TMI3253SH
1MHz 18V 3.0A Synchronous COT Step-Down Converter
Features
Description
⚫
70mΩ/35mΩ Low RDS(ON) internal FETs
The TMI3253SH is a high efficiency 1MHz,
⚫
High Efficiency Synchronous-Mode
Constant-on-Time
Operation
synchronous step-down DC-DC converter capable
(COT)
control
mode
of delivering up to 3.0A current with 1.2V output
⚫
Wide Input Range: 4.5V to 18V
⚫
Output Voltage from 0.6V
⚫
1MHz Switch Frequency
⚫
Up to 3.0A Output Current@1.2VOUT
ripple and small external inductor and capacitor
⚫
COT control to achieve fast transient
size are achieved with 1MHz switching frequency.
responses
It adopts the COT architecture to achieve fast
⚫
Power Save Mode at Light Load
transient responses for high voltage step down
⚫
Integrated internal compensation
applications.
⚫
Stable with Low ESR Ceramic Output
The TMI3253SH requires a minimum number of
Capacitors
readily available standard external components
voltage. TMI3253SH integrates main switch and
synchronous switch with very low RDS(ON) to
minimize the conduction loss. Low output voltage
and is available in a 6-pin SOT23-6 ROHS
⚫
Over Current Protection with Hiccup Mode
⚫
Thermal Shutdown
⚫
Inrush Current Limit and Soft Start
Application
⚫
Build in Input Over Voltage Protection
⚫
⚫ Digital Set Top Boxes
Available in SOT23-6 Package
⚫ Flat Panel Television and Monitors
compliant package.
⚫ Notebook computer
⚫ Wireless and DSL Modems
Typical Application
Efficiency
VOUT=3.3V, TA=25°C
C4
100%
0.1µF
95%
L
BS
CIN1
CIN2
22µF
100nF
2.2µH
90%
VOUT= 3.3V
LX
R3
100kΩ
R1
39kΩ
EN
FB
GND
R2
8.66kΩ
Efficiency
VIN
Cfb
20pF~
100pF
CO1
CO2
22µF
22µF
85%
80%
75%
70%
9V-3.3V
12V-3.3V
16V-3.3V
65%
60%
0.01
TMI and SUNTO are the brands of TOLL microelectronic
TMI3253SH Rev. 1.1 – 2019.11
0.1
1
Output Current (A)
10
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1
TMI3253SH
Absolute Maximum Ratings (Note 1)
Parameter
Min
Max
Unit
Input Supply Voltage, EN
LX Voltages
FB Voltage
BS Voltage
Storage Temperature Range
Junction Temperature (Note2)
Power Dissipation
Lead Temperature (Soldering, 10s)
-0.3
-0.3
-0.3
-0.3
-65
20
20
6
23
150
V
V
V
V
°C
°C
mW
°C
160
1000
260
Package
BS 1
6 LX
GND 2
5 IN
FB 3
4 EN
SOT23-6
Top Marking: TS5XXX
TS5: Device Code
XXX: Inside Code
Order Information
Part Number
Package
Top Marking
Quantity/Reel
TMI3253SH
SOT23-6
TS5XXX
3000
TMI3253SH devices are Pb-free and RoHS compliant.
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TMI3253SH
Pin Functions
Pin
Name
Function
1
BS
2
GND
3
FB
4
EN
5
IN
Power supply Pin
6
LX
Switching Pin
Bootstrap. A capacitor connected between LX and BS pins is required to
form a floating supply across the high-side switch driver.
Ground Pin
Output Voltage feedback input. Connect FB to the center point of the
external resistor divider.
Drive this pin to a logic-high to enable the IC. Drive to a logic-low to
disable the IC and enter micro-power shutdown mode. Don’t floating EN.
ESD Rating
Items
Description
Value
Unit
VESD_HBM
Human Body Model for all pins
±2000
V
VESD_CDM
Charged Device Model for all pins
±2000
V
JEDEC specification JS-001
Recommended Operating Conditions
Items
Description
Min
Max
Unit
Voltage Range
IN
4.5
18
V
TJ
Operating Junction Temperature
-40
125
°C
Thermal Resistance (Note3)
Items
Description
Value
Unit
θJA
Junction-to-ambient thermal resistance
100
°C/W
θJC
Junction-to-case(top) thermal resistance
56
°C/W
ψJC
Junction-to-case(top) thermal characteristic parameter
3.5
°C/W
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TMI3253SH
Electrical Characteristics
VIN=12V, VOUT=3.3V, TA = 25°C, unless otherwise noted.
Parameter
Conditions
Min
Typ
Max
Unit
18
V
Input Voltage Range
4.5
OVP Threshold
18.7
19.3
19.8
V
UVLO Rising Threshold
4.0
4.2
4.35
V
UVLO Hysteresis
0.4
0.45
0.5
V
300
450
μA
5
10
μA
0.6
0.612
V
Quiescent Current
VEN=2V, VFB=VREF x 105%
Shutdown Current
VIN=12V, EN=0V
Regulated Feedback Voltage
TA=25°C, 4.5V≤VIN≤18V
0.588
High-Side Switch On-Resistance
70
mΩ
Low-Side Switch On-Resistance
35
mΩ
High-Side Switch Leakage Current
VEN=0V, VLX=0V
Switch Valley Current Limit
Minimum Duty Cycle
3.7
On Time
VIN=12V, VOUT=1.2V, IOUT=1A
Oscillation Frequency
1
10
μA
4
4.5
A
90
120
160
ns
900
1000
1100
kHz
Maximum Duty Cycle
65
%
Minimum On-Time (Note 4)
60
80
100
ns
Soft Start Time
0.6
0.8
1.2
ms
Hiccup on Time (Note 4)
1.2
ms
Hiccup Time Before Restart (Note 4)
3.6
ms
EN Rising Threshold
0.85
0.95
1.05
V
EN Falling Threshold
0.75
0.85
0.95
V
EN Hysteresis
100
mV
Thermal Shutdown Threshold (Note 4)
165
°C
Thermal Shutdown Hysteresis (Note 4)
30
°C
Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.
Note 2: TJ is calculated from the ambient temperature TA and power dissipation PD according to the
following formula: TJ = TA + PD x θJA. The maximum allowable continuous power dissipation at any
ambient temperature is calculated by PD (MAX) = (TJ(MAX)-TA)/θJA.
Note 3: Measured on JESD51-7, 4-layer PCB. ψJC is measure on top case of device on JESD51-7, 4layer PCB with natural heat dissipation.
Note 4: Guaranteed by design.
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TMI3253SH
Block Diagram
EN
VIN
BS
Regulator
UVLO
OVP
Vuv
+
OTP
Hiccup
Logic
Control
PWM Comparator
FB
+ EA
+
Voltage
Reference
VCOMP
LX
Gate
Driver
+
-
ON time
Generater
+
ZC
-
Soft Start
Current Sense
and OCP
GND
Figure 1. TMI3253SH Block Diagram
Operation Description
Internal Regulator
The TMI3253SH is a constant on-time (COT) step down DC/DC converter that provides excellent
transient response with no extra external compensation components. This device contains low resistance,
high voltage high side and low side power MOSFETs, and operates at 1MHz operating frequency to
ensure a compact, high efficiency design with excellent AC and DC performance.
Error Amplifier
TMI3253SH adopts operational transconductance amplifier (OTA) as error amplifier. The error amplifier
compares the FB pin voltage with the internal FB reference (VREF) and outputs a current proportional to
the difference between the two. This output current is then used to charge or discharge the internal
compensation network to form the VCOMP voltage, which is used to compare with the low side power
MOSFET current sensing signal and trigger on time pulse. The optimized internal compensation network
minimizes the external component counts and simplifies the control loop design.
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TMI3253SH
Internal Soft-Start
The soft-start is implemented to prevent the converter output voltage from overshooting during startup.
When the chip starts, the internal circuitry generates a soft-start voltage (SS) ramping up from 0V to 0.6V.
When it is lower than the internal FB reference (VREF), SS overrides REF so the error amplifier uses SS
as the reference. When SS is higher than VREF, VREF regains control. The SS time is internally fixed to
0.8ms typically.
Over-Current-Protection and Short Circuits Protection
The TMI3253SH has cycle-by-cycle valley current limit function. When the inductor current valley value
is larger than the valley current limit during low side MOSFET on state, the device enters into valley over
current protection mode and low side MOSFET keeps on state until inductor current drops down to the
value equal or lower than the valley current limit, and then on time pulse could be generated and high
side MOSFET could turn on again.
If the output is short to GND and the output voltage drop until feedback voltage VFB is below the output
under-voltage VUV threshold which is typically 65% of VREF, TMI3253SH enters into hiccup mode to
periodically disable and restart switching operation. The hiccup mode helps to reduce power dissipation
and thermal rise during output short condition. The period of TMI3253SH hiccup mode is typically 4.8ms.
Startup and Shutdown
If both VIN and EN are higher than their appropriate thresholds, the chip starts switching operation. The
reference block starts first, generating stable reference voltage and currents, and then the internal
regulator is enabled. The regulator provides stable supply for the remaining circuitries. Three events can
shut down the chip: EN low, VIN low and thermal shutdown. In the shutdown procedure, the signaling
path is first blocked to avoid any fault triggering. The VCOMP voltage and the internal supply rail are then
pulled down. The floating driver is not subject to this shutdown command.
Application Information
Setting the Output Voltage
The external resistor divider is used to set the output voltage (see Typical Application on page 1). Choose
R1 to be around 39kΩ for optimal transient response. R2 is then given by:
Table 1: Selection for Common Output Voltages (VFB=0.6V)
VOUT (V)
R1 (kΩ)
R2 (kΩ)
CFB(pF)
L (μH)
5
39
5.36
33
2.2
3.3
39
8.66
33
2.2
2.5
39
12.4
33
2.2
1.8
39
19.6
33
1.5
1.5
39
26.1
33
1.5
1.2
39
39
33
1.5
1
39
59
33
1.0
R2 =
R1
Vout /VFB − 1
C fb=20pF~100pF
TMI3253SH
VOUT
FB
R1
R2
Figure 2. Feedback Network
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TMI3253SH
Selecting the Inductor
A 1.0μH to 2.2μH inductor with a DC current rating of at least 25% percent higher than the maximum load
current is recommended for most applications. For highest efficiency, the inductor DC resistance should
be as small as possible. For most designs, the inductance value can be derived from the following
equation.
V (Vin − Vout )
L = out
Vin I L fOSC
Where ΔIL is the inductor ripple current. Choose inductor ripple current to be approximately 30% if the
maximum load current, 3A. The maximum inductor peak current is:
I L ( MAX ) = I LOAD +
I L
2
Under light load conditions below 100mA, larger inductance is recommended for improved efficiency.
Selecting the Output Capacitor
The output capacitor (Co1 and Co2) is required to maintain the DC output voltage. Ceramic, tantalum, or
low ESR electrolytic capacitors are recommended. Low ESR capacitors are preferred to keep the output
voltage ripple low. The output voltage ripple can be estimated by:
VOUT =
VOUT VOUT
1
1 −
RESR +
f S L VIN
8 f S C2
Where L is the inductor value and RESR is the equivalent series resistance (ESR) value of the output
capacitor. In the case of ceramic capacitors, the impedance at the switching frequency is dominated by
the capacitance. The output voltage ripple is mainly caused by the capacitance. For simplification, the
output voltage ripple can be estimated by:
V
1 − OUT
8 f S L C2 VIN
In the case of tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching
VOUT =
VOUT
2
frequency. For simplification, the output ripple can be approximated to:
VOUT =
VOUT VOUT
1 −
RESR
f S L VIN
The characteristics of the output capacitor also affect the stability of the regulation system. The
TMI3253SH can be optimized for a wide range of capacitance and ESR values.
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TMI3253SH
Typical Performance Characteristics
Efficiency
Efficiency
VOUT =3.3V, L=2.2μH, DCR=20mΩ
VOUT =5V, L=2.2μH, DCR=30mΩ
95%
90%
90%
Efficiency
100%
95%
Efficiency
100%
85%
80%
75%
70%
60%
0.01
0.1
1
Output Current (A)
80%
75%
70%
9V-3.3V
12V-3.3V
16V-3.3V
65%
85%
10
60%
0.01
Efficiency
90%
1.5%
Efficiency
80%
70%
60%
50%
9V-1.2V
12V-1.2V
16V-1.2V
Output Voltage Regulation
2.0%
20%
0.01
10
VIN=12V, TA=25°C
100%
30%
0.1
1
Output Current (A)
Load Regulation
VOUT=1.2V, L=1.5μH, DCR=20mΩ
40%
9V-5V
12V-5V
16V-5V
65%
Vo=5V
Vo=3.3V
1.0%
Vo=1.2V
0.5%
0.0%
-0.5%
-1.0%
-1.5%
-2.0%
0.1
1
Output Current (A)
10
0
Load Transient
0.5
1
1.5
2
2.5
Output Current (A)
3
3.5
Load Transient
VIN =12V, VOUT =3.3V, Io =0A to 3A
VIN =12V, VOUT =3.3V, Io =1.5A to 3A
Vout=200mV/div
AC coupled
Vout=200mV/div
AC coupled
Io=2A/div
Io=2A/div
Time: 200μs/div
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Time: 200μs/div
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TMI3253SH
Typical Performance Characteristics(continued)
Output Short Entry
Output Short Recovery
VIN =12V, VOUT =3.3V, No Load
VIN=12V, VOUT =3.3V, No Load
Vout=2V/div
Vout=2V/div
Vin=5V/div
Vin=5V/div
LX=10V/div
LX=10V/div
IL=5A/div
Time: 4ms/div
IL=5A/div
Input Power On
Time: 4ms/div
Input Power Down
VIN =12V, VOUT =3.3V, Io =Full Load
VIN =12V, VOUT =3.3V, Io =Full Load
Vout=2V/div
Vin=5V/div
Vout=2V/div
LX=10V/div
Vin=5V/div
LX=10V/div
IL=2A/div
IL=2A/div
Time: 400μs/div
Time: 10ms/div
EN Enable
EN Disable
VIN =12V, VOUT =3.3V, Io =Full Load
VIN =12V, VOUT =3.3V, Io =Full Load
Vout=2V/div
Vout=2V/div
LX=10V/div
LX=10V/div
EN=5V/div
EN=5V/div
IL=2A/div
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IL=2A/div
Time: 400μs/div
Time: 40μs/div
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TMI3253SH
Typical Application Circuits
C4
0.1µF
L
BS
VIN
CIN1
CIN2
22µF
100nF
2.2µH
VOUT=5V
LX
R3
100kΩ
R1
39kΩ
EN
Cfb
20pF~
100pF
FB
CO1
R2
5.36kΩ
GND
CO2
22µF
22µF
Figure 4. 12VIN, 5V Output (VFB=0.6V)
C4
0.1µF
L
BS
VIN
CIN1
CIN2
22µF
100nF
2.2µH
VOUT= 3.3V
LX
R3
100kΩ
R1
39kΩ
Cfb
20pF~
100pF
EN
FB
CO1
R2
8.66kΩ
GND
22µF
CO2
22µF
Figure 5. 12VIN, 3.3V Output (VFB=0.6V)
C4
0.1µF
L 1.5µH
BS
VIN
CIN1
CIN2
22µF
100nF
VOUT= 1.8V
LX
R3
100kΩ
R1
39kΩ
Cfb
20pF~
100pF
EN
FB
GND
CO1
R2
19.6kΩ
22µF
CO2
22µF
Figure 6. 12VIN, 1.8V Output (VFB=0.6V)
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Typical Application Circuits(continued)
C4
0.1µF
L 1.5µH
BS
VIN
CIN1
CIN2
22µF
100nF
VOUT= 1.5V
LX
R3
100kΩ
R1
39kΩ
Cfb
20pF~
100pF
EN
FB
CO1
R2
26.1kΩ
GND
22µF
CO2
22µF
Figure 7. 12VIN, 1.5V Output (VFB=0.6V)
C4
0.1µF
L 1.5µH
BS
VIN
CIN1
CIN2
22µF
100nF
VOUT= 1.2V
LX
R3
100kΩ
R1
39kΩ
Cfb
20pF~
100pF
EN
FB
CO1
R2
39kΩ
GND
22µF
CO2
22µF
Figure 8. 12VIN, 1.2V Output (VFB=0.6V)
C4
0.1µF
L
BS
VIN
CIN1
CIN2
22µF
100nF
1µH
VOUT= 1V
LX
R3
100kΩ
R1
39kΩ
Cfb
20pF~
100pF
EN
FB
GND
CO1
R2
59kΩ
22µF
CO2
22µF
Figure 9. 12VIN, 1V Output (VFB=0.6V)
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TMI3253SH
PCB Layout Guide
PCB layout is very important to achieve stable operation. It is highly recommended to duplicate EVB
layout for optimum performance. If change is necessary, please follow these guidelines and take Figure
3 for reference.
1) Keep the path of switching current short and minimize the loop area formed by Input capacitor, IN pin
and GND.
2) Bypass ceramic capacitors are suggested to be put close to the IN Pin.
3) Ensure all feedback connections are short and direct. Place the feedback resistors as close to the chip
as possible.
4) VOUT, LX away from sensitive analog areas such as FB.
5) Connect IN, LX, and especially GND respectively to a large copper area to cool the chip to improve
thermal performance and long-term reliability.
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Package Information
SOT23-6
Unit: mm
Dimensions In Millimeters
Symbol
Dimensions In Millimeters
Symbol
Min
Typ
Max
Min
Typ
Max
A
2.80
2.90
3.00
L3
1.800
1.900
2.000
B
2.60
2.80
3.00
L4
0.077
0.127
0.177
B1
1.50
1.60
1.70
L5
-
0.250
-
C
-
-
1.05
L6
-
0.600
-
C1
0.60
0.80
1.00
θ
0°
C2
0.35
0.40
0.45
Θ1
10°
12°
14°
C4
0.223
0.273
0.323
Θ2
10°
12°
14°
K
0.000
0.075
0.150
R
-
0.100
-
L
0.325
0.400
0.475
R1
-
0.100
-
L1
0.325
0.450
0.550
R2
-
0.100
-
L2
0.850
0.950
1.050
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TMI3253SH
Tape and Reel Information
Tape Dimensions:
Reel Dimensions:
Note:
1)
All Dimensions are in Millimeter
2)
Quantity of Units per Reel is 3000
3)
MSL level is Level 3.
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