LM3102MHX [NSC]
SIMPLE SWITCHER㈢ Synchronous 1MHz 2.5A Step-Down Voltage Regulator; SIMPLE SWITCHER㈢ 1MHz的同步2.5A降压稳压器
| 型号： | LM3102MHX |
| 厂家： | 
National Semiconductor |
| 描述： | SIMPLE SWITCHER㈢ Synchronous 1MHz 2.5A Step-Down Voltage Regulator |
| 文件： | 总18页 (文件大小：378K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
September 2007
LM3102
SIMPLE SWITCHER® Synchronous 1MHz 2.5A
Step-Down Voltage Regulator
General Description
Features
The LM3102 Synchronously Rectified Buck Converter fea-
tures all required functions to implement a highly efficient and
cost effective buck regulator. It is capable of supplying 2.5A
to loads with an output voltage as low as 0.8V. Dual N-Chan-
nel synchronous MOSFET switches allow a low component
count, thus reducing complexity and minimizing board size.
Low component count and small solution size
Stable with ceramic and other low ESR capacitors
No loop compensation required
High efficiency at a light load by DCM operation
Pre-bias startup
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Ultra-fast transient response
Different from most other COT regulators, the LM3102 does
not rely on output capacitor ESR for stability, and is designed
to work exceptionally well with ceramic and other very low
ESR output capacitors. It requires no loop compensation, re-
sults in a fast load transient response and simple circuit
implementation. The operating frequency remains nearly con-
stant with line variations due to the inverse relationship be-
tween the input voltage and the on-time. The operating
frequency can be externally programmed up to 1 MHz. Pro-
tection features include VCC under-voltage lock-out, output
over-voltage protection, thermal shutdown, and gate drive
under-voltage lock-out. The LM3102 is available in the ther-
mally enhanced eTSSOP-20 package.
Programmable soft-start
Programmable switching frequency up to 1 MHz
Valley current limit
Output over-voltage protection
Precision internal reference for an adjustable output
voltage down to 0.8V
Thermal shutdown
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Typical Applications
5VDC, 12VDC, 24VDC, 12VAC, and 24VAC systems
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Embedded Systems
Key Specifications
Industrial Control
Automotive Telematics and Body Electronics
Input voltage range 4.5V-42V
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Point of Load Regulators
2.5A output current
Storage Systems
0.8V, ±1.5% reference
Broadband Infrastructure
Integrated dual N-Channel main and synchronous
MOSFETs
Direct Conversion from 2/3/4 Cell Lithium Batteries
Systems
Thermally enhanced eTSSOP-20 package
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Typical Application
30021301
SIMPLE SWITCHER® is a registered trademark of National Semiconductor Corporation
© 2007 National Semiconductor Corporation
300213
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Connection Diagram
30021302
20-lead Plastic eTSSOP
NS Package Number MXA20A
Ordering Information
Order Number
LM3102MH
Package Type
Exposed Pad TSSOP-20
NSC Package Drawing
Supplied As
MXA0020
73 units per Anti-Static Tube
2500 Units on Tape and Reel
LM3102MHX
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Pin Descriptions
Pin
1,9,10,12,19,20
2, 3
Name
N/C
Description
No Connection
Switching Node
Application Information
These pins must be left unconnected.
SW
Internally connected to the source of the main
MOSFET and the drain of the Synchronous MOSFET.
Connect to the inductor.
4, 5
6
VIN
Input supply voltage
Supply pin to the device. Nominal input range is 4.5V
to 42V.
BST
Connection for bootstrap capacitor Connect a 33 nF capacitor from the SW pin to this pin.
An internal diode charges the capacitor during the main
MOSFET off-time.
7
8
AGND
SS
Analog Ground
Ground for all internal circuitry other than the PGND
pin.
Soft-start
An 8 µA internal current source charges an external
capacitor to provide the soft- start function.
11
GND
Ground
Must be connected to the AGND pin for normal
operation. The GND and AGND pins are not internally
connected.
13
FB
Feedback
Internally connected to the regulation and over-voltage
comparators. The regulation setting is 0.8V at this pin.
Connect to feedback resistors.
14
15
16
EN
Enable pin
On-time Control
Connect a voltage higher than 1.26V to enable the
regulator.
RON
VCC
An external resistor from the VIN pin to this pin sets the
main MOSFET on-time.
Start-up regulator Output
Nominally regulated to 6V. Connect a capacitor of not
less than 680 nF between the VCC and AGND pins for
stable operation.
17, 18
DAP
PGND
EP
Power Ground
Exposed Pad
Synchronous MOSFET source connection. Tie to a
ground plane.
Thermal connection pad. Connect to the ground plane.
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ESD Rating (Note 2)
Human Body Model
Storage Temperature Range
Junction Temperature (TJ)
Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
±2kV
-65°C to +150°C
150°C
VIN, RON to AGND
SW to AGND
SW to AGND (Transient)
VIN to SW
-0.3V to 43.5V
-0.3V to 43.5V
-2V (< 100ns)
-0.3V to 43.5V
-0.3V to 7V
Operating Ratings (Note 1)
Supply Voltage Range (VIN)
4.5V to 42V
−40°C to +125°C
6.5°C/W
Junction Temperature Range (TJ)
BST to SW
Thermal Resistance (θJC) (Note 3)
All Other Inputs to AGND
-0.3V to 7V
Electrical Characteristics Specifications with standard type are for TJ = 25°C only; limits in boldface type apply
over the full Operating Junction Temperature (TJ) range. Minimum and Maximum limits are guaranteed through test, design, or
statistical correlation. Typical values represent the most likely parametric norm at TJ = 25°C, and are provided for reference
purposes only. Unless otherwise stated the following conditions apply: VIN = 18V, VOUT = 3.3V.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
Start-Up Regulator, VCC
VCC
VCC output voltage
CCC = 680nF, no load
ICC = 2mA
5.0
6.0
50
7.2
200
570
V
VIN - VCC
VIN - VCC dropout voltage
mV
ICC = 20mA
350
65
IVCCL
VCC current limit (Note 4)
VCC = 0V
40
mA
V
VCC-UVLO
VCC under-voltage lockout threshold
(UVLO)
VIN increasing
3.6
3.75
3.9
VCC-UVLO-HYS
tVCC-UVLO-D
IIN
VCC UVLO hysteresis
VIN decreasing
130
3
mV
µs
VCC UVLO filter delay
IIN operating current
No switching, VFB = 1V
0.7
25
1
mA
µA
IIN-SD
IIN operating current, Device shutdown VEN = 0V
40
Switching Characteristics
RDS-UP-ON
RDS- DN-ON
VG-UVLO
Main MOSFET RDS(on)
0.18
0.11
3.3
0.375
0.225
4
Ω
Ω
V
Syn. MOSFET RDS(on)
Gate drive voltage UVLO
VBST - VSW increasing
VSS = 0.5V
Soft-start
ISS
Current Limit
ICL
SS pin source current
6
8
10
µA
A
Syn. MOSFET current limit threshold
ON timer pulse width
2.7
ON/OFF Timer
ton
1.38
0.47
150
260
µs
VIN = 10V, RON = 100 kΩ
VIN = 30V, RON = 100 kΩ
ton-MIN
toff
ON timer minimum pulse width
OFF timer pulse width
ns
ns
Enable Input
VEN
EN Pin input threshold
VEN rising
VEN falling
1.13
1.18
90
1.23
V
VEN-HYS
Enable threshold hysteresis
mV
Regulation and Over-Voltage Comparator
VFB
In-regulation feedback voltage
0.784
0.788
0.888
0.8
0.816
0.812
0.945
V
VSS ≥ 0.8V
TJ = −40°C to +125°C
VSS ≥ 0.8V
TJ = 0°C to +125°C
VFB-OV
IFB
Feedback over-voltage threshold
0.920
5
V
nA
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Symbol
Thermal Shutdown
TSD
Parameter
Conditions
Min
Typ
Max
Units
Thermal shutdown temperature
TJ rising
TJ falling
165
20
°C
°C
TSD-HYS
Thermal shutdown temperature
hysteresis
Note 1: Absolute Maximum Ratings are limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the
device is intended to be functional. For guaranteed specifications and test conditions, see the Electrical Characteristics.
Note 2: The human body model is a 100pF capacitor discharged through a 1.5kΩ resistor into each pin.
Note 3: θJC measurements are performed in general accordance with Mil-Std 883B, Method 1012.1 and utilizes the copper heat sink technique. Copper Heat
Sink @ 60°C.
Note 4: VCC provides self bias for the internal gate drive and control circuits. Device thermal limitations limit external loading.
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Typical Performance Characteristics
All curves are taken at VIN = 18V with the configuration in the typical application circuit for VOUT = 3.3V shown in this datasheet.
TA = 25°C, unless otherwise specified.
Quiescent Current, IIN vs VIN
VCC vs ICC
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30021305
30021307
30021304
30021306
30021308
VCC vs VIN
ton vs VIN
Switching Frequency, fSW vs VIN
VFB vs Temperature
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RDS(on) vs Temperature
Efficiency vs Load Current
(VOUT = 3.3V)
30021309
30021310
VOUT Regulation vs Load Current
(VOUT = 3.3V)
Efficiency vs Load Current
(VOUT = 0.8V)
30021311
30021312
VOUT Regulation vs Load Current
(VOUT = 0.8V)
Power Up
(VOUT = 3.3V, 2.5A Loaded)
30021339
30021313
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Enable Transient
(VOUT = 3.3V, 2.5A Loaded)
Shutdown Transient
(VOUT = 3.3V, 2.5A Loaded)
30021314
30021315
Continuous Mode Operation
(VOUT = 3.3V, 2.5A Loaded)
Discontinuous Mode Operation
(VOUT = 3.3V, 0.025A Loaded)
30021316
30021317
DCM to CCM Transition
(VOUT = 3.3V, 0.15A - 2.5A Load)
Load Transient
(VOUT = 3.3V, 0.25A - 2.5A Load, Current slew-rate: 2.5A/µs)
30021318
30021319
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Simplified Functional Block Diagram
30021320
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Functional Description
VOUT = 0.8V x (RFB1 + RFB2)/RFB2
(3)
The LM3102 Step Down Switching Regulator features all re-
quired functions to implement a cost effective, efficient buck
power converter capable of supplying 2.5A to a load. It con-
tains Dual N-Channel main and synchronous MOSFETs. The
Constant ON-Time (COT) regulation scheme requires no loop
compensation, results in fast load transient response and
simple circuit implementation. The regulator can function
properly even with an all ceramic output capacitor network,
and does not rely on the output capacitor’s ESR for stability.
The operating frequency remains constant with line variations
due to the inverse relationship between the input voltage and
the on-time. The valley current limit detection circuit, with the
limit set internally at 2.7A, inhibits the main MOSFET until the
inductor current level subsides.
Startup Regulator (VCC)
A startup regulator is integrated within the LM3102. The input
pin VIN can be connected directly to a line voltage up to 42V.
The VCC output regulates at 6V, and is current limited to 65
mA. Upon power up, the regulator sources current into an ex-
ternal capacitor CVCC, which is connected to the VCC pin. For
stability, CVCC must be at least 680 nF. When the voltage on
the VCC pin is higher than the under-voltage lock-out (UVLO)
threshold of 3.75V, the main MOSFET is enabled and the SS
pin is released to allow the soft-start capacitor CSS to charge.
The minimum input voltage is determined by the dropout volt-
age of the regulator and the VCC UVLO falling threshold
(≊3.7V). If VIN is less than ≊4.0V, the regulator shuts off and
VCC goes to zero.
The LM3102 can be applied in numerous applications and
can operate efficiently for inputs as high as 42V. Protection
features include output over-voltage protection, thermal shut-
down, VCC under-voltage lock-out, gate drive under-voltage
lock-out. The LM3102 is available in the thermally enhanced
eTSSOP-20 package.
Regulation Comparator
The feedback voltage at the FB pin is compared to a 0.8V
internal reference. In normal operation (the output voltage is
regulated), an on-time period is initiated when the voltage at
the FB pin falls below 0.8V. The main MOSFET stays on for
the on-time, causing the output voltage and consequently the
voltage of the FB pin to rise above 0.8V. After the on-time
period, the main MOSFET stays off until the voltage of the FB
pin falls below 0.8V again. Bias current at the FB pin is nom-
inally 5 nA.
COT Control Circuit Overview
COT control is based on a comparator and a one-shot on-
timer, with the output voltage feedback (feeding to the FB pin)
compared with an internal reference of 0.8V. If the voltage of
the FB pin is below the reference, the main MOSFET is turned
on for a fixed on-time determined by a programming resistor
RON and the input voltage VIN, upon which the on-time varies
inversely. Following the on-time, the main MOSFET remains
off for a minimum of 260 ns. Then, if the voltage of the FB pin
is below the reference, the main MOSFET is turned on again
for another on-time period. The switching will continue to
achieve regulation.
Zero Coil Current Detect
The current of the synchronous MOSFET is monitored by a
zero coil current detection circuit which inhibits the syn-
chronous MOSFET when its current reaches zero until the
next on-time. This circuit enables the DCM operation, which
improves the efficiency at a light load.
The regulator will operate in the discontinuous conduction
mode (DCM) at a light load, and the continuous conduction
mode (CCM) with a heavy load. In the DCM, the current
through the inductor starts at zero and ramps up to a peak
during the on-time, and then ramps back to zero before the
end of the off-time. It remains zero and the load current is
supplied entirely by the output capacitor. The next on-time
period starts when the voltage at the FB pin falls below the
internal reference. The operating frequency in the DCM is
lower and varies larger with the load current as compared with
the CCM. Conversion efficiency is maintained since conduc-
tion loss and switching loss are reduced with the reduction in
the load and the switching frequency respectively. The oper-
ating frequency in the DCM can be calculated approximately
as follows:
Over-Voltage Comparator
The voltage at the FB pin is compared to a 0.92V internal
reference. If it rises above 0.92V, the on-time is immediately
terminated. This condition is known as over-voltage protec-
tion (OVP). It can occur if the input voltage or the output load
changes suddenly. Once the OVP is activated, the main
MOSFET remains off until the voltage at the FB pin falls below
0.92V. The synchronous MOSFET will stay on to discharge
the inductor until the inductor current reduces to zero, and
then switch off.
ON-Time Timer, Shutdown
The on-time of the LM3102 main MOSFET is determined by
the resistor RON and the input voltage VIN. It is calculated as
follows:
(1)
In the continuous conduction mode (CCM), the current flows
through the inductor in the entire switching cycle, and never
reaches zero during the off-time. The operating frequency re-
mains relatively constant with load and line variations. The
CCM operating frequency can be calculated approximately as
follows:
(4)
The inverse relationship of ton and VIN gives a nearly constant
frequency as VIN is varied. RON should be selected such that
the on-time at maximum VIN is greater than 150 ns. The on-
timer has a limiter to ensure a minimum of 150 ns for ton. This
limits the maximum operating frequency, which is governed
by the following equation:
(2)
The output voltage is set by two external resistors RFB1 and
RFB2. The regulated output voltage is
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the main MOSFET is turned off, the inductor current flows
through the load, the PGND pin and the internal synchronous
MOSFET. If this current exceeds 2.7A, the current limit com-
parator toggles, and as a result disabling the start of the next
on-time period. The next switching cycle starts when the re-
circulating current falls back below 2.7A (and the voltage at
the FB pin is below 0.8V). The inductor current is monitored
during the on-time of the synchronous MOSFET. As long as
the inductor current exceeds 2.7A, the main MOSFET will re-
main inhibited to achieve current limit. The operating frequen-
cy is lower during current limit due to a longer off-time.
(5)
The LM3102 can be remotely shutdown by pulling the voltage
of the EN pin below 1V. In this shutdown mode, the SS pin is
internally grounded, the on-timer is disabled, and bias cur-
rents are reduced. Releasing the EN pin allows normal oper-
ation to resume because the EN pin is internally pulled up.
Figure 2 illustrates an inductor current waveform. On aver-
age, the output current IOUT is the same as the inductor
current IL, which is the average of the rippled inductor current.
In case of current limit (the current limit portion of Figure 2),
the next on-time will not initiate until that the current drops
below 2.7A (assume the voltage at the FB pin is lower than
0.8V). During each on-time the current ramps up an amount
equal to:
30021325
FIGURE 1. Shutdown Implementation
Current Limit
Current limit detection is carried out during the off-time by
monitoring the re-circulating current through the synchronous
MOSFET. Referring to the Functional Block Diagram, when
(6)
During current limit, the LM3102 operates in a constant cur-
rent mode with an average output current IOUT(CL) equal to
2.7A + ILR / 2.
30021326
FIGURE 2. Inductor Current - Current Limit Operation
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2.5A output current is possible by increasing the PCB ground
plane area, or reducing the input voltage or operating fre-
quency.
N-Channel MOSFET and Driver
The LM3102 integrates an N-Channel main MOSFET and an
associated floating high voltage main MOSFET gate driver.
The gate drive circuit works in conjunction with an external
bootstrap capacitor CBST and an internal high voltage diode.
CBST connecting between the BST and SW pins powers the
main MOSFET gate driver during the main MOSFET on-time.
During each off-time, the voltage of the SW pin falls to ap-
proximately -1V, and CBST charges from VCC through the
internal diode. The minimum off-time of 260 ns provides
enough time for charging CBST in each cycle.
Soft-Start
The soft-start feature allows the converter to gradually reach
a steady state operating point, thereby reducing startup
stresses and current surges. Upon turn-on, after VCC reaches
the under-voltage threshold, an 8 µA internal current source
charges up an external capacitor CSS connecting to the SS
pin. The ramping voltage at the SS pin (and the non-inverting
input of the regulation comparator as well) ramps up the out-
put voltage VOUT in a controlled manner.
30021340
FIGURE 4. Thermal Derating Curve
An internal switch grounds the SS pin if any of the following
three cases happens: (i) VCC is below the under-voltage lock-
out threshold; (ii) a thermal shutdown occurs; or (iii) the EN
pin is grounded. Alternatively, the output voltage can be shut
off by connecting the SS pin to ground using an external
switch. Releasing the switch allows the SS pin to ramp up and
the output voltage to return to normal. The shutdown config-
uration is shown in Figure 3.
30021327
FIGURE 3. Alternate Shutdown Implementation
Thermal Protection
The junction temperature of the LM3102 should not exceed
the maximum limit. Thermal protection is implemented by an
internal Thermal Shutdown circuit, which activates (typically)
at 165°C to make the controller enter a low power reset state
by disabling the main MOSFET, disabling the on-timer, and
grounding the SS pin. Thermal protection helps prevent
catastrophic failures from accidental device overheating.
When the junction temperature falls back below 145°C (typi-
cal hysteresis = 20°C), the SS pin is released and normal
operation resumes.
Thermal Derating
The LM3102 is capable of supplying 2.5A below an ambient
temperature of 100°C. Under worst case operation, with ei-
ther input voltage up to 42V, operating frequency up to 1 MHz,
or voltage of the RON pin below the absolute maximum of 7V,
the LM3102 can deliver a minimum of 1.9A output current
without thermal shutdown with a PCB ground plane copper
area of 40cm2, 2 oz/Cu. Figure 4 shows a thermal derating
curve for the minimum output current without thermal shut-
down against ambient temperature up to 125°C. Obtaining
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Beware that the higher peak of ILR should not be larger than
the saturation current of the inductor and current limits of the
main and synchronous MOSFETs. Also, the lower peak of
ILR must be positive if CCM operation is required.
Applications Information
EXTERNAL COMPONENTS
The following guidelines can be used to select external com-
ponents.
RFB1 and RFB2 : These resistors should be chosen from stan-
dard values in the range of 1.0 kΩ to 10 kΩ, satisfying the
following ratio:
RFB1/RFB2 = (VOUT/0.8V) - 1
(7)
For VOUT = 0.8V, the FB pin can be connected to the output
directly with a pre-load resistor drawing more than 20 µA. It is
because the converter operation needs a minimum inductor
current ripple to maintain good regulation when no load is
connected.
RON: Equation (2) can be used to select RON if a desired op-
erating frequency is selected. But the minimum value of
RON is determined by the minimum on-time. It can be calcu-
lated as follows:
30021331
(8)
FIGURE 6. Inductor selection for VOUT = 3.3V
If RON calculated from (2) is smaller than the minimum value
determined in (8), a lower frequency should be selected to re-
calculate RON by (2). Alternatively, VIN(MAX) can also be limited
in order to keep the frequency unchanged. The relationship
of VIN(MAX) and RON is shown in Figure 5.
On the other hand, the minimum off-time of 260 ns can limit
the maximum duty ratio. Larger RON should be selected in any
application requiring large duty ratio.
30021332
FIGURE 7. Inductor selection for VOUT = 0.8V
Figure 6 and Figure 7 show curves on inductor selection for
various VOUT and RON. For small RON, according to (8), VIN is
limited. Some curves are therefore limited as shown in the
figures.
30021329
CVCC: The capacitor on the VCC output provides not only noise
filtering and stability, but also prevents false triggering of the
VCC UVLO at the main MOSFET on/off transitions. CVCC
should be no smaller than 680 nF for stability, and should be
a good quality, low ESR, ceramic capacitor.
FIGURE 5. Maximum VIN for selected RON
L: The main parameter affected by the inductor is the ampli-
tude of inductor current ripple (ILR). Once ILR is selected, L can
be determined by:
COUT and COUT3: COUT should generally be no smaller than
10 µF. Experimentation is usually necessary to determine the
minimum value for COUT, as the nature of the load may require
a larger value. A load which creates significant transients re-
quires a larger COUT than a fixed load.
(9)
COUT3 is a small value ceramic capacitor located close to the
LM3102 to further suppress high frequency noise at VOUT. A
100 nF capacitor is recommended.
where VIN is the maximum input voltage and fSW is determined
from (2).
If the output current IOUT is determined, by assuming that
IOUT = IL, the higher and lower peak of ILR can be determined.
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CIN and CIN3: The function of CIN is to supply most of the main
MOSFET current during the on-time, and limit the voltage rip-
ple at the VIN pin, assuming that the voltage source connect-
ing to the VIN pin has finite output impedance. If the voltage
source’s dynamic impedance is high (effectively a current
source), CIN supplies the average input current, but not the
ripple current.
PC BOARD LAYOUT
The LM3102 regulation, over-voltage, and current limit com-
parators are very fast so they will respond to short duration
noise pulses. Layout is therefore critical for optimum perfor-
mance. It must be as neat and compact as possible, and all
external components must be as close to their associated
pins of the LM3102 as possible. Refer to the functional block
diagram, the loop formed by CIN, the main and synchronous
MOSFET internal to the LM3102, and the PGND pin should
be as small as possible. The connection from the PGND pin
to CIN should be as short and direct as possible. Vias should
be added to connect the ground of CIN to a ground plane,
located as close to the capacitor as possible. The bootstrap
capacitor CBST should be connected as close to the SW and
BST pins as possible, and the connecting traces should be
thick. The feedback resistors and capacitor RFB1, RFB2, and
CFB should be close to the FB pin. A long trace running from
VOUT to RFB1 is generally acceptable since this is a low
impedance node. Ground RFB2 directly to the AGND pin (pin
7). The output capacitor COUT should be connected close to
the load and tied directly to the ground plane. The inductor L
should be connected close to the SW pin with as short a trace
as possible to reduce the potential for EMI (electromagnetic
interference) generation. If it is expected that the internal dis-
sipation of the LM3102 will produce excessive junction tem-
perature during normal operation, making good use of the PC
board’s ground plane can help considerably to dissipate heat.
The exposed pad on the bottom of the LM3102 IC package
can be soldered to the ground plane, which should extend out
from beneath the LM3102 to help dissipate heat. The exposed
pad is internally connected to the LM3102 IC substrate. Ad-
ditionally the use of thick traces, where possible, can help
conduct heat away from the LM3102. Using numerous vias to
connect the die attached pad to the ground plane is a good
practice. Judicious positioning of the PC board within the end
product, along with the use of any available air flow (forced or
natural convection) can help reduce the junction temperature.
At the maximum load current, when the main MOSFET turns
on, the current to the VIN pin suddenly increases from zero
to the lower peak of the inductor’s ripple current and ramps
up to the higher peak value. It then drops to zero at turn-off.
The average current during the on-time is the load current.
For a worst case calculation, CIN must be capable of supplying
this average load current during the maximum on-time. CIN is
calculated from:
(10)
where IOUT is the load current, ton is the maximum on-time,
and ΔVIN is the allowable ripple voltage at VIN.
CIN3’s purpose is to help avoid transients and ringing due to
long lead inductance at the VIN pin. A low ESR 0.1 µF ceramic
chip capacitor located close to the LM3102 is recommended.
CBST: A 33 nF high quality ceramic capacitor with low ESR is
recommended for CBST since it supplies a surge current to
charge the main MOSFET gate driver at turn-on. Low ESR
also helps ensure a complete recharge during each off-time.
CSS: The capacitor at the SS pin determines the soft-start
time, i.e. the time for the reference voltage at the regulation
comparator and the output voltage to reach their final value.
The time is determined from the following equation:
(11)
CFB: If the output voltage is higher than 1.6V, CFB is needed
in the Discontinuous Conduction Mode to reduce the output
ripple. The recommended value for CFB is 10 nF.
30021335
Typical Application Schematic for VOUT = 3.3V
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14
30021336
Typical Application Schematic for VOUT = 0.8V
15
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Physical Dimensions inches (millimeters) unless otherwise noted
20-Lead Plastic eTSSOP Package
NS Package Number MXA20A
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16
Notes
17
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Notes
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