February 2005 1 MIC3975
MIC3975 Micrel
Ordering Information
Part Number
Standard Pb-Free Voltage Junction Temp. Range Package
MIC3975-1.65BMM MIC3975-1.65YMM 1.65V –40°C to +125°C MSOP-8
MIC3975-1.8BMM MIC3975-1.8YMM 1.8V –40°C to +125°C MSOP-8
MIC3975-2.5BMM MIC3975-2.5YMM 2.5V –40°C to +125°C MSOP-8
MIC3975-3.0BMM MIC3975-3.0YMM 3.0V –40°C to +125°C MSOP-8
MIC3975-3.3BMM MIC3975-3.3YMM 3.3V –40°C to +125°C MSOP-8
MIC3975-5.0BMM MIC3975-5.0YMM 5.0V –40°C to +125°C MSOP-8
MIC3975BMM MIC3975YMM Adj. –40°C to +125°C MSOP-8
MIC3975
750mA µCap Low-Voltage Low-Dropout Regulator
General Description
The MIC3975 is a 750mA low-dropout linear voltage regula-
tors that provide low-voltage, high-current output from an
extremely small package. Utilizing Micrel’s proprietary Super
βeta PNP™ pass element, the MIC3975 offers extremely low
dropout (typically 300mV at 750mA) and low ground current
(typically 6.5mA at 750mA).
The MIC3975 is ideal for PC add-in cards that need to con-
vert from standard 5V to 3.3V or 3.0V, 3.3V to 2.5V or 2.5V
to 1.8V or 1.65V. A guaranteed maximum dropout voltage
of 500mV over all operating conditions allows the MIC3975
to provide 2.5V from a supply as low as 3.0V and 1.8V or
1.65V from a supply as low as 2.25V.
The MIC3975 is fully protected with overcurrent limiting,
thermal shutdown, and reversed-battery protection. Fixed
voltages of 5.0V, 3.3V, 3.0, 2.5V, 1.8V, and 1.65V are avail-
able. An adjustable output voltage option is available for
voltages down to 1.24V.
For other voltages, contact Micrel.
Typical Applications
Features
• Fixed and adjustable output voltages to 1.24V
• 300mV typical dropout at 750mA
Ideal for 3.0V to 2.5V conversion
Ideal for 2.5V to 1.8V or 1.65V conversion
• Stable with ceramic capacitor
• 750mA minimum guaranteed output current
• 1% initial accuracy
• Low ground current
• Current limiting and thermal shutdown
• Reversed-battery protection
• Reversed-leakage protection
• Fast transient response
• Low-profile MSOP-8
Applications
• Fiber optic modules
• LDO linear regulator for PC add-in cards
• PowerPC™ power supplies
• High-efficiency linear power supplies
• SMPS post regulator
• Multimedia and PC processor supplies
• Battery chargers
• Low-voltage microcontrollers and digital logic
Super βeta PNP is a trademark of Micrel, Inc.
Micrel, Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel + 1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
IN
R1
100k
2.5V
Error
Flag
Output
V
IN
3.3V
10F
ceramic
EN
OUT
FLG
GND
MIC3975-2.5BMM
ENABLE
SHUTDOWN
2.5V/750mA Regulator with Error Flag
IN
R1
1.5V
V
IN
2.5V
10F
ceramic
R2
EN
OUT
ADJ
GND
MIC3975BMM
ENABLE
SHUTDOWN
1.5V/750mA Adjustable Regulator
MIC3975 Micrel
MIC3975 2 February 2005
Pin Configuration
1EN
IN
FLG
OUT
8 GND
GND
GND
GND
7
6
5
2
3
4
MIC3975-x.x
Fixed
MSOP-8 (MM)
1EN
IN
ADJ
OUT
8 GND
GND
GND
GND
7
6
5
2
3
4
Adjustable
Pin Description
Pin No. Pin No. Pin Name Pin Function
Fixed Adjustable
1 1 EN Enable (Input): CMOS-compatible control input. Logic high = enable, logic
low or open = shutdown.
2 2 IN Supply (Input)
3 FLG Flag (Output): Open-collector error flag output. Active low = output under-
voltage.
3 ADJ Adjustment Input: Feedback input. Connect to resistive voltage-divider net-
work.
4 4 OUT Regulator Output
5–8 5–8 GND Ground
February 2005 3 MIC3975
MIC3975 Micrel
Electrical Characteristics(Note 12)
VIN = VOUT + 1V; VEN = 2.25V; TJ = 25°C, bold values indicate –40°C ≤ TJ ≤ +125°C; unless noted
Symbol Parameter Condition Min Typ Max Units
VOUT Output Voltage 10mA –1 1 %
10mA ≤ IOUT ≤ 750mA, VOUT + 1V ≤ VIN ≤ 8V –2 2 %
Line Regulation IOUT = 10mA, VOUT + 1V ≤ VIN ≤ 16V 0.06 0.5 %
Load Regulation VIN = VOUT + 1V, 10mA ≤ IOUT ≤ 750mA, 0.2 1 %
ΔVOUT/ΔT Output Voltage Temp. Coefficient, 40 100
ppm/°C
Note 5
VDO Dropout Voltage, Note 6 IOUT = 100mA, ΔVOUT = –1% 140 200 mV
250 mV
IOUT = 500mA, ΔVOUT = –1% 225 mV
IOUT = 750mA, ΔVOUT = –1% 300 500 mV
IGND Ground Current, Note 7 IOUT = 100mA, VIN = VOUT + 1V 400 µA
IOUT = 500mA, VIN = VOUT + 1V 4 mA
IOUT = 750mA, VIN = VOUT + 1V 7.5 15 mA
IOUT(lim) Current Limit VOUT = 0V, VIN = VOUT + 1V 1.8 2.5 A
Enable Input
VEN Enable Input Voltage logic low (off) 0.8 V
logic high (on) 2.25 V
IEN Enable Input Current VEN = 2.25V 1 15 30 µA
75 µA
VEN = 0.8V 2 µA
4 µA
Flag Output
IFLG(leak) Output Leakage Current VOH = 16V 0.01 1 µA
2 µA
VFLG(do) Output Low Voltage VIN = 2.250V, IOL, = 250µA, Note 9 210 300 mV
400 mV
VFLG Low Threshold % of VOUT 93 %
High Threshold % of VOUT 99.2 %
Hysteresis 1 %
Absolute Maximum Ratings (Note 1)
Supply Voltage (VIN) .......................................–20V to +20V
Enable Voltage (VEN) .................................................. +20V
Storage Temperature (TS) ........................ –65°C to +150°C
Lead Temperature (soldering, 5 sec.) ........................ 260°C
ESD, Note 3
Operating Ratings (Note 2)
Supply Voltage (VIN) ................................... +2.25V to +16V
Enable Voltage (VEN) .................................................. +16V
Maximum Power Dissipation (PD(max)) ..................... Note 4
Junction Temperature (TJ) ........................ –40°C to +125°C
Package Thermal Resistance
MSOP-8 (θJA) ...................................................... 80°C/W
MIC3975 Micrel
MIC3975 4 February 2005
Symbol Parameter Condition Min Typ Max Units
Adjustable Output Only
Reference Voltage 1.228 1.240 1.252 V
1.215 1.265 V
Note 10 1.203 1.277 V
Adjust Pin Bias Current 40 80 nA
120 nA
Reference Voltage Note 11 20
ppm/°C
Temp. Coefficient
Adjust Pin Bias Current 0.1 nA/°C
Temp. Coefficient
Note 1. Exceeding the absolute maximum ratings may damage the device.
Note 2. The device is not guaranteed to function outside its operating rating.
Note 3. Devices are ESD sensitive. Handling precautions recommended.
Note 4. PD(max) = (TJ(max) – TA) ÷ θJA, where θJA depends upon the printed circuit layout. See “Applications Information.”
Note 5. Output voltage temperature coefficient is ΔVOUT(worst case) ÷ (TJ(max) – TJ(min)) where TJ(max) is +125°C and TJ(min) is –40°C.
Note 6. VDO = VIN – VOUT when VOUT decreases to 98% of its nominal output voltage with VIN = VOUT + 1V. For output voltages below 2.25V, dropout
voltage is the input-to-output voltage differential with the minimum input voltage being 2.25V. Minimum input operating voltage is 2.25V.
Note 7. IGND is the quiescent current. IIN = IGND + IOUT.
Note 8. VEN ≤ 0.8V, VIN ≤ 8V, and VOUT = 0V.
Note 9. For a 2.5V device, VIN = 2.250V (device is in dropout).
Note 10. VREF ≤ VOUT ≤ (VIN – 1V), 2.25V ≤ VIN ≤ 16V, 10mA ≤ IL ≤ 750mA, TJ = TMAX.
Note 11. Thermal regulation is defined as the change in output voltage at a time t after a change in power dissipation is applied, excluding load or line
regulation effects. Specifications are for a 200mA load pulse at VIN = 16V for t = 10ms.
Note 12. Specification for packaged product only.
February 2005 5 MIC3975
MIC3975 Micrel
Typical Characteristics
MIC3975 Micrel
MIC3975 6 February 2005
February 2005 7 MIC3975
MIC3975 Micrel
Functional Characteristics
Load Transient Response
TIME (200s/div.)
LOAD CURRENT
(500mA/div.)
OUTPUT VOLTAGE
(200mV/div.)
VIN = 3.3V
VOUT = 2.5V
COUT = 10F Ceramic
750mA
100mA
Load Transient Response
TIME (200s/div.)
LOAD CURRENT
(500mA/div.)
OUTPUT VOLTAGE
(200mV/div.)
VIN = 3.3V
VOUT = 2.5V
COUT = 10F Ceramic
750mA
10mA
VOUT = 2.5V
COUT = 10F Ceramic
ILOAD = 10mA
3.3V
5.0V
Line Transient Response
TIME (200s/div.)
INPUT VOLTAGE
(1V/div.)
OUTPUT VOLTAGE
(50mV/div.)
MIC3975 Micrel
MIC3975 8 February 2005
Functional Diagrams
Ref.
18V
O.V.
ILIMIT
Thermal
Shut-
down
1.240V1.180V
EN
IN
FLAG
GND
OUT
MIC3975 Fixed Regulator with Flag and Enable Block Diagram
Ref.
18V
O.V.
ILIMIT
Thermal
Shut-
down
1.240V
EN
IN
GND
OUT
ADJ
MIC3975 Adjustable Regulator Block Diagram
February 2005 9 MIC3975
MIC3975 Micrel
Applications Information
The MIC3975 is a high-performance low-dropout voltage regu-
lator suitable for moderate to high-current voltage regulator
applications. Its 500mV dropout voltage at full load and over-
temperature makes it especially valuable in battery-powered
systems and as high-efficiency noise filters in post-regulator
applications. Unlike older NPN-pass transistor designs, where
the minimum dropout voltage is limited by the base-to-emit-
ter voltage drop and collector-to-emitter saturation voltage,
dropout performance of the PNP output of these devices is
limited only by the low VCE saturation voltage.
A trade-off for the low dropout voltage is a varying base drive
requirement. Micrel’s Super βeta PNP™ process reduces this
drive requirement to only 2% of the load current.
The MIC3975 regulator is fully protected from damage due to
fault conditions. Linear current limiting is provided. Output cur-
rent during overload conditions is constant. Thermal shutdown
disables the device when the die temperature exceeds the
maximum safe operating temperature. Transient protection
allows device (and load) survival even when the input volt-
age spikes above and below nominal. The output structure
of these regulators allows voltages in excess of the desired
output voltage to be applied without reverse current flow.
Figure 1. Capacitor Requirements
Output Capacitor
The MIC3975 requires an output capacitor for stable opera-
tion. As a µCap LDO, the MIC3975 can operate with ceramic
output capacitors as long as the amount of capacitance is
10µF or greater. For values of output capacitance lower than
10µF, the recommended ESR range is 200mΩ to 2Ω. The
minimum value of output capacitance recommended for the
MIC3975 is 4.7µF.
For 10µF or greater the ESR range recommended is less than
1Ω. Ultra-low ESR ceramic capacitors are recommended
for output capacitance of 10µF or greater to help improve
transient response and noise reduction at high frequency.
X7R/X5R dielectric-type ceramic capacitors are recom-
mended because of their temperature performance. X7R-type
capacitors change capacitance by 15% over their operating
temperature range and are the most stable type of ceramic
capacitors. Z5U and Y5V dielectric capacitors change value
by as much as 50% and 60% respectively over their operat-
ing temperature ranges. To use a ceramic chip capacitor with
Y5V dielectric, the value must be much higher than an X7R
ceramic capacitor to ensure the same minimum capacitance
over the equivalent operating temperature range.
Input Capacitor
An input capacitor of 1µF or greater is recommended when
the device is more than 4 inches away from the bulk ac supply
capacitance or when the supply is a battery. Small, surface
mount, ceramic chip capacitors can be used for bypassing.
Larger values will help to improve ripple rejection by bypass-
ing the input to the regulator, further improving the integrity
of the output voltage.
Error Flag
The MIC3975 features an error flag (FLG), which monitors
the output voltage and signals an error condition when this
voltage drops 5% below its expected value. The error flag is
an open-collector output that pulls low under fault conditions
and may sink up to 10mA. Low output voltage signifies a
number of possible problems, including an overcurrent fault
(the device is in current limit) or low input voltage. The flag
output is inoperative during overtemperature conditions. A
pull-up resistor from FLG to either VIN or VOUT is required
for proper operation. For information regarding the minimum
and maximum values of pull-up resistance, refer to the graph
in the typical characteristics section of the data sheet.
Enable Input
The MIC3975 features an active-high enable input (EN) that
allows on-off control of the regulator. Current drain reduces to
“zero” when the device is shutdown, with only microamperes
of leakage current. The EN input has TTL/CMOS compatible
thresholds for simple logic interfacing. EN may be directly tied
to VIN and pulled up to the maximum supply voltage
Transient Response and 3.3V to 2.5V or 2.5V to 1.8V or
1.65V Conversion
The MIC3975 has excellent transient response to variations in
input voltage and load current. The device has been designed
to respond quickly to load current variations and input voltage
variations. Large output capacitors are not required to obtain
this performance. A standard 10µF output capacitor, is all
that is required. Larger values help to improve performance
even further.
By virtue of its low-dropout voltage, this device does not satu-
rate into dropout as readily as similar NPN-based designs.
When converting from 3.3V to 2.5V or 2.5V to 1.8V or 1.65V,
the NPN based regulators are already operating in dropout,
with typical dropout requirements of 1.2V or greater. To convert
down to 2.5V or 1.8V without operating in dropout, NPN-based
regulators require an input voltage of 3.7V at the very least.
The MIC3975 regulator will provide excellent performance
with an input as low as 3.0V or 2.5V respectively. This gives
the PNP based regulators a distinct advantage over older,
NPN based linear regulators.
Minimum Load Current
The MIC3975 regulator is specified between finite loads. If
the output current is too small, leakage currents dominate
and the output voltage rises. A 10mA minimum load current
is necessary for proper regulation.
MIC3975 Micrel
MIC3975 10 February 2005
Adjustable Regulator Design
IN
R1
VOUT
VIN
COUT
R2
EN
OUT
ADJ
GND
MIC3975
ENABLE
SHUTDOWN
V 1.240V 1 R1
R2
OUT
Figure 2. Adjustable Regulator with Resistors
The MIC3975 allows programming the output voltage any-
where between 1.24V and the 16V maximum operating rating
of the family. Two resistors are used. Resistors can be quite
large, up to 1MΩ, because of the very high input impedance
and low bias current of the sense comparator: The resistor
values are calculated by:
R1 R2 V
1.240 1
OUT
Where VO is the desired output voltage. Figure 2 shows
component definition. Applications with widely varying load
currents may scale the resistors to draw the minimum load
current required for proper operation (see above).
Power MSOP-8 Thermal Characteristics
One of the secrets of the MIC3975’s performance is its power
MSO-8 package featuring half the thermal resistance of a
standard MSO-8 package. Lower thermal resistance means
more output current or higher input voltage for a given pack-
age size.
Lower thermal resistance is achieved by joining the four
ground leads with the die attach paddle to create a single-
piece electrical and thermal conductor. This concept has
been used by MOSFET manufacturers for years, proving
very reliable and cost effective for the user.
Thermal resistance consists of two main elements, θJC (junc-
tion-to-case thermal resistance) and θCA (case-to-ambient
thermal resistance). See Figure 3. θJC is the resistance from
the die to the leads of the package. θCA is the resistance
from the leads to the ambient air and it includes θCS (case-
to-sink thermal resistance) and θSA (sink-to-ambient thermal
resistance).
Using the power MSOP-8 reduces the θJC dramatically and
allows the user to reduce θCA. The total thermal resistance,
θJA (junction-to-ambient thermal resistance) is the limiting
factor in calculating the maximum power dissipation capabil-
ity of the device. Typically, the power MSOP-8 has a θJA of
80°C/W, this is significantly lower than the standard MSOP-8
which is typically 160°C/W. θCA is reduced because pins 5
through 8 can now be soldered directly to a ground plane
which significantly reduces the case-to-sink thermal resistance
and sink to ambient thermal resistance.
Low-dropout linear regulators from Micrel are rated to a
maximum junction temperature of 125°C. It is important not to
exceed this maximum junction temperature during operation
of the device. To prevent this maximum junction temperature
from being exceeded, the appropriate ground plane heat sink
must be used.
JA
JC CA
printed circuit board
ground plane
heat sink area
MSOP-8
AMBIENT
Figure 3. Thermal Resistance
Figure 4 shows copper area versus power dissipation with
each trace corresponding to a different temperature rise
above ambient.
From these curves, the minimum area of copper necessary for
the part to operate safely can be determined. The maximum
allowable temperature rise must be calculated to determine
operation along which curve.
ΔT = TJ(max) – TA(max)
TJ(max) = 125°C
Figure 4. Copper Area vs. Power-MSOP
Power Dissipation (∆TJA)
Figure 5. Copper Area vs. Power-MSOP
Power Dissipation (TA)
February 2005 11 MIC3975
MIC3975 Micrel
TA(max) = maximum ambient operating temperature
For example, the maximum ambient temperature is 50°C,
the ΔT is determined as follows:
ΔT = 125°C – 50°C
ΔT = 75°C
Using Figure 4, the minimum amount of required copper can
be determined based on the required power dissipation. Power
dissipation in a linear regulator is calculated as follows:
PD = (VIN – VOUT) IOUT + VIN × IGND
If we use a 2.5V output device and a 3.3V input at an output
current of 750mA, then our power dissipation is as follows:
PD = (3.3V – 2.5V) × 750mA + 3.3V × 7.5mA
PD = 600mW + 25mW
PD = 625mW
From Figure 4, the minimum amount of copper required to
operate this application at a ΔT of 75°C is 160mm2.
Quick Method
Determine the power dissipation requirements for the design
along with the maximum ambient temperature at which the
device will be operated. Refer to Figure 5, which shows safe
operating curves for three different ambient temperatures:
25°C, 50°C and 85°C. From these curves, the minimum
amount of copper can be determined by knowing the maxi-
mum power dissipation required. If the maximum ambient
temperature is 50°C and the power dissipation is as above,
625mW, the curve in Figure 5 shows that the required area
of copper is 160mm2.
The θJA of this package is ideally 80°C/W, but it will vary
depending upon the availability of copper ground plane to
which it is attached.
MIC3975 Micrel
MIC3975 12 February 2005
Package Information
8-Lead MSOP (MM)
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL + 1 (408) 944-0800 FAX + 1 (408) 474-1000 WEB http://www.micrel.com
The information furnished by Micrel in this datasheet is believed to be accurate and reliable. However, no responsibility is assumed by Micrel for its use.
Micrel reserves the right to change circuitry and specifications at any time without notification to the customer.
Micrel Products are not
reasonably be expected to result in personal injury. Life support devices or systems are devices or systems that (a) are intended for surgical implant into
the body or (b) support or sustain life, and whose failure to perform can be reasonably expected to result in a significant injury to the user. A Purchaser’s
use or sale of Micrel Products for use in life support appliances, devices or systems is at Purchaser’s own risk and Purchaser agrees to fully indemnify
Micrel for any damages resulting from such use or sale.
© 2005 Micrel, Incorporated.
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MIC3975-2.5YMM-TR MIC3975-5.0YMM-TR MIC3975YMM-TR MIC3975-1.65YMM-TR MIC3975-3.3YMM-TR