Texas Instruments TPS43000PW Schematic [ru]
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of Texas Instruments
SLUS489 − OCTOBER 2001
FEATURES
D High-Frequency (2-MHz) Voltage Mode PWM
Controller
D 1.8-V to 9.0-V Input Voltage Range
D 0.8-V to 8.0-V Output Voltage Range (Higher in
Non-Synchronous Boost Topology)
D High-Efficiency Buck, Boost, SEPIC or
Flyback (Buck-Boost) Topology
D Synchronous Rectification for High-Efficiency
D Drives External MOSFETs for High-Current
Applications
D Synchronizable Fixed-Frequency PWM or
Automatic Pulsed Frequency Modulation
(PFM) Mode
D Built-In Soft-Start
D User Programmable Discontinuous or
Continuous Conduction Mode
D Selectable Pulse-by-Pulse Current Limiting or
Hiccup Mode Protection
TYPICAL BUCK APPLICATION
VIN
TPS43000
RTN
5
BUCK
3
RT
SYNC/SD
1
CCM
4
2
CCS
PFM*
6
12
GND
7
COMP FB
VIN
VP
PDRV
SWP
SWN
NDRV
VOUT
9
14
13
15
16
11
10
8
VOUT
UDG−01036
APPLICATIONS
D Networking Equipment
D Servers
D Base Stations
D Cellular Telephones
D Satellite Telephones
D GPS Devices
D Digital Still and Handheld Cameras
D Personal Digital Assistants (PDAs)
DESCRIPTION
The TPS43000 is a high-frequency, voltage-mode,
synchronous PWM controller that can be used in buck,
boost, SEPIC, or flyback topologies. This highly flexible,
full-featured controller is designed to drive a pair of
external MOSFETs (one N-channel and one
P-channel), enabling it for use with a wide range of
output voltages and power levels. With an automatic
PFM mode, a shutdown current of less than 1 µA, a
sleep-mode current of less than 100 µA and a full
operating current of less than 2 mA at 1 MHz, it is ideal
for building highly efficient, dc-to-dc converters.
The TPS43000 operates over a wide input voltage
range of 1.8 V to 9.0 V. Typical power sources are
distributed power systems, two to four nickel or alkaline
batteries, or one to two lithium-ion cells. It can be used
to generate regulated output voltages from as low as
0.8 V to 8 V or higher. It operates either in a
fixed-frequency mode, where the user programs the
frequency (up to 2 MHz), or in an automatic PFM mode.
In the automatic mode, the controller goes to sleep
when the inductor current goes discontinuous, and
wakes up when the output voltage has fallen by 2%. In
this hysteretic mode of operation, very high efficiency
can be maintained over a very wide range of load
current. The device can also be synchronized to an
external clock source using the dual function SYNC/SD
input pin.
semiconductor products and disclaimers thereto appears at the end of this data sheet.
! " #$%! " &$'(#! )!%*
)$#!" # ! "&%##!" &% !+% !%" %," "!$%!"
"!)) -!.* )$#! &#%""/ )%" ! %#%""(. #($)%
!%"!/ (( &%!%"*
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Copyright 2001, Texas Instruments Incorporated
1
SLUS489 − OCTOBER 2001
description (continued)
The TPS43000 features a selectable two-level current-limit circuit which senses the voltage drop across the
energizing MOSFET. The user can select either pulse-by-pulse current limiting or hiccup mode overcurrent
protection. The TPS43000 also features a low-power (LP) mode (which reduces gate charge losses in the
N-channel MOSFET at high input/output voltages), undervoltage lockout, and soft-start. The TPS43000 is
available in a 16-pin TSSOP (PW) package.
absolute maximum ratings over operating free-air temperature (unless otherwise noted)
†w
Input voltage (VIN, VP, VOUT) −0.3 V to 10 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(BUCK, CCM, CCS, PFM
, SYNC/SD) −0.3 V to VIN + 0.3 V. . . . . . . . . . . . . . . . . . . . . . .
(SWN) −0.3 V to 17 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
(SWP) −0.3 V to VIN + 0.3 V. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Storage temperature range, T
Junction temperature range, T
stg
J
−65°C to 150°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
−55°C to 150°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Lead temperature 1,6 mm (1/16 inch) from case for 10 seconds 300°C. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
†
Stresses beyond those listed under “absolute maximum ratings” may cause permanent damage to the device. These are stress ratings only , a nd
functional operation of the device at these or any other conditions beyond those indicated under “recommended operating conditions” is not
implied. Exposure to absolute- maximum-rated conditions for extended periods may affect device reliability. All voltages are with respect to
ground. Currents are positive into, negative out of the specified terminals.
PW PACKAGE
(TOP VIEW)
SYNC/SD
CCS
RT
CCM
BUCK
PFM
COMP
FB
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
SWN
SWP
VP
PDRV
GND
NDRV
VOUT
9
VIN
recommended operating conditions
MIN MAX UNIT
Input voltage, VIN, VP 9
Input voltage, VOUT 8
Input voltage, BUCK, CCM, CCS, PFM, SYNC/SD, SWP 9
Input voltage, SWN 17
Operating junction temperature range, TJ
§
t is not recommended that the device operate for extended periods of time under conditions beyond those specified in this table.
2
§
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−40 85 °C
V
VP = VOUT = 3.5 V, No load
VP = VOUT = 3.5 V, No load
µA
µA
SLUS489 − OCTOBER 2001
electrical characteristics over recommended operating junction temperature range,
= −40_C to 85_C for the TPS43000, RT = 75 kΩ (500 kHz), VIN = VP = 3.5 V, VOUT = 3.1 V, COMP/FB
T
A
pins shorted, BUCK-configured, T
VIN
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Start-up voltage
Undervoltage lockout (UVLO) hysteresis
Shutdown current
Operating current Not in PFM mode, no MOSFETs connected 1.0 1.4 mA
Sleep mode current PFM mode, COMP/FB=900 mV 75 140 µA
BOOST-configured VIN operating current
BOOST-configured VIN sleep mode current
VOUT
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Shutdown current SYNC/SD = VIN 0 2
Operating current Not in PFM mode, no MOSFETs connected 1 5
Sleep mode current PFM mode, COMP/FB=900 mV 0 2
BOOST-configured VOUT operating current
BOOST-configured VOUT sleep mode current
= T
(unless otherwise noted)
A
J
1.45 1.65 1.85 V
No MOSFETs connected
SYNC/SD = 1.6 V 1 10
SYNC/SD = VIN 0.5 2
Not in PFM mode, no MOSFETs connected,
BUCK pin grounded, VIN = 3.1 V,
VP = VOUT = 3.5 V
PFM mode, BUCK pin grounded,
VP = VOUT = 3.5 V, VIN = 3.1 V,
COMP/FB=900 mV
Not in PFM mode, no MOSFETs connected,
BUCK pin grounded, VIN = 3.1 V,
VP = VOUT = 3.5 V
PFM mode, BUCK pin grounded,
VP = VOUT = 3.5 V, VIN = 3.1 V,
COMP/FB=900 mV
60 150 300 mV
30 75 µA
25 60 µA
1.0 1.4 mA
50 120 µA
µA
µA
VP
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Shutdown current SYNC/SD = VIN 0.5 2
Operating current Not in PFM mode, no MOSFETs connected 500 800
Sleep mode current PFM mode, COMP/FB=900 mV 0 2
error amplifier
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
VREG, regulation voltage (COMP/FB pin)
FB input current VFB = 800 mV −150 −10 150 nA
Sourcing current (out of COMP) VFB = (VREG − 100 mV), V
Sinking current (into COMP) VFB = (VREG + 100 mV), V
Maximum ouput voltage (COMP pin) VFB = 0 V, I
Minimum output voltage (COMP pin) VFB = 2 V, I
Unity gain bandwidth See Note 1 5 MHz
NOTE 1: Ensured by design. Not production tested.
1.8 V < VIN < 6 V 784 800 816
VIN = 3.5 V 788 800 812
= 0 V, −2.0 −0.5 mA
COMP
= 2 V 0.5 1.2 mA
COMP
= −100 µA 1.6 2.0 V
COMP
= +100 µA 70 120 mV
COMP
µA
mV
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3
Soft-start time
Oscillator frequency
Constant current source configured if
Constant current source configured if
SLUS489 − OCTOBER 2001
electrical characteristics over recommended operating junction temperature range,
= −40_C to 85_C for the TPS43000, RT = 75 kΩ (500 kHz), VIN = VP = 3.5 V, VOUT = 3.1 V, COMP/FB
T
A
pins shorted, BUCK-configured, T
soft-start
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Soft-start time
oscillator
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Oscillator frequency
SYNC/SD
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Synchronization threshold voltage 0.8 1.25 1.6 V
SYNC pulse width SYNC/SD = 2 V, COMP/FB=600 mV 100 50 ns
SYNC input current SYNC/SD = 1.6 V 0.5 1 µA
SYNC high to shutdown delay time Float COMP, VFB = 0 V 10 22 35 µs
Synchronous range Force COMP/FB to 600 mV 1.1 f
= T
(unless otherwise noted)
A
J
RT = 37.5 kΩ (1 MHz) 1.0 3.0 6.0
RT = 75 kΩ (500 kHz) 2.0 5.5 12.0
RT = 150 kΩ (250 kHz) 4.0 10.5 24.0
RT = 37.5 kΩ (1 MHz), V
RT = 75 kΩ (500 kHz), V
RT = 150 kΩ (250 kHz), V
= 600 mV 0.90 1.00 1.10 MHz
COMP
= 600 mV 450 500 550 kHz
COMP
= 600 mV 225 250 280 kHz
COMP
o
1.5 f
o
ms
current limit
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
Hiccup overcurrent threshold voltage Voltage measured from VIN to SWN 175 250 325 mV
Delay to termination of P-channel gate drive time Measured at PDRV 125 300 ns
BOOST configured hiccup overcurrent threshold
voltage
Delay to termination of N-channel gate drive time Measured at NDRV, BUCK grounded 150 300 ns
Consecutive overcurrent clock cycles before
shutdown
Clock cycles before restart 800 900 1000
CCS threshold voltage
CCS pull-down current
CCS current threshold voltage Measured from VIN to SWN 85 150 225
BOOST-configured CCS current threshold voltage
Voltage measured from SWN to GND,
BUCK grounded
V
> 1 V
CCS
Measured from SWN to GND,
BUCK grounded
175 250 325 mV
50 63 75
0.40 0.70 1.00 V
0.5 1.0 µA
85 150 225
mV
4
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Continuous conduction allowed if
Continuous conduction allowed if
SLUS489 − OCTOBER 2001
electrical characteristics over recommended operating junction temperature range,
= −40_C to 85_C for the TPS43000, RT = 75 kΩ (500 kHz), VIN = VP = 3.5 V, VOUT = 3.1 V, COMP/FB
T
A
pins shorted, BUCK-configured, T
PWM
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
BUCK threshold voltage
BUCK pull-down current
BUCK maximum duty cycle VFB = 0 V 100%
BOOST maximum duty cycle BUCK grounded, VFB = 0 V 70% 90%
Minimum duty cycle VFB = 2 V 0%
CCM threshold voltage
CCM pull-down current
BUCK rectifier zero current threshold voltage Measured from SWP to GND −28 −12 0 mV
BOOST rectifier zero current threshold voltage
Delay to termination of P-channel gate drive time Measured at PDRV, BUCK grounded 200 300 ns
= T
(unless otherwise noted)
A
J
BUCK configured if V
V
> 1 V
CCM
Measured from SWP to VOUT,
BUCK grounded
BUCK
> 1 V
0.4 0.7 1.0 V
0.5 1.0 µA
0.4 0.7 1.0 V
0.5 1.0 µA
0 14 32 mV
pulsed frequency modulation
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
PFM threshold voltage
PFM pull-down current
FB voltage to awaken (exit sleep mode) 768 784 800 mV
Izero pulses required to enter sleep 5 7 9
Start-up delay time after sleep 2 5 µs
PFM mode not allowed if PFM > 1 V
0.4 0.7 1.0 V
0.5 1.0 µA
low power mode
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
VOUT threshold voltage to enter low power mode VP = VIN = 5 V 3.45 3.60 3.80
VIN threshold voltage to enter low power mode
Hysteresis voltage to exit low power mode
VP = VOUT = 5 V,
BUCK grounded (boost configured)
VOUT < (V
VP = VIN = 5 V
VIN < (V
BUCK grounded, VP = VOUT = 5 V
THRESHOLD−VHYST
THRESHOLD−VHYST
),
),
3.45 3.60 3.80
225 312 415
225 312 415
V
mV
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5
C
= 1 nF, VP = VIN = 5 V,
CO = 1 nF, VP = VIN = 5 V,
C
= 1 nF, VIN = 3.1 V,
CO = 1 nF, VIN = 3.1 V,
VP = VIN = 5 V, VOUT = 3.1 V
VP = VIN = 5 V, VOUT = 3.1 V
SLUS489 − OCTOBER 2001
electrical characteristics over recommended operating junction temperature range,
= −40_C to 85_C for the TPS43000, RT = 75 kΩ (500 kHz), VIN = VP = 3.5 V, VOUT = 3.1 V, COMP/FB
T
A
pins shorted, BUCK-configured, T
NDRV
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
VIN driven rise time
VIN driven fall time
VIN driven pull-up resistance
VIN driven pull-down resistance
BUCK P-channel MOSFET off to N-channel
MOSFET on anti-x delay time
VOUT driven rise time
VOUT driven fall time
VOUT driven pull-up resistance
VOUT driven pull-down resistance
BOOST P-channel MOSFET off to N-channel MOS-
FET on anti-x delay time
= T
(unless otherwise noted)
A
J
VOUT = 3.1 V
VP = VIN = 5 V, VOUT = 3.1 V
VP = VIN = 5 V, VOUT = 3.1 V,
PDRV and NDRV transitioning HI delta
VP = VOUT = 5 V, BUCK grounded
VP = VOUT = VIN = 5 V, LP mode activated
VP = VOUT = 5 V, VIN = 3.1 V,
BUCK grounded
25 45
20 40
6.5 10.0
2.25 4.00
10 35 75
25 45
20 40
6.5 10.0
2.25 4.00
10 35 75 ns
ns
Ω
ns
Ω
PDRV
PARAMETER TEST CONDITIONS MIN TYP MAX UNIT
VP driven rise time
VP driven fall time
VP driven pull-up resistance
VP driven pull-down resistance
BUCK N-channel MOSFET off to P-channel MOS-
FET on anti-x delay time
BOOST N-channel MOSFET off to P-channel MOS-
FET on anti-x delay time
CO = 1 nF
VP = VIN = 5 V, VOUT = 3.1 V
VP = VIN = 5 V, VOUT = 3.1 V,
NDRV and PDRV transitioning LO delta
VP = VOUT = 5 V, VIN = 3.1 V,
BUCK grounded
15 40
15 40
2.5 4.0
3.5 6.0
10 30 75
10 30 75
ns
Ω
ns
6
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I/O
DESCRIPTION
SLUS489 − OCTOBER 2001
Terminal Functions
TERMINAL
NAME NO.
Input pin to select topology. Connect this pin to VIN for a buck converter, ground it for a boost or SEPIC.
BUCK 5 I
CCM 4 I
CCS 2 I
COMP 7 O
FB 8 I
GND 12 − Ground pin for the device.
NDRV 11 O
PDRV 13 O
PFM 6 I
RT 3 O A resistor from this pin to ground sets the PWM frequency.
SWP 15 I
SWN 16 I
SYNC/SD 1 I
VP 14 I
VIN 9 I
VOUT 10 O
This configures the logic to the two gate drive outputs, and controls D
pulldown.
Input pin determines whether or not the l
tion. Pulling this pin high ignores the Izero comparator’s output, forcing continuous conduction mode.
Connecting it to ground enables Izero, allowing discontinuous conduction mode (DCM) operation. Note
that even when pulled high, seven detected I
internal pull-down.
Current limit feature allowing selection of either pulse-by-pulse current limiting or hiccup mode overcurrent protection. Connect this pin to VIN to select pulse-by-pulse current limiting, the constant current
source mode. Connect this pin to ground to enable hiccup mode overcurrent protection. This pin has a
weak internal pulldown.
Output of the error amplifier. The compensation components are connected from this pin to the FB pin.
During sleep mode, this pin goes to high impedance, and is severed from the internal error amplifier’s
output so that it may hold its dc potential.
Inverting input to the error amplifier. It is connected to a resistor divider off of VOUT, and to the compensation network.
Gate drive output for the N-channel MOSFET (energizing MOSFET for the boost and SEPIC, rectifier
MOSFET for the buck).
Gate drive output for the P-channel MOSFET (energizing MOSFET for the buck, rectifier MOSFET for the
boost and SEPIC).
Input pin that disables/enables PFM operation. Connecting it to VIN disables PFM mode. Grounding this
pin enables PFM to occur automatically, based on lzero. This pin has a weak internal pulldown.
Connect this pin through a 1-kΩ resistor to the drain of the P-channel MOSFET for all topologies. It detects Izero pulses using the synchronous rectifier MOSFET. For the SEPIC topology, a Schottky clamp
tied to ground must be connected to this pin.
Connect this pin through a 1-kΩ resistor to the drain of the N-channel MOSFET for all topologies. It
senses overcurrent conditions using the inductor energizing MOSFET.
This dual-function pin is used to synchronize the oscillator or shutdown the controller, turning both
MOSFETs off. A pulse from 0 V to 2 V provides synchronization. Duty cycle is not critical, but it must be
at least 100 ns wide. Holding this pin to 2 V or greater for over 35 µs shuts down the device. This pin
has a weak internal pulldown.
Power rail input pin for the P-channel MOSFET gate driver. Connect this pin to VIN for a buck, and to
VOUT for a boost or SEPIC. Provide good local decoupling.
Input supply for the device. It provides power to the device, and may be used for the N−channel gate
drive. Provide good local decoupling
Connect this pin to the power supply output. It may be used for the gate drive to the N−channel MOSFET. Provide good local decoupling.
DESCRIPTION
comparator allows discontinuous conduction mode opera-
ZERO
pulses still initiate PFM mode. This pin has a weak
ZERO
. This pin has a weak internal
MAX
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7
3
S
V
V
SLUS489 − OCTOBER 2001
functional block diagram
300 mV
+
10 mV
LEB
+
800 mV
SOFT
START
++
800 mV
784 mV
200 mV
10
VOUT
9
VIN
R
1.6 R
CCM
4
GND
12
SWP
15
6
PFM
784 mV
8
FB
REFGOOD
HICCUP
7COMP
RT
3
YNC/SD
1
5
BUCK
2
CCS
150 mV
++
250 mV
SWN LEB
16
VREF
1.246 V
SHUTDOWN
TIMER AND
OSCILLATOR
SHUTDOWN
(SD)
+
UVLO
95% MAXIMUM DUTY
CYCLE NON−BUCK
+
+
DELAY
TO ZERO
IZERO
ERROR
AMPLIFIER
+
+
SLEEP
RESET
VINEST 2.75 V
VBEST
REFGOOD
REFBAD
RECTOFF
(STOP SWITCH
RECTIFICATION)
3−BIT UP
COUNTER
PWM
COMPARATOR
+
RESET
6−BIT
UP/DOWN
COUNTER
IMAX
(STOP ENERGIZING INDICATOR)
SQ
SQ
QR
VIN
VOUT
SLEEP
QR
RECTOFF IMAX
RECTIFY
RESET
SHUTDOWN
FOR 900
CYCLES THEN
SOFT−START
+
VINEST
LPM
VINEST
CONDUCTION
TOPOLOGY
PWM ENABLE
HICCUP
(STOP SWITCHING FOR 900
CYCLES THEN SOFT−START)
VDD
3.6 V
3.3 V
ANTI
CROSS
&
STEERING
LOGIC
+
+
SQ
QR
VIN
NDRV_RAIL
SD
REFBAD
SLEEP
HICCUP
LPM
VOUT
VP
14
PDR
13
NDR
11
TPS43000
8
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UDG−0104
SLUS489 − OCTOBER 2001
APPLICATION INFORMATION
general information
The TPS43000 is a high-frequency, synchronous PWM controller optimized for distributed power, or
battery-powered applications where size and efficiency are of critical importance. It includes high-speed,
high-current MOSFET drivers for those applications requiring low R
block diagram).
optimizing efficiency
The TPS43000 optimizes efficiency and extends battery life with its low quiescent current and its synchronous
rectifier topology . The additional features of low-power (LP) mode and PFM mode maintain high efficiency over
a wide range of load current.
modes of operation
The TPS43000 has four distinct modes of operation:
D fixed PWM with discontinuous conduction mode (DCM) possible
external MOSFETs. (See functional
DS(on)
D fixed PWM with forced continuous conduction mode (CCM)
D automatic pulse frequency modulation (PFM) with DCM possible
D PFM with forced CCM
The device mode is controlled by the CCM and PFM
DCM by connecting the pin to ground or to force CCM by connecting the pin to VIN. The PFM
decide whether to allow automatic PFM by connecting the pin to ground or to force fixed PWM by connecting
the pin to VIN.
fixed PWM with DCM possible (PFM tied to VIN; CCM tied to ground)
In this mode, the device behaves like a standard switching regulator with the addition of a synchronous rectifier.
Shortly after the energizing MOSFET turns off, the synchronous rectifier turns on. The synchronous rectifier
turns off either when the inductor current goes discontinuous (DCM) or just prior to the start of the next clock
cycle (CCM) when the energizing MOSFET turns on. During the small time interval when neither the energizing
MOSFET nor the synchronous rectifier are turned on, the synchronous rectifier MOSFET body diode (or an
optional small external Schottky diode in parallel) carries the current to the output until it goes discontinuous.
The efficiency drops off at light loads as the losses become a larger percentage of the delivered load.
pins. The CCM pin lets the user decide whether to allow
pin lets the user
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9
(1)
SLUS489 − OCTOBER 2001
APPLICATION INFORMATION
fixed PWM with forced CCM (PFM and CCM tied to VIN)
CCM is forced under all operating conditions in this mode. The synchronous rectifier turns on shortly after the
energizing MOSFET turns off and remains on until just prior to the start of the next clock cycle when the
energizing MOSFET turns on. The user should design the converter to operate in CCM over its entire operating
range in order to prevent the inductor current from going negative. If the converter is allowed to run
discontinuous, the inductor current goes negative (i.e. the output discharges as the current reverses and goes
back through the rectifier to the input or ground.) With fixed PWM, the efficiency drops off at light loads as the
losses become a larger percentage of the delivered load.
PFM with DCM possible (PFM
In this mode, the device can operate in either fixed PWM or in PFM mode. When the device is initially powered,
it operates in fixed PWM mode until soft-start completion. It remains in this mode until it senses that the converter
is on the verge of breaking into discontinuous operation. When this condition is sensed, the converter enters
PFM mode, invoking a sleep state until the output voltage falls 2% below nominal (a 16-mV drop measured at
the FB pin). At this time, the controller starts up again and operates at its fixed PWM frequency for a short
duration (load dependent, typically 10 to 200 PWM cycles), increasing the output voltage. If the controller again
senses the converter is on the verge of going discontinuous, the cycle repeats. If discontinuous operation is not
sensed, the converter remains in fixed PWM mode. PFM mode results in a very low duty cycle of operation,
reducing all losses and greatly improving light load efficiency. During the sleep state, most of the circuitry internal
to the TPS43000 is powered down. This reduces quiescent current, which lowers the average dc operating
current, enhancing its efficiency.
PFM with forced CCM (PFM
This mode is similar to the PFM with DCM possible mode except that the controller forces the converter to
operate in CCM. The converter can be designed to run discontinuous at light loads. The controller senses
discontinuous operation and enters the PFM mode. With PFM, the converter can maintain a very high efficiency
over a very wide range of load current.
and CCM tied to ground)
tied to ground; CCM tied to VIN)
anticross−conduction and adaptive synchronous rectifier commutation logic
When operating in the continuous conduction mode (CCM), the energizing MOSFET and the synchronous
rectifier MOSFET are simply driven out of phase, so that when one is on the other is off. There is a built-in time
delay of about 40 ns to prevent any cross-conduction.
In the event that the converter is operating in the discontinuous conduction mode (DCM), the synchronous
rectifier needs to be turned off quickly, when the rectifier current drops to zero. Otherwise, the output begins to
discharge as the current reverses and goes back through the rectifier to the input or ground (this obviously
cannot happen when using a conventional diode rectifier). To prevent this, the TPS43000 incorporates a
high-speed comparator that senses the voltage on the synchronous rectifier using the SWP input, which is
connected to the synchronous rectifier MOSFET’s drain through a 1-kΩ resistor. This comparator is used to
determine when the inductor current is on the verge of going discontinuous and is referred to as the I
comparator. I n the boost and SEPIC (single-ended primary inductance converter) topologies, the synchronous
rectifier is turned off when the voltage on the SWP pin decreases to within 12 mV of VOUT. For this reason, it
is important to have the VOUT pin well decoupled. In the buck topology, the synchronous rectifier is turned off
when the voltage on the SWP pin increases to −12 mV with respect to ground. The I
as follows:
+
12 mV
R
DS(on)
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10
l
ZERO
threshold is defined
ZERO
ZERO
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