MIC45212-1/-2
26V, 14A DC-to-DC Power Module
Features
General Description
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The MIC45212 is a synchronous, step-down regulator
module, featuring a unique adaptive ON-time control
architecture. The module incorporates a DC-to-DC controller, power MOSFETs, bootstrap diode, bootstrap
capacitor and an inductor in a single package, simplifying
the design and layout process for the end user.
•
•
•
•
•
•
•
•
•
•
No Compensation Required
Up to 14A Output Current
>93% Peak Efficiency
Output Voltage: 0.8V to 0.85*VIN with
±1% Accuracy
Adjustable Switching Frequency from 200 kHz to
600 kHz
Enable Input and Open-Drain Power Good Output
Hyper Speed Control® (MIC45212-2) Architecture
enables Fast Transient Response
HyperLight Load® (MIC45212-1) improves Light
Load Efficiency
Supports Safe Start-up into Pre-Biased Output
–40°C to +125°C Junction Temperature Range
Thermal Shutdown Protection
Short-Circuit Protection with Hiccup mode
Adjustable Current Limit
Available in 64-Pin 12 mm x 12 mm x 4 mm QFN
Package
This highly integrated solution expedites system
design and improves product time-to-market. The internal MOSFETs and inductor are optimized to achieve
high efficiency at a low output voltage. The fully optimized design can deliver up to 14A current under a
wide input voltage range of 4.5V to 26V, without requiring additional cooling.
The MIC45212-1 uses the HyperLight Load (HLL) while
the MIC45212-2 uses the Hyper Speed Control (HSC)
architecture, which enables ultra-fast load transient
response, allowing for a reduction of output capacitance. The MIC45212 offers 1% output accuracy that
can be adjusted from 0.8V to 0.85*VIN with two external
resistors. Additional features include thermal shutdown
protection, input undervoltage lockout, adjustable current limit and short-circuit protection. The MIC45212
allows for safe start-up into a pre-biased output.
Applications
•
•
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High-Power Density Point-of-Load Conversion
Servers, Routers, Networking, and Base Stations
FPGAs, DSP and Low-Voltage ASIC Power Supplies
Industrial and Medical Equipment
Typical Application Schematic
VIN
12V
PVDD
ANODE
5VDD
BST
PG
RIA
PVIN
VOUT
MIC45212
VIN
CIN
FREQ
FB
RIB
VOUT
0.8V to 0.85 * VIN/Up to 14A
CFF
OFF
COUT
RFB2
SW
ON
RFB1
RLIM
EN
GND
2018 Microchip Technology Inc.
ILIM
PGND
DS20005607B-page 1
MIC45212-1/-2
Package Types
1
PVDD
2
54
53
KEEPOUT
55
BST
56
BST
57
NC
58
BST
GND
59
PG
60
FB
61
VIN
5VDD
62
EN
63
FREQ
GND
64
GND
5VDD
MIC45212-1/-2
64-Pin 12 mm x 12 mm x 4 mm QFN (Top
View)
52 51
50
BST
ANODE
48
RIB
RIA
PVDD
3
ILIM
4
47
PGND
5
46
RIA
6
45
KEEPOUT
SW
7
44
SW
SW
8
43
SW
SW
9
42
SW
SW
10
41
SW
KEEPOUT
11
40
SW
PVIN
12
39
SW
PVIN
13
38
SW
PVIN
14
37
KEEPOUT
PVIN
15
PGND
PGND
SW
PVIN ePAD
36
VOUT
VOUT
VOUT ePAD
PVIN
16
35
PVIN
17
34
VOUT
PVIN
18
33
VOUT
31
VOUT
30
32
VOUT
29
VOUT
VOUT
28
VOUT
27
VOUT
26
VOUT
25
VOUT
24
VOUT
23
KEEPOUT
22
PVIN
21
PVIN
20
PVIN
19
PVIN
DS20005607B-page 2
ANODE
49
2018 Microchip Technology Inc.
MIC45212-1/-2
Functional Block Diagram
VIN
5VDD
VDD
VIN
PVIN
PVDD
PVDD
VOUT
ILIM
ILIM
2018 Microchip Technology Inc.
DS20005607B-page 3
MIC45212-1/-2
1.0
ELECTRICAL CHARACTERISTICS
Absolute Maximum Ratings†
VPVIN, VVIN to PGND................................................................................................................................. –0.3V to +30V
VPVDD, V5VDD, VANODE to PGND ................................................................................................................ –0.3V to +6V
VSW, VFREQ, VILIM, VEN to PGND .................................................................................................. –0.3V to (VIN + 0.3V)
VBST to VSW................................................................................................................................................. –0.3V to +6V
VBST to PGND .......................................................................................................................................... –0.3V to +36V
VPG to PGND .............................................................................................................................. –0.3V to (5VDD + 0.3V)
VFB, VRIB to PGND...................................................................................................................... –0.3V to (5VDD + 0.3V)
PGND to GND ........................................................................................................................................... -0.3V to +0.3V
Junction Temperature........................................................................................................................................... +150°C
Storage Temperature (TS) ..................................................................................................................... –65°C to +150°C
Lead Temperature (soldering, 10s) ...................................................................................................................... +260°C
†
Notice: Stresses above those listed under “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.
Operating Ratings(1)
Supply Voltage (VPVIN, VVIN) ......................................................................................................................... 4.5V to 26V
Output Current ........................................................................................................................................................... 14A
Enable Input (VEN) ............................................................................................................................................ 0V to VIN
Power-Good (VPG) ......................................................................................................................................... 0V to 5VDD
Junction Temperature (TJ)..................................................................................................................... –40°C to +125°C
Junction Thermal Resistance(2)
12 mm x 12 mm x 4 mm QFN-64 (JA) ...........................................................................................................12.6°C/W
12 mm x 12 mm 4 mm QFN-64 (JC) ................................................................................................................3.5°C/W
Note 1: The device is not ensured to function outside the operating range.
2: JA and JC were measured using the MIC45212 evaluation board.
DS20005607B-page 4
2018 Microchip Technology Inc.
MIC45212-1/-2
ELECTRICAL CHARACTERISTICS(1)
TABLE 1-1:
Electrical Specifications: unless otherwise specified, VPVIN = VVIN; VIN = VEN = 12V; VOUT = 3.3V;
VBST – VSW = 5V; TJ = +25°C. Boldface values indicate –40°C TJ +125°C.
Symbol
Parameter
Min.
Typ.
Max.
Units
Test Conditions
Power Supply Input
VIN, VPVIN
Input Voltage Range
4.5
—
26
V
IQ
Quiescent Supply Current
(MIC45212-1)
—
—
0.75
mA
VFB = 1.5V
IQ
Quiescent Supply Current
(MIC45212-2)
—
2.1
3
mA
VFB = 1.5V
—
0.37
—
mA
PVIN = VIN = 12V,
VOUT = 1.8V, IOUT = 0A,
fSW = 600 kHz
—
IIN
Operating Current:
MIC45208-1
—
54
—
ISHDN
Shutdown Supply Current
—
0.1
10
µA
SW = Unconnected, VEN = 0V
VDD
5VDD Output Voltage
4.8
5.1
5.4
V
VIN = 7V to 26V, I5VDD = 10
mA
UVLO
MIC45208-2
5VDD Output
5VDD UVLO Threshold
3.8
4.2
4.6
V
V5VDD Rising
UVLO_HYS 5VDD UVLO Hysteresis
—
400
—
mV
V5VDD Falling
VDD(LR)
0.6
2
3.6
%
0.792
0.8
0.808
0.784
0.8
0.816
—
5
500
nA
LDO Load Regulation
I5VDD = 0 to 40 mA
Reference
VFB
Feedback Reference Voltage
IFB_BIAS
Feedback Bias Current
V
TJ = +25°C
–40°C TJ +125°C
VFB = 0.8V
Enable Control
ENHIGH
EN Logic Level High
1.8
—
—
V
—
ENLOW
EN Logic level Low
—
—
0.6
V
—
ENHYS
EN Hysteresis
—
200
—
mV
—
IENBIAS
EN Bias Current
—
5
10
µA
VEN = 12V
400
600
750
—
350
—
Oscillator
VFREQ = VIN, IOUT = 2A
fSW
Switching Frequency
DMAX
Maximum Duty Cycle
—
85
—
%
—
DMIN
Minimum Duty Cycle
—
0
—
%
VFB = 1V
tOFF(MIN)
Minimum OFF-Time
140
200
260
ns
—
—
3
—
ms
FB Rising from 0V to 0.8V
VCL_OFFSET Current-Limit Threshold
–30
–14
0
mV
VFB = 0.79V
VSC
Short-Circuit Threshold
–23
–7
9
mV
VFB = 0V
ICL
Current-Limit Source Current
50
70
90
µA
VFB = 0.79V
ISC
Short-Circuit Source Current
25
35
45
µA
VFB = 0V
ISW_Leakage
SW, BST Leakage Current
—
—
10
µA
—
IFREQ_LEAK
FREQ Leakage Current
—
—
10
µA
—
kHz
VFREQ = 50% VIN, IOUT = 2A
Soft Start
tSS
Soft Start Time
Short-Circuit Protection
Leakage
Note 1:
Specification for packaged product only.
2018 Microchip Technology Inc.
DS20005607B-page 5
MIC45212-1/-2
TABLE 1-1:
ELECTRICAL CHARACTERISTICS(1) (CONTINUED)
Electrical Specifications: unless otherwise specified, VPVIN = VVIN; VIN = VEN = 12V; VOUT = 3.3V;
VBST – VSW = 5V; TJ = +25°C. Boldface values indicate –40°C TJ +125°C.
Symbol
Parameter
Min.
Typ.
Max.
Units
Test Conditions
Power Good (PG)
VPG_TH
PG Threshold Voltage
85
90
95
%VOUT Sweep VFB from Low-to-High
%VOUT Sweep VFB from High-to-Low
VPG_HYS
PG Hysteresis
—
6
—
tPG_DLY
PG Delay Time
—
100
—
µs
Sweep VFB from Low-to-High
VPG_LOW
PG Low Voltage
—
70
200
mV
VFB < 90% x VNOM,
IPG = 1 mA
Thermal Protection
TSHD
Overtemperature Shutdown
—
160
—
°C
TJ Rising
TSHD_HYS
Overtemperature Shutdown
Hysteresis
—
15
—
°C
—
Note 1:
Specification for packaged product only.
DS20005607B-page 6
2018 Microchip Technology Inc.
MIC45212-1/-2
2.0
Note:
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: Unless otherwise indicated, VIN = VEN = 12V, VOUT = 1.8V, VBST – VSW = 5V, TJ = +25°C.
FIGURE 2-1:
VIN Operating Supply
Current vs. Input Voltage (MIC45212-1).
FIGURE 2-4:
Temperature.
VDD Supply Voltage vs.
FIGURE 2-2:
VIN Operating Supply
Current vs. Temperature (MIC45212-2).
FIGURE 2-5:
Temperature.
Enable Threshold vs.
FIGURE 2-3:
Input Voltage.
FIGURE 2-6:
Temperature.
EN Bias Current vs.
VIN Shutdown Current vs.
2018 Microchip Technology Inc.
DS20005607B-page 7
MIC45212-1/-2
Note: Unless otherwise indicated, VIN = VEN = 12V, VOUT = 1.8V, VBST – VSW = 5V, TJ = +25°C.
FIGURE 2-7:
Temperature.
Feedback Voltage vs.
FIGURE 2-10:
vs. Temperature.
FIGURE 2-8:
vs.Temperature.
Output Voltage
FIGURE 2-11:
Efficiency vs. Output
Current (MIC45212-1, VIN = 5V).
FIGURE 2-9:
vs.Temperature.
Switching Frequency
FIGURE 2-12:
Efficiency vs. Output
Current (MIC45212-1, VIN = 12V).
DS20005607B-page 8
Output Peak Current-Limit
2018 Microchip Technology Inc.
MIC45212-1/-2
Note: Unless otherwise indicated, VIN = VEN = 12V, VOUT = 1.8V, VBST – VSW = 5V, TJ = +25°C.
FIGURE 2-13:
Efficiency vs. Output
Current (MIC45212-1, VIN = 24V).
FIGURE 2-16:
Efficiency vs. Output
Current (MIC45212-2, VIN = 24V).
FIGURE 2-14:
Efficiency vs. Output
Current (MIC45212-2, VIN = 5V).
FIGURE 2-17:
IC Power Dissipation vs.
Output Current (MIC45212-2, VIN = 5V).
FIGURE 2-15:
Efficiency vs. Output
Current (MIC45212-2, VIN = 12V).
FIGURE 2-18:
IC Power Dissipation vs.
Output Current (MIC45212-2, VIN = 12V).
2018 Microchip Technology Inc.
DS20005607B-page 9
MIC45212-1/-2
Note: Unless otherwise indicated, VIN = VEN = 12V, VOUT = 1.8V, VBST – VSW = 5V, TJ = +25°C.
FIGURE 2-19:
IC Power Dissipation
vs. Output Current (MIC45212-2, VIN = 24V).
FIGURE 2-20:
DS20005607B-page 10
FIGURE 2-21:
(MIC45212-1).
Load Regulation
Line Regulation.
2018 Microchip Technology Inc.
MIC45212-1/-2
Note: Unless otherwise indicated, VIN = VEN = 12V, VOUT = 1.8V, VBST – VSW = 5V, TJ = +25°C.
y
VIN Soft Turn On
VIN
(10V/div)
VIN = 12V
VOUT = 1.8V
IOUT = 14A
VOUT
(1V/div)
VEN
(2V/div)
PGOOD
(5V/div)
VOUT
(1V/div)
IIN
(5A/div)
IIN
(2A/div)
Time (2ms/div)
Time (2ms/div)
FIGURE 2-22:
VIN Soft Turn-On.
FIGURE 2-25:
VOUT
(1V/div)
VIN = 12V
VOUT = 1.8V
IOUT = 1A
VPRE-BIAS = 0.5V
VOUT
(1V/div)
PGOOD
(5V/div)
VIN = 12V
VOUT = 1.8V
IOUT = 14A
IIN
(5A/div)
PGOOD
(5V/div)
Time (8ms/div)
Time (2ms/div)
VIN Soft Turn-Off.
FIGURE 2-26:
Output.
y
VIN = 12V
VOUT = 1.8V
IOUT = 14A
VEN
(2V/div)
VOUT
(1V/div)
IIN
(2A/div)
IIN
(2A/div)
Time (2ms/div)
Enable Turn-On Delay and
2018 Microchip Technology Inc.
VIN Start-up with Pre-Biased
ab e u
VOUT
(1V/div)
FIGURE 2-24:
Rise Time.
p
VIN
(10V/div)
VIN
(10V/div)
VEN
(2V/div)
Enable Turn-Off Delay.
p
VIN Soft Turn Off
FIGURE 2-23:
VIN = 12V
VOUT = 1.8V
IOUT = 14A
O / u
O
VIN = 12V
VOUT = 1.8V
IOUT = 14A
Time (8ms/div)
FIGURE 2-27:
Enable Turn-On/Turn-Off.
DS20005607B-page 11
MIC45212-1/-2
Note: Unless otherwise indicated, VIN = VEN = 12V, VOUT = 1.8V, VBST – VSW = 5V, TJ = +25°C.
Output Recovery from Short Circuit
Power-Up Into Short Circuit
VIN
(10V/div)
VOUT
(20mV/div)
VOUT
(1V/div)
VIN = 12V
VOUT = 1.8V
VIN = 12V
VOUT = 1.8V
IOUT = Short = Wire Across Output
IIN
(1A/div)
IOUT
(5A/div)
Time (2ms/div)
FIGURE 2-28:
Time (8ms/div)
Power-up into Short Circuit.
FIGURE 2-31:
Circuit.
VIN = 12V
VOUT = 1.8V
IOUT = Short = Wire Across Output
VOUT
(50mV/div)
VOUT
(1V/div)
VIN = 12V
VOUT = 1.8V
IPK-CL = 20.2A
IOUT
(10A/div)
IIN
(200mA/div)
Time (800μs/div)
FIGURE 2-29:
Output Recovery from Short
Peak Current Limit Threshold
Enabled Into Short Circuit
VEN
(2V/div)
Pulse: 2Hz; 0V - 3.3V; 20ms
Enabled into Short Circuit.
Time (8ms/div)
FIGURE 2-32:
Threshold.
Peak Current-Limit
Short Circuit
VIN = 12V
VOUT = 1.8V
VOUT
(1V/div)
Pulse: 2Hz; 0V - 3.3V; 20ms
IOUT
(5A/div)
Time (2ms/div)
FIGURE 2-30:
Short Circuit During Steady
State with 14A Load.
DS20005607B-page 12
FIGURE 2-33:
Output Recovery from
Thermal Shutdown.
2018 Microchip Technology Inc.
MIC45212-1/-2
Note: Unless otherwise indicated, VIN = VEN = 12V, VOUT = 1.8V, VBST – VSW = 5V, TJ = +25°C.
g
a se t
VIN = 12V
VOUT = 1.8V
IOUT = 14A
VOUT
(20mV/div)
espo se (
VOUT
(100mV/div)
C 5
)
VIN = 12V
VOUT = 1.8V
IOUT = 1A to 8A
VSW
(5V/div)
IOUT
(5A/div)
IOUT
(10A/div)
Time (40μs/div)
Time (1μs/div)
FIGURE 2-34:
di/dt = 2A/μs
COUT = 2 x 100μF + 270μF POS
Switching Waveforms.
FIGURE 2-37:
(MIC45212-1).
Transient Response
p
Switching Waveforms (MIC45212 1)
(
VOUT
(100mV/div)
VOUT
(20mV/div)
AC-Coupled
)
VIN = 12V
VOUT = 1.8V
IOUT = 7A to 14A
VIN = 12V
VOUT = 1.8V
IOUT = 50mA
VSW
(10V/div)
IOUT
(50mA/div)
IOUT
(5A/div)
Time (40μs/div)
Time (20μs/div)
FIGURE 2-35:
(MIC45212-1).
Switching Waveforms
g
(
,
FIGURE 2-38:
(MIC45212-2).
)
Transient Response
OUT
VIN = 12V
VOUT = 1.8V
IOUT = 0A
VOUT
(20mV/div)
di/dt = 2A/μs
COUT = 2 x 100μF + 270μF POS
VEN
(2V/div)
μ
VIN = 12V
VOUT = 1.8V
IOUT = 14A
VOUT
(1V/div)
VSW
(5V/div)
IOUT
(10A/div)
IIN
(2A/div)
Time (1μs/div)
FIGURE 2-36:
Switching Waveforms
(IOUT = 0A, MIC45212-2)
2018 Microchip Technology Inc.
Output ALE cap, 3000μF
Time (8ms/div)
FIGURE 2-39:
Inrush with COUT = 3000 µF.
DS20005607B-page 13
MIC45212-1/-2
3.0
PIN DESCRIPTIONS
The descriptions of the pins are listed in Table 3-1.
TABLE 3-1:
PIN FUNCTION TABLE
MIC45212
Pin Number
Pin Name
1, 56, 64
GND
Analog Ground: Connect bottom feedback resistor to GND. GND and PGND are
internally connected.
2, 3
PVDD
PVDD: Supply input for the internal low-side power MOSFET driver.
4
ILIM
5, 6
PGND
Power Ground: PGND is the return path for the step-down power module power stage.
The PGND pin connects to the sources of the internal low-side power MOSFET, the
negative terminals of input capacitors and the negative terminals of output capacitors.
7-10, 38-44
SW
The SW pin connects directly to the switch node. Due to the high-speed switching on this
pin, the SW pin should be routed away from sensitive nodes. The SW pin also senses the
current by monitoring the voltage across the low-side MOSFET during off time.
12-22
PVIN
Power Input Voltage: Connection to the drain of the internal high-side power MOSFET.
Connects an input capacitor from PVIN to PGND.
24-36
VOUT
Power Output Voltage: Connected to the internal inductor. The output capacitor should
be connected from this pin to PGND, as close to the module as possible.
46, 47
RIA
Pin Function
Current Limit: Connect a resistor between ILIM and SW to program the current limit.
Ripple Injection Pin A: Leave floating, no connection.
48
RIB
49-50
ANODE
Ripple Injection Pin B: Connect this pin to FB.
52-54
BST
Connection to the internal bootstrap circuitry and high-side power MOSFET drive
circuitry. Leave floating, no connection.
55
NC
No Connection.
57
FB
Feedback: Input to the transconductance amplifier of the control loop. The FB pin is
referenced to 0.8V. A resistor divider connecting the feedback to the output is used to
set the desired output voltage. Connect the bottom resistor from FB to GND.
58
PG
Power Good: Open-Drain Output. If used, connect to an external pull-up resistor of at
least 10 kOhm between PG and the external bias voltage.
59
EN
Enable: A logic signal to enable or disable the step-down regulator module operation.
The EN pin is TTL/CMOS compatible. Logic high = enable, logic low = disable or
shutdown. Do not leave floating.
60
VIN
Internal 5V Linear Regulator Input: A 1 µF ceramic capacitor from VIN to GND is
required for decoupling.
61
FREQ
Switching Frequency Adjust: Use a resistor divider from VIN to GND to program the
switching frequency. Connecting FREQ to VIN sets frequency = 600 kHz.
62, 63
5VDD
Internal +5V linear regulator output. Powered by VIN, 5VDD is the internal supply bus for
the device. In the applications with VIN 0.8V and the inductor current
goes slightly negative, then the MIC45212-1 automatically powers down most of the IC circuitry and goes into
a Low-Power mode.
Once the MIC45212-1 goes into Discontinuous mode,
both DL and DH 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.
tOFF(MIN)
FIGURE 4-3:
Response.
DS20005607B-page 16
MIC45212 Load Transient
2018 Microchip Technology Inc.
MIC45212-1/-2
4.4
IL Crosses 0 and VFB > 0.8
Discontinuous Mode Starts
IL
VFB < 0.8V, Wake-up from
Discontinuous Mode
Current Limit
The MIC45212 uses the RDS(ON) of the low-side
MOSFET and the external resistor, connected from the
ILIM pin to the SW node, to set the current limit.
0
VFB
MIC45212
VIN
VIN
VREF
BST
ZC
CIN
SW
SW
CS
R15
ILIM
FB
C15
DH
PGND
Estimated ON-Time
DL
FIGURE 4-4:
MIC45212-1 Control Loop
Timing (Discontinuous Mode).
During Discontinuous mode, the bias current of most
circuits is substantially reduced. As a result, the total
power supply current during Discontinuous mode is only
about 370 µA, allowing the MIC45212-1 to achieve high
efficiency in light load applications.
4.3
Soft Start
Soft start reduces the input power supply surge current
at start-up by controlling the output voltage rise time.
The input surge appears while the output capacitor is
charged up.
The MIC45212 implements an internal digital soft start
by making the 0.8V reference voltage, VREF, ramp from
0 to 100% in about 3 ms with 9.7 mV steps. Therefore,
the output voltage is controlled to increase slowly by a
staircase VFB ramp. Once the soft start cycle ends, the
related circuitry is disabled to reduce current consumption. PVDD must be powered up at the same time or
after VIN to make the soft start function correctly.
2018 Microchip Technology Inc.
FIGURE 4-5:
Circuit.
MIC45212 Current-Limiting
In each switching cycle of the MIC45212, the inductor
current is sensed by monitoring the low-side MOSFET
in the OFF period. The Sensed Voltage, VILIM, is compared with the Power Ground (PGND) after a blanking
time of 150 ns. In this way, the drop voltage over the
resistor, R15 (VCL), is compared with the drop over the
bottom FET generating the short current limit. The
small Capacitor (C15) connected from the ILIM pin to
PGND filters the switching node ringing during the
OFF-time, allowing a better short limit measurement.
The time constant created by R15 and C15 should be
much less than the minimum OFF-time.
The VCL drop allows programming of the short limit
through the value of the Resistor (R15). If the absolute
value of the voltage drop on the bottom FET becomes
greater than VCL, and the VILIM falls below PGND, an
overcurrent is triggered causing the IC to enter Hiccup
mode. The hiccup mode sequence, including the soft
start, reduces the stress on the switching FETs, and
protects the load and supply for severe short
conditions.
The short-circuit current limit can be programmed by
using Equation 4-3.
DS20005607B-page 17
MIC45212-1/-2
EQUATION 4-3:
PROGRAMMING
CURRENT LIMIT
The peak-to-peak inductor current ripple is:
EQUATION 4-4:
(ICLIM + IL(PP) 0.5) RDS(ON) + VCL_OFFSET
R15 =
ICL
Where:
ICLIM = Desired current limit
RDS(ON) = On resistance of low-side power
MOSFET, 6 m typically
VCL_OFFSET = Current-limit threshold (typical
absolute value is 14 mV per Table 1-1)
ICL = Current-limit source current (typical value is
70 µA per Table 1-1)
IL(PP) = Inductor current peak-to-peak; since the
inductor is integrated, use Equation 4-4 to calculate
the inductor ripple current
IL(PP) =
PEAK-TO-PEAK
INDUCTOR CURRENT
RIPPLE
VOUT (VIN(MAX) – VOUT)
VIN(MAX) fSW L
The MIC45212 has a 0.6 µH inductor integrated into
the module. In case of a hard short, the short limit 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 capacitance during soft start is under the folded
short limit; otherwise, the supply will go into hiccup
mode and may not finish the soft start successfully.
The MOSFET RDS(ON) varies 30% to 40% with
temperature; therefore, it is recommended to add a
50% margin to ICLIM in Equation 4-3 to avoid false
current limiting due to increased MOSFET junction
temperature rise.
With R15 = 1.69 k and C15 = 15 pF, the typical output
current limit is 16.8A.
DS20005607B-page 18
2018 Microchip Technology Inc.
MIC45212-1/-2
5.0
APPLICATION INFORMATION
5.1
Setting the Switching Frequency
The MIC45212 switching frequency can be adjusted by
changing the value of resistors, R1 and R2.
MIC45212
VIN
BST
CIN
SW
CS
5.2
Output Capacitor Selection
The type of output capacitor is usually determined by
the application and its Equivalent Series Resistance
(ESR). Voltage and RMS current capability are two
other important factors for selecting the output capacitor. Recommended capacitor types are MLCC,
OS-CON and POSCAP. The output capacitor’s ESR is
usually the main cause of the output ripple. The
MIC45212 requires ripple injection and the output
capacitor ESR affects the control loop from a stability
point of view.
The maximum value of ESR is calculated as in
Equation 5-2:
EQUATION 5-2:
ESR MAXIMUM VALUE
R1
ESRCOUT
FREQ
R2
FB
PGND
VOUT(PP)
IL(PP)
Where:
VOUT(PP) = Peak-to-peak output voltage ripple
FIGURE 5-1:
Adjustment.
Switching Frequency
Equation 5-1 gives the estimated switching frequency:
EQUATION 5-1:
ESTIMATED SWITCHING
FREQUENCY
IL(PP) = Peak-to-peak inductor current ripple
The total output ripple is a combination of the ESR and
output capacitance. The total ripple is calculated in
Equation 5-3:
EQUATION 5-3:
R2
fSW = fO
R1 + R2
VOUT(PP) =
Where:
fO = 600 kHz (typical per TABLE 1-1: “Electrical
Characteristics(1)” table)
TOTAL OUTPUT RIPPLE
IL(PP)
2
2 + (I
L(PP) ESRCOUT)
f
8
OUT
SW
C
R1 = 100 k is recommended
Where:
R2 = Needs to be selected in order to set the
required switching frequency
fSW = Switching frequency
FIGURE 5-2:
COUT = Output capacitance value
Switching Frequency vs. R2.
2018 Microchip Technology Inc.
DS20005607B-page 19
MIC45212-1/-2
As described in Section 4.1 “Theory of Operation” in
Section 4.0 “Functional Description”, the MIC45212
requires at least a 20 mV peak-to-peak ripple at the FB
pin to make the gM amplifier and the error comparator
behave properly. Also, the output voltage 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. Please refer
to Section 5.5 “Ripple Injection” in Section 5.0
“Application Information” for more details.
The output capacitor RMS current is calculated in
Equation 5-4:
EQUATION 5-4:
12
DISSIPATED POWER IN
OUTPUT CAPACITOR
PDISS(COUT) = ICOUT(RMS) ESRCOUT
2
Input Capacitor Selection
POWER DISSIPATED IN
INPUT CAPACITOR
PDISS(CIN(RMS)) = ICIN(RMS)2 ESRCIN
The general rule is to pick the capacitor with a ripple
current rating equal to or greater than the calculated
worst-case RMS capacitor current.
Equation 5-9 should be used to calculate the input
capacitor. Also, it is recommended to keep some
margin on the calculated value:
EQUATION 5-9:
INPUT CAPACITOR
CALCULATION
I
(1 – D)
CIN OUT(MAX)
fSW dV
IL(PP)
The power dissipated in the output capacitor is:
5.3
EQUATION 5-8:
OUTPUT CAPACITOR
RMS CURRENT
ICOUT(RMS) =
EQUATION 5-5:
The power dissipated in the input capacitor is:
Where:
dV = Input ripple
fSW = Switching frequency
5.4
Output Voltage Setting
Components
The MIC45212 requires two resistors to set the output
voltage, as shown in Figure 5-3:
The input capacitor for the Power Stage Input, PVIN,
should be selected for ripple current rating and voltage
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:
RFB1
gM AMP
EQUATION 5-6:
FB
CONFIGURING RIPPLE
CURRENT AND VOLTAGE
RATINGS
RFB2
VIN = IL(pk) ESRCIN
VREF
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 5-7:
RMS VALUE OF INPUT
CAPACITOR CURRENT
FIGURE 5-3:
Configuration.
Voltage/Divider
ICIN(RMS) IOUT(MAX)D(1 – D)
Where:
D = Duty cycle
DS20005607B-page 20
2018 Microchip Technology Inc.
MIC45212-1/-2
The output voltage is determined by Equation 5-10:
The applications are divided into two situations according
to the amount of the feedback voltage ripple:
EQUATION 5-10:
1.
OUTPUT VOLTAGE
DETERMINATION
Enough ripple at the feedback voltage due to the
large ESR of the output capacitors:
As shown in Figure 5-4, the converter is stable
without any ripple injection.
RFB1
VOUT = VFB 1 +
RFB2
Where:
VFB = 0.8V
VOUT
RFB1
A typical value of RFB1 used on the standard evaluation
board is 10 k. If RFB1 is too large, it may allow noise
to be introduced into the voltage feedback loop. If RFB1
is too small in value, it will decrease the efficiency of the
power supply, especially at light loads. Once RFB1 is
selected, RFB2 can be calculated using Equation 5-11:
EQUATION 5-11:
CALCULATING RFB2
RFB2 =
VFB RFB1
VOUT – VFB
MIC45212
5.5
FIGURE 5-4:
ESR.
Enough Ripple at FB from
The feedback voltage ripple is:
EQUATION 5-12:
VFB(PP)
RFB2
VOUT
OPEN
0.8V
40.2 k
1.0V
20 k
1.2V
11.5 k
1.5V
8.06 k
1.8V
4.75 k
2.5V
3.24 k
3.3V
1.91 k
5.0V
Ripple Injection
The VFB ripple required for proper operation of the
MIC45212 gM amplifier and error comparator is 20 mV
to 100 mV. However, the output voltage ripple is generally too small to provide enough ripple amplitude at the
FB pin and this issue is more visible in lower output
voltage applications. If the feedback voltage ripple is so
small that the gM amplifier and error comparator cannot
sense it, then the MIC45212 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.
FEEDBACK VOLTAGE
RIPPLE
RFB2
RFB1 RFB2
ESRCOUT IL(PP)
Where:
VOUT PROGRAMMING
RESISTOR LOOK-UP
2018 Microchip Technology Inc.
COUT
ESR
RFB2
For fixed RFB1 = 10 k, the output voltage can be
selected by RFB2. Table 5-1 provides RFB2 values for
some common output voltages.
TABLE 5-1:
FB
IL(PP) = The peak-to-peak value of the inductor
current ripple
2.
There is virtually inadequate or no ripple at the
FB pin voltage due to the very low-ESR of the
output capacitors; such is the case with the
ceramic output capacitor. In this case, the VFB
ripple waveform needs to be generated by
injecting a suitable signal. MIC45212 has provisions to enable an internal series RC injection
network, RINJ and CINJ, as shown in Figure 5-5,
by connecting RIB to the FB pin. This network
injects a square wave current waveform into the
FB pin, which by means of integration across the
capacitor (C14), generates an appropriate
sawtooth FB ripple waveform.
VOUT
MIC45212
FB
RFB1
C14
COUT
RIB
RINJ
CINJ
RIA
RFB2
ESR
SW
FIGURE 5-5:
FB via RIB Pin.
Internal Ripple Injection at
DS20005607B-page 21
MIC45212-1/-2
The injected ripple is:
EQUATION 5-13:
INJECTED RIPPLE
VFB(PP) VIN Kdiv D (1 – D)
Kdiv =
RFB1//RFB2
RINJ + RFB1//RFB2
Where:
VIN = Power stage input voltage
D = Duty cycle
fSW = Switching frequency
1
fSW
In Equation 5-13 and Equation 5-14, it is assumed that
the time constant associated with C14 must be much
greater than the switching period:
EQUATION 5-14:
CONDITION ON TIME
CONSTANT OF C14
1
T
=
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