LTC4401-1ES6#TR Linear Technology, LTC4401-1ES6#TR Datasheet - Page 10

• Manufacturer Part Number: LTC4401-1ES6#TR
• Description: IC RF POWER CONTROLLER TSOT23-6
• Manufacturer: Linear Technology

Specifications of LTC4401-1ES6#TR

• Rf Type: Cellular, GSM, GPRS, PCS, Wireless Modem, TDMA
• Frequency: 300MHz ~ 2.7GHz
• Features: Single Output
• Package / Case: TSOT-23-6, TSOT-6
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: LTC4401-1ES6TR; LTC44011ES6TR

APPLICATIO S I FOR ATIO
LTC4401-1/LTC4401-2
10
Determining External Loop Gain and Bandwidth
The external loop voltage gain contributed by the RF chan-
nel and directional coupler network should be measured in
a closed-loop configuration. A voltage step is applied to
PCTL and the change in V
voltage is K • PCTL, where K is the internal gain between
PCTL and the RF pin, and the external voltage gain contrib-
uted by the RF power amplifier and directional coupler
network is K • V
the closed-loop configuration accounts for the nonlinear
detector gain that is dependent on RF input voltage and
frequency.
The LTC4401-X unity gain bandwidth specified in the data
sheet assumes that the net voltage gain contributed by the
RF power amplifier and directional coupler is unity. The
bandwidth is calculated by measuring the rise time be-
tween 10% and 90% of the voltage change at V
small step in voltage applied to PCTL.
The LTC4401-X control amplifier unity gain bandwidth
(BW1) is typically 250kHz below a PCTL voltage of 80mV.
For PCTL voltages < 80mV, the RF detected voltage is
0.6PCTL. For PCTL voltages >160mV, RF detected voltage
is 1.22PCTL – 0.1. This change in gain is due to an internal
compression circuit designed to extend the detector range.
For example, to determine the external RF channel loop
voltage gain with the loop closed, apply a 100mV step to
Figure 2. Measured Open-Loop Gain and Phase, PCTL < 80mV
BW1 = 0.35/rise time
–10
–20
–30
–40
–50
–60
60
50
40
30
20
10
80
70
0
100
PCTL
1k
U
/ V
FREQUENCY (Hz)
GAIN
10k
PCA/B
U
VPC
PHASE
. Measuring voltage gain in
100k
is measured. The detected
R
C
PCTL = 60mV
W
LOAD
LOAD
1M
= 33pF
= 2k
4401 F02
10M
140
120
100
80
60
40
20
–20
–60
–80
–100
–120
160
0
–40
U
PCA/B
for a
PCTL from 300mV to 400mV. V
supply enough feedback voltage to the RF pin to cancel
this 100mV step which would be the required detected
voltage step of 122mV. V
1.561V to create the RF output power change required.
The net external voltage gain contributed by the RF power
amplifier and directional coupler network can be calcu-
lated by dividing the 122mV change at the RF pin by the
61mV change at the V
gain would then be approximately 2. The loop bandwidth
extends to 2 • BW1. If BW1 is 130kHz, the loop bandwidth
increases to approximately 260kHz. The phase margin can
be determined from Figures 2 and 3. Repeat the above
voltage gain measurement over the full power and fre-
quency range.
External pole frequencies within the loop will further
reduce phase margin. The phase margin degradation, due
to external and internal pole combinations, is difficult to
determine since complex poles are present. Gain peaking
may occur, resulting in higher bandwidth and lower phase
margin than predicted from the open-loop Bode plot. A
low frequency AC SPICE model of the LTC4401-X power
controller is included to better determine pole and zero
interactions. The user can apply external gains and poles
to determine bandwidth and phase margin. DC, transient
and RF information cannot be extracted from the present
model. The model is suitable for external gain evaluations
up to 6 . The 270kHz PCTL input filter limits the band-
width, therefore, use the RF input as demonstrated in the
model. Gain compression is not modeled.
Figure 3. Measured Open-Loop Gain and Phase, PCTL > 160mV
–20
–30
–40
–50
–60
–10
80
70
60
50
40
30
20
10
0
100
1k
FREQUENCY (Hz)
PCA/B
GAIN
10k
PCA/B
PHASE
pin. The net external voltage
100k
R
C
changed from 1.5V to
LOAD
LOAD
PCA/B
1M
= 33pF
= 2k
4401 F03
will increase to
10M
180
160
140
120
100
80
60
40
20
0
–20
–40
–60
–80
–100
4401fa