TC110
PFM/PWM Step-Up DC/DC Controller
FEATURES
s
s
s
s
s
s
s
s
Space-Saving 5-Pin SOT-23A Package
Guaranteed Start-Up at 0.9V
50
µ
A (Typ) Supply Current (f
OSC
= 100 KHz)
300 mA Output Current @ V
IN
≥
2.7V
0.5
µ
A Shutdown Mode
100 KHz and 300 KHz Switching Frequency Options
Programmable Soft-Start
84% Efficiency
GENERAL DESCRIPTION
The TC110 is a step-up (Boost) switching controller that
furnishes output currents as high as 300 mA while delivering
a typical efficiency of 84%. The TC110 normally operates in
pulse width modulation mode (PWM), but automatically
switches to pulse frequency modulation (PFM) at low output
loads for greater efficiency. Supply current draw for the 100
KHz version is typically only 50
µA,
and is reduced to less
than 0.5
µA
when the SHDN input is brought low. Regulator
operation is suspended during shutdown.
Housed in a tiny 5-pin SOT-23A package, the TC110
occupies minimum board space, and uses tiny external
components (the 300 KHz version allows for less than 5 mm
surface-mount magnetics).
The TC110 accepts input voltages from 2.0V to 10.0V,
with a guaranteed start-up voltage of 0.9V.
TYPICAL APPLICATIONS
s
s
s
s
Palmtops
Battery Powered Systems
Positive LCD Bias Generators
Portable Communicators
TYPICAL OPERATING CIRCUIT
ORDERING INFORMATION
Part
Number
Output
Voltage*
(V)
Package
5.0
3.3
3.0
5.0
3.3
3.0
5-Pin SOT-23A
5-Pin SOT-23A
5-Pin SOT-23A
5-Pin SOT-23A
5-Pin SOT-23A
5-Pin SOT-23A
Osc. Operating
Freq.
Temp.
(KHz) Range
100
100
100
300
300
300
–40 to +85°C
–40 to +85°C
–40 to +85°C
–40 to +85°C
–40 to +85°C
–40 to +85°C
Battery
3V
10
µF
+
47
µH
D1
IN5817
V
OUT
Si9410DY
47
µF
Tantalum
+
5
EXT
4
GND
TC110501ECT
TC110331ECT
TC110301ECT
TC110503ECT
TC110333ECT
TC110303ECT
NOTE: *Other output voltages available. Please contact Microchip
Technology for details.
TC110
V
OUT
V
DD
SHDN/SS
PIN CONFIGURATION
5-Pin SOT-23A
R
OFF ON
1
2
3
C
*RC Optional
5
4
3V to 5V Supply
TC110
1
2
3
© 2001 Microchip Technology Inc.
DS21355A
TC110-2 5/24/99
PFM/PWM Step-Up DC/DC Controller
TC110
ABSOLUTE MAXIMUM RATINGS*
Voltage on V
DD
, V
OUT
, SHDN Pins ............ –0.3V to +12V
EXT Output Current ............................................
±100
mA
Voltage on EXT Pin ............................ –0.3V to V
DD
+0.3V
Power Dissipation ................................................150 mW
Operating Temperature ............................ –40°C to +85°C
Storage Temperature ............................. –40°C to +125°C
*Static-sensitive device. Unused devices must be stored in conductive
material. Protect devices from static discharge and static fields. Stresses
above those listed under Absolute Maximum Ratings may cause perma-
nent damage to the device. These are stress ratings only and functional
operation of the device at these or any other conditions above those
indicated in the operational sections of the specifications is not implied.
Exposure to Absolute Maximum Rating Conditions for extended periods
may affect device reliability.
ELECTRICAL CHARACTERISTICS:
Note 1, T
A
= 25°C, V
IN
= 0.6V X V
R
, V
DD
= V
OUT
, unless otherwise noted.
Symbol Parameter
V
DD
V
START
V
HOLD-UP
I
DD
Supply Voltage
Start-Up Supply Voltage
Oscillator Hold-Up Voltage
Boost Mode Supply Current
Test Conditions
Note 2
I
OUT
= 1mA
I
OUT
= 1mA
V
OUT
= SHDN = (0.95 x V
R
); f
OSC
= 300 KHz; V
R
= 3.0V
V
R
= 3.3V
V
R
= 5.0V
f
OSC
= 100 KHz; V
R
= 3.0V
V
R
= 3.3V
V
R
= 5.0V
V
OUT
= SHDN = (V
R
+ 0.5V); f
OSC
= 300 KHz; V
R
= 3.0V
V
R
= 3.3V
V
R
= 5.0V
f
OSC
= 100 KHz; V
R
= 3.0V
V
R
= 3.3V
V
R
= 5.0V
SHDN = GND, V
O
= (V
R
x 0.95)
V
OUT
= SHDN = (0.95 x V
R
); f
OSC
= 300 KHz
f
OSC
= 100 KHz
Note 3
V
OUT
= SHDN = 0.95 x VR
I
OUT
= 0 mA
V
OUT
= (V
R
x 0.95)
V
OUT
= (V
R
x 0.95)
V
OUT
= SHDN = (V
R
x 0.95); V
R
= 3.0V
V
R
= 3.3V
V
EXT
= (V
OUT
– 0.4V)
V
R
= 5.0V
V
OUT
= SHDN = (V
R
x 0.95); V
R
= 3.0V
V
R
= 3.3V
V
EXT
= 0.4V
V
R
= 5.0V
Min
2.0
—
—
—
—
—
—
—
—
—
—
—
—
—
—
—
255
85
V
R
x 0.975
—
15
0.65
—
—
—
—
—
—
—
—
Typ
—
—
—
120
130
180
50
50
70
20
20
22
11
11
11
0.05
300
100
V
R
—
25
—
—
32
29
20
20
19
13
84
Max
10.0
0.9
0.7
190
200
280
90
100
120
34
35
38
20
20
22
0.5
345
115
V
R
x 1.025
92
35
—
0.20
47
43
29
30
27
19
—
Unit
V
V
V
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
µA
KHz
KHz
V
%
%
V
V
Ω
Ω
Ω
Ω
Ω
Ω
%
I
STBY
Standby Supply Current
I
SHDN
f
OSC
V
OUT
Shutdown Supply Current
Oscillator Frequency
Output Voltage
DTYMAX Maximum Duty Cycle
(PWM Mode)
DTYPFM Duty Cycle
(PFM Mode)
V
IH
SHDN Input Logic High
V
IL
SHDN Input Logic Low
REXTH
EXT ON Resistance to V
DD
REXTL
EXT ON Resistance to GND
η
Efficiency
Notes: 1. For V
R
= 3.0V, I
OUT
= 120mA; For V
R
= 3.3V, I
OUT
= 130mA; For V
R
= 5.0V I
OUT
= 200 mA.
2. See Application Notes “Operating Mode” description for clarification.
3. V
R
is the factory output voltage setting.
TC110-2 5/24/99
2
2001 Microchip Technology Inc.
DS21355A
PFM/PWM Step-Up DC/DC Controller
TC110
PIN DESCRIPTION
Pin Number
1
Name
V
OUT
Description
Power and Voltage Sense Input. This dual function input provides both feedback
voltage sensing and internal chip power. It should be connected to the regulator output.
(See
Applications
section).
Power Supply Voltage Input.
Shutdown Input. A logic low on this input suspends device operation and reduces
supply current to less than 0.5
µA.
Device operation resumes when SHDN is brought
high. An RC circuit connected to this input also determines the soft-start time.
Ground Terminal.
External Switch Transistor Drive Complimentary Output. This pin drives the external
switching transistor. It may be connected to the base of the external bipolar transistor or
gate of the external N-channel MOSFET. (See
Applications
section).
2
3
V
DD
SHDN/SS
4
5
GND
EXT
2001 Microchip Technology Inc.
DS21355A
3
TC110-2 5/24/99
PFM/PWM Step-Up DC/DC Controller
TC110
DETAILED DESCRIPTION
TC110 is a PFM/PWM step-up DC/DC controller for use
in systems operating from two or more cells, or in low
voltage, line-powered applications. It uses PWM as the
primary modulation scheme, but automatically converts to
PFM at output duty cycles less than approximately 10%. The
conversion to PFM provides reduced supply current, and
therefore higher operating efficiency at low loads. The
TC110 uses an external switching transistor, allowing con-
struction of switching regulators with maximum output cur-
rents of 300 mA.
The TC110 consumes only 70
µA,
typical, of supply
current and can be placed in a 0.5
µA
shutdown mode by
bringing SHDN low. The regulator is disabled during shut-
down, and resumes normal operation when SHDN is brought
high. Other features include start-up at V
IN
= 0.9V, an
externally-programmable soft start time and tiny 5-pin
SOT-23A packaging.
Soft Start
Soft start allows the output voltage to gradually ramp
from 0V to rated output value during start-up. This action
minimizes (or eliminates) overshoot, and in general, re-
duces stress on circuit components. Figure 2 shows the
circuit required to implement soft start. Values of 470K and
0.1
µF
for R
SS
and C
SS
are adequate for most applications.
Input Bypass Capacitors
Using an input bypass capacitor reduces peak current
transients drawn from the input supply, and reduces the
switching noise generated by the regulator. The source
impedance of the input supply determines the size of the
capacitor that should be used.
Output Capacitor
The effective series resistance of the output capacitor
directly affects the amplitude of the output voltage ripple.
(The product of the peak inductor current and the ESR
determines output ripple amplitude.) Therefore, a capacitor
with the lowest possible ESR should be selected. Smaller
capacitors are acceptable for light loads or in applications
where ripple is not a concern. The Sprague 595D series of
tantalum capacitors are amongst the smallest of all low ESR
surface mount capacitors available. Table 1 lists suggested
component numbers and manufacturers.
Operating Mode
The TC110 is powered by the voltage present on the
V
DD
input. The applications circuits of Figures 1a and 1b
show operation in the bootstrapped and non-bootstrapped
modes. In bootstrapped mode, the TC110 is powered from
the output (start-up voltage is supplied by V
IN
through the
inductor and Schottky diode while Q1 is off). In bootstrapped
mode, the switching transistor is turned on harder because
its gate voltage is higher (due to the boost action of the
regulator), resulting in higher output current capacity.
The TC110 is powered from the input supply in the non-
bootstrapped mode. In this mode, the supply current to the
TC110 is minimized. However, the drive applied to the gate
of the switching transistor swings from the input supply level
to ground, so the transistor’s ON resistance increases at low
input voltages. Overall efficiency is increased since supply
current is reduced, and less energy is consumed charging
and discharging the gate of the MOSFET. While the TC110
is guaranteed to start up at 0.9V the device performs to
specifications at 2.0V and higher.
Inductor Selection
Selecting the proper inductor value is a trade-off be-
tween physical size and power conversion requirements.
Lower value inductors cost less, but result in higher ripple
current and core losses. They are also more prone to
saturate since the coil current ramps to a higher value.
Larger inductor values reduce both ripple current and core
losses, but are larger in physical size and tend to increse the
start-up time slightly.
A 22
µH
inductor, therefore, is recommended for the 300
KHz versions and a 47µH inductor is recommended for the
100KHz versions. Inductors with a ferrite core (or equiva-
lent) also are recommended. For highest efficiency, use an
inductor with a series resistance less than 20mΩ.
The inductor value directly affects the output ripple
voltage. Equation 3 is derived as shown below, and can be
used to calculate an inductor value, given the required
output ripple voltage and output capacitor series resistance:
Low Power Shutdown Mode
The TC110 enters a low power shutdown mode when
SHDN is brought low. While in shutdown, the oscillator is
disabled and the output switch (internal or external) is shut
off. Normal regulator operation resumes when SHDN is
brought high. SHDN may be tied to the input supply if not
used.
Note:
Because the TC110 uses an external diode, a
leakage path between the input voltage and the output node
(through the inductor and diode) exists while the regulator is
in shutdown. Care must be taken in system design to assure
the input supply is isolated from the load during shutdown.
TC110-2 5/24/99
4
2001 Microchip Technology Inc.
DS21355A
PFM/PWM Step-Up DC/DC Controller
TC110
V
RIPPLE
≈
ESR(di)
Equation 1.
minimum input voltage should be used when calculating the
AC inductor current (Equation 9).
V = L(di)
dt
Equation 7.
where ESR is the equivalent series resistance of the
output filter capacitor, and V
RIPPLE
is in volts.
Expressing di in terms of switch ON resistance and time:
V
RIPPLE
≈
ESR [(V
IN
– V
SW
)t
ON
]
L
Equation 2.
di =
V(dt)
dt
Equation 8.
di =
Solving for L:
L
≈
ESR [(V
IN
– V
SW
)t
ON
]
V
RIPPLE
Equation 3.
[(V
IN(MIN)
– V
SW
)t
ON
]
L
Equation 9.
Care must be taken to ensure the inductor can handle
peak switching currents, which can be several times load
currents. Exceeding rated peak current will result in core
saturation and loss of inductance. The inductor should be
selected to withstand currents greater than I
PK
(Equation 10)
without saturating.
Calculating the peak inductor current is straightforward.
Inductor current consists of an AC (sawtooth) current cen-
tered on an average DC current (i.e. input current). Equation
6 calculates the average DC current. Note that minimum
input voltage and maximum load current values should be
used:
Input Power = Output Power
Efficiency
Equation 4.
where: V
SW
= V
CESAT
of the switch (note if a CMOS
switch is used substitute V
CESAT
for R
DSON
x I
IN
)
Combining the DC current calculated in Equation 6, with
half the peak AC current calculated in Equation 9, the peak
inductor current is given by:
I
PK
= I
IN(MAX)
+ 0.5(di)
Equation 10.
Output Capacitor
The effective series resistance of the output capacitor
directly affects the amplitude of the output voltage ripple.
(The product of the peak inductor current and the ESR
determines output ripple amplitude.) Therefore, a capacitor
with the lowest possible ESR should be selected. Smaller
capacitors are acceptable for light loads or in applications
where ripple is not a concern. The Sprague 959D series of
tantalum capacitors are amongst the smallest of all low ESR
surface mount capacitors available. Table 1 lists suggested
component numbers and manufacturers.
Re-writing in terms of input and output currents and
voltages:
(V
IN(MIN)
) (IN
(MAX)
) =
(V
OUT(MAX)
)(I
OUT(MAX)
)
Efficiency
Equation 5.
Solving for input curent:
I
IN(MAX)
=
(V
OUT(MAX)
)(I
OUT(MAX)
)
(Efficiency)(V
IN(MAX)
)
Equation 6.
The sawtooth current is centered on the DC current
level; swinging equally above and below the DC current
calculated in Equation 6. The peak inductor current is the
sum of the DC current plus half the AC current. Note that
2001 Microchip Technology Inc.
DS21355A
5
TC110-2 5/24/99
京公网安备 11010802033920号
EEWORLD
