TC7660HEPA データシートの表示（PDF） - TelCom Semiconductor Inc => Microchip
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TC7660HEPA Datasheet PDF : 6 Pages
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HIGH FREQUENCY 7660 DC-TO-DC
VOLTAGE CONVERTER
1
TC7660H
C1 +
1.0 µF
1
8
2
7
3 TC7660H 6
4
5
IS
V+
(+5V)
C2
+ 1.0 µF
RL
Figure 1. TC7660H Test Circuit
Detailed Description
The TC7660H contains all the necessary circuitry to
implement a voltage inverter, with the exception of two
external capacitors, which may be inexpensive 1.0µF non-
polarized capacitors. Operation is best understood by con-
sidering Figure 2, which shows an idealized voltage inverter.
Capacitor C1 is charged to a voltage, V+, for the half cycle
when switches S1 and S3 are closed. (Note: Switches S2 and
S4 are open during this half cycle.) During the second half
cycle of operation, switches S2 and S4 are closed, with S1
and S3 open, thereby shifting capacitor C1 negatively by V+
volts. Charge is then transferred from C1 to C2, such that the
voltage on C2 is exactly V+, assuming ideal switches and no
load on C2.
V+
S1
S2
GND
C2
S3
S4
VOUT
= – VIN
To improve low-voltage operation, the LV pin should be
2 connected to GND. For supply voltages greater than 3.5V,
the LV terminal must be left open to ensure latch-up-
proof operation and prevent device damage.
Theoretical Power Efficiency Considerations
In theory, a capacitative charge pump can approach
100% efficiency if certain conditions are met:
(1) The drive circuitry consumes minimal power.
(2) The output switches have extremely low ON
3
resistance and virtually no offset.
(3) The impedances of the pump and reservoir
capacitors are negligible at the pump frequency.
The TC7660H approaches these conditions for nega-
tive voltage multiplication if large values of C1 and C2 are
4 used. Energy is lost only in the transfer of charge
between capacitors if a change in voltage occurs. The
energy lost is defined by:
E = 1/2 C1 (V12 – V22)
V1 and V2 are the voltages on C1 during the pump and
transfer cycles. If the impedances of C1 and C2 are relatively
5 high at the pump frequency (refer to Figure 1), compared to
the value of RL, there will be a substantial difference in
voltages V1 and V2. Therefore, it is not only desirable to
make C2 as large as possible to eliminate output voltage
ripple, but also to employ a correspondingly large value for
C1 in order to achieve maximum efficiency of operation.
Do's and Don'ts
• Do not exceed maximum supply voltages.
6
• Do not connect LV terminal to GND for supply voltages
greater than 3.5V.
• Do not short circuit the output to V+ supply for voltages
above 5.5V for extended periods; however, transient
conditions including start-up are okay.
• When using polarized capacitors in the inverting mode,
the + terminal of C1 must be connected to pin 2 of the
TC7660H and the + terminal of C2 must be connected
7
to GND Pin 3.
Figure 2. Idealized Charge Pump Inverter
TELCOM SEMICONDUCTOR, INC.
8
4-65
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