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参数资料
| 型号： | TC1221ECHTR |
| 元件分类： | 稳压器 |
| 英文描述： | 0.05 A SWITCHED CAPACITOR CONVERTER, 169 kHz SWITCHING FREQ-MAX, PDSO6 |
| 封装： | SOT-23A, 6 PIN |
| 文件页数： | 3/9页 |
| 文件大小： | 101K |
| 代理商： | TC1221ECHTR |
3
TC1221/1222-2 5/4/00
TC1221
TC1222
High Frequency Switched Capacitor
Voltage Converters with Shutdown
in SOT Packages
DETAILED DESCRIPTION
The TC1221/1222 charge pump converters invert 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 opened 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 opened. This action connects C1
across C2, restoring charge to C2.
APPLICATIONS INFORMATION
Output Voltage Considerations
The TC1221/1222 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 25
nominal
at +25
°C and VIN = +5V. VOUT is approximately – 5V at light
loads, and droops according to the equation below:
VDROP = IOUT x ROUT
VOUT = – (VIN – VDROP)
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
2R 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) and
(3) above. These losses are given by Equation 1(b).
(a) PLOSS (2, 3) = IOUT
2 x ROUT
(b) Where ROUT =
[ 1 +8RSWITCH+ 4ESRC1+ ESRC2 ]
fOSC(C1)
The 1/(fOSC)(C1) term in Equation 1(b) is the effective
output resistance of an ideal switched capacitor circuit
(Figures 2a, 2b). The value of RSWITCH can be approximated
at 0.5
for the TC1221/1222.
The remaining losses in the circuit are due to factor
(4) above, and are shown in Equation 2. The output voltage
ripple is given by Equation 3.
PLOSS(4)=
[(0.5)(C1)(V
IN
2– V
OUT
2) + (0.5)(C2)(V
RIPPLE
2
– 2VOUTVRIPPLE)
] x fOSC
VRIPPLE =
IOUT
+2(IOUT)(ESRC2)
(fOSC)(C2)
Equation 2.
Equation 1.
Equation 3.
Figure 2a. Ideal Switched Capacitor Model
Figure 2b. Equivalent Output Resistance
VOUT = – (VIN)
C1
C2
TC1221/1222
VIN
S1
S3
S4
S2
OSC
V+
V
OUT
R
L
C1
C2
f
V+
V
OUT
R
EQUIV
R
EQUIV =
R
L
C2
f x C1
1
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