NCP5007
ANALOG SECTION (Typical values are referenced to T = +25°C, Min & Max values are referenced −25°C to +85°C ambient
a
temperature, unless otherwise noted.)
Rating
Pin
Symbol
Min
Typ
Max
Unit
High Level Input Voltage
Low Level Input Voltage
1
EN
1.3
−
−
−
−
0.4
V
EN Pull Down Resistor
1
4
5
R
−
170
−
100
200
100
−
230
−
kW
mV
ms
EN
Feedback Voltage Threshold
FB
Output Current Stabilizes @ 5% time delay following a
I
outdly
DC−DC startup @ V = 3.6 V, L = 22 mH, I = 20 mA
bat
out
Internal Switch ON Resistor @ T
= +25°C
5
QR
−
1.7
−
W
amb
DSON
5. The overall tolerance depends upon the accuracy of the external resistor.
THEORY OF OPERATION
The DC−DC converter is designed to supply a constant
current to the external load, the circuit being powered from
a standard battery supply. Since the regulation is made by
means of a current loop, the output voltage will vary
depending upon the dynamic impedance presented by the
load.
Considering a high intensity LED, the output voltage can
range from a low of 6.4 V (two LED in series biased with a
low current), up to 22 V, the maximum the chip can sustain
continuously. The basic DC−DC structure is depicted in
Figure 3.
With a 22 V operating voltage capability, the power
device Q1 can accommodate a high voltage source without
any leakage current degradation.
V
bat
L1
22 mH
Vdsense
POR
4
D1
Vds
Q1
TIME_OUT
ZERO_CROSSING
GND
RESET
LOGIC
CONTROL
Vdsense
GND
+
R1
−
1
V(Ipeak)
−
+
R2
xR
C2
Vs
Vref
GND
GND
Figure 3. Basic DC−DC Converter Structure
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