CM1231-02SO Datasheet, PDF (4/12 Pages) ON Semiconductor – 2,4,8-Channel Low-Capacitance ESD Protection Array

CM1231−02SO
SINGLE AND DUAL CLAMP ESD PROTECTION
The following sections describe the standard single clamp ESD protection device and the dual clamp ESD protection
architecture of the CM1231−02SO.
Single Clamp ESD Protection
Conceptually, an ESD protection device performs the following actions upon a strike of ESD discharge into the protected
ASIC (see Figure 1).
1. When an ESD potential is applied to the system
under test (contact or air−discharge), Kirchoff’s
Current Law (KCL) dictates that the Electrical
Overstress (EOS) currents will immediately divide
throughout the circuit, based on the dynamic
impedance of each path
2. Ideally, the classic shunt ESD clamp will switch
within 1 ns to a low−impedance path and return the
majority of the EOS current to the chassis
shield/reference ground. In actuality, if the ESD
component’s response time (t_CLAMP) is slower than
the ASIC it is protecting, or if the Dynamic
Resistance (R_DYN) is not significantly lower than
the ASIC’s I/O cell circuitry, then the ASIC will have
to absorb a large amount of the EOS energy, and may
be more likely to fail.
3. Subsequent to the ESD/EOS event, both devices
must immediately return to their original
specifications, ready for an additional strike. Any
deterioration in parasitics or clamping capability
should be considered a failure, as it can affect signal
integrity or subsequent protection capability (this is
known as “multi−strike” capability.)
ESD Strike
I/O Connector
I_SHUNT
ESD
Protection
Device
ASIC
I_RESIDUAL
Figure 1. Single Clamp ESD Protection Block Diagram
Dual Clamp ESD Protection
In the CM1231−02SO dual clamp architecture, the first
stage begins clamping immediately, as it does in the single
clamp case. The dramatically reduced I_RES current from
stage one passes through the 1 W series element and then
gradually feeds into the stage two ESD device (see Figure 2).
The series inductive and resistive elements further limit the
current into the second stage, and greatly attenuate the
resultant peak incident pulse presented at the ASIC side of
the device.
This disconnection between the outside node and the
inside ASIC node allows the stage one clamps to turn on and
remain in the shunt mode before the ASIC begins to shunt
the reduced residual pulse. This gives the advantage to the
ESD component in the current division equation, and
dramatically reduces the residual energy that the ASIC must
dissipate.
http://onsemi.com
4