TELCOM TC828A

TC828A
Switched Capacitor Voltage Converter
FEATURES
GENERAL DESCRIPTION
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The TC828A is a CMOS “charge-pump” voltage converter 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 switching frequency is 12KHz.
The external component requirement is only two capacitors (10µF 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 38µA typically.
The TC828A is available in a 5-Pin SOT-23A surface
mount package.
Charge Pump in 5-Pin SOT-23A Package
>95% Voltage Conversion Efficiency
Voltage Inversion and/or Doubling
Low 38µA Quiescent Current
Operates from +1.8V to +5.5V
Up to 25mA Output Current
Only Two External Capacitors Required
Lower Power Version of TCM828
APPLICATIONS
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LCD Panel Bias
Cellular Phones
Pagers
PDAs, Portable Dataloggers
Battery-Powered Devices
ORDERING INFORMATION
PIN CONFIGURATION
5-Pin SOT-23A
OUT
1
VIN
2
C–
3
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.
5
C+
4
GND
TC828ECT
NOTE: *5-Pin SOT-23A is equivalent to EIAJ SC-74A
TYPICAL OPERATING CIRCUIT
Voltage Inverter
C+
VIN
INPUT
OUT
V–
OUTPUT
C1
C–
TC828A
GND
C2
TC828A-1
5/1/00 TelCom Semiconductor reserves the right to make changes in the circuitry and specifications of its devices.
Switched Capacitor
Voltage Converters
TC828A
Power Dissipation (TA ≤ 70°C)
5-Pin SOT-23A ...............................................240mW
Storage Temperature (Unbiased) ......... – 65°C to +150°C
Lead Temperature (Soldering, 10 sec) ................. +300°C
ABSOLUTE MAXIMUM RATINGS*
Input Voltage (VIN 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
*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: TA = –40°C to +85°C, VIN = +5V, C1 = C2 = 10 µF, unless otherwise
noted. Typical values are at TA = +25°C.
Symbol
Parameter
IDD
V+
Supply Current
Minimum Supply
Voltage
Maximum Supply
Voltage
Oscillator Frequency
Power Efficiency
Voltage Conversion
Efficiency
Output Resistance
V+
FOSC
PEFF
VEFF
ROUT
Test Conditions
Min
Typ
Max
Unit
RLOAD = 1 KΩ
—
1.8
38
—
80
—
µA
V
RLOAD = 1 KΩ
—
—
5.5
V
RLOAD = 1 KΩ, TA = +25°C
RLOAD = ∞
6
—
95
12
96
99.9
20
—
—
KHz
%
%
IOUT = 5 mA, TA = +25°C
TA = –40°C to +85°C
—
—
25
—
50
65
Ω
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.
PIN DESCRIPTION
Pin No.
(5-Pin SOT-23A)
1
2
3
4
5
TC828A-1 5/1/00
Symbol
OUT
VIN
C1–
GND
+
C1
Description
Inverting charge pump output.
Positive power supply input.
Commutation capacitor negative terminal.
Ground.
Commutation capacitor positive terminal.
2
Switched Capacitor
Voltage Converters
TC828A
(4) Losses that occur during charge transfer (from the
commutation capacitor to the output capacitor)
when a voltage difference between the two capacitors exists.
DETAILED DESCRIPTION
The TC828A charge pump converter inverts the voltage
applied to the VIN 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 VIN 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.
Most of the conversion losses are due to factors (2), (3)
and (4) above. These losses are given by Equation 1.
PLOSS (2, 3, 4) = IOUT2 x ROUT
≅ IOUT2 x
[(f
1
OSC)
C1
+8RSWITCH + 4ESRC1 + ESRC2
]
S2
S1
IN
Equation 1.
The 1/(fOSC)(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.
TC828
C1
C2
S3
S4
VOUT = – (VIN)
[
PLOSS (4) = (0.5)(C1)(VIN2– VOUT2) + (0.5)(C2)(VRIPPLE2
– 2VOUTVRIPPLE)
Figure 1. Ideal Switched Capacitor Charge Pump
] xf
OSC
Equation 2.
APPLICATIONS INFORMATION
Output Voltage Considerations
VRIPPLE =
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 25Ω nominal
at +25°C and VIN = +5V. VOUT is approximately – 5V at light
loads, and droops according to the equation below:
IOUT
+2(IOUT)(ESRC2)
(fOSC)(C2)
Equation 3.
f
V+
VOUT
C2
C1
VDROOP = IOUT x ROUT
VOUT = – (VIN – VDROOP)
Charge Pump Efficiency
RL
Figure 2a. Ideal Switched Capacitor Model
The overall power efficiency of the charge pump is
affected by four factors:
REQUIV
V+
REQUIV =
(1) Losses from power consumed by the internal oscillator, switch drive, etc. (which vary with input voltage, temperature and oscillator frequency).
(2) I2R 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).
VOUT
1
f x C1
C2
RL
Figure 2b. Equivalent Output Resistance
TC828A-1 5/1/00
3
Switched Capacitor
Voltage Converters
TC828A
Capacitor Selection
VIN
C3
10 µF*
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 corresponding output resistance values @ +25°C. It assumes a 0.1Ω
ESRC1 and 2Ω RSW. Table 2 shows the output voltage ripple
for various values of C2. The VRIPPLE values assume 10mA
output load current and 0.1Ω ESRC2.
VOUT
1
2
3
Table 1. Output Resistance vs. C1 (ESR = 0.1Ω)
C1(µF)
ROUT (Ω)
0.1
1
3.3
10
47
100
850
100
42
25
18.3
17.3
IN
C1
10 µF*
TC828
C1–
C2
10 µF*
GND
4
Figure 3. Test Circuit
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 VIN) but will droop at least by ROUT of the
first device multiplied by the IQ 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.
835
254
85
19.7
10.3
...
+
VIN
2
2
3
3
Input Supply Bypassing
C1
The VIN input should be capacitively bypassed to reduce
AC impedance and minimize noise effects due to the switching 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 recommended 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 µF) capacitor from IN to OUT is
sufficient.
4
5
4
C1
TC828
“1”
TC828
“N”
5
1
1
VOUT
...
C2
C2
VOUT = –nVIN
Figure 4. Cascading TC828As to Increase Output Voltage
Paralleling Devices
To reduce the value of ROUT, 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.
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.
TC828A-1 5/1/00
RL
Voltage Inverter
Table 2. Output Voltage Ripple vs. C2 (ESR = 0.1Ω) IOUT 10mA
C2(µF)
VRIPPLE (mV)
1
3.3
10
47
100
5
C1+
OUT
4
Switched Capacitor
Voltage Converters
TC828A
Diode Protection for Heavy Loads
ROUT = ROUT OF SINGLE DEVICE
NUMBER OF DEVICES
+
VIN
2
2
3
3
4
C1
When heavy loads require the OUT pin to sink large
currents being delivered by a positive source, diode protection may be needed. The OUT pin should not be allowed to
be pulled above ground. This is accomplished by connecting a Schottky diode (1N5817) as shown in Figure 7.
...
TC828
“1”
5
4
C1
TC828
“N”
5
1
1
VOUT
GND
4
...
–
VOUT = VIN
C2
TC828
Figure 5. Paralleling TC828As to Reduce Output Resistance
OUT
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 subcircuits 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 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.
+
VIN
2
3
D1, D2 = 1N4148
C1
4
TC828
5
D1
1
–
VOUT = VIN
C2
D2
VOUT = (2VIN) –
(VFD1) – (VFD2)
C3
C4
Figure 6. Combined Doubler and Inverter
TC828A-1 5/1/00
1
5
Switched Capacitor
Voltage Converters
TC828A
TYPICAL CHARACTERISTICS
Circuit of Figure 3, VIN = +5V, C1 = C2 = C3, TA = +25°C, unless otherwise noted.
Output Resistance
vs. Temperature
65
60
55
50
45
40
35
30
25
20
15
10
5
0
45
55
50
45
VIN = 1.8V
40
35
30
VIN = 3.3V
25
VIN = 5.0V
20
2.5
3.5
4.5
15
–40
5.5
OUTPUT CURRENT (mA)
60
1.5
–20
0
20
40
60
VIN = 3.15V, VOUT = – 2.5V
300
VIN = 1.9V, VOUT = – 1.5V
200
150
100
50
0
20
CAPACITANCE (µF)
TC828A-1 5/1/00
VIN = 3.15V, VOUT = – 2.5V
15
10
VIN = 1.9V, VOUT = –1.5V
0 5 10 15 20 25 30 35 40 45 50
Pump Frequency vs. Temperature
15
35
30
25
20
15
10
25
30
0
1.5
14
2
2.5 3 3.5 4 4.5
SUPPLY VOLTAGE (V)
6
5
5.5
VIN = 5.0V
13
12
VIN = 3.3V
11
10
9
5
25
20
CAPACITANCE (µF)
PUMP FREQUENCY (kHz)
350
SUPPLY CURRENT (µA)
VIN = 4.75V, VOUT = – 4.0V
10
25
0
80
40
400
5
30
5
45
500
450
0
35
Supply Current
vs. Supply Voltage
Output Voltage Ripple vs. Capacitance
250
VIN = 4.75V, VOUT = – 4.0V
40
TEMPERATURE (°C)
SUPPLY VOLTAGE (V)
OUTPUT VOLTAGE RIPPLE (mVp-p)
Output Current vs. Capacitance
65
OUTPUT RESISTANCE (Ω)
OUTPUT RESISTANCE (Ω)
Output Resistance
vs. Supply Voltage
8
–40
VIN = 1.5V
–20
0
20
40
TEMPERATURE (°C)
60
80
Switched Capacitor
Voltage Converters
TC828A
TYPICAL CHARACTERISTICS (Cont.)
Circuit of Figure 3, VIN = +5V, C1 = C2 = C3, TA = +25°C, unless otherwise noted.
Efficiency vs. Output Current
100
90
–0.5
80
VIN = 2.0V
–1.5
EFFICIENCY (%)
OUTPUT VOLTAGE (V)
Output Voltage vs. Output Current
0.5
VIN = 3.3V
–2.5
–3.5
VIN = 5.0V
VIN = 5.0V
70
VIN = 2.0V
VIN = 3.3V
60
50
40
30
20
–4.5
10
–5.5
0
0
5 10 15 20 25 30 35 40 45 50
0
OUTPUT CURRENT (mA)
5 10 15 20 25 30 35 40 45 50
OUTPUT CURRENT (mA)
TAPING FORM
Component Taping Orientation for 5-Pin SOT-23A (EIAJ SC-74A) Devices
PIN 1
User Direction of Feed
User Direction of Feed
Device
Marking
Device
Marking
W
PIN 1
P
Standard Reel Component Orientation
TR Suffix Device
(Mark Right Side Up)
Reverse Reel Component Orientation
RT Suffix Device
(Mark Upside Down)
Carrier Tape, Number of Components Per Reel and Reel Size
Package
5-Pin SOT-23A
TC828A-1 5/1/00
Carrier Width (W)
Pitch (P)
Part Per Full Reel
Reel Size
8 mm
4 mm
3000
7 in
7
Switched Capacitor
Voltage Converters
TC828A
represents year and 2-month code
MARKING
SOT-23A-5
represents lot ID number
Part Numbers and Part Marking
& = part number code + temperature range
(two-digit code).
TC828A
TC828AECT
Code
CC
C C
ex: 828ECT = PACKAGE DIMENSIONS
5-Pin SOT-23A (EIAJ SC-74A)
.075 (1.90)
REF.
.071 (1.80)
.059 (1.50)
.122 (3.10)
.098 (2.50)
.020 (0.50)
.012 (0.30)
PIN 1
.037 (0.95)
REF.
.122 (3.10)
.106 (2.70)
.057 (1.45)
.035 (0.90)
.010 (0.25)
.004 (0.09)
10° MAX.
.006 (0.15)
.000 (0.00)
.024 (0.60)
.004 (0.10)
Dimensions: inches (mm)
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: [email protected]
TC828A-1 5/1/00
TelCom Semiconductor, GmbH
Lochhamer Strasse 13
D-82152 Martinsried
Germany
TEL: (011) 49 89 895 6500
FAX: (011) 49 89 895 6502 2
8
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