19-4539; Rev 1; 2/12
Fast Sample-and-Hold Circuit
General Description
The DS1843 is a sample-and-hold circuit useful for cap-
turing fast signals where board space is constrained. It
includes a differential, high-speed switched capacitor
input sample stage, offset nulling circuitry, and an out-
put buffer. The DS1843 is optimized for use in optical
line transmission (OLT) systems for burst-mode RSSI
measurement in conjunction with an external sense
resistor.
o
Fast Sample Time < 300ns
o
Hold Time > 100µs
o
Low Input Offset
o
Buffered Output
o
Small, 8-Pin µDFN (2mm x 2mm) Pb-Free Package
Features
DS1843
Applications
Gigabit Passive Optical Network (GPON) OLT
Gigabit Ethernet Passive Optical Network (GEPON) OLT
GPON Optical Network Unit
Sample and Hold
PART
DS1843D+
DS1843D+TRL
Ordering Information
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
8 µDFN
8 µDFN
+Denotes
a lead(Pb)-free/RoHS-compliant package.
TRL = Tape and reel.
Typical Operating Circuit
SDA
DS1842/
MAX4007
3.3V
V
CC
V
INP
C
IN
R
IN
C
IN
V
INN
DEN
C
S
3.3V
SEN
MON1
DS1843
V
OUTP
BMD
MON3P
MON3N
C
S
V
OUTN
MON4
SCL
I
2
C
INTERFACE
V
CC
MAIN MEMORY
EEPROM/SRAM
A/D CONFIG/RESULTS,
SYSTEM STATUS BITS,
ALARMS/WARNINGS,
LOOKUP TABLES,
USER MEMORY
MOD
DAC
BIAS
DAC
ANALOG MUX
TEMP
SENSOR
12-BIT
ADC
STROBE
SEN
GND
CONTROL
LOGIC
STROBE
CONTROLLER
Pin Configuration appears at end of data sheet.
________________________________________________________________
Maxim Integrated Products
1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Fast Sample-and-Hold Circuit
DS1843
ABSOLUTE MAXIMUM RATINGS
Voltage Range on V
CC
.............................................-0.5V to +6V
Voltage Range on V
OUTP
, V
OUTN
,
V
INP
, V
INN
, SEN, DEN ............................-0.5V to (V
CC
+ 0.5V)*
Continuous Power Dissipation (T
A
= +70°C)
µDFN (derate 4.8mW/°C above +70°C).....................380.6mW
*Subject
to not exceeding +6V.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-55°C to +125°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
RECOMMENDED OPERATING CONDITIONS
(T
A
= -40°C to +85°C, unless otherwise noted.)
PARAMETER
Supply Voltage
SYMBOL
V
CC
(Note 1)
CONDITIONS
MIN
+2.97
TYP
MAX
+5.5
UNITS
V
DC ELECTRICAL CHARACTERISTICS
(V
CC
= +2.97V to +5.5V, T
A
= -40°C to +85°C, unless otherwise noted.)
PARAMETER
Supply Current
Input Capacitance
Sample Capacitance
Logic-Input Low
Logic-Input High
Input Leakage
Input Voltage
Output Voltage
Output Impedance
Output Capacitive Load
Total Input Referenced Voltage
Offset: Differential
Total Input Referenced Voltage
Offset: Single-Ended
SYMBOL
I
CC
C
IN
C
S
V
IL
V
IH
I
IN
V
IN
V
OUT
R
OUTMAX
C
OUT
V
OS-DIFF
V
OS-SE
(Note 1)
All pins (Note 2)
V
INN
and V
INP
(Note 2)
SEN and DEN inputs
SEN and DEN inputs
V
INN
or V
INP,
SEN = 0
V
IN
= V
INP
- V
INN
V
OUT
= V
OUTP
- V
OUTN
; 100k
each output pin
(Note 2)
Capacitance for stable operation
V
CC
= 2.9V, 1µs sample time, V
IN
= 6mV
Voltco (V
CC
= 2.9V to 5.5V)
V
CC
= 2.9V, 1µs sample time, V
IN
= 6mV
Voltco (V
CC
= 2.9V to 5.5V)
3.4
3.6
load on
0
0
1
0.7 x
V
CC
1
1.0
1.0
1.3
50
6.1
1
8
1
5
0.3 x
V
CC
CONDITIONS
MIN
TYP
5.7
MAX
9
7
UNITS
mA
pF
pF
V
V
µA
V
V
k
pF
mV
mV/V
mV
mV/V
2
_______________________________________________________________________________________
Fast Sample-and-Hold Circuit
AC ELECTRICAL CHARACTERISTICS
(V
CC
= +2.97V to +5.5V, T
A
= -40°C to +85°C, unless otherwise noted.) (See the
Timing Diagram.)
PARAMETER
Sample Time Minimum
Delay Time Minimum
Output Time
Hold Time
Output Step Recovery Time
(Note 6)
SYMBOL
t
S
t
DEL
t
OUT
t
HOLD
t
REC
(Note 4)
Delay from SEN falling edge until valid
output at V
OUT
to 1% accuracy
(Note 5)
1V step, DEN = high
3V step, DEN = high or low
t
OUT
CONDITIONS
V
OUT
is within 0.4dB (Note 3)
MIN
300
10
2
100
2
3.5
TYP
MAX
UNITS
ns
ns
µs
µs
µs
DS1843
Note 1:
All voltages are referenced to ground. Currents entering the IC are specified positive and currents exiting the IC are negative.
Note 2:
Guaranteed by design.
Note 3:
V
OUT
at the end of the 10µs hold time is within specified level of V
IN
during the sample window; a 50Ω resistor connected in
series to both V
INP
and V
INN
(V
INP
- V
INN
= 1V). External capacitance to ground for both V
INP
and V
INN
is approximately 10pF.
Note 4:
The sampling capacitor must be removed from the input signal before the input signal changes. Therefore, the SEN pin
must be low for a short period of time, t
DEL
, before the input changes.
Note 5:
V
OUT
at the end of the hold time is within 1% of V
IN
during the sample window (V
INP
- V
INN
= 1V).
Note 6:
Voltage step applied across V
OUTP
to V
OUTN
through a 5pF capacitor connected to each pin. This models the load presented
by an ADC while it is sampling the DS1843’s output. See the
Output Buffer
section. Settled within 1% of initial voltage.
Timing Diagram
V
INP
- V
INN
t
S
t
DEL
SEN
t
OUT
V
OUTP
- V
OUTN
VOLTAGE INVALID
t
REC
t
ADC:ST
t
ADC:CT
EXTERNAL
ADC DATA
t
ADC:ST
= EXTERNAL ADC SAMPLING TIME.
t
ADC:CT
= EXTERNAL ADC CONVERSION TIME.
DEN IS CONNECTED TO V
CC
FOR DIFFERENTIAL OUTPUT.
NOTE:
THIS TIMING DIAGRAM IS APPLICABLE FOR SINGLE-ENDED AND DIFFERENTIAL OUTPUT CONFIGURATIONS.
t
HOLD
DATA VALID
_______________________________________________________________________________________
3
Fast Sample-and-Hold Circuit
DS1843
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
I
CC
vs. V
CC
DS1843 toc01
I
CC
vs. TEMPERATURE
DS1843 toc02
I
CC
vs. TEMPERATURE
DEN = GND
DS1843 toc03
5.9
5.8
5.7
I
CC
(mA)
5.6
5.5
5.4
5.3
2.5
3.0
3.5
4.0
V
CC
(V)
4.5
5.0
DEN = V
CC
DEN = GND
6.5
6.3
6.1
I
CC
(mA)
DEN = V
CC
6.5
6.3
6.1
V
CC
= 5V
V
CC
= 5V
5.9
5.7
5.5
5.3
V
CC
= 3.3V
I
CC
(mA)
5.9
V
CC
= 3.3V
5.7
5.5
5.3
5.5
-40
-15
10
35
60
85
-40
-15
10
35
60
85
TEMPERATURE (°C)
TEMPERATURE (°C)
OUTPUT HOLD TIME vs. TEMPERATURE
DS1843 toc04
OUTPUT HOLD TIME vs. TEMPERATURE
DS1843 toc05
DIFFERENTIAL OUTPUT DURING SAMPLING
(V
INP
= 6mV)
DS1843 toc06
1000
OUTPUT HOLD TIME (SECONDS)
1000
OUTPUT HOLD TIME (SECONDS)
100mV/div
V
OUTP
1.5V/div
V
SEN
V
OUTN
100
DEN = V
CC
10
100
DEN = GND
10
V
OUTP
- V
OUTN
5mV/div
1
-40
-15
10
35
60
85
TEMPERATURE (°C)
1
-40
-15
10
35
60
85
500ns/div
TEMPERATURE (°C)
SINGLE-ENDED OUTPUT DURING SAMPLING
(V
INP
= 6mV)
DS1843 toc07
DIFFERENTIAL OUTPUT, TRANSIENT
WITH 10% V
CC
STEP (V
INP
= 6mV)
100mV/div
V
OUTP
V
CC
= 3.3V
V
SEN
V
OUTN
DS1843 toc08
SINGLE-ENDED OUTPUT, TRANSIENT
WITH 10% V
CC
STEP (V
INP
= 6mV)
V
SEN
2.0V/div
V
CC
= 3.3V
DS1843 toc09
V
SEN
1.5V/div
100mV/div
V
OUTP
ZOOMED
500ns/div
V
OUTP
ZOOM
1V/div
V
CC
= 3.0V
V
OUTP
- V
OUTN
2mV/div
5mV/div
V
CC
= 3.0V
100mV/div
V
OUTP
100µs/div
20ns/div
100µs/div
4
_______________________________________________________________________________________
Fast Sample-and-Hold Circuit
Typical Operating Characteristics (continued)
(T
A
= +25°C, unless otherwise noted.)
DS1843
DIFFERENTIAL OUTPUT, TRANSIENT
WITH 10% V
CC
STEP (V
INP
= 1V)
V
SEN
2V/div
V
CC
= 3.3V
V
OUTP
V
CC
= 3.0V
1V/div
V
OUTP
- V
OUTN
V
OUTN
DS1843 toc10
SINGLE-ENDED OUTPUT, TRANSIENT
WITH 10% V
CC
STEP (V
INP
= 1V)
V
SEN
DS1843 toc11
DIFFERENTIAL OUTPUT STEP RECOVERY,
1V OUTPUT STEP (V
INP
= 6mV)
DS1843 toc12
V
OUTP
(200mV/div)
2V/div
V
CC
= 3.3V
200mV/div
V
OUTP
- V
OUTN
V
CC
= 3V
V
OUTP
10mV/div
V
OUTN
(200mV/div)
V
SEN
(1V/div)
200mV/div
1V/div
100µs/div
100µs/div
50µs/div
SINGLE-ENDED STEP RECOVERY,
1V OUTPUT STEP (V
INP
= 1V)
DS1843 toc13
SINGLE-ENDED OUTPUT, STEP RECOVERY,
1V OUTPUT STEP (V
INP
= 1V, ZOOMED IN)
DS1843 toc14
DIFFERENTIAL OUTPUT STEP RECOVERY,
1V OUTPUT STEP (V
INP
= 1V)
DS1843 toc15
V
OUTP
(200mV/div)
V
OUTP
(200mV/div)
V
SEN
(1V/div)
OUTPUT STEP (200mV/div)
V
SEN
(1V/div)
500mV/div
V
OUTP
500mV/div
200mV/div
V
OUTN
(200mV/div)
V
OUTP
- V
OUTN
V
OUTP
STEP (200mV/div)
50µs/div
50ns/div
50µs/div
DIFFERENTIAL OUTPUT STEP RECOVERY,
1V OUTPUT STEP (V
INP
= 1V, ZOOMED IN)
DS1843 toc16
200mV/div
V
OUTP
V
OUTN
(200mV/div)
V
OUTP
- V
OUTN
(200mV/div)
50ns/div
_______________________________________________________________________________________
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