Datasheet

UNISONIC TECHNOLOGIES CO., LTD
P1786
LINEAR INTEGRATED CIRCUIT
PWM CONTROL 3A
STEP-DOWN CONVERTER
„
DESCRIPTION
UTC P1786 consists of 3A step-down switching regulator control
which includes a reference voltage source, oscillation circuit, error
amplifier, internal PMOS and etc with PWM.
UTC P1786 can provide low-ripple power, high efficiency, and
excellent transient characteristics. An enable function, an over
current protect and short circuit protect function are built inside, so
the operation frequency can be reduced from 300KHz to 30KHz
when OCP or SCP happens. The PWM control circuit can vary the
duty ratio linearly from 100 down to 0%. This converter also includes
an error amplifier circuit as well as a soft-start circuit that prevents
overshoot at startup. Also, to minimum external component counts
for an internal compensation block is built in.
These ICs can work as step-down switching regulators with the
addition of an internal P-channel Power MOS, a coil, capacitors, and
a diode connected externally. They provide such outstanding
features: low current consumption. It is also suitable for the
operation via an AC adapter because this converter accommodate
an input voltage up to 23V.
„
FEATURES
* Input voltage: 4.0V ~ 23V
* Output voltage: 0.8V ~ VCC
* Duty ratio: 0% to 100% PWM control
* Oscillation frequency: 300KHz typ.
* Soft-start, current limit, enable function
* Thermal shutdown function
* Built-in internal SW P-channel MOS
„
ORDERING INFORMATION
Lead Free
P1786L-S08-R
P1786L-S08-T
Ordering Number
Halogen Free
P1786G-S08-R
P1786G-S08-T
P1786L-S08-R
Package
Packing
SOP-8
SOP-8
Tape Reel
Tube
(1) R: Tape Reel, T: Tube
(1)Packing Type
(2)Package Type
(3)Lead Free
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Copyright © 2011 Unisonic Technologies Co., Ltd
(2) S08: SOP-8
(3) G: Halogen Free, L: Lead Free
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LINEAR INTEGRATED CIRCUIT
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PIN CONFIGURATION
„
PIN DESCRIPTIONS
PIN NO.
1
PIN NAME
FB
I/O
I
I
2
EN
3
4
OCSET
VCC
I
5, 6
Output
O
7, 8
VSS
DESCRIPTION
Feedback pin.
Chip enable, H: enable step-down function
L: chip disable
Add an external resistor to set max output current.
IC power supply pin
Switch Pin. Connect external inductor/diode here. Minimize trace area at this
pin to reduce EMI.
GND Pin
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P1786
„
LINEAR INTEGRATED CIRCUIT
BLOCK DIAGRAM
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LINEAR INTEGRATED CIRCUIT
ABSOLUTE MAXIMUM RATINGS
PARAMETER
SYMBOL
RATING
UNIT
VCC Pin Voltage
VCC
VSS - 0.3 ~ VSS + 25
V
Feedback Pin Voltage
VFB
VSS - 0.3 ~ VCC
V
EN Pin Voltage
VEN
VSS - 0.3 ~ VIN + 0.3
V
Switch Pin Voltage
VOUT
VSS - 0.3 ~ VIN + 0.3
V
Power Dissipation
PD
Internally limited
Operating Temperature
TOPR
-20 ~ +125
°C
Storage Temperature
TSTG
-40 ~ +150
°C
Note: Absolute maximum ratings are those values beyond which the device could be permanently damaged.
Absolute maximum ratings are stress ratings only and functional device operation is not implied.
„
THERMAL DATA
PARAMETER
Junction to Ambient
„
SYMBOL
θJA
RATING
65
UNIT
°C/W
ELECTRICAL CHARACTERISTICS (VIN = 12V, TA=25°C, unless otherwise specified)
PARAMETER
Input Voltage
Feedback Voltage
Feedback Bias Current
Switch Current
Standby Current
Line Regulation
Load Regulation
Oscillation Frequency
Frequency of Current Limit or Short
Circuit Protect
EN Pin Input Voltage
EN Pin Input Leakage Current
SYMBOL
VIN
VFB
IFB(BIAS)
ISC
ISTN-BY
ΔVOUT
VOUT
ΔVOUT
VOUT
fOSC
IOUT=0.1A
IOUT=0.1A
VEN =0V
VIN = 5V~23V, IOUT=0.2A
IOUT = 0.1 to 3A
1
2
%
0.2
0.5
%
240
300
360
KHz
fOSC1
Measure waveform at SW pin
10
30
60
KHz
VSH
VSL
ISH
ISL
Evaluate oscillation at SW pin
Evaluate oscillation stop at SW pin
2.0
IOCSET
TSS
Internal MOSFET RDS(ON)
RDS(ON)
η
0.7
75
0.3
VIN=5V, VFB=0V
VIN=12V, VFB=0V
VIN = 12V, VOUT = 5V, IOUT = 3A
UNISONIC TECHNOLOGIES CO., LTD
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MIN TYP MAX UNIT
4
23
V
0.784 0.8 0.816 V
0.1
0.5
μA
3.5
A
10
μA
Measure waveform at SW pin
OCSET Pin Bias Current
Soft-Start Time
Efficiency
CONDITIONS
20
-10
90
2
110
70
91
105
5
150
100
V
V
μA
μA
μA
ms
mΩ
mΩ
%
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LINEAR INTEGRATED CIRCUIT
FUNCTION DESCRIPTION
PWM Control
The UTC P1786 consists of DC/DC converters which employ a PWM system. In this DC/DC converter, the
pulse width varies in a range from 0 to 100% which is according to the load current. Cause the switching frequency
remains constant the ripple voltage which produced by the switching can be removed easily through a filter.
Therefore, these converters provide a low-ripple power over broad ranges of input voltage and load current.
Under Voltage Lockout
The under voltage lockout circuit makes sure that the outputs of high-side MOSFET driver remain in the off state
after the supply voltage drops below 3.3V. When VCC rises above 3.5V normal operation resumes.
RDS(ON) Current Limiting
The current limit threshold is fixed by the external resistor which is connected from VCC supply to OCSET. An
over-current condition is triggered when the PWM voltage is less than the voltage at OCSET.
ILOAD × RDS(ON) = IOCSET × ROCSET
Above formula is setting the current limit value.
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LINEAR INTEGRATED CIRCUIT
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TYPICAL APPLICATION CIRCUIT
VOUT
L1 Value
VIN=12V, IMAX=3A
2.5V
3.3V
15uH
18uH
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+
TEST CIRCUITS
-
„
5V
22uH
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LINEAR INTEGRATED CIRCUIT
TYPICAL CHARACTERISTICS
Input Voltage vs. Frequency
Input Voltage vs. FB
0.84
345
0.83
340
0.82
335
0.81
330
0.80
FB (V)
Oscillation Frequency, Fosc (KHz)
350
325
320
315
0.79
0.78
0.77
310
0.76
VOUT=3.3V
IOUT=0.2A
305
300
0
0.74
10
5
VOUT=3.3V
IOUT=0.2A
0.75
15
20
25
0
5
Input Voltage, VIN (V)
10
20
15
Input Voltage, VIN (V)
Line Regulation
25
Load Regulation
3.40
5.10
Output Voltage, VOUT (V)
Output Voltage, VOUT (V)
5.09
3.35
3.30
3.25
3.20
3.15
VOUT=3.3V
IOUT=0.2A
5
5.07
5.06
5.05
5.04
5.03
5.02
5.01
3.10
0
5.08
10
15
20
25
1.0
2.0
3.0
4.0
Output Current, IOUT (A)
Efficiency (%)
Input Voltage, VIN (V)
5.00
0.0
VIN=12V
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www.unisonic.com.tw
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P1786
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LINEAR INTEGRATED CIRCUIT
TYPICAL CHARACTERISTICS(Cont.)
UTC assumes no responsibility for equipment failures that result from using products at values that
exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or
other parameters) listed in products specifications of any and all UTC products described or contained
herein. UTC products are not designed for use in life support appliances, devices or systems where
malfunction of these products can be reasonably expected to result in personal injury. Reproduction in
whole or in part is prohibited without the prior written consent of the copyright owner. The information
presented in this document does not form part of any quotation or contract, is believed to be accurate
and reliable and may be changed without notice.
UNISONIC TECHNOLOGIES CO., LTD
www.unisonic.com.tw
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