HCS201 Datasheet, PDF (12/28 Pages) Microchip Technology – KEELOQ Code Hopping Encoder

HCS201
5.6 Step Up Regulator
The integrated Step Up regulator can be used to
ensure the power supply voltage to the encoder and
the RF circuit (VDD), is constant independent of what
the battery voltage is (VDDB). Input on VDD pin is com-
pared to VSTEP, the internal reference voltage. If VDD
falls below this voltage the STEP output is pulsed at
fSTEP. This output can be connected to an external cir-
cuit as illustrated in Figure 5-2, to provide a step up
voltage on the device.
The Step Up regulator is inactive when the device is not
transmitting.
Note:
Power to the Step up regulator is taken
from the VDDB pin. While VDD is limited to
a 3.5V minimum, VDDB minimum can be as
low as 2.0V for the Step Up circuit to start
operating.
FIGURE 5-2:
APPLICATION CIRCUIT
VDD
S0
S1
S2
VDDB
2.0-6.0V
VDD
STEP
DATA
VSS
R
Tx out
L
D
Q
C
Three button remote control with Step up regulator
External components sample values:
R = 5.1 KΩ
L = 390 uH
Q = 2N3904
C = 1.0 uF
D = ZHCS400CT (40V 0.4A Zetex)
FIGURE 5-3:
8
7
6
5
4
3
2
1
0
0
TYPICAL LOADING CURVES (FIGURE 5-2 CIRCUIT)
5
10
15
20
Load(mA)
Note: These are typical values not tested in production.
Vddb=2V
Vddb=2.5V
Vddb=3V
Vddb=3.5V
TABLE 5-2: STEP UP CIRCUIT CHARACTERISTICS
Symbol
Parameters
Min.
Typ.
fSTEP
VSTEP
Note:
Output frequency
125
200
Reference voltage
5.5
6.5
These parameters are characterized but not tested.
Max.
250
7.5
Units
kHz
V
Conditions
VDDB = 3V
DS41098C-page 12
© 2001 Microchip Technology Inc.