ISL6141_14 Datasheet, PDF (11/19 Pages) Intersil Corporation – Negative Voltage Hot Plug Controller

Applications Information
ISL6141, ISL6151
GND
R4
UV
V_DD
R5
OV
ISL6141
R6
V_{EE SENSE GATE}
PWRGD
DRAIN
(LOAD)
C1
R3
R2
C2
CL
-48V IN
R1
Q1
RL
-48V OUT
FIGURE 23. TYPICAL APPLICATION WITH MINIMUM COMPONENTS
Typical Values for a representative system; which
assumes:
• 43V to 71V supply range; 48 nominal; UV = 43V;
OV = 71V
• 1Amp of typical current draw; 2.5 Amp Over-Current
• 100µF of load capacitance (CL); equivalent RL of 48Ω
(R = V/I = 48V/1A)
R1: 0.02Ω (1%)
R2: 10Ω (5%)
R3: 18kΩ (5%)
R4: 549kΩ (1%)
R5: 6.49kΩ (1%)
R6: 10kΩ (1%)
C1: 150nF (25V)
C2: 3.3nF (100V)
Q1: IRF530 (100V, 17A, 0.11Ω)
Quick Guide to Choosing Component
Values
(See fig 23 for reference)
This section will describe the minimum components needed
for a typical application, and will show how to select
component values. (Note that “typical” values may only be
good for this application; the user may have to select
alternate component values to optimize performance for
other applications). Each block will then have more detailed
explanation of how the device works, and alternatives.
R4, R5, R6 - together set the Under-Voltage (UV) and Over-
Voltage (OV) trip points. When the power supply ramps up
and down, these trip points (and their hysteresis) will
determine when the GATE is allowed to turn on and off (UV
and OV do not control the PWRGD / PWRGD output). The
11
input power supply is divided down such that when the
voltage on the OV pin is below its threshold and the UV pin is
above its threshold their comparators will be in the proper
state signaling the supply is within its desired range, allowing
the GATE to turn on. The equations below define the
comparator thresholds for an increasing (in magnitude)
supply voltage.
V_UV = -^〈---^R----₍-⁴-_R---+--₅---^R-+---⁵--_R---+--₆---^R₎----⁶---^〉- × 1.255
(EQ. 1)
V_OV
=
-^〈---^R-----⁴----+-----^R----⁵-----+-----^R----⁶---^〉-
(R₆)
×
1.255
(EQ. 2)
The values of R4 = 549K, R5 = 6.49K, and R6 = 10K shown
in figure 23 set the Under-Voltage turn-on threshold to 43V,
and the Over-Voltage turn off threshold to 71V. The Under-
Voltage (UV) comparator has a hysteresis of 135mV (4.6V of
hysteresis on the supply) which correlates to a 38.4V turn off
voltage. The Over-Voltage comparator has a 25mV
hysteresis which translates to a turn on voltage (supply
decreasing) of approximately 69.6V.
Q1 - is the FET that connects the input supply voltage to the
output load, when properly enabled. It needs to be selected
based on several criteria:
• Maximum voltage expected on the input supply (including
transients) as well as transients on the output side.
• Maximum current and power dissipation expected during
normal operation, usually at a level just below the current
limit threshold.
• Power dissipation and/or safe-operating-area
considerations during current limiting and single retry
events.
• Other considerations include the GATE voltage threshold
which affects the r_DS(ON) (which in turn, affects the
voltage drop across the FET during normal operation),
and the maximum GATE voltage allowed (the ICs GATE
output is clamped to ~14V).