MIC28514T-E/PHA [MICROCHIP]
75V HIGH PERFORMANCE BUCK REGULA;
| 型号： | MIC28514T-E/PHA |
| 厂家： | 
MICROCHIP |
| 描述： | 75V HIGH PERFORMANCE BUCK REGULA 开关 |
| 文件： | 总38页 (文件大小：950K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
MIC28514
75V/5A Hyper Speed Control®
Synchronous DC/DC Buck Regulator with External Soft Start
Features
Applications
• Distributed Power Systems
• Communications/Networking Infrastructure
• Industrial Power Supplies
• Solar Energy
• Hyper Speed Control® Architecture Enables:
- High Input to Output Voltage Conversion
Ratio Capability (VIN = 75V and VOUT = 0.6V)
- Small Output Capacitance
• 4.5V to 75V Input Voltage
General Description
• 5A Output Current Capability with up to 95% Efficiency
• Adjustable Output Voltage from 0.6V to 32V
• ±1% FB Accuracy
The MIC28514 is an adjustable frequency,
synchronous buck regulator that features a unique
adaptive on-time control architecture. The MIC28514
operates over an input supply range of 4.5V to 75V, and
provides a regulated output of up to 5A of output
current. The output voltage is adjustable down to 0.6V
with an accuracy of ±1%.
• Any Capacitor™ Stable:
- Zero-ESR to High-ESR Output Capacitors
• 270 kHz to 800 kHz Adjustable Switching Frequency
• Internal Compensation
• Built-in 5V Regulator for Single-Supply Operation
• Auxiliary Bootstrap LDO for Improving System
Efficiency
• Internal Bootstrap Diode
• Adjustable Soft Start Time
Hyper Speed Control architecture allows for an ultra-fast
transient response, while reducing the output capaci-
tance, and also makes high-VIN/low-VOUT operation
possible. This adaptive on-time control architecture
combines the advantages of fixed frequency operation
and fast transient response in a single device.
• Programmable Current Limit
The MIC28514 offers a full suite of features that ensure
the protection of the Integrated Circuit (IC) during Fault
conditions. These features include Undervoltage Lock-
out (UVLO) to ensure proper operation under power sag
conditions, soft start to reduce inrush current, “Hiccup”
mode short-circuit protection and thermal shutdown.
• “Hiccup” Mode Short-Circuit Protection
• Thermal Shutdown
• Supports Safe Start-up into a Prebiased Output
• -40°C to +125°C Junction Temperature Range
• Available in 32-Pin, 6 mm x 6 mm VQFN Package
Typical Application Circuit
MIC28514
2.2
1 μF
PV
SV
DD
IN
2.2 μF
2.2 μF
2.2
V
IN
V
V
IN
DD
9V to 75V
2.2 μF x 3
PG
EN
SS
BST
SW
0.1 μF
8.2 μH
VOUT
5V/5A
1.42 k
10 nF
16.2 k
I
LIM
47 μF
10 k
4.7 nF
0.1 μF
200 k
VIN
FB
FREQ
1.37 k
100 k
EXTVDD
EXTVDD
AGND PGND
1 μF
2017 Microchip Technology Inc.
DS20005693C-page 1
MIC28514
Package Type
MIC28514
6 mm x 6 mm 32-Lead VQFN
32 31
29 28 27 26 25
PGND
30
ILIM
EN
1
24
23
22
21
EXTVDD
PGND
PVDD
PGND 2
3
SW
BST 4
20 SW
19
VIN
VIN
VIN
VIN
5
6
7
8
PGND
18 PGND
PGND
V
SW
IN
17
9 10 11 12 13 14 15 16
Functional Block Diagram
MIC28514
V
DD
SV
IN
V
R3
DD
HV LDO
LV LDO
FREQ
PV
DD
R5
FIXED TON
ESTIMATE
UVLO
R4
PV
VIN
IN
MODIFIED
TOFF
5V to 75V
BST
EXTVDD
C
IN
4.6V
HSD
C
BOOST
CONTROL
VDD
L
LOGIC
TIMER
SOFT-
START
SW
VOUT
3.3V/5A
EN
EN
SS
ICL
V
DD
135 μA
R
ILIM
CL
R1
C
FF
C
ISS
1.4 μA
OUT
R
THERMAL
SHUTDOWN
INJ
OVERCURRENT
PROTECTION
PV
DD
C
INJ
SGND
PGND
LSD
C
SS
COMPENSATION
gm EA
FB
COMP
V
DD
R2
PG
VREF
0.6V
0.9
DS20005693C-page 2
2017 Microchip Technology Inc.
MIC28514
1.0
ELECTRICAL CHARACTERISTICS
Absolute Maximum Ratings†
PVIN, SVIN, FREQ to PGND ....................................................................................................................... -0.3V to +76V
PVDD, VDD to PGND ..................................................................................................................................... -0.3V to +6V
SW, ILIM to PGND .......................................................................................................................... -0.3V to (PVIN + 0.3V)
V
V
BST to VSW .................................................................................................................................................. -0.3V to +6V
BST to PGND............................................................................................................................................. -0.3V to +82V
EN to AGND................................................................................................................................... -0.3V to (SVIN + 0.3V)
FB, PG to AGND............................................................................................................................. -0.3V to (VDD + 0.3V)
EXTVDD to AGND...................................................................................................................................... -0.3V to +12V
PGND to SGND ......................................................................................................................................... -0.3V to +0.3V
Junction Temperature ........................................................................................................................................... +150°C
Storage Temperature ..............................................................................................................................-65°C to +150°C
ESD Rating(1).............................................................................................................................................................1 kV
Operating Ratings‡
Supply Voltage (SVIN, PVIN) .......................................................................................................................... 4.5V to 75V
Bias Voltage (PVDD, VDD) ............................................................................................................................. 4.5V to 5.5V
EN, FB, PG ....................................................................................................................................................... 0V to VDD
EXTVDD ............................................................................................................................................................ 0V to12V
Junction Temperature .............................................................................................................................-40°C to +125°C
† Notice: Stresses above those listed under “Absolute Maximum Ratings” may cause permanent damage to the device.
This is a stress rating only and functional operation of the device at those or any other conditions above those
indicated in the operational sections of this specification is not intended. Exposure to maximum rating conditions for
extended periods may affect device reliability.
‡ Notice: The device is not ensured to function outside its operating ratings.
Note 1: Devices are ESD-sensitive. Handling precautions are recommended. Human body model, 1.5 kΩ in series
with 100 pF.
(1)
ELECTRICAL CHARACTERISTICS
Electrical Characteristics: PVIN = 12V, VOUT = 5V, VDD = 5V, VBST – VSW = 5V; fSW = 300 kHz, RCL = 1.42 k,
L = 8.2 µH; TA = +25°C, unless noted. Boldface values indicate -40°C ≤ TJ ≤ +125°C.
Parameters
Symbol
Min.
Typ.
Max.
Units
Conditions
Power Supply Input
Input Voltage Range
VDD Bias Voltage
PVIN, SVIN
4.5
—
75
V
Operating Bias Voltage
Undervoltage Lockout Trip Level
UVLO Hysteresis
VDD
UVLO
4.8
3.7
—
5.1
4.2
600
—
5.4
4.6
—
V
V
V
DD rising
UVLO_HYS
mV
mV
V
VDD Dropout Voltage
700
4.4
—
1250
4.8
—
VIN = 5.5V, IPVDD = 25 mA
EXTVDD Switchover Voltage
EXTVDD Switchover Hysteresis
Quiescent Supply Current
Shutdown Supply Current
4.6
0.2
1.25
0.15
35
V
IQ
—
—
mA
µA
µA
VFB = 1.5V
IQSHDN
—
2
Power from VIN, VEN = 0V
VIN = VDD = 5.5V, VEN = 0V
—
60
Note 1: Specification for packaged product only.
2: The ICL is trimmed to get the current in the limits at room temperature.
2017 Microchip Technology Inc.
DS20005693C-page 3
MIC28514
(1)
ELECTRICAL CHARACTERISTICS (CONTINUED)
Electrical Characteristics: PVIN = 12V, VOUT = 5V, VDD = 5V, VBST – VSW = 5V; fSW = 300 kHz, RCL = 1.42 k,
L = 8.2 µH; TA = +25°C, unless noted. Boldface values indicate -40°C ≤ TJ ≤ +125°C.
Parameters
Reference
Symbol
Min.
Typ.
Max.
Units
Conditions
Feedback Reference Voltage
VFB
0.597
0.594
—
0.6
0.6
0.603
0.606
—
V
TJ = +25°C
-40°C ≤ TJ ≤ +125°C
IOUT = 0A to 5A
Load Regulation
—
—
0.04
0.1
%
%
Line Regulation
—
—
PVIN = 7V to 75V
VFB = 0.6V
FB Bias Current
IFB_BIAS
—
0.05
0.5
µA
Enable Control
EN Logic Level High
EN Logic Level Low
EN Bias Current
ENHIGH
ENLOW
IENBIAS
1.6
—
—
—
6
—
0.6
30
V
V
—
µA
VEN = 0V
On Timer
Maximum Switching Frequency
Minimum Switching Frequency
Maximum Duty Cycle
FREQ
FREQ
DMAX
720
230
—
800
270
85
880
300
—
kHz
kHz
%
FREQ = PVIN, IOUT = 5A
FREQ = 33% PVIN
VFB = 0V, FREQ = PVIN
(Note 1)
Minimum Duty Cycle
Minimum Off-Time
Minimum On-Time
Soft Start
DMIN
—
0
—
300
—
%
ns
ns
VFB > 0.6V
tOFF(MIN)
tON(MIN)
100
200
60
Soft Start Current Source
Soft Start Period Range
Current Limit
ISS
—
0.8
2.5
1.4
3
µA
ms
40
Current Limit
ICLIM
ICL
5.5
—
6.25
135
0.3
7
A
RCL = 1.42 kꢀ (Note 2)
ILIM Source Current
—
—
µA
I
LIM Source Current Tempco
—
—
µA/°C
Internal FETs
Top MOSFET RDS(ON)
Bottom MOSFET RDS(ON)
SW Leakage Current
PVIN Leakage Current
BST Leakage Current
Power Good (PG)
PG Threshold
RDS(ON)
RDS(ON)
ISWLEAK
IVINLEAK
IBSTLEAK
—
—
—
—
—
25
25
—
—
—
—
—
5
mꢀ
mꢀ
µA
PVIN = 48V, VEN = 0V
PVIN = 48V, VEN = 0V
PVIN = 48V, VEN = 0V
10
10
µA
µA
VPG_TH
VPG_HYS
tPG_DLY
85
—
—
—
90
6
95
—
%
%
VFB rising
VFB falling
VFB rising
PG Threshold Hysteresis
PG Delay Time
150
70
—
µs
mV
PG Low Voltage
VPG_LOW
200
VFB < 90% × VNOM
,
IPG = 1 mA
Thermal Protection
Overtemperature Shutdown
TSHD
—
—
150
15
—
—
°C
°C
TJ rising
Overtemperature Shutdown
Hysteresis
TSHD_HYS
Note 1: Specification for packaged product only.
2: The ICL is trimmed to get the current in the limits at room temperature.
DS20005693C-page 4
2017 Microchip Technology Inc.
MIC28514
TEMPERATURE SPECIFICATIONS
Parameters
Sym.
Min.
Typ.
Max.
Units
Conditions
(Note 1)
Temperature Ranges
Junction Operating Temperature
Storage Temperature Range
Junction Temperature
TJ
TS
TJ
—
-40
-65
—
—
—
—
—
+125
+150
+150
+260
°C
°C
°C
°C
Lead Temperature
—
Soldering, 10s
Package Thermal Resistance
Thermal Resistance, 6 mm x 6 mm,
QFN-32LD
JA
—
33.3
—
°C/W
Note 1: The maximum allowable power dissipation is a function of ambient temperature, the maximum allowable
junction temperature and the thermal resistance from junction to air (i.e., TA, TJ, JA). Exceeding the
maximum allowable power dissipation will cause the device operating junction temperature to exceed the
maximum +125°C rating. Sustained junction temperatures above +125°C can impact the device reliability.
2017 Microchip Technology Inc.
DS20005693C-page 5
MIC28514
NOTES:
DS20005693C-page 6
2017 Microchip Technology Inc.
MIC28514
2.0
TYPICAL CHARACTERISTIC CURVES
Note: The graphs and tables provided following this note are a statistical summary based on a limited number of
samples and are provided for informational purposes only. The performance characteristics listed herein
are not tested or guaranteed. In some graphs or tables, the data presented may be outside the specified
operating range (e.g., outside specified power supply range) and therefore, outside the warranted range.
Note: Unless otherwise indicated, VIN = 12V, VOUT = 5V, IOUT = 0A, fSW = 300 kHz, RCL = 1.42 k, L = 8.2 µH.
100
90
80
70
60
50
40
30
20
10
0
100
90
80
70
60
50
40
30
20
10
0
VOUT = 1.5V
VOUT = 1V
V
= 1.8V
V=1.2V
OUT
OUT
V=2.5V
V=1.5V
OUT
OUT
VOUT = 3.3V
V=1.8V
OUT
VOUT = 5V
V=2.5V
OUT
VOUT = 12V
V
= 3.3V
OUT
V=28V
OUT
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
IOUT (A)
IOUT (A)
FIGURE 2-1:
Efficiency vs. Output
FIGURE 2-4:
Efficiency vs. Output
Current (V = 5V).
Current (V = 48V).
IN
IN
1
0.999
0.998
0.997
0.996
0.995
100
90
80
70
60
50
40
30
20
10
0
VOUT = 1V
V=1.2V
OUT
VOUT = 1.5V
VOUT = 1.8V
VOUT = 2.5V
V
= 12V
= 24V
= 48V
IN
VOUT = 3.3V
V
IN
VOUT = 5V
V
IN
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0
0.5
1
1.5
2
2.5
IOUT (A)
3
3.5
4
4.5
5
IOUT (A)
FIGURE 2-2:
Efficiency vs. Output
FIGURE 2-5:
Current (V
Output Voltage vs. Output
= 1V).
OUT
Current (V = 12V).
IN
100
90
80
70
60
50
40
30
20
10
0
1.785
1.784
1.783
1.782
1.781
1.78
VOUT = 1V
V
= 1.2V
OUT
V=1.5V
OUT
VOUT = 1.8V
VOUT = 2.5V
VOUT = 3.3V
VIN = 12V
V=5V
OUT
V=24V
IN
V
= 12V
V
OUT
V
= 48V
IN
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
IOUT (A)
IOUT (A)
FIGURE 2-3:
Current (V = 24V).
Efficiency vs. Output
FIGURE 2-6:
Current (V
Output Voltage vs. Output
= 1.8V).
OUT
IN
2017 Microchip Technology Inc.
DS20005693C-page 7
MIC28514
Note: Unless otherwise indicated, VIN = 12V, VOUT = 5V, IOUT = 0A, fSW = 300 kHz, RCL = 1.42 k, L = 8.2 µH.
.
3.33
3.328
3.326
3.324
3.322
3.32
1.785
1.784
1.783
1.782
1.781
1.78
VIN = 12V
VIN=24V
V
= 48V
IN
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0
15
30
45
60
75
IOUT (A)
IOUT (A)
FIGURE 2-7:
Output Voltage vs. Output
= 3.3V).
FIGURE 2-10:
Output Voltage vs. Input
= 1.8V).
Current (V
Voltage (V
OUT
OUT
4.99
3.33
3.328
3.326
3.324
3.322
3.32
4.986
V
VIN = 12V
VIN = 24V
4.982
VIN = 48V
4.978
4.974
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
0
15
30
45
60
75
IOUT (A)
IOUT (A)
FIGURE 2-8:
Output Voltage vs. Output
= 5V).
FIGURE 2-11:
Output Voltage vs. Input
= 3.3V).
Current (V
Voltage (V
OUT
OUT
1
0.999
0.998
0.997
0.996
0.995
4.99
4.986
4.982
4.978
4.974
4.97
4.966
0
15
30
45
60
75
0
15
30
IOUT (A)
45
60
75
IOUT (A)
FIGURE 2-9:
Output Voltage vs. Input
= 1V).
FIGURE 2-12:
Output Voltage vs. Input
= 5V).
Voltage (V
Voltage (V
OUT
OUT
DS20005693C-page 8
2017 Microchip Technology Inc.
MIC28514
Note: Unless otherwise indicated, VIN = 12V, VOUT = 5V, IOUT = 0A, fSW = 300 kHz, RCL = 1.42 k, L = 8.2 µH.
1.5
1.45
1.4
1.35
1.3
1.25
1.2
1.15
1.1
1500
1200
900
600
300
0
VOUT = 3.3V
VFB = 1.5V
1.05
1
F
SW = 300 kHz
-40 -25 -10
5
20 35 50 65 80 95 110 125
Temperature (°C)
0
15
30
VIN (V)
45
60 75
FIGURE 2-13:
V
Operating Supply
FIGURE 2-16:
V
Shutdown Current vs.
IN
IN
Current vs. Input Voltage.
Temperature.
1.6
1.5
1.4
1.3
1.2
1.1
1
5.1
5.05
5
I
IVDD = 10 mA
IVDD
I
= 40 mA
4.95
4.9
VOUT = 5V
VFB = 1.5V
4.85
F
SW = 300 kHz
4.8
0
-40 -25 -10
5
20 35 50 65 80 95 110 125
Temperature (°C)
15
30
45
VIN (V)
60
75
FIGURE 2-14:
V
Operating Supply
FIGURE 2-17:
V
Voltage vs. Input
DD
IN
Current vs. Temperature.
Voltage.
2000
1600
1200
800
400
0
5.1
5.05
5
I
IVDD = 10 mA
I
VDD
I
= 40 mA
4.95
4.9
4.85
4.8
-40 -25 -10
5
20 35 50 65 80 95 110 125
Temperature (°C)
0
15
30
45
60
75
VIN (V)
FIGURE 2-15:
V
Shutdown Current vs.
FIGURE 2-18:
V
Voltage vs. Temperature.
IN
DD
Input Voltage.
2017 Microchip Technology Inc.
DS20005693C-page 9
MIC28514
Note: Unless otherwise indicated, VIN = 12V, VOUT = 5V, IOUT = 0A, fSW = 300 kHz, RCL = 1.42 k, L = 8.2 µH.
1.3
1.2
1.1
1
350
340
330
320
310
300
START
STOP
0.9
0
15
30
45
60
75
-40 -25 -10
5
20 35 50 65 80 95 110 125
Temperature (°C)
VIN (V)
FIGURE 2-19:
Enable Threshold vs. Input
FIGURE 2-22:
Switching Frequency vs.
Voltage.
Temperature.
1.4
1.3
1.2
1.1
1
7
6.6
6.2
5.8
5.4
START
STOP
RCL = 1.5 kOhm
0.9
5
0
-40 -25 -10
5
20 35 50 65 80 95 110 125
Temperature (°C)
15
30
45
60
75
VIN (V)
FIGURE 2-20:
Enable Threshold vs.
FIGURE 2-23:
Output Current Limit vs.
Temperature.
Input Voltage.
8
7
6
5
4
350
340
330
320
310
RCL = 1.5 kOhm
300
0
15
30
45
60
75
-40 -25 -10
5
20 35 50 65 80 95 110 125
Temperature (°C)
VIN (V)
FIGURE 2-21:
Switching Frequency vs.
FIGURE 2-24:
Output Current Limit vs.
Input Voltage.
Temperature.
DS20005693C-page 10
2017 Microchip Technology Inc.
MIC28514
Note: Unless otherwise indicated, VIN = 12V, VOUT = 5V, IOUT = 0A, fSW = 300 kHz, RCL = 1.42 k, L = 8.2 µH.
100
80
60
40
20
0
V
IN
10V/div
I
= 1A
OUT
V
OUT
2V/div
Rise
Fall
EN
5V/div
PG
5V/div
-40 -25 -10
5
20 35 50 65 80 95 110 125
Temperature (°C)
2 ms/div
FIGURE 2-25:
Power Good Threshold vs.
FIGURE 2-28:
Enable Turn-On and Rise
Temperature.
Time.
4.5
4.2
3.9
3.6
3.3
V
IN
10V/div
V
OUT
2V/div
= 1A
I
OUT
Rise
Fall
EN
5V/div
PG
5V/div
3
-40 -25 -10
5
20 35 50 65 80 95 110 125
Temperature (°C)
2 ms/div
FIGURE 2-26:
Undervoltage Lockout vs.
FIGURE 2-29:
Enable Turn-Off.
Temperature.
0.602
0.601
0.6
V
OUT
2V/div
V
=3V
PREBIAS
V
IN
10V/div
0.599
SW
5V/div
0.598
-40 -25 -10
5
20 35 50 65 80 95 110 125
Temperature (°C)
2 ms/div
FIGURE 2-27:
Feedback Voltage vs.
FIGURE 2-30:
V
Start-up with Prebiased
IN
Temperature.
Output.
2017 Microchip Technology Inc.
DS20005693C-page 11
MIC28514
Note: Unless otherwise indicated, VIN = 12V, VOUT = 5V, IOUT = 0A, fSW = 300 kHz, RCL = 1.42 k, L = 8.2 µH.
V
IN
10V/div
V
OUT
2V/div
I
= 1A
V
OUT
OUT
V
IN
2V/div
10V/div
EN
5V/div
EN
5V/div
R
= 1.6 k
CL
PG
5V/div
I
L
5A/div
2 ms/div
4 ms/div
FIGURE 2-31:
Enable Turn-On and
FIGURE 2-34:
Enable into Short Circuit.
Turn-Off.
V
OUT
V
20 mV/div
OUT
2V/div
AC coupled
I
L
V
IN
1A/div
10V/div
PG
5V/div
R
= 1.6 k
CL
SW
5V/div
I
L
5A/div
2 ms/div
2 µs/div
FIGURE 2-32:
Switching Waveform
FIGURE 2-35:
Power-up into Short Circuit.
(I
= 0A).
OUT
V
OUT
20 mV/div
AC coupled
V
OUT
2V/div
I
L
2A/div
PG
5V/div
R
= 1.6 k
CL
SW
5V/div
I
L
5A/div
400 µs/div
2 µs/div
FIGURE 2-36:
Behavior when Entering
FIGURE 2-33:
Switching Waveform
Short Circuit.
(I
= 5A).
OUT
DS20005693C-page 12
2017 Microchip Technology Inc.
MIC28514
Note: Unless otherwise indicated, VIN = 12V, VOUT = 5V, IOUT = 0A, fSW = 300 kHz, RCL = 1.42 k, L = 8.2 µH.
V
OUT
100 mV/div
AC coupled
V
OUT
2V/div
PG
5V/div
R
= 1.6 k
CL
I
OUT
I
L
2A/div
5A/div
200 µs/div
2 ms/div
FIGURE 2-37:
Recovery from Short Circuit.
FIGURE 2-40:
Load Transient Response
(0 to 2.5A).
PG
1V/div
V
OUT
100 mV/div
AC coupled
V
OUT
1V/div
I
OUT
100 mA/div
I
OUT
2A/div
SW
5V/div
200 µs/div
4 ms/div
FIGURE 2-38:
Behavior when Entering
FIGURE 2-41:
Load Transient Response
Thermal Shutdown.
(0 to 5A).
V
V
OUT
OUT
100 mV/div
1V/div
5V offset
PG
1V/div
V
IN
2V/div
SW
12V offset
5V/div
I
OUT
100 mA/div
4 ms/div
400 µs/div
FIGURE 2-39:
Recovery from Thermal
FIGURE 2-42:
Line Transient Response
Shutdown.
(12V to 18V).
2017 Microchip Technology Inc.
DS20005693C-page 13
MIC28514
Note: Unless otherwise indicated, VIN = 12V, VOUT = 5V, IOUT = 0A, fSW = 300 kHz, RCL = 1.42 k, L = 8.2 µH.
V
OUT
100 mV/div
5V offset
V
IN
5V/div
12V offset
400 µs/div
FIGURE 2-43:
Line Transient Response
FIGURE 2-45:
Thermal Picture (I
= 5A).
OUT
(12V to 24V).
FIGURE 2-44:
Thermal Picture
(I
= 2.5A).
OUT
DS20005693C-page 14
2017 Microchip Technology Inc.
MIC28514
3.0
PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 3-1.
TABLE 3-1:
PIN FUNCTION TABLE
Pin
Number
Symbol
Description
1
ILIM
Current Limit Adjust Input. Connect a resistor from ILIM to the SW node to set the current
limit. Refer to Section 4.3 “Current Limit” for more details.
2, 16, 17,
18, 19,
22, 29
PGND
Power Ground. PGND is the ground path for the MIC28514 buck converter power stage. The
PGND pin connects to the sources of the low-side N-channel internal MOSFET, the negative
terminals of the input capacitors and the negative terminals of the output capacitors. The
loop for the Power Ground should be as small as possible and separate from the Analog
Ground (AGND) loop.
3, 12, 13,
14, 15,
20
SW
BST
Switch Node (Output). Internal connection for the high-side MOSFET source and low-side
MOSFET drain. Connect one terminal of the Inductor to the SW node.
4
Boost Pin (Output). Bootstrapped voltage to the high-side N-channel internal MOSFET
driver. An internal diode is connected between the PVDD pin and the BST pin. A boost
capacitor of 0.1 μF is connected between the BST pin and the SW pin.
5, 6, 7, 8,
9, 10, 11
PVIN
PVDD
High-Side Internal N-Channel MOSFET Drain Connection (Input). The PVIN operating
voltage range is from 4.5V to 75V. Input capacitors between the PVIN pins and the Power
Ground (PGND) are required and the connection should be kept as short as possible.
21
23
Supply for the MOSFET Drivers. Connect to VDD through a 2ꢀ series resistor. Connect a
minimum 4.7 µF low-ESR ceramic capacitor from PVDD to PGND.
EXTVDD Auxiliary LDO Input. Connect to a supply higher than 4.7V (typical) to bypass the internal
high-voltage LDO or leave unconnected/connected to ground.
Connect a 2.2 µF low-ESR ceramic capacitor between EXTVDD and PGND when EXTVDD
is connected to an external supply.
24
25
EN
Enable (Input). A logic level control of the output. The EN pin is CMOS-compatible. Logic
high = enable, logic low = shutdown. In the OFF state, the VDD supply current of the device
is reduced. Do not pull the EN pin above the VDD supply.
FREQ
Frequency Programming Input. Connect to VIN to set the switching frequency to 800 kHz.
Connect to the mid-point of a resistor divider from PVIN to AGND to set the switching
frequency. Refer to Section 5.1 “Setting the Switching Frequency”.
26
27
SS
FB
Soft Start Adjustment Pin. Connect a capacitor from the SS pin to AGND to adjust the
soft start time. See more details in Section 5.0 “Application Information”.
Feedback (Input). Input to the transconductance amplifier of the control loop. The FB pin is
regulated to 0.6V. A resistor divider connecting the feedback to the output is used to adjust
the desired output voltage.
28
30
31
32
AGND
VDD
Analog Ground. Reference node for all the control logic circuits inside the MIC28514.
Connect AGND to PGND at one point; see Section 6.0 “PCB Layout Guidelines” for
details.
VDD Bias (Input). Power to the internal reference and control sections of the MIC28514. The
VDD operating voltage range is from 4.5V to 5.5V. A 2.2 µF ceramic capacitor from the VDD
pin to the PGND pin must be placed next to the IC.
SVIN
PG
Input Voltage to the internal regulator, which powers the internal reference and control
section of the MIC28514. Connect to PVIN through a 2ꢀ resistor. Connect a 1 µF capacitor
from this pin to AGND.
Open-Drain Power Good Output. PG is pulled to ground when the output voltage is below
90% of the target voltage. Pull-up to VDD through a 10 kꢀ resistor to set a logic high level
when the output voltage is above 90% of the target voltage.
2017 Microchip Technology Inc.
DS20005693C-page 15
MIC28514
NOTES:
DS20005693C-page 16
2017 Microchip Technology Inc.
MIC28514
The maximum duty cycle is obtained from the 240 ns
4.0
FUNCTIONAL DESCRIPTION
tOFF(MIN)
:
The MIC28514 is an adaptive on-time synchronous,
step-down DC/DC regulator. It is designed to operate
over a wide input voltage range, from 4.5V to 75V, and
provides a regulated output voltage at up to 5A of
output current. An adaptive on-time control scheme is
employed in order to obtain a constant switching
frequency and to simplify the control compensation.
Overcurrent protection is implemented with the use of
an external sense resistor which sets the current limit.
The device includes a programmable soft start function
that reduces the power supply input surge current at
start-up by controlling the output voltage rise time.
EQUATION 4-2:
tS – tOFFMIN
DMAX = ---------------------------------- = 1 – --------------
tS
tS
240ns
Where:
tS = 1/fSW
It is not recommended to use the MIC28514 with an
off-time close to tOFF(MIN) during steady-state operation.
The actual on-time and resulting switching frequency will
vary with the part-to-part variation in the rise and fall
times of the internal MOSFETs, the output load current,
and variations in the VDD voltage. Also, the minimum tON
results in a lower switching frequency in high VIN to VOUT
applications, such as 75V to 1.0V.
4.1
Theory of Operation
The MIC28514 Functional Block Diagram appears on
page 2. The output voltage is sensed by the MIC28514
Feedback pin, FB, via the voltage dividers, R1 and R2,
and compared to a 0.6V reference voltage (VREF), at
the main comparator, through a low-gain transconduc-
tance (gm) amplifier. If the feedback voltage decreases
and the output of the gm amplifier is below 0.6V, then
the main comparator will trigger the control logic and
generate an on-time period. The on-time period is
predetermined by the fixed tON estimator circuitry value
from Equation 4-1:
Figure 4-1 shows the MIC28514 control loop timing
during steady-state operation. During steady-state oper-
ation, the gm amplifier senses the feedback voltage
ripple. The feedback ripple is proportional to the output
voltage ripple, and the inductor current ripple, to trigger
the on-time period. The on-time is predetermined by the
tON estimator. The termination of the off-time is controlled
by the feedback voltage. At the valley of the feedback
voltage ripple, which occurs when VFB falls below VREF
,
the off period ends and the next on-time period is
triggered through the control logic circuitry.
EQUATION 4-1:
VOUT
tONESTIMATED = -----------------------
VIN fSW
I
L
IL(PP)
I
OUT
Where:
V
VOUT = Output Voltage
OUT
V
= ESR
OUT x L(PP)
OUT(PP) C
I
VIN
fSW
= Power Stage Input Voltage
= Switching Frequency
V
FB
R
2
V
= V
x
FB(PP)
OUT(PP)
V
REF
DH
R + R
1 2
At the end of the on-time period, the internal high-side
driver turns off the high-side MOSFET and the low-side
driver turns on the low-side MOSFET. The off-time
period length depends upon the feedback voltage in
most cases. When the feedback voltage decreases
and the output of the gm amplifier is below 0.6V, the
on-time period is triggered and the off-time period
ends. If the off-time period, determined by the feedback
Trigger On-Time if V is Below V
FB
REF
Estimated On-Time
FIGURE 4-1:
Timing.
MIC28514 Control Loop
voltage, is less than the minimum off-time, tOFF(MIN)
,
which is about 240 ns, then the MIC28514 control logic
will apply the tOFF(MIN) instead. The minimum tOFF(MIN)
period is required to maintain enough energy in the
Boost Capacitor (CBST) to drive the high-side MOSFET.
2017 Microchip Technology Inc.
DS20005693C-page 17
MIC28514
Figure 4-2 shows the operation of the MIC28514 during
load transient. The output voltage drops due to the
sudden load increase, which causes VFB to be less than
VREF. This will cause the error comparator to trigger an
on-time period. At the end of the on-time period, a
minimum off-time is generated to charge CBST because
the feedback voltage is still below VREF. Then, the next
on-time period is triggered due to the low feedback
voltage. Therefore, the switching frequency changes
during the load transient, but returns to the nominal fixed
frequency once the output has stabilized at the new load
current level. With the varying duty cycle and switching
frequency, the output recovery time is fast and the output
voltage deviation is small in the MIC28514 converter.
4.2
Soft Start
Soft start reduces the power supply input surge current
at start-up by controlling the output voltage rise time.
The input surge appears while the output capacitor is
charged up. A slower output rise time will draw a lower
input surge current.
The MIC28514 features an adjustable soft start time.
The soft start time can be adjusted by adjusting the
value of the capacitor connected from the SS pin to
AGND. The soft start time can be adjusted from 5 ms
to 100 ms. The MIC28514 forces 1.4 µA current from
the SS pin. This constant current flows through the
capacitor connected from the SS pin to AGND to adjust
the soft start time.
I
Full Load
OUT
4.3
Current Limit
The MIC28514 uses the low-side MOSFET RDS(ON) to
sense the inductor current. In each switching cycle of
the MIC28514 converter, the inductor current is sensed
by monitoring the voltage across the low-side MOSFET
during the off period of the switching cycle, during
which, the low-side MOSFET is on. An internal current
source of 135 µA generates a voltage across the
No Load
V
OUT
V
FB
external Current Limit Setting Resistor, RCL
.
V
REF
The ILIM Pin Voltage (VILIM) is the difference of the volt-
age across the low-side MOSFET and the voltage
across the resistor (VCL). The sensed voltage, VILIM,is
compared with the Power Ground (PGND) after a
blanking time of 150 ns.
DH
If the absolute value of the voltage drop across the
low-side MOSFET is greater than the absolute value of
the voltage across the current setting resistor (VCL), the
MIC28514 triggers the current limit event. A consecu-
tive eight current limit events trigger the Hiccup mode.
Once the controller enters into Hiccup mode, it initiates
a soft start sequence after a hiccup time-out of 4 ms
(typical). Both the high-side and low-side MOSFETs
are turned off during a hiccup time-out. The hiccup
sequence, including the soft start, reduces the stress
on the switching FETs, and protects the load and
supply from severe short conditions.
T
OFF(MIN)
FIGURE 4-2:
Response.
MIC28514 Load Transient
Unlike true Current-mode control, the MIC28514 uses
the output voltage ripple to trigger an on-time period.
The output voltage ripple is proportional to the inductor
current ripple if the ESR of the output capacitor is large
enough.
In order to meet the stability requirements, the
MIC28514 feedback voltage ripple should be in phase
with the inductor current ripple and large enough to be
sensed by the gm amplifier. The recommended feed-
back voltage ripple is 20 mV ~ 100 mV. If a low-ESR
output capacitor is selected, then the feedback voltage
ripple may be too small to be sensed by the gm ampli-
fier and the error comparator. Also, the output voltage
ripple and the feedback voltage ripple are not neces-
sarily in phase with the inductor current ripple if the
ESR of the output capacitor is very low. For these appli-
cations, ripple injection is required to ensure proper
operation. Refer to Section 5.8 “Ripple Injection”
under Section 5.0 “Application Information” for
details about the ripple injection technique.
Since the MOSFET RDS(ON) varies from 30% to 40%
with temperature, it is recommended to consider the
RDS(ON) variation, while calculating RCL in the above
equation, to avoid false current limiting due to
increased MOSFET junction temperature rise.
To improve the current limit variation, the MIC28514
adjusts the internal Current Limit Source Current (ICL
)
at a rate of 0.3 µA/°C when the MIC28514 junction tem-
perature changes to compensate the RDS(ON) variation
of the low-side MOSFET. Figure 2-23 indicates the
temperature variation of the current limit with
RCL= 1.5 k.
DS20005693C-page 18
2017 Microchip Technology Inc.
MIC28514
A small capacitor (CCL) can be connected from the ILIM
pin to PGND to filter the switch node ringing during the
off period, allowing a better current sensing. The time
constant of RCL and CCL should be less than the
minimum off-time.
The drive voltage is derived from the PVDD supply volt-
age. The nominal low-side gate drive voltage is PVDD
and the nominal high-side gate drive voltage is approx-
imately PVDD – VDIODE, where VDIODE is the voltage
drop across the internal diode. An approximate 30 ns
delay between the high-side and low-side driver transi-
tions is used to prevent current from simultaneously
flowing unimpeded through both MOSFETs.
4.4
Negative Current Limit
The MIC28514 implements a negative current limit by
sensing the SW voltage when the low-side MOSFET is
on. If the SW node voltage exceeds 48 mV, typical, or
an equivalent of 2A, the device turns off the low-side
MOSFET for 500 ns.
4.6
Auxiliary Bootstrap LDO
(EXTVDD)
The MIC28514 features an auxiliary bootstrap LDO
which improves the system efficiency by supplying the
MIC28514 internal circuit bias power and gate drivers
from the converter output voltage. This LDO is enabled
when the voltage on the EXTVDD pin is above 4.6V
(typical), and at the same time, the main LDO which
operates from VIN is disabled to reduce power
consumption.
4.5
Internal MOSFET Gate Drive
The functional block diagram shows a bootstrap circuit,
consisting of an internal diode from PVDD to BST and
an external capacitor connected from the SW pin to the
BST pin (CBST). This circuit supplies energy to the
high-side drive circuit. Capacitor, CBST, is charged
while the low-side MOSFET is on and the voltage on
the SW pin is approximately 0V. Energy from CBST is
used to turn on the high-side MOSFET. As the
high-side MOSFET turns on, the voltage on the SW pin
increases to approximately VIN. The internal diode is
reverse-biased and CBST floats high while continuing to
keep the high-side MOSFET on. The bias current of the
high-side driver is less than 10 mA, so a 0.1 μF to 1 μF
is sufficient to hold the gate voltage with minimal droop
for the power stroke (high-side switching) cycle (i.e.,
∆BST = 10 mA x 4 μs/0.1 μF = 400 mV). When the
low-side MOSFET is turned back on, CBST is
recharged through D1. A small resistor in series with
CBST can be used to slow down the turn-on time of the
high-side N-channel MOSFET.
2017 Microchip Technology Inc.
DS20005693C-page 19
MIC28514
NOTES:
DS20005693C-page 20
2017 Microchip Technology Inc.
MIC28514
The output voltage is determined by Equation 5-3:
5.0
5.1
APPLICATION INFORMATION
Setting the Switching Frequency
EQUATION 5-3:
R1
VO = VFB 1 + -----
The MIC28514 is an adjustable frequency, synchro-
nous buck regulator that features an adaptive on-time
control architecture. The switching frequency can be
adjusted between 270 kHz and 800 kHz by changing
the resistor divider network, consisting of R3 and R4.
R2
Where:
VFB = 0.6V
A typical value of R1 can be between 3 kꢀ and 10 kꢀ.
If R1 is too large, it may allow noise to be introduced
into the voltage feedback loop. If R1 is too small, it will
decrease the efficiency of the power supply, especially
at light loads. Once R1 is selected, R2 can be
calculated using Equation 5-4.
Equation 5-1 gives the estimated switching frequency.
EQUATION 5-1:
R3
------------------
fSWADJ = fO
R3 + R4
Where:
EQUATION 5-4:
fO = Switching Frequency when R4 is 100 kꢀ
and R3 is open. fO is typically 800 kHz.
VFB R1
R2 = -----------------------------
VOUT – VFB
5.2
Setting the Soft Start Time
The output soft start time can be set by connecting a
capacitor from SS to AGND.
5.4
Setting the Current Limit
The Source Current Limit (ICL) is trimmed at the factory
to achieve a higher current limit accuracy with
RCL = 1.42 kꢀ, as specified in Table in Section 1.0
“Electrical Characteristics”. It is possible to adjust
other current limits by changing the RCL value using
Equation 5-5.
The value of the capacitor can be calculated using
Equation 5-2.
EQUATION 5-2:
ISS tSS
CSS = -------------------
VREF
EQUATION 5-5:
Where:
CSS = Capacitor from SS pin to AGND
ILPP
ILIM + ------------------ RDSON
ISS
tSS
= Internal Soft Start Current(1.4 μA, typical)
2
RCL = --------------------------------------------------------------------
= Output Soft Start Time
ICL
VREF = 0.6V
Where:
ILIM
= Load Current Limit
RDS(ON) = On-Resistance of the Low-Side MOSFET
(25 mꢀ, typical)
5.3
Setting Output Voltage
The MIC28514 requires two resistors to set the output
voltage, as shown in Figure 5-1.
ΔIL(PP) = Inductor Ripple Current
ICL
= Current Limit Source Current (135 μA, typical)
R1
FB
gm AMP
R2
VREF
FIGURE 5-1:
Voltage Divider Configuration.
2017 Microchip Technology Inc.
DS20005693C-page 21
MIC28514
Maximizing efficiency requires the proper selection of
core material while minimizing the winding resistance.
The high-frequency operation of the MIC28514 requires
the use of ferrite materials for all but the most
cost-sensitive applications. Lower cost iron powder
cores may be used, but the increase in core loss will
reduce the efficiency of the power supply. This is
especially noticeable at low output power. The winding
resistance decreases efficiency at the higher output cur-
rent levels. The winding resistance must be minimized,
although this usually comes at the expense of a larger
inductor. The power dissipated in the inductor is equal to
the sum of the core and copper losses. At higher output
loads, the core losses are usually insignificant and can
be ignored. At lower output currents, the core losses can
be significant. Core loss information is usually available
from the magnetics vendor. Copper loss in the inductor
is calculated by Equation 5-10.
5.5
Inductor Selection
Values for inductance, peak and RMS currents are
required to select the inductor. The input voltage, output
voltage, switching frequency and the inductance value
determine the peak-to-peak inductor ripple current. Gen-
erally, higher inductance values are used with higher
input voltages. Larger peak-to-peak ripple currents will
increase the power dissipation in the inductor and
MOSFETs. Larger output ripple currents will also require
more output capacitance to smooth out the larger ripple
current. Smaller peak-to-peak ripple currents require a
larger inductance value, and therefore, a larger and
more expensive inductor. A good compromise between
size, loss and cost is to set the inductor ripple current to
be equal to 20% of the maximum output current. The
inductance value is calculated by Equation 5-6.
EQUATION 5-6:
EQUATION 5-10:
VOUT VINMAX – VOUT
L = ----------------------------------------------------------------------------------------
INMAX fSW 20% IOUTMAX
V
PINDUCTORCU = ILRMS2 RWINDING
Where:
fSW
= Switching Frequency
The resistance of the copper wire, RWINDING, increases
with the temperature. The value of the winding resistance
used should be at the operating temperature.
20%
= Ratio of AC Ripple Current to DC Output
Current
VIN(MAX) = Maximum Power Stage Input Voltage
EQUATION 5-11:
RWINDINGHT
= RWINDING20C 1 + 0.004 TH – T20C
For a selected inductor, the peak-to-peak inductor
current ripple is:
Where:
EQUATION 5-7:
TH
= Temperature of Wire Underload
= Ambient Temperature
T20C
VOUT VIN – VOUT
ILPP = -----------------------------------------------------
VIN fSW L
RWINDING(20C) = Room Temperature Winding Resistance
(usually specified by the manufacturer)
The peak inductor current is equal to the average
output current plus one-half of the peak-to-peak
inductor current ripple.
5.6
Output Capacitor Selection
The type of the output capacitor is usually determined by
its Equivalent Series Resistance (ESR). Voltage and
RMS current capability are two other important factors
for selecting the output capacitor. Recommended
capacitor types are ceramic, low-ESR aluminum
electrolytic, OS-CON, and POSCAP. The output capaci-
tor’s ESR is usually the main cause of the output ripple.
The output capacitor ESR also affects the control loop
from a stability point of view. The maximum value of the
ESR is calculated using Equation 5-12.
EQUATION 5-8:
ILPK = IOUT + 0.5 ILPP
The RMS inductor current is used to calculate the I2R
losses in the inductor.
EQUATION 5-9:
2
ILPP
EQUATION 5-12:
2
ILRMS
=
IOUT + --------------------
12
VOUTPP
ILPP
---------------------------
ESRC
OUT
Where:
ΔVOUT(PP) = Peak-to-Peak Output Voltage Ripple
ΔIL(PP)
= Peak-to-Peak Inductor Current Ripple
DS20005693C-page 22
2017 Microchip Technology Inc.
MIC28514
The total output ripple is a combination of the ESR and
output capacitance. The total ripple is calculated in
Equation 5-13.
5.7
Input Capacitor Selection
The input capacitor for the power stage input, VIN,
should be selected for ripple current rating and voltage
rating. Tantalum input capacitors may fail when sub-
jected to high inrush currents caused by turning on the
input supply. A tantalum input capacitor’s voltage rating
should be at least two times the maximum input voltage
to maximize reliability. Aluminum electrolytic, OS-CON
and multilayer polymer film capacitors can handle the
higher inrush currents without voltage derating. The
input voltage ripple will primarily depend on the input
capacitor’s ESR. The peak input current is equal to the
peak inductor current, so:
EQUATION 5-13:
VOUTPP
ILPP
COUT fSW 8
+ ILPP ESRC 2
2
-------------------------------------
=
OUT
Where:
COUT = Output Capacitance Value
fSW = Switching Frequency
EQUATION 5-16:
As described in Section 4.1 “Theory of Operation”, a
subsection of Section 4.0 “Functional Description”,
the MIC28514 requires at least 20 mV peak-to-peak
ripple at the FB pin to make the gm amplifier and the
error comparator behave properly. Also, the output volt-
age ripple should be in phase with the inductor current.
Therefore, the output voltage ripple caused by the
output capacitors’ value should be much smaller than
the ripple caused by the output capacitor ESR. If
low-ESR capacitors, such as ceramic capacitors, are
selected as the output capacitors, a ripple injection
method should be applied to provide enough feedback
voltage ripple. Refer to Section 5.8 “Ripple Injection”
for details.
VIN = ILPK CESR
The input capacitor must be rated for the input current
ripple. The RMS value of the input capacitor current is
determined at the maximum output current. Assuming
the peak-to-peak inductor current ripple is low:
EQUATION 5-17:
I
CINRMS IOUTMAX D 1 – D
The voltage rating of the capacitor should be 20%
greater for aluminum electrolytic or OS-CON. The
output capacitor RMS current is calculated in
Equation 5-14.
The power dissipated in the input capacitor is:
EQUATION 5-18:
PDISSCIN = ICINRMS2 CESR
EQUATION 5-14:
ILPP
IC
= ------------------
12
OUTRMS
The power dissipated in the output capacitor is:
EQUATION 5-15:
PDISSCOUT = ICOUTRMS2 ESRCOUT
2017 Microchip Technology Inc.
DS20005693C-page 23
MIC28514
With the feed-forward capacitor, the feedback
voltage ripple is very close to the output voltage
ripple.
5.8
Ripple Injection
The VFB ripple required for proper operation of the
MIC28514 gm amplifier and comparator is 20 mV to
100 mV. However, the output voltage ripple is generally
designed as 1% to 2% of the output voltage. For low
output voltages, such as 1V, the output voltage ripple is
only 10 mV to 20 mV and the feedback voltage ripple is
less than 20 mV. If the feedback voltage ripple is so
small that the gm amplifier and comparator cannot
sense it, then the MIC28514 loses control and the out-
put voltage is not regulated. In order to have sufficient
VFB ripple, a ripple injection method should be applied
for low output voltage ripple applications.
EQUATION 5-20:
VFB(PP) ESRCOUT IL(PP)
3. Virtually no ripple at the FB pin voltage due to
the very low-ESR of the output capacitors.
In this situation, the output voltage ripple is less
than 20 mV. Therefore, additional ripple is
injected into the FB pin from the Switching
Node, SW, via a resistor, RINJ, and a capacitor,
CINJ, as shown in Figure 5-4.
The applications are divided into three situations
according to the amount of the feedback voltage ripple:
1. Enough ripple at the feedback voltage due to the
large ESR of the output capacitors (Figure 5-2).
The converter is stable without any ripple
injection.
L
SW
CINJ
COUT
R1
RINJ
MIC28514
FB
CFF
R2
ESR
L
SW
R1
COUT
MIC28514
FB
FIGURE 5-4:
Invisible Ripple at FB.
R2
ESR
The injected ripple is:
EQUATION 5-21:
FIGURE 5-2:
Enough Ripple at FB.
1
----------------
VFBPP = VIN KDIV D 1 – D
fSW
The feedback voltage ripple is:
Where:
EQUATION 5-19:
VIN = Power Stage Input Voltage
R2
------------------
VFBPP
=
ESR
ILPP
COUT
D
= Duty Cycle
R1 + R2
fSW = Switching Frequency
Where:
= (R1//R2//RINJ) x Cff
τ
ΔIL(PP) = Peak-to-Peak Value of the Inductor
Current Ripple
EQUATION 5-22:
2. Inadequate ripple at the feedback voltage due to
the small ESR of the output capacitors.
R1//R2
KDIV = -----------------------------------
RINJ + R1//R2
In this situation, the output voltage ripple is fed into
the FB pin through a Feed-Forward Capacitor, Cff,
as shown in Figure 5-3. The typical Cff value is
between 1 nF and 22 nF.
In Equation 5-21 and Equation 5-22, it is assumed that
the time constant associated with Cff must be much
greater than the switching period:
L
SW
EQUATION 5-23:
COUT
R1
MIC28514
1
T
FB
Cff
---------------- = -- « 1
fSW
R2
ESR
FIGURE 5-3:
Inadequate Ripple at FB.
DS20005693C-page 24
2017 Microchip Technology Inc.
MIC28514
If the voltage divider resistors, R1 and R2, are in the kꢀ
range, a Cff of 1 nF to 22 nF can easily satisfy the large
time constant requirements. Also, a 100 nF Injection
Capacitor, CINJ, is used in order to be considered as
short for a wide range of the frequencies.
5.9
Thermal Measurements
Measuring the IC’s case temperature is recommended
to ensure it is within its operating limits. Although this
might seem like a very elementary task, it is easy to get
erroneous results. The most common mistake is to use
the standard thermocouple that comes with a thermal
meter. This thermocouple wire gauge is large, typically
22 gauge, and behaves like a heat sink, resulting in a
lower case measurement.
The process of sizing the ripple injection resistor and
capacitors is as follows.
1. Select Cff to feed all output ripples into the Feed-
back pin and make sure the large time constant
assumption is satisfied. A typical choice for Cff is
1 nF to 22 nF if R1 and R2 are in the kꢀ range.
Two methods of temperature measurement are using a
smaller thermocouple wire or an infrared thermometer.
If a thermocouple wire is used, it must be constructed
of 36 gauge wire or higher (smaller wire size) to
minimize the wire heat sinking effect. In addition, the
thermocouple tip must be covered in either thermal
grease or thermal glue to make sure that the thermo-
couple junction is making good contact with the case of
the IC.
2. Select RINJ according to the expected feedback
voltage ripple using Equation 5-24:
EQUATION 5-24:
VFBPP
fSW
D 1 – D
----------------------- ----------------------------
KDIV
=
VIN
Wherever possible, an infrared thermometer is recom-
mended. An optional stand makes it easy to hold the
beam on the IC for long periods of time.
Then, the value of RINJ is obtained as:
EQUATION 5-25:
1
RINJ = R1//R2 ------------ – 1
KDIV
3. Select CINJ as 100 nF, which could be considered
as short for a wide range of the frequencies.
2017 Microchip Technology Inc.
DS20005693C-page 25
MIC28514
NOTES:
DS20005693C-page 26
2017 Microchip Technology Inc.
MIC28514
6.3
Inductor
6.0
PCB LAYOUT GUIDELINES
• Keep the inductor connection to the Switch Node
(SW) short.
PCB layout is critical to achieve reliable, stable and
efficient performance. A ground plane is required to
control EMI and minimize the inductance in power,
signal and return paths. The thickness of the copper
planes is also important in terms of dissipating heat.
The 2 oz. copper thickness is adequate from a thermal
point of view and a thick copper plain helps in terms of
noise immunity. Keep in mind, thinner planes can be
easily penetrated by noise. The following guidelines
should be followed to ensure proper operation of the
MIC28514 converter.
• Do not route any digital lines underneath or close
to the inductor.
• Keep the Switch Node (SW) away from the
Feedback (FB) pin.
6.4
Output Capacitor
• Use a wide trace to connect the output capacitor
ground terminal to the input capacitor ground
terminal.
6.1
IC
• Phase margin will change as the output capacitor
value and ESR changes. Contact the factory if the
output capacitor is different from what is shown in
the BOM.
• The 2.2 µF ceramic capacitor, which is connected
to the VDD pin, must be located right at the IC.
The VDD pin is very noise-sensitive and
placement of the capacitor is very critical. Use
wide traces to connect to the VDD pin.
• The feedback trace should be separate from the
power trace and connected as close as possible
to the output capacitor. Sensing a long
high-current load trace can degrade the DC load
regulation.
• The Signal Ground pin (SGND) must be
connected directly to the ground planes. The
SGND and PGND connection should be done at a
single point near the IC. Do not route the SGND
pin to the PGND pad on the top layer.
• Use thick traces to route the input and output
power lines.
6.2
Input Capacitor
• Place the input capacitor next to the power pins.
• Place the input capacitors on the same side of the
board and as close to the IC as possible.
• Keep both the PVIN pin and PGND connections
short.
• Place several vias to the ground plane, close to
the input capacitor ground terminal.
• Use either X7R or X5R dielectric input capacitors.
Do not use Y5V or Z5U-type capacitors.
• If a tantalum input capacitor is placed in parallel
with the input capacitor, it must be recommended
for switching regulator applications and the
operating voltage must be derated by 50%.
• In hot-plug applications, a tantalum or electrolytic
bypass capacitor must be used to limit the
overvoltage spike seen on the input supply when
power is suddenly applied.
2017 Microchip Technology Inc.
DS20005693C-page 27
MIC28514
NOTES:
DS20005693C-page 28
2017 Microchip Technology Inc.
MIC28514
7.0
7.1
PACKAGING INFORMATION
Package Marking Information
32-Pin VQFN (6 x 6 mm)
Example
MIC28514
1704256
Legend: XX...X Customer-specific information
Y
YY
Year code (last digit of calendar year)
Year code (last 2 digits of calendar year)
WW
NNN
Week code (week of January 1 is week ‘01’)
Alphanumeric traceability code
e
3
Pb-free JEDEC designator for Matte Tin (Sn)
This package is Pb-free. The Pb-free JEDEC designator (
can be found on the outer packaging for this package.
*
)
3
e
Note: In the event the full Microchip part number cannot be marked on one line, it will
be carried over to the next line, thus limiting the number of available
characters for customer-specific information.
2017 Microchip Technology Inc.
DS20005693C-page 29
MIC28514
32-Lead Very Thin Plastic Quad Flat, No Lead Package (PHA) - 6x6 mm Body [VQFN]
Wettable Flanks, Multiple Exposed Pads
Note: For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging
(A3)
D
A
B
E
N
NOTE 1
1
2
(DATUM B)
(DATUM A)
DETAIL 1
2X
0.15 C
2X
TOP VIEW
0.15 C
32X
A1
0.08 C
K2
K2
D4
A
D3
D5
K3
E3
0.10 C
SIDE VIEW
D5
e
2
DETAIL 2
K2
E2
32X b
0.10
0.05
2
C A B
C
A
1
0.10
C A B
N
A
NOTE 1
K1
L
e
D2
BOTTOM VIEW
Microchip Technology Drawing C04-1196A Sheet 1 of 2
DS20005693C-page 30
2017 Microchip Technology Inc.
MIC28514
32-Lead Very Thin Plastic Quad Flat, No Lead Package (PHA) - 6x6 mm Body [VQFN]
Wettable Flanks, Multiple Exposed Pads
Note: For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging
R0.05
0.064
R0.125
DETAIL 2
DETAIL 1
ROTATED 180°
0.15
0.045
SECTION A-A
Units
Dimension Limits
MILLIMETERS
NOM
MIN
MAX
Number of Terminals
Pitch
Overall Height
Standoff
Terminal Thickness
Overall Length
Overall Width
Exposed Pad Length
Exposed Pad Width
Exposed Pad Length
Exposed Pad Width
Exposed Pad Length
Exposed Pad Length
Exposed Pad Width
Terminal Width
Terminal Length
N
32
0.65 BSC
0.85
e
A
A1
A3
D
0.80
0.00
0.90
0.05
0.02
0.203 REF
6.00 BSC
6.00 BSC
4.80
2.315
2.085
2.645
2.340
0.695
1.995
0.30
E
D2
E2
D3
E3
D4
D5
E5
b
4.70
2.215
1.985
2.545
2.240
0.595
1.895
0.25
4.90
2.415
2.185
2.745
2.440
0.795
2.095
0.35
0.50
-
L
0.30
0.40
Terminal-to-Exposed Pad
Exposed Pad-to-Exposed Pad
Pacakge Edgel-to-Exposed Pad
K1
K2
K3
0.20
0.20
0.18
-
0.26
-
-
-
Notes:
1. Pin 1 visual index feature may vary, but must be located within the hatched area.
2. Package is saw singulated
3. Dimensioning and tolerancing per ASME Y14.5M
BSC: Basic Dimension. Theoretically exact value shown without tolerances.
REF: Reference Dimension, usually without tolerance, for information purposes only.
Microchip Technology Drawing C04-1196A Sheet 2 of 2
2017 Microchip Technology Inc.
DS20005693C-page 31
MIC28514
32-Lead Very Thin Plastic Quad Flat, No Lead Package (PHA) - 6x6 mm Body [VQFN]
Wettable Flanks, Multiple Exposed Pads
Note: For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging
C1
X2
E
E
2
Y1
32
1
X1
2
EV
Y2
C2
Y3
ØV
Y5
X3
SILK SCREEN
EV
X5
X4
RECOMMENDED LAND PATTERN
Units
MILLIMETERS
Dimension Limits
MIN
NOM
MAX
Contact Pitch
E
0.65 BSC
Contact Pad Width (X32)
X1
0.35
0.75
Contact Pad Length (X32)
Contact Pad Spacing
Contact Pad Spacing
Inner Pad Length
Inner Pad Width
Inner Pad Length
Inner Pad Width
Inner Pad Length
Inner Pad Length
Inner Pad Width
Y1
C1
C2
X2
Y2
X3
Y3
X4
X5
Y5
V
6.10
6.10
4.85
2.36
2.13
2.69
2.39
0.74
2.04
Thermal Via Diameter (X26)
Thermal Via Pitch
0.30
1.00
EV
Notes:
1. Dimensioning and tolerancing per ASME Y14.5M
BSC: Basic Dimension. Theoretically exact value shown without tolerances.
2. For best soldering results, thermal vias, if used, should be filled or tented to avoid solder loss during
reflow process
Microchip Technology Drawing C04-3196A
DS20005693C-page 32
2017 Microchip Technology Inc.
MIC28514
APPENDIX A: REVISION HISTORY
Revision C (May 2017)
The following is the list of modifications:
• Updated the Typical Application Circuit.
• Updated the Functional Block Diagram.
Revision B (April 2017)
The following is the list of modifications:
• Updated the Functional Block Diagram.
• Updated the Electrical Characteristics(1) section.
Revision A (February 2017)
• Original Release of this Document.
2017 Microchip Technology Inc.
DS20005693C-page 29
MIC28514
NOTES:
DS20005693C-page 30
2017 Microchip Technology Inc.
MIC28514
PRODUCT IDENTIFICATION SYSTEM
To order or obtain information, e.g., on pricing or delivery, refer to the factory or the listed sales office.
PART NO.
Device
X
X
XXX
Examples:
Media Type
a) MIC28514T-E/PHA: 75V, 5A Synchronous Buck Regulator,
Temperature
Package
®
Hyper Speed Control with Soft Start,
-40°C to +125°C,
Extended Temperature Range,
32-Lead QFN package
®
Device:
MIC28514T: 75V, 5A Hyper Speed Control Synchronous
DC/DC Buck Regulator with External Soft Start
Media Type:
T
E
=
=
5000/Reel
Temperature:
Extended Temperature Range
(-40°C to +125°C)
Package:
PHA
=
32-Lead, 6x6 mm VQFN
2017 Microchip Technology Inc.
DS20005693C-page 31
MIC28514
NOTES:
DS20005693C-page 32
2017 Microchip Technology Inc.
Note the following details of the code protection feature on Microchip devices:
•
Microchip products meet the specification contained in their particular Microchip Data Sheet.
•
Microchip believes that its family of products is one of the most secure families of its kind on the market today, when used in the
intended manner and under normal conditions.
•
There are dishonest and possibly illegal methods used to breach the code protection feature. All of these methods, to our
knowledge, require using the Microchip products in a manner outside the operating specifications contained in Microchip’s Data
Sheets. Most likely, the person doing so is engaged in theft of intellectual property.
•
•
Microchip is willing to work with the customer who is concerned about the integrity of their code.
Neither Microchip nor any other semiconductor manufacturer can guarantee the security of their code. Code protection does not
mean that we are guaranteeing the product as “unbreakable.”
Code protection is constantly evolving. We at Microchip are committed to continuously improving the code protection features of our
products. Attempts to break Microchip’s code protection feature may be a violation of the Digital Millennium Copyright Act. If such acts
allow unauthorized access to your software or other copyrighted work, you may have a right to sue for relief under that Act.
Information contained in this publication regarding device
applications and the like is provided only for your convenience
and may be superseded by updates. It is your responsibility to
ensure that your application meets with your specifications.
MICROCHIP MAKES NO REPRESENTATIONS OR
WARRANTIES OF ANY KIND WHETHER EXPRESS OR
IMPLIED, WRITTEN OR ORAL, STATUTORY OR
OTHERWISE, RELATED TO THE INFORMATION,
INCLUDING BUT NOT LIMITED TO ITS CONDITION,
QUALITY, PERFORMANCE, MERCHANTABILITY OR
FITNESS FOR PURPOSE. Microchip disclaims all liability
arising from this information and its use. Use of Microchip
devices in life support and/or safety applications is entirely at
the buyer’s risk, and the buyer agrees to defend, indemnify and
hold harmless Microchip from any and all damages, claims,
suits, or expenses resulting from such use. No licenses are
conveyed, implicitly or otherwise, under any Microchip
intellectual property rights unless otherwise stated.
Trademarks
The Microchip name and logo, the Microchip logo, AnyRate, AVR,
AVR logo, AVR Freaks, BeaconThings, BitCloud, CryptoMemory,
CryptoRF, dsPIC, FlashFlex, flexPWR, Heldo, JukeBlox, KEELOQ,
KEELOQ logo, Kleer, LANCheck, LINK MD, maXStylus,
maXTouch, MediaLB, megaAVR, MOST, MOST logo, MPLAB,
OptoLyzer, PIC, picoPower, PICSTART, PIC32 logo, Prochip
Designer, QTouch, RightTouch, SAM-BA, SpyNIC, SST, SST
Logo, SuperFlash, tinyAVR, UNI/O, and XMEGA are registered
trademarks of Microchip Technology Incorporated in the U.S.A.
and other countries.
ClockWorks, The Embedded Control Solutions Company,
EtherSynch, Hyper Speed Control, HyperLight Load, IntelliMOS,
mTouch, Precision Edge, and Quiet-Wire are registered
trademarks of Microchip Technology Incorporated in the U.S.A.
Adjacent Key Suppression, AKS, Analog-for-the-Digital Age, Any
Capacitor, AnyIn, AnyOut, BodyCom, chipKIT, chipKIT logo,
CodeGuard, CryptoAuthentication, CryptoCompanion,
CryptoController, dsPICDEM, dsPICDEM.net, Dynamic Average
Matching, DAM, ECAN, EtherGREEN, In-Circuit Serial
Programming, ICSP, Inter-Chip Connectivity, JitterBlocker,
KleerNet, KleerNet logo, Mindi, MiWi, motorBench, MPASM, MPF,
MPLAB Certified logo, MPLIB, MPLINK, MultiTRAK, NetDetach,
Omniscient Code Generation, PICDEM, PICDEM.net, PICkit,
PICtail, PureSilicon, QMatrix, RightTouch logo, REAL ICE, Ripple
Blocker, SAM-ICE, Serial Quad I/O, SMART-I.S., SQI,
SuperSwitcher, SuperSwitcher II, Total Endurance, TSHARC,
USBCheck, VariSense, ViewSpan, WiperLock, Wireless DNA, and
ZENA are trademarks of Microchip Technology Incorporated in the
U.S.A. and other countries.
SQTP is a service mark of Microchip Technology Incorporated in
the U.S.A.
Microchip received ISO/TS-16949:2009 certification for its worldwide
headquarters, design and wafer fabrication facilities in Chandler and
Tempe, Arizona; Gresham, Oregon and design centers in California
and India. The Company’s quality system processes and procedures
are for its PIC® MCUs and dsPIC® DSCs, KEELOQ® code hopping
devices, Serial EEPROMs, microperipherals, nonvolatile memory and
analog products. In addition, Microchip’s quality system for the design
and manufacture of development systems is ISO 9001:2000 certified.
Silicon Storage Technology is a registered trademark of Microchip
Technology Inc. in other countries.
GestIC is a registered trademark of Microchip Technology
Germany II GmbH & Co. KG, a subsidiary of Microchip Technology
Inc., in other countries.
All other trademarks mentioned herein are property of their
respective companies.
QUALITYꢀMANAGEMENTꢀꢀSYSTEMꢀ
CERTIFIEDꢀBYꢀDNVꢀ
© 2017, Microchip Technology Incorporated, All Rights Reserved.
ISBN: 978-1-5224-1725-5
== ISO/TSꢀ16949ꢀ==ꢀ
2017 Microchip Technology Inc.
DS20005693C-page 33
Worldwide Sales and Service
AMERICAS
ASIA/PACIFIC
ASIA/PACIFIC
EUROPE
Corporate Office
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Technical Support:
http://www.microchip.com/
support
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Tel: 86-592-2388138
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DS20005693C-page 34
2017 Microchip Technology Inc.
11/07/16
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