MAX845ESA+ Maxim Integrated Products, MAX845ESA+ Datasheet - Page 14

• Manufacturer Part Number: MAX845ESA+
• Description: IC DRVR XFRMR CMOS PCMCIA 8SOIC
• Manufacturer: Maxim Integrated Products

Specifications of MAX845ESA+

• Applications: Transformer Driver, PCMCIA
• Voltage - Input: 3.3V, 5V
• Number Of Outputs: 1
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Supply Current: 1.1 mA
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Minimum Operating Temperature: - 40 C
• Output Current: 200 mA
• Output Voltage: 12 V
• Supply Voltage: 5V
• Digital Ic Case Style: SOIC
• No. Of Pins: 8
• No. Of Regulated Outputs: 2
• Operating Temperature Range: -40°C To +85°C
• Device Type: Transformer
• Filter Terminals: SMD
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

Since the output voltage is not regulated against
changes in the input voltage or load current, an output
voltage regulator may be needed. A series linear regu-
lator gives good performance and reasonably good
efficiency at low cost. A shunt regulator costs less,
occupies less space, and gives adequate performance
for some applications.
Series regulators such as the MAX666, MAX667,
MAX882/MAX883/MAX884, or MAX603/MAX604 simpli-
fy designs. Just select one with the desired output volt-
age and current capability, and connect it.
Isolated Transformer Driver
for PCMCIA Applications
Figure 12. Shunt-Regulator Circuits
14
______________________________________________________________________________________
PROGRAMMABLE-IC SHUNT REGULATOR WITH DISCRETE PNP
PROGRAMMABLE-IC SHUNT REGULATOR (STAND ALONE)
R
S
R
S
22k
22k
22k
22k
R
SIMPLE SHUNT ZENER
S
1k
TL431
TL431
Output Regulator
2N2907
5V OUTPUT
5V OUTPUT
The simplest voltage regulator is the shunt zener shown
in Figure 12. The series resistor (R
high as possible to still deliver the maximum expected
load current with minimum input voltage. Be sure that no
ratings are exceeded at maximum input voltage and
minimum load current conditions; under such conditions,
the zener diode may have to dissipate much more power
than the load. Alternatively, start with the maximum allow-
able zener dissipation and select the series resistor
under light-load, high-line conditions. Then verify that
there is sufficient output current available with worst-
case low input voltage.
For better regulation than the simple shunt zener, con-
sider a shunt regulator IC such as the TL431. This
device behaves like a zener diode whose voltage can
be programmed by a resistor ratio. It can be used as a
stand-alone device or can be boosted above its 150mA
maximum rating without compromising its accuracy by
adding a discrete PNP transistor, as shown in Figure 12.
The input power of a shunt regulator is nearly indepen-
dent of load, so efficiency at light loads tends to be
worse than it would be with a series regulator.
Ceramic capacitors can be used as output capacitors
because of the lower level of output ripple current. In
applications where output ripple is not critical, a 0.33µF
chip or ceramic capacitor is normally sufficient. Refer to
Table 3 for suggested capacitor suppliers.
In applications sensitive to output-ripple noise, the out-
put filter capacitor (C2) should have a low equivalent
series resistance (ESR) and a low equivalent series
inductance (ESL), and its capacitance should remain
fairly constant over temperature.
Sprague 595D surface-mount solid tantalum capacitors
and Sanyo OS-CON through-hole capacitors are recom-
mended, if space allows, due to their extremely low ESR.
Capacitor ESR usually rises at low temperatures, but OS-
CON capacitors provide very low ESR below 0°C.
The input bypass capacitor (C1) is not critical. Unlike
switching regulators, the MAX845’s supply current is
fairly constant, and is therefore less dependent on the
input bypass capacitor. A low-cost 0.33µF chip or
ceramic capacitor is normally sufficient for input
bypassing.
Input Bypass Capacitor
Output Filter Capacitor
S
) value should be as