MAX1785EUU+T Maxim Integrated, MAX1785EUU+T Datasheet - Page 14

• Manufacturer Part Number: MAX1785EUU+T
• Description: Battery Management Smart Battery-Pack Controller
• Manufacturer: Maxim Integrated
• Series: MAX1785r

±15kV ESD-Protected, Fail-Safe, 20Mbps, Slew-Rate-
Limited RS-485/RS-422 Transceivers in a SOT
ESD performance depends on a number of conditions.
Contact Maxim for a reliability report that documents
test setup, methodology, and results.
Figure 15a shows the Human Body Model, and Figure
15b shows the current waveform it generates when dis-
charged into a low impedance. This model consists of
a 100pF capacitor charged to the ESD voltage of inter-
est, which is then discharged into the device through a
1.5kΩ resistor.
The IEC 1000-4-2 standard covers ESD testing and per-
formance of finished equipment; it does not specifically
refer to integrated circuits.
The main difference between tests done using the
Human Body Model and IEC 1000-4-2 is higher peak
current in IEC 1000-4-2. Because series resistance is
lower in the IEC 1000-4-2 ESD test model (Figure 16), the
ESD withstand voltage measured to this standard is gen-
erally lower than that measured using the Human Body
Model. The Air-Gap test involves approaching the
device with a charged probe. The Contact Discharge
method connects the probe to the device before the
probe is energized.
The Machine Model for ESD testing uses a 200pF stor-
age capacitor and zero-discharge resistance. It mimics
the stress caused by handling during manufacturing
and assembly. All pins (not just RS-485 inputs) require
this protection during manufacturing. Therefore, the
Machine Model is less relevant to the I/O ports than are
the Human Body Model and IEC 1000-4-2.
The standard RS-485 receiver input impedance is 12kΩ
(one-unit load), and the standard driver can drive up to
32-unit loads. The MAX3060E family of transceivers have
a 1/8-unit-load receiver input impedance (96kΩ), allow-
ing up to 256 transceivers to be connected in parallel on
one communication line. Any combination of these
devices and/or other RS-485 transceivers with a total of
32 unit loads or less can be connected to the line.
The MAX3060E and MAX3061E are slew-rate limited,
minimizing EMI and reducing reflections caused by
improperly terminated cables. Figure 17 shows the dri-
ver output waveform and its Fourier analysis of a 25kHz
14
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Applications Information
Reduced EMI and Reflections
256 Transceivers on the Bus
ESD Test Conditions
Human Body Model
Machine Model
IEC 1000-4-2
Figure 15a. Human Body ESD Test Model
signal transmitted by a MAX3062E. High-frequency
harmonic components with large amplitudes are evi-
dent. Figure 18 shows the same signal displayed for a
MAX3061E transmitting under the same conditions.
Figure 15b. Human Body Current Waveform
Figure 16. IEC 1000-4-2 ESD Test Model
AMPERES
VOLTAGE
VOLTAGE
SOURCE
SOURCE
HIGH-
HIGH-
DC
DC
I
P
36.8%
100%
90%
10%
CHARGE-CURRENT
CHARGE-CURRENT
LIMIT RESISTOR
0
LIMIT RESISTOR
50MΩ to 100MΩ
0
1MΩ
R
t
R
RL
100pF
C
150pF
C
C s
C s
STORAGE
CAPACITOR
STORAGE
CAPACITOR
CURRENT WAVEFORM
RESISTANCE
RESISTANCE
TIME
DISCHARGE
DISCHARGE
1.5kΩ
330Ω
R
R
D
D
t
DL
I r
PEAK-TO-PEAK RINGING
(NOT DRAWN TO SCALE)
DEVICE
DEVICE
UNDER
UNDER
TEST
TEST