Datasheet
Data Sheet REF19x Series
Rev. L | Page 21 of 28
t
S
t
L
T
L
T
P
25
TIME 25°C TO PEAK
T
SMAX
PREHEAT AREA
MAXIMUM RAMP DOWN RATE = 6°C/s
MAXIMUM RAMP UP RATE = 3°C/s
T
SMIN
T
C
= –5°C
t
P
SUPPLIER
t
P
SUPPLIER
T
P
≥ T
C
T
C
T
C
= –5°C
USER
t
P
USER
T
P
≤ T
C
TEMPERATUR
E
TIME
00371-123
Figure 23. Classification Profile (Not to Scale)
SOLDER HEAT EFFECT
The mechanical stress and heat effect of soldering a part to a
PCB can cause output voltage of a reference to shift in value.
The output voltage of REF195 shifts after the part undergoes the
extreme heat of a lead-free soldering profile, like the one shown
in Figure 23. The materials that make up a semiconductor device
and its package have different rates of expansion and contraction.
The stress on the dice has changed position, causing shift on the
output voltage, after exposed to extreme soldering temperatures.
This shift is similar but more severe than thermal hysteresis.
Typical result of soldering temperature effect on REF19x output
value shift is shown in Figure 24. It shows the output shift due
to soldering and does not include mechanical stress.
0
0371-124
6
5
4
3
2
1
0
–0.16
–0.14
–0.12
–0.10
–0.08
–0.06
–0.04
–0.02
0
0.02
0.04
0.06
0.08
0.10
0.12
0.16
0.14
NUMBER OF UNITS
SHIFT DUE TO SOLDER HEAT EFFECT (%)
Figure 24. Output Shift due to Solder Heat Effect
CURRENT-BOOSTED REFERENCES WITH CURRENT
LIMITING
Whereas the 30 mA rated output current of the REF19x series is
higher than is typical of other reference ICs, it can be boosted to
higher levels, if desired, with the addition of a simple external
PNP transistor, as shown in Figure 25. Full-time current limiting is
used to protect the pass transistor against shorts.
U1
REF196
(SEE TABLE)
R4
2Ω
R1
1kΩ
R2
1.5kΩ
Q2
2N3906
C2
100µF
25V
D1
R3
1.82kΩ
C1
10µF/25V
(TANTALUM)
S
F
C3
0.1µF
F
S
R1
Q1
TIP32A
(SEE TEXT)
+
V
S
= 6
V
TO 9V
(SEE TEXT)
V
S
COMMON
V
C
V
OUT
COMMON
OUTPUT TABLE
U1
REF192
REF193
REF196
REF194
REF195
V
OUT
(V)
2.5
3.0
3.3
4.5
5.0
+V
OUT
3.3V
@ 150mA
2
6
+
1N4148
(SEE TEXT
ON SLEEP)
3
+
4
00371-023
Figure 25. Boosted 3.3 V Referenced with Current Limiting
In this circuit, the power supply current of reference U1 flowing
through R1 to R2 develops a base drive for Q1, whose collector
provides the bulk of the output current. With a typical gain of 100
in Q1 for 100 mA to 200 mA loads, U1 is never required to furnish
more than a few mA, so this factor minimizes temperature-related
drift. Short-circuit protection is provided by Q2, which clamps
the drive to Q1 at about 300 mA of load current, with values as
shown in Figure 25. With this separation of control and power
functions, dc stability is optimum, allowing most advantageous
use of premium grade REF19x devices for U1. Of course, load