LTC3721-1
Push-Pull PWM Controller
FEATURES
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DESCRIPTIO
High Efficiency Push-Pull PWM
1.5A Sink, 1A Source Output Drivers
Adjustable Push-Pull Dead-Time
Adjustable System Undervoltage Lockout and
Hysteresis
Adjustable Leading Edge Blanking
Low Start-Up and Quiescent Currents
Current Mode Operation
Single Resistor Slope Compensation
V
CC
UVLO and 25mA Shunt Regulator
Programmable Fixed Frequency Operation to 1MHz
Soft-Start, Cycle-by-Cycle Current Limiting and
Hiccup Mode Short-Circuit Protection
5V, 15mA Low Dropout Regulator
16-Pin SSOP and (4mm
×
4mm) QFN Packages
The LTC
®
3721-1 push-pull PWM controller provides all of
the control and protection functions necessary for com-
pact and highly efficient, isolated power converters. High
integration minimizes external component count, while
preserving design flexibility.
The robust push-pull output stages switch at half the
oscillator frequency. Dead-time is independently pro-
grammed with an external resistor. A UVLO program input
provides precise system turn-on and turn off voltages. The
LTC3721-1 features peak current mode control with pro-
grammable slope compensation and leading edge
blanking.
The LTC3721-1 features extremely low operating and
start-up currents and reliable short-circuit and
overtemperature protection. The LTC3721-1 is offered in
16-pin SSOP and (4mm
×
4mm) QFN packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
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Telecommunications, Infrastructure Power Systems
Distributed Power Architectures
Server Power Supplies
High Density Power Modules
TYPICAL APPLICATIO
V
IN
Isolated Push-Pull Converter
V
OUT
UVLO
FROM
AUXILIARY
WINDING
V
CC
DPRG
V
REF
C
T
R
LEB
DRVA
DRVB
CS
R
CS
LTC3721-1
V
REF
V
OUT
SS
COMP
V
OUT
V
+
COLL
COMP
LT1431
R
TOP
R
REF
R
MID
FB GND
GND-F GND-S
U
+
37211 TA01
U
U
sn37211 37211fs
1
LTC3721-1
ABSOLUTE
AXI U RATI GS
V
CC
to GND (Low Impedance Source) .......– 0.3V to 10V
(Chip Self-Regulates at 10.3V)
UVLO to GND ............................................. – 0.3V to V
CC
All Other Pins to GND
(Low Impedance Source) .........................– 0.3V to 5.5V
V
CC
(Current Fed) ................................................. 40mA
PACKAGE/ORDER I FOR ATIO
TOP VIEW
V
REF
NC
NC
DRVB
V
CC
DRVA
GND
C
T
1
2
3
4
5
6
7
8
16 NC
15 UVLO
14 SS
13 FB
12 R
LEB
11 COMP
10 CS
9
DPRG
UVLO
V
REF
NC
LTC3721EGN-1
16 15 14 13
DRVB 1
V
CC
2
DRVA 3
PGND 4
5
SGND
6
C
T
7
NC
8
DPRG
17
12 FB
11 R
LEB
10 COMP
9 CS
SS
ORDER PART
NUMBER
GN PART
MARKING
37211
GN PACKAGE
16-LEAD PLASTIC SSOP
T
JMAX
= 125°C,
θ
JA
= 100°C/W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 9.5V unless otherwise noted.
SYMBOL
Input Supply
V
CCUV
V
CCHY
I
CCST
I
CCRN
V
SHUNT
R
SHUNT
SUVLO
SHYST
V
CC
Undervoltage Lockout
V
CC
UVLO Hysteresis
Start-Up Current
Operating Current
Shunt Regulator Voltage
Shunt Resistance
System UVLO Threshold
System UVLO Hysteresis Current
Measured on V
CC
Measured on V
CC
V
CC
= V
UVLO
– 0.3V
No Load on Outputs
Current into V
CC
= 10mA
Current into V
CC
= 10mA to 17mA
Measured on UVLO Pin, 10mA into V
CC
Current Flows Out of UVLO Pin, 10mA into V
CC
4.8
8.5
●
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
2
U
U
W
W W
U
W
(Note 1)
V
REF
Output Current ............................... Self-Regulated
Operating Temperature (Notes 5,6)
LTC3721-1 ......................................... – 40°C to 85°C
Storage Temperature Range ................. – 65°C to 125°C
Lead Temperature (GN Package only)
(Soldering, 10sec) ............................................ 300°C
TOP VIEW
ORDER PART
NUMBER
LTC3721EUF-1
UF PART
MARKING
37211
UF PACKAGE
16-LEAD (4mm
×
4mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 100°C/W
EXPOSED PAD IS GND
(PIN17) MUST BE SOLDERED TO PCB
MIN
TYP
10.25
MAX
10.7
230
6
10.8
3.5
5.2
11.5
UNITS
V
V
µA
mA
V
Ω
V
µA
3.8
4.2
145
3
10.3
1.4
5.0
10
sn37211 37211fs
LTC3721-1
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 9.5V unless otherwise noted.
SYMBOL
ROS
I
RMP
I
SLP
DCMAX
DCMIN
DTADJ
Oscillator
OSCI
OSCT
OSCV
V
FB
FB
I
AVOL
I
IB
V
OH
V
OL
I
SOURCE
I
SINK
Reference
V
REF
REFLD
REFLN
REFTV
REFSC
DRVH(x)
DRVL(x)
RDH(x)
RDL(x)
TDR(x)
TDF(x)
CLPP
CLSD
CLDEL
SSI
Initial Accuracy
Load Regulation
Line Regulation
Total Variation
Short-Circuit Current
Output High Voltage
Output Low Voltage
Pull-Up Resistance
Pull-Down Resistance
Rise-Time
Fall-Time
Pulse by Pulse Current Limit Threshold
Shutdown Current Limit Threshold
Current Limit Delay to Output
Soft-Start Current
T
A
= 25°C, Measured on V
REF
Load on V
REF
= 100µA to 5mA
V
CC
= 6.5V to 9.5V
Line, Load and Temperature
V
REF
Shorted to GND
I
OUT(x)
= –100mA
I
OUT(x)
= 100mA
I
OUT(x)
= –10mA to –100mA
I
OUT(x)
= –10mA to –100mA
C
OUT(x)
= 1nF
C
OUT(x)
= 1nF
Measured on CS
Measured on CS
100mV Overdrive on CS, (Note 2)
SS = 2.5V
10
280
475
●
ELECTRICAL CHARACTERISTICS
PARAMETER
Ramp Offset Voltage
Ramp Discharge Current
Slope Compensation Current
Maximum Duty Cycle
Minimum Duty Cycle
Dead-Time
Initial Accuracy
V
CC
Variation
C
T
Ramp Amplitude
FB Input Voltage
FB Input Range
Open-Loop Gain
Input Bias Current
Output High
Output Low
Output Source Current
Output Sink Current
CONDITIONS
Measured on COMP, CS = 0V
CS = 1V, COMP = 0V, C
T
= 4V
Measured on CS, C
T
= 1V
C
T
= 2.25V
COMP = 4.5V
COMP = 0V
●
●
MIN
TYP
0.65
50
30
68
MAX
UNITS
V
mA
µA
µA
Pulse Width Modulator
47
48.2
0
130
50
%
%
ns
T
A
= 25°C, C
T
= 270pF
V
CC
= 6.5V to 9.5V
Measured on C
T
COMP = 2.5V, (Note 3)
Measured on FB, (Note 4)
COMP = 1V to 3V, (Note 3)
COMP = 2.5V, (Note 3)
Load on COMP = –100µA
Load on COMP = 100µA
COMP = 2.5V
COMP = 2.5V
●
220
–3
250
2.35
280
3
kHz
%
V
Error Amplifier
1.172
– 0.3
70
4.7
400
2
4.925
90
5
4.92
0.27
700
5
5.00
2
1
4.900
18
5.000
30
9.2
0.17
2.9
1.7
10
10
300
600
80
13
16
320
725
5.075
15
10
5.100
45
0.5
50
1.2
1.22
2.5
V
V
dB
nA
V
V
µA
mA
V
mV
mV
V
mA
V
V
Ω
Ω
ns
ns
mV
mV
ns
µA
Push-Pull Outputs
Current Limit and Shutdown
sn37211 37211fs
3
LTC3721-1
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
CC
= 9.5V unless otherwise noted.
SYMBOL
SSR
FLT
PARAMETER
Soft-Start Reset Threshold
Fault Reset Threshold
CONDITIONS
Measured on SS
Measured on SS
MIN
0.7
4.5
TYP
0.4
4.2
MAX
0.1
3.5
UNITS
V
V
ELECTRICAL CHARACTERISTICS
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
Includes leading edge blanking delay, R
LEB
= 20k, not tested in
production.
Note 3:
FB is driven by a servo loop amplifier to control V
COMP
for these
tests.
Note 4:
Set FB to –0.3V, 2.5V and insure that COMP does not phase invert.
Note 5:
The LTC3721–1 is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 6:
This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
TYPICAL PERFOR A CE CHARACTERISTICS
Start-Up I
CC
vs V
CC
200
150
100
10.00
FREQUENCY (kHz)
I
CC
(µA)
V
CC
(V)
50
0
0
2
4
V
CC
(V)
6
Leading Edge Blanking Time
vs R
LEB
350
300
5.00
5.05
250
BLANK TIME (ns)
V
REF
(V)
200
150
100
V
REF
(V)
50
0
0 10 20 30 40 50 60
R
LEB
(kΩ)
70 80 90 100
372311 G04
4
U W
8
(T
A
= 25°C unless otherwise noted)
Oscillator Frequency vs
Temperature
260
C
T
= 270pF
V
CC
vs I
SHUNT
10.50
10.25
250
240
9.75
230
9.50
10
372311 G01
0
10
30
20
I
SHUNT
(mA)
40
50
372311 G02
220
– 60 – 40 – 20 0
20 40 60
TEMPERATURE (°C)
80
100
372311 G03
V
REF
vs I
REF
5.01
V
REF
vs Temperature
T
J
= 25°C
5.00
T
J
= 85°C
4.95
4.99
4.90
T
J
= –40°C
4.85
4.98
4.80
0
5
10
15 20 25
I
REF
(mA)
30
35
40
4.97
– 60 – 40 – 20 0
20 40 60
TEMPERATURE (°C)
80
100
372311 G05
372311 G06
sn37211 37211fs
LTC3721-1
TYPICAL PERFOR A CE CHARACTERISTICS
Error Amplifier Gain/Phase
190
100
80
60
40
20
0
–180
–270
–360
10
100
1k
10k
100k
FREQUENCY (Hz)
1M
10M
GAIN (dB)
DELAY (ns)
I
CC
(µA)
PHASE (DEG)
Slope Current vs Temperature
90
80
70
C
T
= 2.25V
10.5
10.4
FB VOLTAGE (V)
CURRENT (µA)
60
50
40
30
20
10
0
–55
–25
5
35
65
TEMPERATURE (°C)
95
125
C
T
= 1V
SHUNT VOLTAGE (V)
U W
(T
A
= 25°C unless otherwise noted)
Start-Up I
CC
vs Temperature
275
250
225
Deadtime vs R
DPRG
180
170
160
150
140
130
120
110
100
–55
–25
5
35
65
TEMPERATURE (°C)
95
125
200k PREBIAS
200
175
150
125
100
75
50
0
50 100 150 200 250 300 350 400 450 500
R
DPRG
(kΩ)
372311 G09
NO 200k PREBIAS
372311 G07
372311 G08
V
CC
Shunt Voltage vs
Temperature
I
CC
= 10mA
1.205
1.204
1.203
1.202
1.201
1.200
1.199
1.198
–25
5
35
65
TEMPERATURE (°C)
95
125
FB Input Voltage vs Temperature
10.3
10.2
10.1
10.0
9.9
9.8
–55
1.197
–55
–25
5
35
65
TEMPERATURE (°C)
95
125
372311 G10
372311 G11
372311 G12
sn37211 37211fs
5
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