ISL6296A Datasheet, PDF (18/20 Pages) Intersil Corporation – FlexiHash For Battery Authentication

ISL6296A
VDD_HOST
HOST PROCESSOR
Rpu
LOGIC
A
VBAT
R2
VDD
ISL6296A
R1 _XSD
D1
Q1
VSS
LOGIC
FIGURE 13. TYPICAL APPLICATION BLOCK DIAGRAM
XSD Pin Series Resistor Selection
A series resistor may be used to improve ESD performance
of the XSD input. In Figure 13, resistor R1 and zener diode
D1 provide ESD protection for the ISL6296A XSD pin.
Resistor R1 must be selected to provide valid V_IL logic level at
the host processor (point ‘A’ in Figure 13) when the ISL6296A is
asserting the bus low by turning on Q1. The maximum
resistance value of R1 can be calculated if one knows the
VDD_HOST voltage, the V_IL requirements of the host processor,
the Rpu resistor value, and the R_DS(ON) of Q1.
The maximum R_DS(ON) of Q1 in Figure 13 is 400Ω, as per
the XSD pin VOL specification in the “Electrical
Specifications” on page 3. Point ‘A’ voltage, with Q1 on, is
given by Equation 2.
V_A
=
VDD_HOST
----------⁽--^R-----¹-----+-----⁴---⁰---⁰----^Ω-----⁾----------
(R1 + 400Ω + Rpu)
(EQ. 2)
To be detected as a logic '0' by the host, voltage at point ‘A’
must be no greater than the host’s VIL input voltage.
V_A ≤ V_IL
(EQ. 3)
Therefore,
VDD_{HOST (}---_R-----₁--⁽--^R-+----¹⁴----₀-+--₀---⁴-_Ω--⁰---⁰-+---^Ω--_R---⁾--_p----_u----₎ ≤ V_IL
(EQ. 4)
For example, suppose the XSD pull-up voltage is 2.6V, a
4.7kΩ pull-up is used, and the host’s VIL threshold is 35% of
its supply voltage.
VDD_HOST = 2.6V
Rpu = 4.7kΩ
(EQ. 5)
(EQ. 6)
V_IL(HOST) = VDD_HOST × 35% = 0.91V
(EQ. 7)
Solving for R1:
R1 ≤ 2131Ω
(EQ. 9)
VDD Pin Series Resistor Selection
A series resistor may be used to improve ESD performance
of the VDD input as shown by R2 in Figure 13.
Resistor R2 must be selected to allow operation of the
ISL6296A at the minimum VBAT voltage at which
communication must be successful. The maximum
resistance of R2 can be calculated if one knows the
minimum VBAT voltage, maximum ISL6296A supply current,
and minimum ISL6296A supply voltage, using the formula in
Equation 10.
R2 ≤ ⁽---^V----^B-----^A----^T----^M-----^I--^N-----–-----^V----^D-----^D----^M-----^I--^N-----⁾
IDD_MAX
(EQ. 10)
For example, suppose the minimum VBAT voltage in the
application is 2.8V. The minimum ISL6296A VDD voltage is
2.6V, and maximum supply current is 55µA, as per the
“Electrical Specifications” table on page 3. The maximum
value for R2 can then be calculated.
R2 ≤ ⁽---²---^.--⁸---₅-^V---₅--–-_μ----^2A---^.--⁶----^V----⁾
(EQ. 11)
R2 ≤ 3.636kΩ
(EQ. 12)
Additional Application Information
See “Related Literature” on page 1 for additional application
information.
Plugging these constants into Equation 4:
2.6V ₍---_R-----₁----⁽-+--^R--₄--¹--₀---₀^+----_Ω-⁴---⁰--+--⁰---₄-^Ω--_.--₇-⁾---_k---_Ω------₎ ≤ 0.91V
(EQ. 8)
18
FN6567.3
April 15, 2010