TC828A-1 5/1/00 TelCom Semiconductor reserves the right to make changes in the circuitry and specifications of its devices.
TC828A
Switched Capacitor Voltage Converter
FEATURES
s
Charge Pump in 5-Pin SOT-23A Package
s
>95% Voltage Conversion Efficiency
s
Voltage Inversion and/or Doubling
s
Low 38
A Quiescent Current
s
Operates from +1.8V to +5.5V
s
Up to 25mA Output Current
s
Only Two External Capacitors Required
s
Lower Power Version of TCM828
APPLICATIONS
s
LCD Panel Bias
s
Cellular Phones
s
Pagers
s
PDAs, Portable Dataloggers
s
Battery-Powered Devices
GENERAL DESCRIPTION
The TC828A is a CMOS "charge-pump" voltage con-
verter in an ultra-small 5-Pin SOT-23A package. It can invert
and/or double an input voltage that can range from +1.8V to
+5.5V. Conversion efficiency is typically >95%, and switch-
ing frequency is 12KHz.
The external component requirement is only two ca-
pacitors (10
F nominal) for standard voltage inverter appli-
cations. With a few additional components a positive
doubler can also be built. All other circuitry, including
control, oscillator, power MOSFETs are integrated on-chip.
Supply current is 38
A typically.
The TC828A is available in a 5-Pin SOT-23A surface
mount package.
TYPICAL OPERATING CIRCUIT
ORDERING INFORMATION
Part No.
Package
Temp. Range
TC828AECT
5-Pin SOT-23A
40
C to +85
C
NOTE: 5-Pin SOT-23A is equivalent to EIAJ-SC74A.
PIN CONFIGURATION
5-Pin SOT-23A
NOTE: *5-Pin SOT-23A is equivalent to EIAJ SC-74A
Voltage Inverter
TC828A
V
IN
V
OUTPUT
C
+
C
C
1
C
2
INPUT
GND
OUT
C+
C
OUT
TC828ECT
1
2
3
5
GND
VIN
4
2
Switched Capacitor
Voltage Converters
TC828A
TC828A-1 5/1/00
ABSOLUTE MAXIMUM RATINGS*
Input Voltage (V
IN
to GND) ......................... +6.0V, 0.3V
Output Voltage (OUT to GND) .................... 6.0V, + 0.3V
Current at OUT Pin .................................................. 50mA
Short-Circuit Duration OUT to GND ................ Indefinite
Operating Temperature Range ............... 40
C to +85
C
Power Dissipation (T
A
70
C)
5-Pin SOT-23A ............................................... 240mW
Storage Temperature (Unbiased) ......... 65
C to +150
C
Lead Temperature (Soldering, 10 sec) ................. +300
C
*This is a stress rating 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:
T
A
= 40
C to +85
C, V
IN
= +5V, C1 = C2 = 10
F, unless otherwise
noted. Typical values are at T
A
= +25
C.
Symbol
Parameter
Test Conditions
Min
Typ
Max
Unit
I
DD
Supply Current
--
38
80
A
V
+
Minimum Supply
R
LOAD
= 1 K
1.8
--
--
V
Voltage
V
+
Maximum Supply
R
LOAD
= 1 K
--
--
5.5
V
Voltage
F
OSC
Oscillator Frequency
6
12
20
KHz
P
EFF
Power Efficiency
R
LOAD
= 1 K
, T
A
= +25
C
--
96
--
%
V
EFF
Voltage Conversion
R
LOAD
=
95
99.9
--
%
Efficiency
R
OUT
Output Resistance
I
OUT
= 5 mA, T
A
= +25
C
--
25
50
T
A
= 40
C to +85
C
--
--
65
PIN DESCRIPTION
Pin No.
(5-Pin SOT-23A)
Symbol
Description
1
OUT
Inverting charge pump output.
2
V
IN
Positive power supply input.
3
C
1
Commutation capacitor negative terminal.
4
GND
Ground.
5
C
1
+
Commutation capacitor positive terminal.
NOTE: 1. Capacitor contribution is approximately 20% of the output impedance [ESR = 1 / pump frequency x capacitance)].
2. All 40
C to +85
C specifications above are guaranteed by design.
3
TC828A
Switched Capacitor
Voltage Converters
TC828A-1 5/1/00
DETAILED DESCRIPTION
The TC828A charge pump converter inverts the voltage
applied to the V
IN
pin. Conversion consists of a two-phase
operation (Figure 1). During the first phase, switches S2 and
S4 are open and S1 and S3 are closed. During this time, C1
charges to the voltage on V
IN
and load current is supplied
from C2. During the second phase, S2 and S4 are closed,
and S1 and S3 are open. This action connects C1 across
C2, restoring charge to C2.
APPLICATIONS INFORMATION
Output Voltage Considerations
The TC828A performs voltage conversion but does not
provide
regulation. The output voltage will droop in a linear
manner with respect to load current. The value of this
equivalent output resistance is approximately 25
nominal
at +25
C and V
IN
= +5V. V
OUT
is approximately 5V at light
loads, and droops according to the equation below:
V
DROOP
= I
OUT
x R
OUT
V
OUT
= (V
IN
V
DROOP
)
Charge Pump Efficiency
The overall power efficiency of the charge pump is
affected by four factors:
(1) Losses from power consumed by the internal oscil-
lator, switch drive, etc. (which vary with input volt-
age, temperature and oscillator frequency).
(2) I
2
R losses due to the on-resistance of the MOSFET
switches on-board the charge pump.
(3) Charge pump capacitor losses due to effective
series resistance (ESR).
Figure 1. Ideal Switched Capacitor Charge Pump
(4) Losses that occur during charge transfer (from the
commutation capacitor to the output capacitor)
when a voltage difference between the two capaci-
tors exists.
Most of the conversion losses are due to factors (2), (3)
and (4) above. These losses are given by Equation 1.
P
LOSS (2, 3, 4)
= I
OUT
2
x R
OUT
I
OUT
2
x
[
1
+8R
SWITCH
+ 4ESR
C1
+ ESR
C2
]
(f
OSC
) C1
The 1/(f
OSC
)(C1) term in Equation 1 is the effective
output resistance of an ideal switched capacitor circuit
(Figures 2a, 2b).
The losses in the circuit due to factor (4) above
are also shown in Equation 2. The output voltage ripple is
given by Equation 3.
P
LOSS (4)
=
[
(0.5)(C1)(V
IN
2
V
OUT
2
) + (0.5)(C2)(V
RIPPLE
2
2V
OUT
V
RIPPLE
)
]
x f
OSC
V
RIPPLE
=
I
OUT
+2(I
OUT
)(ESR
C2
)
(f
OSC
)(C2)
Figure 2a. Ideal Switched Capacitor Model
Figure 2b. Equivalent Output Resistance
V
OUT
=
(V
IN
)
C1
C2
TC828
IN
S1
S3
S4
S2
V
+
V
OUT
R
L
C1
C2
f
V
+
V
OUT
R
EQUIV
R
EQUIV =
R
L
C2
f x C1
1
Equation 2.
Equation 1.
Equation 3.
4
Switched Capacitor
Voltage Converters
TC828A
TC828A-1 5/1/00
Capacitor Selection
In order to maintain the lowest output resistance and
output ripple voltage, it is recommended that low ESR
capacitors be used. Additionally, larger values of C1 will
lower the output resistance and larger values of C2 will
reduce output ripple. (See Equation 1(b)).
Table 1 shows various values of C1 and the correspond-
ing output resistance values @ +25
C. It assumes a 0.1
ESR
C1
and 2
R
SW
. Table 2 shows the output voltage ripple
for various values of C2. The V
RIPPLE
values assume 10mA
output load current and 0.1
ESR
C2
.
Table 1. Output Resistance vs. C1 (ESR = 0.1
)
C1(
F)
R
OUT
(
)
0.1
850
1
100
3.3
42
10
25
47
18.3
100
17.3
Table 2. Output Voltage Ripple vs. C2 (ESR = 0.1
) I
OUT
10mA
C2(
F)
V
RIPPLE
(mV)
1
835
3.3
254
10
85
47
19.7
100
10.3
Input Supply Bypassing
The V
IN
input should be capacitively bypassed to reduce
AC impedance and minimize noise effects due to the switch-
ing internal to the device. The recommended capacitor
depends on the configuration of the TC828A.
If the device is loaded from OUT to GND it is recom-
mended that a large value capacitor (at least equal to C1) be
connected from the input to GND. If the device is loaded
from IN to OUT a small (0.1
F) capacitor from IN to OUT is
sufficient.
Voltage Inverter
The most common application for charge pump devices
is the inverter (Figure 3). This application uses two external
capacitors C1 and C2 (plus a power supply bypass
capacitor, if necessary). The output is equal to V
IN
plus any
voltage drops due to loading. Refer to Table 1 and Table 2
for capacitor selection.
Cascading Devices
Two or more TC828As can be cascaded to increase
output voltage (Figure 4). If the output is lightly loaded, it will
be close to ( 2 x V
IN
) but will droop at least by R
OUT
of the
first device multiplied by the I
Q
of the second. It can be seen
that the output resistance rises rapidly for multiple cascaded
devices. For large negative voltage requirements see the
TC682 or TCM680 data sheets.
Paralleling Devices
To reduce the value of R
OUT
, multiple TC828As can be
connected in parallel (Figure 5). The output resistance will
be reduced by a factor of N where N is the number of
TC828As. Each device will require it's own pump capacitor
(C1), but all devices may share one reservoir capacitor (C2).
However, to preserve ripple performance the value of C2
should be scaled according to the number of paralleled
TC828As.
Figure 3. Test Circuit
C1
C1
C2
5
5
4
3
4
1
2
2
1
3
C2
V
IN
V
OUT
V
OUT = n
V
IN
+
TC828
"1"
TC828
"N"
. . .
. . .
Figure 4. Cascading TC828As to Increase Output Voltage
3
2
4
5
1
C3
10
F*
C1
10
F*
C2
10
F*
V
IN
V
OUT
R
L
TC828
C1
IN
OUT
C1+
GND
Voltage Inverter
5
TC828A
Switched Capacitor
Voltage Converters
TC828A-1 5/1/00
Diode Protection for Heavy Loads
When heavy loads require the OUT pin to sink large
currents being delivered by a positive source, diode protec-
tion may be needed. The OUT pin should not be allowed to
be pulled above ground. This is accomplished by connect-
ing a Schottky diode (1N5817) as shown in Figure 7.
Layout Considerations
As with any switching power supply circuit good layout
practice is recommended. Mount components as close
together as possible to minimize stray inductance and
capacitance. Also use a large ground plane to minimize
noise leakage into other circuitry.
Voltage Doubler/Inverter
Another common application of the TC828A is shown in
Figure 6. This circuit performs two functions in combination.
C1 and C2 form the standard inverter circuit described
above. C3 and C4 plus the two diodes form the voltage
doubler circuit. C1 and C3 are the pump capacitors and C2
and C4 are the reservoir capacitors. Because both sub-
circuits rely on the same switches if either output is loaded,
both will droop toward GND. Make sure that the total current
drawn from both the outputs does not total more
than 40 mA.
Figure 6. Combined Doubler and Inverter
Figure 7. High V
Load Current
C1
D1
D2
D1, D2 = 1N4148
5
4
1
2
3
C2
C4
C3
V
IN
+
V
OUT =
V
IN
V
OUT = (
2V
IN
)
(V
FD1
)
(V
FD2
)
TC828
TC828
GND
OUT
4
1
Figure 5. Paralleling TC828As to Reduce Output Resistance
C1
C1
5
5
4
3
4
1
2
2
1
3
C2
V
OUT
V
OUT =
V
IN
R
OUT =
R
OUT
OF SINGLE DEVICE
V
IN
+
NUMBER OF DEVICES
TC828
"1"
TC828
"N"
. . .
. . .
6
Switched Capacitor
Voltage Converters
TC828A
TC828A-1 5/1/00
TYPICAL CHARACTERISTICS
Circuit of Figure 3, V
IN
= +5V, C1 = C2 = C3, T
A
= +25
C, unless otherwise noted.
40
35
30
25
20
15
10
5
0
1.5
2.5
3
2
3.5
4
4.5
5
5.5
SUPPLY VOLTAGE (V)
Supply Current
vs. Supply Voltage
45
SUPPLY CURRENT (
A)
60
55
50
45
40
0
30
25
20
15
35
10
5
1.5
2.5
3.5
4.5
5.5
SUPPLY VOLTAGE (V)
Output Resistance
vs. Supply Voltage
65
OUTPUT RESISTANCE (
)
60
55
50
45
40
25
20
15
35
30
40
20
0
20
40
60
80
TEMPERATURE (
C)
Output Resistance
vs. Temperature
65
OUTPUT RESISTANCE (
)
V
IN
= 1.8V
V
IN
= 3.3V
V
IN
= 5.0V
Output Current vs. Capacitance
CAPACITANCE (
F)
OUTPUT CURRENT (mA)
40
35
30
25
20
5
0
15
10
0
10
5
15
25
20
30 35 40 45 50
45
V
IN
= 1.9V, V
OUT
= 1.5V
V
IN
= 4.75V, V
OUT
= 4.0V
V
IN
= 3.15V, V
OUT
= 2.5V
450
400
350
300
250
50
0
200
150
100
0
10
5
25
20
25
30
CAPACITANCE (
F)
Output Voltage Ripple vs. Capacitance
500
OUTPUT VOLTAGE RIPPLE (mVp-p)
V
IN
= 4.75V, V
OUT
= 4.0V
V
IN
= 3.15V, V
OUT
= 2.5V
V
IN
= 1.9V, V
OUT
= 1.5V
14
13
12
8
11
10
9
40
0
20
20
40
60
80
TEMPERATURE (
C)
Pump Frequency vs. Temperature
15
PUMP FREQUENCY (kHz)
V
IN
= 5.0V
V
IN
= 1.5V
V
IN
= 3.3V
7
TC828A
Switched Capacitor
Voltage Converters
TC828A-1 5/1/00
TAPING FORM
TYPICAL CHARACTERISTICS (Cont.)
Circuit of Figure 3, V
IN
= +5V, C1 = C2 = C3, T
A
= +25
C, unless otherwise noted.
User Direction of Feed
User Direction of Feed
Device
Marking
Component Taping Orientation for 5-Pin SOT-23A (EIAJ SC-74A) Devices
Device
Marking
PIN 1
PIN 1
Standard Reel Component Orientation
TR Suffix Device
(Mark Right Side Up)
Reverse Reel Component Orientation
RT Suffix Device
(Mark Upside Down)
W
P
Package
Carrier Width (W)
Pitch (P)
Part Per Full Reel
Reel Size
5-Pin SOT-23A
8 mm
4 mm
3000
7 in
Carrier Tape, Number of Components Per Reel and Reel Size
0.5
1.5
2.5
4.5
5.5
3.5
0
10
5
15
25
20
30 35 40 45 50
OUTPUT CURRENT (mA)
Output Voltage vs. Output Current
0.5
OUTPUT VOLTAGE (V)
V
IN
= 2.0V
V
IN
= 3.3V
V
IN
= 5.0V
90
80
70
60
50
20
10
0
40
30
0
10
5
15
25
20
30 35 40 45 50
OUTPUT CURRENT (mA)
Efficiency vs. Output Current
100
EFFICIENCY (%)
V
IN
= 5.0V
V
IN
= 2.0V
V
IN
= 3.3V
8
Switched Capacitor
Voltage Converters
TC828A
TC828A-1 5/1/00
Sales Offices
TelCom Semiconductor, Inc.
1300 Terra Bella Avenue
P.O. Box 7267
Mountain View, CA 94039-7267
TEL: 650-968-9241
FAX: 650-967-1590
E-Mail: liter@telcom-semi.com
TelCom Semiconductor, GmbH
Lochhamer Strasse 13
D-82152 Martinsried
Germany
TEL: (011) 49 89 895 6500
FAX: (011) 49 89 895 6502 2
TelCom Semiconductor H.K. Ltd.
10 Sam Chuk Street, Ground Floor
San Po Kong, Kowloon
Hong Kong
TEL: (011) 852-2350-7380
FAX: (011) 852-2354-9957
PACKAGE DIMENSIONS
Dimensions: inches (mm)
SOT-23A-5
MARKING
Part Numbers and Part Marking
&
= part number code + temperature range
(two-digit code).
TC828A
Code
TC828AECT
CC
ex: 828ECT =
kkkk
represents year and 2-month code
represents lot ID number
C C
5-Pin SOT-23A (EIAJ SC-74A)
.071 (1.80)
.059 (1.50)
.122 (3.10)
.098 (2.50)
.075 (1.90)
REF.
.020 (0.50)
.012 (0.30)
PIN 1
.037 (0.95)
REF.
.122 (3.10)
.106 (2.70)
.057 (1.45)
.035 (0.90)
.006 (0.15)
.000 (0.00)
.024 (0.60)
.004 (0.10)
10
MAX.
.010 (0.25)
.004 (0.09)
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