capacitor located at the high-side driver input. This is beneficial
during startup to provide sufficient drive signal to the external
high-side MOSFET and to attain fast turn-on response, which is
essential for minimizing switching losses. The integrated highand low-side MOSFET drivers operate in complementary
fashion with built-in anti cross conduction circuitry to prevent
unwanted shoot through current that may potentially damage the
MOSFETs or reduce efficiency because of excessive power loss.
To minimize the chance of negative inductor current buildup,
an on-board zero-cross comparator turns off all high- and lowside switching activities when the inductor current approaches
the zero current line, causing the system to enter idle mode,
where the high- and low-side MOSFETs are turned off. To ensure
idle mode entry, a 10 mV offset, connected in series at the SW
node, is implemented (see Figure 75).
ZERO-CROSS
COMPARATOR
SW
IQ2
10mV
LS
ADP1879 POWER SAVING MODE (PSM)
Q2
09441-075
SYNCHRONOUS RECTIFIER
Figure 75. Zero-Cross Comparator with 10 mV of Offset
A power saving mode is provided in the ADP1879. The ADP1879
operates in the discontinuous conduction mode (DCM) and
pulse skips at light to medium load currents. The controller outputs
pulses as necessary to maintain output regulation. Unlike the
continuous conduction mode (CCM), DCM operation prevents
negative current, thus allowing improved system efficiency at
light loads. Current in the reverse direction through this pathway,
however, results in power dissipation and, therefore, a decrease in
efficiency.
As soon as the forward current through the low-side MOSFET
decreases to a level where
10 mV = IQ2 × RON(Q2)
the zero-cross comparator (or IREV comparator) emits a signal to
turn off the low-side MOSFET. From this point, the slope of the
inductor current ramping down becomes steeper (see Figure 76)
as the body diode of the low-side MOSFET begins to conduct
current and continues conducting current until the remaining
energy stored in the inductor has been depleted.
Rev. A | Page 21 of 40
ADP1878/ADP1879
Data Sheet
ANOTHER tON EDGE IS
TRIGGERED WHEN VOUT
FALLS BELOW REGULATION
SW
The tON timer uses a feedforward technique that, when applied
to the constant on-time control loop, makes it a pseudo fixed
frequency to a first-order approximation.
tON
Second-order effects, such as dc losses in the external power
MOSFETs (see the Efficiency Consideration section), cause some
variation in frequency vs. load current and line voltage. These
effects are shown in Figure 23 to Figure 34. The variations in
frequency are much reduced compared with the variations
generated if the feedforward technique is not used.
HS AND LS
IN IDLE MODE
LS
The feedforward technique establishes the following relationship:
ZERO-CROSS COMPARATOR
DETECTS 10mV OFFSET AND
TURNS OFF LS
1
where fSW is the controller switching frequency (300 kHz,
600 kHz, and 1.0 MHz).
09441-076
ILOAD
0A
10mV = RON × ILOAD
Figure 76. 10 mV Offset to Ensure Prevention of Negative Inductor Current
The system remains in idle mode until the output voltage drops
below regulation. Next, a PWM pulse is produced, turning on the
high-side MOSFET to maintain system regulation. The ADP1879
does not have an internal clock; it switches purely as a hysteretic
controller, as described in this section.
The tON timer senses VIN and VOUT to minimize frequency
variation as previously explained. This provides pseudo fixed
frequency as explained in the Pseudo Fixed Frequency section.
To allow headroom for VIN and VOUT sensing, adhere to the
following equations:
VREG ≥ VIN/8 + 1.5
TIMER OPERATION
The ADP1878/ADP1879 employ a constant on-time architecture,
which provides a variety of benefits, including improved load
and line transient response when compared with a constant
(fixed) frequency current-mode control loop of comparable
loop design. The constant on-time timer, or tON timer, senses
the high-side input voltage (VIN) and the output voltage (VOUT)
using SW waveform information to produce an adjustable one
shot PWM pulse. The pulse varies the on-time of the high-side
MOSFET in response to dynamic changes in input voltage, output
voltage, and load current conditions to maintain output regulation. The timer generates an on-time (tON) pulse that is inversely
proportional to VIN.
where K is a constant that is trimmed using an RC timer product
for the 300 kHz, 600 kHz, and 1.0 MHz frequency options.
VREG
tON
VIN
C
I
R (TRIMMED)
09441-077
SW
INFORMATION
Figure 77. Constant On-Time Time
The constant on-time (tON) is not strictly constant because it
varies with VIN and VOUT. However, this variation occurs in such
a way as to keep the switching frequency virtually independent
of VIN and VOUT.
VREG ≥ VOUT/4
For typical applications where VREG is 5 V, these equations are
not relevant; however, for lower VREG inputs, care may be required.
PSEUDO FIXED FREQUENCY
The ADP1878/ADP1879 employ a constant on-time control
scheme. During steady state operation, the switching frequency
stays relatively constant, or pseudo fixed. This is due to the one
shot tON timer that produces a high-side PWM pulse with a
fixed duration, given that external conditions such as input
voltage, output voltage, and load current are also at steady state.
During load transients, the frequency momentarily changes for
the duration of the transient event so that the output comes
back within regulation quicker than if the frequency were fixed,
or if it were to remain unchanged. After the transient event is
complete, the frequency returns to a pseudo fixed value.
To illustrate this feature more clearly, this section describes one
such load transient event—a positive load step—in detail. During
load transient events, the high-side driver output pulse width
stays relatively consistent from cycle to cycle; however, the off
time (DRVL on time) dynamically adjusts according to the
instantaneous changes in the external conditions mentioned.
When a positive load step occurs, the error amplifier (out of phase
with the output, VOUT) produces new voltage information at its
output (COMP). In addition, the current sense amplifier senses
new inductor current information during this positive load
transient event. The output voltage reaction of the error amplifier is
compared with the new inductor current information that sets
the start of the next switching cycle. Because current information
is produced from valley current sensing, it is sensed at the down
ramp of the inductor current, whereas the voltage loop information
Rev. A | Page 22 of 40
Data Sheet
ADP1878/ADP1879
is sensed through the counter action upswing of the output
(COMP) of the error amplifier.
The result is a convergence of these two signals (see Figure 78),
which allows an instantaneous increase in switching frequency
during the positive load transient event. In summary, a positive
load step causes VOUT to transient down, which causes COMP to
transient up and, therefore, shortens the off time. This resulting
increase in frequency during a positive load transient helps to
quickly bring VOUT back up in value and within the regulation
window.
Similarly, a negative load step causes the off time to lengthen in
response to VOUT rising. This effectively increases the inductor
demagnetizing phase, helping to bring VOUT within regulation.
In this case, the switching frequency decreases, or experiences a
foldback, to help facilitate output voltage recovery.
Because the ADP1878/ADP1879 have the ability to respond rapidly
to sudden changes in load demand, the recovery period in which
the output voltage settles back to its original steady state operating
point is much quicker than it would be for a fixed frequency
equivalent. Therefore, using a pseudo fixed frequency results in
significantly better load transient performance compared to
using a fixed frequency.
the internal switch is turned on, PGOOD is internally pulled low
when the output voltage via the FB pin is outside this regulation
window.
The power-good window is defined with a typical upper specification of +90 mV and a lower specification of −70 mV below
the FB voltage of 600 mV. When an overvoltage event occurs at the
output, there is a typical propagation delay of 12 μs prior to the
deassertion (logic low) of the PGOOD pin. When the output
voltage reenters the regulation window, there is a propagation
delay of 12 μs prior to PGOOD reasserting back to a logic high
state. When the output is outside the regulation window, the
PGOOD open-drain switch is capable of sinking 1 mA of
current and providing 140 mV of drop across this switch. The
user is free to tie the external pull-up resistor (RRES) to any
voltage rail up to 20 V. The following equation provides the
proper external pull-up resistor value:
140 mV
1 mA
where:
RPGD is the PGOOD external resistor.
VEXT is a user chosen voltage rail.
VEXT
1mA
+
140mV
–
690mV
LOAD CURRENT
DEMAND
RPGD
PGOOD
FB
600mV
CS AMP
OUTPUT
ERROR AMP
OUTPUT
fSW
Figure 79. Power Good, Output Voltage Monitoring Circuit
OUTPUT OVERVOLTAGE
PGOOD DEASSERT
>fSW
690mV
09441-078
PWM OUTPUT
VALLEY
TRIP POINTS
09441-079
530mV
640mV
FB
HYSTERESIS (50mV)
PGOOD
REASSERT
600mV
Figure 78. Load Transient Response Operation
530mV
POWER-GOOD MONITORING
0V
SOFT START
PGOOD
DEASSERTION
AT POWER-DOWN
VEXT
tPGD
PGOOD
0V
tPGD
tPGD
tPGD
09441-080
The ADP1878/ADP1879 power-good circuitry monitors the
output voltage via the FB pin. The PGOOD pin is an opendrain output that can be pulled up by an external resistor to a
voltage rail that does not necessarily have to be VREG. When
the internal NMOS switch is in high impedance (off state), this
means that the PGOOD pin is logic high and the output voltage
via the FB pin is within the specified regulation window. When
PGOOD
ASSERTION
AT POWER-UP
Figure 80. Power-Good Timing Diagram, tPGD = 12 μs (Diagram May Look
Disproportionate For Illustration Purposes)
Rev. A | Page 23 of 40
ADP1878/ADP1879
Data Sheet
APPLICATIONS INFORMATION
FEEDBACK RESISTOR DIVIDER
Table 8. Recommended Inductors
The required resistor divider network can be determined for a
given VOUT value because the internal band gap reference (VREF)
is fixed at 0.6 V. Selecting values for RT and RB determine the
minimum output load current of the converter. Therefore, for a
given value of RB, the RT value can be determined through the
following expression:
L
(μH)
0.12
0.22
0.47
0.72
0.9
1.2
1.0
1.4
2.0
0.8
0.6 V
0.6 V
INDUCTOR SELECTION
The inductor value is inversely proportional to the inductor
ripple current. The peak-to-peak ripple current is given by
∆
Dimensions
(mm)
10.2 × 7
10.2 × 7
14.2 × 12.8
10.5 × 10.2
14 × 12.8
10.5 × 10.2
10.2 × 10.2
14 × 12.8
10.2 × 10.2
Manufacturer
Würth Elek.
Würth Elek.
Würth Elek.
Würth Elek.
Würth Elek.
Würth Elek.
Würth Elek.
Würth Elek.
Würth Elek.
Sumida
Model
Number
744303012
744303022
744355147
744325072
744318120
744325120
7443552100
744318180
7443551200
CEP125U-0R8
The output ripple voltage is the ac component of the dc output
voltage during steady state. For a ripple error of 1.0%, the output
capacitor value needed to achieve this tolerance can be determined
using the following equation. (Note that an accuracy of 1.0% is
possible during steady state conditions only, not during load
transients.)
where KI is typically 0.33.
The equation for the inductor value is given by
∆
where:
VIN is the high voltage input.
VOUT is the desired output voltage.
fSW is the controller switching frequency (300 kHz, 600 kHz, and
1.0 MHz).
When selecting the inductor, choose an inductor saturation
rating that is above the peak current level, and then calculate
the inductor current ripple (see the Valley Current-Limit
Setting section and Figure 81).
∆I = 50%
∆I = 40%
ΔVRR = (0.01) × VOUT
OUTPUT CAPACITOR SELECTION
The primary objective of the output capacitor is to facilitate the
reduction of the output voltage ripple; however, the output capacitor
also assists in the output voltage recovery during load transient
events. For a given load current step, the output voltage ripple
generated during this step event is inversely proportional to the
value chosen for the output capacitor. The speed at which the
output voltage settles during this recovery period depends on
where the crossover frequency (loop bandwidth) is set. This
crossover frequency is determined by the output capacitor, the
equivalent series resistance (ESR) of the capacitor, and the
compensation network.
To calculate the small signal voltage ripple (output ripple voltage) at
the steady state operating point, use the following equation:
∆I = 33%
∆
1
∆
8
∆
where ESR is the equivalent series resistance of the output
capacitors.
To calculate the output load step, use the following equation:
6
8
10
12
14
16
18
20
22
VALLEY CURRENT LIMIT (A)
24
26
28
30
09441-081
PEAK INDUCTOR CURRENT (A)
ISAT
(A)
55
30
50
35
32
25
16
24
23
27.5
OUTPUT RIPPLE VOLTAGE (ΔVRR)
3
52
50
48
46
44
42
40
38
36
34
32
30
28
26
24
22
20
18
16
14
12
10
8
DCR
(mΩ)
0.33
0.33
0.8
1.65
1.6
1.8
3.8
3.2
2.6
2
Figure 81. Peak Inductor Current vs. Valley Current Limit for 33%, 40%, and
50% of Inductor Ripple Current
∆
∆
∆
where ΔVDROOP is the amount that VOUT is allowed to deviate for
a given positive load current step (ΔILOAD).
Rev. A | Page 24 of 40
Data Sheet
ADP1878/ADP1879
Ceramic capacitors are known to have low ESR. However, there
is a trade-off in using the popular X5R capacitor technology
because as much as 80% of its capacitance may be lost due to
derating as the voltage applied across the capacitor is increased
(see Figure 82). Although X7R series capacitors can also be
used, the available selection is limited to 22 μF maximum.
Error Amplifier Output Impedance (ZCOMP)
Assuming CC2 is significantly smaller than CCOMP, CC2 can be
omitted from the output impedance equation of the error
amplifier. The transfer function simplifies to
20
and
10
X7R (50V)
1
12
where fZERO, the zero frequency, is set to be 1/4th of the crossover
frequency for the ADP1878.
–20
–30
–40
Error Amplifier Gain (Gm)
–50
X5R (25V)
–60
–70
Gm = 500 μA/V (μs)
X5R (16V)
–80
10µF TDK 25V, X7R, 1210 C3225X7R1E106M
22µF MURATA 25V, X7R, 1210 GRM32ER71E226KE15L
47µF MURATA 16V, X5R, 1210 GRM32ER61C476KE15L
–90
–100
The error amplifier gain (transconductance) is
0
5
10
15
20
DC VOLTAGE (VDC)
25
Current-Sense Loop Gain (GCS)
30
09441-082
CAPACITANCE CHARGE (%)
0
–10
The current-sense loop gain is
1
⁄
Figure 82. Capacitance vs. DC Voltage Characteristics for Ceramic Capacitors
Electrolytic capacitors satisfy the bulk capacitance requirements
for most high current applications. However, because the ESR of
electrolytic capacitors is much higher than that of ceramic capacitors, mount several MLCCs in parallel with the electrolytic
capacitors to reduce the overall series resistance.
where:
ACS (V/V) is programmable for 3 V/V, 6 V/V, 12 V/V, and 24 V/V
(see the Programming Resistor (RES) Detect Circuit and Valley
Current-Limit Setting sections).
RON is the channel impedance of the low-side MOSFET.
COMPENSATION NETWORK
Crossover Frequency
Due to its current-mode architecture, the ADP1878/ADP1879
require Type II compensation. To determine the component
values needed for compensation (resistance and capacitance
values), it is necessary to examine the overall loop gain (H) of the
converter at the unity-gain frequency (fSW/10) when H = 1 V/V:
The crossover frequency is the frequency at which the overall
loop (system) gain is 0 dB (H = 1 V/V). It is recommended for
current-mode converters, such as the ADP1878, that the user set
the crossover frequency between 1/10th and 1/15th of the switching
frequency.
1
12
1 V⁄V
Examining each variable at high frequency enables the unitygain transfer function to be simplified to provide expressions
for the RCOMP and CCOMP component values.
Output Filter Impedance (ZFILT)
The relationship between CCOMP and fZERO (zero frequency) is as
follows:
1
2
The zero frequency is set to 1/4th of the crossover frequency.
Examining the transfer function of the filter at high frequencies
simplifies to
Combining all of the above parameters results in
1
1
1
1
at the crossover frequency (s = 2πfCROSS). ESR is the equivalent
series resistance of the output capacitors.
1
where ESR is the equivalent series resistance of the output
capacitors.
1
2
Rev. A | Page 25 of 40
1
ADP1878/ADP1879
Data Sheet
800
An important criteria to consider in constructing a dc-to-dc
converter is efficiency. By definition, efficiency is the ratio of the
output power to the input power. For high power applications at
load currents of up to 20 A, the following are important MOSFET
parameters that aid in the selection process:
720




VGS (TH) is the MOSFET voltage applied between the gate
and the source that starts channel conduction.
RDS (ON) is the on resistance of the MOSFET during channel
conduction.
QG is the total gate charge.
CN1 is the input capacitance of the high-side switch.
CN2 is the input capacitance of the low-side switch.
640
560
480
400
320
240
80
300
Channel Conduction Loss
During normal operation, the bulk of the loss in efficiency is due
to the power dissipated through MOSFET channel conduction.
Power loss through the high-side MOSFET is directly proportional
to the duty cycle (D) for each switching period, and the power
loss through the low-side MOSFET is directly proportional to
1 − D for each switching period. The selection of MOSFETs is
governed by the maximum dc load current that the converter is
expected to deliver. In particular, the selection of the low-side
MOSFET is dictated by the maximum load current because a
typical high current application employs duty cycles of less than
50%. Therefore, the low-side MOSFET is in the on state for
most of the switching period.
1
1
400
500
600
700
800
900
1000
SWITCHING FREQUENCY (kHz)
Figure 83. Internal Rectifier Voltage Drop vs. Switching Frequency
MOSFET Switching Loss
Channel conduction loss (both of the MOSFETs).
MOSFET driver loss.
MOSFET switching loss.
Body diode conduction loss (low-side MOSFET).
Inductor loss (copper and core loss).
1, 2
+125°C
+25°C
–40°C
160
The following are the losses experienced through the external
component during normal switching operation:





VREG = 2.7V
VREG = 3.6V
VREG = 5.5V
09441-083

RECTIFIER VOLTAGE DROP (mV)
EFFICIENCY CONSIDERATION
The SW node transitions due to the switching activities of the
high- and low-side MOSFETs. This causes removal and replenishing of charge to and from the gate oxide layer of the MOSFET,
as well as to and from the parasitic capacitance associated with
the gate oxide edge overlap and the drain and source terminals.
The current that enters and exits these charge paths presents
additional loss during these transition times. This can be approximately quantified by using the following equation, which represents
the time in which charge enters and exits these capacitive regions:
tSW-TRANS = RGATE × CTOTAL
where:
CTOTAL is the CGD + CGS of the external MOSFET.
RGATE is the gate input resistance of the external MOSFET.
The ratio of this time constant to the period of one switching cycle
is the multiplying factor to be used in the following expression:
-TRANS
2
or
2
MOSFET Driver Loss
PSW(LOSS) = fSW × RGATE × CTOTAL × ILOAD × VIN × 2
Other dissipative elements are the MOSFET drivers. The contributing factors are the dc current flowing through the driver
during operation and the QGATE parameter of the external MOSFETs.
PDR(LOSS) = [VDR × (fSWCupperFETVDR + IBIAS)] + [VREG ×
(fSWClowerFETVREG + IBIAS)]
where:
CupperFET is the input gate capacitance of the high-side MOSFET.
ClowerFET is the input gate capacitance of the low-side MOSFET.
IBIAS is the dc current flowing into the high- and low-side drivers.
VDR is the driver bias voltage (that is, the low input voltage (VREG)
minus the rectifier drop (see Figure 83)).
VREG is the bias voltage.
Body Diode Conduction Loss
The ADP1878/ADP1879 employ anti cross conduction circuitry
that prevents the high- and low-side MOSFETs from conducting
current simultaneously. This overlap control is beneficial, avoiding
large current flow that may lead to irreparable damage to the
external components of the power stage. However, this blanking
period comes with the trade-off of a diode conduction loss
occurring immediately after the MOSFETs change states and
continuing well into idle mode.
Rev. A | Page 26 of 40
Data Sheet
ADP1878/ADP1879
The amount of loss through the body diode of the low-side
MOSFET during the anti overlap state is given by the following
expression:
2
where:
tBODY(LOSS) is the body conduction time (refer to Figure 84 for
dead time periods).
tSW is the period per switching cycle.
VF is the forward drop of the body diode during conduction.
(Refer to the selected external MOSFET data sheet for more
information about the VF parameter.)
If bulk electrolytic capacitors are used, it is recommended to use
multilayered ceramic capacitors (MLCC) in parallel due to their
low ESR values. This dramatically reduces the input voltage ripple
amplitude as long as the MLCCs are mounted directly across the
drain of the high-side MOSFET and the source terminal of the
low-side MOSFET (see the Layout Considerations section).
Improper placement and mounting of these MLCCs may cancel
their effectiveness due to stray inductance and an increase in
trace impedance.
+125°C
+25°C
–40°C
1MHz
300kHz
72
,
56
48
40
32
VMAX,RIPPLE = VRIPP + (ILOAD,MAX × ESR)
24
16
8
2.7
,
The maximum input voltage ripple and maximum input capacitor
rms current occur at the end of the duration of 1 − D while the
high-side MOSFET is in the off state. The input capacitor rms
current reaches its maximum at time D. When calculating the
maximum input voltage ripple, account for the ESR of the input
capacitor as follows:
64
3.4
4.1
VREG (V)
4.8
5.5
09441-084
BODY DIODE CONDUCTION TIME (ns)
80
capacitors have such high ESR that they cause undesired input
voltage ripple magnitudes and are generally not effective at high
switching frequencies.
Figure 84. Body Diode Conduction Time vs. Low Voltage Input (VREG)
where:
VRIPP is usually 1% of the minimum voltage input.
ILOAD,MAX is the maximum load current.
ESR is the equivalent series resistance rating of the input capacitor.
Inserting VMAX,RIPPLE into the charge balance equation to
calculate the minimum input capacitor requirement gives
Inductor Loss
During normal conduction mode, further power loss is caused
by the conduction of current through the inductor windings,
which have dc resistance (DCR). Typically, larger sized inductors
have smaller DCR values.
The inductor core loss is a result of the eddy currents generated
within the core material. These eddy currents are induced by the
changing flux, which is produced by the current flowing through
the windings. The amount of inductor core loss depends on the
core material, the flux swing, the frequency, and the core volume.
Ferrite inductors have the lowest core losses, whereas powdered iron
inductors have higher core losses. It is recommended to use shielded
ferrite core material type inductors with the ADP1878/ADP1879
for a high current, dc-to-dc switching application to achieve
minimal loss and negligible electromagnetic interference (EMI).
INPUT CAPACITOR SELECTION
The goal in selecting an input capacitor is to reduce or minimize
input voltage ripple and to reduce the high frequency source
impedance, which is essential for achieving predictable loop
stability and transient performance.
The problem with using bulk capacitors, other than their physical
geometries, is their large equivalent series resistance (ESR) and
large equivalent series inductance (ESL). Aluminum electrolytic
1
,
,
,
or
,
,
4
,
where D = 50%.
THERMAL CONSIDERATIONS
The ADP1878/ADP1879 are used for dc-to-dc, step down, high
current applications that have an on-board controller, an on-board
LDO, and on-board MOSFET drivers. Because applications may
require up to 20 A of load current and be subjected to high ambient
temperature, the selection of external high- and low-side MOSFETs
must be associated with careful thermal consideration to not
exceed the maximum allowable junction temperature of 125°C.
To avoid permanent or irreparable damage, if the junction temperature reaches or exceeds 155°C, the part enters thermal shutdown,
turning off both external MOSFETs, and is not reenabled until
the junction temperature cools to 140°C (see the On-Board Low
Dropout (LDO) Regulator section).
In addition, it is important to consider the thermal impedance
of the package. Because the ADP1878/ADP1879 employ an
on-board LDO, the ac current (fxCxV) consumed by the internal
drivers to drive the external MOSFETs, adds another element of
Rev. A | Page 27 of 40
ADP1878/ADP1879
Data Sheet
power dissipation across the internal LDO. Equation 3 shows the
power dissipation calculations for the integrated drivers and for
the internal LDO. Table 9 lists the thermal impedance for the
ADP1878/ADP1879, which are available in a 14-lead LFCSP_WD.
The rise in package temperature is directly proportional to its
thermal impedance characteristics. The following equation
represents this proportionality relationship:
Table 9. Thermal Impedance for 14-Lead LFCSP_WD
where:
θJA is the thermal resistance of the package from the junction to
the outside surface of the die, where it meets the surrounding air.
PDR(LOSS) is the overall power dissipated by the IC.
Package
14-Lead LFCSP_WD θJA
4-Layer Board
Thermal Impedance
30°C/W
Figure 85 specifies the maximum allowable ambient temperature
that can surround the ADP1878/ADP1879 IC for a specified
high input voltage (VIN). Figure 85 illustrates the temperature
derating conditions for each available switching frequency for
low, typical, and high output setpoints for the 14-lead LFCSP_WD
package. All temperature derating criteria are based on a
maximum IC junction temperature of 125°C.
120
110
The bulk of the power dissipated is due to the gate capacitance of
the external MOSFETs and current running through the on-board
LDO. The power loss equations for the MOSFET drivers and
internal low dropout regulator (see the MOSFET Driver Loss
section and the Efficiency Consideration section) are:
PDR(LOSS) = [VDR × (fSWCupperFETVDR + IBIAS)] +
[VREG × (fSWClowerFET VREG + IBIAS)]
PDISS(LDO) = PDR(LOSS) + (VIN – VREG) × (fSW × CTOTAL ×
VREG + IBIAS
100
300kHz
600kHz
1MHz
90
5.5
(2)
(3)
where:
CupperFET is the input gate capacitance of the high-side MOSFET.
ClowerFET is the input gate capacitance of the low-side MOSFET.
IBIAS is the dc current (2 mA) flowing into the high- and lowside drivers.
VDR is the driver bias voltage (the low input voltage (VREG) minus
the rectifier drop (see Figure 83)).
VREG is the LDO output/bias voltage.
7.0
8.5
VOUT = 0.8V
VOUT = 1.8V
VOUT = HIGH SETPOINT
10.0
11.5
13.0
14.5
16.0
17.5
19.0
VIN (V)
Figure 85. Ambient Temperature vs. VIN,
4-Layer Evaluation Board, CIN = 4.3 nF (High-/Low-Side MOSFET)
The maximum junction temperature allowed for the ADP1878/
ADP1879 IC is 125°C. This means that the sum of the ambient
temperature (TA) and the rise in package temperature (TR), which is
caused by the thermal impedance of the package and the internal
power dissipation, should not exceed 125°C, as dictated by the
following expression:
TJ = TR × TA
(4)
where PDISS(LDO) is the power dissipated through the pass device
in the LDO block across VIN and VREG.
09441-085
MAXIMUM ALLOWABLE AMBIENT
TEMPERATURE (°C)
130
TR = θJA × PDR(LOSS)
PDR(LOSS) is the MOSFET driver loss.
VIN is the high voltage input.
VREG is the LDO output voltage and bias voltage.
CTOTAL is the CGD + CGS of the external MOSFET.
IBIAS is the dc input bias current.
For example, if the external MOSFET characteristics are θJA
(14-lead LFCSP_WD) = 30°C/W, fSW = 300 kHz, IBIAS = 2 mA,
CupperFET = 3.3 nF, ClowerFET = 3.3 nF, VDR = 4.62 V, and VREG = 5.0 V,
then the power loss is
(1)
where:
TJ is the maximum junction temperature.
TR is the rise in package temperature due to the power
dissipated from within.
TA is the ambient temperature.
PDR(LOSS) = [VDR × (fSWCupperFETVDR + IBIAS)] +
[VREG × (fSWClowerFETVREG + IBIAS)]
= (4.62 × (300 × 103 × 3.3 × 10−9 × 4.62 + 0.002)) +
(5.0 × (300 × 103 × 3.3 × 10−9 × 5.0 + 0.002))
= 57.12 mW
PDISS(LDO) = (VIN – VREG) × (fSW × CTOTAL × VREG + IBIAS) =
(13 V – 5 V) × (300 × 103 × 3.3 × 10−9 × 5 + 0.002)
= 55.6 mW
PDISS(TOTAL) = PDISS(LDO) + PDR(LOSS)
= 77.13 mW + 55.6 mW
= 132.73 mW
Rev. A | Page 28 of 40
Data Sheet
ADP1878/ADP1879
The rise in package temperature (for a 14-lead LFCSP_WD) is
Current-Limit Programming
The valley current is approximately
TR = θJA × PDR(LOSS)
15 A − (5 A × 0.5) = 12.5 A
= 30°C × 132.05 mW
= 4.0°C
Assuming a maximum ambient temperature environment of 85°C,
TJ = TR × TA = 4.0°C + 85°C = 89.0°C,
which is below the maximum junction temperature of 125°C.
DESIGN EXAMPLE
The ADP1878/ADP1879 are easy to use, requiring only a few
design criteria. For example, the example outlined in this section
uses only four design criteria: VOUT = 1.8 V, ILOAD = 15 A (pulsing),
VIN = 12 V (typical), and fSW = 300 kHz.
Input Capacitor
The maximum input voltage ripple is usually 1% of the
minimum input voltage (11.8 V × 0.01 = 120 mV).
Assuming a low-side MOSFET RON of 4.5 mΩ and 13 A, as the
valley current limit from Table 7 and Figure 71 indicate, a programming resistor (RES) of 100 kΩ corresponds to an ACS
of 24 V/V.
Choose a programmable resistor of RRES = 100 kΩ for a current
sense gain of 24 V/V.
Output Capacitor
Assume that a load step of 15 A occurs at the output and no more
than 5% output deviation is allowed from the steady state operating
point. In this case, the advantage of the ADP1878 is that because
the frequency is pseudo fixed, the converter is able to respond
quickly because of the immediate, though temporary, increase
in switching frequency.
ΔVDROOP = 0.05 × 1.8 V = 90 mV
VRIPP = 120 mV
Assuming the overall ESR of the output capacitor ranges from
5 mΩ to 10 mΩ,
VMAX,RIPPLE = VRIPP − (ILOAD,MAX × ESR)
= 120 mV − (15 A × 0.001) = 45 mV
,
,
4
,
4
300
15 A
10
∆
2
105 mV
2
= 120 μF
Choose five 22 μF ceramic capacitors. The overall ESR of five
22 μF ceramic capacitors is less than 1 mΩ.
IRMS = ILOAD/2 = 7.5 A
PCIN = (IRMS)2 × ESR = (7.5 A)2 × 1 mΩ = 56.25 mW
Inductor
300
∆
15 A
10
90 mV
= 1.11 mF
Therefore, an appropriate inductor selection is five 270 μF
polymer capacitors with a combined ESR of 3.5 mΩ.
Assuming an overshoot of 45 mV, determine if the output
capacitor that was calculated previously is adequate
Determining inductor ripple current amplitude:
∆
∆
5A
3
1
1.8
Then, calculating for the inductor value
10
15 A
45 mV
1.8
= 1.4 mF
,
∆
13.2 V – 1.8 V
5 V 300 10
,
1.8 V
13.2 V
Choose five 270 μF polymer capacitors.
The rms current through the output capacitor is
1
2
= 1.03 μH
The inductor peak current is approximately
1
2
15 A + (5 A × 0.5) = 17.5 A
Therefore, an appropriate inductor selection is 1.0 μH with
DCR = 3.3 mΩ (Würth Elektronik 7443552100) with a peak
current handling of 20 A.
1
,
√3
1 13.2 V – 1.8 V
√3 1 μF 300 103
,
1.8 V
1.49 A
13.2 V
The power loss dissipated through the ESR of the output
capacitor is
PCOUT = (IRMS)2 × ESR = (1.5 A)2 × 1.4 mΩ = 3.15 mW
= 0.003 × (15 A)2 = 675 mW
Rev. A | Page 29 of 40
ADP1878/ADP1879
Data Sheet
Feedback Resistor Network Setup
Loss Calculations
Choosing RB = 1 kΩ as an example. Calculate RT as follows:
Duty cycle = 1.8/12 V = 0.15
1 kΩ
1.8 V 0.6 V
0.6 V
RON(N2) = 5.4 mΩ
2 kΩ
tBODY(LOSS) = 20 ns (body conduction time)
Compensation Network
To calculate RCOMP, CCOMP, and CPAR, the transconductance
parameter and the current sense gain variable are required. The
transconductance parameter (Gm) is 500 μA/V, and the current
sense loop gain is
1
1
24 0.005
VF = 0.84 V (MOSFET forward voltage)
CIN = 3.3 nF (MOSFET gate input capacitance)
QN1,N2 = 17 nC (total MOSFET gate charge)
RGATE = 1.5 Ω (MOSFET gate input resistance)
8.33 A/V
1,
where ACS and RON are taken from setting up the current limit
(see the Programming Resistor (RES) Detect Circuit section
and the Valley Current-Limit Setting section).
The crossover frequency is 1/12th of the switching frequency:
300 kHz/12 = 25 kHz
The zero frequency is 1/4th of the crossover frequency:
1
1
1.8
0.6
2π
25 kΩ
1
2π
500
1
10
= 57.12 mW
6.25 kΩ
1.8/15
25 kΩ
8.3
0.0035
0.0035
PDISS(LDO) = (VIN – VREG) × (fSW × CTOTAL × VREG + IBIAS)
= (13 V – 5 V) × (300 × 103 × 3.3 × 10−9 × 5 + 0.002)
= 55.6 mW
0.0011
0.0011
15
1.8
PCOUT = (IRMS)2 × ESR = (1.5 A)2 × 1.4 mΩ = 3.15 mW
2
= 0.003 × (15 A)2 = 675 mW
PDCR( LOSS)  DCR  I LOAD
1
PCIN = (IRMS)2 × ESR = (7.5 A)2 × 1 mΩ = 56.25 mW
2
PLOSS = PN1,N2 + PBODY(LOSS) + PSW + PDCR + PDR + PDISS(LDO) + PCOUT
+ PCIN = 1.215 W + 151.2 mW + 534.6 mW + 57.12 mW +
55.6 + 3.15 mW + 675 mW + 56.25 mW = 2.655 W
1
3.14
60.25
= 20 ns × 300 × 103 × 15 A × 0.84 × 2
= 151.2 mW
(5.0 × (300 × 103 × 3.3 × 10−9 × 5.0 + 0.002))
= 60.25 kΩ
2
2
=(4.62 × (300 ×103 × 3.3 × 10−9 × 4.62 + 0.002)) +
25 kΩ
1
= (0.15 × 0.0054 + 0.85 × 0.0054) × (15 A)2
= 1.215 W
PDR(LOSS) = [VDR × (fSWCupperFETVDR + IBIAS)] + [VREG ×
(fSWClowerFETVREG +IBIAS)]
1
√25 kΩ
1
PSW(LOSS) = fSW × RGATE × CTOTAL × ILOAD × VIN × 2
= 300 × 103 × 1.5 Ω × 3.3 × 10−9 × 15 A × 12 × 2
= 534.6 mW
25 kHz/4 = 6.25 kHz
1
1
10
6.25
10
= 423 pF
Rev. A | Page 30 of 40
Data Sheet
ADP1878/ADP1879
EXTERNAL COMPONENT RECOMMENDATIONS
The configurations listed in Table 10 are with fCROSS = 1/12 × fSW, fZERO = ¼ × fCROSS, RRES = 100 kΩ, RBOT = 1kΩ, RON = 5.4 mΩ (BSC042N03MS G),
VREG = 5 V (float), and a maximum load current of 14 A. The ADP1879 models listed in Table 10 are the PSM versions of the device.
Table 10. External Component Values
Model
ADP1878ACPZ-0.3-R7/
ADP1879ACPZ-0.3-R7
ADP1878ACPZ-0.6-R7/
ADP1879ACPZ-0.6-R7
ADP1878ACPZ-1.0-R7/
ADP1879ACPZ-1.0-R7
VOUT
(V)
0.8
1.2
1.8
2.5
3.3
5
7
1.2
1.8
2.5
3.3
5
7
0.8
1.2
1.8
2.5
1.2
1.8
2.5
3.3
5
1.2
1.8
2.5
3.3
5
7
0.8
1.2
1.8
2.5
1.2
1.8
2.5
3.3
5
1.2
1.8
2.5
3.3
5
7
VIN
(V)
13
13
13
13
13
13
13
16.5
16.5
16.5
16.5
16.5
16.5
5.5
5.5
5.5
5.5
13
13
13
13
13
16.5
16.5
16.5
16.5
16.5
16.5
5.5
5.5
5.5
5.5
13
13
13
13
13
16.5
16.5
16.5
16.5
16.5
16.5
CIN
(μF)
5 × 222
5 × 222
4 × 222
4 × 222
5 × 222
4 × 222
4 × 222
4 × 222
3 × 222
3 × 222
3 × 222
3 × 222
3 × 222
5 × 222
5 × 222
5 × 222
5 × 222
3 × 222
5 × 109
5 × 109
5 × 109
5 × 109
3 × 109
4 × 109
4 × 109
4 × 109
4 × 109
4 × 109
5 × 222
5 × 222
3 × 222
3 × 222
3 × 109
4 × 109
4 × 109
5 × 109
4 × 109
3 × 109
3 × 109
4 × 109
4 × 109
3 × 109
3 × 109
COUT (μF)
5 × 5603
4 × 5603
4 × 2704
3 × 2704
2 × 3305
3305
222 + ( 4 × 476)
4 × 5603
4 × 2704
4 × 2704
2 × 3305
2 × 1507
222 + 4 × 476
4 × 5603
4 × 2704
3 × 2704
3 × 1808
5 × 2704
3 × 3305
3 × 2704
2 × 2704
1507
4 × 2704
2 × 3305
3 × 2704
3305
4 × 476
3 × 476
4 × 2704
2 × 3305
3 × 1808
2704
3 × 3305
3 × 2704
2704
2704
3 × 476
4 × 2704
3 × 2704
3 × 1808
2704
3 × 476
222 + 476
1
See the Inductor Selection section and Table 11.
22 μF Murata 25 V, X7R, 1210 GRM32ER71E226KE15L (3.2 mm × 2.5 mm × 2.5 mm).
3
560 μF Panasonic (SP-series) 2 V, 7 mΩ, 3.7 A EEFUE0D561LR (4.3 mm × 7.3 mm × 4.2 mm).
4
270 μF Panasonic (SP-series) 4 V, 7 mΩ, 3.7 A EEFUE0G271LR (4.3 mm × 7.3 mm × 4.2 mm).
5
330 μF Panasonic (SP-series) 4 V, 12 mΩ, 3.3 A EEFUE0G331R (4.3 mm × 7.3 mm × 4.2 mm).
6
47 μF Murata 16 V, X5R, 1210 GRM32ER61C476KE15L (3.2 mm × 2.5 mm × 2.5 mm).
7
150 μF Panasonic (SP-series) 6.3 V, 10 mΩ, 3.5 A EEFUE0J151XR (4.3 mm × 7.3 mm × 4.2 mm).
8
180 μF Panasonic (SP-series) 4 V, 10 mΩ, 3.5 A EEFUE0G181XR (4.3 mm × 7.3 mm × 4.2 mm).
9
10 μF TDK 25 V, X7R, 1210 C3225X7R1E106M.
2
Rev. A | Page 31 of 40
L1
(μH)
0.72
1.0
1.2
1.53
2.0
3.27
3.44
1.0
1.0
1.67
2.00
3.84
4.44
0.22
0.47
0.47
0.47
0.47
0.47
0.90
1.00
1.76
0.47
0.72
0.90
1.0
2.0
2.0
0.22
0.22
0.22
0.22
0.22
0.47
0.47
0.72
1.0
0.47
0.47
0.72
0.72
1.2
1.2
RC
(kΩ)
56.9
56.9
56.9
57.6
56.9
40.7
40.7
56.9
56.9
57.6
56.9
41.2
40.7
56.2
56.9
56.9
56.9
56.9
56.2
57.6
57.6
40.7
56.9
53.6
57.6
53.0
41.2
40.7
54.9
49.3
56.9
54.9
53.6
56.9
54.9
56.2
40.7
56.9
56.9
56.9
56.2
40.7
40.7
CCOMP
(pF)
620
620
470
470
470
680
680
620
470
470
510
680
680
300
270
220
220
360
270
240
240
360
300
270
270
270
360
300
200
220
130
130
200
180
180
180
220
270
220
200
180
220
180
CPAR
(pF)
62
62
47
47
47
68
68
62
47
47
51
68
68
300
27
22
22
36
27
24
24
36
30
27
27
27
36
30
20
22
13
13
20
18
18
18
22
27
22
20
18
22
18
RTOP
(kΩ)
0.3
1.0
2.0
3.2
4.5
7.3
10.7
1.0
2.0
3.2
4.5
7.3
10.7
0.3
1.0
2.0
3.2
1.0
2.0
3.2
4.5
7.3
1.0
2.0
3.2
4.5
7.3
10.7
0.3
1.0
2.0
3.2
1.0
2.0
3.2
4.5
7.3
1.0
2.0
3.2
4.5
7.3
10.7
ADP1878/ADP1879
Data Sheet
Table 11. Recommended Inductors
L (μH)
0.12
0.22
0.47
0.72
0.9
1.2
1.0
1.4
2.0
0.8
DCR (mΩ)
0.33
0.33
0.8
1.65
1.6
1.8
3.8
3.2
2.6
ISAT (A)
55
30
50
35
32
25
16
24
23
27.5
Dimension (mm)
10.2 × 7
10.2 × 7
14.2 × 12.8
10.5 × 10.2
14 × 12.8
10.5 × 10.2
10.2 × 10.2
14 × 12.8
10.2 × 10.2
Manufacturer
Würth Elektronik
Würth Elektronik
Würth Elektronik
Würth Elektronik
Würth Elektronik
Würth Elektronik
Würth Elektronik
Würth Elektronik
Würth Elektronik
Sumida
Model Number
744303012
744303022
744355147
744325072
744318120
744325120
7443552100
744318180
7443551200
CEP125U-0R8
Table 12. Recommended MOSFETs
VGS = 4.5 V
High-Side MOSFET
(Q1/Q2)
Low-Side MOSFET
(Q3/Q4)
RON (mΩ)
5.4
10.2
6.0
9
5.4
10.2
6.0
ID (A)
47
53
19
14
47
82
19
VDS (V)
30
30
30
30
30
30
30
CIN (nF)
3.2
1.6
2.4
3.2
1.6
QTOTAL (nC)
20
10
35
25
20
10
35
Rev. A | Page 32 of 40
Package
PG-TDSON8
PG-TDSON8
SO-8
SO-8
PG-TDSON8
PG-TDSON8
SO-8
Manufacturer
Infineon
Infineon
Vishay
International Rectifier
Infineon
Infineon
Vishay
Model Number
BSC042N03MS G
BSC080N03MS G
Si4842DY
IRF7811
BSC042N03MS G
BSC080N03MS G
Si4842DY
Data Sheet
ADP1878/ADP1879
LAYOUT CONSIDERATIONS
Figure 86 shows the schematic of a typical ADP1878/ADP1879
used for a high current application. Blue traces denote high current
pathways. VIN, PGND, and VOUT traces should be wide and
possibly replicated, descending down into the multiple layers.
Vias should populate, mainly around the positive and negative
terminals of the input and output capacitors, alongside the source
of Q1/Q2, the drain of Q3/Q4, and the inductor.
The performance of a dc-to-dc converter depends highly on
how the voltage and current paths are configured on the printed
circuit board (PCB). Optimizing the placement of sensitive
analog and power components are essential to minimize output
ripple, maintain tight regulation specifications, and reduce
PWM jitter and electromagnetic interference.
HIGH VOLTAGE INPUT
VIN = 12V
JP3
CC
430pF
RC
57kΩ
VREG
VOUT
R7 10kΩ
RTOP 2kΩ
RBOT
1kΩ
RRES
100kΩ
C2
0.1µF
ADP1878/
ADP1879
1
VIN
BST 14
2
COMP
3
EN
DRVH 12
4
FB
PGND 11
5
GND
DRVL 10
6
RES
PGOOD 9
7
VREG
CBST
100nF
Q1
SS 8
C5
22µF
C6
22µF
1.0µH
Q3
5kΩ
Q4
RSNB
2Ω
CSNB
1.5nF
C8
N/A
C9
N/A
VOUT = 1.8V, 15A
C20
270µF
C24
N/A
VREG
CSS
34nF
C7
22µF
Q2
SW 13
C1
1µF
C4
22µF
+
+
C21
270µF
C25
N/A
+
+
C22
270µF
C26
N/A
+
+
C23
270µF
C27
N/A
+
+ C14 TO C19
N/A
MURATA: (HIGH VOLTAGE INPUT CAPACITORS)
22µF, 25V, X7R, 1210 GRM32ER71E226KE15L
PANASONIC: (OUTPUT CAPACITORS)
270µF, SP-SERIES, 4V, 7mΩ, EEFUE0G271LR
INFINEON FETs:
BSC042N03MS G (LOWER SIDE)
BSC080N03MS G (UPPER SIDE)
WÜRTH INDUCTORS:
1µH, 3.8mΩ, 16A, 7443552100
Figure 86. ADP1878 High Current Evaluation Board Schematic (Blue Traces Indicate High Current Paths)
SENSITIVE ANALOG
COMPONENTS
LOCATED FAR
FROM NOISY
POWER SECTION
SEPARATE ANALOG
GROUND PLANE FOR
COMPENSATION AND
FEEDBACK RESISTORS
OUTPUT
CAPACITORS
ARE MOUNTED
AT RIGHTMOST
AREA OF
EVALUATION
BOARD
INPUT CAPACITORS
ARE MOUNTED CLOSE
TO DRAIN OF Q1/Q2
AND SOURCE OF Q3/Q4
09441-087
CPAR
53pF
C3
22µF
Figure 87. Overall Layout of the ADP1878/ADP1879 High Current Evaluation Board
Rev. A | Page 33 of 40
09441-086
CVIN
22µF
Data Sheet
09441-088
ADP1878/ADP1879
Figure 88. Layer 2 of Evaluation Board
TOP RESISTOR
FEEDBACK TAP
09441-089
VOUT SENSE TAP LINE
EXTENDING BACK TO THE
TOP RESISTOR IN THE
FEEDBACK DIVIDER
NETWORK. THIS OVERLAPS
WITH PGND SENSE TAP
LINE EXTENDING TO THE
ANALOG GROUND PLANE
Figure 89. Layer 3 of Evaluation Board
Rev. A | Page 34 of 40
Data Sheet
ADP1878/ADP1879
BOTTOM
RESISTOR TAP
TO ANALOG
GROUND PLANE
09441-090
PGND SENSE TAP FROM
NEGATIVE TERMINALS OF
THE OUTPUT BULK
CAPACITORS. THIS
TRACK PLACEMENT
SHOULD BE DIRECTLY
BELOW THE VOUT SENSE
LINE OF LAYER 3.
Figure 90. Layer 4 (Bottom Layer) of Evaluation Board
IC SECTION (LEFT SIDE OF EVALUATION BOARD)
A dedicated plane for the analog ground plane (GND) should
be separate from the main power ground plane (PGND). With
the shortest path possible, connect the analog ground plane to
the GND pin (Pin 5). Place this plane on the top layer only of
the evaluation board. To avoid crosstalk interference, do not
allow any other voltage or current pathway directly below this
plane on Layer 2, Layer 3, or Layer 4. Connect the negative
terminals of all sensitive analog components to the analog
ground plane. Examples of such sensitive analog components
include the bottom resistor of the resistor divider, the high
frequency bypass capacitor for biasing (0.1 μF), and the
compensation network.
Mount a 1 μF bypass capacitor directly across the VREG pin
(Pin 7) and the PGND pin (Pin 11). In addition, tie a 0.1 μF
across the VREG pin (Pin 7) and the GND pin (Pin 5).
POWER SECTION
As shown in Figure 87, an appropriate configuration to localize
large current transfer from the high voltage input (VIN) to the
output (VOUT) and then back to the power ground is to put the
VIN plane on the left, the output plane on the right, and the main
power ground plane in between the two. Current transfers from
the input capacitors to the output capacitors, through Q1/Q2,
during the on state (see Figure 91). The direction of this current
(yellow arrow) is maintained as Q1/Q2 turns off and Q3/Q4 turns
on. When Q3/Q4 turns on, the current direction continues to be
maintained (red arrow) as it circles from the power ground
terminal of the bulk capacitor to the output capacitors, through
the Q3/Q4. Arranging the power planes in this manner minimizes
the area in which changes in flux occur if the current through
Q1/Q2 stops abruptly. Sudden changes in flux, usually at the
source terminals of Q1/Q2 and the drain terminal of Q3/Q4,
cause large dV/dt at the SW node.
The SW node is near the top of the evaluation board. The SW
node should use the least amount of area possible and be away
from any sensitive analog circuitry and components. This is
because the SW node is where most sudden changes in flux
density occur. When possible, replicate this pad onto Layer 2
and Layer 3 for thermal relief and eliminate any other voltage and
current pathways directly beneath the SW node plane. Populate
the SW node plane with vias, mainly around the exposed pad of
the inductor terminal and around the perimeter of the source of
Q1/Q2 and the drain of Q3/Q4.
The output voltage power plane (VOUT) is at the rightmost end of
the evaluation board. This plane should be replicated, descending
down to multiple layers with vias surrounding the inductor
terminal and the positive terminals of the output bulk capacitors.
Ensure that the negative terminals of the output capacitors are
placed close to the main power ground (PGND), as previously
mentioned. All of these points form a tight circle (component
geometry permitting) that minimizes the area of flux change as
the event switches between D and 1 − D.
Rev. A | Page 35 of 40
ADP1878/ADP1879
Data Sheet
SW
Figure 91. Primary Current Pathways During the On State of the High-Side
MOSFET (Left Arrow) and the On State of the Low-Side MOSFET (Right Arrow)
DIFFERENTIAL SENSING
Because the ADP1878/ADP1879 operate in valley current-mode
control, a differential voltage reading is taken across the drain
and source of the low-side MOSFET. Connect the drain of the
low-side MOSFET s as close as possible to the SW pin (Pin 13) of
the IC. Likewise, connect the source as close as possible to the
PGND pin (Pin 11) of the IC. When possible, keep both of
these track lines narrow and away from any other active device
or voltage/current path.
LAYER 1: SENSE LINE FOR SW
(DRAIN OF LOWER MOSFET)
LAYER 1: SENSE LINE FOR PGND
(SOURCE OF LOWER MOSFET)
09441-092
09441-091
PGND
Figure 92. Drain/Source Tracking Tapping of the Low-Side MOSFET for CS
Amp Differential Sensing (Yellow Sense Line on Layer 2)
In addition, employ differential sensing between the outermost
output capacitor and the feedback resistor divider (see Figure 89
and Figure 90). Connect the positive terminal of the output
capacitor to the top resistor (RT). Connect the negative terminal
of the output capacitor to the negative terminal of the bottom
resistor, which connects to the analog ground plane as well.
Keep both of these track lines, as previously mentioned, narrow
and away from any other active device or voltage/ current path.
Rev. A | Page 36 of 40
Data Sheet
ADP1878/ADP1879
TYPICAL APPLICATION CIRCUITS
12 A, 300 kHz HIGH CURRENT APPLICATION CIRCUIT
HIGH VOLTAGE INPUT
VIN = 12V
JP3
CVIN
22µF
CPAR
56pF
R7 10kΩ
VREG
RTOP 2kΩ
VOUT
RBOT
1kΩ
RRES
100kΩ
C2
0.1µF
ADP1878/
ADP1879
1
VIN
2
COMP
3
EN
DRVH 12
4
FB
PGND
5
GND
DRVL 10
6
RES
7
VREG
BST 14
CBST
100nF
Q1
C4
22µF
1.2µH
Q3
11
SS 8
C1
1µF
C6
22µF
5kΩ
C7
22µF
C8
N/A
C9
N/A
Q2
SW 13
PGOOD 9
C5
22µF
Q4
VOUT = 1.8V, 12A
RSNB
2Ω
CSNB
1.5nF
C20
270µF
C24
N/A
+
+
C21
270µF
C25
N/A
+
+
C22
270µF
C26
N/A
+
+
C23
270µF
C27
N/A
+
+ C14 TO C19
N/A
VREG
MURATA: (HIGH VOLTAGE INPUT CAPACITORS)
22µF, 25V, X7R, 1210 GRM32ER71E226KE15L
PANASONIC: (OUTPUT CAPACITORS)
270µF (SP-SERIES), 4V, 7mΩ, EEFUE0G271LR
INFINEON MOSFETs:
BSC042N03MS G (LOWER SIDE)
BSC080N03MS G (UPPER SIDE)
WÜRTH INDUCTORS:
1.2µH, 2mΩ, 20A, 744325120
CSS
34nF
09441-093
CC
560pF
RC
49.3kΩ
C3
22µF
Figure 93. Application Circuit for 12 V Input, 1.8 V Output, 12 A, 300 kHz (Q2/Q4 No Connect)
5.5 V INPUT, 600 kHz CURRENT APPLICATION CIRCUIT
HIGH VOLTAGE INPUT
VIN = 5.5V
JP3
CVIN
22µF
CF
22pF
VREG
VOUT
R7 10kΩ
RTOP 32kΩ
RBOT
1kΩ
RRES
100kΩ
C2
0.1µF
C1
1µF
ADP1878/
ADP1879
1
VIN
2
COMP
3
EN
DRVH 12
4
FB
PGND 11
5
GND
DRVL 10
6
RES
7
VREG
BST 14
CBST
100nF
Q1
SS 8
C5
22µF
C6
22µF
0.47µH
Q3
5kΩ
C7
22µF
C8
N/A
C9
N/A
Q2
SW 13
PGOOD 9
C4
22µF
Q4
RSNB
2Ω
CSNB
1.5nF
VOUT = 2.5V, 12A
C20
180µF
C24
N/A
+
+
C21
180µF
C25
N/A
+
+
C22
180µF
C26
N/A
+
+
C27
N/A
C23
N/A
+
+ C14 TO C19
N/A
VREG
CSS
34nF
MURATA: (INPUT CAPACITORS)
22µF, 25V, X7R, 1210 GRM32ER71E226KE15L
PANASONIC: (OUTPUT CAPACITORS)
180µF (SP-SERIES), 4V, 10mΩ, EEFUE0G181XR
INFINEON MOSFETs:
BSC042N03MS G (LOWER SIDE)
BSC080N03MS G (UPPER SIDE)
WÜRTH INDUCTORS:
0.47µH, 0.8mΩ, 30A, 744355147
Figure 94. Application Circuit for 5.5 V Input, 2.5 V Output, 12 A, 600 kHz (Q2/Q4 No Connect)
Rev. A | Page 37 of 40
09441-094
CC
220pF
RC
56.9kΩ
C3
22µF
ADP1878/ADP1879
Data Sheet
300 kHz HIGH CURRENT APPLICATION CIRCUIT
HIGH VOLTAGE INPUT
VIN = 13V
JP3
CVIN
22µF
CPAR
56pF
VREG
VOUT
R7 10kΩ
RTOP 2kΩ
RBOT
1kΩ
RRES
100kΩ
C2
0.1µF
C1
1µF
ADP1878/
ADP1879
1
VIN
BST 14
2
COMP
3
EN
DRVH 12
4
FB
PGND 11
5
GND
DRVL 10
6
RES
PGOOD 9
7
VREG
CBST
100nF
Q1
C5
22µF
C6
22µF
1.2µH
Q3
5kΩ
C7
22µF
C8
N/A
C9
N/A
Q2
SW 13
SS 8
C4
22µF
Q4
RSNB
2Ω
CSNB
1.5nF
VOUT = 1.8V, 12A
C20
270µF
C24
N/A
+
+
C21
270µF
C25
N/A
+
+
C22
270µF
C26
N/A
+
+
C23
270µF
C27
N/A
+
+ C14 TO C19
N/A
VREG
CSS
34nF
MURATA: (HIGH VOLTAGE INPUT CAPACITORS)
22µF, 25V, X7R, 1210 GRM32ER71E226KE15L
PANASONIC: (OUTPUT CAPACITORS)
270µF (SP-SERIES), 4V, 7mΩ, EEFUE0G271LR
INFINEON MOSFETs:
BSC042N03MS G (LOWER SIDE)
BSC080N03MS G (UPPER SIDE)
WÜRTH INDUCTORS:
1.2µH, 2mΩ, 20A, 744325120
Figure 95. Application Circuit for 13 V Input, 1.8 V Output, 12 A, 300 kHz (Q2/Q4 No Connect)
Rev. A | Page 38 of 40
09441-095
CC
560pF
RC
49.3kΩ
C3
22µF
Data Sheet
ADP1878/ADP1879
PACKAGING AND ORDERING INFORMATION
OUTLINE DIMENSIONS
4.10
4.00
3.90
3.40
3.30
3.15
0.10
REF
0.20 MIN
8
0.30
REF
TOP VIEW
0.80
0.75
0.70
SEATING
PLANE
SIDE VIEW
0.30
0.25
0.20
0.50 BSC
END VIEW
1.80
1.70
1.55
EXPOSED
PAD
7
0.50
0.40
0.30
0.05 MAX
0.02 NOM
COPLANARITY
0.08
0.15 REF
1
BOTTOM VIEW
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
COMPLIANT TO JEDEC STANDARDS MO-229-WEGD
Figure 96. 14-Lead Lead Frame Chip Scale Package [LFCSP_WD]
4 mm × 3 mm Body, Very Very Thin Dual
(CP-14-2)
Dimensions shown in millimeters
Rev. A | Page 39 of 40
101309-A
0.90
REF
3.10
3.00
2.90
PIN 1 INDICATOR
(LASER MARKING)
14
ADP1878/ADP1879
Data Sheet
ORDERING GUIDE
Model1
ADP1878ACPZ-0.3-R7
ADP1878ACPZ-0.6-R7
ADP1878ACPZ-1.0-R7
ADP1878-0.3-EVALZ
ADP1878-0.6-EVALZ
ADP1878-1.0-EVALZ
ADP1879ACPZ-0.3-R7
ADP1879ACPZ-0.6-R7
ADP1879ACPZ-1.0-R7
ADP1879-0.3-EVALZ
ADP1879-0.6-EVALZ
ADP1879-1.0-EVALZ
1
Temperature Range
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
−40°C to +125°C
Package Description
14-Lead Frame Chip Scale Package [LFCSP_WD]
14-Lead Frame Chip Scale Package [LFCSP_WD]
14-Lead Frame Chip Scale Package [LFCSP_WD]
Evaluation Board
Evaluation Board
Evaluation Board
14-Lead Frame Chip Scale Package [LFCSP_WD]
14-Lead Frame Chip Scale Package [LFCSP_WD]
14-Lead Frame Chip Scale Package [LFCSP_WD]
Evaluation Board
Evaluation Board
Evaluation Board
Package Option
CP-14-2
CP-14-2
CP-14-2
CP-14-2
CP-14-2
CP-14-2
Z = RoHS Compliant Part.
©2011–2012 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D09441-0-6/12(A)
www.analog.com/ADP1878/ADP1879
Rev. A | Page 40 of 40