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参数资料
| 型号： | TC1237EUNRT |
| 元件分类： | 稳压器 |
| 英文描述： | SWITCHED CAPACITOR CONVERTER, 170 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封装： | MSOP-10 |
| 文件页数： | 4/10页 |
| 文件大小： | 1046K |
| 代理商： | TC1237EUNRT |
3
TC1235
TC1236
TC1237
Inverting Dual (–VIN, –2VIN)
Charge Pump Voltage Converters
with Shutdown
TC1235/6/7-1 3/24/00
2001 Microchip Technology Inc.
DS21371A
DETAILED DESCRIPTION
The TC1235/1236/1237 dual charge pump converters
perform both a –1x and –2x multiply of the voltage applied
to the VIN pin. Output ‘– VIN’ provides a negative voltage
inversion of the VIN supply, while output ‘-2 VIN’ provides a
negative doubling inversion of VIN. Conversion is performed
using two synchronous switching matrices and four exter-
nal capacitors. When the shutdown input is held at a logic
low both stages go into a very low power mode of operation
consuming less than 1uA of supply current.
Figure 1 (below) is a block diagram representation of the
TC1235/1236/1237 architecture. The first switching stage
inverts the voltage present at VIN and the second stage uses
the ‘–VIN’ output generated from the first stage to produce
the ‘–2VIN’ output function from the second stage switching
matrix.
Each device contains an on-board oscillator that syn-
chronously controls the operation of the charge pump switch-
ing matrices. The TC1235 synchronously switches at 12KHz,
the TC1236 synchronously switches at 35KHz, and the
TC1237 synchronously switches at 125KHz. The different
oscillator frequencies for this device family allow the user to
trade-off capacitor size versus supply current. Faster oscil-
lators can use smaller external capacitors but will consume
more supply current (see Electrical Characteristics Table).
When the shutdown input is in a low state, the oscillator
and both switch matrices are powered off placing the TC1235/
1236/1237 in the shutdown mode. When the VIN supply
input is powered from an external battery, the shutdown
mode minimizes power consumption, which in turn will
extend the life of the battery.
Figure 1. Functional Block Diagram
APPLICATIONS INFORMATION
Output Voltage Considerations
The TC1235/1236/1237 performs voltage conversions
but does not provide any type of regulation. The two output
voltage stages will droop in a linear manner with respect to
their respective load currents. The value of the equivalent
output resistance of the ‘-VIN’ output is approximately 50
nominal at +25
°C and VIN = +5V. The value of the ‘-2VIN’
output and is approximately 140
nominal at +25°C and VIN
= +5V. In this particular case, ‘-VIN’ is approximately – 5V
and ‘–2VIN’ is approximately –10V at very light loads, and
each stage will droop according to the equation below:
VDROOP = IOUT x ROUT
[-VIN OUTPUT] = VOUT1 = – (VIN – VDROOP1)
[-2VIN OUTPUT] = VOUT2 = VOUT1 – (VIN – VDROOP2)
where VDROOP1 is the output voltage droop contributed
from stage 1 loading , and VDROOP2 is the output voltage
droop from stage 2 loading.
Charge Pump Efficiency
The overall power efficiency of the two charge pump
stages is affected by four factors:
(1) Losses from power consumed by the internal oscil-
lator, switch drive, etc. (which vary with input voltage,
temperature and oscillator frequency).
(2) I
2R losses due to the on-resistance of the MOSFET
switches on-board each charge pump.
(3) Charge pump capacitor losses due to effective
series resistance (ESR).
(4) Losses that occur during charge transfer (from the
commutation capacitor to the output capacitor) when a
voltage difference between the two capacitors exists.
Most of the conversion losses are due to factor (2), (3)
and (4) above. The losses for the first stage are given by
Equation 1a and the losses for the second stage are given
by Equation 1b.
P1LOSS (2, 3, 4) = IOUT1
2 x R
OUT1
where ROUT1 = [ 1 / [ fOSC(C1) ] + 8RSWITCH1 +
4ESRC1 + ESRCOUT1 ]
—2VIN
—VIN
+
COUT1
COUT2
VIN
SWITCH MATRIX
(1st STAGE)
SWITCH MATRIX
(2nd STAGE)
OSCILLATOR
SHDN
ENABLE
C1
+
C2
+
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