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AD53500 Datasheet(PDF) 5 Page - Analog Devices

Part No. AD53500
Description  High Speed, High Current Capability Pin Driver
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Maker  AD [Analog Devices]
Homepage  http://www.analog.com
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AD53500 Datasheet(HTML) 5 Page - Analog Devices

   
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AD53500
–5–
REV. 0
capacitor to the positive supply (and the VLDCPL capacitor to the
negative supply)—failure to do so causes considerable thermal
stress in the current-limiting resistor(s) during normal supply
sequencing and may ultimately cause them to fail, rendering the
part nonfunctional. Finally, the AD53500 may appear to func-
tion normally for small output steps (less than 3 V or so) if one
or both of these caps is absent, but it may exhibit excessive rise
or fall times for steps of larger amplitude.
The AD53500 does not require special power-supply sequenc-
ing. However, good design practice dictates that digital and
analog control signals not be applied to the part before the sup-
plies are stable. Violating this guideline will not normally de-
stroy the part, but the active inputs can draw considerable
current until the main supplies are applied.
RISING-EDGE SLEW
CONTROL CURRENT
5
V+
VHDCPL
LEVEL-SHIFTED
LOGIC DRIVE
VH
V–
Q49
OUT
Q50
Q48
Figure 2. Simplified Schematic of the AD53500 Output
Stage and Positive Current-Limit Circuitry
APPLICATION INFORMATION
Power Supply Distribution, Bypassing and Sequencing
The AD53500 draws substantial transient currents from its
power supplies when switching between states and careful de-
sign of the power distribution and bypassing is key to obtaining
specified performance. Supplies should be distributed using
broad, low inductance traces or (preferably) planes in a multi-
layered board with a dedicated ground-plane layer. All of the
device’s power supply pins should be used to minimize the inter-
nal inductance presented by the part’s bond wires. Each supply
must be bypassed to ground with at least one 0.1
µF capacitor;
chip-style capacitors are preferable as they minimize inductance.
One or more 10
µF (or greater) Tantalum capacitors per board
are also advisable to provide additional local energy storage.
The AD53500’s current-limit circuitry also requires external
bypass capacitors. Figure 2 shows a simplified schematic of the
positive current-limit circuit. Excessive collector current in
output transistor Q49 creates a voltage drop across the 5
resistor, which turns on PNP transistor Q48. Q48 diverts the
rising-edge slew current, shutting down the current mirror and
removing the output stage’s base drive. The VHDCPL pin should
be bypassed to the positive supply with a 0.039
µF capacitor,
while the VLDCPL pin (not shown) requires a similar capacitor to
the negative supply. These capacitors ensure that the AD53500
does not current-limit during normal output transitions up its
full 8 V rated step size. Both capacitors must have minimum-
length connections to the AD53500. Here again, chip capacitors
are ideal.
Several points about the current-limit circuitry should be noted.
First, the limiting currents are not tightly controlled, as they are
functions of both absolute transistor VBE and junction tempera-
ture; higher dc output current is available at lower junction
temperatures. Second, it is essential to connect the VHDCPL


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