tc7660h Microchip Technology Inc., tc7660h Datasheet - Page 4

• Manufacturer Part Number: tc7660h
• Description: High Frequency 7660 Dc-to-dc Voltage Converte
• Manufacturer: Microchip Technology Inc.

TC7660H-2 10/1/96
TC7660H
Simple Negative Voltage Converter
tive supply where a positive supply is available. A similar
scheme may be employed for supply voltages anywhere in
the operating range of +1.5V to +10V, keeping in mind that
pin 6 (LV) is tied to the supply negative (GND) only for supply
voltages below 3.5V.
those of a nearly ideal voltage source in series with 70 .
Thus, for a load current of – 10 mA and a supply voltage of
+5V, the output voltage would be – 4.3V.
primarily, to capacitive reactance of the charge transfer
capacitor (C
output for only 1/2 of the cycle, the equation is:
where f = 150kHz and C
Cascading Devices
to produce larger negative multiplication of the initial supply
voltage. However, due to the finite efficiency of each device,
the practical limit is probably 10 devices for light loads. The
output voltage is defined by:
where n is an integer representing the number of devices
cascaded. The resulting output resistance would be ap-
proximately the weighted sum of the individual TC7660H
R
OUT
Figure 3 shows typical connections to provide a nega-
The output characteristics of the circuit in Figure 3 are
The dynamic output impedance of the TC7660H is due,
The TC7660H may be cascaded as shown in (Figure 4)
values.
*
1.0 F
1. V OUT = –n V + for 1.5V
1
NOTES:
). Since this capacitor is connected to the
X
+
C
V
=
OUT
1
2 f C
1
2
3
4
= 1.0 F.
= – n (V
2
TC7660H
1
"1"
= 2.12
IN
V
Figure 4. Increased Output Voltage by Cascading Devices
+
)
8
7
6
5
10V
V +
1.0 F
4
+
Paralleling Devices
paralleled to reduce output resistance (Figure 4). The reser-
voir capacitor, C
requires its own pump capacitor, C
resistance would be approximately:
Changing the TC7660H Oscillator Frequency
other considerations) to increase or decease the oscillator
frequency. This can be achieved by overdriving the oscilla-
tor from an external clock, as shown in Figure 6. In order to
prevent possible device latch-up, a 1k
used in series with the clock output. In a situation where the
designer has generated the external clock frequency using
TTL logic, the addition of a 10k pull-up resistor to V
is required. Note that the pump frequency with external
clocking, as with internal clocking, will be 1/2 of the clock
frequency. Output transitions occur on the positive-going
edge of the clock.
1.0 F
Any number of TC7660H voltage converters may be
It may be desirable in some applications (due to noise or
HIGH FREQUENCY 7660 DC-TO-DC
C 1
*
1
2
3
4
NOTES:
+
TC7660H
R
Figure 3. Simple Negative Converter
OUT
"n"
1. V OUT = –n V + for 1.5V
1
2
3
4
2
=
, serves all devices, while each device
TC7660H
n (number of devices)
8
7
6
5
R
VOLTAGE CONVERTER
OUT
(of TC7660H)
© 2001 Microchip Technology Inc.
8
7
6
5
V
+
1
V +
+
. The resultant output
10V
1.0 F
resistor must be
V OUT
+
C 2
*
1.0 F
V OUT
+
supply
DS21466A
*