LTC1923 LINER [Linear Technology], LTC1923 Datasheet - Page 23

• Manufacturer Part Number: LTC1923
• Description: High Efficiency Thermoelectric Cooler Controller
• Manufacturer: LINER [Linear Technology]

APPLICATIO S I FOR ATIO
the total gate charges of the NMOS and PMOS on one side
of the bridge, and f is the oscillator frequency. The factor
of 2 arises from there being two sets of MOSFETs that
make up the full bridge. Note that increasing the switching
frequency will increase the dynamic current and therefore
power dissipation by the same factor. This power loss is
independent of TEC current.
Example: Q
V
3) The DC resistances of the external bridge MOSFETs,
filter inductors and sense resistor are typically the domi-
nant loss mechanism at the high end TEC current. The
conduction path of the current includes one NMOS, one
PMOS, two inductors and the sense resistor so the DC
resistances associated with the components dissipate
power.
Example:
DD
Power loss = 2 • f • (Q
R
R
R
R
I
R
TEC
DS(ON)NMOS
DS(ON)PMOS
S
L
TEC
= 5V
= 0.1 ,
= 0.1
= 1A
= 2.5
N
= 10nC max, Q
NTC
10k
at 5V = 0.055 max
at 5V = 0.08 max
U
10k
P
U
+ Q
P
N
= 15nC max, f = 225kHz,
) • V
LTC1658
REF
W
DD
= 56mW
V
Figure 14. Low Input Supply Voltage Circuit
OUT
250
250
U
+
–
LTC2053
1 F
A = 10
REF
This represents a 17% efficiency loss due to conduction
losses. The other two power loss mechanisms comprise
a little more than a 3% efficiency loss at this output power
level. This may sound alarming if electrical efficiency is the
primary concern and can be easily improved by choosing
lower R
tors and a smaller valued sense resistor. If temperature
rise is the primary concern, this power dissipation may be
acceptable. At higher current levels, this example does
illustrate that lower resistance components should be
selected.
Low Voltage Requirements
All components shown on the front page of this data sheet
will operate with a 2.7V input supply. Minor modifications
are required to guarantee correct operation. The voltage
on the REF input of the LTC2053 should be at least 1V
below V
dividing down the 2.5V reference with 500 of imped-
ance, feeding this to the REF input of the LTC2053 and the
integrating resistor of the LTC1923 error amplifier, any
common mode issues will be avoided.
Total series resistance = 0.055 + 0.08 + 2 • 0.1 + 0.1
Power Loss = (1A)
Output Power = (1A)
100k
DS(ON)
DD
10M
. Figure 14 shows how to implement this. By
MOSFETs, lower series resistance induc-
4.7 F
CNTRL V
EAOUT
FB
V
V
2
LTC1923GN
SET
THRM
• 0.435 = 0.435W
2
• 2.5 = 2.5W
= 0.435
V
REF
DD
1923 F14
V
2.7V TO 3.3V
DD
1 F
LTC1923
23
1923f