SI871X Datasheet, PDF (16/35 Pages) Silicon Laboratories – Industrial automation

Si871x/2x
3.2. Device Startup
During startup-up, for the Si8716, Output V_O is high until V_DD rises above the UVLO+ threshold for a minimum time
period of t_START. Following this, the output is low when the current flowing from anode to cathode is > I_F(ON). Device
startup, normal operation, and shutdown behavior for the Si8716 is shown in Figure 7. Note that Figure 7 assumes
that Enable is asserted and that the outputs are operating in their normal operating condition (inverting for the
Si8716). See Table 10 for more details on the Enable function.
UVLO+
UVLO-
V_DD
VDD_HYS
I_F(ON)
I_F
I_HYS
t_START
t_PLH
t_PHL
t_START
t_PLH
Voltage level
determined by
external pull-up
supply
V_O
Figure 7. Si8716 Operating Behavior (I_F > I_F(MIN) when V_F > V_F(MIN))
3.3. Under Voltage Lockout (UVLO)
The UVLO circuit unconditionally drives V_O to its default state when V_DD is below the lockout threshold. Referring
to Figure 8, upon power up, the Si871x/2x is maintained in UVLO until VDD rises above VDD_UV+. During power
down, the Si871x/2x enters UVLO when VDD falls below the UVLO threshold plus hysteresis (i.e., VDD < VDD_UV+
– VDD_HYS).
VDDUV+ (Typ)
1.7 1.8 1.9 2.0 2.1 2.2 2.3 2.4 2.5
Supply Voltage (V_DD - GND) (V)
Figure 8. Si871x/2x UVLO Response
16
Rev. 1.0