PS10 Datasheet, PDF (6/13 Pages) Supertex, Inc – Quad Power Sequencing Controller

Undervoltage/Overvoltage Operation
GND
UV_OFF
UV_ON
Vin
OV_ON
OV_OFF
PWRGD
SET RESET
Start-up Timing (PS11 PWRGD-A Active Low)
t_PWRGD-A is the time delay from V_EEUV(on) to PWRGD-A going
active. It can be approximated by
t_PWRGD-A = C_RAMP x (V_INT-1.17)/I_RAMP
where
C_RAMP = capacitor connected from RAMP pin to V_EE pin
V_INT = internal regulated power supply voltage (10V typ)
I_RAMP = 10µA charge current
PS10/PS11
PWRGD Flags Delay Programming
When the ramp voltage hits Vint – 1.17V, PWRGD-A be-
comes active indicating that the input supply voltage is
within the programmed limits. PWRGD-B goes active after
a programmed time delay after PWRGD-A went active.
PWRGD-C goes active after a programmed time delay
after PWRGD-B went active. PWRGD-D goes active after
a programmed time delay after PWRGD-C went active.
The resistors connected from TB, TC, and TD to V_EE pin
determines the delay times between the PWRGD flags.
The value of the resistors determines the capacitor charg-
ing and discharging current of a triangular wave oscillator.
The oscillator output is fed into an 8-bit counter to gener-
ate the desired time delay.
The respective time delay is defined by the following equa-
tion:
t_TX = (255 x 2 x C_OSC x V_PP)/I_CD
and
I_CD = Vbg / (4 x R_TX)
Where
t_TX = Time delay between respective PWRGD flags
C_OSC = 120pF (internal oscillator capacitor)
V_PP = 8.2V (peak-to-peak voltage swing of oscillator)
I_CD = Charge and discharge current of oscillator
Vbg = 1.17V (internal band gap reference)
R_TX = Programming resistor at TB, TC, or TD
Combining the two equations and solving for R_TX yields:
R_TX
= (Vbg x t_TX) / (2040 x C_OSC x V_PP)
= 0.585 x 10⁶ x t_TX
For a time delay of 200ms
R_TX
= 0.585 x 10⁶ x 0.2 = 117k
For a time delay of 5ms
R_TX
= 0.585 x 10⁶ x 0.005 = 2.925k
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A051204