MIC28512
70VIN, 2A Synchronous Buck Regulator
Features
General Description
• 4.6V to 70V Operating Input Voltage Supply
• Up to 2A Output Current
• Integrated High-Side and Low-Side N-Channel
MOSFETs
• HyperLight Load® (MIC28512-1) and Hyper
Speed Control® (MIC28512-2) Architecture
• Enable Input and Power Good (PGOOD) Output
• Programmable Current-Limit and Foldback
“Hiccup” Mode Short-Circuit Protection
• Built-In 5V Regulator for Single-Supply Operation
• Adjustable 200 kHz to 680 kHz Switching
Frequency
• Fixed 5 ms Soft-Start
• Internal Compensation and Thermal Shutdown
• Thermally-Enhanced 24-Pin 3 mm x 4 mm
FCQFN Package
• –40°C to +125°C Junction Temperature Range
The MIC28512 is a synchronous step-down switching
regulator with internal power switches capable of
providing up to 2A output current from a wide input
supply range from 4.6V to 70V. The output voltage is
adjustable down to 0.8V with a guaranteed accuracy of
±1%. A constant switching frequency can be
programmed from 200 kHz to 680 kHz. The Hyper
Speed Control® and HyperLight Load® architectures of
the MIC28512 allow for high VIN (low VOUT) operation
and ultra-fast transient response while reducing the
required output capacitance and providing very good
light-load efficiency.
The MIC28512 offers a full suite of features to ensure
protection under fault conditions. These include
undervoltage lockout to ensure proper operation under
power sag conditions, internal soft-start to reduce
inrush current, foldback current-limit, “hiccup” mode
short-circuit protection and thermal shutdown.
Applications
2016-2018 Microchip Technology Inc.
Package Type
FREQ
PGND
PGND
SW
MIC28512
24-Pin 3 mm x 4 mm FCQFN (FL)
24
23
22
21
1
20
PVDD
PGND
2
19
VDD
DH
3
18
ILIM
PVIN
4
17
VIN
LX
5
16
EN
BST
6
15
PGOOD
PVIN
7
14
FB
PVIN
8
13
AGND
9
10
11
12
PGND
PGND
SW
27 (SW)
26 (PGND)
DL
25 (PVIN)
Industrial Power Supplies
Distributed Supply Regulation
Base Station Power Supplies
Wall Transformer Regulation
High-Voltage Single-Board Systems
PVIN
•
•
•
•
•
DS20005524B-page 1
MIC28512
Typical Application Circuit
MIC28512
3x4 FQFN
VDD
PVDD
BST
EN
VIN
6V – 60V
ILIM
PVIN
VOUT
5V (0A TO 2A)
SW
MIC28512
VIN
FREQ
LX
FB
AGND
PGND
Functional Block Diagram
VIN
CIN
DBST
CVDD
VIN
VDD PVDD
17
19
PVIN
20
4, 7, 8, 9, 25
BST
LINEAR
REGULATOR
6
UVLO
RBST
3 DH
THERMAL
SHUTDOWN
ON
HSD
OFF
M1
EN
R4
FREQ
L
12, SW
21,
27
16
R3
CBST
FIXED TON
ESTIMATION
24
CONTROL
LOGIC
5
ZCD
VOUT
LX
SOFT-START
LSD
3.3V
15
POWER GOOD
COMPARATOR
gm
PGOOD
X90%
COMPENSATION
RPGOOD
CURRENT
LIMIT
DETECTION
COUT
1 DL
PVDD
RLIM
M2
PGND
10,
11,
22,
23,
26
RINJ
2
VREF
0.8V
PGND
CINJ
18
ILIM
R1
13
AGND
14
CFF
FB
R2
DS20005524B-page 2
2016-2018 Microchip Technology Inc.
MIC28512
1.0
ELECTRICAL CHARACTERISTICS
Absolute Maximum Ratings †
PVIN, VIN to PGND..................................................................................................................................... –0.3V to +76V
VDD, PVDD to PGND..................................................................................................................................... –0.3V to +6V
VBST to VSW, VLX ......................................................................................................................................... –0.3V to +6V
VBST to PGND.....................................................................................................................................–0.3V to (VIN + 6V)
VSW, VLX to PGND...........................................................................................................................–0.3V to (VIN + 0.3V)
VFREQ, VILIM, VEN to AGND .............................................................................................................–0.3V to (VIN + 0.3V)
VFB, VPG to AGND ......................................................................................................................... –0.3V to (VDD + 0.3V)
PGND to AGND ........................................................................................................................................ –0.3V to +0.3V
ESD Rating(1) (HBM) .............................................................................................................................................. 1.5 kV
ESD Rating(1) (MM) ..................................................................................................................................................150V
Operating Ratings ‡
Supply Voltage (PVIN, VIN)......................................................................................................................... +4.6V to +70V
Enable Input (VEN) ..............................................................................................................................................0V to VIN
VSW, VFREQ, VILIM ...............................................................................................................................................0V to VIN
† 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 guaranteed 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.
2016-2018 Microchip Technology Inc.
DS20005524B-page 3
MIC28512
TABLE 1-1:
ELECTRICAL CHARACTERISTICS
Electrical Characteristics: VIN = 12V, TA = 25°C, unless noted. Bold values indicate –40°C ≤ TJ ≤ +125°C.
(Note 1).
Parameters
Min.
Typ.
Max.
Units
Conditions
4.6
—
70
V
—
0.4
0.75
—
0.7
1.5
—
0.1
10
µA
SW unconnected, VEN = 0V
VDD Output Voltage
4.8
5.2
5.4
V
VIN = 7V to 70V, IVDD = 10 mA
VDD UVLO Threshold
3.8
4.2
4.6
V
VDD rising
VDD UVLO Hysteresis
—
400
—
mV
—
Load Regulation at 40 mA
0.6
2
4.0
%
—
0.792
0.8
0.808
0.784
0.8
0.816
—
5
500
EN Logic Level High
1.8
—
—
EN Logic Level Low
—
—
0.6
EN Hysteresis
—
200
—
mV
—
EN Bias Current
—
5
40
µA
VEN = 12V
450
680
800
—
340
—
Maximum Duty Cycle
—
85
—
Minimum Duty Cycle
—
0
—
110
200
270
High-Side NMOS
On-Resistance
—
77
—
Low-Side NMOS
On-Resistance
—
43
—
Current-Limit Threshold
–30
–14
0
Short-Circuit Threshold
–24
–7
8
Current-Limit Source Current
50
70
90
Short-Circuit Source Current
25
36
43
Power Supply Input
Input Voltage Range (PVIN,
VIN)
Quiescent Supply Current
Shutdown Supply Current
mA
—
VFB = 1.5V (MIC28512-1)
VFB = 1.5V (MIC28512-2)
VDD Supply
Reference
Feedback Reference Voltage
FB Bias Current
V
nA
+25°C (±1.0%)
–40°C ≤ TJ ≤ +125°C (±2%)
VFB = 0.8V
Enable Control
V
—
—
Oscillator
Switching Frequency
Minimum Off-Time
kHz
%
ns
VFREQ = VIN
VFREQ = 50% x VIN
—
VFB > 0.8V
—
Internal MOSFET
—
mΩ
—
Short-Circuit Protection
Note 1:
mV
µA
VFB = 0.79V
VFB = 0V
VFB = 0.79V
VFB = 0V
Specification for packaged product only.
DS20005524B-page 4
2016-2018 Microchip Technology Inc.
MIC28512
TABLE 1-1:
ELECTRICAL CHARACTERISTICS (CONTINUED)
Electrical Characteristics: VIN = 12V, TA = 25°C, unless noted. Bold values indicate –40°C ≤ TJ ≤ +125°C.
(Note 1).
Parameters
Min.
Typ.
Max.
Units
Conditions
—
—
50
µA
PGOOD Threshold Voltage
85
90
95
PGOOD Hysteresis
—
6
—
PGOOD Delay Time
—
100
—
µs
Sweep VFB from low to high
PGOOD Low Voltage
—
70
200
mV
VFB < 90% x VNOM, IPGOOD = 1 mA
Overtemperature Shutdown
—
160
—
°C
TJ Rising
Overtemperature Shutdown
Hysteresis
—
15
—
°C
—
—
5
—
ms
—
Leakage
SW, BST Leakage Current
—
Power Good (PGOOD)
%VOUT
Sweep VFB from low to high
Sweep VFB from high to low
Thermal Protection
Soft-Start
Soft-Start Time
Note 1:
Specification for packaged product only.
2016-2018 Microchip Technology Inc.
DS20005524B-page 5
MIC28512
TEMPERATURE SPECIFICATIONS
Parameters
Sym.
Min.
Typ.
Max.
Units
Conditions
Junction Operating Temperature
TJ
–40
—
+125
°C
Note 1
Temperature Ranges
Storage Temperature Range
TS
–65
—
+150
°C
—
Maximum Junction Temperature
TJ
—
—
+150
°C
—
Lead Temperature
—
—
—
+300
°C
Soldering, 10s
JA
—
30
—
°C/W
Package Thermal Resistances
Thermal Resistance 3 mm x 4 mm
FCQFN-24LD
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, θJA). 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.
DS20005524B-page 6
2016-2018 Microchip Technology Inc.
MIC28512
2.0
TYPICAL PERFORMANCE CURVES
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:
4.9
Rising
VOUT = 5V
IOUT = 0A
FSW = 300kHz
4.0
4.7
4.5
VIN THRESHOLD (V)
SUPPLY CURRENT (mA)
5.0
3.0
2.0
4.3
4.1
Falling
3.9
3.7
1.0
VIN=12V
IOUT= 0A
3.5
0.0
5 10 15 20 25 30 35 40 45 50 55 60 65 70
INPUT VOLTAGE (V)
-50
6.0
30.0
5.0
20.0
15.0
10.0
VEN = 0V
REN_PHI = OPEN
5.0
0.0
5.0
FIGURE 2-2:
Input Voltage.
18.0
31.0
44.0
57.0
INPUT VOLTAGE (V)
100
125
VIN = 12V
VOUT = 5V
fSW = 300kHz
4.0
3.0
2.0
-25
FIGURE 2-5:
vs. Temperature.
1.20
Falling
0.90
0.60
Hyst
0.00
5 10 15 20 25 30 35 40 45 50 55 60 65 70
INPUT VOLTAGE (V)
Enable Threshold vs. Input
2016-2018 Microchip Technology Inc.
FEEDBACK VOLTAGE (V)
ENABLE THRESHOLD (V)
75
0
25
50
75
TEMPERATURE (°C)
100
125
Output Peak Current Limit
0.812
Rising
FIGURE 2-3:
Voltage.
50
VIN ULVO Threshold vs.
0.0
-50
1.50
0.30
25
1.0
70.0
VIN Shutdown Current vs.
0
FIGURE 2-4:
Temperature.
35.0
25.0
-25
TEMPERATURE (°C)
CURRENT LIMIT (A)
SHUTDOWN CURRENT (μA)
FIGURE 2-1:
VIN Operating Supply
Current vs. Input Voltage (MIC28512-1).
3.3
VIN = 12V
VOUT = 5.0V
IOUT = 1A
0.808
0.804
0.800
0.796
0.792
-50
-25
0
25
50
75 100
TEMPERATURE (°C)
125
FIGURE 2-6:
Feedback Voltage vs.
Temperature (MIC28512-1).
DS20005524B-page 7
MIC28512
5.3
5.2
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
5.2
5.1
5.0
4.9
VOUT = 5V
IOUT = 1A
fSW = 300kHz
4.8
4.7
5 10 15 20 25 30 35 40 45 50 55 60 65 70
5.1
5.0
4.9
VIN = 12V
VOUT = 5V
4.8
0.0
INPUT VOLTAGE (V)
FIGURE 2-7:
Voltage.
Output Voltage vs. Input
5.0V
3.3V
90
Rising
1.4
EFFICIENCY (%)
ENABLE THRESHOLD (V)
100
1.5
1.3
1.2
1.1
Falling
1.0
0.9
0.8
80
70
60
50
40
30
0.7
VIN = 12V
VDD = 5V
0.6
-25
FIGURE 2-8:
Temperature.
0
25
50
75
TEMPERATURE (°C)
100
20
10
0.01
125
Enable Threshold vs.
90
EFFICIENCY (%)
500
450
400
350
300
250
150
100
0.0
10
0.5
1.0
1.5
OUTPUT CURRENT (A)
80
5.0V
3.3V
70
60
50
40
30
VIN = 12V
VOUT = 5V
20
2.0
FIGURE 2-9:
Switching Frequency vs.
Output Current (MIC28512-2).
DS20005524B-page 8
0.1
1
OUTPUT CURRENT (A)
100
550
200
fSW = 300kHz
FIGURE 2-11:
Efficiency (VIN = 12V) vs.
Output Current (MIC28512-1).
600
SWITCHING FREQUENCY (kHz)
2.0
FIGURE 2-10:
Output Voltage vs. Output
Current (MIC28512-1).
1.6
0.5
-50
0.5
1.0
1.5
OUTPUT CURRENT (A)
10
0.01
fSW = 300kHz
0.1
1
OUTPUT CURRENT (A)
10
FIGURE 2-12:
Efficiency (VIN = 24V) vs.
Output Current (MIC28512-1).
2016-2018 Microchip Technology Inc.
MIC28512
5.2
5.0V
3.3V
80
70
60
50
40
30
5.0
4.9
VIN = 12V
VOUT = 5V
fSW = 300kHz
20
10
0.01
0.1
1
10
OUTPUT CURRENT (A)
FIGURE 2-13:
Efficiency (VIN = 48V) vs.
Output Current (MIC28512-1).
SUPPLY CURRENT (mA)
5.1
4.8
0.0
20.0
5.0V
3.3V
90
16.0
14.0
12.0
10.0
8.0
6.0
VOUT = 5V
IOUT = 0A
fSW = 300kHz
4.0
2.0
0.796
50
40
fSW = 300kHz
0.1
1
OUTPUT CURRENT (A)
100
90
5.0V
3.3V
80
70
60
50
40
30
fSW = 300kHz
20
0.792
-50
10
FIGURE 2-17:
Efficiency (VIN = 12V) vs.
Output Current (MIC28512-2).
EFFICIENCY (%)
0.800
60
10
0.01
VIN = 12V
VOUT = 5.0V
IOUT = 0A
0.804
70
20
0.812
0.808
80
30
5 10 15 20 25 30 35 40 45 50 55 60 65 70
INPUT VOLTAGE (V)
FIGURE 2-14:
VIN Operating Supply
Current vs. Input Voltage (MIC28512-2).
FEEDBACK VOLTAGE (V)
2.0
100
18.0
0.0
0.5
1.0
1.5
OUTPUT CURRENT (A)
FIGURE 2-16:
Output Voltage vs. Output
Current (MIC28512-2).
EFFICIENCY (%)
EFFICIENCY (%)
90
OUTPUT VOLTAGE (V)
100
-25
0 25 50 75 100 125
TEMPERATURE (°C)
FIGURE 2-15:
Feedback Voltage vs.
Temperature (MIC28512-2).
2016-2018 Microchip Technology Inc.
10
0.01
0.1
1
OUTPUT CURRENT (A)
10
FIGURE 2-18:
Efficiency (VIN = 24V) vs.
Output Current (MIC28512-2).
DS20005524B-page 9
MIC28512
EFFICIENCY (%)
90
5.0V
3.3V
80
70
60
50
40
30
f SW = 300kHz
20
10
0.01
0.1
1
OUTPUT CURRENT (A)
IC POWER DISSIPATION (W)
2.4
100
0.8
0.4
0
0.5
1
1.5
OUTPUT CURRENT (A)
2
FIGURE 2-22:
IC Power Dissipation vs.
Output Current (VIN = 48V).
2.5
VIN =12V
fSW = 300kHz
0.8
OUTPUT CURRENT (A)
IC POWER DISSIPATION (W)
5.0V
3.3V
1.2
0.0
1.0
0.6
0.4
5.0V
3.3V
0.2
0
0.5
1
1.5
OUTPUT CURRENT (A)
2
2.0
5.0V
3.3V
1.5
Vin =12V
fSW = 300kHz
Tjmax =125°C
Ĭja = 30°C/W
40°C/W
1.0
0.5
0.0
25
40
55
70
85
100
AMBIENT TEMPERATURE (°C)
FIGURE 2-20:
IC Power Dissipation vs.
Output Current (VIN = 12V).
FIGURE 2-23:
1.2
12V Input Thermal Derating.
2.5
OUTPUT CURRENT (A)
IC POWER DISSIPATION (W)
1.6
10
FIGURE 2-19:
Efficiency (VIN = 48V) vs.
Output Current (MIC28512-2).
0.0
Vin
VIN ==24V
48V
fSW
== 300kHz
300kHz
SW
2.0
VIN =24V
Vin
=24V
fSW = 300kHz
1.0
0.8
5.0V
3.3V
0.6
0.4
0.2
0.0
0
0.5
1
1.5
2
2.0
1.5
1.0
0.5
0.0
25
OUTPUT CURRENT (A)
FIGURE 2-21:
IC Power Dissipation vs.
Output Current (VIN = 24V).
DS20005524B-page 10
FIGURE 2-24:
5.0V
3.3V
Vin =24V
fSW = 300kHz
Tjmax =125°C
Ĭja = 30°C/W
40
55
70
85
100
AMBIENT TEMPERATURE (°C)
24V Input Thermal Derating.
2016-2018 Microchip Technology Inc.
MIC28512
OUTPUT CURRENT (A)
2.5
2.0
1.5
1.0
VIN
(10V/div)
5.0V
3.3V
VSW
(10V/div)
VIN =48V
fSW = 300kHz
TJmax =125°C
ĬJA = 30°C/W
VOUT
(5V/div)
0.5
0.0
25
40
55
70
85
100
AMBIENT TEMPERATURE (°C)
VIN = 12V
VOUT = 5V
IOUT = 2A
IL
(2A/div)
Time (2ms/div)
FIGURE 2-25:
48V Input Thermal Derating.
FIGURE 2-28:
(MIC28512-2).
VIN Shutdown
SWITCHING FREQUENCY (kHz)
305
300
295
VEN
(2V/div)
290
285
280
275
270
VOUT
(2V/div)
fSW(SET) = 300kHz
VOUT = 5V
IOUT = 0A
265
260
VIN = 12V
VOUT = 5V
IOUT = 2A
IL
(1A/div)
255
7.0
16.0
25.0
34.0
43.0
52.0
61.0
70.0
INPUT VOLTAGE (V)
Time (2ms/div)
FIGURE 2-26:
Switching Frequency vs.
Input Voltage (MIC28512-2).
VIN
(10V/div)
FIGURE 2-29:
Enable Turn-On Delay and
Rise Time (MIC28512-2).
VEN
(2V/div)
VSW
(10V/div)
VOUT
(2V/div)
VOUT
(5V/div)
VIN = 12V
VOUT = 5V
IOUT = 2A
IL
(2A/div)
Time (4ms/div)
FIGURE 2-27:
(MIC28512-2).
VIN Soft Start Turn-On
2016-2018 Microchip Technology Inc.
IL
(1A/div)
VIN = 12V
VOUT = 5V
IOUT = 2A
Time (2ms/div)
FIGURE 2-30:
Enable Turn-Off Delay and
Fall Time (MIC28512-2).
DS20005524B-page 11
MIC28512
VIN
(2V/div)
VSW
(10V/div)
VIN = 12V
VOUT = 5V
VEN
(1V/div)
VIN = 12V
VOUT = 5V
IOUT = 2A
VOUT
(2V/div)
IL
(1A/div)
IL
(2A/div)
Time (400ms/div)
Time (1ms/div)
FIGURE 2-31:
VIN Start-Up with 1V
Pre-Biased Output (MIC28512-2).
FIGURE 2-34:
Enable into Short Circuit.
IDC = 10mA
ILDO = 1mA
VIN = 3.6V
VIN
(10V/div)
VSW
(10V/div)
VOUT
(2V/div)
VIN = 12V
VOUT = 5V
IOUT = 2A
VOUT
(2V/div)
VIN = 12V
VOUT = 5V
IL
(1A/div)
IL
(2A/div)
Time (4μs/div)
Time (400ms/div)
FIGURE 2-32:
VIN Start-Up with 2V
Pre-Biased Output (MIC28512-2).
FIGURE 2-35:
Inductor Peak Current
(Output Short Applied) (MIC28512-2).
VIN = 12V
VOUT = 5V
VIN = 12V
VOUT = 5V
VIN
(5V/div)
VOUT
(2V/div)
IL
(1A/div)
IL
(2A/div)
Time (20μs/div)
Time (200ms/div)
FIGURE 2-33:
(MIC28512-2).
DS20005524B-page 12
Start-Up Into Short Circuit
FIGURE 2-36:
Short Circuit (MIC28512-2).
2016-2018 Microchip Technology Inc.
MIC28512
VIN = 12V
VOUT = 5V
VOUT
(2V/div)
VOUT
(2V/div)
VIN = 12V
VOUT = 5V
IL
(1A/div)
IL
(1A/div)
Time (1ms/div)
Time (4μs/div)
FIGURE 2-37:
Inductor Peak Current
(Output Short Applied) (MIC28512-1).
FIGURE 2-40:
Output Recovery from Short
Circuit to No Load.
VIN = 12V
VOUT = 5V
VIN = 12V
VOUT = 5V
VOUT
(2V/div)
VOUT
(2V/div)
IL
(1A/div)
IL
(1A/div)
Time (100μs/div)
Time (20μs/div)
FIGURE 2-38:
Short Circuit (MIC28512-1).
VIN = 12V
VOUT = 5V
VOUT
(2V/div)
IL
(1A/div)
Short Circuit. (MIC28512-1)
VIN = 12V
VOUT = 5V
VIN
(5V/div)
IL
(1A/div)
Time (1ms/div)
FIGURE 2-39:
Circuit to 2A.
FIGURE 2-41:
Output Recovery from Short
2016-2018 Microchip Technology Inc.
Time (100μs/div)
FIGURE 2-42:
Input Voltage Applied with
Output Shorted (MIC28512-1).
DS20005524B-page 13
MIC28512
VIN
(10V/div)
VIN
(5V/div)
IOUT = 2A
VOUT = 5V
VIN = 12V
VOUT
(2V/div)
VPGOOD
(2V/div)
VOUT
(2V/div)
VIN = 12V
VOUT = 5V
IOUT = 2A
IL
(1A/div)
Time (1ms/div)
FIGURE 2-43:
VIN Soft Start Turn-On with
IOUT = 2A (MIC28512-1).
IL
(1A/div)
FIGURE 2-46:
(MIC28512-1).
Time (1ms/div)
Soft Start Power Good
VPREBIAS = 2V
IOUT = 0A
VOUT = 5V
VIN = 12V
VIN
(5V/div)
VOUT
(2V/div)
VOUT
(2V/div)
VIN = 12V
VOUT = 5V
IOUT = 2A
IL
(1A/div)
IL
(1A/div)
Time (200μs/div)
FIGURE 2-44:
(MIC28512-1).
Time (1ms/div)
VIN Shutdown
FIGURE 2-47:
VIN Start-up with Pre-Biased
Output and IOUT = 0A (MIC28512-1).
VPREBIAS = 2V
IOUT = 2A
VOUT = 5V
VIN = 12V
VIN
(5V/div)
IOUT = 0A
VOUT = 5V
VIN = 12V
VOUT
(2V/div)
IL
(1A/div)
IL
(1A/div)
Time (1ms/div)
FIGURE 2-45:
VIN Soft Start Turn-On with
IOUT = 0A (MIC28512-1).
DS20005524B-page 14
VOUT
(2V/div)
Time (1ms/div)
FIGURE 2-48:
VIN Start-up with Pre-Biased
Output and IOUT = 2A (MIC28512-1).
2016-2018 Microchip Technology Inc.
MIC28512
VOUT
AC-Coupled
(50mV/div)
IOUT = 0A
VIN = 12V
VOUT = 5V
VSW
(5V/div)
VOUT
(AC-Coupled)
(20mV/div)
IOUT = 2A
VIN = 12V
VOUT = 5V
VSW
(5V/div)
Time (400μs/div)
Time (1μs/div)
FIGURE 2-49:
MIC28512-1 Switching
Waveform (IOUT = 0A).
VOUT
AC-Coupled
(20mV/div)
IOUT = 0A
VIN = 12V
VOUT = 5V
FIGURE 2-52:
MIC28512-2 Switching
Waveform (IOUT = 2A).
IOUT = 0A to 2A
VIN = 12V
VOUT = 5V
VOUT
(AC-Coupled)
(100mV/div)
IOUT
(1A/div)
VSW
(5V/div)
Time (4ms/div)
Time (1μs/div)
FIGURE 2-50:
MIC28512-2 Switching
Waveform (IOUT = 0A).
VOUT
(AC-Coupled)
(20mV/div)
IOUT = 2A
VIN = 12V
VOUT = 5V
VSW
(5V/div)
FIGURE 2-53:
MIC28512-1 Load Transient
Response (0A to 2A).
IOUT = 0A to 2A
VIN = 12V
VOUT = 5V
VOUT
(AC-Coupled)
(100mV/div)
IOUT
(1A/div)
Time (1μs/div)
FIGURE 2-51:
MIC28512-1 Switching
Waveform (IOUT = 2A).
2016-2018 Microchip Technology Inc.
Time (40μs/div)
FIGURE 2-54:
MIC28512-2 Load Transient
Response (0A to 2A).
DS20005524B-page 15
MIC28512
IOUT = 0.6A to 1.2A
VIN = 12V
VOUT = 5V
IOUT = 0.6A to 1.2A
VIN = 12V
VOUT = 5V
VOUT
(AC-Coupled)
(50mV/div)
VOUT
(AC-Coupled)
(50mV/div)
IOUT
(0.5A/div)
IOUT
(1A/div)
Time (40μs/div)
Time (40μs/div)
FIGURE 2-55:
MIC28512-1 Load Transient
Response (0A to 0.6A).
FIGURE 2-58:
MIC28512-2 Load Transient
Response (0.6A to 1.2A).
IOUT = 0A to 0.6A
VIN = 12V
VOUT = 5V
IOUT = 1.2A to 2A
VIN = 12V
VOUT = 5V
VOUT
(AC-Coupled)
(50mV/div)
VOUT
(AC-Coupled)
(100mV/div)
IOUT
(500mA/div)
IOUT
(1A/div)
Time (40μs/div)
FIGURE 2-56:
MIC28512-2 Load Transient
Response (0A to 0.6A).
IOUT = 0A to 0.6A
VIN = 12V
VOUT = 5V
VOUT
(AC-Coupled)
(50mV/div)
IOUT
(500mA/div)
FIGURE 2-59:
MIC28512-1 Load Transient
Response (1.2A to 2A).
VOUT
(AC-Coupled)
(100mV/div)
IOUT = 1.2A to 2A
VIN = 12V
VOUT = 5V
IOUT
(1A/div)
Time (1ms/div)
FIGURE 2-57:
MIC28512-1 Load Transient
Response (0.6A to 1.2A).
DS20005524B-page 16
Time (40μs/div)
Time (40μs/div)
FIGURE 2-60:
MIC28512-2 Load Transient
Response (1.2A to 2A).
2016-2018 Microchip Technology Inc.
MIC28512
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
DL
Low-Side Gate Drive. Internal low-side power MOSFET gate connection. This pin must
be left unconnected or floating.
2
PGND
PGND is the return path for the low-side driver circuit. Connect to the source of low-side
MOSFET’s (PGND, pins 10, 11 22, 23, and 26) through a low-impedance path.
3
DH
4, 7, 8, 9, 25
(25 is ePad)
PVIN
Power Input Voltage. The PVIN pins supply power to the internal power switch. Connect
all PVIN pins together and bypass locally with ceramic capacitors. The positive terminal
of the input capacitor should be placed as close as possible to the PVIN pins, the
negative terminal of the input capacitor should be placed as close as possible to the
PGND pins 10,11, 22, 23, and 26.
5
LX
The LX pin is the return path for the high-side driver circuit. Connect the negative
terminal of the bootstrap capacitor directly to this pin. Also connect this pin to the SW
pins 12, 21, and 27, with a low-impedance path. The controller monitors voltages on this
and PGND for zero current detection.
6
BST
Bootstrap Pin. This pin provides bootstrap supply for the high-side gate driver circuit.
Connect a 0.1 µF capacitor and an optional resistor in series from the LX (pin 5) to the
BST.
10, 11, 22, 23,
26
(26 is ePad)
PGND
Power Ground. These pins are connected to the source of the low-side MOSFET. They
are the return path for the step-down regulator power stage and should be tied together.
The negative terminal of the input decoupling capacitor should be placed as close as
possible to these pins.
12, 21, 27
(27 is ePad)
SW
Switch Node. The SW pins are the internal power switch outputs. These pins should be
tied together and connected to the output inductor.
13
AGND
Analog Ground. The analog ground for VDD and the control circuitry. The analog ground
return path should be separate from the power ground (PGND) return path.
14
FB
Feedback Input. The FB pin sets the regulated output voltage relative to the internal
reference. This pin is connected to a resistor divider from the regulated output such that
the FB pin is at 0.8V when the output is at the desired voltage.
15
PGOOD
The power good output is an open drain output requiring an external pull-up resistor to
external bias. This pin is a high impedance open circuit when the voltage at FB pin is
higher than 90% of the feedback reference voltage (typically 0.8V).
16
EN
Enable Input. The EN pin enables the regulator. When the pin is pulled below the
threshold, the regulator will shut down to an ultra-low current state. A precise threshold
voltage allows the pin to operate as an accurate UVLO. Do not tie EN to VDD
17
VIN
Supply voltage for the internal LDO. The VIN operating voltage range is from 4.6V to
70V. A ceramic capacitor from VIN to AGND is required for decoupling. The decoupling
capacitor should be placed as close as possible to the supply pin.
18
ILIM
Current Limit Setting. Connect a resistor from this pin to the SW pin node to allow for
accurate current limit sensing programming of the internal low-side power MOSFET.
19
VDD
Internal +5V Linear Regulator: VDD is the internal supply bus for the IC. Connect to an
external 1 µF bypass capacitor. When VIN is 0.8V and the inductor current goes slightly
negative, then the MIC28512-1 automatically powers
down most of the IC circuitry and goes into a low-power
mode.
NO LOAD
VOUT
VFB
VREF
VDH
TOFF(MIN)
FIGURE 4-3:
Response.
In order to meet the stability requirements, the
MIC28512 feedback voltage ripple should be in phase
with the inductor current ripple and large enough to be
sensed by the gM amplifier and the error comparator.
The recommended feedback voltage ripple is 20 mV ~
100 mV.
MIC28512 Load Transient
Once the MIC28512-1 goes into discontinuous mode,
both DH and DL are low, which turns off the high-side
and low-side MOSFETs. The load current is supplied
by the output capacitors and VOUT drops. If the drop of
VOUT causes VFB to go below VREF, then all the circuits
will wake up into normal continuous mode. First, the
bias currents of most circuits reduced during the
discontinuous mode are restored, and then a tON pulse
is triggered before the drivers are turned on to avoid
any possible glitches. Finally, the high-side driver is
turned on. Figure 4-4 shows the control loop timing in
discontinuous mode.
Unlike true current-mode control, the MIC28512 uses
the output voltage ripple to trigger an ON-time period.
The output voltage ripple is proportional to the inductor
2016-2018 Microchip Technology Inc.
DS20005524B-page 19
MIC28512
4.5
IL
IL CROSSES 0 AND VFB > 0.8.
DISCONTINUOUS MODE STARTS
VFB < 0.8. WAKEUP FROM
DISCONTINUOUS MODE.
0
VFB
VREF
ZC
Current Limit
The MIC28512 uses the RDS(ON) of the internal
low-side power MOSFET to sense overcurrent
conditions. In each switching cycle, the inductor current
is sensed by monitoring the low-side MOSFET during
its ON period. The sensed voltage, V(ILIM), is compared
with the power ground (PGND) after a blanking time of
150 ns. The voltage drop of the resistor RILIM is
compared with the low-side MOSFET voltage drop to
set the overcurrent trip level. The small capacitor
connected from the ILIM pin to PGND can be added to
filter the switching node ringing, allowing a better short
limit measurement. The time constant created by RILIM
and the filter capacitor should be much less than the
minimum off time.
The overcurrent limit can be programmed by using
Equation 4-3:
VDH
EQUATION 4-3:
VDL
ESTIMATED ON-TIME
I CLIM + 0.5 I L PP R DS ON + V CL
R ILIM = ----------------------------------------------------------------------------------------------------I CL
Where:
FIGURE 4-4:
MIC28512-1 Control Loop
Timing (Discontinuous Mode).
During discontinuous mode, the bias current of most
circuits are reduced. As a result, the total power supply
current during discontinuous mode is only about
450 μA, allowing the MIC28512-1 to achieve high
efficiency in light load applications.
4.3
VDD Regulator
ICLIM
Desired Output Current Limit
RDS(ON)
On-Resistance of Low-Side Power
MOSFET
VCL
Current limit threshold.
14 mV (typical).
See the Electrical Characteristics table.
ICL
Current-limit source current.
70µA (typical). See the Electrical Characteristics table.
∆IL(PP)
Inductor Current Peak-to-Peak
Use Equation 4-4 to calculate the
inductor ripple current
The MIC28512 provides a 5V regulated VDD to bias
internal circuitry for VIN ranging from 5.5V to 70V.
When VIN is less than 5.5V, VDD should be tied to VIN
pins to bypass the internal linear regulator.
The peak-to-peak inductor current ripple is calculated
with Equation 4-4.
4.4
EQUATION 4-4:
Soft-Start
Soft-start reduces the power supply inrush current at
startup by controlling the output voltage rise time while
the output capacitor charges.
The MIC28512 implements an internal digital soft-start
by ramping up the 0.8V reference voltage (VREF) from
0 to 100% in about 5 ms with 9.7 mV steps. This
controls the output voltage rate of rise at turn on,
minimizing inrush current and eliminating output
voltage overshoot. Once the soft-start cycle ends, the
related circuitry is disabled to reduce current
consumption.
DS20005524B-page 20
V OUT V IN MAX – V OUT
I L PP = -------------------------------------------------------------------V IN MAX f SW L
The MOSFET RDS(ON) varies 30% to 40% with
temperature; therefore, it is recommended to use the
RDS(ON) at maximum junction temperature with a 20%
margin to calculate RILIM in Equation 4-3.
In case of hard short, the current-limit threshold is
folded down to allow an indefinite hard short on the
output without any destructive effect. It is mandatory to
make sure that the inductor current used to charge the
output capacitor during soft-start is under the folded
short limit; otherwise the supply will go into hiccup
mode and may not be finishing the soft-start
successfully.
2016-2018 Microchip Technology Inc.
MIC28512
When operating at higher input voltages, it is
recommended to look at safe operating area (SOA)
curves while selecting output current limit threshold.
SOA curves for MIC28512 are given in Figure 2-24 and
Figure 2-25 in the Typical Performance Curves section.
4.6
Output Current Thermal Derating
MIC28512 is packaged in a 3 mm x 4 mm FQFN
package. The output current derates with temperature
when operating with higher input voltages at higher
temperatures as shown in Figure 2-24 and
Figure 2-25.
4.7
Power Good (PG)
The power good (PG) pin is an open-drain output that
indicates logic-high when the output is nominally 90%
of its steady state voltage.
4.8
MOSFET Gate Drive
The Functional Block Diagram shows a bootstrap
circuit, consisting of DBST, CBST, and RBST. 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.
When the high-side MOSFET driver is turned on,
energy from CBST is used to turn the MOSFET on. As
the high-side MOSFET turns on, the voltage on the SW
pin increases to approximately VIN. Diode DBST is
reverse-biased and CBST floats high while continuing to
bias the high-side gate driver. The bias current of the
high-side driver is less than 10 mA, so a 0.1 μF to 1 μF
capacitor is sufficient to hold the gate voltage with
minimal droop for the power stroke (high-side
switching) cycle, i.e. ∆BST = 10 mA x 1.25 μs/0.1 μF =
125 mV. When the low-side MOSFET is turned back
on, CBST is then recharged through the boost diode. A
30Ω resistor RBST, which is in series with the CBST
capacitor, is required to slow down the turn-on time of
the high-side N-channel MOSFET.
2016-2018 Microchip Technology Inc.
DS20005524B-page 21
MIC28512
5.0
APPLICATION INFORMATION
5.2
5.1
Output Voltage Setting
Components
The MIC28512 switching frequency can be adjusted
between 200 kHz and 680 kHz by changing the resistor
divider network from VIN.
Setting the Switching Frequency
The MIC28512 requires two resistors to set the output
voltage as shown in Figure 5-1.
VIN
R3
MIC28512
R1
FB
gM AMP
FREQ
R2
R4
VREF
FIGURE 5-1:
Configuration.
GND
Voltage Divider
The output voltage is determined by Equation 5-1.
FIGURE 5-2:
Adjustment.
Switching Frequency
Equation 5-3 gives the estimated switching frequency.
EQUATION 5-3:
EQUATION 5-1:
R4
f SW = f 0 --------------------
R3 + R4
R1
V OUT = V FB 1 + -------
R2
Where:
Where:
VFB
0.8V
Figure 5-3 shows the switching frequency versus the
resistor R4 when R3 = 100 kΩ.
700
5 Nȍ,OUT = 1A 9,1 9
600
SW FREQ (kHz)
A typical value of R1 used on the standard evaluation
board is 10 kΩ. If R1 is too large, it may allow noise to
be introduced into the voltage feedback loop. If R1 is
too small in value, it will decrease the efficiency of the
buck regulator, especially at light loads. Once R1 is
selected, R2 can be calculated using Equation 5-2:
Switching frequency when R4 is open;
typically 680 kHz.
f0
EQUATION 5-2:
V FB R1
R2 = ----------------------------V OUT – V FB
9,1 9
500
9,1 9
400
300
200
100
0
10
1000
100
10000
R4 (k)
FIGURE 5-3:
5.3
Switching Frequency vs. R4.
Inductor Selection
Values for inductance, peak, and RMS currents are
required to select the output inductor. The input and
output voltages and the inductance value determine
the peak-to-peak inductor ripple current. Generally,
higher inductance values are used with higher input
voltages. Larger peak-to-peak ripple currents will
increase the power dissipation in the inductor and
DS20005524B-page 22
2016-2018 Microchip Technology Inc.
MIC28512
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:
ignored. At lower output currents, the core losses can
be a significant contributor. Core loss information is
usually available from the magnetics vendor. Copper
loss in the inductor is calculated by Equation 5-7:
EQUATION 5-4:
The resistance of the copper wire, DCR, increases with
the temperature. The value of the winding resistance
used should be at the operating temperature.
V OUT V IN MAX – V OUT
L = -------------------------------------------------------------------V IN MAX I L PP f SW
EQUATION 5-7:
2
P L CU = I L RMS DCR
EQUATION 5-8:
Where:
fSW
Switching Frequency
∆IL(PP)
The peak-to-peak inductor current
ripple; typically 20% of the maximum
output current
In continuous conduction mode, the peak inductor
current is equal to the average output current plus one
half of the peak-to-peak inductor current ripple.
EQUATION 5-5:
Where:
TH
Temperature of wire under full load
T20C
Room temperature
DCR(20C)
Room temperature winding resistance
(usually specified by the manufacturer)
5.4
I L PK = I OUT + 0.5 I L PP
The RMS inductor current is used to calculate the I2R
losses in the inductor.
EQUATION 5-6:
2
I L RMS =
DCR HT = DCR 20C 1 + 0.0042 T H – T 20C
2 I L PP
I OUT MAX + --------------------12
Output Capacitor Selection
The type of the output capacitor is usually determined
by its equivalent series resistance (ESR). Voltage and
RMS current capability are also important factors in
selecting an output capacitor. Recommended capacitor
types are ceramic, tantalum, low-ESR aluminum
electrolytic, OS-CON and POSCAP. For high ESR
electrolytic capacitors, ESR is the main cause of the
output ripple. The output capacitor ESR also affects the
control loop from a stability point of view. For a low ESR
ceramic output capacitor, ripple is dominated by the
reactive impedance. The maximum value of ESR is
calculated by Equation 5-9.
EQUATION 5-9:
ESR C
Maximizing efficiency requires the proper selection of
core material and minimizing the winding resistance.
The high-frequency operation of the MIC28512
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 buck regulator. This is
especially noticeable at low output power. The winding
resistance decreases efficiency at the higher output
current levels.
OUT
V OUT PP
--------------------------I L PP
Where:
∆VOUT(PP)
Peak-to-Peak Output Voltage Ripple
∆IL(PP)
Peak-to-Peak Inductor Current Ripple
The total output ripple is a combination of voltage
ripples caused by the ESR and output capacitance.
The total ripple is calculated by Equation 5-10.
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
2016-2018 Microchip Technology Inc.
DS20005524B-page 23
MIC28512
EQUATION 5-10:
EQUATION 5-13:
V OUT PP =
2
I L PP
------------------------------------- + I L PP ESR COUT 2
C OUT f SW 8
Where:
COUT
Output Capacitance Value
fSW
Switching Frequency
As described in the Theory of Operation subsection of
the Functional Description, the MIC28512 requires at
least 20 mV peak-to-peak ripple at the FB pin for the gM
amplifier and the error comparator to operate properly.
Also, the ripple on FB pin 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 the
enough feedback voltage ripple. Refer to the Ripple
Injection subsection for details.
The voltage rating of the capacitor should be twice the
output voltage for a tantalum and 20% greater for
aluminum electrolytic or OS-CON. The output capacitor
RMS current is calculated in Equation 5-11.
EQUATION 5-11:
IC
OUT RMS
I L PP
= -----------------12
The power dissipated in the output capacitor is
calculated by using:
EQUATION 5-12:
2
P DISS COUT = I COUT RMS ESR COUT
5.5
V IN = I L PK ESR CIN
The input capacitor must be rated for the input current
ripple. The RMS value of input capacitor current is
determined at the maximum output current. Assuming
the peak-to-peak inductor current ripple is low:
EQUATION 5-14:
I CIN RMS I OUT MAX D 1 – D
The power dissipated in the input capacitor is:
EQUATION 5-15:
2
P DISS CIN = I CIN RMS ESR CIN
5.6
Ripple Injection
The VFB ripple required for proper operation of the
MIC28512’s gM amplifier and error comparator is
20 mV to 100 mV. However, the output voltage ripple is
generally designed as 1% to 2% of the output voltage.
If the feedback voltage ripple is so small that the gM
amplifier and error comparator can’t sense it, then the
MIC28512 will lose control and the output voltage is not
regulated. In order to have some amount of VFB ripple,
a ripple injection method is applied for low output
voltage ripple applications.
The applications are divided into three situations
according to the amount of the feedback voltage ripple:
• Enough ripple at the feedback voltage due to the
large ESR of the output capacitors (Figure 5-4).
The converter is stable without any ripple
injection.
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
subjected to high inrush currents, caused by turning the
input supply on. 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
de-rating. 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:
DS20005524B-page 24
FIGURE 5-4:
Enough Ripple at FB.
The feedback voltage ripple is:
2016-2018 Microchip Technology Inc.
MIC28512
EQUATION 5-16:
EQUATION 5-19:
R2
V FB PP = -------------------- ESR C I L PP
OUT
R1 + R2
Where:
1
V FB PP = V IN K div D 1 – D ----------------f SW
Where:
∆IL(PP)
Peak-to-Peak Value of the Inductor
Current Ripple
VIN
Power stage input voltage
D
Duty cycle
• Inadequate ripple at the feedback voltage due to
the small ESR of the output capacitors.
fSW
Switching frequency
τ
(R1//R2//RINJ) x CFF
The output voltage ripple is fed into the FB pin
through a feed-forward capacitor, CFF in this
situation, as shown in Figure 5-5. The typical CFF
value is selected by using Equation 5-17.
EQUATION 5-17:
10
R1 C FF -------f SW
With the feed-forward capacitor, the feedback
voltage ripple is very close to the output voltage
ripple.
EQUATION 5-18:
V FB PP ESR I L PP
EQUATION 5-20:
R1//R2
K div = ----------------------------------R INJ + R1//R2
In Equation 5-19 and Equation 5-20, it is assumed that
the time constant associated with CFF must be much
greater than the switching period:
EQUATION 5-21:
1 - T
---------------= --- « 1
f SW
If the voltage divider resistors R1 and R2 are in the kΩ
range, a CFF of 1 nF to 100 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.
The process of sizing the ripple injection resistor and
capacitors is as follows.
FIGURE 5-5:
Inadequate Ripple at FB.
• 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 5-6.
• Select CFF to feed all output ripples into the
feedback pin and make sure the large time
constant assumption is satisfied. Typical choice of
CFF is 1 nF to 100 nF if R1 and R2 are in the kΩ
range.
• Select RINJ according to the expected feedback
voltage ripple using Equation 5-22:
EQUATION 5-22:
f SW
V FB PP
K div = ----------------------- ---------------------------V IN
D 1 – D
The value of RINJ is calculated using Equation 5-23.
EQUATION 5-23:
FIGURE 5-6:
Invisible Ripple at FB.
The injected ripple is calculated via:
2016-2018 Microchip Technology Inc.
1
R INJ = R1//R2 ---------- – 1
K div
• Select CINJ as 100 nF, which could be considered
as short for a wide range of the frequencies.
DS20005524B-page 25
MIC28512
5.7
Output Current Thermal Derating
with SOA at High Input Voltage
For the MIC28512, at VIN = 70V, VOUT = 5V, TA = 25°C,
the maximum output current IOUT(MAX) is about 1.8A
because the IOUT(MAX) starts derating to less than 2A at
a TA around 15°C. The IOUT(MAX) further reduces as the
ambient temperature increases. When output current
derating starts, the IOUT(MAX) is inversely proportional
to the device package thermal resistance θJA, and
output voltage VOUT, and is directly proportional to the
factor η/(1 – η) where η is the converter efficiency. The
derate-starting ambient temperature depends on the
MIC28512 device maximum operating junction
temperature TJ(MAX), the maximum output current
IOUT(MAX) without derating (which is the desired
maximum output current limit ICLIM), the output voltage
VOUT, the device package thermal resistance θJA, and
the factor (1 – η)/η. For the examples of typical output
current derating curves (SOA curves) for MIC28512,
please refer to Figure 2-24 and Figure 2-25.
The maximum output current of MIC28512 with the
device at the maximum junction temperature TJ(MAX)
operating over the ambient temperature TA range can
be estimated by Equation 5-24.
EQUATION 5-24:
T J MAX
1
I OMAX TJMAX = – -------- T A + -------------------- + P D L ------------------------------------ JA
JA
V OUT 1 –
Where:
θJA = Device Package Thermal Resistance, which is 30°C/W for the 3 mm x 4 mm FCQFN-24LD.
η = Buck Converter Efficiency, for VOUT = 5V about 72% at VIN = 70V, 82% at VIN = 48V, 88% at VIN = 24V.
TJ(MAX) = Device Maximum Operating Junction Temperature, which is 125°C.
TA = Ambient Temperature.
VOUT = Output Voltage.
PD(L) = Inductor Power Dissipation due to DCR.
The inductor power dissipation due to DCR in
Equation 5-24 can be approximated by Equation 5-25.
EQUATION 5-25:
Because the maximum output current without thermal
derating in the SOA curve is equal to the desired output
current limit ICLIM, the maximum output current in the
SOA curve can be defined by Equation 5-26.
EQUATION 5-26:
2
P D L I OUT DCR
Where:
IOUT = Output Current.
DCR = Power Inductor DC Resistance.
I CLIM for T A T A DS
I OUT MAX =
I OMAX TJMAX for T A T A DS
Where:
ICLIM = Desired Output Current Limit.
TA(DS) = Derate-Starting Ambient Temperature.
The derate-starting ambient temperature can be predicted using Equation 5-27.
EQUATION 5-27:
1–
T A DS T J MAX – I CLIM V OUT ------------ – P D L JA
DS20005524B-page 26
2016-2018 Microchip Technology Inc.
MIC28512
If the IOUT(MAX) starts derating at an ambient temperature less than the user’s actual maximum operating ambient
temperature TA(MAX,OP), the IOUT(MAX) at TA(MAX,OP) in the SOA curve will be less than the desired output current limit
ICLIM. Then, the desired output current limit ICLIM needs to be reduced to avoid the actual operating output current being
out of the SOA curve boundary and to ensure safe operation. The output current limit in such condition can be estimated
by Equation 5-28.
EQUATION 5-28:
T J MAX – T A MAX,OP
I CLIM ------------------------------------------------------ + P D L ------------------------------------V OUT 1 –
JA
Where:
TA(MAX,OP) = User’s Actual Maximum Operating Ambient Temperature.
TJ(MAX) = Device Maximum Operating Junction Temperature, which is 125°C.
θJA = Device Package Thermal Resistance, which is 30°C/W for the 3 mm x 4 mm FCQFN-24LD.
2016-2018 Microchip Technology Inc.
DS20005524B-page 27
MIC28512
6.0
PCB LAYOUT GUIDELINES
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 and
signal return paths.
Figure 6-1 is optimized from a small form-factor point of
view and shows the top and bottom layers of a
four-layer PCB. It is recommended to use Mid-Layer 1
as a continuous ground plane.
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
with power is suddenly applied.
6.3
• Do not route any digital lines underneath or close
to the SW node.
• Keep the switch node (SW) away from the
feedback (FB) pin.
6.4
FIGURE 6-1:
Top and Bottom Layers of a
Four-Layer Board.
The following guidelines should be followed to ensure
proper operation of the MIC28512 converter.
6.1
IC
• The analog ground pin (AGND) must be
connected directly to the ground planes. Do not
route the AGND pin to the PGND pin on the top
layer.
• Place the IC close to the point-of-load (POL).
• Use copper planes to route the input and output
power lines.
• Analog and power grounds should be kept
separate and connected at only one location.
6.2
Input Capacitor
• Place the input capacitors on the same side of the
board and as close to the PVIN and PGND pins as
possible.
• 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.
• Do not replace the ceramic input capacitor with
any other type of capacitor. Any type of capacitor
can be placed in parallel with the input capacitor.
• If a Tantalum input capacitor is placed in parallel
with the input capacitor, it must be recommended
for switching regulator applications and the
SW Node
Output Capacitor
• Use a copper island to connect the output
capacitor ground terminal to the input capacitor
ground terminal.
• 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 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.
6.5
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 thermal couple that comes with a thermal
meter. This thermal couple wire gauge is large, typically
22 gauge, and behaves like a heat sink, resulting in a
lower case measurement.
Two methods of temperature measurement are using a
smaller thermal couple wire or an infrared
thermometer. If a thermal couple wire is used, it must
be constructed of 36 gauge wire or higher then (smaller
wire size) to minimize the wire heat-sinking effect. In
addition, the thermal couple tip must be covered in
either thermal grease or thermal glue to make sure that
the thermal couple junction is making good contact with
the case of the IC. Omega brand thermal couple
(5SC-TT-K-36-36) is adequate for most applications.
Wherever possible, an infrared thermometer is
recommended. The measurement spot size of most
infrared thermometers is too large for an accurate
reading on a small form factor ICs. However, an IR
thermometer from Optris has a 1 mm spot size, which
makes it a good choice for measuring the hottest point
on the case. An optional stand makes it easy to hold the
beam on the IC for long periods of time.
For more information about the Evaluation board layout, please contact Microchip sales.
DS20005524B-page 28
2016-2018 Microchip Technology Inc.
MIC28512
7.0
PACKAGING INFORMATION
7.1
Package Marking Information
24-Lead FQFN*
Legend: XX...X
Y
YY
WW
NNN
e3
*
Example
Product code or customer-specific information
Year code (last digit of calendar year)
Year code (last 2 digits of calendar year)
Week code (week of January 1 is week ‘01’)
Alphanumeric traceability code
Pb-free JEDEC® designator for Matte Tin (Sn)
This package is Pb-free. The Pb-free JEDEC designator ( e3 )
can be found on the outer packaging for this package.
●, ▲, ▼ Pin one index is identified by a dot, delta up, or delta down (triangle
mark).
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. Package may or may not include
the corporate logo.
Underbar (_) and/or Overbar (⎯) symbol may not be to scale.
2016-2018 Microchip Technology Inc.
DS20005524B-page 29
MIC28512
24-Lead FQFN 3 mm x 4 mm Package Outline and Recommended Land Pattern
Note:
For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging.
DS20005524B-page 30
2016-2018 Microchip Technology Inc.
MIC28512
Note:
For the most current package drawings, please see the Microchip Packaging Specification located at
http://www.microchip.com/packaging.
2016-2018 Microchip Technology Inc.
DS20005524B-page 31
MIC28512
NOTES:
DS20005524B-page 32
2016-2018 Microchip Technology Inc.
MIC28512
APPENDIX A:
REVISION HISTORY
Revision A (April 2016)
• Converted Micrel document MIC28512 to Microchip data sheet template DS20005520A.
• Minor text changes throughout.
Revision B (July 2018)
• Updated VIN value in Typical Application Circuit.
• Updated Equation 4-3, Equation 5-6, Equation 510.
• Updated Absolute Maximum Ratings †.
• Updated content in Section 4.5, Current Limit.
• Added Section 4.6, Output Current Thermal Derating.
• Added Section 5.7, Output Current Thermal Derating with SOA at High Input Voltage.
• Added Section 7.1, Package Marking Information.
• Various typographical edits.
2016-2018 Microchip Technology Inc.
DS20005524B-page 33
MIC28512
NOTES:
DS20005524B-page 34
2016-2018 Microchip Technology Inc.
MIC28512
PRODUCT IDENTIFICATION SYSTEM
To order or obtain information, e.g., on pricing or delivery, contact your local Microchip representative or sales office.
PART NO.
Device
X
X
Architecture Temperature
Device:
MIC28512:
Architecture:
1
2
=
=
HyperLight Load
Hyper Speed Control
Temperature:
Y
=
–40°C to +125°C
Package:
FL
=
Media Type:
T5
TR
XX
Package
-XX
Examples:
a) MIC28512-1YFL-T5:
Media
Type
–40°C to +125°C Junction
Temperature Range,
24LD FQFN, 500/Reel
70VIN, 2A Synchronous Buck Regulator
b) MIC28512-1YFL-TR:
Note 1:
=
=
c) MIC28512-2YFL-T5:
70VIN, 2A Synchronous Buck
Regulator, Hyper Speed Control,
–40°C to +125°C Junction
Temperature Range,
24LD FQFN, 500/Reel
d) MIC28512-2YFL-TR:
FQFN is a lead-free package. Pb-Free lead finish is Matte Tin.
70VIN, 2A Synchronous Buck
Regulator, Hyper Speed
Control, –40°C to +125°C
Junction Temperature Range,
24LD FQFN, 5,000/Reel
Note 1:
2016-2018 Microchip Technology Inc.
70VIN, 2A Synchronous Buck
Regulator, HyperLight Load,
–40°C to +125°C Junction
Temperature Range,
24LD FQFN, 5,000/Reel
24-Pin 3 mm x 4 mm FQFN; Note 1
500/Reel
5,000/Reel
70VIN, 2A Synchronous Buck
Regulator, HyperLight Load,
Tape and Reel identifier only appears in the
catalog part number description. This identifier is
used for ordering purposes and is not printed on
the device package. Check with your Microchip
Sales Office for package availability with the
Tape and Reel option.
DS20005524B-page 35
MIC28512
NOTES:
DS20005524B-page 36
2016-2018 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
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.
SQTP is a service mark of Microchip Technology Incorporated in
the U.S.A.
QUALITY MANAGEMENT SYSTEM
CERTIFIED BY DNV
== ISO/TS 16949 ==
2016-2018 Microchip Technology Inc.
The Microchip name and logo, the Microchip logo, AnyRate, AVR,
AVR logo, AVR Freaks, BitCloud, chipKIT, chipKIT logo,
CryptoMemory, CryptoRF, dsPIC, FlashFlex, flexPWR, Heldo,
JukeBlox, KeeLoq, Kleer, LANCheck, LINK MD, maXStylus,
maXTouch, MediaLB, megaAVR, MOST, MOST logo, MPLAB,
OptoLyzer, PIC, picoPower, PICSTART, PIC32 logo, Prochip
Designer, QTouch, 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, CodeGuard,
CryptoAuthentication, CryptoAutomotive, CryptoCompanion,
CryptoController, dsPICDEM, dsPICDEM.net, Dynamic Average
Matching, DAM, ECAN, EtherGREEN, In-Circuit Serial
Programming, ICSP, INICnet, Inter-Chip Connectivity,
JitterBlocker, KleerNet, KleerNet logo, memBrain, Mindi, MiWi,
motorBench, MPASM, MPF, MPLAB Certified logo, MPLIB,
MPLINK, MultiTRAK, NetDetach, Omniscient Code Generation,
PICDEM, PICDEM.net, PICkit, PICtail, PowerSmart, PureSilicon,
QMatrix, 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
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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.
© 2016-2018, Microchip Technology Incorporated, All Rights
Reserved.
ISBN: 978-1-5224-3360-6
DS20005524B-page 37
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