NJM3517
■ PURPOSE OF EXTERNAL COMPONENTS
For figures 3 and 4. Note that “Larger than …” is normally the vice versa of
“Smaller than … .”
Component Purpose
Value
Larger than value Smaller than value
D1, D2
Passes low power to I = 1A
f
motor and prevents
high power from
shorting through low
power supply
Increases price
Decreases max
current capability
1N4001, UF4001
D3 … D6
Inductive current
supressor
I = 1A
f
Increases price
Decreases current
turn-off capability
t
= 100nS
Slows down turn- Speeds up turn-
off time. Voltage off time.
at anode might
exceed voltage
breakdown
rr
e.g. BYV27
UF4001
RGPP10G
RGPP30D
R1
Base drive current
limitter
R = 20ohm
Slows down Q1’s Speeds up Q1’s
turn-on and Q4’s turn-on and Q4’s
2
V
mm
P = R1
turn-off time.
turn-off time.
(
)
R + R
1
2
R2, R3
Base discharge resistor R = 240ohm
V
Slows down Q1’s Speeds up Q1’s
turn-off and Q4’s turn-off and Q4’s
2
mm
P = R1
turn-on time.
)
Decreases ext.
turn-on time.
(
R + R
1
2
R4 … R7 External transistor base
driver
Increases ext.
transistor I max. transistor I max.
V - V - V
mm be ce
R =
C C
Lowers 3517 Increases 3517
power dissipation. power dissipation.
V
be
I -
4
(
Check hfe.
)
R12
2
P > (I ) • R4
4
R8, R9
ØA, ØB pull-up
resistors
R = 5kohm @ pull-up Increases noise
voltage = 5V. sensitivity, worse immunity, better
logic-level logic-level
definition definition.
Increases noise
2
(V
)
CC
P =
R
Less stress on ØA, Stress on ØA, ØB
ØB output output
transistors transistors.
R10, R11 Limit max. motor
current. Resistors may
V
R =
-V
mm Motor CESat
-V
Decreases motor Increases motor
current.
current.
I
Motor max
be omitted. (Check
motor specifications
first.)
V
be
R12 … R15 External transistor base
discharge.
Slows down
Speeds up
R =
15
Ω
=
external transistor external transistor
turn-off time. turn-off time.
Lowers 3517 Increases 3517
power dissipation power dissipation
I
12
P > V • I
be 12
RT, CT
C1, C2
Sets L and L on time R = 47kohm, C = 10nf Increases on time. Decreases on time.
A B
when triggered by
STEP.
P < 250mW
Stores the doubling
voltage.
C = 100µF
Increases effective Decreases
on-time during effective on-time
voltage doubling during voltage
doubling.
V ≥ 45V
C
C3 … C5
Filtering of supply-
voltage ripple and take-
up of energy feedback
from D3 … D6
C ≥ 10 µF
Increases price, Decreases price,
better filtering, more compact
decreases risk of solution.
IC breakdown
V
>V
,V or V Increases price
ss cc
Risk for capacitor
breakdown.
Rated
mm
Q1, Q2
Q3, Q4
Activation transistor of
voltage doubling.
I
as motor requires. Increases price. Decreases max I
during voltage
doubling.
C
m
- V -V ) • C1
CE
(V
mm
Charging of voltage
doubling capacitor
f
I
=
C
1
- 0.55 • R • C
T
T
( )
f
Step
Increases max
current capability. current capability.
Q5 … Q8 Motor current drive
transistor.
I
C
as motor requires.
PNP power trans.
Decreases max
NJRC [ NEW JAPAN RADIO ]
