TC1037 Datasheet, PDF (5/18 Pages) Microchip Technology – Linear Building Block . Single Comparator in SOT Packages

TC1037/TC1038/TC1039
3.0 DETAILED DESCRIPTION
The TC1037/TC1038/TC1039 are a series of very low
power, linear building block products targeted at low
voltage, single supply applications. The TC1037/
TC1038/TC1039 minimum operating voltage is 1.8V
and typical supply current is only 4µA for the TC1037
and TC1038 (fully enabled) and 6µA for the TC1039.
3.1 Comparator
The TC1037/8/9 contain one comparator. The
comparator’s input range extends beyond both supply
voltages by 200mV and the outputs will swing to within
several millivolts of the supplies depending on the load
current being driven.
The comparator exhibits a propagation delay and
supply current which is largely independent of supply
voltage. The low input bias current and offset voltage
makes it suitable for high impedance precision
applications.
The TC1038 comparator is disabled during shutdown
and has a high impedance output.
3.2 Voltage Reference
A 2.0% tolerance, internally biased, 1.20V bandgap
voltage reference is included in the TC1039. It has a
push-pull output capable of sourcing and sinking at
least 50µA.
3.3 Shutdown Input (TC1038 Only)
SHDN at V_IL disables the comparator and reduces the
supply current to less than 0.3µA. The SHDN input
cannot be allowed to float. When not used, connect it to
V_DD. The comparator’s output is in a high impedance
state when the TC1038 is disabled. The comparator’s
inputs can be driven from rail-to-rail by an external
voltage when the TC1038 is disabled. No latchup will
occur when the device is driven to its enabled state
when SHDN is set to V_IH.
4.0 TYPICAL APPLICATIONS
The TC1037/TC1038/TC1039 family lends itself to a
wide variety of applications, particularly in battery
powered systems. It typically finds application in power
management, processor supervisory and interface
circuitry.
4.1 External Hysteresis (Comparator)
Hysteresis can be set externally with two resistors
using positive feedback techniques (see Figure 4-1).
The design procedure for setting external comparator
hysteresis is as follows:
1. Choose the feedback resistor R_C. Since the
input bias current of the comparator is at most
100pA, the current through R_C can be set to
100nA (i.e., 1000 times the input bias current)
and retain excellent accuracy. The current
through R_C at the comparator’s trip point is V_R /
R_C where V_R is a stable reference voltage.
2. Determine the hysteresis voltage (V_HY) between
the upper and lower thresholds.
3. Calculate R_A as follows:
EQUATION 4-1:
R_A
=
R_C


-V----^H----^Y- ^
V _{D D}^
4. Choose the rising threshold voltage for V_SRC
(V_THR).
5. Calculate R_B as follows:
EQUATION 4-2:
R_B = ----------------------------1------------------------------


----V----^T----^H---^R------
V_R × R_A


–---1----
R_A
–
---1----
R_C
6. Verify the threshold voltages with these
formulas:
V_SRC rising:
EQUATION 4-3:
V_THR
=
(V_R)(R_A)
 _--1-----
 _RA
+
 _---1----
 _RB
+
 _---1----
 _RC
V_SRC falling:
EQUATION 4-4:
V_THF = V_THR –
 ^R_-----^A_----^×_-----^V_----^D_----^D_--
 _RC 
© 2002 Microchip Technology Inc.
DS21344B-page 5