TCM828
TCM829
Switched Capacitor Voltage Converters
FEATURES
s
s
s
s
s
s
s
Charge Pump in 5-Pin SOT-23A Package
>95% Voltage Conversion Efficiency
Voltage Inversion and/or Doubling
Low 50
µ
A (TCM828) Quiescent Current
Operates from +1.5V to +5.5V
Up to 25mA Output Current
Only Two External Capacitors Required
GENERAL DESCRIPTION
The TCM828/829 are CMOS “charge-pump” voltage
converters in ultra-small 5-Pin SOT-23A packages. They
invert and/or double an input voltage which can range from
+1.5V to +5.5V. Conversion efficiency is typically >95%.
Switching frequency is 12kHz for the TCM828 and 35kHz for
the TCM829.
External component requirement is only two capacitors
(3.3µF nominal) for standard voltage inverter applications.
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 50µA (TCM828) and 115µA (TCM829).
The TCM828 and TCM829 are available in a 5-Pin
SOT-23A surface mount package.
APPLICATIONS
s
s
s
s
s
LCD Panel Bias
Cellular Phones
Pagers
PDAs, Portable Dataloggers
Battery-Powered Devices
PIN CONFIGURATION
*5-Pin SOT-23A
ORDERING INFORMATION
Part No.
Package
5-Pin SOT-23A
5-Pin SOT-23A
Temp. Range
– 40°C to +85°C
– 40°C to +85°C
OUT
1
5
C+
TCM828ECT
TCM829ECT
NOTE: 5-Pin SOT-23A is equivalent to EIAJ SC-74A.
VIN
2
TCM828ECT
TCM829ECT
C–
3
4
GND
NOTE: *5-Pin SOT-23A is equivalent to EIAJ SC-74A
TYPICAL OPERATING CIRCUIT
Voltage Inverter
C
+
C
1
C
–
TCM828
TCM829
OUT
GND
C
2
V
–
OUTPUT
V
IN
INPUT
© 2001 Microchip Technology Inc.
DS21488A
TCM828/829-4 5/22/00
Switched Capacitor
Voltage Converters
TCM828
TCM829
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
= 0°C to +85°C, V
IN
= +5V, C1 = C2 = 10µF (TCM828), C1 = C2 = 3.3µF
(TCM829), unless otherwise noted. Typical values are at T
A
= +25°C.
Symbol Parameter
I
DD
V
+
V
+
F
OSC
P
EFF
V
EFF
R
OUT
Supply Current
Minimum Supply
Voltage
Maximum Supply
Voltage
Oscillator Frequency
Power Efficiency
Voltage Conversion
Efficiency
Output Resistance
Device
TCM828
TCM829
Test Conditions
T
A
= +25°C
R
LOAD
= 10kΩ: T
A
= 0°C to +85°C
R
LOAD
= 10kΩ
Min
—
—
1.5
—
8.4
24.5
—
95
—
—
Typ
50
115
—
—
12
35
96
99.9
25
—
Max
90
260
—
5.5
15.6
45.5
—
—
50
65
Unit
µA
V
V
kHz
%
%
Ω
TCM828
TCM829
T
A
= +25°C
I
LOAD
= 3mA, T
A
= +25°C
R
LOAD
=
∞
I
OUT
= 5mA, T
A
= 25°C
T
A
= 0°C to +85°C
NOTE:
1. Capacitor contribution is approximately 20% of the output impedance [ESR = 1 / pump frequency x capacitance)].
ELECTRICAL CHARACTERISTICS:
T
A
= – 40°C to +85°C, V
IN
= +5V, C1 = C2 = 10µF (TCM828), C1 = C2 = 3.3µF
(TCM829) unless otherwise noted. Typical values are at T
A
= +25°C. (Note 2)
Symbol Parameter
I
DD
V
+
F
OSC
R
OUT
Supply Current
Supply Voltage Range
Oscillator Frequency
Output Resistance
Device
TCM828
TCM829
Test Conditions
Min
—
—
1.5
6
19
—
Typ
—
—
—
—
—
—
Max
115
325
5.5
20
54.3
65
Unit
µA
V
kHz
Ω
R
LOAD
= 10kΩ
TCM828
TCM829
I
OUT
= 5mA
NOTE:
2. All – 40°C to +85°C specifications above are guaranteed by design.
PIN DESCRIPTION
Pin No.
(5-Pin SOT-23A)
1
2
3
4
5
Symbol
OUT
V
IN
–
C
1
GND
+
C
1
Description
Inverting charge pump output.
Positive power supply input.
Commutation capacitor negative terminal.
Ground.
Commutation capacitor positive terminal.
TCM828/829-4
5/22/00
2
© 2001 Microchip Technology Inc.
DS21488A
Switched Capacitor
Voltage Converters
TCM828
TCM829
DETAILED DESCRIPTION
The TCM828/829 charge pump converters invert 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.
(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
OUT2
x R
OUT
≅
I
OUT2
x
S1
IN
C1
TCM828/829
S2
[
(f
1
+8R
SWITCH
+ 4ESR
C1
+ ESR
C2
OSC
) C1
Equation 1.
]
C2
S3
S4
V
OUT
= – (V
IN
)
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
IN2
– V
OUT2
) + (0.5)(C2)(V
RIPPLE2
– 2V
OUT
V
RIPPLE
)
[
]
xf
OSC
Figure 1. Ideal Switched Capacitor Charge Pump
Equation 2.
APPLICATIONS INFORMATION
Output Voltage Considerations
The TCM828/829 perform voltage conversion but do
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 25Ω 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
)
V
RIPPLE
=
I
OUT
+2(I
OUT
)(ESR
C2
)
(f
OSC
)(C2)
Equation 3.
f
V
+
V
OUT
R
L
C1
C2
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).
© 2001 Microchip Technology Inc.
DS21488A
Figure 2a. Ideal Switched Capacitor Model
R
EQUIV
V
+
R
EQUIV =
1
f x C1
V
OUT
C2
R
L
Figure 2b. Equivalent Output Resistance
3
TCM828/829-4 5/22/00
Switched Capacitor
Voltage Converters
TCM828
TCM829
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 0.1Ω
ESR
C1
and 2Ω R
SW
. Table 2 shows the output voltage ripple
for various values of C2. The V
RIPPLE
values assume 10mA
output load current and 0.1Ω ESR
C2
.
*10µF (TCM828)
C3
3.3µF*
V
OUT
1
OUT
C1+
5
C2
3.3µF*
C1
3.3µF*
4
R
L
V
IN
2
3
IN TCM828
TCM829
C1–
GND
Table 1. Output Resistance vs. C1 (ESR = 0.1
Ω
)
Voltage Inverter
Figure 3. Test Circuit
C1(
µ
F)
0.1
1
3.3
10
47
100
TCM828 R
OUT
(
Ω
)
850
100
42
25
18
17
TCM829 R
OUT
(
Ω
)
302
45
25
19
17
17
Cascading Devices
Two or more TCM828/829’s 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.
Table 2. Output Voltage Ripple vs. C2 (ESR = 0.1
Ω
) I
OUT
10mA
C2(
µ
F)
TCM828 V
RIPPLE
(mV) TCM829 V
RIPPLE
(mV)
1
3.3
10
47
100
835
254
85
20
10
286
88
31
8
5
...
V
IN
2
3
3
4
5
...
C2
V
OUT = –n
V
IN
C2
2
+
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 TCM828/829.
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 (0.1µF) capacitor from IN to OUT is
sufficient.
C1
4
5
TCM828
TCM829
"1"
C1
1
TCM828
TCM829
"n"
1
V
OUT
Figure 4. Cascading TCM828s or TCM829s to Increase Output Voltage
Paralleling Devices
To reduce the value of R
OUT
, multiple TCM828/829s
can be connected in parallel (Figure 5). The output resis-
tance will be reduced by a factor of N where N is the number
of TCM828/829’s. 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 TCM828/829’s.
4
© 2001 Microchip Technology Inc.
DS21488A
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– plus any
IN
voltage drops due to loading. Refer to Table 1 and Table 2
for capacitor selection.
TCM828/829-4
5/22/00
Switched Capacitor
Voltage Converters
TCM828
TCM829
R
OUT
=
R
OUT
OF SINGLE DEVICE
NUMBER OF DEVICES
V
IN
2
3
4
5
C1
1
...
–
V
OUT =
V
IN
C2
3
4
5
+
...
2
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.
C1
TCM828
TCM829
"1"
TCM828
TCM829
"n"
...
1
V
OUT
GND
4
TCM828
TCM829
Figure 5. Paralleling TCM828s or TCM829s to Reduce Output Resistance
Voltage Doubler/Inverter
Another common application of the TCM828/829 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 40mA.
+
V
IN
D1, D2 = 1N4148
OUT
1
Figure 7. High V
–
Load Current
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.
3
C1
4
TCM828
TCM829
2
D1
1
C2
D2
–
V
OUT =
V
IN
5
C3
C4
V
OUT = (
2V
IN
) –
(V
FD1
)
–
(V
FD2
)
Figure 6. Combined Doubler and Inverter
© 2001 Microchip Technology Inc.
DS21488A
5
TCM828/829-4 5/22/00
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