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ADM3252EABCZ Datasheet PDF : 16 Pages
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Data Sheet
CHARGE PUMP VOLTAGE CONVERTER
The charge pump voltage converter consists of a 200 kHz
oscillator and a switching matrix. The converter generates a
±6.6 V supply from the 3.3 V input level. This is achieved in
two stages by using a switched capacitor technique, as shown
in Figure 17 and Figure 18.
VISO
GND
S1
S3
+
S2
C1 S4
+
C3
V+ = 2VISO
VISO
INTERNAL
OSCILLATOR
Figure 17. Charge Pump Voltage Doubler
FROM V+
VOLTAGE
DOUBLER
GNDISO
S1
S3
+
S2
C2 S4
+
C4
GNDISO
V– = –(V+)
INTERNAL
OSCILLATOR
Figure 18. Charge Pump Voltage Inverter
In the first stage, the 3.3 V input supply is doubled to 6.6 V using
C1 as the charge storage element. In the second stage, the +6.6 V
level is inverted to generate −6.6 V using C2 as the storage element.
In Figure 17, C3 is connected between V+ and VISO, but it is
equally effective if C3 is connected between V+ and GNDISO.
Use Capacitor C3 and Capacitor C4 to reduce the output ripple.
Their values are not critical and can be increased, if needed.
Larger capacitors (up to 10 µF) can be used in place of C1, C2,
C3, and C4.
ADM3252E
3.3 V LOGIC TO EIA/TIA-232E TRANSMITTER
The transmitter driver converts the 3.3 V logic input levels
into RS-232 output levels. When driving an RS-232 load with
VCC = 3.3 V, the output voltage swing is typically ±6.6 V.
EIA/TIA-232E TO 3.3 V LOGIC RECEIVER
The receiver is an inverting level shifter that accepts the RS-232
input level and translates it into a 3.3 V logic output level. The
input has an internal 5 kΩ pull-down resistor to ground and is
protected against overvoltages of up to ±30 V. An unconnected
input is pulled to 0 V by the internal 5 kΩ pull-down resistor,
resulting in a Logic 1 output level for an unconnected input or
for an input connected to GND. The receiver has a Schmitt
trigger input with a hysteresis level of 0.1 V. This ensures error
free reception for both a noisy input and for an input with slow
transition times.
HIGH BAUD RATE
The ADM3252E offers high slew rates, permitting data trans-
mission at rates well in excess of the EIA/TIA-232E specifications.
Higher data rates are possible when running at reduced RS-232
capacitive load levels. A smaller capacitive load, in effect, limits
the cable length. See Figure 7 for transmit output voltage levels
at 1 Mbps and Figure 19 for a scope plot at 1 Mbps.
Tx INPUT
1
2
Tx OUTPUT
CH1 2.00V CH2 2.00V
M400ns
RL = 3kΩ
CL = 470pF
A CH2 680mV
Figure 19. Scope Plot, 1 Mbps Operation
Rev. 0 | Page 11 of 16
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