HV301/HV311
10V
Design Information, cont’d.
C
2
48V
10µA
0.75nF
Cload
Undervoltage/Overvoltage Operation
1
: 2
mirror
10µA
GND
RAMP
terminal
GATE
Termial
Isink
V
SENSE
UV
OFF
UV
ON
Vsense
Rsense
10n=Cramp
VIN
5k
Internal Circuitry
OV
OV
ON
OFF
ON
OFF
Pass
Transistor
1. Choose circuit breaker trip point eg. 8A as follows
100mV 100mV
Rsense =
=
= 12.5mΩ
From the calculated resistor values the OV and UV start up
threshold voltages can be calculated as follows:
ICB
8
2. Choose inrush level, for example Inrush=1A
Inrush*Rsense 1A ×12.5mΩ
R2 + R3
R1 + R2 + R3
UVON = VUVH = 1.26 = VEEUV(on)
OVON = VOVL = 1.16 = VEEOV(on)
×
×
3. Calculate Isink =
=
= 2.5µA
5kΩ
4. Calculate C2 discharge limit
= 10µA-Isink = 7.5µA (typical)=iC2
5kΩ
R3
R1 + R2 + R3
Where |VEEUV(on)| and |VEEOV(on)| are Under & Over Voltage Start
Up Threshold points relative to VEE.
4a. Adjust for Auto-retry disable, if used →
Max Vt of a typical
power FET
Then
Vtmax
4V
2.5MΩ
≅
e.g.
= 1.6µA
Rdisable
R1 + R2 + R3
R2 + R3
VEEUV(on) = 1.26 ×
⇒ e.g. iC2 =10µA-Isink -1.6µA
487kΩ + 6.81kΩ + 9.76kΩ
In this example we assume Auto-retry is enabled so
VEEUV(on) = 1.26 ×
And
= 38.29V
= 59.85V
6.81kΩ + 9.76kΩ
ignore 1.6µA, ∴ iC2 = 10µA-Isink = 7.5µA
dv
dt
dv
dt
dv
dt
5. Note: i= C
iC2 = C2 ×
Inrush= Cload ×
R1 + R2 + R3
VEEOV(on) = 1.16 ×
R3
Note VIN is fixed and VRAMP is constant during limiting
487kΩ + 6.81kΩ + 9.76kΩ
9.76kΩ
dv
dt
dv
dt
VEEOV(on) = 1.16 ×
⇒
across Cload
=
across C2 (as they share a
common node and their other terminals are fixed during inrush)
Therefore, the circuit will start when the input supply voltage is
in the range of 38.29V to 59.85V.
iC2 Inrush
iC2 × Cload
=
⇒ Inrush=
C2
Cload
C2
by conservation of charge on RAMP Node iC2 = 7.5µA
Programming Inrush and ICB (Circuit Breaker)
7.5µA × Cload
7.5µA × Cload
Inrush=
⇒ C2 =
C2
Inrush
Method 1: Inrush independent of ICB
7.5µA ×100nF
10V
Vin
=
= 750pF = 0.75nF
C
2
–
+
1A
+
–
7.5µA
10µA
Cload=100µF
inrush
Cgd
7.5µA
Note that RAMP is protected by AC divider and Gate
is clamped internally.
GATE
0µA
RAMP
(DRAIN)
Cdb
+ K –
2.5µA
0µA
VSENSE
+
Vgs
gm(Vgs-Vt)
10n
Cgs
–
VSENSE
5k
Rsense=12.5mΩ
dv
df
on Cramp constant
during limiting so no
current flowing into cap
6
SUPERTEX [ Supertex, Inc ]
