Sample &
Buy
Product
Folder
Support &
Community
Tools &
Software
Technical
Documents
Reference
Design
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
UCC24636 Synchronous Rectifier (SR) Controller
With Ultra-Low Standby Current
1 Features
3 Description
•
The UCC24636 SR is a compact, 6-pin secondaryside synchronous rectifier MOSFET controller and
driver for high efficiency Flyback converters operating
in Discontinuous (DCM) and Transition mode (TM).
Unlike traditional SR controllers which measure the
SR MOSFET drain voltage, UCC24636 implements a
volt-second balance control method to determine the
turn off transition of the SR MOSFET; hence, SR
conduction time is independent of the MOSFET
RDSON, parasitic inductance or ringing allowing
flexibility to designers in component slelction and
PCB layout. This control method enables maximum
SR conduction time and highest rectifier efficiency for
a given MOSFET.
1
•
•
•
•
•
•
•
•
•
Secondary-Side SR Controller Optimized for 5-V
to 24-V Output Discontinuous/Transition Mode
Only Flyback Converters
Volt-Second Balance Control Enables Highest
Rectifier Efficiency
Compatible with PSR and SSR Flyback
Controllers
Ultra Low 110-µA Standby Current Consumption
Auto-Detect Standby Mode Disables SR Switching
for Lower No-Load Power Consumption
SR Turn-Off Independent of RDSON and Parasitic
Inductance
Operating Frequency Up to 130 kHz
Wide VDD Range from 3.6 V to 28 V
Adaptive Gate Drive Clamp
Open and Short Pin Fault Protection
2 Applications
•
•
•
•
•
AC/DC Adapters For Smartphones and Tablets
USB Chargers with Type-C Connectors
Notebook and Ultrabook Adapters
High Efficiency Flyback Converters in Industrial
SMPS
High Efficiency Auxilliary Power In Server and
Desktop Applications
The controller has built in intelligence to detect
converter no load operation and automatically enters
standby mode. While in standby mode, it disables the
SR MOSFET and lowers its bias supply current to
110uA to further reduce overall system standby
power consumption. The wide VDD operating range
for the controller allows direct bias from the converter
output for fixed or variable output voltage designs.
This eliminates the need for an auxilliary winding on
the main transformer, which simplifies the circuit
design and reduces the cost.
Device Information(1)
PART NUMBER
UCC24636
PACKAGE
SOT23 (6)
BODY SIZE (NOM)
2.92 mm x 1.30 mm
(1) For all available packages, see the orderable addendum at
the end of the data sheet.
Simplified Schematic
Gate-Drive Timing vs VDS Sensing SR Driver
+
VOUT
CB2
CB1
NP
NS
15 A
COUT
1-mŸ RDSON MOSFET Example
±
RVSC1
VAC
6
RVPC1
VDD
RVPC2
UCC28740
1
VPC
4
DRV
VSC
RVSC2
UCC24636
VDD
5A
2
HV
DRV
VS
TBLK
3
GND
5
TL431
CS
0.85 A
Secondary
Current
RTBLK
FB
GND
Gate Drive
VDS Sensing
Driver
300 ns
Gate Drive
UCC24636
5 Ps
1
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
Table of Contents
1
2
3
4
5
6
7
8
Features ..................................................................
Applications ...........................................................
Description .............................................................
Revision History.....................................................
Device Comparison Table.....................................
Pin Configuration and Functions .........................
Specifications.........................................................
1
1
1
2
3
3
4
7.1
7.2
7.3
7.4
7.5
7.6
7.7
4
4
4
4
5
6
7
Absolute Maximum Ratings ......................................
ESD Ratings..............................................................
Recommended Operating Conditions.......................
Thermal Information ..................................................
Electrical Characteristics...........................................
Timing Requirements ...............................................
Typical Characteristics ..............................................
Detailed Description .............................................. 9
8.1 Overview ................................................................... 9
8.2 Functional Block Diagram ......................................... 9
8.3 Feature Description................................................. 10
8.4 Device Functional Modes........................................ 19
9
Application and Implementation ........................ 20
9.1 Application Information............................................ 20
9.2 Typical Application ................................................. 20
9.3 Do's and Don'ts ...................................................... 27
10 Power Supply Recommendations ..................... 27
11 Layout................................................................... 28
11.1 Layout Guidelines ................................................. 28
11.2 Layout Example .................................................... 29
12 Device and Documentation Support ................. 30
12.1
12.2
12.3
12.4
12.5
Device Support ....................................................
Documentation Support ........................................
Trademarks ...........................................................
Electrostatic Discharge Caution ............................
Glossary ................................................................
30
30
30
30
30
13 Mechanical, Packaging, and Orderable
Information ........................................................... 30
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Original (December 2015) to Revision A
•
2
Page
Changed device status from Product Preview to Production Data and released full data sheet........................................... 1
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
UCC24636
www.ti.com
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
5 Device Comparison Table
PART NUMBER
CCM DEAD TIME CONTROL
tOFF (µs)
FSW(MAX) (kHz)
UCC24636
No
4.35
130
UCC24630
Yes
2.5
200
6 Pin Configuration and Functions
DBV Package
6-Pin SOT23
Top View
VPC
1
6
VDD
VSC
2
5
GND
TBLK
3
4
DRV
Pin Functions
PIN
NO.
NAME
I/O (1)
DESCRIPTION
1
VPC
I
The Voltage during Primary Conduction pin is connected to a resistor divider from the SR MOSFET
drain. This pin determines a sample of the primary-side MOSFET volt seconds during the primary ontime. This voltage programs a voltage controlled current source for the internal VPC ramp charging
current.
2
VSC
I
The Voltage during Secondary Conduction pin is connected to a resistor divider from the power-supply
output. This pin determines a sample of the secondary-side output voltage used to determine SR
MOSFET conduction time. This voltage programs a voltage controlled current source for the internal VSC
ramp charging current.
3
TBLK
–
TIME BLANK pin is used to select the blanking time of the VPC rising edge. A programmable range from
200 ns to 2 µs is available to prevent false detection of the primary on-time due to ringing during DCM
operation.
4
DRV
O
DRIVE is an output used to drive the gate of an external synchronous rectifier N-channel MOSFET
switching transistor, with source pin connected to GND.
5
GND
G
The GROUND pin is both the reference pin for the controller and the low-side return for the drive output.
Special care should be taken to return all AC decoupling capacitors as close as possible to this pin and
avoid any common trace length with analog signal return paths.
6
VDD
P
VDD is the bias supply input pin to the controller. A carefully placed bypass capacitor to GND is required
on this pin.
(1)
P = Power, G = Ground, I = Input, O = Output, I/O = Input/Output
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
3
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
7 Specifications
7.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted) (1)
MIN
MAX
UNIT
–0.3
30
V
Continuous gate current sink, DRV
50
mA
Continuous gate current source, DRV
–50
mA
IVPC
Peak VPC pin current
–1.2
mA
VDRV
Gate drive voltage at DRV
–0.3
Self-limiting
V
VVPC, VVSC
Voltage range, VPC, VSC
–0.3
4.5
V
TJ
Operating junction temperature range
–55
150
°C
TL
Lead temperature 0.6 mm from case for 10 seconds
260
°C
Tstg
Storage temperature
150
°C
VVDD
Bias supply voltage, VDD
IDRV
IDRV
(1)
–65
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress ratings
only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under Recommended
Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device reliability.
7.2 ESD Ratings
VALUE
Electrostatic
discharge
V(ESD)
(1)
(2)
Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001 (1)
±2000
Charged-device model (CDM), per JEDEC specification JESD22-C101 (2)
±500
UNIT
V
JEDEC document JEP155 states that 2000-V HBM allows safe manufacturing with a standard ESD control process. Pins listed as
±2000 V may actually have higher performance.
JEDEC document JEP157 states that 500-V CDM allows safe manufacturing with a standard ESD control process. Pins listed as ±500 V
may actually have higher performance.
7.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)
MIN
MAX
VVDD
Bias supply operating voltage
3.75
28
CVDD
VDD bypass capacitor
0.22
TJ
Operating junction temperature
VVPC, VVSC
Operating range
UNIT
V
µF
-40
125
°C
–0.3
2.2
V
7.4 Thermal Information
UCC24636
THERMAL METRIC (1)
DBV (SOT23)
UNIT
6 PINS
RθJA
Junction-to-ambient thermal resistance
180
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
71.2
°C/W
RθJB
Junction-to-board thermal resistance
44
°C/W
ψJT
Junction-to-top characterization parameter
5.1
°C/W
ψJB
Junction-to-board characterization parameter
13.8
°C/W
(1)
4
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
UCC24636
www.ti.com
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
7.5 Electrical Characteristics
over operating free-air temperature, VDD = 12 V, TA = –40°C to 125°C, TA = TJ (unless otherwise noted)
PARAMETER
TEST CONDITION
MIN
TYP
MAX
UNIT
SUPPLY INPUT
IRUN
Supply current, run
IDRV = 0, run state, FSW = 0 kHz
0.9
1.2
mA
ISTBY
Supply current, standby
IDRV = 0, standby mode
110
160
µA
UNDER-VOLTAGE LOCKOUT
VVDD(on)
VDD turn-on threshold
VVDD low to high
3.9
4
4.3
V
VVDD(off)
VDD turn-off threshold
VVDD high to low
3.3
3.6
3.7
V
RDRVLS
DRV low-side drive resistance
IDRV = 100 mA
VDRVST
DRV pull down in start-up
VDD= 0 to 2 V, IDRV= 10 µA
VDRCL
DRV clamp voltage
VVDD = 30 V
11
VPMOS
Disable PMOS high-side drive
VDD voltage to disable rail-to-rail
drive, VDD rising
VPMOS-HYS
PMOS enable hysteresis
VDD voltage hysteresis to enable rail
to rail drive, VDD falling
VDRHI
DRV pull-up high voltage
VVSCEN
DRV
2
Ω
0.95
V
13
15
V
9.3
10
10.5
V
0.75
1
1.25
V
VVDD = 5 V, IDRV = 15 mA
4.6
4.75
5
V
SR enable voltage
VVSC > VVSCEN, VVSC rising
250
300
340
VVSC-HYS
SR enable hysteresis
VVSC falling
VVSCDIS
SR disable voltage
220
250
280
mV
IVSC
Input bias current
VVSC = 2 V
–0.25
0
0.4
µA
VVPCEN
SR enable voltage
VVPCEN < VVPC
345
400
450
mV
VVPCDIS
VPC threshold to disable SR
VVPC > VVPCDIS
2.6
2.85
3.1
V
VVPC-TH
Threshold of VVPC rising edge
VVPC = 0.95 V, VVPC-TH = 0.85 x VVPC
previous cycle
0.76
0.808
0.86
V
VVPC-TH-CLP
Clamp threshold of VVPC rising edge
VVPC = 2 V
0.9
1
1.1
V
IVPC
Input bias current
VVPC = 2 V
–0.25
0
0.4
µA
VVPC = 1.25 V, tVPC = 1 µs,
VVSC = 1.25 V
3.97
4.17
4.35
VVPC = 1.25 V, tVPC = 5 µs,
VVSC = 1.25 V
3.95
4.17
4.37
VVPC = 2 V, tVPC = 1 µs,
VVSC = 1.25 V
3.85
4.09
4.26
VVPC = 1.25 V, tVPC = 1 µs,
VVSC = 0.45 V
3.85
4.07
4.28
1
VSC INPUT
50
mV
mV
VPC INPUT
CURRENT EMULATOR
RatioVPC_VSC
KVPC/KVSC
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
5
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
Electrical Characteristics (continued)
over operating free-air temperature, VDD = 12 V, TA = –40°C to 125°C, TA = TJ (unless otherwise noted)
PARAMETER
TEST CONDITION
MIN
TYP
MAX
UNIT
STANDBY OPERATION
nENTO
Number of switching cycles to enter
standby operation during tENTO
64
nEN
Number of switching cycles to exit
standby operation during tEN (1)
32
OVER TEMPERATURE PROTECTION
T(STOP)
(1)
Thermal shutdown temperature
Internal junction temperature
165
°C
The device exits standby operation as soon as nEN occurs within tEN.
7.6 Timing Requirements
over operating free-air temperature range, VDD = 12 V, TA = –40°C to 125°C, TA = TJ (unless otherwise noted)
PARAMETER
TEST CONDITION
MIN
TYP
MAX
UNIT
DRV
VVDD = 12 V, CL = 3.3 nF, VDRV = 2 V to 8 V
27
54
VVDD = 5 V, CL = 3.3 nF, VDRV = 1 V to 4 V
50
100
VVDD = 12 V, CL = 3.3 nF, VDRV = 8 V to 2 V
20
54
VVDD = 5 V, CL = 3.3 nF, VDRV = 4 V to 1 V
15
50
Propagation delay to DRV High
VVPC = 1 V to –0.05 V falling to DRV high,
VVDD = 12 V, VDRV = 0 V to 2 V
80
160
ns
Propagation delay to DRV Low
Test mode
65
95
ns
100
125
ns
tR
DRV high-side rise time
tF
DRV low-side fall time
tDRVON
tDRVOFF
ns
ns
VPC INPUT
tVPC-SPL
VPC sampling time window
tVPC-BLK
Minimum VPC pulse for SR DRV
operation
81
RTBLK = 5 kΩ
169
203
239
ns
RTBLK = 50 kΩ
0.85
1.01
1.18
µs
SR ON CONTROL
tSRONMIN
SR minimum on time after VPC falling.
300
350
425
ns
tOFF
SR off blanking time from DRV falling.
3.96
4.35
4.75
us
11.5
12.8
14.1
ms
2.3
2.56
2.82
ms
STANDBY OPERATION
tENTO
Time to disable SR operation, enter
standby
Time to disable DRV
tEN
Time to enable SR operation, exit
standby operation
Time to enable DRV (1)
(1)
6
The device exits standby operation as soon as nEN occurs within tEN.
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
UCC24636
www.ti.com
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
7.7 Typical Characteristics
VVDD = 12 V, TJ = 25°C, unless otherwise noted.
4.75
150
4.63
140
4.50
4.38
130
VVDD(On)
ISTBY (µA)
VVDD (V)
4.25
4.13
4.00
3.88
120
110
3.75
100
VVDD(Off)
3.63
3.50
90
3.38
3.25
80
±50
0
±25
25
50
75
100
125
150
Temperature (oC)
±50
0
475
375
450
350
VVSCEN (mV)
400
400
375
50
75
100
125
150
C002
Figure 2. Standby Current vs Temperature
500
425
25
Temperature (oC)
Figure 1. VDD Turn-On and Turn-Off Threshold vs
Temperature
V VPCEN (mV)
±25
C001
325
300
275
250
350
225
325
200
300
-50
-25
0
25
50
75
100
125
±50
150
±25
0
25
50
75
100
125
150
Temperature (oC)
Temperature (C°)
C004
Figure 4. VSC Enable Threshold vs Temperature
Figure 3. VPC Enable Threshold vs Temperature
4.60
4.80
4.50
4.60
4.40
4.30
RatioVPC_VSC
RatioVPC_VSC
4.40
4.20
4.10
4.00
4.20
4.00
3.80
3.90
3.60
3.80
3.70
3.40
±50
±25
0
25
50
75
Temperature (oC)
VVPC = 1.25 V
tVPC = 1 µs
100
125
150
0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8
VVPC (V)
C005
VVSC = 1.25 V
Figure 5. VPC-to-VSC Ramp Gain Ratio vs Temperature
VVSC = 1.25 V
C006
tVPC × VVPC = 3 V-µs
Figure 6. VPC-to-VSC Ramp-Gain Ratio vs VPC Voltage
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
7
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
Typical Characteristics (continued)
VVDD = 12 V, TJ = 25°C, unless otherwise noted.
4.8
300
280
4.6
240
4.2
220
tBLK (ns)
RatioVPC_VSC
260
4.4
4.0
200
180
160
3.8
140
3.6
120
3.4
100
0.3 0.5 0.7 0.9 1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.7
VVSC (V)
VVPC = 1.25 V
±50
0
25
50
75
100
125
Temperature (oC)
tVPC = 2 µs
150
C009
RTBLK = 5 kΩ
Figure 7. VPC-to-VSC Ramp-Gain Ratio vs VSC Voltage
Figure 8. VPC Blanking Time vs Temperature (Minimum
Setting)
1.30
400
1.25
390
1.20
380
1.15
370
1.10
tSRONMIN (ns)
tVPC-BLK (µs)
±25
C007
1.05
1.00
0.95
0.90
360
350
340
330
0.85
320
0.80
310
0.75
300
0.70
±50
±25
0
25
50
75
100
125
Temperature (oC)
150
±50
±25
0
25
50
75
Temperature (oC)
C010
100
125
150
C014
RTBLK = 50 kΩ
Figure 9. VPC Blanking Time vs Temperature (Maximum
Setting)
Figure 10. DRV Minimum On Time vs Temperature
5.5
5.25
tOFF (Ps)
5
4.75
4.5
4.25
4
3.75
3.5
-50
-25
0
25
50
75
Temperature (qC)
100
125
150
D013
Figure 11. DRV Minimum Off Time vs Temperature
8
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
UCC24636
www.ti.com
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
8 Detailed Description
8.1 Overview
The UCC24636 SR controller is targeted for flyback converters operating in DCM and TM modes of operation.
The control method to determine SR on time is based on the volt-second balance principle of primary and
secondary conduction volt-second product. In converters operating in DCM and TM, the secondary current
always returns to zero in each cycle. The inductor charge voltage and time product is equal to the discharge
voltage and time product. The device uses internal current ramp emulators to predict the proper SR on time
based on voltage and time information on the VPC and VSC pins.
To achieve very low standby power in the converter, the UCC24636 has a standby mode of operation that
disables the SR MOSFET drive and reduces the device bias current to ISTBY. The device monitors the average
switching frequency of the converter to enter and exit the standby mode of operation, and is compatible with
converters operating in burst mode or constant frequency in light-load mode.
8.2 Functional Block Diagram
Thermal
SD
VPC
S&H
VPC
Thresh
UVLO
4.0/3.6 V
+
VDD
SR Control Bias
+
Bias
VVPCEN
Fsw Detect
Stand By
tVPC-BLK
VPC
Blanking
Timer
Stand By
VPC
Min tOFF
TBLK
DRV
Min tON
SR_On
Detect
S
Q
R
Q
SRon
GND
+
DRV
Enable
Ramp
Enable
VVSCEN
VPC Ramp
+
+
VSC Ramp
One
Shot
+
VSC
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
9
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
8.3 Feature Description
8.3.1 Start Up and UVLO
The UCC24636 features a wide operating VDD range and low UVLO thresholds. The start up of the device is
dependent on voltage levels on three pins: VDD, VPC and VSC. The VDD pin can be directly connected to the
power supply output on converters from 5-V to 24-V nominal outputs. The start UVLO threshold is VVDD(on), 4.0 V
typical, and stop threshold is VVDD(off), 3.6 V typical. The DRV output is not enabled unless the voltage on the
VPC pin is greater than VVPCEN for a time longer than tVPC-BLK and the voltage on the VSC pin is greater than
VVSCEN. Once the VDD, VSC and VPC voltage and time thresholds are met, there is an internal initialization time
before the DRV output is enabled.
Refer to Figure 12 for a startup sequence that illustrates the timing sequence and configurable DRV output
based on VDD level. In most converter designs, the conditions for the VPC and VSC voltage to enable the
device are met before the VDD start-voltage threshold, this is reflected in the timing diagram. When VDD
exceeds VVDD(on) UVLO threshold the device starts the initialization sequence of 150 µs to 250 µs illustrated as
tINITIALIZE. After the device initialization, there is a logic initialization of 20 µs at which time VTBLK is enabled (high).
At VDD < VPMOS the driver high-side PMOS device is enabled and the DRV peak will be close to VDD. When
VDD exceeds VPMOS the PMOS device is disabled and the driver is operating as a high-side NMOS only and
DRV is approximately 1.2 V to 1.5 V lower than VDD. As VDD continues to increase, the DRV output is limited to
VDRCL regardless of VDD up to the recommended maximum rating.
VPMOS
VVDD
VVDD(on)
tINITIALIZE
20 µs
VTBLK
VVPC
VDRCL
VDRV
t
Figure 12. Start-Up Operation
10
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
UCC24636
www.ti.com
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
Feature Description (continued)
8.3.2 Volt-Sec SR Driver On-Time Control
Refer to the timing diagrams in Figure 13 for functional details of the UCC24636 volt-sec on-time control.
VIN/NPS
Pri Volt-Sec
VOUT
SR VDS
Sec VoltSec
VVPC Pk
VVPC-TH (0.85 VVPC Pk)
VVPC
VVPCEN
DRV
Enable
ramp EN
Primary Drive
and VDRV
VPC Blanking Time
VPC Sample Time
Primary
MOSFET
Primary
MOSFET
DRV
DRV
tVPC-BLK
tVPC-SPL
tOFF
DRV Inhibit
tOFF
tOFF
VPC Ramp
V/s Control
Ramps
VPC Ramp
VSC Ramp
Normalized Pri
and Sec Current
IPRI
tPRI
ISEC/NPS
VSC Ramp
IPRI
ISEC/NPS
tVSC TH
tSEC DIS
Figure 13. Operation in DCM
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
11
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
Feature Description (continued)
The UCC24636 uses the VPC and VSC pins to sense the SR MOSFET VDS voltage and converter VOUT voltage
through resistor dividers. The information of VIN/NPS, tPRI, and VOUT can be obtained from the information on VPC
and VSC pins. The SR MOSFET turn on is determined when the SR MOSFET body diode starts conducting and
the VPC pin voltage falls to near zero; the SR MOSFET turn off is determined by the current emulator control
ramps.
The UCC24636 volt-sec control generates the internal VPC ramp and VSC ramp to emulate the transformer VoltSec balancing as shown in Figure 13.
The secondary current discharge time, tSEC-DIS can be determined indirectly. The primary volt-sec ramp and
secondary volt-sec ramp both start when VPC rises above VVPC-EN and VVPC-TH. The charge currents for the VPC
and VSC ramps are determined by the voltage on the VPC and VSC pins respectively.
When VPC is higher than VVPC-EN and VVPC-TH for t > tVPC-BLK, the VPC pulse is qualified as a primary conduction
pulse and the SR can be enabled on the VPC falling edge. The VPC ramp continues to rise until the VPC falling
edge based on the real time voltage on the VPC pin and holds the peak for the cycle. The DRV output is turned
on during the VPC falling edge near zero volts, and DRV is turned off when the VSC rising ramp crosses the
VPC ramp held level.
Both VPC and VSC ramps are reset to zero on each VPC rising edge above the VVPC-EN and VVPC-TH thresholds.
To discriminate primary on-time pulses from DCM ringing, there are voltage and time criteria that must be
satisfied on the VPC pin to enable the DRV output. tVPC-BLK can be adjusted through the resistor on TBLK pin.
At the rising edge of VPC when the voltage exceeds VVPC-EN and VVPC-TH the blanking time tVPC-BLK is initiated. At
the end of tVPC-BLK, the VPC voltage is sampled during tVPC-SPL window, which is 100 ns nominal. Also at the end
of tVPC-BLK, the DRV output can be enabled.
The VPC voltage sampled during tVPC-SPL determines the VPC dynamic threshold VVPC-TH which is normally 85%
of the sampled VPC voltage. The dynamic threshold provides the ability to reject the DCM ringing and detect the
primary on-time. Noise immunity during the turn-on event of DRV at the falling edge of the VPC pin is enhanced
by a minimum DRV on time of tSRONMIN, which is 350 ns nominal.
During the falling edge of DRV, the tOFF timer is initiated which inhibits turn on of the SR until tOFF expires. This
eliminates false turn on of DRV if the DCM ringing is close to ground.
12
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
UCC24636
www.ti.com
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
Feature Description (continued)
The UCC24636 is designed to operate in a variety of flyback converter applications over a wide operating range.
The internal volt-sec control ramps do have a dynamic range limit based on volt-sec on the VPC pin. As shown
in Figure 14, a Volt-sec product exceeding 7 V-µs on the VPC pin will result in saturation of the VPC volt-sec
control ramp. Operation beyond this point results in a DRV on-time less than expected. For example, if VVPC =
0.5 V, tVPC should be < 14 µs, or if VVPC = 2.0 V, tVPC should be < 3.5 µs, to operate within the dynamic range of
the device. Assuming a converter operating in transition mode at low line and full load with a 50% duty cycle, the
operating period is 28 µs which results in a frequency that is under 40 kHz. The UCC24636 low-frequency
operating range extends to the standby mode threshold of 5 kHz; but each switching cycle VVPC Volt-sec product
should be less than 7 V-µs.
RatioVPC_VSC
The device can support switching frequencies exceeding 130 kHz but the following timing limits need to be
confirmed to be compatible with the power train. The minimum primary on time when the device is expected to
be active needs to be compatible with the minimum VPC blanking time (tVPC-BLK) setting of 203 ns plus the
sampling window (tVPC-SPL) of 100 ns. The minimum secondary current conduction time should be greater than
the minimum SR on time (tSRONMIN) of 350 ns. The minimum time from the SR drive turn off until the next SR
drive turn on should be greater than the SR minimum off time (tOFF) of 4.35 µs.
4.5
4.4
4.3
4.2
4.1
4.0
3.9
3.8
3.7
3.6
3.5
3.4
3.3
3.2
3.1
3.0
0.5
1.5
2.5
3.5
4.5
5.5
6.5
7.5
VPC V-us (uWb)
8.5
C008
Figure 14. RatioVPC_VSC vs VPC V-µs
IOUT
VOUT
Ns
VSEC
RVSC1
VDD
RVPC1
RVPC2
VSC
VPC
RPL
UCC24636
DRV
COUT
RVSC2
TBLK
GND
RTBLK
GND
Figure 15. SR Controller Components
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
13
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
Feature Description (continued)
Determining the VPC and VSC divider resistors is based on the operating voltage ranges of the converter and
RatioVPC-VSC gain ratio. Referring to Figure 15, the following equation determines the VPC divider values.
For RVPC2, a value of 10 kΩ is recommended for minimal impact on time delay, and low-resistor dissipation. A
higher RVPC2 value reduces resistor divider dissipation but may increase the DRV turn-on delay due to the time
constant of ~2 pF pin capacitance and divider resistance. A lower RVPC2 value can be used with the tradeoff of
higher dissipation in the resistor divider. A factor of 10% over the VPC threshold, VVPCEN, is shown in Equation 1
for design margin.
éæ VIN(min)
ù
ö
+ VOUT(min) ÷÷ - VVPCEN ´ 1.1ú ´ R VPC2
êçç
êè NPS
ø
ûú
R VPC1 = ë
VVPCEN ´ 1.1
where
•
•
•
•
VIN(min) is the converter minimum primary bulk capacitor voltage.
VOUT(min) is the minimum converter output voltage in normal operation.
VVPCEN is the VPC enable threshold, use the specified maximum value.
NPS is the transformer primary to secondary turns ratio.
(1)
The operating voltage range on the VPC pin should be within the range of 0.45 V < VVPC < 2.2 V. Referring to
Figure 6, if VVPC is greater than 2.3 V the linear dynamic range is exceeded and RatioVPC_VSC is reduced; in this
condition the DRV on time is less than expected. If VVPC is greater than 2.6 V for 500 ns, a fault is generated and
DRV is disabled for the cycle, refer to Pin Fault Protection. To ensure the maximum voltage is within range
confirm with Equation 2.
æ VIN(max)
ö
+ VOUT(max) ÷ ´ R VPC2
ç
NPS
ø
VVPC(max) = è
R VPC1 + R VPC2
where
•
•
•
VIN(max) is the converter maximum primary bulk capacitor voltage.
VOUT(max) is the maximum converter output voltage at OVP.
NPS is the transformer primary-to-secondary turns ratio.
(2)
The program voltage on the VSC pin is determined by the VPC divider ratio and the device's parameter
RatioVPC_VSC. The current emulator ramp gain is higher on the VPC pin by the multiple RatioVPC_VSC, so the VSC
resistor divider ratio is reduced by the same RatioVPC_VSC accordingly. Determine the VSC divider resistors using
Equation 3 below. To minimize resistor divider dissipation, a recommended range for RVSC2 is 25 kΩ to 50 kΩ.
Higher RVSC2 values results in increasing offset due to VSC input current, IVSC. Lower RVSC2 values increases the
resistor divider dissipation. To ensure DRV turn off slightly before the secondary current reaches zero, 10%
margin is shown for initial values. Use a nominal value of 4.15 for RatioVPC_VSC.
éæ R VPC1 + R VPC2 ö ù
êç
÷ ú
R VPC2
÷ - 1ú ´ R VSC2
R VSC1 = êç
êç Ratio VPC _ VSC ´ 1.1 ÷ ú
êç
÷ ú
ø û
ëè
where
•
14
RatioVPC_VSC is the device parameter VPC and VSC gain ratio, use a value of 4.15.
Submit Documentation Feedback
(3)
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
UCC24636
www.ti.com
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
Feature Description (continued)
The operating voltage on the VSC pin should be within the range of 0.3 V < VVSC < 2.2 V. Referring to Figure 7, if
VVSC is greater than 2.3 V, the linear dynamic range is exceeded and RatioVPC_VSC is increased; in this condition
the DRV on time is more than expected, resulting in possible negative current conduction. To ensure the VSC
voltage is within range, confirm with Equation 4 and Equation 5.
R VSC2
´ VOUT(min) ³ 0.3V
R VSC1 + R VSC2
(4)
R VSC2
´ VOUT(max) £ 2.2 V
R VSC1 + R VSC2
where
•
•
VOUT(min) is the minimum converter output operating voltage of the SR controller.
VOUT(max) is the maximum converter output operating voltage of the voltage at OVP.
(5)
Discrimination of ringing during DCM operation from valid primary on-time is achieved by a dynamic VPC rising
threshold and programmable blanking time. The dynamic threshold VVPC-TH is 85% typical ratio of the previous
VPC pin peak voltage. Referring to Figure 13, the VPC pin voltage is sampled after the VPC voltage is greater
than VVPCEN and VVPC-TH for t > tVPC-BLK. The function of the dynamic threshold VVPC-TH is to reject the ringing in
DCM operation from the primary conduction pulses. The dynamic threshold has an active range from the
minimum VVPCEN voltage to a maximum of 1-V clamp. The blanking time is programmable from 200 ns to 2 µs in
order to accommodate a variety of converter designs.
Refer to Figure 16 for guidance on selecting the blanking time. The blanking time should be selected as long as
reasonable and still accommodate the minimum primary on-time at light-load condition and high-line voltage. In
the high-line minimum load condition, select a blanking time that meets the following criteria (Equation 6) to
accommodate tolerance of the blanking time and the tVPC-SPL sampling time window.
tVPC-BLK = (tPRI x 0.85) – 120 ns
(6)
For rejection of DCM ringing, the blanking time should be longer than the time that the ring is above the VVPC-TH
dynamic threshold, which is 85% of the minimum SR VDS peak voltage. Determine these criteria at low line and
maximum load condition. It is recommended that the transformer turns ratio be selected such that the secondary
reflected voltage is < 85% of VIN(min) bulk capacitor voltage at the highest load when DCM operation occurs at the
low line input condition.
To determine the resistor value for tVPC-BLK use Equation 7 to select from a range of 200 ns to 2 µs.
- 100 ns
t
RTBLK = VPC-BLK
18 pF
where
•
tVPC-BLK is the target blanking time.
(7)
Additional discrimination for proper SR timing control is provided by the tOFF function. Refer to Figure 13 for the
timing details. After the DRV turn off, the DRV is inhibited from turning on again until the tOFF timer expires. This
protects against SR false turn on from SR VDS DCM ringing below ground.
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
15
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
Feature Description (continued)
High Line Minimum Load
Low Line Maximum Load
Vout
SR VDS
VVPC-TH (1V)
VPC Pk
VVPC-TH (0.85 X VPC Pk)
VVPC
tVPC-BLK
tVPC-BLK
tVPC-SPL
tVPC-SPL
tVPC-BLK
t
tVPC-BLK
tPRI
Figure 16. VPC Blanking Time Criteria
16
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
UCC24636
www.ti.com
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
Feature Description (continued)
8.3.3 Standby Operation
To minimize power consumption at very light load and standby conditions, the UCC24636 disables the SR DRV
output and enters a low current operating state. The criteria for operating in standby mode or normal operation
are determined by the average frequency detected on the VPC pin. The frequency detection is compatible with
burst mode operation or continuous low frequency FM operation. At start up the device is in normal operation to
enable DRV to the SR MOSFET. If < 64 cycles occur in tENTO,12.8 ms typical, the device disables the DRV
output and enters low-current operating mode with bias current of ISTBY. In standby mode the criteria to enter
normal operating mode is when > 32 cycles occur within tEN, 2.56 ms typical. The device enters normal operation
as soon as the 32 cycles occur to reduce the response time exiting standby operation. The average frequency of
entering standby mode is 5 kHz typical, and the average frequency of exiting standby mode is 12.5 kHz typical.
Refer to Figure 17 for an illustration of standby mode timing.
Fsw Averaging
Window
tENTO
tEN
tEN
tENTO
> 32 cycles
5 kHz the device is
in normal operation determining the DRV time based on volt-sec control. IDD will be IRUN.
1. The device operates in volt-sec control based on the VPC and VSC volt-sec control ramps.
8.4.3 Standby Operation
If the number of VPC pulses is less than nENTO, 64, during tENTO the device enters standby mode. DRV operation
stops and most device functions are shut down. IDD is ISTBY during standby operation. To exit standby mode the
number of VPC pulses must exceed nEN, 32, during tEN. IDD returns to IRUN and the DRV output starts after the
initialization time as outlined in Figure 12.
8.4.4 Conditions to Stop Operation
The following conditions can disable DRV operation; IDD is IRUN during these conditions.
1. VPC overvoltage: When VVPC > VVPCDIS for >500 ns the DRV output is disabled for the cycle.
2. VSC undervoltage: When VVSC < VVSCEN, the DRV output is disabled.
3. VPC undervoltage: When VVPC< VVPCEN, the DRV output is disabled.
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
19
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
9 Application and Implementation
NOTE
Information in the following applications sections is not part of the TI component
specification, and TI does not warrant its accuracy or completeness. TI’s customers are
responsible for determining suitability of components for their purposes. Customers should
validate and test their design implementation to confirm system functionality.
9.1 Application Information
The UCC24636 is a high performance controller driver for N-channel MOSFET power devices used for
secondary-side synchronous rectification. The UCC24636 is designed to operate as a companion device to a
primary-side controller to help achieve efficient synchronous rectification in switching power supplies. The
controller features a high-speed driver and provides appropriately timed logic circuitry that seamlessly generates
an efficient synchronous rectification system. With its current emulator architecture, the UCC24636 has enough
versatility to be applied in DCM and TM operation. The UCC24636 SR on-time adjustability allows optimizing for
PSR and SSR applications. Additional features such as pin fault protection, dynamic VPC threshold sensing, and
voltage sense blanking time and make the UCC24636 a robust synchronous controller.
9.2 Typical Application
9.2.1 AC-to-DC Adapter, 5 V, 15 W
This design example describes the design of a 15-W off-line flyback converter providing 5 V at 3-A maximum
load and operating from a universal AC input. The design uses the UCC28740 AC-to-DC valley-switching
primary-side controller in a DCM type flyback converter and achieves over 86% full-load efficiency with the use of
the secondary side UCC24636 synchronous rectifier controller.
• The design requirements are detailed in Design Requirements
• The design procedure for selecting the component circuitry for use with the UCC24636 is detailed in
Calculation of Component Values.
• Test results shown in Application Waveforms And Curves highlight the unique advantages of using the
UCC24636.
20
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
UCC24636
www.ti.com
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
L1
F1
3
7447462471
-
+
1
1
R1
100k
C1
330pF
R2
330k
10
9
2
1
C2
12µF/400V
4
5
C3
12µF/400V
7
8
N1
R6
150
L4
R4
100k
GND
1,2,3
7,8
5,6,
GND
D4
DFLR1600-7
VAUX
C6
0.1µF
C5
680µF
20
1000pF
D5
BAS20HT1
D3
C4
680µF
R5
750342752
R7
150
950 ohm
C7
4
VAUX
2
T1
GND
Q1
CSD18503
GND
R9
147k
R31
130
BAS20HT1
4
2
~
L3
RLTI-1081
806µH
VOUT
D1
MDB6S
~
4
39213150000
3
L2
R8
2.0
R10
R13
10
U3
R11
115k
0
4
R12
68k
R14
U4
VDD
2
VS
3
FB
4
GND
HV
8
0
DRV
6
R15
CS
5
VPC
Q2
AOD7N65
1
VDD
6
DRV
4
VSC
2
GND
5
3
1
1
D6
DFLZ27-7
27V
1.5k
3
TBLK
UCC28740DR
UCC24636
R17
39k
C8
10µF
R18
20.0k
R19
1.0
R20
2.0
R21
10k
C9
NP
R22
20k
C10
1µF
C11
R23
220pF 47k
C12
100pF
GND
GND
GND
GND
R24
1.00k
C13
U5
4
1
3
2
R25
R26
2.00k
22k
U6
TL431AIDBZR
R29
10.0k
3
C16
1µF
NA
C15
0.022µF
TCMT1107
1
100k
C14
NA
2
R28
R27
10.0k
GND
Figure 18. AC-to-DC Charger: 5 V, 15 W
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
21
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
9.2.2 Design Requirements
For this design example, use the parameters listed in Table 1.
Table 1. Performance Specifications AC-to-DC Charger 5 V, 15 W
PARAMETER
TEST CONDITIONS
MIN
NOM
MAX
UNIT
VRMS
INPUT CHARACTERISTICS
VACIN
Input voltage
90
115/230
265
fLINE
Frequency
47
50/60
64
VAC(uvlo)
Brownout voltage
VAC(run)
Brownout recovery voltage
IIN
Input current
IOUT = IOUT(nom)
VACIN = VACIN(min), IOUT = IOUT(nom)
Hz
72
VRMS
85
VRMS
335
mA
OUTPUT CHARACTERISTICS
VOUT
Output voltage
VACIN = VACIN(min) to VACIN(max),
IOUT = 0 to IOUT(nom)
IOUT(nom)
Nominal output current
VACIN = VACIN(min) to VACIN(max)
3.0
A
IOUT(min)
Minimum output current
VACIN = VACIN(min) to VACIN(max)
0
A
ΔVOUT
Output voltage ripple
VACIN = VACIN(min) to VACIN(max),
IOUT = 0 to IOUT(nom)
80
mV
POUT
Output power
VACIN = VACIN(min), IOUT = IOUT(nom)
15
W
4.9
5.0
5.1
V
SYSTEM CHARACTERISTICS
ηavg
Average efficiency
VACIN = VACIN(nom), IOUT = 25%, 50%, 75%, 100% of IOUT(nom)
ƞ10%
10% Load efficiency
VACIN = VACIN(nom), IOUT = 10% of IOUT(nom)
PNL
No load power
VACIN = VACIN(nom), IOUT = 0
22
Submit Documentation Feedback
85%
87%
73.5%
82.5%
14
22
mW
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
UCC24636
www.ti.com
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
9.2.3 Calculation of Component Values
IOUT
VOUT
Ns
R11
VSEC
VDD
R9
R21
VSC
VPC
COUT
RPL
UCC24636
R23
DRV
TBLK
GND
R22
GND
Figure 19. UCC24636 Circuit Design
For ease of understanding, Figure 19 is a modified version of Figure 15 where the component reference
designators are the same as the schematic drawing of Figure 18.
9.2.3.1 VPC Input
For designs operating in constant current (CC) with low VOUT, there are two cases to examine. At maximum
power, VIN(MIN) will be lower but VOUT is nominal. In constant current operation, VOUT is the minimum but VIN(MIN)
will be higher. Determine R9 for both conditions, and choose the lowest value.
For minimal power dissipation, select:
R21=10k
Nominal VOUT , maximum power, minimum VIN case
ª§ VIN(min)
º
·
+VOUT ¸¸ -VVPC_EN×1.1» ×R21
«¨¨
«© NPS
»¼
¹
R9= ¬
VVPC_EN×1.1
VOUT =5 V
NPS =15
VIN(min) =65 V
VVPC_EN =0.45 V
R9 = 179 k
(8)
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
23
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
Minimum VOUT , constant current operation case
ª§ VIN(min)CC
º
·
+VOUT(min) ¸¸ -VVPC_EN ×1.1» ×R21
«¨¨
«© NPS
¹
¼»
R9= ¬
VVPC_EN ×1.1
VOUT(min) =1.8 V
VIN(min)CC =89 V
R9 = 146 k
Select standard value based on 146 k
With R9 = 147 kΩ :
VIN(max)
(
NPS
VVPC(max)
VVPC(max)
UHVult.
(9)
VOUT(max) ) u R21
R9 R21
1.95 V
(10)
Therefore, VVPC is within the recommended range of 0.45 V to 2.2 V.
24
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
UCC24636
www.ti.com
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
9.2.3.2 VSC Input
The value of R23 is recommended to be with the range of 25 kΩ to 50 kΩ.
There is a 10% margin included for the initial value calculation of R11 to provide timing margin during initial
operation verification.
R23 = 47 kW
éæ
R9 + R21
ö ù
êç
÷ ú
R9
R11 = êç
÷ - 1ú ´ R23
êçç Ratio VPC _ VSC ´ 1.1 ÷÷ ú
ø ûú
ëêè
R11 = 115 kW
(11)
With R11 = 115 kΩ, the operating range of the VSC pin is:
R23
ª
º
VVSC(min) «(
)» u VOUT(min)
¬ R11 R23 ¼
VVSC(min)
VVSC(max)
VVSC(max)
0.52 V
(12)
R23
ª
º
«( R11 R23 )» u VOUT(max)
¬
¼
1.74 V
(13)
Therefore, VVSC is within the recommended range of 0.3 V to 2.2 V.
The UCC24636 SR timing can be optimized (SR on time increased) by increasing the R115 value after initial
operation confirmation. The RatioVPC_VSC parameter has a positive tolerance of 5.3%. Using 1% divider resistors
for VPC and VSC should allow reducing the 10% initial SR timing margin.
9.2.3.3 TBLK Input
The blanking time is set with resistor R22.
Select the blanking time to meet the following criteria based on 660-ns minimum primary on-time at high line.
tVPC-BLK = (tPRI × 0.85) – 120 ns
spacer
R22 =
t VPC-BLK - 100 ns
18 pF
(14)
A value of R22 = 20 kΩ results in a blanking time of approximately 460 ns.
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
25
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
9.2.4 Application Waveforms And Curves
CH2 (Blue): Drain of synchronous rectifier Q1, 10V/Div
CH3 (Mag): VOUT, 2V/Div
CH4 (Green): DRV signal to Q1, 10V/Div
CH2 (Blue): Drain of synchronous rectifier Q1, 10V/Div
CH3 (Mag): VOUT, 2V/Div
CH4 (Green): DRV signal to Q1, 10V/Div
Figure 20. DRV Timing at 115 VAC, 5 V, 3 A
Figure 21. DRV Timing at 230 VAC, 5 V, 3 A
CH2 (Blue): Drain of synchronous rectifier Q1, 10V/Div
CH3 (Mag): VOUT, 2V/Div
CH4 (Green): DRV signal to Q1, 10V/Div
CH2 (Blue): Drain of synchronous rectifier Q1, 10V/Div
CH3 (Mag): VOUT, 2V/Div
CH4 (Green): DRV signal to Q1, 10V/Div
Figure 22. DRV Timing at 115 VAC, 5 V, 300 mA
Figure 23. DRV Timing at 115 VAC, 1.8 V, 3.3 A
90
5.5
88
5
86
4.5
Output Voltage (V)
Efficiency (%)
84
82
80
78
76
74
3
2.5
2
1.5
90 VAC
115 VAC
230 VAC
264 VAC
1
115 VAC
230 VAC
72
70
0.5
0
0
0.3
0.6
0.9
1.2 1.5 1.8 2.1
Output Current (A)
2.4
2.7
3
Figure 24. Efficiency vs Output Current
26
4
3.5
3.3
0
0.3 0.6 0.9 1.2 1.5 1.8 2.1 2.4 2.7
Output Current (A)
3
3.3 3.6
Figure 25. Output Voltage vs Output Current
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
UCC24636
www.ti.com
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
9.3 Do's and Don'ts
•
•
•
•
•
•
Do operate the device within the recommended operating maximum parameters. Consider output overvoltage
conditions when determining stress.
Do consider the guideline for setting the blanking time resistor value illustrated in Figure 16.
Do not use the UCC24636 in CCM flyback converter designs. For CCM designs, use the UCC24630 with the
CCM dead time control function.
Do not use the UCC24636 in LLC converters as they can operate in CCM.
Do not add capacitance to the TBLK pin.
Do not add significant external capacitance to the VPC pin as there will be increased delay of the signal. If
filtering is necessary a recommended maximum capacitance is 15 pF with a lower resistor divider network
value of 10 kΩ.
10 Power Supply Recommendations
The VDD operating range allows direct connection to converter outputs from 5 V to 24 V. Since the driver and
control share the same VDD and ground, it is recommended to place a good quality ceramic capacitor as close
as possible to VDD and GND pins. To reduce VDD noise and eliminate high-frequency ripple current injected
from the converter output, it is recommended to place a small resistance of 2.2 Ω to 10 Ω between the converter
output and VDD. The device can tolerate VDD rise times from 100 µs to very long rise times typical of constant
current chargers. The start-up sequence will always be as shown in Figure 12. VDD can be connected to an
external bias to extend the device's operating range to be compatible with converter output voltages below 3.5 V
or above 24 V.
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
27
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
11 Layout
11.1 Layout Guidelines
In general, try to keep all high current loops as short as possible. Keep all high current/high frequency traces
away from other traces in the design. If necessary, high-frequency/high-current traces should be perpendicular to
signal traces, not parallel to them. Shielding signal traces with ground traces can help reduce noise pick up.
Always consider appropriate clearances between the high-voltage connections and any low-voltage nets.
11.1.1 VDD Pin
The VDD pin must be decoupled to GND with good quality, low ESR, low ESL ceramic bypass capacitors with
short traces to the VDD and GND pins. To eliminate high-frequency ripple current in the SR control circuit, it is
recommended to place a small value resistance of 2.2 Ω to 10 Ω between VDD and the converter output voltage.
11.1.2 VPC Pin
The trace between the resistor divider and the VPC pin should be as short as possible to reduce/eliminate
possible noise coupling. The lower resistor of the resistor divider network connected to the VPC pin should be
returned to GND with short traces. Avoid adding any significant external capacitance to the VPC pin so that there
is no delay of signal. If filtering is necessary a recommended maximum capacitance is 15 pF with a lower resistor
divider network value of 10 kΩ. Avoid high dV/dt traces close to the VPC pin and connection trace such as the
SR MOSFET drain and DRV output.
11.1.3 VSC Pin
The trace between the resistor divider and the VSC pin should be as short as possible to reduce/eliminate
possible noise coupling. The lower resistor of the resistor divider network connected to the VSC pin should be
returned to GND with short traces. External capacitance can be added to the VSC pin for noise filtering. The
maximum capacitance consideration is a time constant of the capacitor and the resistor divider resistance that is
less than 1/4 the minimum rise time of the converter output during startup. Avoid high dV/dt traces close to the
VSC pin and connection trace such as the SR MOSFET drain and DRV output.
11.1.4 GND Pin
The GND pin is the power and signal ground connection for the controller. The effectiveness of the filter
capacitors on the signal pins depends upon the integrity of the ground return. Place all decoupling capacitors as
close as possible to the device pins with short traces. The device ground and power ground should meet at the
output bulk capacitor’s return. Try to ensure that high frequency/high current from the power stage does not go
through the signal ground.
11.1.5 TBLK Pin
The programming resistor is placed on TBLK to GND, with short traces. The value may have to be adjusted
based on the time delay required. Avoid high dV/dt traces close to the TBLK pin and connection trace such as
the SR MOSFET drain and DRV output.
11.1.6 DRV Pin
The track connected to DRV carries high dv/dt signals. Minimize noise pickup by routing the trace to this pin as
far away as possible from tracks connected to the device signal inputs, VPC, VSC, and TBLK.
28
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
UCC24636
www.ti.com
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
11.2 Layout Example
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
29
UCC24636
SLUSCG2A – MARCH 2016 – REVISED MARCH 2016
www.ti.com
12 Device and Documentation Support
12.1 Device Support
12.1.1 Device Nomenclature
12.1.1.1 Definition of Terms (For Design Example)
• VIN(min) = 65 V: converter minimum primary bulk capacitor voltage at maximum power
• VIN(min)CC = 89 V: converter minimum primary bulk capacitor voltage when in CC operation at VOUT(min)
• VIN(max) = 370 V: converter maximum primary bulk capacitor voltage
• VOUT(min) = 1.8 V: minimum converter output operating voltage of the UCC24636
• VOUT(max) = 6 V: maximum converter output operating voltage of the UCC24636
• VVPC_EN = 0.45 V: synchronous rectifier enable voltage
• VVPC(max) = 2.2 V: maximum linear operating level of VPC
• NPS = 15: transformer primary to secondary turns ratio
• RatioVPC_VSC = 4.15 : Current emulator gain KVPC/KVSC
• tVPC_BLK: Minimum VPC pulse for synchronous rectifier operation
12.2 Documentation Support
12.2.1 Related Documentation
For related documentation see the following:
• Using the UCC24636EVM Secondary-Side Synchronous Rectifier Controller Diode-Replacement
Demonstration Board, Texas Instruments Literature Number (SLUUBE7)
• UCC24636 Design Calculator (SLUC604)
• UCC24630 Synchronous Rectifier Controller with Ultra-Low Standby Current (SLUSC82)
• UCC28740 Constant-Voltage, Constant-Current Flyback Controller Using Opto-Coupler Feedback (SLUSBF3)
12.3 Trademarks
12.4 Electrostatic Discharge Caution
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
12.5 Glossary
SLYZ022 — TI Glossary.
This glossary lists and explains terms, acronyms, and definitions.
13 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
30
Submit Documentation Feedback
Copyright © 2016, Texas Instruments Incorporated
Product Folder Links: UCC24636
PACKAGE OPTION ADDENDUM
www.ti.com
10-Dec-2020
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
UCC24636DBVR
ACTIVE
SOT-23
DBV
6
3000
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
U636
UCC24636DBVT
ACTIVE
SOT-23
DBV
6
250
RoHS & Green
NIPDAU
Level-1-260C-UNLIM
-40 to 125
U636
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of
工商网监
湘ICP备2023018690号
