Datasheet TK65433MTL, TK65430MTL, TK65425MTL, TK65427MTL, TK65424MTL Datasheet (TOKO)

ADVANCED INFORMATION

V

OUT

LBO

V

IN

SW

GND

LBI/SB

TK654xx

ADVANCED

STEP-DOWN CONVERTER WITH BATTERY MONITOR

INFORMATION

FEATURES

■ Minimum External Component Count (1 coil, 1 cap)

■ Miniature 6 Pin SOT23L-6 Surface Mount Package

■ Up To 95% Efficient

■ Extremely Low Operating Current (24 µA)

■ Low Quiescent Current (18 µA)

■ Low Ripple

■ Fast Transient Response

■ Linear Dropout Characteristics

■ Short Circuit Protection

■ Regulates Down to 1.8 V

■ Synchronous Rectification

■ Internal Battery Monitor

DESCRIPTION

The TK654xx low power step-down converter is designed
for portable battery systems, capable of operating from a
single Li-ion battery cell or multiple alkaline or rechargeable
(NiCd or NiMH) battery cells (up to 6 V). The TK654xx
provides the power switch, synchronous rectifier, and the
control circuit for a buck step-down converter. Only two
external components are required to complete the step­down conversion.

APPLICATIONS

■ Battery Powered Systems

■ Cellular Telephones

■ Pagers

■ Personal Communications Equipment

■ Radio Controlled Systems

■ Toys

Driving the SB pin low will disable the TK654xx and drop
the quiescent current on the input supply to approximately
18 µA.

Pulse Current Amplitude control is used to regulate the
voltage at the V
of the TK654xx drops below the regulation threshold, a
current pulse is transferred from the input supply to the
output. The TK654xx utilizes a proprietary control scheme,
where the average amplitude of the current pulse is varied
depending upon the current loads. The proprietary
architecture allows fast transient response and minimal
ripple while maintaining ease-of-use and low component
count.

The TK654xx is available in a miniature 6-pin SOT23L-6
surface mount package.

pin of the IC. When the output voltage

OUT

TK654xxM

The TK654xx provides laser-trimmed output voltages
ranging from 1.8 V to 3.3 V. The low resistance MOSFET
switch and synchronous rectifier allow average currents
up to 200 mA, while maintaining peak efficiencies up to
95%. A low-battery threshold and turn-off threshold can
be individually programmed by the user, utilizing a single
resistor divider connected to the Low Battery Input (LBI)
pin. When the resistively-divided supply voltage on the
LBI pin drops below approximately 1.22 V, the Low Battery

BLOCK DIAGRAM

Output (LBO) pin will become asserted. The dual-function
LBI pin can alternatively be used as a Standby (SB) pin.

V

IN

ORDERING INFORMATION

V

OUT

REF

LBI/SB

Voltage Code

VOLTAGE CODE

18 = 1.8 V
21 = 2.1 V
24 = 2.4 V
25 = 2.5 V

27 = 2.7 V
30 = 3.0 V
33 = 3.3 V

TK654xxM

Tape/Reel Code

TAPE/REEL CODE

TL: Tape Left

September 1999 TOKO, Inc. Page 1

CONTROL

CIRCUIT

BATTERY
MONITOR

SW

GND

LBOOFF

LBO

TK654xx

ADVANCED INFORMATION

ABSOLUTE MAXIMUM RATINGS

All Pins Except GND ............................................... 6.5 V

Power Dissipation (Note 1) ................................ 400 mW

Storage Temperature Range ................... -55 to +150 °C

Operating Temperature Range ...................-20 to +80 °C

Junction Temperature ...........................................150 °C

Lead Soldering Temperature (10 s.) .....................235 °C

TK654xx ELECTRICAL CHARACTERISTICS

Test conditions: VIN = 5 V, I

LOBMYSRETEMARAPSNOITIDNOCTSETNIMPYTXAMSTINU

= 1 mA, T

OUT

= TJ = Full Operating Temperature Range, unless otherwise specified.

A

V

V

∆V
∆V

I

I

V
V

NI

)GER(TUO

)DAOL(TUO

)ENIL(TUO

)TUOV(Q

)NIV(Q

)IBL(HT

)BS(HT

egatloVtupnI26V

TAT=

egatloVtuptuO

J

)2etoN(C°52=%3-V

GER

%3V

%5-%5+V

noitalugeRdaoLI

noitalugeReniLV

VotnitnerruCtnecseiuQ

VotnitnerruCtnecseiuQ

niP

TUO

niPV

NI

dlohserhTtupnIIBLT

dlohserhTybdnatST

NI

V

AT=J

AT=J

DAOL

V=

TUO

)GER(TUO

)3etoN(

V=

TUO

)GER(TUO

C°52=751.122.1282.1V
C°52=751.122.1282.1V

)3etoN(,Am001ot0=54021Vm

)3etoN(,V6ot4=602Vm

Vm05+

0105Aµ

P

Vm05+5156Aµ

3etoN0An

I

)BS(B

I

)XAM(TUO

I

)CS(TUO

I

)VNOC(Q

I

YBTS

FFEycneiciffEretrevnoC

V

PORD

Note 1: Power dissipation is 400 mW when mounted as recommended. Derate at 3.2 mW/°C for operation above 25 °C. Power dissipation is 200
mW in Free Air. Derate at 1.6 mW/°C for operation above 25 °C
Note 2: V
Note 3: When using test circuit.
Note 4: When using test circuit and ramping VIN down.
Note 5: When using test circuit with SB pin resistors removed and tied to VIN. (VIN = 1.8 V)
Note 6: When using test circuit with SB pin resistors removed and tied to VIN. (VIN = 3.3 V)

= 3.3, 3.0, 2.7, 2.5, 2.4, 2.1, 1.8 V.

REG

tnerruCsaiBtupnIBS

V(ta4etoN

)BS(HT

)Vm001-0040270001An

tnerruCtuptuOmumixaM)3etoN(001Am

tnerruCtiucriCtrohS)3etoN(052Am

tnerruCtnecseiuQretrevnoCI)3etoN(

TUO

Am0=4209Aµ

tnerruCybdnatSretrevnoCnepo1niP,V0=nipBS8156Aµ

I

TUO

TAT=

J

I

TUO

TAT=

J

I

TUO

TAT=

egatloVtuoporD

I

TAT=

J

TUO

J

)3etoN(,Am05=

)81456KT(C°52=

)3etoN(,Am05=

)33456KT(C°52=

)5etoN(,Am05=

)6etoN(,Am05=

6819%

0959%

)81456KT(C°52=

)33456KT(C°52=

001591Vm

57541Vm

Page 2

September 1999 TOKO, Inc.

ADVANCED INFORMATION

TK654xx

1.820

1.815

I

Q(CONV)

V

= 5 V

IN

C

3

10 µF

I

OUT

V

OUT

C

10 µF

1

C

10 µF

+

2

TEST CIRCUIT

R

3

300 K

I

Q(VOUT)

L

1

100 µH

V

LBO

OUT

SW

LBI/SB

GND

V

IN

L

1

C1,C3: Ceramic 10 µF
C2: Tantalum 10 µF

TYPICAL PERFORMANCE CHARACTERISTICS

USING TEST CIRCUIT

TK65418

LINE REGULATION

I

= 1 mA

OUT

3.330

3.325

R

1

634 K

R

2

287 K

I

Q(VIN)

: Toko D10F Coil, PN A814AY-101K

L1:

TK65433

LINE REGULATION

I

= 1 mA

OUT

1.810

(V)

1.805

OUT

V

1.800

1.795

1.790

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0
V

(V)

IN

TK65418

LOAD REGULATION

1.82

VIN = 5 V

1.80

(V)

OUT

V

1.78

1.76
0 20 40 60 80 100 120

I

(mA)

OUT

3.320

(V)

3.315

OUT

V

3.310

3.305

3.300

3.4 3.8 4.2 4.6 5.0 5.4 5.8 6.0
V

(V)

IN

TK65433

3.35

LOAD REGULATION

3.3

(V)

OUT

V

3.25

3.2
0 20 40 60 80 100 120 140 160

I

(mA)

OUT

VIN = 5 V

September 1999 TOKO, Inc. Page 3

TK654xx

ADVANCED INFORMATION

TYPICAL PERFORMANCE CHARACTERISTICS

USING TEST CIRCUIT (CONT.)

LOAD AND TEMPERATURE

TK65418

1.90

REGULATION

1.88

1.86

1.84

(V)

OUT

V

1.82

1.8

1.78

1.76

I

OUT

= 1 mA

I

OUT

I

OUT

= 100 mA

= 50 mA

1.74

1.72

-50 -25 0 25 50 75 100 125
TEMPERATURE (°C)

TK65418

EFFICIENCY vs.

OUTPUT CURRENT

100

90
80
70

60
50

40

30

EFFICIENCY (%)

20
10

0

0 20 40 60 80 100 120

I

(mA)

OUT

LOAD AND TEMPERATURE

TK65433

3.55

REGULATION

3.45

I

= 50 mA

I

OUT

OUT

= 1 mA

(V)

OUT

V

3.35

3.25

3.15

3.05

-50 -25 0 25 50 75 100 125
TEMPERATURE (°C)

TK65433

EFFICIENCY vs.

OUTPUT CURRENT

100

90
80
70

60
50

40

30

EFFICIENCY (%)

20
10

0

0 40 80 120 160

I

(mA)

OUT

I

OUT

= 100 mA

Page 4

EFFICIENCY vs. TEMPERATURE

100

TK65418

95

I

= 50 mA

90

OUT

85

EFFICIENCY (%)

80

75

-50 -25 0 25 50 75 100 125
TEMPERATURE (°C)

EFFICIENCY vs. TEMPERATURE

99
97

95

TK65433

I

OUT

= 50 mA

93
91

EFFICIENCY (%)

89
87

85

-50 -25 0 25 50 75 100 125
TEMPERATURE (°C)

September 1999 TOKO, Inc.

TYPICAL PERFORMANCE CHARACTERISTICS

CONVERTER QUIESCENT
INPUT SUPPLY VOLTAGE

26

25.5
25

24.5

(µA)

24

23.5

Q(CONV)

I

23

22.5
22

2 3 4 5 6

CONVERTER QUIESCENT

200

150

TK65418

CURRENT vs.

VIN (V)

TK65418

CURRENT vs.

TEMPERATURE

ADVANCED INFORMATION

USING TEST CIRCUIT (CONT.)

No Load

No Load

26

25.5
25

24.5

(µA)

24

23.5

Q(CONV)

I

23

22.5
22

3.5 4 4.5 5 5.5 6

200

150

CONVERTER QUIESCENT
INPUT SUPPLY VOLTAGE

CONVERTER QUIESCENT

TK65433

CURRENT vs.

VIN (V)

TK65433

CURRENT vs.

TEMPERATURE

No Load

No Load

TK654xx

(µA)

100

Q(CONV)

I

50

0

-50 -25 0 25 50 75 100 125
TEMPERATURE (°C)

TK65418

STANDBY CURRENT vs.

INPUT SUPPLY VOLTAGE

25

20

(µA)

15

STBY

I

10

5

2 2.5 3 3.5 4 4.5 5 5.5 6

VIN (V)

(µA)

100

Q(CONV)

I

50

0

-50 -25 0 25 50 75 100 125
TEMPERATURE (°C)

STANDBY CURRENT vs.

INPUT SUPPLY VOLTAGE

25

20

(µA)

15

STBY

I

10

5

2 2.5 3 3.5 4 4.5 5 5.5 6

TK65433

VIN (V)

September 1999 TOKO, Inc. Page 5

TK654xx

ADVANCED INFORMATION

TYPICAL PERFORMANCE CHARACTERISTICS (CONT.)

TK65418

STANDBY CURRENT vs.

80

60

(µA)

40

STBY

I

20

0

-50 -25 0 25 50 75 100 125

350
300

250

(mA)

200

TEMPERATURE

TEMPERATURE (°C)

TK65418

MAX OUTPUT CURRENT vs.

INDUCTOR VALUE

STANDBY CURRENT vs.

80

60

(µA)

40

STBY

I

20

0

-50 -25 0 25 50 75 100 125

MAX OUTPUT CURRENT vs.

350

300

250

(mA)

200

TK65433

TEMPERATURE

TEMPERATURE (°C)

TK65433

INDUCTOR VALUE

150

OUT(MAX)

I

100

50

0

60 90 120 150 180

INDUCTOR VALUE (µH)

150

OUT(MAX)

I

100

50

0

60 90 120 150 180

INDUCTOR VALUE (µH)

Page 6

September 1999 TOKO, Inc.

ADVANCED INFORMATION

TYPICAL PERFORMANCE CHARACTERISTICS (CONT.)

USING RIPPLE TEST CIRCUIT

V

= 5 V

IN

C

3

V

OUT

10 µF

L

1

+

C

2

100 µH

C

1

LBO

OPEN

V

OUT

SW

LBI/SB

GND

V

IN

L1: Toko D10F Coil, PN A814AY-101K
C1 = See Figure Below
C2 = Tantalum 10 µF
C3 = Ceramic 10 µF

TK654xx

PEAK TO PEAK RIPPLE VOLTAGE

RIPPLE vs. OUTPUT CURRENT

70
60

50
40

30

RIPPLE (mV)

20
10

0

0 20 40 60 80 100

C2 = 10 µF Tantalum

C1 = 10 µF

I

OUT

C1 = 20 µF

C1 = 80 µF

(mA)

C1 = 50 µF

September 1999 TOKO, Inc. Page 7

TK654xx

ADVANCED INFORMATION

TYPICAL PERFORMANCE CHARACTERISTICS (CONT.)

STARTUP TRANSIENT WAVEFORMS

TK65418 - Power Up No Load

TK65418 - Power Up 100mA Load

Output Voltage (1V / div)

Inductor Current (100mA / div)

Output Voltage (1V / div)

1.8V

0.0V

200mA

0mA

1.8V

0.0V

200mA

TK65433 - Power Up No Load

3.3V

Output Voltage (2V / div)

0.0V

200mA

Inductor Current (100mA / div)

0mA

TK65433 - Power Up 100mA Load

3.3V

Output Voltage (2V / div)

0.0V

Inductor Current (100mA / div)

200mA

Page 8

Inductor Current (100mA / div)

TK65418 - Power Up using SB Pin (100mA Load)

Output Voltage (1V / div)

Inductor Current (100mA / div)

0mA

1.8V

0.0V

200mA

0mA

0mA

TK65433 - Power Up using SB Pin (100mA Load)

3.3V

Output Voltage (2V / div)

0.0V

Inductor Current (100mA / div)

200mA

0mA

September 1999 TOKO, Inc.

ADVANCED INFORMATION

TYPICAL PERFORMANCE CHARACTERISTICS (CONT.)

TURN OFF TRANSIENT WAVEFORMS

TK654xx

TK65418 - Power Down using SB Pin (100mA Load)

Output Voltage (1V / div)

Inductor Current (100mA / div)

LOAD TRANSIENT RESPONSE WAVEFORMS

TK65418 - Transient Load (0mA to 100mA Step)

Output Voltage (50mV / div)

Inductor Current (100mA / div)

1.8V

0.0V

200mA

0mA

200mA

TK65433 - Power Down using SB Pin (100mA Load)

3.3V

Output Voltage (2V / div)

0.0V

200mA

Inductor Current (100mA / div)

0mA

TK65433 - Transient Load (0mA to 100mA Step)

Output Voltage (50mV / div)

Inductor Current (100mA / div)

200mA

TK65418 - Transient Load (100mA to 0mA Step)

Output Voltage (50mV / div)

Inductor Current (100mA / div)

0mA

TK65433 - Transient Load (100mA to 0mA Step)

Output Voltage (50mV / div)

200mA

Inductor Current (100mA / div)

0mA

0mA

200mA

0mA

September 1999 TOKO, Inc. Page 9

TK654xx

ADVANCED INFORMATION

THEORY OF OPERATION

Figure 1 illustrates a circuit diagram for a simple buck
(step-down) converter. Typically, the input voltage (VIN) is
greater than the output voltage (V
switching action of switch SW1, the output voltage (V

). By modulating the

OUT

OUT

can be regulated to a constant voltage that is relatively
independent of variations in the input supply (VIN) or the
current load on the V

node. The TK654xx contains all

OUT

the control circuitry, logic, and power switch (SW1) for
implementing a simple step-down or "buck" converter, as
shown in Figure 1.

In general, a switching converter utilizing the TK654xx
controller will be operating in one of three states:

1. "ON" STATE: During this state of operation SW1 will be
turned on. Current through the inductive element (L) will be
increasing at a rate proportional to the voltage difference
between VIN and V

. In this state, there is a direct

OUT

current path from the input supply to the output load
through the inductor L.

2. "OFF" STATE: During this state of operation SW1 will
be turned off. Current through the inductive element will be
greater than zero and flowing either through the external
schottky rectifier (D) or the synchronous rectifier internal to
the TK654xx. During the "off" state, current through the
inductive element (L) will be decreasing at a rate
approximately proportional to V

. In this state, the

OUT

current drawn from the input supply is essentially zero.
Current to the load is provided by stored energy in the
inductive element.

3. "NULL" STATE: During this state of operation SW1 will
be turned off. Current through the inductive element will be
approximately zero. The internal synchronous rectifier will
be turned off. All current demands of the load will be
provided by the output filter capacitor (C). In this state, the
current drawn from the input supply is essentially zero.
Since the inductive current is zero, no additional energy is
available from the inductor. If the current demands of the
load are very light, the current will be provided by the
stored charge in the output filter capacitor. If the voltage of
the filter capacitor drops below the regulation threshold, an
"on" state will be initiated and additional energy will be
transferred from the input supply to the output.

LSW1

V

OUT

+

V

)

IN

CD

FIGURE 1: SIMPLE "BUCK" CONVERTER

The control scheme for the TK654xx forces the converter
to step through the "on," "off," and "null" states in sequence.
Assume that the controller is initially in the "null" state and
V

is greater than the regulation threshold. As soon as

OUT

the output voltage drops below this threshold, the controller
will switch from "null" state to the "on" state. During the "on"
state, current through inductor (L) will be increasing.
Current will flow from the input supply to the output
capacitor through the inductive element. In this state,
energy is transferred directly from the input supply to the
output through the inductor. The maximum duration of the
"on" state is inversely proportional to the difference between
the input voltage (VIN) and the output voltage (V

The transition from the "on" state to the "off" state can be
initiated by one of two different means. As mentioned
above, the maximum duration of the "on" state is inversely
proportional to the difference between the input voltage
(VIN) and the output voltage (V

). If the duration of the

OUT

"on" cycle exceeds this maximum, the controller
immediately switches to the "off" state independent of
other factors. Understanding that when the converter is in
a dropout condition (VIN ≈ V

), the maximum “on” time

OUT

is infinite and the “on” state is constantly applied. By
limiting the duration of the "on" cycle, the peak inductor
current is also being limited. The second method for
initiating the "off" cycle is triggered when the duration of the
"on" cycle exceeds a minimum on-time duration and the
output voltage (V

) exceeds the regulation threshold.

OUT

Therefore, the actual duration of the "on" cycle will vary
between a minimum on-time (T
on-time (T

ON(MAX)

) depending upon the load current. At

ON(MIN)

) and a maximum

very light loads the on-time duration will be at a minimum;
at very heavy loads the on-time will be at a maximum. This
ability to vary the duration of the on cycle is a proprietary
control scheme which can produce a ten-fold reduction in
ripple when compared to competing devices.

OUT

).

Page 10

The transition from the "off" state to the "null" state occurs
after sufficient time has been allowed for the inductor
current to return to zero. The actual duration of the "off"

September 1999 TOKO, Inc.

ADVANCED INFORMATION

THEORY OF OPERATION (CONT.)

TK654xx

cycle will be dependent upon the duration of the preceding
"on" cycle and the sensed input and the output voltages.

The approximate duration of the "off" cycle can be predicted
as follows:

T

= TON X (VIN - V

OFF

OUT

) / V

OUT

During the majority of the "off" cycle, a power switch is
turned on. The turn-on point of the switch is synchronized
with the initiation of the "off" cycle. The turn-off point is near
the end of the "off" cycle. The addition of this switch
reduces the voltage drop across the external rectifying
device and provides significant improvements in converter
efficiency.

BATTERY MONITOR SECTION

In a typical voltage monitor, which uses an external resistive
divider for setting the voltage monitor threshold, the input
bias current to the monitor pin is essentially zero. In this
type of scenario, the voltage on the monitor input would be
a resistively divided version of the battery voltage. The
Battery Monitor of the TK654xx introduces a small feedback
current (-I

) which introduces a “plateau” into the transfer

LBI

characteristics between the battery voltage and the voltage
monitoring pin. The width of this plateau is dependent
upon the current range of the feedback current (-I

LBI

) and
the values of the external resistor network. Figure 2
illustrates the typical relationship between the battery
voltage (VIN), the feedback current (-I
on the monitoring pin (V

LBI

).

) and the voltage

LBI

As the battery voltage drops, the voltage on the V

pin will

LBI

drop proportionately. When the voltage on the LBI input pin
passes through approximately 1.22 V, the output of the
first comparator (LBO) will transition from a high to a low
state and the synchronous rectifier N-channel MOSFET
will stop being switched. There is about 50 mV of hysteresis
between the LBO trip point and its reset point. Shortly after
the LBO output has been asserted, as the input voltage
continues to drop, the magnitude of the current out of the
V

pin will begin to flow and proportionately increase as

LBI

the input voltage decreases. An op-amp feedback loop
internal to the Battery Monitor of the TK654xx will attempt
to maintain the voltage on the V

pin at a constant value

LBI

of approximately 1.22 V (thus, the plateau). As the battery
voltage continues to drop, there comes a point where the
feedback current stops increasing at about 720 nA. At this
point, the voltage on the LBI pin will resume a proportional
drop with the input voltage and the TK654xx converter will
turn off.

For details on how to properly select the resistor divider,
refer to the “Design Considerations” section.

V

LBO

V

IN

V

LBI

1.22 V

V

OFF

720 nA

0 nA

-I

In selecting a resistor divider network, there are typically

LBI

two degrees of freedom when selecting values. The first
criteria in selecting the divider is the ratio of the two
resistors. Selecting the ratio defines the upper threshold of

LBO

the voltage monitor. The second degree of freedom when
selecting the resistor divider is the absolute resistance

OFF

values. This second degree of freedom can be utilized to
set a secondary monitoring threshold (V
the first.

) lesser than

OFF

FIGURE 2: BATTERY MONITOR OPERATION

GRAPHS

Typically, when the battery voltage is relatively high, the
voltage on the LBI input pin will be a resistively divided
version of the battery voltage.

September 1999 TOKO, Inc. Page 11

TK654xx

ADVANCED INFORMATION

PIN DESCRIPTION

INPUT VOLTAGE PIN (VIN)

This pin is the positive input supply for the TK654xx. Current
flowing into this pin provides power to the IC and to the
converter output through the inductive element. During the
"on" state, the majority of the current flowing into this pin is
flowing through the inductor. During the "off" and "null" states,
the current into this pin is very small (approximately 18 µA).
The voltage source driving this pin should have relatively low
AC impedance. Good design practices dictate decoupling to
the GND pin.

GROUND PIN (GND)

This pin provides the ground connection for the IC.

OUTPUT VOLTAGE PIN (V

This pin senses the output voltage of the buck converter.
Input current into this pin is very low (approximately 10 µA).
The output voltage is resistively divided in the IC and compared
to the bandgap voltage. If the output voltage remains greater
than the regulation threshold, the TK654xx remains in a
standby state. As soon as the output voltage drops below the
regulation threshold, the TK654xx will initiate an "on" and "off"
cycle to boost the output voltage.

OUT

)

The second function of this pin is to act as a Standby (SB)
input. If this pin is greater than approximately 1.22 V, the
converter will operate normally. Driving this pin low will force
the converter into a "standby" mode where the DC/DC
conversion is disabled. In this "standby" mode, the current
through the inductive element goes to zero; only the filter
capacitor will provide current to the output.

If neither the Low-Battery or Standby features are needed,
this input pin should be connected directly to the VIN pin.
Under this mode of operation, the TK654xx will not turn off. As
the input voltage approaches the regulation voltages the
TK654xx will act as a P-Channel pass element with
approximately a 2 Ω resistance, going into the linear mode of
operation.

LOW BATTERY OUTPUT PIN (LBO)

This pin provides a Low Battery Output (LBO) signal to
indicate when the voltage on the LBI input pin has dropped
below the low battery threshold (1.22 V). This open-drain
output is normally pulled up to either the input supply or the
output supply through a resistive pull-up. The LBO output pin
provides an active-low output. If the LBO is not going to be
used, the pin may be left open.

SW PIN

This pin is normally connected to one pin of the inductive
element and an external optional passive schottky rectifier
(optional to increase efficiency). The external schottky rectifier
is connected between this pin and ground. It is recommended
that the lead lengths between the rectifier and the pins of the
TK654xx be kept as short as possible to minimize parasitic
inductances.

LOW BATTERY INPUT/STANDBY PIN (LBI/SB)

This input pin is capable of performing two separate functions
which will be dependent upon the application's requirements.

In some applications, this input pin can be used as a Low
Battery Input (LBI). In such an application, this input pin is
typically driven by a resistively divided version of the input
supply (VIN). For detailed information on selecting values for
the resistor divider, please refer to Design Considerations on
pages 13 and 14.

Page 12

September 1999 TOKO, Inc.

ADVANCED INFORMATION

DESIGN CONSIDERATIONS

TK654xx

INDUCTOR SELECTION

One of the positive features of the TK654xx is the ability to
limit the magnitude of the short circuit current without the
need for external current sensing resistors. Since the
maximum on-time duration is limited, and the converter
always operates in discontinuous conduction mode (DCM),
the maximum load current is essentially dependent upon
the selection of the inductor value. The following table
defines the maximum load current as a function of the
inductor value.

L MAX LOAD

47 µH 305 mA
100 µH 140 mA
220 µH 65 mA
470 µH 20 mA

OUTPUT FILTER CAPACITOR SELECTION

The purpose of the filter capacitor on the output is to
temporarily provide current to the load as inductor current
is ramping upward or downward. In general, larger
capacitors will reduce the magnitude of the ripple.

shutdown threshold which occurs at a voltage lower than
the LBI threshold. Both the LBI threshold and the shutdown
threshold can be set utilizing a single resistive divider.

For the following explanation, please refer to Figure 3.
When the battery voltage (VIN) is very high, the current
from the LBI input pin is essentially zero. The voltage on
the LBI input pin is simply a resistively-divided version of
the VIN pin.

V

IN

300 k

R

1

LBO

OUTPUT

V

LBO

OUT

SW

LBI/SB

GND

V

IN

R

2

FIGURE 3: LOW BATTERY MONITOR

As the voltage on the LBI input pin drops and passes
through the bandgap voltage (1.22 V), the LBI input pin will
begin to source current. At this same point, the LBO output
will be asserted. The assertion of the LBO output is
typically used as an early warning, indicating that battery
failure is approaching.

INPUT FILTER CAPACITOR SELECTION

As the voltage on the VIN pin continues to drop, the current

sourced by the LBI input pin will continue to linearly
Typically, the power supply or battery source connected to
the VIN pin contains an inductive and resistive component.
Since the current draw from the input supply varies with
time, such a scenario would exhibit ripple on the input
supply. Adding a bypass capacitor between the VIN pin

increase with the drop-in supply voltage. The current from

the LBI input pin will attempt to keep the voltage pin at the

same potential as the bandgap reference (1.22 V).

Throughout this region, the LBO output is continuously

asserted.
and ground, in some cases, will dramatically decrease
ripple on the input supply. An input supply bypass capacitor
in the range of 1 to 10 µF will work well for most converter
applications up to 100 mA. Bypass capacitors on the input
pin should exhibit relatively good ESR characteristics.

The current sourced from the LBI input pin is internally

limited to a maximum of approximately 720 nA. As

mentioned above, the current from the LBI input pin

continues to increase as the supply voltage drops. When

the current from the LBI input pin reaches the 720 nA

LOW BATTERY MONITOR

threshold, the TK654xx will turn off. This essentially provides

a second threshold, less than the LBI/SB threshold, where
The TK654xx utilizes a proprietary method for sensing and

the system will turn off.
handling low battery voltages. Using a single input pin and
resistive divider, the TK654xx not only provides an early
warning system of a low battery, it also provides a later

September 1999 TOKO, Inc. Page 13

TK654xx

ADVANCED INFORMATION

DESIGN CONSIDERATIONS (CONT.)

The thresholds for the Low Battery Input (LBI) and the turnoff (V
divider. Equations and a chart for selecting the LBI and V

LBI threshold = 1.22 V X (R1 + R2) / R
V

threshold = LBI threshold - 720 nA X R

OFF

2

1

4.0 V

3.5 V

V

THRESHOLD (R1 = 243 K)

OFF

3.0 V

THRESHOLD

OFF

2.5 V

LBI/V

2.0 V

0.6 1.0 1.4 1.8

(R1 = 487 K)
(R1 = 732 K)
(R1 = 976 K)

OFF

RATIO OF R1/R

) can be set independently using a single resistive

OFF

thresholds are provided below:

LBI THRESHOLD

2

DROPOUT CHARACTERISTICS

In battery powered applications, the input supply is not typically a constant value. As the battery discharges, the input
voltage will approach the output voltage. As the voltage on the input of the converter drops, the following two
characteristics can be observed: (a) as the battery voltage drops, output ripple will increase, (b) at very low battery levels
and high current loads, the output voltage may drop significantly below the regulation threshold.

In some applications, the above characteristics may not present a problem. For those applications that may be sensitive
to these characteristics, the LBO output can provide an early warning system indicating that battery failure is near. As
the battery voltage continues to drop, the turnoff feature of the TK654xx will ultimately turn the converter off (see LBI
Indicator section).

Page 14

September 1999 TOKO, Inc.

ADVANCED INFORMATION

TK654xx

NOISE CONSIDERATIONS

GENERAL

Because of the switching waveforms inherent to the operation of DC-DC converters, they tend to be noisier than their
linear counterparts. A DC-DC converter uses switching techniques to do the power conversion at higher efficiencies than
a linear regulator at the price of noisier output ripple. The TK654xx is no exception to this, even though the proprietary
architecture chosen was centered in providing the user fast transient response, low quiescent current and minimum
ripple.

INPUT/OUTPUT CAPACITORS (GENERAL)

By the nature of their operation, DC-DC converters generate large switching currents on both the input and output of the
circuit. The input and output capacitors should be as large as practical with a low Equivalent Series Resistance (ESR).
Since low temperatures cause the value of capacitance to decrease and the ESR to increase, care should be taken to
select capacitors that have acceptable characteristics over the desired operating temperature range.

INPUT CAPACITOR

The function of the input capacitor is to reduce the supply impedance and to provide sufficient input current during
switching for stable circuit operation. The input capacitor should be physically located as close as posssible to the
converter to minimize the lead inductance and to reduce the impedance of the source at high frequencies. By having
the capacitor close to the converter, the switching current pulses are supplied locally by the capacitor instead of running
across the printed circuit board by long etch runs. This greatly reduces the noise on the board.

OUTPUT CAPACITOR

The function of the output capacitor is to reduce the ripple voltage appearing on the converter output. The output ripple
voltage is the AC voltage which appears on the regulated DC output. It is inherent in all DC-DC converters and is the
result of the conversion of the input DC to AC and then back to output DC. The output ripple is the result of two factors,
which are 90° out of phase. The first factor is the result of the change in the stored charge of the output capacitor as it
is charged by the switching current from the converter and then discharged by the load current. This factor determines
the value (µF) of the output capacitor. The second factor is the product of the capacitor’s charge/discharge current times
its ESR. This factor determines the requirement for low ESR capacitors. In DC-DC converters, the ripple produced by
the capacitor ESR is often larger than the ripple produced by the change in charge. For this reason, high quality ceramic,
tantalum, or aluminum filter capacitors are required to minimize the output ripple. This contribution to output ripple and
noise can also be minimized by the addition of a small (0.01 µF to 0.1 µF) ceramic capacitor in parallel with the bulk output
capacitor. Adding a Pi filter as shown below (Figure 4) can further reduce output noise. The Pi filter has a tendency to
reduce the efficiency by a couple of percentage points and yet the noise improves by 20 dB/decade.

V

OUT

1Ω

22 µF

C

22 µF

LBO

V

OUT

SW

L

1

1

100 µH

D

1

LL 103

LBI

GND

V

IN

VIN = 5 V

OPTIONAL

FILTER

FIGURE 4: OPTIONAL PI FILTER

September 1999 TOKO, Inc. Page 15

TK654xx

ADVANCED INFORMATION

NOISE CONSIDERATIONS (CONT.)

COIL

The coil magnetic field can also be a source of noise. This noise is more characteristic of radiated Electromagnetic
Interference (EMI). This radiated noise can interfere with RF communications systems if care is not taken by the system
designer. A shielded coil can improve this source of EMI.

SNUBBER

When the inductor current flowing through the output diode decays to zero, the parasitic capacitance at the switch pin
(pin 3) resulting from the internal switch and external diode has energy which rings back into the inductor. This high
frequency ringing is an undesirable source of radiated noise. Fortunately, due to the low amount of energy in this ringing,
a simple RC snubber as shown in Figure 5 easily eliminates it. In low noise applications the RC snubber is recommended,
although an efficiency penalty of approzimately 2% will result.

V

OUT

= 3 V

C

22 µF

LBO

V

OUT

SW

L

1

1

100 µH

D

LL 103

1

220
PF

1 K

LBI

GND

V

IN

VIN = 5 V

FIGURE 5: OPTIONAL SNUBBER

Page 16

September 1999 TOKO, Inc.

ADVANCED INFORMATION

TK654xx

COIL CONSIDERATIONS

There are several issues to consider when choosing the proper coil for the TK654xx Step-Down Converter.
An important consideration is the coil manufacturer. Toko Inc. has been in the coil business for many years and has been

a leader in this market with high quality of product, low cost, and high volume delivery distribution.
The test circuit in this data sheet uses the D10F type series for its low resistance (0.27 Ω for 100 µH). This coil should

be considered when the user is interested in high efficiency.

TYPE D10F

For Reflow Soldering
Frequency Range:
Inductance Range:

1 kHz ~ 1 MHz
10 ~ 1500 µH

Unit:mm

A major issue today is space as well as height. Toko makes a low profile surface mount coil series which may accomodate
this requirement. The D52 series dimensions are shown below. The 100 µH coil has a maximum rated DC resistance
of 1.6 Ω.

TYPE D52FU

Frequency Range:
Inductance Range:

1 kHz ~ 2 MHz
100 µH ~ 6800 µH

FEATURES

• Low profile (2.0 mm typ. height) and 5 mm square

• Magnetically shielded version, unshielded also available

• Available on tape and reel for auto insertion

• Suitable for reflow soldering

September 1999 TOKO, Inc. Page 17

TK654xx

ADVANCED INFORMATION

COIL CONSIDERATIONS (CONT.)

Toko makes other series of coils which fall between the D10F and D52 series.
The D73/D75 coils should be kept in mind.

TYPE D73C, D75C

For Reflow Soldering
Frequency Range:
Inductance Range:

10 kHz ~ 1 MHz
1-560 µH

D73C D75C

FEATURES

• Miniature surface mount type

• Low profile (3.0 ~ 5.1 mm max height)

• Inductance range: 1-560 µH

• Available in magnetically shielded or unshielded versions

• Supplied on tape and reel for auto insertion

• Ideal for a variety of DC-DC Converter inductor applications

D75

Unit:mm

D73

Unit:mm

Page 18

September 1999 TOKO, Inc.

ADVANCED INFORMATION

APPLICATION INFORMATION

TK654xx

LBO

V

OUT

V

= 3 V

OUT

22 µF

C

1

L

100 µH

SW

1

FIGURE 6: MINIMUM DEVICE COUNT

V

= 5 V

IN

R

3

300 k

LB OUT

V

= 3 V

OUT

C

22 µF

1

L

100 µH

LBO

V

OUT

SW

1

LBI

GND

V

IN

LBI

GND

V

VIN = 5 V

LBO

V

OUT

V

= 3 V

OUT

22 µF

C

1

L

100 µH

SW

1

SB

GND

V

STANDBY

IN

VIN = 5 V

FIGURE 7: CONVERTER WITH STANDBY

V

= 5 V

R

1

634 K

R

2

287 K

IN

IN

R

10 µF

1

634 K

R

2

287 K

C

2

R

3

300 k

LB OUT

V

= 3 V

OUT

20 µF

C

1

L

100 µH

LBO

V

OUT

SW

1

D

1

(optional)

LBI

GND

V

IN

FIGURE 8: LOW BATTERY DETECTOR

V

IN

GND

V

OUT

LBO

FIGURE 9B: EVALUATION BOARD ARTWORK

FIGURE 9: EVALUATION BOARD SCHEMATIC

D1

V

OUT

L1

V

IN

R3

LBO

R1

R2

GND

C1
C1

C2

*

*D1 Optional

FIGURE 9C: EVALUATION BOARD COMPONENT

PLACEMENT

September 1999 TOKO, Inc. Page 19

TK654xx

ADVANCED INFORMATION

APPLICATION INFORMATION (CONT.)

The portable market, computing market and communications market, appear to not only be growing very fast, but also to
be converging.
Whether a computer incorporates communications capability or the phone incorporates the data / file transfer capability,
both markets as we approach the next millenium certainly are portable and require high efficiencies as well as long standby
times in order to extend the battery life. As the user gets more and more comfortable with his portable system, he will want
longer and longer time before recharging the battery.

WIRELESS PORTABLE SYSTEM USING LINEAR REGULATORS

Power

Amp

Enable A

Enable B

Enable D Enable E

Enable A

µ Controller

Enable B
Enable D
Enable E

FIGURE 10: Linear regulators power up wireless application

Page 20

September 1999 TOKO, Inc.

ADVANCED INFORMATION

TK654xx

APPLICATION INFORMATION (CONT.)

New microprocessors are earnestly addressing this power issue by reducing the voltage. Battery manufacturers are
waking up right before the end of the century with the introduction of the “polymer electrolyte battery” which allows for higher
volumetric and gravimetric densities. Furthermore, these types of batteries come with much better form factors.
Unfortunately the wireless transmit and receive section of the portable system is very sensitive and requires very clean
analog voltages to keep a clean reception and transmission. This RF requirement reigns over the power management
section of the system and creates a dilemma to the system engineer. How do you extend the battery life with “efficient
switchers” when they are so “dirty” in performance compared to “linears”?
The industry has made attempts to get away from a sole linear system shown in Fig. 10 by considering a “PWM” switcher
in front of the linear as shown if Fig. 11.

The system of Fig. 10 has the advantage of very clean voltages for the RF section, but lacks high efficiency. Specifically
as the processor voltage drops and the battery makers refine the Li-Polimer battery (which ranges from 2.7V min to 4.2V
max).

The system of Fig. 11 has the advantage of high efficiency followed by clean RF due to the linears, but lacks the ability
to turn off (turn on) fast when the system is in standby operation. This is specifically due to the PWM architecture which
uses Continuous Conduction Mode (CCM) to build up the current in the coil.

WIRELESS PORTABLE SYSTEM USING PWM SWITCHER TO IMPROVE EFFICIENCY

Power

Amp

Enable A

Enable B

µ Controller

Enable A
Enable B
Enable C

Enable C

FIGURE 11: PWM Switcher embedded to improve wireless system efficiency

September 1999 TOKO, Inc. Page 21

TK654xx

ADVANCED INFORMATION

APPLICATION INFORMATION (CONT.)

The industry is presently in a frame of mind that unless the switcher is PWM with a fixed frequency (to fix the harmonics
away from the RF), the wireless RF section will not be clean. It is the intention of this application to open the mind of system
designers to consider this new concept which addresses a real issue. Several major IC manufacturers of PWM step down
converters are taunting the “Burst Mode” capability. This can be misleading since under the burst mode, the fixed
frequency of the PWM is no longer present. (Therefore harmonics are all over the place). Furthermore, the purpose of
the Burst Mode is to allow the system to go into a standby mode in order to save battery life. Yet these state of the art PWMs
with Burst mode ability still lack in response time due to the architecture which requires the coil current to slowly build up.
This build up in current is a barrier to the present day requirements.

This Buck and Linear Wireless application proposes a system as shown in Fig. 12, which allows for all 3 important aspects
of the design:

1) Clean RF

2) High efficiency (At full, mid, and light loads)

3) Low standby currents with fast “wake up” response.
The approach shown in Fig. 12 requires a new architecture for the Buck (Step down) switching converter with very fast

transient characteristics, specifically during the transition from a Buck mode to Linear mode while a RF transmission/
reception is eminent or during a wake up out of standby mode.

WIRELESS PORTABLE SYSTEM USING BUCK AND LINEAR REGULATORS

Buck

Enable
Buck

LDO

Linear

Enable
Linear

µ Controller

*

Transmit
Receive

* Not necessary if LDO is active low

Power

Amp

FIGURE 12: Buck and Linear embedded to improve wireless system efficiency, standy time, and clean RF

Page 22

September 1999 TOKO, Inc.

ADVANCED INFORMATION

TK654xx

APPLICATION INFORMATION (CONT.)

Toko Inc. has come up with such a proprietary architecture implemented in their TK654XX switching step down converter.
This device is full of features as itemized in the following section:

TK654XX Features

1) Minimum pin count. Only 6 pins in a SOT23L package

2) Minimum external components required:

Coil and Filter cap

3) Synchronous Rectification

4) Extremely low operating current (25uA).

5) 18uA Standby Currents

6) Internal power devices good for greater than 200mA loads

7) Inherent short circuit protection

8) No instabilities

9) Fast transient response

10) High efficiencies up to 95%

11) Regulation down to 1.8V

12) Proprietary architecture specifically aims at low ripple voltage.

13) Low Dropout operation (100% Duty Cycle)

14) Designed for battery operated equipment

15) Battery Monitor included

16) Easy to design with (Reduce the coil to increase the load current)

Explanation of Figs. 10, 11, 12 follows:

Figure 10, shows a battery operated system with communications capability. The microcontroller is programmed to turn
on / off the Linear Low Dropout regulators (LDOs) at the appropriate time. This enabling capability is useful in extending
the battery life. Please note the LDO C, which powers the microcontroller is always active.

Figure 11, takes advantage of LDO C having to be active continuously and replaces it with a PWM step down controller.
Though the PWM is always active like the LDO C of Figure 10, the PWM is more efficient and therefore is penetrating the
Wireless market in order to increase battery life. It must be pointed out in Figure 11, the role of the LDOs is important to
maintain the clean voltages for Transmission and reception modes. Figure 11 also points out that if there is small activity
with the microcontroller which controls the other LDOs, the system could trip to the “Burst Mode” taunted by semiconductor

manufacturers. This mode is intended to reduce the current consumption of the PWM and increase the overall battery
life. Unfortunately, the speed that this Burst mode-to-PWM mode can react in is not very fast. Those systems, which are

compromised to increase response time, will inevitably hurt in ripple and therefore noise performance.
Figure 12, replaces the PWM with a Buck (step down) converter which has a unique architecture to respond very fast from

“Burst mode” to full load operation and a linear in parallel, rather than in series which can be enabled at the time the system
requires to transmit or receive. It is only due to the clean RF that the LDO is necessary. The majority of the time these
wireless systems are in a mode which can operate with some noise in the main voltage line. Some readers may have
noticed that Figure 12 only requires 1 LDO versus 3 LDOs in Figure 11. This principal may point out that the overall system
may turn out to be more cost effective. The system shown in Figure 12, therefore not only extends the overall battery life
by allowing the system to go into standby modes where the overall current is in the order of 25 uA, but at full load can run
in the 95% efficiency (no Transmission / Receive mode). Figure 12 can maintain the clean RF requirements for wireless
communications and reduce the overall cost.

September 1999 TOKO, Inc. Page 23

TK654xx

ADVANCED INFORMATION

APPLICATION INFORMATION (CONT.)

Wireless Application Extend battery life, yet keep RF clean

Application results with waveforms for TK65430 in a Buck and Linear Mode

Figure 13 is a schematic of an application board available from Toko as APO14-99 from which the results shown
below were obtained. This application uses the TK11330 Low Dropout Regulator with the control function enabling

the regulator on when this control pin is low.

LBO

Note A: This is a low ESR
(80 mΩ) capacitor from
AVX TPSD107 M010R0080

Note B: Coil used to obtain
waveforms was D63LCB type
A921CY-101M from Toko

3.0 V

3.0 V

Note A

Note A

100 µF

Note B

100 µH

100 µH

Control

Control

Noise

Noise

Bypass

Bypass

LBO

V

V

OUT

OUT

TK65430

TK65430

SW

SW

GND

GND

TK11330

TK11330

TK11330

TK11330

1000 pF

1000 pF

SB

SB

GND

GND

V

V

IN

IN

V

V

IN

IN

GND

GND

V

V

OUT

OUT

10 µF

10 µF

Transmit/

Transmit/

Receive

Receive

FIGURE 13: BUCK AND LINEAR SCHEMATIC

V

IN

CON

V

875FU-xxxM

OUT

TK654xx
1

C

IN

10 µF

TK113xxBM

1

C

1000pF

100 µF

N

C

L

GND

D

1

Optional

TOKO

AP014-99

V

V

IN

IN

Page 24

FIGURE 14: BUCK AND LINEAR APPLICATION BOARD LAYOUT

September 1999 TOKO, Inc.

ADVANCED INFORMATION

TK654xx

APPLICATION INFORMATION (CONT.)

TK65430 in a Buck and Linear Mode

During the transient response between the “Buck” and “Linear” control modes the output voltage needs to stay within
the regulation requirements.

The following scope pictures show the changes in the output voltage during these transients. As can be seen, the
maximum drop is about 80 mV and maximum overshoot is negligible.

In switching from the “Buck” mode to the “Linear” mode the settling time is less than 250 µsec over the supply range
of 5 V to 3.2 V for this 3.0 V application.

VIN = 5 V I

Full Cycle

= 100 mA

OUT

VIN = 3.2 V I

Full Cycle

= 100 mA

OUT

Switching to Linear

September 1999 TOKO, Inc. Page 25

Switching to Linear

TK654xx

ADVANCED INFORMATION

APPLICATION INFORMATION (CONT.)

VIN = 5 V I

Switching to Buck

= 100 mA VIN = 3.2 V I

OUT

Switching to Buck

= 100 mA

OUT

Characteristics of this application under lighter loads but similar supply range are shown below.

VIN = 5 V I

= 20 mA

OUT

VIN = 3.2 V I

OUT

= 20 mA

Full Cycle Full Cycle

In conclusion, the ability to provide a clean signal during transmission/reception can be done with linear regulators in a
predictable way, the novelty comes in considering the Buck and Linear concept which has the advantage of high
efficiency while not compromising the linear regulator’s low noise characteristics.

The overall effect being longer battery life while maintaining low RF interference in a wireless system.

Page 26

September 1999 TOKO, Inc.

ADVANCED INFORMATION

NOTES

TK654xx

September 1999 TOKO, Inc. Page 27

TK654xx

SOT23L-6

6

123

e e

+0.15

0.4

- 0.05

0.95 0.95

+0.3

- 0.1

3.5

(3.4)

0.32

ADVANCED INFORMATION

PACKAGE OUTLINE

Marking Information

Marking

0.1

M

0.6

*TK65419 419
*TK65420 420

Marking

1.0

*TK65422 422
*TK65423 423
TK65424 424

3.0
e1

*TK65426 426
*TK65428 428

*TK65429 429

+0.15

- 0.05

0.1

M

Recommended Mount Pad

ee

0.95 0.95

*TK65431 431
*TK65432 432

* These voltages available upon request

2.2

0.3

TK65418 418

TK65421 421

TK65425 425
TK65427 427

TK65430 430

TK65433 433

1.2

1.4 max

0.1

Dimensions are shown in millimeters
Tolerance: x.x = ± 0.2 mm (unless otherwise specified)

0 - 0.1

+0.15

- 0.05

0.15

Toko America, Inc. Headquarters
1250 Feehanville Drive, Mount Prospect, Illinois 60056
Tel: [phone] Fax: [phone]

TOKO AMERICA REGIONAL OFFICES

Midwest Regional Office
Toko America, Inc.
1250 Feehanville Drive
Mount Prospect, IL 60056
Tel: [phone]
Fax: [phone]

Western Regional Office
Toko America, Inc.
2480 North First Street , Suite 260
San Jose, CA 95131
Tel: [phone]
Fax: [phone]

Visit our Internet site at http://www.tokoam.com

15 max

+ 0.3

3.3

Eastern Regional Office

Toko America, Inc.

107 Mill Plain Road

Danbury, CT 06811

Tel: [phone]

Fax: [phone]

0.4

Semiconductor Technical Support
Toko Design Center
4755 Forge Road
Colorado Springs, CO 80907
Tel: [phone]
Fax: [phone]

The information furnished by TOKO, Inc. is believed to be accurate and reliable. However, TOKO reserves the right to make changes or improvements in the design, specification or manufacture of its
products without further notice. TOKO does not assume any liability arising from the application or use of any product or circuit described herein, nor for any infringements of patents or other rights of
third parties which may result from the use of its products. No license is granted by implication or otherwise under any patent or patent rights of TOKO, Inc.

Page 28

All Rights Reserved

IC-260-TK654xx

0899O0.0K

September 1999 TOKO, Inc.

Printed in the USA© 1999 Toko, Inc.